On the charge storage mechanism at RuO2/0.5 M H2SO4 interface

Comparative study of capacitative properties of RuO2/0.5 M H2SO4 and Ru/0.5 M H2SO4 interfaces has been performed with a view to find out the nature of electrochemical processes involved in the charge storage mechanism of ruthenium (IV) oxide. The methods of cyclic voltammetry and scanning electron microscopy (SEM) were employed for the investigation of electrochemical behavior and surface morphology of RuO2 electrodes. It has been suggested that supercapacitor behavior of RuO2 phase in the potential E range between 0.4 and 1.4 V vs reference hydrogen electrode (RHE) should be attributed to double-layer-type capacitance, related to non-faradaic highly reversible process of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{RuO}}_2^ + \cdot \left( {{\text{OH}}^ - } \right)_{{\text{ad}}} $$\end{document} ionic pair formation and annihilation at RuO2/electrolyte interface as described by following summary equation: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{RuO}}_{2} \cdot {\text{H}}_{2} {\text{O}} \Leftrightarrow {\text{RuO}}^{ + }_{2} \cdot {\left( {{\text{OH}}^{ - } } \right)}_{{{\text{ad}}}} + {\text{H}}^{ + } + {\text{e}}^{ - } _{{{\left( {{\text{CB}}} \right)}}} ,$$\end{document}where \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{RuO}}_2^ + $$\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{e}}^{ - } _{{{\left( {{\text{CB}}} \right)}}} $$\end{document} represent holes and electrons in valence and conduction bands, respectively. The pseudocapacitance of interface under investigation is related to partial reduction of RuO2 layer at E < 0.2 V and its subsequent recovery during the anodic process.