Catalyst Engineering for Urea-Assisted Water Splitting: Bridging Energy and Remediation

Electrocatalytic water splitting (EWS) offers a sustainable route for green hydrogen (H2) generation; however, the anodic oxygen evolution reaction (OER) suffers from sluggish kinetics and high thermodynamic overpotential, severely hindering overall system efficiency. Replacing the traditional OER with the urea oxidation reaction (UOR) offers a highly attractive alternative, as it lowers the cell voltage needed for hydrogen evolution and can contribute to the treatment of urea-containing wastewater, provided that urea is converted selectively to N2. This review comprehensively examines recent advances in electrocatalytic materials for urea-assisted water splitting (UAWS). It highlights key catalyst engineering strategies, including compositional tuning, heteroatom doping, and modification of structural and morphological, phase and interface properties, electronic conductivity, and durability of advanced electrocatalyst classes to accelerate UOR and hydrogen evolution. Furthermore, the work discusses degradation mechanisms, in situ characterization, interfacial dynamics, and structural effects in wastewater environments, bridging fundamental reaction mechanisms with EWS operation. By coupling hydrogen production with nitrogen removal from urea-containing wastewater, this work provides critical insights and guidelines for designing high-performance, cost-effective, and scalable resource-positive energy systems. Rather than cataloging individual studies, this review evaluates the reported catalysts against four criteria: the working anodic phase after surface reconstruction, product selectivity (N2 versus nitrite/nitrate), the test conditions behind each reported voltage saving, and the use of authentic urea-containing feeds. It also states the application scenarios in which urea oxidation is justified.