Mold-like CuO@Co3O4 Nanocrystals with Abundant Metal Oxide Heterojunctions Enable Efficient Nitrate Electroreduction and Zinc-Nitrate Batteries

Electrocatalytic nitrate reduction (NITRR) serves as a green and promising strategy that combines eco-friendly ammonia (NH3) synthesis and nitrate wastewater remediation. Nevertheless, various nitrogenous side products together with the competitive hydrogen evolution reaction (HER) render the reaction pathways intricate, bringing about excess power loss and inferior product selectivity. Herein, mold-like CuO@Co3O4 nanocrystals with an abundance of metal oxide heterojunction on carbon nanotubes (CNTs) were successfully synthesized through a straightforward one-pot solvothermal approach. Furthermore, the component proportion of CuO/Co3O4 in the catalyst can be accurately tuned via modulating the molar ratio between copper and cobalt precursors introduced in the synthetic procedure. Compared to the alone CuO interface, the formation of the CuO@Co3O4 heterojunction interface effectively modulates the catalyst's capacity to activate water molecules and generate reactive hydrogen species. This, in turn, substantially facilitates the further selective hydrogenation of reactive species adsorbed on the CuO interface to form NH3.The synthesized CuO@Co3O4/CNTs catalyst demonstrates an impressive Faradaic efficiency for NH3 production (FENH3) of 96.19 ± 0.71% at -0.8 V vs RHE, even under extremely low nitrate concentrations, significantly outperforming the CuO/CNTs counterpart. In addition, the assembled NITRR||ZnOR cell with CuO@Co3O4/CNTs as cathode and zinc foil as anode achieves a peak power density of 5.29 mW cm-2 when the discharge current density reaches 14 mA cm-2. The present research puts forward an innovative design route for high-efficiency metal oxide heterojunction electrocatalysts applied in nitrate electroreduction for ammonia synthesis.