No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Cu Doped Zinc Cobalt Oxide Based Solid-State Symmetric Supercapacitors: A Promising Key for High Energy Density
Abstract
Improvement in the capacitance and energy density of zinc cobalt oxides based materials is vital for creating supercapacitors with excellent electrochemical performance. We synthesised Cu doped Zinc Cobalt oxides (Zn1-xCuxCo2O4) nanostructures via a facile hydrothermal method to accomplish excellent supercapacitive performance. Significantly, the incorporation of Cu into ZnCo2O4 brings a 2 times increase in specific surface area (52 m2g-1) and decrease in charge transfer resistance for Zn0.7Cu0.3Co2O4 (x=0.3) sample. Consequently, Cu doped Zn0.7Cu0.3Co2O4 electrode displays high specific capacitance of 1425 Fg-1, which is 1.55-fold increased as compared to 917 Fg-1 of pristine ZnCo2O4 electrode. About 96 % of capacitance is retained by the Zn0.7Cu0.3Co2O4 after 2000 charge-discharge cycles. Later, Zn0.7Cu0.3Co2O4 based solid-state symmetric supercapacitor has been fabricated, which displays the potential window of 1.5 V with enlarged cycling stability. The assembled device shows high energy density of 55 Whkg-1 at a power density of 2621 WKg-1 and successfully lighten the yellow LED of 1.5 V. The immense improvement in electrochemical performance is credited to increased surface area and electronic conductivity of electrode. The obtained results clearly evidenced that fabricated solid-state symmetric supercapacitor has the potential to be used in flexible energy storage devices.
... The improved performance can be attributed to the increased surface area and enhanced electronic conductivity achieved through Cu doping. Figure 5 provides a schematic depiction of the device preparation process and includes performance and cyclic stability graphs [63]. ZnCo2O4, an appropriate mixture of precursors was blended and subjected to hydrothermal treatment (120 °C, 6 h), followed by calcination (450 °C for 2 h). ...
... The improved performance can be attributed to the increased surface area and enhanced electronic conductivity achieved through Cu doping. Figure 5 provides a schematic depiction of the device preparation process and includes performance and cyclic stability graphs [63]. In addition, Patil et al., (2020) employed a gold-reduced graphene oxide composite (Au@rGO) to enhance the electrochemical performance of ZnCo2O4 electrodes. ...
... Sharma et al., (2019) achieved a remarkable performance (1425 F g −1 ) enhancement in ZnCo2O4 electrodes by doping them with Cu, leading to a retention rate of 96% after 2000 cycles. This improvement can be attributed to the increased surface area and enhanced electronic conductivity resulting from Cu doping [63]. ...
ZnCo2O4 has emerged as a promising electrode material for supercapacitor applications due to its unique properties and potential for high-performance energy storage. As a transition metal oxide, ZnCo2O4 offers eco-friendly characteristics and favorable diffusion properties, making it an attractive candidate for sustainable energy storage systems. However, the poor conductivity and low surface area of ZnCo2O4 have posed challenges for its optimal utilization in supercapacitors. Various innovative approaches have been explored to overcome these limitations, including the development of ZnCo2O4 with different morphologies such as core-shell and porous structures. This review work aims to provide a comprehensive analysis of diverse synthesis methods employed in recent studies, including hydrothermal growth, solvothermal synthesis, wet chemical methods, and miscellaneous synthesis techniques, each offering unique advantages and influencing the properties of the synthesized materials. The synthesis conditions, such as precursor concentrations, temperature, annealing time, and the incorporation of dopants or additional materials, were found to play a crucial role in determining the electrochemical performance of ZnCo2O4-based supercapacitor electrodes. Core-shell heterostructures based on ZnCo2O4 exhibited versatility and tunability, with the choice of shell material significantly impacting the electrochemical performance. The incorporation of different materials in composite electrodes, as well as doping strategies, proved effective in enhancing specific capacitance, stability, surface area, and charge transfer characteristics. Controlled synthesis of ZnCo2O4 with diverse morphologies and porosity was crucial in improving mechanical strength, surface area, and ion diffusion capabilities. The findings provide valuable insights for the design and engineering of high-performance supercapacitor electrodes based on ZnCo2O4, and suggest exciting avenues for further exploration, including advanced characterization techniques, novel doping strategies, scale-up of synthesis methods, and integration into practical supercapacitor devices. Continued research and development in this field will contribute to the advancement of energy storage technologies and the realization of efficient and sustainable energy storage systems.
... Various synthesis methods such as chemical precipitation, the hydrothermal method, the sol-gel method, photothermal synthesis, etc., are used for the synthesis of pseudocapacitive materials based on Co 3 O 4 [31][32][33][34][35]. To achieve high electrochemical parameters, Co 3 O 4 supercapacitor electrodes are made on the basis of films and porous structures [32,33], composites consisting of an electrically conductive matrix with a large specific surface area, in which Co 3 O 4 nanoparticles are embedded and fixed in the matrix by adhesion forces or a suitable binder [34][35][36][37][38][39][40][41][42][43][44][45][46][47], and also various binary and ternary systems of oxides of cobalt and Mo, Mn, and Cu [38,[44][45][46][47]. Doping is used to improve the electrical conductivity of cobalt oxide [48,49]. Although cobalt oxide has a very high theoretical capacitance (3560 F g −1 ), the practically achievable specific capacitance is much lower. ...
... Various synthesis methods such as chemical precipitation, the hydrothermal method, the sol-gel method, photothermal synthesis, etc., are used for the synthesis of pseudocapacitive materials based on Co 3 O 4 [31][32][33][34][35]. To achieve high electrochemical parameters, Co 3 O 4 supercapacitor electrodes are made on the basis of films and porous structures [32,33], composites consisting of an electrically conductive matrix with a large specific surface area, in which Co 3 O 4 nanoparticles are embedded and fixed in the matrix by adhesion forces or a suitable binder [34][35][36][37][38][39][40][41][42][43][44][45][46][47], and also various binary and ternary systems of oxides of cobalt and Mo, Mn, and Cu [38,[44][45][46][47]. Doping is used to improve the electrical conductivity of cobalt oxide [48,49]. ...
... The volume specific capacitance in the manufacture of supercapacitors is also very important; highly porous materials and aerogels do not satisfy this condition. The method of forming electrodes using active material powder and a suitable binder is adequate to achieve high loading [31,34,37,42,46,49,51]. This method is practically important due to the scaling potential; therefore, it is being intensively developed. ...
Electrochemical pseudocapacitors, along with batteries, are the essential components of today’s highly efficient energy storage systems. Cobalt oxide is widely developing for hybrid supercapacitor pseudocapacitance electrode applications due to its wide range of redox reactions, high theoretical capacitance, low cost, and presence of electrical conductivity. In this work, a recovery annealing approach is proposed to modify the electrochemical properties of Co3O4 pseudocapacitive electrodes. Cyclic voltammetry measurements indicate a predominance of surface-controlled redox reactions as a result of recovery annealing. X-ray diffraction, Raman spectra, and XPES results showed that due to the small size of cobalt oxide particles, low-temperature recovery causes the transformation of the Co3O4 nanocrystalline phase into the CoO phase. For the same reason, a rapid reverse transformation of CoO into Co3O4 occurs during in situ oxidation. This recrystallization enhances the electrochemical activity of the surface of nanoparticles, where a high concentration of oxygen vacancies is observed in the resulting Co3O4 phase. Thus, a simple method of modifying nanocrystalline Co3O4 electrodes provides much-improved pseudocapacitance characteristics.
... The electrode of the pseudocapacitors exhibits high theoretical capacitance, excellent electrochemical properties and exceptional reversibility. Electrochemical properties of the electrode are strongly influenced by mechanical and active surface sites which are the key element in capacitor give the optimum characteristics to supercapacitors [6,7]. According to the previous reported literature, mechanical properties and active surface sites are the key properties which determined the electrochemical properties of the electrode such as take the example of carbon based material like Graphene, carbon naotube, and carbon nitrogen dot which are extensively usedwith nanoparticles just to improve the mechanical properties and surface area of the electrode [8][9][10]. ...
... Among all concentrations Zn 0.50 Mn 0.50 O 3 records best specific capacitance due to its good crystallinity and high surface area as it was confirmed via XRD and BET. The peaks can be contributed to electrochemical reaction of Zn/Mn on basis of following equations (7)(8)(9)(10)(11). From above results it is observed that Zn/Mn binary oxides exhibit lesser reduction potential compared to ZnO and MnO electrodes. ...
... The impedance spectra of all samples show the same features with semicircle. Small semicircle shows the Faradaic charge transfer method of reactions between electrolyte and electrode [7,48]. The diameter of electrode Zn 0.50 Mn 0.50 O 3 is less than other doping concentrations and pristine ZnO and MnO showing less charge transfer resistance and allows ion diffusion effortlessly in redox reaction. ...
Transition metal oxides have been explored in supercapacitor applications owing to their safety, low cost, high specific capacitance and high electrochemical activity. Among all transition metal oxides, zinc oxide based materials show remarkable response for designing the supercapacitors with high electrochemical activity. Here in, Mn doped ZnO (Zn1-xMnxO3 with x = 0, 0.25, 0.50, 0.75 and 1) was synthesized by a facile hydrothermal method. Doping of Mn into the ZnO increased the surface area and decease the charge transfer resistance for the Zn0.5Mn0.5O3. All the synthesized materials were characterized by x-ray diffraction (XRD), scanning electron microscopy SEM), BET, electrochemical tests and other various analytical techniques to confirm the structural, morphological, textural and suprcapacitive properties. The synthesized material Zn0.5Mn0.5O3 having the porous nanoribons structure with BET surface area (2490 cm²/g). The electrochemical studies showed significantly enhanced response toward pseudocapacitive nature. The synthesized material exhibited the excellent specific capacitance (515F/g), specific energy (28.61 Wh/kg) and specific power (1000 W/kg) at current density of 2 mA/g. Such impressive and superior properties make the MnZnO3 material as promising candidate for new generation supercapacitor applications.
... In the last decade, transition metal oxides (TMOs) having variable oxidation states, which perform redox reactions, have been tested more as energy storage materials, because of their high theoretical specific capacitances. Recently, binary TMOs having spinel structures such as MCo 2 O 4 (M = Ni, Co, Cu, Zn, Mn) [12][13][14][15], MMn 2 O 4 (M = Zn, Co, Ni) [16][17][18], and MFe 2 O 4 (M = Ni, Co, Zn, Mn) [19,20], etc. have gained huge research interest as these exhibit enhanced electronic conductivities, higher specific capacitance, the lower activation energy for charge transfer between cations, good structural stability and more active sites for rapid reversible faradic reactions than that of unitary metal oxides. ...
