"Inner" and "outer" active surface of RuO2 electrodes
TL;DR: In this paper, the dependence of the voltammetric surface charge q* on solution pH and potential scan rate has been investigated using a set of RuO2 electrodes prepared by thermal decomposition of RuCl3 at temperatures in the range 300-500°C.
About: This article is published in Electrochimica Acta.The article was published on 1990-01-01. It has received 1367 citations till now. The article focuses on the topics: Surface charge & Active surface.
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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
TL;DR: In this article, the fundamental principles, performance, characteristics, present and future applications of electrochemical capacitors are presented in this communication, and different applications demanding large ECs with high voltage and improved energy and power density are under discussion.
4,175 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: This work quantifies the kinetics of charge storage in T-Nb2O5: currents that vary inversely with time, charge-storage capacity that is mostly independent of rate, and redox peaks that exhibit small voltage offsets even at high rates.
Abstract: Pseudocapacitance is commonly associated with surface or near-surface reversible redox reactions, as observed with RuO2·xH2O in an acidic electrolyte. However, we recently demonstrated that a pseudocapacitive mechanism occurs when lithium ions are inserted into mesoporous and nanocrystal films of orthorhombic Nb2O5 (T-Nb2O5; refs 1, 2). Here, we quantify the kinetics of charge storage in T-Nb2O5: currents that vary inversely with time, charge-storage capacity that is mostly independent of rate, and redox peaks that exhibit small voltage offsets even at high rates. We also define the structural characteristics necessary for this process, termed intercalation pseudocapacitance, which are a crystalline network that offers two-dimensional transport pathways and little structural change on intercalation. The principal benefit realized from intercalation pseudocapacitance is that high levels of charge storage are achieved within short periods of time because there are no limitations from solid-state diffusion. Thick electrodes (up to 40 μm thick) prepared with T-Nb2O5 offer the promise of exploiting intercalation pseudocapacitance to obtain high-rate charge-storage devices.
3,725 citations
TL;DR: The overall catalytic activities for these reaction as a function of a more fundamental property, a descriptor, OH-M(2+δ) bond strength (0 ≤ δ ≤ 1.5), provide the foundation for rational design of 'active sites' for practical alkaline HER and OER electrocatalysts.
Abstract: Design and synthesis of materials for efficient electrochemical transformation of water to molecular hydrogen and of hydroxyl ions to oxygen in alkaline environments is of paramount importance in reducing energy losses in water–alkali electrolysers. Here, using 3d-M hydr(oxy)oxides, with distinct stoichiometries and morphologies in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) regions, we establish the overall catalytic activities for these reaction as a function of a more fundamental property, a descriptor, OH–M2+δ bond strength (0 ≤ δ ≤ 1.5). This relationship exhibits trends in reactivity (Mn < Fe < Co < Ni), which is governed by the strength of the OH–M2+δ energetic (Ni < Co < Fe < Mn). These trends are found to be independent of the source of the OH, either the supporting electrolyte (for the OER) or the water dissociation product (for the HER). The successful identification of these electrocatalytic trends provides the foundation for rational design of ‘active sites’ for practical alkaline HER and OER electrocatalysts. Efficient electrochemical transformation of water to molecular hydrogen and of hydroxyl ions to oxygen in alkaline environments is important for reducing energy losses in water–alkali electrolysers. Insight into the activities of hydr(oxy)oxides on platinum catalyst surfaces for hydrogen and oxygen evolution reactions should prove significant for designing practical alkaline electrocatalysts.
2,271 citations
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TL;DR: In this article, the electrochemical behavior of RuO2 film electrodes, prepared by the thermal decomposition of Ru Cl3 on metallic supports, has been investigated in solutions of inert electrolytes.
Abstract: The electrochemical behaviour of RuO2 film electrodes, prepared by the thermal decomposition of Ru Cl3 on metallic supports has been investigated in solutions of inert electrolytes. Steady-state pot entiostatici/E curves, cyclic voltammetry and charging curves are presented. The procedure for the preparation of electrodes is described.
271 citations
TL;DR: In this paper, the authors investigated the reaction order with respect to active sites and activation energy on two kinds of RuO2-based electrodes; compact and cracked (porous) films.
Abstract: Oxygen evolution from acid solutions has been investigated on two kinds of RuO2-based electrodes; compact and cracked (porous) films The kinetic study has been carried out by means of potentiostatic curves A method is suggested to estimate the surface concentration of active sites The reaction order with respect to active sites and the activation energy have been determined The mechanism is shown to differ on the two kinds of film in relation to theS(site)-OH bond strength and the surface concentration of intermediates The behaviour of films on silica glass substrates is reported for the first time
262 citations
TL;DR: In this article, the electrochemical behavior of Co3O4 layers deposited by thermal decomposition of Co(NO3)2 at 200-500°C on titanium supports with and without an interlayer of RuO2 has been studied by cyclic voltammetry, chronopotentiometry and potential step experiments in alkaline solutions.
Abstract: The electrochemical behaviour of Co3O4 layers deposited by thermal decomposition of Co(NO3)2 at 200–500°C on titanium supports with and without an interlayer of RuO2 has been studied by cyclic voltammetry, chronopotentiometry and potential step experiments in alkaline solutions. Such variables as the calcination temperature, the solution pH, the potential sweep rate and the oxide loading have been investigated in detail to determine their influence on voltammetric peaks and voltammetric charge. Insight has been gained into the relevance of the latter to surface area determination and to proton diffusion into the oxide layer. The role of the support-active layer interface and especially that of the RuO2 interlayer has been scrutinized. The importance of surface studies for the understanding of the electrocatalytic behaviour of Co3O4 electrodes has been analysed.
214 citations
169 citations
TL;DR: In this paper, the variation of voltammetric charge with real surface area was investigated for RuO2-coated titanium foils with a view to establishing an electrochemical technique for the estimation of the latter.
151 citations