To meet the increasing demand for clean energy, environmentally friendly and e cient 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 prepared a catalyst by a two-step hydrothermal method, 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 is 0.6 mmol, a phase transition occurred, and forming NiSe@Ni 3 Se 2 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 was increased to 0.6 mmol, the prepared FNS/0.6 demonstrated excellent HER performance. At 10 mA cm -2 current density, the overpotential was only 156 mV. Moreover, the monolithic hydrolysis electrolyzer assembled with FNS/0.6 as the anode and cathode electrodes showed a low cell voltage of 1.7 V at a current density of 10 mA cm -2 , and almost no attenuation was observed after a 72 h stability test. The excellent electrocatalytic performance of the prepared catalysts was attributed to the formation of nickel-selenide heterostructures and the synergistic effect of two-dimensional Fe-doped MOF, which provide abundant active sites. This study provides a good idea for the development of high activity and high stability catalysts.