... For simple mathematical calculations equation (12) can be rearranged as Fig. 9(c) shows the graph between v 1/2 vs i p /v 1/2 for a prominent anodic peak at -0.12 V. From the slope and y-axis intercept of this curve, the value of variables k 1 and k 2 can be determined, which can further be used to find out the quantitative contribution of capacitive currents, and that of diffusion-controlled current in the total current at specific voltage and sweep rate using equation (12). In Fig. 9(d) the blue lines shaded region (k 1 v) shows the contribution of capacitive currents (fast kinetics) and the white region (k 2 v 1/2 ) represents the contribution of diffusive currents (slow kinetics) to the total current (solid red line). ...
... For simple mathematical calculations equation (12) can be rearranged as Fig. 9(c) shows the graph between v 1/2 vs i p /v 1/2 for a prominent anodic peak at -0.12 V. From the slope and y-axis intercept of this curve, the value of variables k 1 and k 2 can be determined, which can further be used to find out the quantitative contribution of capacitive currents, and that of diffusion-controlled current in the total current at specific voltage and sweep rate using equation (12). In Fig. 9(d) the blue lines shaded region (k 1 v) shows the contribution of capacitive currents (fast kinetics) and the white region (k 2 v 1/2 ) represents the contribution of diffusive currents (slow kinetics) to the total current (solid red line). ...
In material science, the synergistic effect comes into the picture when the physical and/or chemical properties of a composite material improve noticeably in comparison to that demonstrated by its forming individual components. This work represents the facile synthesis of CoMn2O4 (CMO) and CoMn2O4@MoS2 (CMOS) nanocomposites via a co-precipitation synthesis approach. In this study, amounts of CMO precursors were kept constant and the effect of MoS2 addition on the electrochemical properties of the nanocomposite has been investigated. The substantial improvement in the electrochemical performance of the nanocomposite after adding MoS2 contents with CMO can be attributed to the synergistic effect. The CMOS nanocomposite synthesized using 20% MoS2 uniform dispersion (abbreviated as CMOS20) exhibits maximum improvement in the electrochemical properties which is ascribed to its higher specific surface area (74 m2 g−1) and hierarchical pore size distribution. When examined in a conventional three-electrode system with 2 M KOH aqueous electrolyte, CMOS20 nanocomposite demonstrates high specific capacitances of 422 F g−1 at 0.5 A g−1, good cyclability, high-rate capability and higher diffusion coefficients (1.96 × 10−10 cm2 s−1). An asymmetric supercapacitor device designed using CMOS20 nanocomposite cathode and activated carbon anode exhibit maximum specific energy of 37 W h kg−1 and the maximum specific power of 5000 W kg−1. This practical device can light up a red LED for more than 3 min. We believe the facile synthesis approach and promising electrochemical results assert the potential of our designed CMOS20 nanocomposite in the development of high-performance practical supercapacitor devices.
... In the beginning, Fe 2 O 3 @NiCo 2 O 4 and activated carbon electrodes (1 × 1 cm 2 ) were fabricated. Afterward, PVA/KOH gel electrolyte was prepared, as previously reported by our group [35]. In brief, 6 g PVA was mixed in a 6 M KOH aqueous solution and kept for further constant stirring until gel paste was not achieved. ...
... The Fe 2 O 3 @NiCo 2 O 4 electrode provides the highest discharge time due to improved electrochemical performance than Fe 2 O 3 and NiCo 2 O 4 at the same current density of 1 A g − 1 . When current density increases, discharge time decreases owing to lesser accommodation of ions on the electrode surface [35,56]. The specific capacity (C s ) value is calculated using the CV curves using the below equation: ...
The need for a cost-effective and efficient energy storage system instigates researchers to develop emerging electrode materials for energy storage devices. The α-Fe2O3-based electrode material for supercapacitor application has received interest due to its good electrochemical performance, high mechanical strength, corrosion resistance, low cost, and abundant availability. This work develops a cost-effective, robust Fe2O3@NiCo2O4 core-shell composite with spikey surface via a facile hydrothermal strategy for high-performance electrode material for supercapacitors. The spikes of Fe2O3 are developed on NiCo2O4 to collaborate in a more accessible surface area, with robust morphological stability throughout electrochemical performances. The Fe2O3@NiCo2O4 core-shell composite exhibits a high specific capacity of 364 C g⁻¹ at the scan rate of 5 mV s⁻¹ and 81% cycling stability up to 10,000 successive charge-discharge cycles at the current density of 15 A g⁻¹. Moreover, an asymmetric solid-state supercapacitor (ASSC) device was fabricated using Fe2O3@NiCo2O4 composite as a positive electrode and commercially purchased activated carbon as a negative electrode assembled via PVA/KOH gel electrolyte. The fabricated device offers a significant energy density of 31.7 W h Kg⁻¹ at a power density of 700 W Kg⁻¹. The ASSC exhibits excellent capacitance retention of 90% with ultra-high coulombic efficiency of 99.7% up to 10,000 GCD cycles. The ASSC can illuminate the red and yellow LED light. This work indicates that a robust Fe2O3@NiCo2O4 core-shell composite can be an economic strategy for fabricating high-performance practical supercapacitor applications.
... The appearance of a vertical line in the low frequency regions suggests that there is an ionic diffusion occurring from the bulk of the solution towards the surface of the electrode [55][56][57][58]. Higher the vertical line lower would be the diffusive resistance of OHions [59][60][61][62]. As we could see from the inset of Fig. 8, the straight line is more vertical for the Co 3 O 4 -H electrode suggesting lower diffusive resistance of OHions from the bulk of the solution towards electrode. ...
... Transition metal oxides (TMOs) are being investigated as potential energy storage materials due to their high theoretical specific capacitances, which result from their capacity to undergo redox reactions due to their multiple oxidation states. Spinel-structured TMOs, such as MCo 2 O 4 (where M can be Mn, Co, Ni, Cu, or Zn) [14][15][16][17][18][19][20] and MMn 2 O 4 (where M can be Ni, Co, Cu or Zn) [21][22][23][24], are now of significant importance due to their ability to deliver better specific capacitance while requiring less activation energy for charge transfer. MnCo 2 O 4 exhibits outstanding pseudocapacitive performance which is attributed to the combined influence of Mn +2 and Co +3 ions. ...
This study aims to determine how Zn doping at the cobalt site of MnCo2O4 (MCO) affects its electrochemical properties. Synthesized MnZn0.4Co1.6O4 (0.4ZMCO) sample's electrode provides an enormous improvement in electrochemical characteristics as compared to that of MCO because of its higher BET surface area (74 m2/ g) and mesoporous distribution of pore sizes. The 0.4ZMCO exhibits specific capacitances of 720 F g− 1 at 0.5 A g− 1, along with satisfactory rate capability. In addition, this electrode exhibits outstanding cyclability, maintaining a
capacitance retention of 91 % and a coulombic efficiency of 99.78 % throughout 10,000 continuous cycles, even under high current density of 10 A g− 1. An
symmetric supercapacitor (ASC) device is constructed using 0.4ZMCO as the cathode and activated carbon as the anode electrode. This ASC device performs with a good specific energy density of 49 Wh kg− 1 and a power density of 8.64 kW kg− 1. Furthermore, the ASC device exhibits 99.40 % coulombic efficiency and 91.84 % capacitance retention up to 30,000 GCD cycles in PVA/KOH gel electrolyte at a specific current density of 8 A g− 1. Additionally, a single device illuminates a red LED, while connecting two devices in series illuminates red and green LED for more than 15 and 12 min, respectively. We believe Zn-doped MCO has great potential in constructing higher-performance supercapacitor devices due to its straightforward synthesis process and excellent electrochemical properties.
... Subsequently, a gradual decline in stability was observed for both electrodes, with Co 3 O 4 -AC retaining 90% and Co 3 O 4 -SG retaining 88% stability up to 5000 cycles. This trend of substantial capacitance retention aligns with findings from various cobalt oxide spinel-structured systems, as reported by Sharma et al. (2020), Ghosh et al. (2016), and Thorat et al. (2017). ...
The present investigation involves two synthesis methods, autocombustion (Co3O4-AC) and sol–gel (Co3O4-SG), for producing nearly spherical-shaped and polygonal shaped nanomaterials of spinel cobalt oxide (Co3O4) respectively as electrode materials. TEM image analysis unveiled distinct particle morphologies for the two samples. The Co3O4-AC particles exhibited a nearly spherical shape, whereas the Co3O4-SG particles displayed a polygonal shape. The phase purity of the Co3O4 samples were confirmed via XRD patterns analysis and the crystallite size was calculated to be 44 nm for Co3O4-AC and 36 nm for Co3O4-SG. The surface area, estimated via BET experiments, of Co3O4-AC was found to be 15 m2/g, while Co3O4-SG exhibited a slightly lower surface area of 11 m2/g. Co3O4-AC exhibited a higher specific capacitance (Cs) of 162 F/g at 0.25 A/g, indicating its superior energy storage capability. On the other hand, Co3O4-SG shows a Cs of 98 F/g, indicating slightly lower performance compared to Co3O4-AC. Both nanomaterials exhibited better stability, with more than 85% capacity retention after 5000 charge–discharge cycles.
... . Both electrode show almost same capacitance retention up to 1000 cycles of experiments. A similar feature of high degree of capacitance retention has been reported for various spinel-structure cobalt oxide systsems(Sharma et al. 2020;Ghosh et al. 2016;Thorat et al. 2017). ...
In present work, we investigated the synthesis methods for producing spherical-shaped nanomaterials of spinel cobalt oxide (Co 3 O 4 ) as electrode materials. Two synthesis methods, autocombustion (Co 3 O 4 -AC) and sol-gel (Co 3 O 4 -SG), were employed to synthesize cobalt oxide nanopowders with a spherical shape. Characterization techniques including XRD, TEM, BET, and XPS analyses were conducted to evaluate the synthesized samples. The phase purity of the cobalt oxide samples were probed using XRD analysis and the crystallite size was determined to be 44 nm for Co 3 O 4 -AC and 36 nm for Co 3 O 4 -SG. TEM analysis further confirmed the desired spherical morphology of the particles. The surface area of Co 3 O 4 -AC was found to be 15 m ² /g, while Co 3 O 4 -SG exhibited a slightly lower surface area of 11 m ² /g. The energy storage experiments were conducted in terms of CV and GCD to enhance the electrochemical performance of the samples. Co 3 O 4 -AC exhibited a higher Cs 162 F/g at Im (current density) 0.25 A/g, indicating its superior energy storage capability. On the other hand, Co 3 O 4 -SG shows a Cs 98 F/g, indicating slightly lower execution compared to Co 3 O 4 -AC. Both nanomaterials exhibited excellent stability, showing no degradation over 1000 charge-discharge cycles. Overall, the study successfully synthesized spherical-shaped cobalt oxide nanomaterials using autocombustion and sol-gel methods. The obtained results demonstrate the promising energy storage properties of Co 3 O 4 -AC and Co 3 O 4 -SG, with Co 3 O 4 -AC exhibiting higher specific capacitance.
