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A representative (a) SEM image and (b) enlarged SEM image of highly porous carbon spheres (AC8K30, activated carbon spheres). (c) TEM image and (d) HRTEM image of the highly porous carbon spheres. The inset in (d) shows the FFT pattern revealing the amorphous structure of the carbon sphere.
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Electrochemical flow capacitors (EFCs) are highly promising for grid-scale energy storage since they benefit from having advantages of both electrochemical capacitors and flow batteries, including their high power density, long cycle lifetime, and scalable energy capacity. Here, we demonstrate a high-performance flow capacitor using redox-active hy...
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... for a large portion of the total volume of the slurry electrode. 18,19 We have utilized highly porous carbon spheres (AC8K30) as the active capacitive material to produce the owable elec- trodes. The morphology of the carbon spheres was examined by eld emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Fig. 2a and b show the SEM images of the highly porous carbon spheres that range in diameter from about 2 to 8 mm. From the TEM image (Fig. 2c), we also conrmed their spherical shape. Fig. 2d shows the high- resolution TEM (HRTEM) image of a porous carbon sphere and the corresponding fast Fourier transform (FFT) pattern (inset in Fig. 2d), which ...
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... active capacitive material to produce the owable elec- trodes. The morphology of the carbon spheres was examined by eld emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Fig. 2a and b show the SEM images of the highly porous carbon spheres that range in diameter from about 2 to 8 mm. From the TEM image (Fig. 2c), we also conrmed their spherical shape. Fig. 2d shows the high- resolution TEM (HRTEM) image of a porous carbon sphere and the corresponding fast Fourier transform (FFT) pattern (inset in Fig. 2d), which reveals the amorphous structure of the carbon sphere. N 2 adsorption/desorption isotherms of the AC8K30 porous carbon spheres (Fig. ...
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... elec- trodes. The morphology of the carbon spheres was examined by eld emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Fig. 2a and b show the SEM images of the highly porous carbon spheres that range in diameter from about 2 to 8 mm. From the TEM image (Fig. 2c), we also conrmed their spherical shape. Fig. 2d shows the high- resolution TEM (HRTEM) image of a porous carbon sphere and the corresponding fast Fourier transform (FFT) pattern (inset in Fig. 2d), which reveals the amorphous structure of the carbon sphere. N 2 adsorption/desorption isotherms of the AC8K30 porous carbon spheres (Fig. S1 in the ESI †) showed their signicantly high ...
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... (TEM). Fig. 2a and b show the SEM images of the highly porous carbon spheres that range in diameter from about 2 to 8 mm. From the TEM image (Fig. 2c), we also conrmed their spherical shape. Fig. 2d shows the high- resolution TEM (HRTEM) image of a porous carbon sphere and the corresponding fast Fourier transform (FFT) pattern (inset in Fig. 2d), which reveals the amorphous structure of the carbon sphere. N 2 adsorption/desorption isotherms of the AC8K30 porous carbon spheres (Fig. S1 in the ESI †) showed their signicantly high specic surface area (SSA) of $3600 m 2 g À1 ...
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... s À1 for a slurry with a solid-to-liquid mass ratio of 1 : 4). 14 For the unmodied double-layer capacitive slurry electrode and the HQ-based pseudocapacitive slurry electrode, X-ray photoelectron spectroscopy (XPS) analysis was performed to conrm the difference between the two samples and the successful adsorption of HQ on the carbon spheres ( Fig. S2-S5 in the ESI ...
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Citations
... A promising perspective would consist of using pseudo-capacitive flow electrodes by introducing active redox species, such as quinone derivatives, in the formulations. This approach has already been proved to be efficient at increasing performances of flow electrochemical systems [38][39][40][41][42]. ...
Flowable electrodes, a versatile alternative to traditional solid electrodes for electrochemical applications, exhibit challenges of high viscosity and carbon content, limiting flow and device performances. This study introduces colloidal suspensions of thin multiwall carbon nanotubes (MWCNTs) with diameters of 10–15 nm as electrode materials. These thin nanotubes, stabilized in water with a surfactant, form percolated networks, exhibiting high conductivity (50 ms/cm) and stability at a low carbon content (below 2 wt%). Colloidal clustering is enhanced by weak depletion attractive interactions. The resulting suspensions display yield stress and a shear thinning behavior with a low consistency index. They can easily flow at a nearly constant shear over a broad range of shear rates. They remain electrically conductive under shear, making them a promising option for flow electrochemical applications. This work suggests that the use of depletion-induced MWVNT aggregates addresses crucial issues in flow electrochemical applications, such as membrane fragility, operating energy, and pressure. These conductive colloidal suspensions thereby offer potential advancements in device performance and lifespan.
