Construction of hierarchical nanostructures and NiO nanosheets@nanorods for efficient urea electrooxidation

Hierarchical NiO nanosheets@nanorods have been rationally designed and constructed for efficient urea electrooxidation in an alkaline solution. The critical synthetic strategy, engaging the one-step anion-competitive reaction, precisely integrates two nickel-based materials into a heterostructure with Ni(OH)₂ nanosheets and NiC₂O₄ nanorods. Benefiting from the hierarchically porous structure and high specific surface area, the NiO NNs can improve the escape efficiency of gas in electrochemical reactions and maintain sustainability. Furthermore, this distinctive structure can expose highly dispersed active sites for enhancing urea molecules' adsorption, surface-dependent redox reactions, and electrical conductivities. As a result, these hierarchical NiO nanosheets@nanorods exhibit superior activity with a low overpotential of 156 mV at 10 mA/cm², and a slight Tafel slope of 40.7 mV/dec, and high stability with almost no decay of 12,000 s for urea electrooxidation. This work promotes the application of well-designed hierarchical structure in electrooxidizing urea and provides a possibility for highly efficient electrolysis of alkaline urea wastewater.