INFLUENCE OF TEMPERATURE ON THE VOLTAMMETRIC RESPONSE OF THERMAL RUTHENIUM OXIDE ELECTRODES

Thermal ruthenium oxide (RuO(x)) electrodes were voltammetrically cycled in 0.1 M H2SO4 at varying solution temperatures from 22 to 65-degrees-C. A systematic increase in the voltammetric charge (q) with temperature was noted the magnitude of which was dependent on the oxide loading of the Ti substrate. This increase obeyed an Arrhenius temperature dependence and activation enthalpies of approximately 4-5 kJ mol-1 were deduced from plots of 1n q vs T-1. The magnitude of the activation enthalpy was insensitive to oxide loading in the range 0.7-4.0 mg cm-2 and the switching potential at the upper limit from 0.40 to 0.90 V (vs sce). In stark contrast to the behavior in acidic electrolytes, cyclic voltammograms in 0.1 M K2SO4 revealed negligible temperature dependence at potentials below the O2 evolution reaction. These results are interpreted in terms of a two time-constant model for charge storage/transport in RuO(x) involving the external and interior surfaces of the oxide micropore structure. The temperature dependence is tentatively assigned to a diffusion or hopping mechanism involving protons at the external surfaces of the oxide micropore structure.