Photoelectrochemical nitrogen reduction: A step toward achieving sustainable ammonia synthesis

Industrial NH3 production mainly employs the well-known Haber-Bosch (H-B) process, which is associated with significant energy consumption and carbon emissions. Photoelectrochemical nitrogen reduction reaction (PEC-NRR) under ambient conditions is considered a promising alternative to the H-B process and has been attracting increasing attention owing to its associated energy efficiency and environmentally friendly characteristics. The performance of a PEC-NRR system, such as the NH3 yield, selectivity, and stability, is essentially determined by its key component, the photocathode. In this review, the latest progress in the development of photocathode materials employed in PEC-NRR is evaluated. The fundamental mechanisms and essential features required for the PEC-NRR are introduced, followed by a discussion of various types of photocathode materials, such as oxides, sulfides, selenides, black silicon, and black phosphorus. In particular, the PEC-NRR reaction mechanisms associated with these photocathode materials are reviewed in detail. Finally, the present challenges and future opportunities related to the further development of PEC-NRR are also discussed. This review aims to improve the understanding of PEC-NRR photocathode materials while also shedding light on the new concepts and significant innovations in this field.