It is urgent to develop highly efficient, stable and low-cost bifunctional electrocatalysts for overall water splitting. Herein, an iron-nickel phosphide (Fe₂P/Ni₂P) heterostructure, constructed by Fe₂P nanoparticles embedded on Ni₂P nanosheets, is strategically fabricated on nickel foam via a facile process. As a bifunctional electrocatalyst, the Fe₂P/Ni₂P heterostructure delivers a very low overpotential of 64 mV (or 185 mV) to reach current density of 10 mA cm⁻² for hydrogen (or oxygen) evolution reaction. When simultaneously employed as both the anode and cathode electrodes, it demonstrates an ultralow cell voltage of 1.49 V@10 mA cm⁻² for full water splitting with nearly 100% Faradaic efficiency, and superior long-term stability even over 100 h. Density functional theory calculations manifest that a strong heterointerface interaction could cause electron redistribution near the Fe₂P/Ni₂P heterointerface and optimize the ΔG_H* of P sites, thus enhancing catalytic activity. Additionally, the 3D porous heterostructure is benefit to expose rich active sites and facilitate ion diffusion and gas bubble release, thus promoting the catalytic performance. This work opens up a new strategical approach for rational design of metal phosphide-based heterostructures as highly efficient and stable bifunctional electrocatalysts for water splitting.

迫切需要开发高效、稳定、低成本的双功能全分解水电催化剂。在此，铁镍磷化物 (Fe ₂ P/Ni ₂ P) 异质结构由嵌入 Ni ₂ P 纳米片上的 Fe ₂ P 纳米颗粒构成，通过简单的工艺在镍泡沫上制造。作为双功能电催化剂，Fe ₂ P/Ni ₂ P 异质结构提供了 64 mV（或 185 mV）的极低过电势，以达到 10 mA cm ^{-2 的}电流密度，用于析氢（或氧）析出反应。当同时用作阳极和阴极电极时，它表现出 1.49 V@10 mA cm ^-2的超低电池电压用于全水分解，法拉第效率接近 100%，即使超过 100 小时也具有出色的长期稳定性。密度泛函理论计算表明，强烈的异质界面相互作用可以导致Fe ₂ P/Ni ₂ P异质界面附近的电子重新分布，优化P位点的ΔG _H*，从而提高催化活性。此外，3D多孔异质结构有利于暴露丰富的活性位点，促进离子扩散和气泡释放，从而提高催化性能。这项工作为合理设计金属磷化物基异质结构作为高效稳定的双功能水分解电催化剂开辟了新的战略途径。