A highly active copper-nanoparticle-based nitrate reduction electrocatalyst prepared by in situ electrodeposition and annealing.

In recent years, copper-based electrodes have attracted intense attention for the electrochemical reduction of nitrate (NO3-), the so-called ECRN. However, these electrodes suffer from low activity and selectivity. Herein, we report a novel Cu-based electrode (IE-Cu-400) for the ECRN fabricated by loading Cu-based nanoparticles onto graphite felt using in situ electrodeposition followed by annealing. Compared with traditional Cu-based electrodes, the IE-Cu-400 is comprised of smaller particles and the copper is present in a high oxidation state (Cu2+ in CuO). During operation, the CuO is converted to Cu, which is the active ECRN species. In addition, an increased surface area and high density of grain boundaries resulting from the reduction of CuO were observed for IE-Cu-400. This resulted in a 3.38-fold increase in the NO3- removal rate and a 1.36-fold increase in NH4+ selectivity. Further analyses revealed that the enhanced ECRN performance of IE-Cu-400 is linked to its increased number of active sites, as well as its improved adsorption and reduction ability for NO2-. Moreover, IE-Cu-400 displays high stability for the ECRN. Finally, the produced NH4+ was effectively oxidised to N2 with approximately 100% selectivity via chlorination. Hence, the two-stage treatment strategy (i.e. ECRN by IE-Cu-400 + chlorination treatment) presented here shows great potential for the complete electrocatalytic denitrification of water. Further, this work highlights the beneficial effect of decreasing the particle size and controlling the surface oxidation of Cu-based catalysts simultaneously for enhancing the ECRN and offers new suggestions for the design of high-performance electrode materials for the ECRN.