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

Abstract

The photoelectrochemical reduction of nitrate to ammonia (PEC NO₃RR) has emerged as a promising pathway for facilitating the natural nitrogen cycle. The PEC NO₃RR 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 NO₃RR 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_RHE). CuSn/TiO₂/Sb₂S₃ photoelectrodes achieved an ammonia faradic efficiency of 97.82 % at a low applied potential of 0.4 V_RHE, and an ammonia yield of 16.96 μmol h^-1 cm^-2 at 0 V_RHE under one sun illumination. Dynamics experiments and theoretical calculations have demonstrated that CuSn/TiO₂/Sb₂S₃ has an enhanced charge separation and transfer efficiency, facilitating photogenerated electrons to participate in PEC NO₃RR quickly. Meanwhile, moderate NO₂* adsorption on this photocathode optimizes the catalytic activity and increases the NH₄ ⁺ yield. This work opens an avenue for designing sulfide-based photocathodes for the efficient route of solar-to-ammonia conversion.