Lattice Hydrogen Involved Electrocatalytic Nitrate Reduction to Hydroxylamine

Abstract

Electrocatalytic nitrate reduction to hydroxylamine (ENRH) provides a sustainable strategy for NH₂OH synthesis under ambient conditions. At present, active hydrogen (*H) derived from water dissociation has been widely used as a H-source for nitrate hydrogenation, bringing a big challenge for ENRH. On the one hand, insufficient *H would lead to the accumulation of nitrite. On the other hand, sufficient *H with high reduction ability would induce over-hydrogenation of hydroxylamine to ammonia. To overcome this challenge, herein, we propose to utilize lattice hydrogen (H_lat) with an appropriate reduction ability as the H-source for ENRH. We design and construct a Cu-MnO₂H_x electrocatalyst, in which the Cu-triggered Jahn-Teller distortion of [MnO₆] octahedron significantly increases the number of H_lat. The Faradaic efficiency and yield of NH₂OH are as high as 91.1% and 396.6 mmol g_cat.^-1 h^-1 over Cu-MnO₂H_x, outperforming most of the reported catalysts. The combined results of isotopic tracking experiments and theoretical calculations prove the enrichment and buffer functions of H_lat, which can provide an abundant H-source for nitrate's selective reduction to hydroxylamine.