Achieving Higher Efficiency on N₂ Reduction Reaction through Mo- and Bi-Based Active Sites for Sustainable Photoelectrochemical Ammonia Production

Hydrogen energy from water splitting is considered the highly anticipated modern energy resource; however, storage and transportation require complex and high-cost facilities, which argue about the efficiency of hydrogen fuel compared to conventional fuels. Thereby, ammonia (NH₃), which is a liquid at ambient conditions, promises a lower cost of storage and transportation, but the production of ammonia imposes difficulties with selectivity and efficiency over several products and, notably, hydrogen evolution reaction. Among several methods combining the advantages of electrochemical and photocatalytic properties, the photoelectrochemical (PEC) method is destined to improve the efficiency of ammonia production from N₂ reduction reaction (NRR). Because of the multistep NRR process, enormous negative potentials, and poor reaction kinetics, the activity and selectivity of NRR are severely compromised. Therefore, Mo- and Bi-based catalysts are rationally developed to promote the activity and selectivity of NRR processes. Combining the benefits of Mo- and Bi-based catalysts is anticipated to result in highly effective PEC NRR activity. This review is predicted to emphasize the role and characteristics of PEC NRR and the value of Mo and Bi catalysts in raising ammonia's activity and selectivity.