Cu, Fe Dual-modified Ni3S2 nanosheets on nickel foam for bifunctional electrocatalytic water spitting

There are three fundamental issues in heterogeneous electrocatalysis, including the mass transport, the charge transfer and the electrochemical reaction kinetics. For 2D materials, the anisotropy brings advantage in charge transfer. However, the mass transport is often affected by the random stack of the 2D structures; the reaction kinetics is hampered by the exposed low-energy facets. Herein, we applied a two-step hydrothermal strategy to engineer the surface of nickel foam (NF) to prepare a bifunctional Cu3Fe7-Ni3S2/NF electrode for water electrolysis. This electrode combined several merits in electrocatalysis. The nanosheet structure of Ni3S2 is arrayed on the NF, and the surface is roughened by the doping. The roughened nanosheet array structure is efficient for mass transport; the autologous Ni3S2 provides rapid charge transfer between electrocatalyst and the metal substrate; the mixed metal sulfides display high intrinsic activity for water splitting. By the engineering of the 2D nanosheets, the prepared electrode has superior electrocatalytic performance and stability for overall water splitting under alkaline conditions. The bifunctional electrode exhibits an overpotential (eta) of 267 mV to drive a current density of 100 mA cm-2 for the oxygen evolution reaction (OER) and an overpotential of 148 mV to drive a current density of 10 mA cm-2 for the hydrogen evolution reaction (HER). It can be installed in two-electrode water electrolyzer to achieve a current density of 20 mA cm-2 with a cell voltage of 1.56 V.