Engineering Ni(OH)2 with Pd for Efficient Electrochemical Urea Oxidation.

Urea-assisted water electrolysis offers a promising and energy-efficient alternative to conventional water splitting, requiring only 0.37 V-860 mV lower than the 1.23 V needed for water splitting. Ni(OH)2 is a well-established catalyst for this process, but its stability is hindered by CO2 adsorption, which poisons active sites. In this study, we demonstrate that incorporating Pd into Ni(OH)2 (Pd/Ni(OH)₂) enhances catalytic performance, reducing the overpotential by 40 mV at 10 mA cm-2 compared to Ni(OH)2. A lower Tafel slope and charge transfer resistance indicate improved reaction kinetics, leading to a maximum current density of 380 mA cm-2 at 1.5 V which is higher than that of Ni(OH)2 (180 mA cm-2). XAS analysis reveals that while Pd remains metallic in the bulk, the surface is enriched with the oxide phase. Pd incorporation prevents strong CO2 adsorption, significantly enhancing stability to 300 h. DFT calculations further elucidate the reaction mechanism, highlighting Pd's role in improving catalytic efficiency. Additionally, operando Raman and IR spectroscopy provide insights into active site formation and intermediate species during urea electrooxidation. This study underscores the potential of Pd/Ni(OH)2 as an efficient and durable catalyst for urea-assisted electrolysis.