Surface characterization and electrocatalytic properties of the Ti/Ir0.3Ti(0.7-x)Pb x O2-coated electrodes for oxygen evolution reaction in acidic media

Abstract

In this work a systematic investigation was carried out of the surface characterization and electrocatalytic activity of Ti/Ir0.3Ti(0.7-x)Pb x O2-coated electrodes (0 <= x <= 0.7), using the oxygen evolution reaction (OER) in 0.5 mol dm-3 H2SO4 as model. The electrodes were prepared by thermal decomposition of IrCl3, TiCl3 and Pb(NO3)2 at 600 °C for 1 h using Ti as support. X-ray diffraction shows that the layers are crystalline and that the corresponding metal oxides are present. The surface morphology of the samples, before and after use under extensive oxygen evolution (Tafel experiment), was characterized by Scanning Electron Microscopy and the micrograph analyses show that the OER promotes the dissolution of the oxide layer. The redox processes occurring on the surface were characterized by cyclic voltammetry at 20 mV s-1 in 0.5 mol dm-3 aqueous H2SO4, at room temperature, and were controlled by the Ir3+/Ir4+ couple. The measured anodic voltammetric charge is related to the active area of the electrode showing that the replacement of TiO2 by PbO2 increases the surface area with the higher value being at 50 mol% PbO2. After oxygen evolution, the surface area increases slightly. Tafel slopes are independent of Pb content with the values around 60 mV decade-1, which suggest that only Ir sites are active for OER. The values of normalized current (i/q a) show some inhibition of the OER as TiO2 is replaced by PbO2 suggesting that PbO2, can be a good choice, with potential to improve the selectivity of the system. The reaction order with respect to H+ ion is zero at constant overpotential and ionic strength. The values of Tafel slope and reaction order indicate that a single reaction mechanism is operating.