... Firstly, PELAC electrodes were fabricated on a graphite sheet (round shaped by a cutting die of a diameter of 12 mm) as a current collector. Next, PVA/KOH gel electrolyte was prepared [42]. Initially, 6 g of PVA powder was mixed with 6 M KOH electrolyte solution. ...
... Transition metal oxides (TMOs) are being investigated as potential energy storage materials due to their high theoretical specific capacitances, which result from their capacity to undergo redox reactions due to their multiple oxidation states. Spinel-structured TMOs, such as MCo 2 O 4 (where M can be Mn, Co, Ni, Cu, or Zn) [14][15][16][17][18][19][20] and MMn 2 O 4 (where M can be Ni, Co, Cu or Zn) [21][22][23][24], are now of significant importance due to their ability to deliver better specific capacitance while requiring less activation energy for charge transfer. MnCo 2 O 4 exhibits outstanding pseudocapacitive performance which is attributed to the combined influence of Mn +2 and Co +3 ions. ...
A synergistic effect occurs in material science when a composite material's physical and chemical properties increase significantly as compared to its individual components. In the present work, MnCo 2 O 4 (MCO) and MnCo 2 O 4 @MoS 2 (MCOS) nanocomposites have been synthesized using the co-precipitation synthesis process. The main focus of the present research is to observe the impact of MoS 2 on the electrochemical characteristics of the nanocomposites while keeping the MCO precursor quantity constant. The MCOS nanocomposite was synthesized with a homogeneous dispersion of 20 % MoS 2 (MCOS20). It has the most significant enhancement in electrochemical properties due to its larger specific surface area (44 m 2 g − 1) and mesoporous distribution of pore size. The MCOS20 nanocomposite as a single electrode possesses larger specific capacitances of 512 F g − 1 at 0.5 A g − 1 and exhibits a good rate capability. Besides that, the electrode exhibits excellent cycling stability of 91.87 % along with the coulombic efficiency of 99.57 % up to 5000 consecutive cycles, even at a high current density of 8 A g − 1. An asymmetric supercapacitor (ASC) device has been fabricated with the MCOS20 nanocomposite as a cathode and commercially purchased activated carbon as an anode electrode to examine the practical utility of synthesized composite material. The device displays the highest specific energy density and power density of 36 Wh kg − 1 and 19 kW kg − 1 , respectively. The device shows excellent stability up to 20,000 cycles at 3.5 A g − 1 with a coulombic efficiency of 98.85 % and capacitance retention of 94.28 % in 6 M KOH gel electrolyte. Furthermore, the two devices illuminate red, blue, and yellow LEDs. It lights up for more than 3 min a red LED. We believe that our proposed MCOS20 nanocomposite has potential for use as electrodes in the fabrication of high-performance supercapacitor devices, owing to its simple manufacturing method and good electrochemical performance.
... However, with a mighty power density of 10,000 Wkg − 1 , the ASC device maintains a good energy density of 42 Whkg − 1 . Compared to the other reports (Table S3), the present work demonstrates a promising performance of supercapacitor properties [50][51][52][53][54]. The ASC device was charged at a current density of 2 Fg − 1 and then discharged to supply power to a LED light (Fig. 7f). ...
... Also, it confirms the minimal role of grains in the conduction mechanism [54]. The grain boundaries facilitate irregular distribution of Columbic field and thereby increase grain resistance [55] in lower temperature regions. However, the increase in temperature improves electrical conductivity and the same is substantiated by the reduction of an area in Z ′ v/s Zs emicircle. ...
Cobalt oxide-based spinels in the form of Co3O4, NiCo2O4 and ZnCo2O4 are synthesized by the co-precipitation technique. Powder X-ray diffraction studies confirm the arrangement of ions in spinel structure with minor secondary phases of native oxides. Scanning electron micrographs of spinels show the formation of fine nanostructures with an overall grain size below 90 nm for Co3O4 and ZnCo2O4. However, the grain size of NiCo2O4 varied from 100 to 250 nm. Dielectric measurements of all spinels exhibit low dielectric loss in lower temperature regions indicating superior dielectric behavior. Almost stable dielectric loss at lower temperatures confirms the usability of these spinels in supercapacitor applications. The dielectric loss increases with temperature due to
the dominance of conductive grains and thereby demonstrates improved electrical conductivity. Temperaturedependent dielectric constant studies show the dominance of space charge polarization in lower temperature regions and orientation polarization in higher temperature regions, respectively. The temperature-dependent dcconductivity of all spinels exhibits NTCR behavior and the same is confirmed by the Cole-Cole plots. The cyclic voltammettry measurement shows highest specific capacitance of 767 F/g for NiCo2O4 spinel followed 600 F/g for ZnCo2O4 and 439 F/g for Co3O4 coated electrodes. Electrochemical impedance measurement shows no sign of a semicircle along with low internal resistance for Ni and Zn-substituted Co3O4 spinels. This endorses the significance of substitution in improving the electrochemical behavior of Co3O4 spinel and their use in supercapacitor applications.
... At high frequencies, the real part (Z′) intercept refers to total internal resistance (R S ), the sum of the active material's contact resistance and the electrolyte resistance. 27 At midfrequencies range, a small semicircular arc encompasses the charge transfer resistance (R ct ) induced by electrons swinging at the interfacial contacts of the FeWO 4 NRs. 28 The inset of Figure 7b shows the equivalent model circuit and parameter extracted by fitting Nyquist plot data, displays in Table 1. ...
Understanding the role of fundamental structural engineering of materials to unravel the underlying rudimentary electronic structure-dependent charge storage mechanisms is crucial for developing new strategic approaches toward high-performance electrochemical energy storage devices. Here, we demonstrate the role of strain engineering by V doping-induced lattice contraction in NiCo2O4 for increasing the energy density and power density of aqueous asymmetric hybrid supercapacitors. For application in energy storage, we demonstrate the influence of electron-deficient V4+/5+ doping in electron-rich Ni2+ sites, which has been found to result in the formation of a hypo-hyper electronically coupled cation pair causing a shift in the d-band and O-2p band centres and distortion of CoO6 octahedra, thereby affecting the d-orbital e2g occupancy. Optimization of V doping to 3 mol %, achieved by a binder-free one-step hydrothermal method, has yielded a 96 % increase in specific capacitance of up to 2316 F g-1 from 1193 F g-1 in pristine materials at 1 A g-1 in three-electrode configuration with a Columbic efficiency (η%) of 94% and a 24% increase in rate capacity. A two-fold increase in specific capacitance in the pouch cell device, fabricated with a functionalized carbon nanosphere positive electrode, has been observed for the V-doped samples at 1 A g-1 with a η % of 97 % and a maximum energy density of 96.3 W h Kg-1 and a maximum power density of 8733.6 W Kg-1 which are 41% and 24.3 % higher than the pristine device, respectively. Excellent cycling stability of 95.4 % capacitance retention has been observed after 6000 cycles. DFT calculations have been carried out to understand the previously unexplored role of lattice strain on charge transport, quantum capacitance, and ultimately its effect on the transition state kinetics of energy storage faradaic reaction mechanisms. The aim of this work is to establish a fresh perspective on developing a deep understanding of fundamental electronic and structural properties of materials by drawing in concepts from descriptor models in electrocatalysis to reveal the role of lattice strain and d-band centre tailoring in enabling pseudocapacitive energy storage.
The suitable proportion of diffusion contribution during the electrochemical process could influence the electrochemical performance of electrode materials. An effective method is that tuning the diffusion reaction contribution via doping heteroatom, introducing defects or surface modification. In this work, a unique core-shell structure material Cu-Mn-Co LDO-C is obtained. Benefitting from Cu pre-doped into Mn[sbnd]Co LDO, large amount of oxygen vacancies is introduced to enhance electrochemical performance; N-6 doped porous carbon shell protects Cu-Mn-Co LDO core and improves electrochemical performance of Cu-Mn-Co LDO-C further. In addition, doping Cu broadens potential window of Cu-Mn-Co LDO-C surprisingly. Cu-Mn-Co LDO-C presents 5028.7 mF cm⁻² at a current density of 1 mA cm⁻² with a facilely reached potential window of 0–0.65 V finally, and retains 73.4 % diffusion contribution at a scan rate of 1 mV s⁻¹, 18.3 % at 100 mV s⁻¹. After 10,000 cycles at 2 mA cm⁻², Cu-Mn-Co LDO-C keeps 90.3 % of initial capacitance. Using Cu-Mn-Co LDO-C as positive and Fe3O4-C as negative to fabricate a solid flexible asymmetrical supercapacitor (SAS), this SAS presents a considerable energy density that attribute to the high working potential of positive Cu-Mn-Co LDO-C. SAS could working stably at a potential window of 0–2.2 V, and presents the highest energy density 243.1 μWh cm⁻² at a power density of 2.8 mW cm⁻², remains 203.0 μWh cm⁻² at the highest power density of 55.4 mW cm⁻². A hand ring that was assembled by three SAS which contacted in series could light a highest rated voltage white LED more than 10 min. As a result, Cu-Mn-Co LDO-C is an ideal candidate for flexible positive electrode in the field of smart, portable energy storage.
In this paper, we report the magneto-caloric properties of the Graphdiyne structure with mixed 3/2 and 1 spins investigated by Monte Carlo simulations. Such calculations were performed under the Metropolis algorithm. We illustrate the magnetizations and dM/dT of the Graphdiyne system with these mixed spins. It is found that the magnetic entropy of the Graphdiyne changes when varying the temperature values for several values of the external magnetic field. The maximum magnetic entropy variations of the system are deduced. The relative cooling power (RCP) coefficient of the Graphdiyne system has been estimated for several values of the external magnetic field. To complete this work, we have illustrated the magnetic hysteresis cycles of the Graphdiyne for fixed values of the other physical parameters.
With the energy crisis and environmental problems increasingly intensified, traditional energy can no longer meet the requirements of the new era. Therefore, supercapacitors have become popular energy storage devices because of their excellent performance. However, its low energy density limits its application scenarios. Here, we propose a composite material of ZnCo2O4/ZnCo2O4/[email protected]/GO (ZCG-2) with a hierarchical structure synthesized by a simple hydrothermal method as a cathode material for asymmetric supercapacitors. The material mainly uses the different structures of the same ZnCo2O4 material to form a hierarchical structure, thereby reducing the introduction of excessive elements. The specific capacitance is 1255.0 F g⁻¹ at 1 A g⁻¹. The asymmetric supercapacitor is prepared with ZCG-2 as positive electrode and activated carbon (AC) as negative electrode, which has a specific capacitance of 238.8 F g⁻¹ at 1 A g⁻¹, and a capacity retention rate of 85.5% after 10,000 cycles. More importantly, at a power density of 800 W kg⁻¹, it has a specific energy as high as 84.9 Wh kg⁻¹. This proves that the composite material obtained by this strategy has certain application potential in the field of electrochemical energy storage.
