LAUSR

Reasonable development of high-efficiency and robust electrocatalysts for efficient electrocatalytic water splitting at high current density is hopeful for renewable energy, but the real challenge is substituting the precious metal catalysts. Herein, ultrathin Fe-modified Ni2P/Ni5P4 nanosheet arrays hybridized with N-doped carbon grown on Ni foam (Fe-Ni2P/Ni5P4@N-C) were synthesized via a solvothermal-pyrolysis strategy. Theoretical calculations and in situ Raman characterizations confirm that the Fe sites can facilitate the surface reconstruction of highly active NiOOH species and significantly lower the energy barrier for the formation of the *OOH intermediate owing to the electron coupling effect between Fe and the Ni2P/Ni5P4 heterostructure. On account of the structural advantages and compositional synergy, the optimized Fe-Ni2P/Ni5P4@N-C exhibits superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities with an overpotential of 105 and 280 mV to reach 10 and 50 mA cm-2, respectively, and can work stably for 60 h at 100 mA cm-2. Impressively, the electrolyzer with Fe-Ni2P/Ni5P4@N-C only needs 1.56 V to achieve 10 mA cm-2 current density for water splitting. This protocol not only provides inspiration for designing transitional metal electrocatalysts for water splitting but also puts forward a pathway for practical application.