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

Electrochemical conversion of NO₃⁻ to NH₃ via the nitrate reduction reaction (NO₃⁻RR) is a promising approach for ammonia production and storage of “green hydrogen”. Co₃O₄ has shown satisfactory Faradaic efficiency toward NH3(FENH3) and stability, making it a potential electrocatalyst for the NO₃⁻-to-NH₃ conversion. However, the high overpotential required for triggering the NO₃⁻RR on Co₃O₄ limits its conversion efficiency. In this study, we synthesized Cu-doped Co₃O₄ porous hollow nanospheres (Cu−Co₃O₄ PHNSs) for NO₃⁻RR. Cu-doping effectively reduced the required overpotential and improved the NH₃ yield rate on the Co₃O₄ matrix without reducing FENH3 and stability. Both experimental and theoretical analyses demonstrated that Cu-doping up-shifted the highest occupied state (HOS) of Co₃O₄, narrowed the energy barrier between the HOS of Co₃O₄ and the lowest unoccupied molecular orbital of NO₃⁻, and thus reduced the overpotential required for triggering the electron transfer from Co₃O₄ to NO₃⁻, thereby endowing the as-prepared Cu−Co₃O₄ PHNSs with outstanding electrocatalytic activity and durability for the NO₃⁻-to-NH₃ conversion. This study provides a novel theoretical perspective on the regulation of electrochemical performance.[Figure not available: see fulltext.]