Activating Janus charge distribution on the P-doped Ni3S2/Co9S8 interface for enhancing charge-matched urea adsorption: boosting high current hydrogen production via coupled urine degradation

Abstract

The urea oxidation reaction (UOR) is emerging as a thermodynamically favorable alternative to the oxygen evolution reaction, offering significant potential for energy-efficient H₂ production and simultaneous treatment of urea-rich wastewater. However, the 6 e⁻ transfer process of the UOR results in sluggish kinetics, necessitating the development of highly efficient electrocatalysts. Herein, a Janus charge distribution surface is constructed by incorporating phosphorus (P) into the Ni₃S₂/Co₉S₈ heterojunction to enhance the UOR performance and accelerate urea-assisted H₂ production. The P incorporation facilitates electron transfer from Ni₃S₂ to Co₉S₈, creating a local electrophilic/nucleophilic interface that enhances the adsorption of urea molecules with the electron-withdrawing CO group and electron-donating amino groups. As a result, the modified P-Ni₃S₂/Co₉S₈ exhibits ultralow potentials of 1.22, 1.30 and 1.39 V (versus the reversible hydrogen electrode) to reach 10, 100 and 1000 mA cm⁻² for the UOR, respectively. Remarkably, when alkaline urine is used as the electrolyte, the P-Ni₃S₂/Co₉S₈ catalyst, functioning as a bifunctional electrocatalyst in an anion-exchange membrane electrolyzer, can stably deliver a high current density of 1000 mA cm⁻² for H₂ production over 180 h. This work highlights the importance of designing electrocatalysts by activating interfacial charge distribution to enhance reactant adsorption and trigger chemical bond cleavage.