Multiple Vacancies on (111) Facets of Single-Crystal NiFe2O4 Spinel Boost Electrocatalytic Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) as the rate-determining reaction of water splitting has been attracting enormous attention. As present, only some noble-metal oxide materials (IrO 2 and RuO 2 ) have been reported as efficient OER electrocatalysts for OER. However, the high cost and scarcity of these noble-metal oxide materials greatly hamper their large-scale practical application. Herein, we synthesize 100% (111) faceted NiFe 2 O 4 single crystals with multiple vacancies (cation vacancies and O vacancies). The (111) facets can supply enough platform to break chemical bonds and enhance electrocatalytic activity, due to its high density of atomic steps and kink atoms. Compared to NiFe 2 O 4 (without vacancies), the as-synthesized NiFe 2 O 4 -Ar (with vacancies) exhibits a dramatically improved OER activity. The NiFe 2 O 4 -Ar-30 shows the lowest onset potential (1.45 V vs RHE) and the best electrocatalytic OER activity with the lowest overpotential of 234 mV at 50 mA cm -2 . Furthermore, based on the theoretical calculations that the introduction of multiple vacancies can effectively modulate the electronic structure of active centers to accelerate charge transfer and reaction intermediates adsorption, which can reduce the reaction energy barrier and enhance the activity of electrochemical OER.