Atomically Dispersed Unsaturated Cu‐N3 Sites on High‐Curvature Hierarchically Porous Carbon Nanotube for Synergetic Enhanced Nitrate Electroreduction to Ammonia

Abstract Cu‐based single‐atom catalysts (SACs) are regarded as promising candidates for electrocatalytic reduction of nitrate to ammonia (NO3RR) owing to the appropriate intrinsic activity and the merits of SACs. However, most reported Cu SACs are based on 4N saturated coordination and supported on planer carbon substrate, and their performances are unsatisfactory. Herein, low‐coordinated Cu‐N3 SACs are designed and constructed on high‐curvature hierarchically porous N‐doped carbon nanotube (NCNT) via a stepwise polymerization–surface modification–electrostatic adsorption–carbonization strategy. The Cu‐N3 SACs/NCNT exhibits outstanding NO3RR performance with maximal Faradaic efficiency of 89.64% and NH3 yield rate of up to 30.09 mg mgcat−1 h−1 (70.8 mol gCu−1 h−1), superior to most reported SACs and Cu‐based catalysts. The results integrated from potassium thiocyanide poisoning experiments, online differential electrochemical mass spectrometry, in situ Fourier transform infrared spectroscopy, and density functional theory calculations demonstrate: 1) unsaturated Cu is active site; 2) Cu‐N3 SACs/NCNT possesses NO*‐HNO*‐H2NO*‐H2NOH* pathway; 3) low‐coordinated Cu‐N3 sites and high‐curvature carbon support synergetic promote reaction dynamics and reduce rate‐determining step barrier. This study inspires a synergetic enhancement catalysis strategy of creating unsaturated coordination environment and regulating support structure.