A porous copper catalyst for electrochemical nitrate reduction to ammonium

Ammonia (NH₃) is one of the main components in the global nitrogen (N) cycle and an essential fertilizer and chemical feedstock. However, NH₃ is mostly synthesized from energy-intensive Haber-Bosch process, which accounts for 1.8 % of global energy consumption and 1.4 % of global CO₂ emissions. Also, fertilizer-intensive agriculture and large amount of NH₃ used in industry normally generate nitrate (NO₃^-)-containing wastewater. Therefore, electrocatalytic reduction of nitrate to ammonium emerges as a sustainable alternative to tackle current challenges in ammonium production and establish a closed N-cycle. In the present study, we synthesized a highly porous copper catalyst, which demonstrated an outstanding performance in reduction reaction and ammonium production. The designer copper catalysts achieved a nitrate conversion of 84 %, ammonium selectivity of 85 %, and ammonium yield of 71 % with an ammonium Faradaic efficiency of 58 % at the reduction potential of −0.75 V (versus saturated calomel electrode). Further analysis suggests that enhanced catalytic activity is contributed from the abundant electrochemical active sites within the highly porous structure in copper catalysts. This work not only presents the significance of structural engineering on promoting electrocatalytic performance but also paves a way for the development of a greener and more efficient strategy in ammonium synthesis.