Surface, kinetics and electrocatalytic properties of the Ti/Ti + Ru+Ce)O2-system for the oxygen evolution reaction in alkaline medium

Ti-supported (Ti + Ru + Ce)O-2 electrodes, prepared at 450 degrees C, were characterised by XRD, open-circuit potential (E-oc), capacity data (C) and morphology factor (phi) determinations. XRD measurements showed mixed oxides present a low degree of crystallinity. E-oc-data and CV-spectra support surface electrochemistry of mixed oxides is governed by the Ru(III)/Ru(IV) redox couple. In situ surface characterisation revealed the active surface area increases on increasing nominal CeO2-content. phi-Values remained in the 0.18-0.3 interval supporting the coatings have a low electrochemical porosity. Kinetics was studied recording polarisation and chronopotentiometric curves, which permitted to determine the Tafel slope and reaction order (with respect to OH-), in the low and high overpotential domains. Tafel slope data, b, presented a dependence on overpotential and oxide composition indicating the OER electrode mechanism depends on these variables. A unit reaction order with respect to OH- was found for all electrode compositions investigated. The theoretical analysis of the electrode mechanism permitted to analyse the changes in the experimental Tafel slopes taking into account modifications in the apparent electronic transfer coefficient, alpha(ap). Analysis of the true and apparent electrocatalytic activities revealed the O-2-evolution reaction rate is affected by oxide composition due to morphologic effects. (c) 2005 Elsevier Ltd. All rights reserved.