Water electrolyzers coupled with fuel cells offer a close loop of sustainable energy, requiring supercapacitors as energy storage devices; however, the performance of such devices largely depends on corresponding electrode materials. Metal oxides and sulfides containing Fe, Co, and Ni metals, in particular, have created significant interest due to their tunable and high theoretical energy performance for such devices. Herein, metal-organic framework (MOF) derived cobalt oxide (MOF-Co3O4) and sulfide (MOF-Co9S8) have been synthesized using solvothermal and hydrothermal strategies. The MOF-Co3O4 exhibited an overpotential of 375 and 213 mV for OER and HER, whereas, MOF-Co9S8 being a better electrocatalyst, displayed an overpotential of 278 and 212 mV for the same, respectively, at 10 mA/cm². The theoretical evaluation suggested that incorporation of S-atoms with Co active sites in MOF-Co9S8 significantly reduced the energy barriers for crucial elementary processes of OER and HER, endowing its electrocatalytic activity. In addition, MOF-Co9S8 with a specific capacitance of 2831 F/g was found to have over four times higher energy storage capacity than MOF-Co3O4 with a 674 F/g specific capacitance @1 mA/cm².
In carbon-based electric double-layer capacitors (EDLC), an ideal electrode should have convenient mass transport, ensuring rich porosity and rapid electron transfer, guaranteeing the electrode bulk's high conductivity. In this study, ultrafine Cu nanoparticles inserted carbon flocculation is formed on carbon cloth using polydopamine and cupric chloride precursors via pyrolysis and electrochemical oxidation reaction. As a result, the obtained electrode has a large surface area of 55.5 m²g⁻¹ and high conductivity of 48.7 S/mm, which shows excellent charge storage capability with high specific capacitance of 3546 mF cm⁻² at a current density of 1 mA cm⁻². Moreover, when the as-prepared electrode is used as electrodes in symmetric EDLC, it can provide a high energy density of 23 mWh cm⁻³ with a power density of 179 mW cm⁻³, making it as a promising carbon electrode for practical EDLCs.
Many researchers have focused on enhancing the performance of energy storage devices to satisfy the growing demand for energy worldwide. This paper is an attempt to tune the capacitive behavior of pristine ZnO through its Cd doping via the simple synthetic method. To examine their electrochemical behavior, samples of modified ZnO with three concentrations of the dopant (Cd) (3, 6, and 9 wt% Cd-doped ZnO) were prepared. The as-prepared products were characterized by spectral as well as analytical techniques. The 9 wt% Cd-doped ZnO electrode, featuring fast electrolyte permeation and rich electrochemically active sites, showed an excellent specific capacitance (Csp) of 627 Fg⁻¹ at a current density of 1 Ag⁻¹ and substantial cycling stability of 93.3% even after 5000 GCD cycles. The addition of dopants enhanced electrical conductivity due to effective charge transfer and electron transport. The unique nanorod-like structure was found to be responsible for the exceptional electrochemical properties of the samples. Until now, there were no reports on Cd-doped ZnO nanorods as electrode material for supercapacitors. This work provides a simple and cost-effective method for fabricating a 9 wt% Cd-doped ZnO electrode, which may open up new possibilities for efficient electrodes in next-generation supercapacitors.
Zinc cobaltite(ZnCo2O4) micro-star shaped porous superstructure, on coating with zinc oxide(ZnO) nano-stubs, and coupling with porous flaky activated carbon(AC) from green tea, yielded asymmetric supercapacitor(ASC) with greatly enhanced performance parameters: specific capacitance(SC) of 557 F g⁻¹, energy and power density(E and P) maxima of 173 Wh kg⁻¹ and ∼3 kW kg⁻¹, compared to reported ASCs of carbon/ZnCo2O4 composites and pure ZnCo2O4 or ZnO. Sub-stoichiometry in ZnO overlayer endows it with good electrical conductivity (14.6 mS cm⁻¹), enhancing overall electron circulation in composite and due to direct contact between two oxides, with different morphologies and sufficient porosity, electrolyte penetration is deep, and ample ion-accommodation sites prevail in [email protected]2O4 composite, which translate into increased SC, E, P, rate-response and cycle life. Usefulness of high-performance AC//[email protected]2O4 ASC is ratified by connecting it in its fully charged state to electrochromic device (ECD) of polyaniline and tungsten oxide, and large integrated transmission modulation of 45.8% was rendered in ECD over bulk of visible region (480–800 nm). This demonstration of self-powering ECD proved efficacy of these devices for futuristic applications, where, dual functions of energy storage and saving can be tapped, by using such low cost, highly efficient devices, that can not only work independently, but can also work in tandem.
This book presents a state-of-the-art outlines of the research and development in designing the electrode and electrolyte materials for energy storage/conversion devices (Li-ion batteries and Supercapacitors). Further, the green energy production through water splitting by an emerging device (hydroelectric cell; HEC) is also explored. Chapters are focused on the fundamentals of the battery, supercapacitor, and hydroelectric cell and deliver a synopsis of the development and selection criteria of numerous kinds of electrode and electrolyte material for developing competent devices.
Cu-doped Co3O4 (1, 3, 5 and 7 wt%) nanoparticles were synthesized through the decomposition of cobalt (II) acetylacetonate, cobalt (III) acetylacetonate and copper (II) acetylacetonate in the least toxic polar solvent through solvothermal method. XRD analysis confirmed the formation of cubic spinel structure with reduced crystallite size of 20 nm and slight lattice expansion upon Cu doping. The spectral analysis carried out by FTIR and Raman studies expressed the existence of functional group and active vibrational modes. UV–Vis analysis revealed the increase in bandgap value with increasing dopant concentration. Slightly dissociated nanosheets and cubic structure were observed in HR-SEM and HR-TEM analyses with an average particle size of 25 nm. SAED pattern indicated the polycrystalline nature of the synthesized nanoparticles. The weak ferromagnetic nature with low coercivity and remanent ratio is deliberated from magnetic measurement. The Cu dopant was found to enhance the electrochemical performance of Co3O4 nanoparticles with high specific capacitance, since it possesses larger surface area due to reduced particle size.
A new two- dimensional covalent organic polymers material (ST-1) was synthesized by the condensation of squaric acid and melamine. The preparation is simple and cheap. Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, powder X-ray diffraction (XRD), scanning electron microscopy(SEM) and thermogravimetric analysis(TGA) were employed to characterize the structure and properties of ST-1. This material presents the highest specific capacitance value of 177.6 F∙g-1 at current density of 0.3 A g-1 in three electrode configuration in the 6 M potassium hydroxide electrolyte. Retention rate of specific capacitance can be maintained about 60.24 % when the current density was increased by 50 times. It is worth mentioning that ST-1 also demonstrates about 94 % capacitance retention after 10000 galvanostatic charge-discharge cycles.
Capacitor starts its journey from 1745, and still moves forward in form of supercapacitor. Supercapacitor is one of the advanced forms of capacitor with higher energy density that bridges between capacitor and battery. The energy storage through the formation of electrical-double-layer is pivotal for supercapacitor technology. To further improve the energy density, surface-Faradaic (pseudocapacitive) processes are employed, and henceforth, the journey of chemical supercapacitors is commenced. The materials, mechanisms and constructions of chemical supercapacitors based on metallic compounds and conducting polymers are vividly discussed. Inherent limitations of these materials are addressed, and the feasible mitigation measures are identified. Poor conductivity, slow diffusion kinetics and rapid structural disintegration over cycling are the common constraints of metallic compounds, and that can be overcome by preparing conductive nanocomposites. Versatile conductive nanocomposites of metal oxides, hydroxides, carbides, nitrides, phosphides, phosphates, phosphites, chalcogenides are elaborated. Lack of structural integrity is the prime obstacle for realization of conducting polymers based supercapacitors, and it may be overruled by forming composites with robust supports from carbonaceous materials or metallic compounds. Consequently, the composites of polyaniline, polypyrrole, polythiophene and polythiophene-derivatives are discussed. The historical accounts of early stages of works are emphasised in order to review the developmental pathways of chemical supercapacitors. Constructions of full cells and their performance data are presented herein that synchronize the behaviour of practical scaled-up devices. To best of our knowledge, this review is the first holistic description of chemical supercapacitors based on metallic compounds and conducting polymers from first reports to recent advancements.
The impact of Zn dopant on the phase, energy gap, functional group, microstructure,
cyclic voltmeter and GCD behavior of CeO2 quantum dots prepared via a simple precipitation method is discussed in this article. The XRD analysis indicates that Zn doping doesn’t alter the basic FCC structure of CeO2. The crystalline size and lattice constant were found to decrease with increasing the Zn dopant. The optical studies disclose that Zn2+ doping increases the bandgap (Eg) of CeO2 from 3.37 to 3.86 eV. The blue shift in the absorption edge confirmed the quantum confinement effect. The photoluminescence spectra displayed strong UV emission due to Zn doping in CeO2 quantum dots. FESEM and TEM study reveals that the synthesized samples consist of spherical to nanoclusters morphology and the particle size varies between 11- 4 nm. The presence of Ce-Zn-O bonds has been identified via FT-IR and EDS analysis. The electrochemical analysis suggests that the reported samples exhibit
better electrochemical behavior. GCD study confirmed the 5wt% Zn doped CeO2 quantum
dots exhibit a higher specific capacitance of 358Fg−1 at a current density of 10Ag-1. The
electrode stability was tested for Zn doped CeO2 electrode it shows 96% of cyclic stability
even after 1000 continuous charge-discharge cycles. The cyclic voltmeter, GCD, power
density, energy density and cyclic stability analysis suggest that the Zn doped CeO2 quantum dots could be utilized as electrode material for supercapacitor application.
This article focuses on structural, optical, magnetic, and dielectric behavior of Ni-substituted CeO2 quantum dots synthesized by efficient chemical precipitation technique. Synthesized nanopowders were analyzed by XRD, FESEM, TEM, FT-IR, UV, PL, dielectric, electrochemical, and magnetic behavior. X-ray diffraction technique stipulated the nanopowders that exhibit FCC structure and don't have any unwanted phases. FESEM and TEM analyses showed that the particles are in the nanometer range and the microstructure alternation evidenced from spherical to the nanorods. The functional group and compositional study confirmed the substitution of Ni within CeO2. The UV–Vis absorption spectrum approved the blue shift in absorption and increase in bandgap from 3.39 to 4.20 eV. The photoluminescence study confirmed the strong blue emission with the increase of Ni concentration. VSM analysis demonstrated that the Ni-doped CeO2 quantum dots are ferromagnetic nature and the magnetization increased. The electrochemical analysis confirmed the increase of supercapacitance property of CeO2 nanoparticles with Ni at a low scan rate. The dielectric analysis suggested that the CeO2: Ni can be utilized for the capacitor application.
