Examination of RuO2 single-crystal surfaces: charge storage mechanism in H2SO4 aqueous solution

Systematic voltammetric and impedance studies of RuO2 ‘as-grown’ single crystals were carried out using the (101), (110) and (002) faces in 0.5 mol dm-3 sulphuric acid solution and applying the hanging electrolyte meniscus technique. The crystal surfaces, prepared by the vapor transfer technique at high temperature, show well-defined XRD patterns. The dependence of the voltammetric characteristics on potential scan rate modulations was investigated. The charge storage mechanism was examined in the following cases for differences: (i) in the anodic surface charge qa* and the atomic distribution of ideal surfaces, (ii) between the total anodic charge qa*tot and the anodic charge associated with the electrochemical process qa** due to the redox couple in the solid state. A systematically higher charge for the (101) face in the same potential range represents a probe for the crystal face specificity of the redox process.