Investigação das propriedades superficiais e eletrocatalítcas do sistema Ti/(Ru+Ce+Ti)O2 para a reação de desprendimento de oxigênio em meio alcalino

Abstract

Ti/Ruo.3Ti(o.7-x)Ce02 electrodes were prepared by thermal decomposition (450°C, air), and characterised by XRD, open-circuit potential (£<») and CV measurements. XRD measurements revealed mixed oxides presení a low degree of crystallinity, which is attributed to the low interaction between the rutile (RuO2, TiO2) and cerianite (CeO2) crystallographic structures. Eoc-data support surface electrochemistry of mixed oxides is govemed by the Ru(III)/Ru(IV) redox couple. The increase in f/a-values with increasing CeO2-content reveals partial substitution of TiO2 by CeO2 increases the electrochemically active surface area. Extensive (interfaciaJ capacities: Cr, Ce and Ci) and intensive surface parameters (the morphology factor, (p) support substitution of CeO2 with TiO2 increases roughness while not afifecting significantly electrode porosity. The kinetic study revealed a Tafel slope depends on overpotential and oxide composition: introduction of CeO2 decreases Tafel slope values, especially in the high overpotential domain. A unitary reaction order with respect to OIT-ion was obtained for all electrodes. Tafel slope and the reaction order data support the OER electrode process is adequately described, in alkaline médium, by Yeager’s mechanism. According to this mechanism changes in Tafel slope find their origin in changes in the affinity between the active surface site, =S, and the adsorbed OIT-ion (low overpotential domain) and in the bond strength of the active surface complex site =SZ—OH (high overpotential domain). From an electronic point of view such changes affects electron transfer process modifying the apparent electronic transfer coefficient, a. Calculation of a, showed the values to reach a maximum of 0.8 with decreasing CeO2-content, denouncing a decrease in the electric component of the energy barrier of the electron transfer. The apparent electrocatalytic activity was dependent on CeO2 for films having [CeO2]N 60% mol which is attributed to the Chemical nature of the electrode and its geometry. Best real electrocatalytic activity was observed for the Ti/RuojTio.iCh and Ti/Ruo.3Ceo.702 compositions. Service life tests under conditions of accelerated corrosion revealed Service life, tw, and degree of instability, A, are both dependent on [CeO2]N. Final electrode deactivation occurs by Ti-support passsivation before total coating consumptions is observed, especially for CeO2-rich films. A mathematical model is proposed to describe the degree of instability, A, which is capable to explain the electrochemical impedance spectroscopic, EIS, data. EIS-data support the real electrocatalytic OER performance of the electrodes depends on anodization time and that the rugous/porous films behave close to ideal as supported by the low frequency dispersion.