Kinetics and mechanism of the oxygen evolution reaction at oxide-coated Co-Ni amorphous alloy electrodes

Abstract

Oxygen evolution reaction (o.e.r.) kinetics in NaOH solutions have been studied on both fresh and oxide covered Co50Ni25Si15B10 amorphous alloy (G-16) electrodes. Steady state polarization curves obtained in different aqueous xM NaOH (0.1 ⩽ x ⩽ 4) in the 30–80°C range fulfill Tafel relationships at low overpotentials; the Tafel slope is close to 2.3(RT/F) V dec−1 for both G-16 and oxide coated G-16 electrodes. At high overpotentials, ohmic relationships with slopes becoming increasingly steep, regardless of the NaOH concentration, are observed. In the Tafel region, the reaction order with respect to OH− is near 2. The apparent current density at constant potential, for oxide coated G-16 electrodes, is greater than that for uncoated G-16. The high catalytic activity of the oxide coated G-16 for the o.e.r. is attributed to its spinel-type structure. The kinetics of the o.e.r. at low overpotentials is explained through a mechanism involving a first electron transfer step followed by a rate-determining chemical step.