The practical exploration of electrode materials with complex hollow structures is of considerable significance in energy storage applications. Mixed-metal selenides (MMSs) with favorable architectures emerge as new electrode materials for supercapacitor (SC) applications owing to their excellent conductivity. Herein, a facile and effective metal-organic framework (MOF)-derived strategy is introduced to encapsulate multi-shelled zinc-cobalt selenide hollow nanospheres positive, and yolk-double shell cobalt iron selenide hollow nanospheres negative electrode materials with controlled shell numbers in graphene network (denoted as G/MSZCS-HS and G/YDSCFS-HS, respectively) for SC applications. Due to the considerable electrical conductivity and unique structures of both electrodes, the G/MSZCS-HS positive and G/YDSCFS-HS negative electrodes reveal remarkable capacities (~376.75 mAh g-1 and 293.1 mAh g-1 respectively, at 2 A g-1), superior rate performances (83.4%, and 74%, respectively), and amazing cyclability (96.8% and 92.9%, respectively). Furthermore, an asymmetric device (G/MSZCS-HS//G/YDSCFS-HS) has been fabricated with the ability to deliver an exceptional energy density (126.3 W h kg-1 at 902.15 W kg-1), high robustness of 91.7%, and reasonable capacity of 140.3 mAh g-1.
The present work reports the synthesis of a composite of TiO2 nanosheets (NS) with reduced graphene oxide (rGO) for supercapacitor applications. The formation of composite has been achieved via a simple one-pot hydrothermal method. The rGO/TiO2 NS composite was used to fabricate a flexible electrode which, in presence of 1 M H2SO4 as an electrolyte, has shown a high specific capacitance of 233.67 F/g at a current density of 1 A/g within a potential window of 0–1 V. This enhanced supercapacitance of the rGO/TiO2 NS electrode is attributed to the synergistic effects from TiO2 and rGO NS which help in to attain a low equivalent series resistance and enhanced ion diffusion. Furthermore, the fabricated composite electrode has displayed a long-term cyclic stability, retaining a specific capacitance of 98.2% even after 2000 charge–discharge cycles. The proposed rGO/TiO2 NS electrode has delivered high values of energy (32.454 Wh/kg) and power (716.779 W/kg) densities. Interestingly, it is possible to retrieve a sufficiently high energy density of 24.576 Wh/kg which could generate a power density value of as high as 2142.84 W/kg. The above results reveal that the herein proposed thin film composite of rGO/TiO2 NS can offer extraordinary performance as a supercapacitor electrode compared to its nanotubes or nanoparticles.
The search for faster, safer and more efficient energy storage systems continues to inspire researchers to develop new energy storage materials with ultrahigh performance. Mesoporous nanostructures are interesting for supercapacitors because of their high surface area, controlled porosity and large number of active sites, which promise the utilization of the full capacitance of active materials. Herein, highly ordered mesoporous CuCo2O4 nanowires have been synthesized by nanocasting from a silica SBA-15 template. These nanowires exhibit superior pseudocapacitance of 1210 F g-1 in the initial cycles. Electro-activation of the electrode in the subsequent 250 cycles causes a significant increase in capaci-tance to 3080 F g-1. An asymmetric supercapacitor composed of mesoporous CuCo2O4 nanowires for the positive elec-trode and activated carbon for the negative electrode demonstrates an ultrahigh energy density of 42.8 Wh kg-1 with a power density of 15 kW kg-1 plus excellent cycle life. We also show that two asymmetric devices in series can efficiently power 5 mm diameter blue, green, and red LED indicators for 60 min. This work could lead to a new generation of hy-brid supercapacitors to bridge the energy gap between chemical batteries and double layer supercapacitors.
Fiber electrochemical capacitors show advantages for lightweight and flexible, and may be also easily integrated or woven into various electronic devices with low cost and high efficiency. In this work, we report the preparation of ZnCo2O4 nanorods on a Ni wire as the fiber electrodes, using a simple and rapid single-step hydrothermal process. The electrochemical properties of the free-standing supercapacitor were analyzed using a two electrode system. The supercapacitor achieved a specific capacitance of 10.9 F/g. An energy density of 76 mWh/kg and a power density up to 1.9 W/kg were also obtained for the fiber supercapacitors. The flexible supercapacitor exhibited remarkable electrochemical stability when subjected to bending at various angles, illustrating the promise for use as electrodes for wearable energy storage.
Hierarchical porous ZnCo2O4 microspheres have been successfully synthesized via a solvothermal method followed by an annealing process. The ZnCo2O4 electrode shows a high specific capacitance of 647.1 F g-1 at 1 A g-1 and 440.6 F g-1at 10 A g−1 in 2 M KOH. After 2000 cycles, the capacity loss is only 8.5%.
Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.
Here we reported a novel route to synthesize a hierarchical nanocomposite (PANI-frGO) of polyaniline (PANI) nanowire arrays covalently bonded on reduced graphene oxide (rGO). In this strategy, nitrophenyl groups were initially grafted on rGO via C-C bond, and then reduced to aminophenyl to act as anchor sites for the growth of PANI arrays on rGO. The functionalized process was confirmed by atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and thermogravimetric analysis. The electrochemical properties of the PANI-frGO as supercapacitor materials were investigated. The PANI-frGO nanocomposites showed high capacitance of 590 F g(-1) at 0.1 A g(-1), and had no loss of capacitance after 200 cycles at 2 A g(-1). The improved electrochemical performance suggests promising application of the PANI-frGO nanocomposites in high-performance supercapacitors.
Vanadium oxides may offer high pseudocapacitance but limited electrical conductivity and specific surface area. Atomic layer deposition allowed uniform deposition of smooth nanostructured vanadium oxide coatings on the surface of multi-walled carbon nanotube (MWCNT) electrodes, thus offering a novel route for the formation of binder-free flexible composite electrode fabric for supercapacitor applications with large thickness, controlled porosity, greatly improved electrical conductivity and cycle stability. Electrochemical measurements revealed stable performance of the selected MWCNT–vanadium oxide electrodes and remarkable capacitance of up to 1550 F g−1 per active mass of the vanadium oxide and up to 600 F g−1 per mass of the composite electrode, significantly exceeding specific capacitance of commercially used activated carbons (100–150 F g−1). Electrochemical performance of the oxide layers was found to strongly depend on the coating thickness.
In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).
Capacitance loss with the increase of mass loading, originating from the slow electron and ion migration kinetics through the thick electrode materials, has been the subject of intense investigation in the field of supercapacitor. In this work, we report the preparation of a mixed-valence molybdenum oxide (MoO3-x) electrode with ultrahigh mass loading of 15.4 mg cm-2 on functionalized partial-exfoliated graphite substrate using a facile electrochemical method. In addition to the highly open graphene nanosheets atop, the unique layered structures of intercalated graphite sheets ensure efficient ionic transport in the entire MoO3-x electrode. The oxygen-containing functional groups on the exfoliated graphene can bind strongly with the MoO3-x via formation of C-O-Mo bonding, which provides fast electron transport path from graphene to MoO3-x and thus allows high reversible capacity and excellent rate performance. The optimized MoO3-x electrode delivers an outstanding areal capacitance of 4.03 F cm-2 at 3 mA cm-2 with an excellent rate capability which is significantly higher than the values of other molybdenum oxide based electrodes reported to date. More importantly, the areal capacitance increases proportionally with the MoO3-x mass loading, indicating that the capacitive performance is not limited by ion diffusion even at such a high mass loading. An asymmetric supercapacitor (ASC) assembled with MoO3-x anode delivers a maximum volumetric energy density of 2.20 mWh cm-3 at a volumetric power density of 3.60 mW cm-3, which is superior to the majority of the state-of-the-art supercapacitors.
The development of high-capacity, stable cycling, and high mass loading cathode materials for asymmetric supercapacitors has been the subject of intense exploration. In this work, a morphology-controlled growth of well-aligned zinc-nickel-cobalt ternary (oxy)hydroxide (Zn-Ni-Co TOH) nanostructure is used, for the first time, as a high-performance cathode material for supercapacitors. Our findings demonstrate that precursor Zn-Ni-Co TOH materials can deliver superior capacity and rate capability to the Zn-Ni-Co oxide. A high mass loading of 7 mg cm-2 on carbon cloth substrate is achieved, accompanied with the substantially improved facile ionic and electric transport due to the highly open well-defined nanoarray architecture. The growing mechanism of Zn-Ni-Co TOH was studied in depth by scanning electron microscopy analysis. The optimized Zn-Ni-Co TOH-130 nanowire array electrode delivered an outstanding areal capacitance of 2.14 F cm-2 (or a specific capacitance of 305 F g-1) at 3 mA cm-2 and an excellent rate capability. Moreover, the asymmetric supercapacitor assembled with our Zn-Ni-Co TOH-130 cathode exhibited a maximum volumetric energy density of 2.43 mWh cm-3 at a volumetric power density of 6 mW cm-3 and a long-term cycling stability (153% retention in 10,000 cycles), which are superior to the majority of the state-of-the-art supercapacitors. This work paves the way to the construction of high-capacity cathode materials for widespread applications including next-generation wearable energy-storage devices.
Pure LiNi1−xCoxPO4 (x = 0, 0.2, 0.5, 0.8, 1) was synthesized by spray pyrolysis followed by heat treatment. The X-ray diffraction (XRD) patterns of LiNi1−xCoxPO4 were indexed to olivine structure with a Pnma space group. The peak shift and variation of lattice parameters suggested that LiNi1−xCoxPO4 solid solution was formed. Moreover, LiNi1−xCoxPO4/C (x = 0, 0.2, 0.5, 0.8, 1) nanocomposites were successfully synthesized by a combination of spray pyrolysis and wet ball milling followed by heat treatment. The XRD patterns of all samples were indexed to olivine structure with a Pnma space group. From scanning electron microscopy images, the primary particle sizes of LiNi1−xCoxPO4/C nanocomposites were reduced to the range of approximately 50–100 nm. LiNi0.5Co0.5PO4/C cathode exhibited a higher first discharge capacity and cyclability than those of pure LiNi0.5Co0.5PO4. Cyclic voltammetry data demonstrated that reduction peaks of LiNi0.5Co0.5PO4/C cathode occur at 4.44 V and 4.71 V, which were ascribed to Co³⁺/Co²⁺ and Ni³⁺/Ni²⁺ reduction couples, respectively. Electrochemical impedance spectroscopy data revealed that the LiNi0.5Co0.5PO4/C cathode had a smaller charge transfer resistance, resulting in a faster redox reaction kinetics for the lithium insertion and extraction, due to reduced particle size and introduced conductive carbon.
The specific surface area and pore size of illustrative electrode material is a promising task to achieve better performance of energy storage devices. In this respect, Mg-substituted Ni1-xMgxCo2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) samples were synthesized by cost-effective and facile hydrothermal method. As-prepared samples were evaluated as the electrode material for a battery application. The structural and electrochemical characterization analysis has been carried out systematically. Among different samples, NMC50 (x = 0.5) exhibit highest BET surface area of 61 m²g⁻¹ with a suitable pore volume of 0.3029 cm³g⁻¹ and narrow pore size distribution of 2–10 nm. It is verified that the special features of the NMC50 including uniformity of the surface texture and porosity bring significant effect on the electrochemical performances. Consequently, the excellent specific capacity of 302 mAhg⁻¹ is observed for NMC50 sample at a current density of 1.1 Ag⁻¹ and a remarkable cyclic stability of ∼95% is maintained over 2000 continuous charge-discharge cycles. The improved electrochemical performance of NMC50, undoubtedly makes it worth as an excellent electrode material for high-performance energy storage applications.
