Regulating the Adsorption Strength of Urea on Transition Metal Oxide-Based Electrocatalysts for Accelerated Electrooxidation of Urea

Exploiting high-efficiency catalytic materials for the electrocatalytic urea oxidation reaction (UOR) is essential for advancing urea-based energy transformation and storage technologies. This study evaluates the UOR performance of common transition metal oxides (Fe, Co, Ni, Cu, and Mn), elucidating potential structure-property relationships for various metal-based catalysts. Through both in situ experiments and theoretical calculations, we reveal that the adsorption strength of the urea molecule acts as a critical descriptor for urea electrooxidation. Inadequate substrate adsorption impedes sufficient reactant availability, while excessive substrate adsorption obstructs the diffusion of substrates and intermediates. Among the catalysts examined, NiO, which exhibits moderate adsorption energy, demonstrates superior performance for urea electrooxidation. Building on this understanding, we subsequently modified the urea adsorption energy on NiO through element doping to further enhance its UOR electrocatalytic activity. Consequently, the optimized Cu-NiO exhibits remarkable performance in various practical applications, including 100 h of two-electrode full urine electrolysis at 10 mA cm^-2, 100 h of hydrogen production in a membrane electrode assembly under industrial-level current density, and 100 h of operation in a Zn-urea-air battery.