Nanointerfacial Engineering of a Copper-Based Electrocatalyst for the Selective Electrogeneration of Ammonia from Nitrate Pollution.

Abstract

Nitrate (NO3-) pollution, driven by anthropogenic activities, is contaminating groundwater sources. Simultaneously, the demand for ammonia (NH3) is increasing due to its widespread applications. The electrochemical reduction of nitrate (ERN) is a popular method for converting nitrate into a high-value product (NH3) but is severely limited by the utilization of expensive and scarce platinum group metal (PGM) electrocatalysts. This study aims to address this issue by creating a cost-effective, green, and earth-abundant electrocatalyst without the addition of PGMs to enable ERN under galvanostatic operation. The surface of copper foam was modified through a combination of electrosynthesis and thermal treatment to incorporate CuO and Cu2O nanostructures on the Cu foam interface, directly impacting the ratios of Cu2+ to (Cu0 + Cu1+) and lattice oxygen to oxygen vacancies. The optimization of these ratios resulted in the development of a Cu-ET electrocatalyst that achieved 91% conversion of nitrate with 97.6% selectivity (46.5% increase) toward ammonia production within 1 h of ERN. The electrocatalyst maintained this excellent performance when monitored over continuous ERN cycles and demonstrated a reduction in material cost of over 5300x when compared to the average PGM electrocatalysts reported in the literature. This scalable and earth-abundant Cu-ET electrocatalyst surpasses the efficiency of PGM technologies at a fraction of the cost. Furthermore, the high selectivity demonstrates effective recovery and reuse of NH3, establishing a circular system and addressing both the issue of NO3- contamination and the demand for sustainable NH3 production.