Highly active transition metal phosphides for urea oxidation: Design strategies, application advances, and perspectives

In recent years, the discharge of urea-containing wastewater from industrial and domestic sources has posed a continuing threat to aquatic ecosystems and human health. In this context, the urea oxidation reaction (UOR) has attracted significant attention due to its low thermodynamic potential of 0.37 V (vs. RHE). Compared with oxygen evolution reaction (OER), this reaction can significantly reduce the energy consumption of electrolysis while realizing wastewater treatment, and has the dual functions of hydrogen energy preparation and wastewater purification. However, UOR involves complex six-electron transfer and intermediate adsorption/desorption processes, resulting in slow reaction kinetics. Therefore, the development of economical and efficient catalysts has become a research focus, among which transition metal phosphides (TMPs) stand out due to their low cost, excellent activity and adjustable electronic structure. Compared with other non-noble metal systems, TMPs have unique electronic structure and surface properties that can adsorb and activate urea molecules more efficiently. However, there is still a lack of systematic reviews on TMP catalysts at present. Therefore, this review aims to deeply and systematically elaborate the design strategies of TMP catalysts and their applications in UOR, thoroughly discuss the current progress, challenges and future directions, and provide theoretical support and design ideas for the development of a new generation of efficient and stable UOR catalysts.