The in situ phosphorization inducing oxygen vacancies in the core–shell structured NiFe oxides boosts the electrocatalytic activity for the oxygen evolution reaction†

Abstract

Transition metal-based oxides have been reported as an important family of electrocatalysts for water splitting owing to their possible large-scale applications that are highly desirable for the hydrogen generation industry. Herein, we report a facile method for the preparation of phosphate-decorated NiFe oxides on nickel foam as efficient oxygen evolution reaction (OER) electrocatalysts for water oxidation. The OER electrocatalysts were developed through the pyrolysis of MIL(Fe) metal–organic frameworks (MOFs), which were modified with Ni and P species. It was found that the formation of NiO on the Fe₂O₃ surface (NiO@Fe₂O₃) can enrich electrocatalytic active sites for the OER. Meanwhile, the incorporation of P into NiO@Fe₂O₃ (P_x-NiO@Fe₂O₃) creates abundant oxygen vacancies, which facilitates the surface charge transfer for OER electrocatalysis. Benefiting from the structure and composition advantages, P_2.0-NiO@Fe₂O₃/NF exhibits the best performance for OER electrocatalysis among other prepared electrocatalysts, with an overpotential of 208 mV at the OER current density of 10 mA cm⁻² and a small Tafel slope of 69.64 mV dec⁻¹ in 1 M KOH solution. Additionally, P_2.0-NiO@Fe₂O₃/NF shows an outstanding durability for the OER electrocatalysis, maintaining the OER current density above 20 mA cm⁻² for more than 100 h.