KINETICS AND MECHANISM OF THE OXYGEN EVOLUTION REACTION AT OXIDE-COATED CO-NI AMORPHOUS ALLOY ELECTRODES

Oxygen evolution reaction (o.e.r.) kinetics in NaOH solutions have bee n studied on both fresh and oxide covered Co50Ni25Si15B10 amorphous al loy (G-16) electrodes. Steady state polarization curves obtained in di fferent aqueous xM NaOH (0.1 less-than-or-equal-to x less-than-or-equa l-to 4) in the 30-80-degrees-C range fulfill Tafel relationships at lo w overpotentials; the Tafel slope is close to 2.3(RT/F) V dec-1 for bo th G-16 and oxide coated G-16 electrodes. At high overpotentials, ohmi c relationships with slopes becoming increasingly steep, regardless of the NaOH concentration, are observed. In the Tafel region, the reacti on order with respect to OH- is near 2. The apparent current density a t constant potential, for oxide coated G-16 electrodes, is greater tha n that for uncoated G-16. The high catalytic activity of the oxide coa ted G-16 for the o.e.r. is attributed to its spinel-type structure. Th e 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.