Modulating the valence electronic structure of Co3O4 to improve catalytic activity of electrochemical nitrate-to-ammonia conversion

Electrochemical conversion of NO 3 − to NH 3 via the nitrate reduction reaction (NO 3 − RR) is a promising approach for ammonia production and storage of “green hydrogen”. Co 3 O 4 has shown satisfactory Faradaic efficiency toward NH 3 ( FE NH 3 ) and stability, making it a potential electrocatalyst for the NO 3 − -to-NH 3 conversion. However, the high overpotential required for triggering the NO 3 − RR on Co 3 O 4 limits its conversion efficiency. In this study, we synthesized Cu-doped Co 3 O 4 porous hollow nanospheres (Cu−Co 3 O 4 PHNSs) for NO 3 − RR. Cu-doping effectively reduced the required overpotential and improved the NH 3 yield rate on the Co 3 O 4 matrix without reducing FE NH 3 and stability. Both experimental and theoretical analyses demonstrated that Cu-doping up-shifted the highest occupied state (HOS) of Co 3 O 4 , narrowed the energy barrier between the HOS of Co 3 O 4 and the lowest unoccupied molecular orbital of NO 3 − , and thus reduced the overpotential required for triggering the electron transfer from Co 3 O 4 to NO 3 − , thereby endowing the as-prepared Cu−Co 3 O 4 PHNSs with outstanding electrocatalytic activity and durability for the NO 3 − -to-NH 3 conversion. This study provides a novel theoretical perspective on the regulation of electrochemical performance.