Ion Irradiation Inducing Oxygen Vacancy-Rich NiO/NiFe₂O₄ Heterostructure for Enhanced Electrocatalytic Water Splitting

Oxygen evolution reaction (OER) is an obstacle to the electrocatalytic water splitting due to its unique four-proton-and-electron-transfer reaction process. Many methods, such as engineering heterostructure and introducing oxygen vacancy, have been used to improve the catalytic performance of electrocatalysts for OER. Herein, the above two kinds of regulation are simultaneously realized in a catalyst by using unique ion irradiation technology. A nanosheet structured NiO/NiFe2O4 heterostructure with rich oxygen vacancies converted from nickel-iron layered double hydroxides by Ar+ ions irradiation shows significant enhancement in both OER and hydrogen evolution reaction performance. Density functional theory (DFT) calculations reveal that the construction of NiO/NiFe2O4 can optimize the free energy of O* to OOH* process during OER reaction. The oxygen vacancy-rich NiO/NiFe2O4 nanosheets have an overpotential of 279 mV at 10 mA cm(-2) and a low Tafel slope of 42 mV dec(-1). Moreover, this NiO/NiFe2O4 electrode shows an excellent long-term stability at 100 mA cm(-2) for 450 h. The synergetic effects between NiO and NiFe2O4 make NiO/NiFe2O4 heterostructure have high conductivity and fast charge transfer, abundant active sites, and high catalytic reactivity, contributing to its excellent performance.