Electrodeposited zinc cobalt bimetallic phosphate as a bifunctional catalyst for hydrogen evolution and urea oxidation

The theoretical potential of the urea oxidation reaction (UOR) is a mere 0.37 V(vs.RHE), significantly lower than the 1.23 V (vs. RHE) of the oxygen evolution reaction (OER). Thus, substituting the OER with the UOR can effectively reduce the voltage required for electrolysis. Transition metal phosphates (TM-Pi), with their unique physical properties, can partly replace precious metal catalysts and hold great application potential. However, further modification is necessary to enhance their catalytic activity and stability. Therefore, this study prepared a coral-like cluster Co/Zn-Pi@NF (Pi represents phosphate) catalyst, which was grown in situ on nickel foam (NF) using the constant current electrodeposition method. The catalyst exhibited superior catalytic performance in 1 M KOH, with the required overpotentials for the hydrogen evolution reaction (HER) and OER reaching 10 mA·cm ⁻² being 36.6 mV and 343.4 mV, respectively. In 1 M KOH containing 0.5 M urea, the urea oxidation potential was only 1.4 V, which remained stable for 60 hours. The Co/Zn-Pi@NF nanoparticles were used as the anode and cathode for water-urea electrolysis, and the electrolysis voltage was 1.43 V at a current density of 10 mA·cm ⁻², which was 290 mV lower than that of electrolyzed water. This study demonstrates that zinc-cobalt bimetallic phosphate can be used as a dual-function electrocatalyst for hydrogen evolution and urea oxidation.