Bifunctional transition-metal catalysts for energy-saving hydrogen generation from nitrogenous wastewater

Wastewater from industrial chemical synthesis, agricultural activities, and domestic sewage usually contains high levels of nitrogenous compounds, endangering environmental health and human well-being. Nitrogenous wastewater electrolysis (NWE), despite its ecological merits, is inherently hampered by sluggish kinetics. To improve process efficiency, lower costs, and avoid cross-contamination between the anode and cathode, a range of bifunctional transition-metal catalysts capable of efficient operation at both electrodes have recently been developed. This review outlines the progress in these catalysts for the energy-saving production of hydrogen from nitrogenous wastewater, including urea, hydrazine, and ammonia. It highlights their dual role in both degrading nitrogenous pollutants and generating hydrogen energy. The review meticulously introduces the key performance metrics of the NWE system and surveys the latest advancements in bifunctional transition-metal catalysts, along with their catalytic mechanisms. It culminates in a detailed summary and comparative analysis of representative bifunctional catalysts, emphasizing their electricity consumption and energy-saving efficiency. Lastly, the existing challenges and research prospects are thoroughly discussed.