Oxygen Evolution Behavior of Ni-Containing Alloy Electrodes in NaOH–KOH Hydrate Melt

We investigated the oxygen evolution behavior of nine types of commercially available Ni-containing alloys in a NaOH–KOH hydrate melt. The oxygen overpotential of all Ni-containing alloys was lower than that of the Ni electrode (453 mV) at 500 mA cm –2 and 150°C. The Kovar (Fe–Ni–Co alloy) electrode exhibited the lowest oxygen overpotentials of 280 mV at 150°C and 227 mV at 200°C. The Tafel slope of the Kovar electrode at 150°C was 63 mV dec –1 , which was slightly lower than that of the Ni electrode (67 mV dec –1 ). The upper limit of the Tafel region for the Kovar electrode was extended to a higher current density of 300 mA cm –2 compared to that for the Ni electrode (100 mA cm –2 ) at 150°C. It further extended to 1000 mA cm –2 at 200°C, indicating that highly efficient water electrolysis can be expected.