Tuning the size and chemisorption of FeP4 by trace Ru doping for hydrazine-assisted hydrogen evolution in seawater at large‐current‐density

Integrating thermodynamically favorable hydrazine oxidation reactions (HzOR) with seawater electrolysis will avoid chlorine evolution reaction (ClER) and realize decoupled hydrogen evolution. Herein, the self-supporting Ru-doped FeP4 nanosheets (Ru-FeP4/IF) grown on iron foam are successfully constructed as bifunctional electrocatalysts to facilitate H2 production and HzOR simultaneously. Benefiting from trace Ru doping tuning the size and chemisorption of FeP4, the as-prepared Ru-FeP4/IF requires low potential of 318.0 mV and 335.0 mV to drive 1000 mA cm−2 for HER and HzOR in alkaline seawater, respectively. Notably, only an ultralow voltage of 0.90 V is required to reach 1000 mA cm−2 with outstanding long-term stability and 100% Faradaic efficiency when Ru-FeP4/IF is assembled in a two-electrode cell for overall hydrazine splitting (OHzS). Density functional theory (DFT) calculations show that Ru-doped modulates electronic structure to optimize adsorption free energy of H* (ΔGH*) for HER and decrease dehydrogenation of *N2H4 to *N2H3 for HzOR on FeP4.