Highly Accessible Electrocatalyst with I n 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 (Cu ₁ /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 NO ₃ ^- adsorption and subsequent protonation on the unique Cu ₃ -N ₄ 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 N ₂ oxidization and nitrate electroreduction cascade reaction manifests the great potential of the Cu ₁ /hNCNC electrocatalyst in sustainable NH ₃ synthesis. These findings offer valuable insights into the design of effective catalysts for electrosynthetic reactions.