Water electrolysis for energy-efficient H₂ production coupled with hydrazine oxidation reaction (HzOR) is prevailing, while the sluggish electrocatalysts are strongly hindering its scalable application. Herein, we schemed a novel porous Ce-doped Ni₃N nanosheet arrays grown on nickel foam (Ce-Ni₃N/NF) as a remarkable bifunctional catalyst for both hydrogen evolution reaction and HzOR. Significantly, the overall hydrazine splitting system can achieve low cell voltages of 0.156 and 0.671 V at 10 and 400 mA·cm⁻², and the system is remarkably stable to operate over 100 h continuous test at the high-current-density of 400 mA·cm⁻². Various characterizations prove that the porous nanosheet arrays expose more active sites, and more excellent diffusion kinetics and lower charge-transfer resistance, therefore boosting catalytic performance. Furthermore, density functional theory calculation reveals that the incorporation of Ce can effectively optimize the free energy of hydrogen adsorption and promote intrinsic catalytic activity of Ni₃N.