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 (H_ads) 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 H_ads 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.