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

Abstract

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 ${\text{RuO}}_2^ + \cdot \left( {{\text{OH}}^ - } \right)_{{\text{ad}}}$ ionic pair formation and annihilation at RuO₂/electrolyte interface as described by following summary equation:

$${\text{RuO}}_{2} \cdot {\text{H}}_{2} {\text{O}} \Leftrightarrow {\text{RuO}}^{ + }_{2} \cdot {\left( {{\text{OH}}^{ - } } \right)}_{{{\text{ad}}}} + {\text{H}}^{ + } + {\text{e}}^{ - } _{{{\left( {{\text{CB}}} \right)}}} ,$$

where ${\text{RuO}}_2^ +$ and ${\text{e}}^{ - } _{{{\left( {{\text{CB}}} \right)}}}$ 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.