Charge Storage Mechanism of MnO2 Electrode Used in Aqueous Electrochemical Capacitor
TL;DR: The charge storage mechanism in MnO2 electrode, used in aqueous electrolyte, was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy as discussed by the authors.
Abstract: The charge storage mechanism in MnO2 electrode, used in aqueous electrolyte, was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy. Thin MnO2 films deposited on a platinum substrate and thick MnO2 composite electrodes were used. First, the cyclic voltammetry data established that only a thin layer of MnO2 is involved in the redox process and electrochemically active. Second, the X-ray photoelectron spectroscopy data revealed that the manganese oxidation state was varying from III to IV for the reduced and oxidized forms of thin film electrodes, respectively, during the charge/discharge process. The X-ray photoelectron spectroscopy data also show that Na+ cations from the electrolyte were involved in the charge storage process of MnO2 thin film electrodes. However, the Na/Mn ratio for the reduced electrode was much lower than what was anticipated for charge compensation dominated by Na+, thus suggesting the involvement of protons in the pseudofaradaic mechanism. An important finding o...
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TL;DR: This work has shown that 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.
Abstract: 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.
14,213 citations
Cites background from "Charge Storage Mechanism of MnO2 El..."
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TL;DR: 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.
Abstract: 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).
7,642 citations
TL;DR: This work synthesized a porous carbon with a Brunauer-Emmett-Teller surface area, a high electrical conductivity, and a low oxygen and hydrogen content that has high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes.
Abstract: Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp 2 -bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.
5,486 citations
TL;DR: In this article, the pseudocapacitance properties of transition metal oxides have been investigated and a review of the most relevant pseudo-capacitive materials in aqueous and non-aqueous electrolytes is presented.
Abstract: Electrochemical energy storage technology is based on devices capable of exhibiting high energy density (batteries) or high power density (electrochemical capacitors). There is a growing need, for current and near-future applications, where both high energy and high power densities are required in the same material. Pseudocapacitance, a faradaic process involving surface or near surface redox reactions, offers a means of achieving high energy density at high charge–discharge rates. Here, we focus on the pseudocapacitive properties of transition metal oxides. First, we introduce pseudocapacitance and describe its electrochemical features. Then, we review the most relevant pseudocapacitive materials in aqueous and non-aqueous electrolytes. The major challenges for pseudocapacitive materials along with a future outlook are detailed at the end.
3,930 citations
TL;DR: The latest progress in supercapacitors in charge storage mechanisms, electrode materials, electrolyte materials, systems, characterization methods, and applications are reviewed and the newly developed charge storage mechanism for intercalative pseudocapacitive behaviour is clarified for comparison.
Abstract: Electrochemical capacitors (i.e. supercapacitors) include electrochemical double-layer capacitors that depend on the charge storage of ion adsorption and pseudo-capacitors that are based on charge storage involving fast surface redox reactions. The energy storage capacities of supercapacitors are several orders of magnitude higher than those of conventional dielectric capacitors, but are much lower than those of secondary batteries. They typically have high power density, long cyclic stability and high safety, and thus can be considered as an alternative or complement to rechargeable batteries in applications that require high power delivery or fast energy harvesting. This article reviews the latest progress in supercapacitors in charge storage mechanisms, electrode materials, electrolyte materials, systems, characterization methods, and applications. In particular, the newly developed charge storage mechanism for intercalative pseudocapacitive behaviour, which bridges the gap between battery behaviour and conventional pseudocapacitive behaviour, is also clarified for comparison. Finally, the prospects and challenges associated with supercapacitors in practical applications are also discussed.
2,698 citations
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TL;DR: In this article, different types of capacitors with a pure electrostatic attraction and/or pseudocapacitance effects are presented, and their performance in various electrolytes is studied taking into account the different range of operating voltage (1V for aqueous and 3 V for aprotic solutions).
4,091 citations
TL;DR: In this article, the authors compared the power density characteristics of ultracapacitors and batteries with respect to the same charge/discharge efficiency and showed that the battery can achieve energy densities of 10 Wh/kg or higher with a power density of 1-2 kW/kg.
2,603 citations
TL;DR: In this paper, the double-layer capacitance of carbon powder electrodes has been used as a means of storing electrical energy in a supercapacitor or an ultracapacitor, where the pseudocapacitance arises when, for thermodynamic reasons, the charge q required for progression of an electrode process is a continuous function of potential, V ; then the derivative d q /d V corresponds to a capacitance but one of a Faradaic kind.
1,417 citations
TL;DR: In this paper, the performance of thin films of manganese dioxide on nickel foils was studied by cyclic voltammetry in the range 0.0-0.9 V (SCE) and by chronopotentiometry in unbuffered solution.
Abstract: Thin films of manganese dioxide were formed on nickel foils by electrodeposition and by both dip‐coating and drop‐coating with manganese dioxide suspensions (sols) and their subsequent gelation and calcination. The performance of these films as ultracapacitors was studied by cyclic voltammetry in the range 0.0–0.9 V (SCE) and by chronopotentiometry in unbuffered solution. The cyclic voltammograms of ultrathin, dip‐coated sol‐gel‐derived films indicated better capacitive behavior and gave differential specific capacitance values as high as 698 F/g compared to values half to two‐thirds as great for the electrodeposited films. Multilayer drop‐coated sol‐gel films were prepared to attain film thicknesses comparable to the electrodeposited films, and these were found to provide charge‐storage capacity as high as , more than three times greater than that of the electrodeposited films. All films, except electrodeposited films that were not thermally cured, exhibited good cycling stability, losing not much more than 10% of capacity after 1500 cycles. © 2000 The Electrochemical Society. All rights reserved.
1,014 citations
TL;DR: Amorphous MnO2·nH2O in a mild 2 M KCl aqueous electrolyte proves to be an excellent electrode for a faradaic electrochemical capacitor cycled between −0.2 and +1.0 V versus SCE.
1,006 citations