Highly Accessible Electrocatalyst with In Situ Formed Copper-Cluster Active Sites for Enhanced Nitrate-to-Ammonia Conversion

Ammonia synthesis via nitrate electroreduction is more attractive and sustainable than the energy-extensive Haber-Bosch process and intrinsically sluggish nitrogen electroreduction. Herein, we have designed a single-site Cu catalyst on hierarchical nitrogen-doped carbon nanocage support (Cu₁/hNCNC) for nitrate electroreduction, which achieves an ultrahigh ammonia yield rate (YR_NH3) of 99.4 mol h^-1 g_Cu^-1 (2.30 mol h^-1 g_cat.^-1) with ammonia Faradaic efficiency (FE_NH3) of 99.3%, far beyond the most reported single-site catalysts on carbon-based supports. The combined operando characterization and theoretical studies indicate that the in situ formed Cu-cluster active sites are responsible for the high YR_NH3 and FE_NH3 due to the enhanced NO₃^- adsorption and subsequent protonation on the unique Cu₃-N₄ moieties, and meanwhile, the hierarchical hNCNC support facilitates the mass/charge transfer kinetics, thus promoting the high expression of intrinsic activity. The demonstration of plasma N₂ oxidization and nitrate electroreduction cascade reaction manifests the great potential of the Cu₁/hNCNC electrocatalyst in sustainable NH₃ synthesis. These findings offer valuable insights into the design of effective catalysts for electrosynthetic reactions.