Zeolitic imidazolate frameworks have stimulated great attention due to their some potential applications in energy storage, catalysis, gas sensing, drug delivery and etc. In this paper, a three-dimensional porous nanomaterials Co3O4/ZnCo2O4/CuO with hollow polyhedral nanocages structures and highly enhanced electrochemical performances are synthesized successfully by a zeolitic imidazolate framework-67 route. The composites hold the shape of the ZIF-67 templates well and the shell has multi-compositions. In the process, we first synthesized the nanostructure hydroxide precursors and then transformed them into corresponding metal oxide composites by thermal annealing in air. In addition, the mass ratio of Zn to Cu in this material is discussed and optimized. We found that when the mass ratio is 3, the composite material has better electrochemical properties. When applied as electrode material, the Co3O4/ZnCo2O4/CuO-1 shows enhanced pseudocapacitive property and good cycling stablity compared with Co3O4/ZnCo2O4, Co3O4/CuO and Co3O4/ZnCo2O4/CuO-2, Co3O4/ZnCo2O4/CuO-3. The assembled Co3O4/ZnCo2O4/CuO-1//AC hybrid device can be reversibly cycled in a large potential range of 0-1.6 V and deliver high energy density of 35.82 Wh kg-1 as well as the maximum power density of 4799.25 W kg-1.
In pursuit of high specific capacitance and high energy density; morphology, specific surface area and conductivity of electrode material are key factors. In this context, Ni1-xMgxCo2O4@C (x = 0.0, 0.5) nanostructures are synthesized via facile hydrothermal route using the cotton template. Notably; the morphology altered from flowers to rods with the incorporation of cotton templates. Additionally, Mg dopant ion helps to attain greater electrical conductivity while preventing the morphology. Besides, Influence of Mg doping on the pseudocapacitance of NiCo2O4 electrode was investigated by electrochemical analysis in 6 M KOH electrolyte. This remarkable synergy display superb electrochemical performance for Ni0.5Mg0.5Co2O4@C rods, i.e a high specific capacitance of 1340 Fg⁻¹ at a current density of 1 Ag⁻¹ and admirable cyclic stability of ∼97% up to 2000 charge-discharge cycles (at 15 Ag⁻¹). Further, the proposed Ni0.5Mg0.5Co2O4@C rods electrode delivered high values of energy (59.5 Wh/Kg) & power (799.2 W/Kg) densities at a current density of 1 Ag⁻¹, which is 2 times more as compared to flowers structured material. This can be attributed to increase in the specific surface area with more porous nature of rods. This work conveys the deeper understanding of the morphology and chemical composition effect on the supercapcitive performance of Ni0.5Mg0.5Co2O4@C. Thus, Ni0.5Mg0.5Co2O4@C ([email protected]) rods may be an excellent electrode material for high-performance supercapacitor due to its exceptional electrochemical performances.
Mn-doped ZnCo2O4 nanoparticle has been synthesized by hydrothermal method without adding any surfactants. Structural, morphological and electrochemical performances have been studied for the pure and various concentration of Mn-doped ZnCo2O4 nanoparticles. XRD and Raman studies demonstrate the crystalline structure of the material. Specific capacitance of the 10 wt% Mn doped ZnCo2O4 nanomaterial is analysed using the three-electrode system. 10 wt% Mn-doped ZnCo2O4 has a maximum capacitance of 707.4 F g⁻¹ at a current density of 0.5 A g⁻¹. Coulombic efficiency of the material is 96.3% for 500 cycles in the KOH electrolyte medium. A two-electrode device using 10 wt% Mn-doped ZnCo2O4 exhibits the highest specific capacitance of 6.5 F g⁻¹ at a current density of 0.03 A g⁻¹ which is the suitable material for supercapacitor application.
Abstract
Novel heterostructure is fabricated by combining electrochemically and optically active materials for high supercapacitive response of 896 F/g at 5 A/g. Network of ZnCo2O4 nanorods (NRs) are directly grown on three dimensional matrix of H:ZnO NRs (ZnCo2O4/H:ZnO NRs) that offers synergistic advantages by providing an optimum ion/charge transportation path, large electrochemically active surface area and stable capacitive response during electrolytic process. Furthermore, the fabricated solid-state asymmetric supercapacitor, ZnCo2O4/H:ZnO NRs//activated carbon induces a large potential window of 1.5 V that offers excellent energy and power densities. In addition, optically active ZnCo2O4/H:ZnO NRs is also used for the conversion of optical energy in a broad wavelength range thus as-fabricated asymmetric solid-state supercapacitor could easily provide the required power for the operation of a photodetector. Therefore, unique heterostructure of ZnCo2O4/H:ZnO NRs not only presents excellent supercapacitive response but also demonstrates great potential for energy conversion.
Herein, zinc cobaltite (ZnCo2O4) nanoparticles (synthesized via hydrothermal treatment) were blended with polyaniline (PANI) (synthesized via chemical oxidative polymerization) to form PANI-ZnCo2O4 nanocomposite. The structural crystallinity and phase purity of PANI-ZnCo2O4 nanocomposite were authenticated by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The morphological studies showed that the spinel structured ZnCo2O4 nanoparticles were well embedded on tubular-shaped PANI matrix, suggesting the effective connection between ZnCo2O4 nanoparticles with PANI matrix. The electrochemical performance studies of PANI-ZnCo2O4 nanocomposite for supercapacitor exhibited enhanced specific capacity of 398 C/g at a current density of 1 A/g as compared with ZnCo2O4 nanoparticles and PANI. The enhancement of electrochemical performance was contributed from the augmentation of electroactive sites for redox reaction, rapid electron transfer rate and the synergistic effect of ZnCo2O4 nanoparticles and highly conductive PANI. The fabricated PANI-ZnCo2O4//activated carbon based hybrid supercapacitor achieved high energy density (13.25 Wh/kg at 375 W/kg) as well as excellent cycling stability (∼90% retention after 3000 cycles). Furthermore, PANI-ZnCo2O4 nanocomposite was employed as a hydrazine sensor which exhibited good sensitivity of 0.43 μA μM⁻¹ in the linear range of 0.1–0.6 mM with a low detection limit of 0.2 μM.
Prussian blue and its analogues are promising for energy storage devices owing to the rigid open framework, yet suffer from poor conductivity and relatively low energy density. Herein, we report a facile preparation of cobalt hexacyanoferrate/reduced graphene oxide nanocomposites (CoHCF/rGO) for supercapacitors with enhanced performance. The CoHCF nanoparticles with a size of around 50 nm are adhered onto the rGO nanosheets, which, in turn, not only prevent the agglomeration of the CoHCF nanoparticles but also provide conductive network for fast electron transport. The CoHCF/rGO nanocomposite delivers a maximum specific capacitance of 361 F g⁻¹ in Na2SO4 aqueous electrolyte. Asymmetric supercapacitor cells are assembled by pairing up an optimized nanocomposite electrode with an activated carbon negative electrode, which exhibits a wide reversible operating voltage of 2.0 V and a high energy density of 39.6 Wh kg⁻¹. The enhanced electrochemical performance of CoHCF/rGO benefits from the strong synergistic utilization of CoHCF nanoparticles and rGO nanosheets, rendering the nanocomposites a great promise for high-performance supercapacitors.
Ternary ZnCo2O4/reduced graphene oxide/NiO (ZCGNO) nanowire arrays were grown directly on a piece of Ni foam using a simple, facile, cost effective hydrothermally assisted thermal annealing process without the addition of any Ni precursor salt and used as a binder-free supercapacitor electrode. Ni foam was utilized successively as the NiO precursor, binder, and current collector. The resulting 3D ternary composite possessed an ultrahigh specific capacitance of 1,256 F/g at a current density of 3 A/g in 6 M KOH solution. Moreover, the three dimensional electrode exhibited superior electrochemical performance, such as excellent cyclic stability (~ 80% capacitance retention after 3,000 cycles), maximum energy density of 62.8 Wh/kg, maximum power density of 7,492.5 W/kg, and low equivalent series resistance (0.58 Ω). The effects of the electrolyte concentration on the electrochemical performance of ZCGNO were also examined. ZCGNO with this remarkable electrochemical performance may be considered a prospective candidate for high performance supercapacitor applications.
Mesoporous Ni-doped MnCo2O4 hollow nanotubes (denoted as MCNO-HNTs) are successfully prepared through simple single-nozzle electrospinning combined with thermal treatment. MCNO-HNTs obviously exhibit a hollow structure and are assembled by a lot of small nanoparticles. When used as an anode material for sodium-ion batteries (SIBs), this electrode exhibits remarkable capacity retention of 81% at 1 A g⁻¹ even after 11000 cycles. The outstanding electrochemical performance can be attributed to the unique hollow mesoporous structure that alleviates stress caused by large volume changes, suppresses the agglomeration of the pulverized nanoparticles, and facilitates the transfer of electrons and electrolyte ions during prolonged cycling. Furthermore, the pseudocapacitive behavior of this material also effectively improves the electrochemical reaction kinetics. Therefore, due to the simple single-nozzle electrospinning technique and high electrochemical performance, mesoporous MCNO-HNTs have great potential as an anode material for rechargeable SIBs.
Three dimensional free-standing film electrode has aroused great interest for energy storage devices. However, small volumetric capacity and low operating voltage limit its practical application for large energy storage applications. Herein, a facile and novel nanofoaming process was demonstrated to boost the volumetric electrochemical capacitance of the devices via activation of Ni nanowires to form ultrathin nanosheets and porous nanostructures. The as-designed free-standing Ni@Ni(OH)2 film electrodes display a significantly enhanced volumetric capacity (462 C/cm3 at 0.5 A/cm3) and excellent cycle stability. Moreover, the as-developed hybrid supercapacitor employed Ni@Ni(OH)2 film as positive electrode and graphene-carbon nanotube film as negative electrode exhibits a high volumetric capacitance of 95 F/cm3 (at 0.25 A/cm3) and excellent cycle performance (only 14% capacitance reduction for 4500 cycles). Furthermore, the volumetric energy density can attain to 33.9 mWh/cm3, which is much higher than most thin film lithium batteries (1–10 mWh/cm3). This work gives an insight for designing high-volumetric three dimensional electrodes and paves a new way to construct binder-free film electrode for high-performance HSC applications.
