Advances in Nanostructured Catalysts for Urea-Assisted Water Splitting and Zn-Urea Batteries

Electrochemical water splitting driven by renewable energy provides a sustainable route for generating high-purity hydrogen, yet its efficiency is hampered by the sluggish and economically unfavorable oxygen evolution reaction (OER) at the anode. Replacing OER with the urea oxidation reaction (UOR) has emerged as an attractive strategy to reduce energy input and simultaneously achieve wastewater remediation. Nevertheless, the six-electron transfer process of UOR still suffers from kinetic limitations, highlighting the urgent need for robust and cost-effective electrocatalysts. Recent progress has demonstrated that nanostructure-engineered catalysts enable precise regulation of surface electronic structures, optimization of intermediate adsorption energies, and enhancement of catalytic activity. In this review, we systematically summarize the recent advancements of nanostructural catalysts for UOR-assisted hydrogen evolution, highlighting how rational nanostructuring and compositional engineering contribute to improved intrinsic performance and energy efficiency. The underlying reaction mechanisms are critically discussed based on both experimental and theoretical perspectives. In addition, the practical application of the Zn-urea battery system is introduced, encompassing its electrochemical performance and potential for integrated energy storage and hydrogen production. Finally, we present the current challenges and propose future research directions aimed at bridging the gap between laboratory-scale studies and practical implementation.