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Schematic of the (negative) electrode-electrolyte interface in EDLCs working with solvent-based (top) and IL (bottom) electrolytes. While energy storage in the former is based on double-layer compression and thus requires transport of electrolyte ions, local ordering transitions (i.e. changes in the ion coordination numbers) are responsible for the energy storage in the absence of a solvent.
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Extending the range of analysis of previous measurements on energy storage in ionic liquid (IL)-based supercapacitors with very well defined carbon materials indicates that there are two distinct processes at play: the one at lower voltages is (classically) related to the micropore inclusion of single ions, while a previously unknown high voltage t...
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Context 1
... a rather typical EDLC-like appearance (Fig. 2c). This voltage peak translates to a much higher transition enthalpy of above 350-450 kJ mol À1 , which is higher than that of covalent bonds, but in the range of the melting of salts and other collective properties and structural transitions involving serious changes in the ion coordination numbers (Fig. ...
Context 2
... solvent. On the contrary, ion rearrangement towards lower coordination numbers is an effect that can progress for nanometers into the bulk phase of the ionic liquid and is therefore not controlled by the specific surface area but rather by pore volume, in agreement with the experimental findings (Fig. 3). and (e) the corresponding pore size distributions indicating that the high voltage peak is related to processes enabled by the incorporation of ...
Citations
... Separate storage is maintained for the reaction products. The reaction products are recombined exothermically during the discharge process, and the heat of the reaction may be utilised [44,45]. ...
Solar air heaters are the most cost-effective method of converting solar energy into heat and are used for room heating, crop drying, and other industrial uses. However, they suffer from poor thermal efficiency. The leading cause behind the poor performance of solar air heaters is heat losses from its different parts. Researchers have used various innovative methods to improve solar air heaters thermal performance by reducing heat losses using energy storage material. The present work demonstrates the state-of-the-art review of different solar air heaters loaded with sensible heat storage materials. This investigation has found that integrating sensible heat storage systems such as pebbles, sand, metal chips, oil and gravels with solar air heaters effectively reduces heat losses and increases thermal efficiency. This study revealed that Therminol-55 gave better efficiency than engine oil. For blacked pebble stones, free convection solar air heater provided better efficiency than forced convection. The cement gave better thermal efficiency than concrete. Gravels integrated with iron chips showed more efficiency than used alone. Pure iron chips contributed maximum efficiency compared to other metal chips. The desert sand furnished better efficiency compared to different types of sand. The overall best performing sensible heat storage material is found as a mixture of desert sand and granular carbon having the highest thermal efficiency of 80.05%; however, the lowest performance is demonstrated by cement with 9.5% of thermal efficiency.
... This study thereby opens up the way to the application of pore-confined ILs as reaction media for the catalytic activation and conversion of small molecules, such as dinitrogen in NRR, at unusual high local concentrations of up to 20 wt %. The further presence of an electric field may induce ordering transitions in the IL ions 32,40 and thus change the solubility of gas molecules even further. We found the interaction between IL ions and dinitrogen to be strong; that is, it is constant in the examined temperature range, but the gas is rather cooperatively released when reaching a "order−disorder" transition above 60°C. ...
Ionic liquids are well known for their high gas absorption capacity. It is shown that this is not a solvent constant, but can be enhanced by another factor of 10 by pore confinement, here of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate (EmimOAc) in the pores of carbon materials. A matrix of four different carbon compounds with micro- and mesopores as well as with and without nitrogen doping is utilized to investigate the influence of the carbons structure on the nitrogen uptake in the pore-confined EmimOAc. In general, the absorption is most improved for IL in micropores and in nitrogen-doped carbon. This effect is so large that it is already seen in TGA and DSC experiments. Due to the low vapor pressure of the IL, standard volumetric sorption experiments can be used to quantify details of this effect. It is reasoned that it is the change of the molecular arrangement of the ions in the restricted space of the pores that creates additional free volume to host molecular nitrogen.
