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

The electrocatalytic NO 3 - reduction reaction (NO 3 RR) to NH 3 provides a promising pathway for ambient NH 3 synthesis and environmental pollution treatment. Cu and its oxides are recognized as effective NO 3 RR 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-Cu x O/C-0.3 featured a Cu/Cu 2 O heterostructure and demonstrated the lowest Cu valence state. The resulting Cu/Cu 2 O 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 NO 3 RR catalysts and emphasizes their potential significance in efficient ammonia production.