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

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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.