... They also brought about a better understanding of the origin of this capacitance increase. The increase is now attributed to the partial desolvation of ions resulting in ion accessibility to subnanometre pores 27,28,30,31,39,42,43,50,51 , leading to a specific organization of the electrolyte confined in these nanopores 51,52 as well as the creation of image charges 40,53 on the carbon surface, and denser ion packing 39,54,55 . Figure 2b-d summarizes the current understanding of EDLC theory provided by these theoretical and computational studies. ...
... Mastering the electrode/ electrolyte interface is also a key challenge for Li-ion batteries; this is particularly true with the current trend to develop all solid-state Li-ion batteries based on inorganic ceramic electrolytes. There is then a common interest in developing and sharing techniques for characterizing the electrode/electrolyte interface, as well as underlying basic science 12,27,31,32,34,52 . ...
Electrochemical capacitors can store electrical energy harvested from intermittent sources and deliver energy quickly, but their energy density must be increased if they are to efficiently power flexible and wearable electronics, as well as larger equipment. This Review summarizes progress in the field of materials for electrochemical capacitors over the past decade as well as outlines key perspectives for future research. We describe electrical double-layer capacitors based on high-surface-area carbons, pseudocapacitive materials such as oxides and the two-dimensional inorganic compounds known as MXenes, and emerging microdevices for the Internet of Things. We show that new nanostructured electrode materials and matching electrolytes are required to maximize the amount of energy and speed of delivery, and different manufacturing methods will be needed to meet the requirements of the future generation of electronic devices. Scientifically justified metrics for testing, comparison and optimization of various kinds of electrochemical capacitors are provided and explained.
... [4] The storage of electricity by electrochemistry is one of the most appropriate methods that have been growing dramatically in the last decade. [5] Low pollution, high efficiency, and diverse application are some of the most important reasons for increasing attention to electrochemical energy. Extensive researches have been done on electrochemical energy storage in recent decades. ...
This review investigates the synthesis and electrochemical performance of the electrode of the electrochemical energy storage (EES) devices obtained from peels and scraps of the citrus fruits. The EES devices include batteries, supercapacitors, and hybrid systems that have considerable value and various applications. The electrode is considered as the most important part of all EES devices. Tremendous efforts have been done to enhance the electrochemical energy storage electrode (EESE). The citrus fruits abundance leads to a decrease in their price and makes possible to use them as ingredients to fabricate EESE. Also, the electrochemical analyses determined that citrus fruits have considerable potential to use as the EESE. Using citrus fruits peels and scraps as biomass substances to prepare EESE leads to the electrodes which have low cost, environmentally friendly and appropriate electrochemical applications.
... As shown in Figs S14-S16, the specific capacitance at low scan rate of 2 mV s −1 increases from 193.5 to 255 F g −1 with increasing N/O/S content of the materials, which also indicates that The CV curves of the GT13-800 display nearly rectangular shapes at different scan rates (Fig. 4a), underlining its high electronic conductivity. The observed peak at lower scan rates typically occurs during slow cycling in the IL electrolyte and was recently attributed to structural transitions of ions inside the micropores during charging/ discharging [41][42][43]. The galvanostatic charging/discharge curves of GT13-800 are nearly symmetric (Fig. 4c), and the Nyquist plot exhibits a nearly vertical line in the low-frequency region (Fig. 4d). ...
“C2N”-species have emerged as a promising material with carbon-like applications in sorption, gas separation and energy storage, while with much higher polarity and functionality. Controlled synthesis of “C2N” structure is still based on complex and less-sustainable monomers, which prohibits its broader industrial application. Here we report a class of well-defined C2(NxOySz)1 carbons with both high content of N/O/S heteroatoms and large specific surface area of up to 1704 m2 g−1, which can be efficiently synthesized through a simple additive condensation process using simple gallic acid and thiourea as the building blocks, without sub-tractive activation. This 1,4-para tri-doped C2(NxOySz)1 structure leads to sufficient CO2 adsorption capacity (3.0 mmol g−1 at 273 K, 1 bar) and a high CO2/N2 selectivity (47.5 for a 0.15/0.85 CO2/N2 mixture at 273 K). Related to the polarity, the polar frameworks can be used as supercapacitor electrodes, with record specific capacitances as high as 255 F g−1at 3.5 V for a symmetric supercapacitor in ionic liquid electrolyte. This work discloses a general way for preparing a novel family of multifunctional, high heteroatom-doped porous materials for various applications.
