Mixed-valence Cu-based heterostructures for efficient electrochemical nitrate reduction to ammonia

The electrocatalytic NO₃^- reduction reaction (NO₃RR) to NH₃ provides a promising pathway for ambient NH₃ synthesis and environmental pollution treatment. Cu and its oxides are recognized as effective NO₃RR electrocatalysts due to their favorable d-orbital energy levels and superior kinetics. In this work, mixed-valence Cu-based catalysts with tunable valence states were constructed via an inorganic salt-induced MOF-derived strategy. Notably, optimized Cu-CuO/C-0.3 featured a Cu/Cu₂O heterostructure and demonstrated the lowest Cu valence state. The resulting Cu/Cu₂O heterointerface facilitated electron transfer and increased the density of electrochemically active sites, leading to an enhanced faradaic efficiency of 81.4% and a remarkable yield rate of 13.38 mg h^-1 cm^-2 (ca. 2.39 mol h^-1 g_cat.^-1) at -0.8 V vs. RHE. This work presents insights for designing multi-phase heterostructured NO₃RR catalysts and emphasizes their potential significance in efficient ammonia production.