... Copyright 2017, Elsevier. 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) [39] , alizarin red S [40] , p-phenylenediamine (PPD) [41] , and thiourea (TU) [42] , are being frequently reported. Yoon investigated the influence of HQ concentration on the capacitance of the as-prepared device. ...
With the continuous advancement in the dual-carbon strategy, the upswell in the demand for renewable energy sources has motivated extensive research on the development of novel energy storage technologies. As a new type of energy storage device, carbon-based redox-enhanced supercapacitors (RE-SCs) are designed by employing soluble redox electrolytes into the existing devices, exploiting the merits of the diffusion-controlled faradaic process of the redox electrolyte at the surface of carbon electrodes, thus leading to improved energy density without the cost of power density. During the past years, great progress has been made in the design of novel redox electrolytes and the configuration of new devices. However, the development of these systems is plagued by severe self-discharge. Herein, a comprehensive picture of the fundamentals, together with a discussion and outline of the challenges and future perspectives of RE-SCs, are provided. We highlight the impacts of redox electrolytes on capacitance, energy density, and power output. Notably, the self-discharge behavior owing to the introduction of redox electrolyte and its mechanism are also discussed, followed by a summary of the strategies from materials to system optimization. Furthermore, possible directions for future research are discussed.
... The equivalent circuit fitting result confirms that both Warburg resistance (ZwR (Ω)) and Warburg time constant (ZwT (s)) values of AG and MoS2@AG electrodes are about 2-5 times smaller than those of MoS2. The ion diffusion coefficient is inversely proportional to the inverse ratio values of ZwT and ZwR 2 [43]. In addition, the Nyquist plots of the pristine AG, pristine MoS2, and 20−MoS2@AG electrodes were obtained after two cycles at a current density of 35 mA g −1 , as shown in Figure S9. ...
The demand for fast-charging lithium-ion batteries (LIBs) with long cycle life is growing rapidly due to the increasing use of electric vehicles (EVs) and energy storage systems (ESSs). Meeting this demand requires the development of advanced anode materials with improved rate capabilities and cycling stability. Graphite is a widely used anode material for LIBs due to its stable cycling performance and high reversibility. However, the sluggish kinetics and lithium plating on the graphite anode during high-rate charging conditions hinder the development of fast-charging LIBs. In this work, we report on a facile hydrothermal method to achieve three-dimensional (3D) flower-like MoS2 nanosheets grown on the surface of graphite as anode materials with high capacity and high power for LIBs. The composite of artificial graphite decorated with varying amounts of MoS2 nanosheets, denoted as MoS2@AG composites, deliver excellent rate performance and cycling stability. The 20−MoS2@AG composite exhibits high reversible cycle stability (~463 mAh g−1 at 200 mA g−1 after 100 cycles), excellent rate capability, and a stable cycle life at the high current density of 1200 mA g−1 over 300 cycles. We demonstrate that the MoS2-nanosheets-decorated graphite composites synthesized via a simple method have significant potential for the development of fast-charging LIBs with improved rate capabilities and interfacial kinetics.
... The adsorption of quinone moieties on carbon is due to a combination of hydrogen bonding and π-π interactions between the treated carbon surface and the quinone-based molecules [24,69]. The affinity of Ctn for the carbon surface, among other factors, affects the mass loading of Ctn. ...
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Graphical Abstract
... The parallel connection of resistance (R ct ) and capacitance (C dl ) signifies the electrodes charge-transport resistance and electric double layer capacitance participation. The tiny deviation in observed in low-frequency plateau was closely fitted with the Warburg element (W) ascribed to the electrodes diffusion control mechanism [71,72]. R s describes the internal resistance as well as the ionic resistance of the electrode material and electrolyte solution, respectively [73,74]. ...