... Synergetic relationships between electrode materials and electrolytes play a vital role in the energy/power performance of SCs [3][4][5]. Independent research over the last decade has sought to improve the energy/power performance of electrochemical energy storage (EES) through the development of novel separators with high ionic conductivity, elucidating the roles of electrolytes with different solvents, and developing new nanostructured materials for high-capacitance electrodes [6][7][8]. Among these strategies, the development of new electrode materials with high capacitance, temperature tolerance, high conductivity, high surface area, and excellent electrochemical stability is a promising approach to increasing SC performance [9,10]. ...
This work describes the carbothermal preparation of silicon-oxy-carbide (SiOC) lamellae using two-dimensional siloxene sheets and alginic acid as precursors. X-ray photoelectron spectra, X-ray diffraction, Fourier-transform infrared spectra, high-resolution transmission electron micrographs, and Raman spectra revealed the formation of lamella-like SiOC nanostructures. Symmetric supercapacitors (SSCs) were fabricated using SiOC nanostructures as electrodes and evaluated in aqueous (1 M Li2SO4) and organic (1 M TEABF4) electrolytes. SiOC SSC fabricated with Li2SO4 electrolyte operated over a voltage window of 2.0 V, with an energy density of 14.2 Wh kg−1 and a power density of 6666 W kg−1. SiOC SSC fabricated using TEABF4 electrolyte operates over a voltage window of 3.0 V and delivered a device capacitance of about 16.71 F g−1, energy density of 20.89 Wh kg−1, with excellent cyclic stability and superior rate capability. Strikingly, the high-power density of the TEABF4-based SiOC SSC (15,000 W kg−1) reached the required power target for next-generation electric vehicles and is suitable for high-performance supercapacitor devices.
... They further showed the possibility of a change in coordination geometry of RTILs when confined in a porous carbon environment, triggered by an applied electric potential ( Tazi et al., 2010;Kiyohara et al., 2011;Fedorov and Kornyshev, 2014;Rotenberg and Salanne, 2015;Futamura et al., 2017;Yan et al., 2018). These phase transitions may play a crucial role for the conservation of electroneutrality and thus for energy storage in RTIL-based EDLCs ( Antonietti et al., 2018). This new mode of energy storage was recently proposed based on a series of experiments on porous carbon materials and the presence of mesopores with diameters as large as the dimensions of a few RTIL ion layers was found to play a particularly important role ( Antonietti et al., 2018;Lai et al., 2018;Yan et al., 2018). ...
... These phase transitions may play a crucial role for the conservation of electroneutrality and thus for energy storage in RTIL-based EDLCs ( Antonietti et al., 2018). This new mode of energy storage was recently proposed based on a series of experiments on porous carbon materials and the presence of mesopores with diameters as large as the dimensions of a few RTIL ion layers was found to play a particularly important role ( Antonietti et al., 2018;Lai et al., 2018;Yan et al., 2018). However, the influence of carbon pore structure and structure of the RTIL on this phenomenon remains still poorly understood. ...
... In the latter cases an applied potential causes a gathering of ions as "mirror charges" on the surface of the respective electrode and an increasing thickness and compression of the double layer with progressing potential ramp. This mechanism cannot be applied to RTIL-based electrolytes, as they are solely composed of ions without a surrounding dielectric medium ( Antonietti et al., 2018). Therefore, the ions exhibit an intrinsic local structuring called coulombic ordering, where each ion is surrounded by a shell of counterions and the local density of ions has to be nearly the same on the electrode surface and within the bulk electrolyte. ...
