Boosting Alkaline HER Performance through Oxygen Vacancy Modulation in Ni/NiO Catalysts

Developing efficient and stable catalysts is the key to water splitting, which is a promising technology for green hydrogen production. In this work, oxygen vacancies are introduced to the nanoporous Ni/NiO (np-Ni/NiO) hydrogen evolution reaction (HER) catalyst by a simple electrochemical anodic polarization (EAP) method. The effects of oxygen vacancies on the electronic structure and the adsorption–desorption behavior of reaction intermediates are investigated. The appropriate amount of oxygen vacancies can significantly enhance the HER performance. The np-Ni/NiO catalyst subjected to the EAP treatment exhibits an overpotential of 46 mV at 10 mA cm–2 and a Tafel slope of 53 mV dec–1, which are much lower than those of the Ni/NiO catalyst without EAP treatment. Also, the np-Ni/NiO catalyst maintains excellent activity at higher current densities of 100 mA cm–2. Oxygen vacancies can regulate the occupancy state of d orbitals, optimize adsorption energy states, and facilitate adsorption and desorption processes of reaction-state products, which accelerate the kinetics of the HER. The catalyst also shows remarkable stability during prolonged hydrogen evolution. In addition, the EAP is very easy to process at an industrial level. These advantages favor the large-scale industrial applications of the np-Ni/NiO catalyst.