Development of Ni-Ir Oxide Composites as Oxygen Catalysts for an Anion-Exchange Membrane Water Electrolyzer

Abstract

In water splitting, anode catalysts for the oxygen evolution reaction (OER), which is the rate-determining step, are more critical than cathode catalysts. Herein, the authors prepare Ni-IrOx composite catalysts consisting of NiO and IrO2 for the OER by a solid-state reaction with different ratios of NiO to IrO2 and reaction temperatures. In particular, Ni-IrOx-400 with a molar ratio of NiO/IrO2 = 1:1 heated at 400 degrees C shows the best OER performance. In the overall water splitting test using an anion exchange membrane (AEM) water electrolyzer, the single cell with Ni-IrOx-400 as the anode catalyst shows current densities of 1454.8 mA cm(-2), respectively, measured at 1.8 V. Furthermore, the stability tests of the AEM single cells are carried out at 50 degrees C under a constant current density of 500 mA cm(-2). The single cell with Ni-IrOx-400 shows only a slight increase in the overpotential (rate: 2.0 mV h(-1)) for 100 h owing to the enhanced stability of Ni-IrOx-400 compared to IrO2 (12.5 mV h(-1)). The improved OER performance of the Ni-IrOx-400 may be attributed to a composite structure that can prevent particle agglomeration and thus preserve the active sites during the OER.