Recent research on ionic liquid electrolyte-based supercapacitors indicated the contribution of phase transitions of the electrolytes at high cell voltages to the energy stored. This mechanism can be exploited to significantly increase the energy density of supercapacitors, which up to now remains their major drawback. It was found that these ordering transitions require the presence of mesopores within the carbon electrode materials and that porosity in general is a key factor to trigger them, but details of the mechanism remains unexplained. To get a more profound understanding of this phenomenon, carbon materials with different pore diameters and volumes were synthesized and the effect of those properties on the phase transitions in the ionic liquids was studied by means of cyclic voltammetry. A clear correlation between the peak current and the mesopore volume is revealed and an optimal pore diameter was determined, exceeding which does not improve the phase transition behavior. These findings are useful as guidelines for the rational design of carbon mesopores in order to utilize the new energy storage modes which are neither fully capacitive, nor redox-based.
... 78 becomes the limiting factor, leading to the drastic drop of capacitance (Figure 3.30b). Thus, larger amount of mesopores (STC-8 and STC-16) and nitrogen doping (NDSTC-2 and NDSTC-4) are needed here(Scheme 3.4, second line), resulting in the increase of accessible surface areas and higher capacitance at this rate. ...
... Besides, ILs are solely composed of ions without slovents. Thus they can hardly be compressed into a compression double-layer on the electrode surface,78 where the traditional electric double-layer theory is not applicable. Therefore, their energy storage mechanism remains unclear. ...
Supercapacitors are electrochemical energy storage devices with rapid charge/discharge rate and long cycle life. Their biggest challenge is the inferior energy density compared to other electrochemical energy storage devices such as batteries. Being the most widely spread type of supercapacitors, electrochemical double-layer capacitors (EDLCs) store energy by electrosorption of electrolyte ions on the surface of charged electrodes. As a more recent development, Na-ion capacitors (NICs) are expected to be a more promising tactic to tackle the inferior energy density due to their higher-capacity electrodes and larger operating voltage. The charges are simultaneously stored by ion adsorption on the capacitive-type cathode surface and via faradic process in the battery-type anode, respectively. Porous carbon electrodes are of great importance in these devices, but the paramount problems are the facile synthetic routes for high-performance carbons and the lack of fundamental understanding of the energy storage mechanisms. Therefore, the aim of the present dissertation is to develop novel synthetic methods for (nitrogen-doped) porous carbon materials with superior performance, and to reveal a deeper understanding energy storage mechanisms of EDLCs and NICs. The first part introduces a novel synthetic method towards hierarchical ordered meso-microporous carbon electrode materials for EDLCs. The large amount of micropores and highly ordered mesopores endow abundant sites for charge storage and efficient electrolyte transport, respectively, giving rise to superior EDLC performance in different electrolytes. More importantly, the controversial energy storage mechanism of EDLCs employing ionic liquid (IL) electrolytes is investigated by employing a series of porous model carbons as electrodes. The results not only allow to conclude on the relations between the porosity and ion transport dynamics, but also deliver deeper insights into the energy storage mechanism of IL-based EDLCs which is different from the one usually dominating in solvent-based electrolytes leading to compression double-layers. The other part focuses on anodes of NICs, where novel synthesis of nitrogen-rich porous carbon electrodes and their sodium storage mechanism are investigated. Free-standing fibrous nitrogen-doped carbon materials are synthesized by electrospinning using the nitrogen-rich monomer (hexaazatriphenylene-hexacarbonitrile, C18N12) as the precursor followed by condensation at high temperature. These fibers provide superior capacity and desirable charge/discharge rate for sodium storage. This work also allows insights into the sodium storage mechanism in nitrogen-doped carbons. Based on this mechanism, further optimization is done by designing a composite material composed of nitrogen-rich carbon nanoparticles embedded in conductive carbon matrix for a better charge/discharge rate. The energy density of the assembled NICs significantly prevails that of common EDLCs while maintaining the high power density and long cycle life.
Here, an unusual MXene with a high ratio of oxygen functional groups was prepared by hydrothermal treatment of HF-etched MXene in aqueous KOH solution. The prepared MXene (H-220) exhibits ultrahigh...
