ELectrochemical impedance, SEM, EDX and voltammetric study of oxygen evolution on Ir + Ti + Pt ternary-oxide electrodes in alkaline solution

Abstract

The oxygen evolution reaction (OER) in alkaline solution has been studied for various Ti supported Ir 0.3Ti (0.7 − x) Pt x O 2 anodes with 0 ≤ x ≤ 0.7 by impedance measurements (EIS) at potentials between −0.6 and 1.0 V vs. Hg HgO (NMOE). The electrical parameters of the electrode solution interface were obtained by fitting the experimental impedance data either to a R Ω(R fC f)(R ctC dl)L (for the Ir 0.3Ti 0.7O 2 electrode) or a R′ Ω(QR ct)L (for PtO x -containing electrodes) equivalent circuit, where Q = constant phase element. The impedance spectrum in the inert region, −0.6 to 0.45V, is an almost vertical line, indicating that the interfacial impedance is essentially capacitive. The ohmic component obtained from EIS ( R Ω = 2.2Ω cm 2 ) for the Ir 0.3Ti 0.7O 2 electrode is consistent with the value obtained from the Tafel plot ( R Ω = 2.4Ω cm 2 ). The substitution of Pt for Ti in the binary system results in a dramatic increase in the R ct , value, ie, the reaction becomes more difficult in the presence of this oxide. It was also observed that the introduction of PtO x causes large morphological changes in the binary system. The different behaviour of the IrO 2 + TiO 2 system from the other oxide compositions is attributed to the instability of the latter oxides in alkaline solution.