Tailored Ni(OH)<sub>2</sub>/CuCo/Ni(OH)<sub>2</sub> Composite Interfaces for Efficient\nand Durable Urea Oxidation Reaction

Electrocatalytic urea oxidation reaction is a promising\nalternative\nto water oxidation for more efficient hydrogen production due to its\nsignificantly lower thermodynamic potential. However, achieving efficient\nelectrochemical urea oxidation remains a formidable challenge, and\ndevelopment of an improved electrocatalyst with an optimal physicochemical\nand electronic structure toward urea oxidation is desired. This can\nbe accomplished by designing a tailored two-dimensional composite\nwith an abundance of active sites in a favorable electronic environment.\nIn this study, we demonstrate the fabrication of a self-supported,\nelectrochemically grown metal/mixed metal hydroxide composite interface\nvia a two-step electrodeposition method. Specifically, Ni(OH)<sub>2</sub> was electrodeposited on the top of the CuCo layer (Ni(OH)<sub>2</sub>/CuCo/Ni(OH)<sub>2</sub>), and the resultant 2D composite\nstructure required 1.333 ± 0.006 V to oxidize urea electrochemically\nto achieve a current density of 10 mA cm<sup>–2</sup>, which\noutperformed the potential required for individual components, Ni(OH)<sub>2</sub> and CuCo. The high density of Ni<sup>3+</sup> active sites\nin the composite structure facilitated high electrocatalyst activity\nand stability. Ni(OH)<sub>2</sub>/CuCo/Ni(OH)<sub>2</sub> was stable\nfor at least 50 h without any noticeable degradation in the activity\nor alteration of the morphology. As a bifunctional electrocatalyst,\nthe material also exhibited excellent performance for water oxidation\nwith 260 mV overpotential and 50 h stability. In a two-electrode configuration\ncoupled with a NiMo cathode catalyst, the electrolyzer required 1.42\nV cell voltage for overall urea splitting. Overall, the engineered\nNi(OH)<sub>2</sub>/CuCo/Ni(OH)<sub>2</sub> composite demonstrated\nexceptional potential as an efficient and stable electrocatalyst for\nboth urea and water oxidation reactions, paving the way for more effective\nhydrogen production technologies.