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 (YRNH3) of 99.4 mol h-1 gCu-1 (2.30 mol h-1 gcat.-1) with ammonia Faradaic efficiency (FENH3) 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 YRNH3 and FENH3 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.