To meet the increasing demand for clean energy, environmentally friendly and efficient transition metal selenides (TMSes) electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are being developed. There is an urgent need for a rational design of bifunctional non-precious metal catalysts with advanced structure and superior composition. In water splitting for the production of clean hydrogen energy, transition metal selenides have promising applications. We prepare a catalyst by a two-step hydrothermal method, and the crystal structure of the catalysts can be easily adjusted by adjusting the concentration of the selenizing agent; when the concentration of the selenizing agent (Na₂SeO₃) is 0.6 mmol, a phase transition occurred, forming the NiSe@Ni₃Se₂ heterostructure, reaching a current density of 10 mA cm⁻² at an overpotential of 214 mV with a low Tafel slope of 41 mV dec⁻¹. When the concentration of selenide is increased to 0.6 mmol, the prepared NiFeSe_0.6-MOF (metal organic framework) demonstrates excellent HER performance. At 10 mA cm⁻² current density, the overpotential is only 156 mV. Moreover, the monolithic hydrolysis electrolyzer assemble with NiFeSe_0.6-MOF as the anode and cathode electrodes shows a low cell voltage of 1.7 V at a current density of 10 mA cm⁻², and almost no attenuation is observed after a 72-h stability test. The excellent electrocatalytic performance of the prepared catalysts is attributed to the formation of nickel selenide heterostructures and the synergistic effect of two-dimensional ferrum-doped MOF, which provide abundant active sites. This study provides a good idea for the development of high activity and high stability catalysts.

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