Dual-strategy engineered nickel phosphide for achieving efficient hydrazine-assisted hydrogen production in seawater

Electrocatalytic hydrogen production in seawater to alleviate freshwater shortage pressures is promising, but is hindered by the sluggish oxygen evolution reaction and detrimental chloride electrochemistry. Herein, a dual strategy approach of Fe-doping and CeO₂-decoration in nickel phosphide (Fe-Ni₂P/CeO₂) is rationally designed to achieve superior bifunctional catalytic performance for the hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) in seawater. Notably, the two-electrode Fe-Ni₂P/CeO₂-based hybrid seawater electrolyzer realizes energy-efficient and chlorine-free hydrogen production with ultralow cell voltages of 0.051 and 0.597 V at 10 and 400 mA cm^-2, which are significantly lower than those needed in the hydrazine-free seawater electrolyzer. Density functional theory calculations manifest that the combination of Fe doping and heterointerface construction between Fe-Ni₂P and CeO₂ can adjust the electronic structure of the Ni₂P and optimize the water dissociation barrier and hydrogen adsorption free energy, leading to improvement of the intrinsic catalytic performance. This route affords a feasible solution for future large-scale hydrogen generation using abundant ocean water.