Urea oxidation reaction electrocatalysts: Correlation of structure, activity, and selectivity

Summary

The urea oxidation reaction (UOR) holds tremendous applications in various catalysis processes. Given the general unsatisfied urea degradation (<100%), exploration of highly selective and efficient catalysts for the UOR is highly desirable. Metal-organic frameworks (MOFs) with tailorable metal nodes, organic ligands, homogeneous microenvironments, and structurally identifiable features represent an ideal platform for understanding the relationship between structure, activity, and product selectivity. This review summarizes the UOR mechanisms of nickel-based catalysts, including Ni³⁺/Ni⁴⁺-mediated mechanisms (adsorbate evolution mechanism and lattice oxygen mechanism), the dual-step mechanism associated with Ni²⁺ (urea decomposition reaction + UOR), and the three pathways of urea dissociation (i.e., the final products of NO₂⁻, N₂, and NH₃). Additionally, we also review the modulation strategies (metal node, organic ligands, and morphology) in Ni-MOFs, along with urea product analysis and in situ detection methods. This work provides useful insights into the relationships between structure, activity, and product selectivity for the UOR.