Metal-organic frameworks (MOFs) with porous and diverse structures have created to devote research for MOF based materials for energy storage application, but their inadequate conductivity and sturdiness impede their realistic progress. MOF-derived transition metal phosphides (TMPs) materials could maintain the architectural diversity and porosity of MOFs, as well as, boost their electrical conductivity and durability. Herein, for the first time, we unravel the influence of interfacial tailoring in MOF templated cobalt copper phosphide (CoCuP) composite as electrode material for supercapacitor with battery-type behavior. The as-synthesized MOF-derived cobalt copper phosphide electrode (CoCuP@400) prepared at optimum 400 °C phosphorization temperature exhibits outstanding electrochemical performance by delivering a specific capacity (Csp) of 549 C/g (152.5-mAh/g) at a specific current of 1 A/g in aqueous electrolyte (6 M KOH). Additionally, by applying CoCuP@400 as a positive electrode (energy source) and lima bean shell-derived oxygen, nitrogen, and sulfur-enriched porous carbon (O, N, S@AC) as a negative electrode (power source), a hybrid supercapacitor device fabricated, which unveiled a widespread working potential window of 1.5 V. In addition, the hybrid supercapacitor device revealed a specific capacity of 38-mAh/g with a maximum specific energy (Esp) of 37.3 Wh/kg and a maximum specific power (Psp) of 12308.8 W/kg as well as exceptional cyclic stability over 10,000 uninterrupted galvanostatic charge/discharge cycles with 89% of initial capacity retention. As a result, after synthetic phosphorization technique for synthesizing electrode materials offers a new avenue for using battery-type supercapacitors.
... Compared to lithium−ion batteries (LIBs) using the reduction and oxidation of Li sources, symmetric supercapacitors (SCs) mainly use the electrostatic adsorption and desorption of electrolyte components, which exhibits a faster electrochemical behavior than Faradaic reactions. [1][2][3] Therefore, SCs can realize higher power performance and much longer cycle life than LIBs. 4,5 With these advantages, SCs are used in electric vehicles requiring high power performance 6,7 and in hybrid energy storage systems (HESS) of renewable sources such as solar, wind, and tidal energies. ...
This study examined the electrochemical and physicochemical degradation of commercial supercapacitors (SCs) at elevated temperatures depending on their voltages. After being stored in the charged state (2.5 V), the capacitance decreased rapidly to 80 % of its initial capacitance, and the resistance at 1 kHz increased continuously to 2.5 times its initial resistance. After being stored in the discharged state (~ 0 V), the capacitance was almost constant, but the resistance increased more than four times. In the charged state, oxidation products were deposited in the meso-/micropores of the positive electrode. They reduced the specific surface area of the positive electrode, which led to a rapid decrease in the capacitance and an increase in the resistance of SCs. In the discharged state, the supersaturation and precipitation of electrolyte salt hindered ion transport in the macro-/mesopores, increased the charge transfer resistance (Rct), and decreased the double-layer capacitance (Cdl). These phenomena were verified by electrochemical impedance spectroscopy, cyclic voltammetry, in situ FT-IR for the electrolyte, N2 adsorption-desorption analysis, and FE-SEM image for each electrode. Finally, the SC with better performance and durability at high temperature was verified by applying organic solvent with a high boiling point but not so high dielectric constant.
... The hydrogen storage mechanism is influenced by the electrochemical and physical properties of conductive particles used in slurry electrodes. Specific surface area (SSA), pore size distribution, and open-pore volume of particles in slurry electrodes are all factors that influence the hydrogen storage mechanism [8,35]. Creating an electrical double layer at the surface of the material as well as inside its pores is necessary to manage hydrogen electrosorption [36,37]. ...
Electrochemical hydrogen storage in porous carbon particles in slurry electrodes is a function of particle size, shape, and material. Ideal slurry electrodes have high electrical (both electronic and proton) conductivity to minimise the electric resistance and ohmic power loss, and low viscosity to minimise parasitic pumping power, while utilising porous particles with high surface areas for hydrogen storage. In this paper we show that although carbon black (CB) particles have higher electronic conductivity than activated carbon (aC) particles, their proton conductivity is significantly lower, and they cannot be used for hydrogen storage. We increase the electronic conductivity of aC slurries by adding CB particles. We demonstrate that the addition of a 1:10 ratio by weight of CB to aC particles reduces the electric resistance and ohmic power loss by 50%, while parasitic pumping power increases by only 15% compared to slurries with no CB particles. We conclude that at low Reynolds numbers, for 5 to 20 wt% aC slurries with different particle sizes, slurries containing 20 wt% spherical aC particles smaller than 50 mm mixed with 2 wt% CB particles provide the highest electronic and proton conductivity, while not significantly increasing parasitic pumping power.
... This indicates serial and parallel resis from the electrode and electrolyte, respectively [53], and can be rationalized by a quantity of quinones grafting onto the carbon surface that decreases the pore-access (Figure 5c) to the AC-CSS and furthermore exhibits strong deviation from ideal rectangular shape at a scan rate of 20 mV s −1 . This indicates serial and parallel resistance from the electrode and electrolyte, respectively [53], and can be rationalized by a high quantity of quinones grafting onto the carbon surface that decreases the poreaccessibility [54]. This deposition may also originate from MHQ decomposition products that are redox active. ...
