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.

https://hal.archives-ouvertes.fr/hal-02417326/document

Materials for electrochemical capacitors

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).

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A review of electrode materials for electrochemical supercapacitors

Electrochemical supercapacitors (ECs), characteristic of high power and reasonably high energy densities, have become a versatile solution to various emerging energy applications. This critical review describes some materials science aspects on manganese oxide-based materials for these applications, primarily including the strategic design and fabrication of these electrode materials. Nanostructurization, chemical modification and incorporation with high surface area, conductive nanoarchitectures are the three major strategies in the development of high-performance manganese oxide-based electrodes for EC applications. Numerous works reviewed herein have shown enhanced electrochemical performance in the manganese oxide-based electrode materials. However, many fundamental questions remain unanswered, particularly with respect to characterization and understanding of electron transfer and atomic transport of the electrochemical interface processes within the manganese oxide-based electrodes. In order to fully exploit the potential of manganese oxide-based electrode materials, an unambiguous appreciation of these basic questions and optimization of synthesis parameters and material properties are critical for the further development of EC devices (233 references).

Manganese oxide-based materials as electrochemical supercapacitor electrodes

In the past decade, there have been exciting developments in the field of lithium ion batteries as energy storage devices, resulting in the application of lithium ion batteries in areas ranging from small portable electric devices to large power systems such as hybrid electric vehicles. However, the maximum energy density of current lithium ion batteries having topatactic chemistry is not sufficient to meet the demands of new markets in such areas as electric vehicles. Therefore, new electrochemical systems with higher energy densities are being sought, and metal-air batteries with conversion chemistry are considered a promising candidate. More recently, promising electrochemical performance has driven much research interest in Li-air and Zn-air batteries. This review provides an overview of the fundamentals and recent progress in the area of Li-air and Zn-air batteries, with the aim of providing a better understanding of the new electrochemical systems.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1002/aenm.201000010

Metal–Air Batteries with High Energy Density: Li–Air versus Zn–Air

MnO2 is currently under extensive investigations for its capacitance properties. MnO2 crystallizes into several crystallographic structures, namely, α, β, γ, δ, and λ structures. Because these structures differ in the way MnO6 octahedra are interlinked, they possess tunnels or interlayers with gaps of different magnitudes. Because capacitance properties are due to intercalation/deintercalation of protons or cations in MnO2, only some crystallographic structures, which possess sufficient gaps to accommodate these ions, are expected to be useful for capacitance studies. In order to examine the dependence of capacitance on crystal structure, the present study involves preparation of these various crystal phases of MnO2 in nanodimensions and to evaluate their capacitance properties. Results of α-MnO2 prepared by a microemulsion route (α-MnO2(m)) are also used for comparison. Spherical particles of about 50 nm, nanorods of 30−50 nm in diameter, or interlocked fibers of 10−20 nm in diameters are formed, which d...

Effect of Crystallographic Structure of MnO2 on Its Electrochemical Capacitance Properties

Manganese dioxide has been electrochemically deposited on a Ni substrate from a neutral electrolyte in the presence of a surface-active agent, namely, sodium lauryl sulfate ~SLS!, for supercapacitor application. The potentiodynamically prepared oxide provides higher capacitance than the potentiostatically and galvanostatically prepared oxides. Owing to adsorption of the surfactant molecules at the interface during electrodeposition, the manganese dioxide possesses higher specific surface area. Specific capacitance of 310 F g−1 obtained for the oxide prepared in the presence of SLS over an extended charge-discharge cycling is higher by about 25% in relation to the oxide prepared in the absence of SLS. © 2005 The Electrochemical Society. @DOI: 10.1149/1.1922869# All rights reserved.

High Capacitance of Electrodeposited MnO2 by the Effect of a Surface-Active Agent

Electrochemical studies of cobalt hydroxide — an additive for nickel electrodes

There has been increasing interest on various properties and applications of electronically conducting polymers. Polyethylenedioxythiophene (PEDOT) is an interesting polymer of this type as it exhibits very high ionic conductivity. In the present study, PEDOT has been electrochemically deposited on stainless steel (SS) substrate for supercapacitor studies. PEDOT/SS electrodes prepared in 0.1M H2SO4 in presence of a surfactant, sodium dodecylsulphate (SDS), have been found to yield higher specific capacitance (SC) than the electrodes prepared from neutral aqueous electrolyte. The effects of concentration of H(2)SO4(,) concentration of SDS, potential of deposition, and nature of supporting electrolytes used for capacitor studies on SC of the PEDOT/SS electrodes have been studied. SC values as high as 250 F/g in 1M oxalic acid have been obtained during the initial stages of cycling. However, there is a rapid decrease in SC on repeated charge-discharge cycling. Spectroscopic data reflect structural changes in PEDOT on extended cycling. (C) 2007 Wiley Periodicals, Inc.

Supercapacitor studies of electrochemically deposited PEDOT on stainless steel substrate

Platinum nanoparticles on a conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), exhibit a high catalytic activity for electrooxidation of methanol. Pt nanoparticles are prepared by potentiostatic deposition in chloroplatinic acid solution at 0.1 V versus standard calomel electrode (SCE) on PEDOT coated carbon paper. PEDOT on the substrate facilitates the formation of uniform, well-dispersed, small clusters of Pt that consist of nanosize particles. The cyclic voltammogram of methanol oxidation is characterized by a forward oxidation peak current at 0.60 V vs SCE and a backward oxidation peak current at 0.50 V vs SCE. The mass specific peak current is found to be as high as 614 mA mg(-1), The effects of concentration of H2SO4, mass of Pt, and quantity of PEDOT on mass specific activity are studied.

N. Munichandraiah

Papers

High Capacitance of Electrodeposited MnO2 by the Effect of a Surface-Active Agent

Electrochemical studies of cobalt hydroxide — an additive for nickel electrodes

Supercapacitor studies of electrochemically deposited PEDOT on stainless steel substrate

Electrooxidation of methanol on Pt-modified conductive polymer PEDOT.

Surface films of lithium: an overview of electrochemical studies