Sustainable ammonia synthesis from nitrate wastewater via graphdiyne Mo–Cu–C≡C interfaces

Abstract

Electrochemical green ammonia (NH3) production using renewable electricity is sustainable but suffers from selectivity-activity-stability trade-off under industrial conditions. Here we report an atomic interface engineering strategy enabling in-situ assembly and coupling of hexaethynylbenzenes on molybdenum-copper oxidesto form an sp-hybridized Mo/Cu-C≡C heterointerface. It features dual d-orbital hybridization (Mo 4d-C 2p and Cu 3d-C 2p) weakening N–O bond by 36.85% and lowering activation barrier by 0.43 eV, reversible electron-buffer facilitating proton-coupled electron transfer, and self-regulated charge compensation between metal atoms and -C≡C- atomic wires, collectively endowing high activity and near-complete hydrogen evolution reaction suppression. The resulting catalyst achieves high NH3 yielding rate (YNH3, 2.45 mmol h−1 cm−2) and Faradaic efficiency (~100%) under ambient conditions. A prototype flow electrolyzer operating with this catalyst sustains industrial-current densities of 500 mA cm−2 for 300 hours with <3% activity decay, yielding potable water from nitrate wastewater. The membrane electrode assembly (MEA) achieves 380 h stable operation at the same current density with YNH3 of 3.64 mmol h−1 cm−2. Converting nitrate-polluted water into ammonia offers a sustainable alternative to the Haber-Bosch process. Here, authors report a catalyst with sp-C~metal bonds that achieves high selectivity and stability at high currents, enabling fertilizer production and water purification.