Amorphous Ni(Ⅲ)-based sulfides as bifunctional water and urea oxidation anode electrocatalysts for hydrogen generation from urea-containing water

It is highly desired to design high-performance bifunctional electrocatalysts for an efficient oxygen evolution reaction (OER) and urea oxidation reaction (UOR) as anode water electrolysis reactions, which can be used for hydrogen production by using urea-containing water. Herein, a novel electrocatalyst composed of amorphous Ni(OH)S nanosheets was prepared by hydrolysis of NiCl₂(CH₃CSNH₂)₄ at room temperature. From spectroscopic characterization and density functional theory (DFT) calculations, the Ni(OH)S catalyst contains a Ni³⁺-rich phase, which can significantly accelerate the reaction kinetics. The anode electrocatalyst shows excellent OER activity, generating 10 mA cm^-2 with only 250 mV overpotentials. When employed as a UOR anode, it could reach 10 mA cm^-2 at 1.34 V, 140 mV lower than OER. Notably, the Ni(OH)S/NF anode exhibits decent bifunctional UOR and OER activities and presents the lowest overpotentials compared to a NiFe-PBA/NF UOR catalyst and a typical RuO₂/NF OER catalyst. This work provides a novel strategy for synthesizing amorphous Ni(Ⅲ)-based sulfides nanosheets for bifunctional OER/UOR electrocatalysts, which is significant for efficient and stable hydrogen production by using urea-containing wastewater.