ZnCo2O4 nanoparticles (NPs) with four different and unique morphologies were synthesized using different mass ratio of polyvinyl pyrrolidone (PVP) with respect to metal oxides: 0.55 wt% PVP (P1), 1.09 wt% PVP (P2), 1.64 wt% PVP (P3) and 2.18 wt% PVP (P4), through a facile hydrothermal process followed by heat treatment and used as electrodes for high performance pseudocapacitor. In this study, PVP served as surface stabilizer and growth modifier during NPs synthesis. Each mass ratio of PVP with respect to metal oxides resulted to different unique morphologies: rods, ring, oval “rice grain”, and hexagonal-like shape composed of numerous ZnCo2O4 NPs. The resulting products were analyzed by using thermo gravimetric analysis (TGA), x-ray diffraction (XRD), field emission scanning electron micrographs (FE-SEM) coupled with energy dispersive X-ray spectrometer (EDX), high-resolution transmission electron microscopy (HR-TEM) and Brunauer-Emmett-Teller (BET). ZnCo2O4 NPs with ring-like morphology (P2) showed the highest specific capacitance of 2834.18 F g⁻¹ at a scan rate of 2 mV s⁻¹. Additionally, P2 material also showed the highest specific capacitance of 1152.19 F g⁻¹ at a current density of 5 A g⁻¹ and displayed excellent cycling ability even after 3000 cycles at 50 mV s⁻¹ scan rate.
Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling fl exible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices. © 2010 Nature Publishing Group, a division of Macmillan Publishers Limited and published by World Scientific Publishing Co. under licence. All Rights Reserved.
Hierarchical ZnCo2O4 nanoneedle arrays are vertically grown on porous carbon nanofibers (PCFs) to form a core-shell heterostructure through a facile hydrothermal method followed by thermal treatment. Such a unique configuration makes full use of the synergistic effects from both excellent electrical conductivity of PCFs and high specific capacitance of ZnCo2O4, endowing the hybrid to be an excellent electrode for flexible supercapacitors. Benefiting from their intriguing structural features, the PCF@ZnCo2O4 hybrid possesses fascinating electrochemical performance as an integrated binder-free electrode for supercapacitors. Remarkably, this PCF@ZnCo2O4 electrode could achieve a high capacitance of 1384 F g-1 at a scan rate of 2 mV s-1. Moreover, an all-solid-state asymmetric supercapacitor fabricated with the as-prepared PCF@ZnCo2O4 hybrid as the positive electrode and PCFs as the negative electrode achieves a high energy density of 49.5 W h kg-1 (based on the total mass of the material on the two electrodes) at a power density of 222.7 W kg-1. Furthermore, the all-solid-state asymmetric supercapacitor device exhibits remarkable cycling stability with 90% specific capacitance retention after 3000 cycles. Therefore, these fascinating electrochemical performances make this material hold great promise for next-generation high-energy supercapacitor applications.
Hierarchically mesoporous carbon nanopetals (CNPs) are synthesized on unidirectional carbon fibers (UCFs) by catalytic chemical vapour deposition. The CNPs synthesized on UCFs (CNPs/UCFs) are further used as electrode-cum-current collectors for fabricating a flexible supercapacitor. Highly bendable and electrically conductive UCFs are used as both the substrate for the growth of CNPs and current collectors for the supercapacitor and no other separate current collectors are used in this study. The CNPs/UCF hybrids are characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and Brunauer-Emmett-Teller surface area measurements. The electrochemical performance of the CNPs/UCF supercapacitor is examined by electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge/discharge measurements. The mesoporous CNPs/UCF hybrid electrode based symmetric supercapacitor is highly bendable and the performance of the supercapacitor is unaltered even at severe bending angles. The CNPs/UCF supercapacitor exhibits a high gravimetric capacitance of 154 F g-1 with a high specific power density of 32 kW kg-1 at a current density of 16.66 mA cm-2. The enhanced supercapacitive performance of the CNPs/UCF supercapacitor is mainly due to the mesoporous electrode nanostructure as well as due to the presence of oxygen-containing functional groups on the surface of CNPs/UCF hybrids. The CNPs/UCF supercapacitor possesses a super-long cyclic stability of more than 28 900 cycles. The supercapacitive performance of the CNPs/UCF supercapacitor is comparable to that of those utilizing other carbon nanomaterial based electrodes.
Electrodes with rationally designed hybrid nanostructures can offer many opportunities for enhanced performance in electrochemical energy storage. In this work, hierarchical ZnCo2O4/polypyrrole (PPy) nanostructures on Ni foam were rationally designed and successfully fabricated through a facile two-step method and were directly used as an integrated electrode for supercapacitors. The novel nanoscale morphology has been proven to be responsible for their excellent capacitive performance. When used as electrodes in supercapacitors, the hybrid nanostructures demonstrated prominent electrochemical performance with a high specific capacitance (1559 F g-1 at a current density of 2 mA cm-2), a good rate capability (89% when the current density increases from 2 to 20 mA cm-2), and a good cycling ability (90% of the initial specific capacitance remained after 5000 cycles at a high current density of 10 mA cm-2). Moreover, the high specific energy density is 30.9 W h kg-1 at a current density of 2 mA cm-2 in a two-electrode system. The excellent electrochemical performance of hierarchical ZnCo2O4/PPy nanostructures can be mainly ascribed to the enhanced adherent force between electrode materials and Ni foam to hold the electrode fragments together by means of ZnCo2O4 nanowires, the good electrical conductivity of PPy, and the short ion diffusion pathway in ordered porous PPy nanofilms and ZnCo2O4 nanowires.
Mesoporous NiCo2O4 nanosheets can be directly grown on various conductive substrates, such as Ni foam, Ti foil, stainless-steel foil and flexible graphite paper, through a general template-free solution method combined with a simple post annealing treatment. As a highly integrated binder- and conductive-agent-free electrode for supercapacitors, the mesoporous NiCo2O4 nanosheets supported on Ni foam deliver ultrahigh capacitance and excellent high-rate cycling stability.
Mesoporous zinc cobaltite (ZnCo2O4) microspheres have been successfully prepared by a facile solvothermal method followed by an annealing process. The as-prepared ZnCo2O4 displays uniform sphere-like morphology composed of interconnected ZnCo2O4 nanoparticles. The Brunauer–Emmett–Teller (BET) surface area of mesoporous ZnCo2O4 microspheres is about 51.4 m2 g−1 with dominant pore diameter of 7.5 nm. The novel ZnCo2O4 material exhibits high specific capacitance of 953.2 F g−1 and 768.5 F g−1 at discharge current densities of 4 A g−1 and 30 A g−1, respectively. The energy density can be estimated to be 26.68 Wh kg−1 at a power density of 8 kW kg−1. The specific capacitance retention is 97.8% after 3000 cycles, suggesting its excellent cycling stability. The superior electrochemical performance is mainly attributed to the uniformity of the surface structure and the porosity of the microspheres, which benefit electrons and ions transportation, provide large electrode-electrolyte contact area, and meanwhile reduce volume change during the charge–discharge process. This method of constructing porous microspheres is very effective, yet simple, and it could be applied in other high-performance metal oxide electrode materials for electrochemical capacitors, as well as in Li-ion batteries.
Cobalt oxide nanoparticles synthesized through simple microwave method are employed for supercapacitor studies. XRD analysis reveals the cubic phase of the synthesized nanoparticles. TEM image indicate uniform distribution of the nanoparticles. The blue shift of the band gap energy as obtained through optical absorption studies confirms the quantum confinement effect. PL spectra recorded at room temperature exhibit a broad emission in the UV/Violet region. Maximum specific capacitance of 519 F/g was obtained from charge-discharge studies. After 1000 cycles of continuous charge-discharge cycles, only about 1.3% degradation in specific capacitance could be noticed. The microwave-assisted synthesized cobalt oxide nanoparticle appears to be a promising electrode material for supercapacitor application.
Uniform ZnCo2O4 nanowire arrays were directly grown on nickel foam through a facile hydrothermal method and subsequent thermal treatment process. The ZnCo2O4 nanowires have diameters of about 100 nm and lengths of up to 5 μm. The as-obtained ZnCo2O4 nanowire array loaded nickel foam can be directly applied as an electrode for high-performance supercapacitors. Electrochemical measurements show that the ZnCo2O4/nickel foam electrode has high specific capacitance (1625 F g−1 at 5 A g−1), excellent rate capability (59% capacitance retention at 80 A g−1) and good cycling stability (94% capacitance retention over 5000 charge–discharge cycles). This work demonstrates that ZnCo2O4 nanowires are highly desirable for application as advanced electrochemical electrode materials.
A series of hybrid electrochemical capacitors were fabricated by using the flower-like cobalt hydroxide (Co(OH)2) and urchin-like vanadium nitride (VN) as the positive and negative electrode materials, respectively. Both Co(OH)2 and VN electrode materials showed excellent electrochemical performance due to their unique structure and fast reversible Faradic reaction characteristics. With different operation voltage window (OVW) and negative/positive mass ratios, the impact on capacitance performance of the hybrid supercapacitor was investigated thoroughly, which demonstrated that both mass ratio and OVW played an important role in their capacitance performance. Furthermore, theoretical modeling was performed and the simulation result was found to be in agreement with the experimental result for the influence of the negative/positive mass ratio on capacitance performance of the hybrid supercapacitor. When an optimized negative/positive mass ratio was located, the Co(OH)2//VN hybrid supercapacitor could be cycled reversibly in the high-voltage region of 0–1.6 V and delivered a high energy density of 22 W h kg−1. Even at a large power density of 15.9 kW kg−1, the hybrid supercapacitor still possessed a desirable specific energy density of 9 W h kg−1. Such an impressive hybrid supercapacitor was expected to be a highly promising candidate for application in high-performance energy storage systems.
A new electrochemical synthesis route was developed to prepare spinel-type ZnCo2O4 and Co3O4 as high quality thin film-type electrodes for use as electrocatalysts for oxygen evolution reaction (OER). Whereas Co3O4 contains Co2+ in the tetrahedral sites and Co3+ in the octahedral sites in the spinel structure, ZnCo2O4 contains only Co3+ in the octahedral sites; Co2+ in the tetrahedral sites is replaced by Zn2+. Therefore, by comparing the catalytic properties of ZnCo2O4 and Co3O4 electrodes prepared with comparable surface morphologies and thicknesses, it was possible to examine whether Co2+ in Co3O4 is catalytically active for OER. The electrocatalytic properties of ZnCo2O4 and Co3O4 for OER in both 1 M KOH (pH 13.8) and 0.1 M phosphate buffer (pH 7) solutions were investigated and compared. The results suggest that the Co2+ in Co3O4 is not catalytically critical for OER and ZnCo2O4 can be a more economical and environmentally benign replacement for Co3O4 as an OER catalyst.
