Surface, kinetics and electrocatalytic properties of Ti/(IrO2+Ta2O5) electrodes, prepared using controlled cooling rate, for ozone production

Ti-supported IrO2 + Ta2O5 electrodes, prepared at 550 degreesC using a controlled cooling rate of 2 degreesC min(-1), were characterised by open-circuit potential (E-oc), capacity data (C) and morphology factor (psi) determinations. Sur-face characterisation revealed controlled cooling rate results in compact coatings. E-oc data and CV spectra support surface electrochemistry of mixed oxides of as prepared electrodes is controlled by the Ir(III)/Ir(IV) redox couple, being the relative surface composition given by a(Ir(III)) congruent to 5a(Ir(IV)). A minimum in the active surface area and electrochemical porosity was observed for the 40-50 mol% IrO2-contents. Kinetics were studied recording polarisation curves for different conditions of temperature and supporting electrolyte. Tafel slope data showed the oxygen evolution reaction (OER)/electrochemical ozone production (EOP) processes to depend on both nominal electrode composition and nature of the supporting electrolyte. The anomalous dependence on temperature of the Tafel slope is attributed to anion adsorption and gas bubble adherence. The activation energy for the OER process depends on electrode composition and nature of the supporting electrolyte. Current efficiency data for EOP (Phi(EOP)) were calculated at 0 degreesC for all electrodes and supporting electrolytes investigated and showed low performance for this reaction. (C) 2004 Elsevier Ltd. All rights reserved.