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

Abstract

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.