A series of flexible nanocomposite electrodes were fabricated by facile electro-deposition of cobalt and nickel double hydroxide (DH) nanosheets on porous NiCo2O4 nanowires grown radially on carbon fiber paper (CFP) for high capacity, high energy, and power density supercapacitors. Among different stoichiometries of CoxNi1–xDH nanosheets studied, Co0.67Ni0.33 DHs/NiCo2O4/CFP hybrid nanoarchitecture showed the best cycling stability while maintaining high capacitance of 1.64 F/cm2 at 2 mA/cm2. This hybrid composite electrode also exhibited excellent rate capability; the areal capacitance decreased less than 33% as the current density was increased from 2 to 90 mA/cm2, offering excellent specific energy density (33 Wh/kg) and power density (41.25 kW/kg) at high cycling rates (up to150 mA/cm2).
CuCo2O4 nanostructures were synthesized through a facile solution combustion method. Electrochemical investigations demonstrate a novel electrode material for supercapacitors with remarkable performance including high-rate capability, high-power density (22.11 kW kg(-1)) and desirable cycling stability at different current densities.
Much attention has been paid to explore electrode materials with enhanced supercapacitor performance as well as relatively low cost and environmental friendliness. In this work, the NiMoO4 nanospheres and nanorods have been synthesized by facile hydrothermal methods. The hierarchical NiMoO4 nanospheres were about 2.5 μm in diameter and assembled from thin mesoporous nanosheets with a thickness of about 10-20 nm. The NiMoO4 nanorods were about 80 nm in diameter and about 300 nm to 1 μm in length. Then their electrochemical properties were investigated as electrode materials for supercapacitors (SCs). The NiMoO4 nanospheres exhibited a higher specific capacitance, better cycling stability and rate capability, which were attributed to the large surface area and high electrical conductivity. The specific capacitances were 974.4, 920.8, 875.5, 859.1, and 821.4 F/g at different current densities of 1, 2, 4, 6, and 10 A/g, respectively. Remarkably, the energy density could reach to 20.1 Wh/kg at a power density of 2100 W/kg. After 2000 cycles, The NiMoO4 nanospheres still displayed a high specific capacitance about 631.8 F/g at a current density of 5 A/g. These results implied that the hierarchical NiMoO4 nanospheres could be a promising candidate for high performance SCs.
We develop a facile synthesis route to prepare Cu doped hollow structured manganese oxide mesocrystals with controlled phase structure and morphology using manganese carbonate as the reactant template. It is shown that Cu dopant is homogeneously distributed among the hollow manganese oxide microspherical samples, and it is embedded in the lattice of manganese oxide by substituting Mn3+ in the presence of Cu2+. The crystal structure of manganese oxide products can be modulated to bixbyite Mn2O3 and tetragonal Mn3O4 in the presence of annealing gas of air and nitrogen, respectively. The incorporation of Cu into Mn2O3 and Mn3O4 induces a great microstructure evolution from core-shell structure for pure Mn2O3 and Mn3O4 samples to hollow porous spherical Cu-doped Mn2O3 and Mn3O4 samples with a larger surface area, respectively. The Cu-doped hollow spherical Mn2O3 sample displays a higher specific capacity of 642 mAhg-1 at a current density of 100 mA g-1 after 100 cycles, which is about 1.78 times improvement compared to that of 361 mA h g-1 for pure Mn2O3 sample, displaying a coulombic efficiency of up to 99.5%. The great enhancement of the electrochemical lithium storage performance can be attributed to the improvement of the electronic conductivity and lithium diffusivity of electrodes. The present results have verified the ability of Cu doping to improve electrochemical lithium storage performances of manganese oxides.
Hierarchical ZnCo2O4/nickel foam architectures were first fabricated from a simple scalable solution approach, exhibiting outstanding electrochemical performance in supercapacitors with high specific capacitance (～1400 F g-1 at 1 A g-1), excellent rate capability (72.5 % capacity retention at 20 A g-1), and good cycling stability (only 3% loss after 1000 cycles at 6 A g-1). All-solid-state supercapacitors were also fabricated by assembling two pieces of the ZnCo2O4-based electrodes, showing superior performance in terms of high specific capacitance and long cycling stability. Our work confirms that the as-prepared architectures can not only be applied in high energy density fields, but also be used in high power density applications, such as electric vehicles, flexible electronics, and energy storage devices.
The bare V2O5 and doped (V1.95M0.05)O5 (M = Nb, Ta) nano/submicron sized compounds were prepared by the simple polymer precursor method. The compounds were characterized by different physical and electroanalytical techniques. The effects of doping and different synthesis conditions on the energy storage performance of the V2O5 compounds were discussed. All compounds delivered a discharge capacity (at the end of the 2nd cycle) in the range 245 to 261 (±3) mA h g−1, except for the tantalum doped compound (V1.95Ta0.05)O5 which exhibited a discharge capacity of 210 (±3) mA h g−1, cycled in the range 2.0–4.0 V at a current rate of 120 mA g−1. An excellent cycling stability of 96% till twenty cycles was achieved for the compound V2O5 prepared by the polymer precursor method. Electrochemical impedance spectroscopy studies at different voltages during discharge and charge cycles were discussed in detail.
Co-doped NiO nanoflake arrays with a cellular-like morphology are fabricated by low temperature chemical bath deposition. As anode material for lithium ion batteries (LIBs), the array film shows a capacity of 600mAhg−1 after 50 discharge/charge cycles at low current density of 100mAg−1, and it retains 471mAhg−1 when the current density is increased to 2Ag−1. Appropriate electrode configuration possesses some unique features, including high electrode–electrolyte contact area, direct contact between each naonflake and current collector, fast Li+ diffusion. The Co2+ partially substitutes Ni3+, resulting in an increase of holes concentration, and therefore improved p-type conductivity, which is useful to reduce charge transfer resistance during the charge/discharge process. The synergetic effect of these two parts can account for the improved electrochemical performance.
Pure and doped manganese dioxides were prepared by wet-chemical method using fumaric acid and potassium permanganate as raw materials. X-ray diffraction patterns show that pure and Al, Cu and Mg doped manganese dioxides (d-MnO2) crystallized in the cryptomelane-MnO2 structure. Thermal analysis show that, with the assistance of potassium ions inside the 2×2 tunnel, the presence of Al, Cu and Mg doping elements increases the thermal stability of d-MnO2. The electrical conductivity of d-MnO2 increases in comparison with pure MnO2, while Al-doped MnO2 exhibits the lower resistivity. As shown in the magnetic measurements, the value of the experimental effective magnetic moment of Mn ions decreases with introduction of dopants, which is attributed to the presence of a mixed valency of high-spin state Mn4+/Mn3+. Doped MnO2 materials show good capacity retention in comparison with virgin MnO2. Al-doped MnO2 shows the best electrochemical results in terms of capacity retention and recharge efficiency.
Niobium doped lithium titanate with the composition of Li4Ti4.95Nb0.05O12 has been prepared by a sol–gel method. X-ray diffraction (XRD) and scanning electron microscope (SEM) are employed to characterize the structure and morphology of Li4Ti4.95Nb0.05O12. The Li4Ti4.95Nb0.05O12 electrode presents a higher specific capacity and better cycling performance than the Li4Ti5O12 electrode prepared by the similar process. The Li4Ti4.95Nb0.05O12 exhibits an excellent rate capability with a reversible capacity of 135mAhg−1 at 10C, 127mAhg−1 at 20C and even 80mAhg−1 at 40C. Electrical resistance measurement and electrochemical impedance spectra (EIS) reveal that the Li4Ti4.95Nb0.05O12 exhibits a higher electronic conductivity and faster lithium-ion diffusivity than the Li4Ti5O12, which indicates that niobium doped lithium titanate (Li4Ti4.95Nb0.05O12) is promising as a high rate anode for the lithium-ion batteries.
Hierarchical Cu doped vanadium pentoxide (V2O5) flowers were prepared via a simple hydrothermal approach followed by an annealing process. The flower precursors are self-assembled with 1D nanobelts surrounding a central core. The morphological evolution is investigated and a plausible mechanism is proposed. As the cathode material for lithium ion batteries, the Cu doped V2O5 samples exhibit improved electrochemical performance compared to the un-doped ones. Among them Cu0.02V1.98O5 delivered higher reversible specific capacities, better cycling stabilities and excellent rate capabilities, e.g. 97 mA h g(-1) at 20.0 C.
Various activated carbons from the PICA Company have been tested in supercapacitor cells in order to compare their performances. The differences measured in terms of specific capacitance and cell resistance are presented. Porosity measurements made on activated carbon powders and electrode allowed a better understanding of the electrochemical behaviour of these activated carbons. In this way, the PICACTIF SC carbon was found to be an interesting active material for supercapacitors, with a specific capacitance as high as 125 F/g.
Antimony doped SnO2 (ATO) microspheres composed of ATO nanoparticles were prepared by using a hydrothermal process in a nonaqueous and template-free solution from the inorganic precursors (SnCl4 and Sb(OC2H5)3). The physical properties of the as-synthesized samples were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, and X-ray photoelectron spectrum (XPS). The resulting particles were highly crystalline ATO microspheres in the diameter range of 3–10 μm and with many pores. The as-prepared samples were used as negative materials for lithium-ion battery, whose charge–discharge properties, cyclic voltammetry, and cycle performance were examined. The results showed that a high initial discharge capacity of 1981 mAh g−1 and a charge capacity of 957 mAh g−1 in a potential range of 0.005–3.0 V was achieved, which suggests that tin oxide-based materials work as high capacity anodes for lithium-ion rechargeable batteries. The cycle performance is improved because the conducting ATO nanoparticles can also perform as a better matrix for lithium-ion battery anode.
- Y Wang
- Y Xia
Y. Wang and Y. Xia, Adv. Mater., 2013, 25, 5336-5342.
- K A Wallace
- M Cychosz
- D Thommes
- E A Su
- R S Stach
- Ruoff
Wallace, K. A. Cychosz, M. Thommes, D. Su, E. A. Stach and R. S. Ruoff, Science, 2011,
332, 1537-1541.
- G Wang
- L Zhang
- J Zhang
G. Wang, L. Zhang and J. Zhang, Chem. Soc. Rev., 2012, 41, 797-828.
- L Yuan
- X. -H Lu
- X Xiao
- T Zhai
- J Dai
- F Zhang
- B Hu
- X Wang
- L Gong
- J Chen
- C Hu
- Y Tong
- J Zhou
- Z L Wang
L. Yuan, X. -H. Lu, X. Xiao, T. Zhai, J. Dai, F. Zhang, B. Hu, X. Wang, L. Gong, J. Chen, C.
Hu, Y. Tong, J. Zhou and Z. L. Wang, ACS Nano, 2012, 6, 656-661.
- K Naoi
- W Naoi
- S Aoyagi
- J. -I Miyamoto
- T Kamino
K. Naoi, W. Naoi, S. Aoyagi, J. -I. Miyamoto and T. Kamino, Acc. Chem. Res., 2013, 46,
1075-1083.
- Z. -Y Jin
- A. -H Lu
- Y. -Y Xu
- J. -T Zhang
- W. -C Li
Z. -Y. Jin, A. -H. Lu, Y. -Y. Xu, J. -T. Zhang and W. -C. Li, Adv. Mater., 2014, 26, 3700-3705.