Enhanced Charge-Carrier Dynamics and Efficient Photoelectrochemical Nitrate-to-Ammonia Conversion on Antimony Sulfide-Based Photocathodes.

The photoelectrochemical reduction of nitrate to ammonia (PEC NORR) has emerged as a promising pathway for facilitating the natural nitrogen cycle. The PEC NORR can lower the reduction potential needed for ammonia synthesis through photogenerated voltage, showcasing the significant potential for merging abundant solar energy with sustainable nitrogen fixation. However, it is influenced by the selective photocathodes with poor carrier kinetics, low catalytic selectivity, and ammonia yields. There are few reports on suitable photoelectrodes owning efficient charge transport on PEC NORR at low overpotentials. Herein, we rationally constructed the CuSn alloy co-catalysts on the antimony sulfides with a highly selective PEC ammonia and an ultra-low onset potential (0.62 V). CuSn/TiO/SbS photoelectrodes achieved an ammonia faradic efficiency of 97.82 % at a low applied potential of 0.4 V, and an ammonia yield of 16.96 μmol h cm at 0 V under one sun illumination. Dynamics experiments and theoretical calculations have demonstrated that CuSn/TiO/SbS has an enhanced charge separation and transfer efficiency, facilitating photogenerated electrons to participate in PEC NORR quickly. Meanwhile, moderate NO* adsorption on this photocathode optimizes the catalytic activity and increases the NH yield. This work opens an avenue for designing sulfide-based photocathodes for the efficient route of solar-to-ammonia conversion.