Ru-Doped NiFe-MIL-53 with Facilitated Reconstruction and Active Hydrogen Supplement for Enhanced Nitrate Reduction

The Electrochemical reduction of nitrate to ammonia (NH3) is a process of great significance to energy utilization and environmental protection. However, it suffers from sluggish multielectron/proton-involved steps involving coupling reactions between different reaction intermediates and active hydrogen species (Hads) produced by water decomposition. In this study, a Ru-doped NiFe-MIL-53 (NiFeRu-MIL-53) supported on Ni foam (NF) has been designed for the nitrate reduction reaction (NO3RR). The NiFeRu-MIL-53 exhibits excellent NO3RR activity with a maximum Faradaic efficiency (FE) of 100% at −0.4 V vs. RHE for NH3 and a maximum NH3 yield of 62.39 mg h–1 cm–2 at −0.7 V vs. RHE in alkaline media. This excellent performance for the NO3RR is attributed to a strong synergistic effect between Ru and reconstructed NiFe(OH)2. Additionally, the doped Ru facilitates water dissociation, leading to an appropriate supply of Hads required for N species hydrogenation during NO3RR, thereby further enhancing its performance. Furthermore, in situ Raman analysis reveals that incorporating Ru facilitates the reconstruction of MOFs and promotes the formation of hydroxide active species during the NO3RR process. This work provides a valuable strategy for designing electrocatalysts to improve the efficiency of the reduction of electrochemical nitrate to ammonia.