Molybdenum Selenide nanosheets Surrounding nickel Selenides Sub-microislands on nickel foam as high-performance bifunctional electrocatalysts for water Splitting

Transition metal selenides supported on three-dimensional metal foams have attracted extensive attention as promising electrocatalysts for water splitting. Herein, the direct growth of misaligned and intertwined molybdenum selenide nanosheets surrounding nickel selenide sub-microislands on nickel foam (denoted as Mo–Ni–[email protected]) was demonstrated via a simple one-step hydrothermal approach. The as-prepared Mo–Ni–[email protected] demonstrates excellent electrocatalytic activity for hydrogen evolution reaction (HER) in alkaline electrolyte, demanding a low overpotential of 113 mV to achieve the current density of 10 mA cm−2, and a small Tafel slope of 85.7 mV dec−1. It also displays good catalytic performance towards oxygen evolution reaction (OER) with an overpotential of 397 mV at the current density of 100 mA cm−2, and a Tafel slope of 44.9 mV dec−1. Moreover, when applied as both anode and cathode in a two-electrode electrolyzer for overall water splitting, low voltages of 1.583 and 2.098 V are allowed to reach the current densities of 20 and 100 mA cm−2, respectively. Large electrochemical surface area, low electron-transfer resistance, and good stability were demonstrated during the test. The superior activity of Mo–Ni–[email protected] is largely attributed to the seamless integration of the three-dimensional and conductive Ni foam substrate, the direct growth of molybdenum selenide nanosheets on Ni foam with sufficient active sites, and the metallic nickel selenide sub-microislands with good activity and electronic conductivity for the electrons transfer from the substrate to the active sites on molybdenum selenide nanosheets during electrocatalytic process. This work can inspire the optimal design of bimetal selenides on metal foam as efficient and low-cost electrocatalysts for overall water splitting.