CO₂ Laser-Synthesized NiCoCu Borate Enables Efficient Nitrate-to-Ammonia Electrosynthesis and Durable Zinc-Nitrate...

The electrocatalytic NO₃ ^- reduction reaction (eNO₃RR) is a facile and green method for the generation of electricity with the simultaneous production of NH₃. Herein, we report the synthesis of hierarchical nickel-cobalt-copper borate ((Ni_1/3Co_1/3Cu_1/3)₃B₂O₆) nanosheets via a carbon dioxide (CO₂) laser irradiation method and investigate their eNO₃RR performance in a 1 m KOH electrolyte containing 0.1 m KNO₃. Initially, (Ni_1/3Co_1/3Cu_1/3)₃B₂O₆ is synthesized via CO₂ laser irradiation within a short processing period of 1 min, where this method enables a rapid material synthesis compared with conventional methods, such as hydrothermal, solvothermal, and wet-chemical approaches. The (Ni_1/3Co_1/3Cu_1/3)₃B₂O₆ catalyst achieves a maximum NH₃ yield rate of 4.1 mg h^-1 cm^-2 and a Faradaic efficiency of 90.69% at -0.3 V vs. the reversible hydrogen electrode. In-depth analysis of eNO₃RR kinetics using in situ Raman, ex situ X-ray diffraction, and ex situ Fourier transform infrared spectroscopy reveals information on the reaction intermediates and reaction pathways involved. Extended density functional theory calculations further corroborate the experimental findings related to reaction intermediates and pathways during the eNO₃RR. A zinc (Zn)-NO₃ ^- battery assembled using (Ni_1/3Co_1/3Cu_1/3)₃B₂O₆ as the cathode and a Zn plate as the anode exhibits an open-circuit voltage of 1.44 V at 12 mA cm^-2.