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 (Ni 3 S 2 ) is a highly promising electrocatalyst for urea oxidation reaction (UOR), and NiOOH formed by the surface phase transition of Ni 3 S 2 during UOR is the ideal catalytic active species. However, the strong covalent bonds of Ni 3 S 2 hinders the generation of NiOOH, limiting the further improvement of UOR activity. Herein, the Ni 3 S 2 @Ni 3 P 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 Ni 3 P on the surface of Ni 3 S 2 can rapidly form highly active γ-NiOOH with low energy consumption, and the formed Ni 3 S 2 @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 Ni 3 S 2 @Ni 3 P//Ni 3 S 2 @Ni 3 P 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 Ni 3 S 2 during UOR electrocatalysis, revealing the enhanced UOR mechanism of Ni 3 S 2 @Ni 3 P, which can promote the development of urea-assisted hydrogen production .