In Situ Synthesis of CuxO/N Doped Graphdiyne with Pyridine N Configuration for Ammonia Production via Nitrate Reduction

Electroreduction of nitrate to ammonia provides an interesting pathway for wastewater treatment and valorization. Cu-based catalysts are active for the conversion of NO₃ ^- to NO₂ ^- but suffer from an inefficient hydrogenation process of NO₂ ^-. Herein, Cu_xO/N-doped graphdiyne (Cu_xO/N-GDY) with pyridine N configuration are in situ prepared in one pot. Benefiting from the synergistic effect of pyridinic N in GDY and Cu_xO, the prepared Cu_xO/N-GDY tested in a commercial H-cell achieved a faradaic efficiency of 85% toward NH₃ at -0.5 V versus RHE with a production rate of 340 µmol h^-1 mg_cat ^-1 in 0.1 M KNO₃. When integrating the Cu_xO/N-GDY in an anion exchange membrane flow electrolyzer, a maximum Faradaic efficiency of 89% is achieved at a voltage of 2.3 V and the production rate is 1680 µmol h^-1 mg_cat ^-1 at 3.3 V in 0.1 M KNO₃ at room temperature. Operation at 40 °C further promoted the overall reaction kinetics of NO₃ ^- to NH₃, but penalized its selectivity with respect to hydrogen evolution reaction. The high selectivity and production rate in this device configuration demonstrate its potential for industrial application.