High Ammonia Yield Rate from Dilute Nitrate Solutions Using a Cu(100)-Rich Foil: A Step Closer to Large-Scale...

The electrochemical reduction of nitrate (NO₃^-) ions to ammonia (NH₃) provides an alternative method to eliminate harmful NO₃^- pollutants in water as well as to produce highly valuable NH₃ chemicals. The NH₃ yield rate however is still limited to the μmol h^-1 cm^-2 range when dealing with dilute NO₃^- concentrations found in waste streams. Copper (Cu) has attracted much attention because of its unique ability to effectively convert NO₃^- to NH₃. We have reported a simple and scalable electrochemical method to produce a Cu foil having its surface covered with a porous Cu nanostructure enriched with (100) facets, which efficiently catalyzes NO₃^- to NH₃. The Cu(100)-rich electrocatalyst showed a very high NH₃ production rate of 1.1 mmol h^-1 cm^-2 in NO₃^- concentration as low as 14 mM NO₃^-, which is 4-5 times higher than the best-reported values. Increasing the NO₃^- concentration (140 mM) resulted in an NH₃ production yield rate of 3.34 mmol h^-1 cm^-2. The durability test conducted for this catalyst foil in a flow cell system showed greater than 100 h stability with a Faradaic efficiency greater than 98%, demonstrating its potential to be used on an industrially relevant scale. Further, density functional theory (DFT) calculations have been performed to understand the better catalytic activity of Cu(100) compared to Cu(111) facets toward NO₃^-RR.