NiFe2O4 @Co3O4 heterostructure with abundant oxygen vacancies as a bifunctional electrocatalyst for overall water splitting

Exploring robust and high-performance bifunctional electrocatalysts for overall water splitting is crucial for converting electric power to hydrogen energy, especially for the flexible utilization of intermittent green energy resources. Herein, pine-needle-like NiFe2O4 @Co3O4 heterostructure nanoarrays with abundant oxygen vacancies were deposited onto nickel foam via hydrothermal reaction, cathodic electrodeposition, and CaH2 reduction. The synergistic approach boosts the electrochemical activity of catalyst by improving conductivity, mass diffusion efficiency, and active site quantity. Accordingly, the optimal electrocatalyst exhibits outstanding catalytic activity with high electrochemical stability in an alkaline medium, providing low overpotentials of 251 mV and 77 mV respectively to achieve 10 mA·cm−2 for catalyzing OER and HER. Moreover, the as-fabricated bifunctional electrocatalyst only requires a cell voltage of 1.56 V to enable a current density of 10 mA·cm−2 for realizing water electrolysis, outperforming many other previously reported catalysts. This work provides an inspiration for developing open structure materials with synergistic effect, and demonstrates a feasible method to synthesis high-efficiency electrocatalysts for water splitting.