Proton Exchange Membrane Electrode Assembly for Ammonia Electrosynthesis from Nitrate

Green ammonia synthesis and elimination of nitrate pollution from water are two global challenges that need to be dealt with. Electrocatalytic nitrate reduction to ammonia (e-NRA) using renewable electricity has been considered a potential solution to these challenges simultaneously. Although great research progress has been achieved in developing high-activity catalysts, insufficient attention has been paid to the electrolyzer design, which also has a vital impact on the e-NRA performance. Herein, we first abandoned anion exchange membranes due to the inevitable high nitrate permeability and then studied a proton exchange membrane electrode assembly (PEMEA) coupled with high-performance oxide-derived Cu nanoneedle cathodes toward practical application of e-NRA. Our results illustrated that the architecture of cathodes should be rationally designed to overcome the competing hydrogen evolution reaction aggravated by the utilization of proton exchange membranes. As a result, an optimized PEMEA achieved a high ammonia faradic efficiency of 90% at a high current density of 400 mA cm–2 in an electrolyte with 0.1 M nitrate concentration, and the corresponding ammonia yield was 1.6 mmol h–1 cm–2. In addition, nearly 100% conversion of nitrate to ammonia was demonstrated in the wastewater treatment of actual enterprises. We believe this work will facilitate the industrialization process of e-NRA.