Metallized Ni(OH)2·NiO/FeOOH on Ni Foam as a Highly Effective Water Oxidation Catalyst Prepared by Surface Treatment: Oxidation–Corrosion Equilibrium

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The surface treatment method has a great influence on the structure and properties of applied materials for interface catalysis. In this study, we prepare Ni(OH)2·NiO/FeOOH by surface treatment in acid solution using oxidation–corrosion equilibrium (OCE). For comparison, we also treat Ni foam with the same process in alkaline solution. Ni(OH)2·NiO/FeOOH can achieve steady morphology and metallization by OCE and exhibits superior catalytic activity as a water oxidation catalyst. Ni(OH)2·NiO/FeOOH(OCE) needs only 232 mV to reach a current density of 10 mA cm–2, while it is 254 mV for a reference IrO2/Ni foam. The mechanism study shows that the small charge transfer resistance (2.04 Ω cm2) is favorable for the rapid interface electron exchange between Ni(OH)2·NiO/FeOOH(OCE) and reactive species in water oxidation. In addition, the results of X-ray photoelectron spectroscopy and series impedance show that the catalyst is metallic in property in virtue of the exposed metal Ni in Ni(OH)2·NiO/FeOOH(OCE). The volume ratio of hydrogen to oxygen (around 2:1) indicates overall water splitting by the double-electrode system. When the volume ratio of hydrogen to oxygen is 2:1, the Faraday efficiency of H2 or O2 is close to 100%. Ni(OH)2·NiO/FeOOH(OCE) exhibits good stability for 1 month. The research results provide a feasible approach for finding low-cost metallized catalysts to replace noble metals as water oxidation catalysts and improving the efficiency of water splitting.