Rapid B-Ni charge transfer pathway induced Ni/Ni sites reversible conversions enabling efficient urea oxidation assisted hydrogen production.

The high energy consumption induced by the sluggish anodic oxygen evolution reaction (OER) severely limits the efficiency of hydrogen production in water splitting. Replacing OER with urea oxidation reaction (UOR) with lower theoretical voltage with nickel-based layered double hydroxides (NiM-LDHs) as the electrocatalyst enables highly efficient hydrogen production. Herein, a reversible Ni/Ni conversion mechanism through rapid B-Ni charge transfer for efficient UOR is first reported. The introduction of the B sites accelerates the surface reconstruction of Ni into Ni in B-NiCo-LDH, ensuring the rapid generation of the active Ni species. In the presence of urea, the rapid B-Ni charge transfer accelerates the reduction process of partial Ni into Ni species, avoiding the overaccumulation of Ni and the over-adsorption of *COO on the catalyst, thereby effectively reducing the energy barrier of UOR. Thus, B-NiCo-LDH demonstrates an ultra-low voltage of 1.39 V vs. RHE to deliver 100 mA cm for UOR. More importantly, the constructed urea-assisted water electrolysis electrolyzer by coupling B-NiCo-LDH at the anode and an HER catalyst (Pt/C) at the cathode achieves 100 mA cm with cell voltages of only 1.55 V and 1.57 V, in alkaline freshwater and seawater, respectively, also exhibiting excellent stability for at least 100 h.