Accelerating the generation of NiOOH by in-situ surface phosphating nickel sulfide for promoting the proton-coupled electron transfer kinetics of urea electrolysis

Nickel sulfide (Ni₃S₂) is a highly promising electrocatalyst for urea oxidation reaction (UOR), and NiOOH formed by the surface phase transition of Ni₃S₂ during UOR is the ideal catalytic active species. However, the strong covalent bonds of Ni₃S₂ hinders the generation of NiOOH, limiting the further improvement of UOR activity. Herein, the Ni₃S₂@Ni₃P core–shell nanorods have been constructed by an in-situ surface phosphating method to boost UOR performance, realizing high catalytic activity (100/1000 mA cm⁻² at 1.36/1.49 V vs. RHE, respectively) and a rapid kinetics (19.13 mV dec^-1). The Ni₃P on the surface of Ni₃S₂ can rapidly form highly active γ-NiOOH with low energy consumption, and the formed Ni₃S₂@γ-NiOOH accelerates proton-coupled electron transfer (PCET) kinetics through reducing the energy barrier of urea dehydrogenation process, thereby enhancing UOR intrinsic activity. In addition, we also demonstrate a Ni₃S₂@Ni₃P//Ni₃S₂@Ni₃P urea electrolysis device with low voltages of 1.54 and 1.69 V at current densities of 100 and 500 mA cm⁻², respectively. This work proposes an efficient strategy to accelerate the generation of NiOOH on the surface of Ni₃S₂ during UOR electrocatalysis, revealing the enhanced UOR mechanism of Ni₃S₂@Ni₃P, which can promote the development of urea-assisted hydrogen production.