Investigation of copper-based catalysts for the electroreduction of nitrate to ammonia

Ammonia synthesis is key to stable food production as it is present in most of the common fertilizers. However, its synthesis is very energy intensive and leads to significant CO 2 emissions. An alternative approach is to electrochemically generate ammonia from nitrates. In neutral-to-alkaline media, copper and its alloys have shown promising activity for this reaction, but it is difficult to assess which catalyst is the most promising given the variety of synthetic approaches and experimental conditions (pH, nitrate concentration, stirring, cell design, etc.) used in the literature. In this work, Cu x M 100−x (M = Co, Fe or Ni) nanoparticles were prepared by the same technique, pulsed laser ablation in liquids, in the same conditions to allow for an easier comparison. Their activity and selectivity for the electroreduction of nitrates to ammonia was then assessed. Analysis of transmission electron microscope images revealed that Cu, Cu 50 Co 50 and Cu 50 Ni 50 had a size of ≈ 12 nm whereas Cu 50 Fe 50 nanoparticles were ≈ 21 nm. All nanoparticles were copper-rich compared to their targets, as determined by emission spectroscopy. Of the four catalysts tested, Cu 50 Ni 50 had the lowest onset potential for nitrate reduction. However, Cu 50 Ni 50 (as Cu and Cu 50 Fe 50 ) produces mostly nitrite at this potential (~ 90%). Cu 50 Co 50 nanoparticles were found to display the best selectivity for ammonia production. In the optimal conditions of this study, a maximum FE of 86 ± 9 at − 1.1 V was observed for Cu 50 Co 50 NPs on carbon cloth with a partial current density for ammonia production of − 8 ± 2 mA cm −2 .