Coffee, as one of the most traded resources, generates a vast amount of biogenic by-products. Coffee silver skins (CSS), a side stream from the roasting process, account for about 4 wt.%. Despite the abundancy of CSS, possible routes to generate added value for broad applications are limited. Herein, we present an approach to use CSS as a precursor material for supercapacitor electrodes. KOH activated carbon (AC) was produced from CSS. The resulting AC—CSS was characterized by X-ray diffraction, gas sorption analysis, scanning electron microscopy, and Raman spectroscopy. The highly porous AC—CSS exposes a specific surface area of more than 2500 m2 g−1. Electrodes formed with AC—CSS were electrochemically characterized by performing cyclic voltammetry and galvanostatic cycling. The electrodes were further assembled into a supercapacitor device and operated using 1 M sulfuric acid as electrolyte. In addition, various quinones were added to the electrolyte and their impact on the capacitance of AC—CSS electrodes was analyzed. In this work, we were able to show that CSS are a valuable source for supercapacitor applications and that coffee-waste-derived quinones can act as capacitance enhancers. Thus, the findings of this research show a valuable path towards sustainable and green energy storage solutions.
... In principle, the charge storage in FE systems originates because of different mechanisms such as electric double-layer formation and faradic reactions [6,8], surface redox reactions [9,10], intercalation [11], polymer redox [12,13], and hybrid mechanisms [14,15]. The operating performance of the FEs relies on support from the diffusion of the ions [16], electronic charge in and out of the pores via a particle-current collector, particle-particle interactions [17], and the formation of the electrical double layer (EDL) at the pore surface [18,19]. ...
Aqueous electrochemical flow capacitors (EFCs) have demonstrated high-power capabilities and safety at low cost, making them promising energy storage devices for grid applications. A primary performance metric of an EFC is the steady-state electrical current density it can accept or deliver. Performance prediction, design improvements, and up-scaling are areas in which modeling can be useful. In this paper, a novel stochastic superparticle (SP) modeling approach was developed and applied to study the charging of carbon electrodes in the EFC system, using computational superparticles representing real carbon particles. The model estimated the exact values of significant operating parameters of an EFC, such as the number of particles in the flow channel and the number of electrolytic ions per carbon particle. Optimized model parameters were applied to three geometrical designs of an EFC to estimate their performance. The modeling approach allowed study of the charge per carbon particle to form the electric double-layer structure. The linear relationship between the concentration of SPs and the ionic charge was observed when optimized at a constant voltage of 0.75 V. The simulation results are in excellent agreement with experimental data, providing a deep insight into the performance of an EFC and identifying limiting parameters for both engineers and material scientists to consider.
... It demonstrates that the best performance is found by using modified aC particles for storage material. Like other charge storage phenomena, hydrogen adsorption, as a pseudo-capacitive storage mechanism in supercapacitors, depends on the electro-chemico-physical parameters of the porous carbonbased electrode, pore size distribution, existent open pore volume, and specific surface area (SSA) [126,127]. The electrosorption of hydrogen is controlled by electrical double layer formation at the surface as well as in the pores. ...
... Stored hydrogen has widespread applications in sustainable stationary and portable power technologies due to its zero carbon content, highest energy content per unit mass and/or the advantage to meet long-term energy storage needs economically [66,[154][155][156][157][158][159][160] via fuel cell operation. Hydrogen can be stored by physisorption with highly porous active materials [118,[161][162][163][164][165], chemisorption on metal hydrides or porous carbon-based materials [126,[166][167][168], compressed under high pressure [169][170][171], or liquefication [172,173], depending on the type of applications and safety issues involved [174]. Table 2 shows the range of carbon-based materials used to store hydrogen. ...
... When a redox mediator H2Q/Q was used in a pseudocapacitive slurry electrode, the theoretical analysis revealed more HQ coverage in the pores with a small diameter [126]. ...
Electrochemical energy storage using slurry flow electrodes is now recognised for potentially widespread applications in energy storage and power supply. This study provides a comprehensive review of capacitive charge storage techniques using carbon-based slurry electrodes. Carbon particle properties and their effects on the performance of slurry flow electrodes are thoroughly reviewed. A detailed analysis of electrochemical properties of slurry flow electrodes is provided, including their dependence on the concentration ratio of electrolyte to carbon, flow behaviour, and design flow channel configuration. This paper also identifies key challenges and research gaps to be addressed by future research studies for improving the performance of carbon-based slurry flow electrodes on their path to further commercialisation.
