Highly Accessible Electrocatalyst with 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/hNCNC) for nitrate electroreduction, which achieves an ultrahigh ammonia yield rate (YR) of 99.4 mol h g (2.30 mol h g) with ammonia Faradaic efficiency (FE) of 99.3%, far beyond the most reported single-site catalysts on carbon-based supports. The combined characterization and theoretical studies indicate that the formed Cu-cluster active sites are responsible for the high YR and FE due to the enhanced NO adsorption and subsequent protonation on the unique Cu-N 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 oxidization and nitrate electroreduction cascade reaction manifests the great potential of the Cu/hNCNC electrocatalyst in sustainable NH synthesis. These findings offer valuable insights into the design of effective catalysts for electrosynthetic reactions.