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

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 ((Ni1/3Co1/3Cu1/3)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, (Ni1/3Co1/3Cu1/3)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 (Ni1/3Co1/3Cu1/3)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 (Ni1/3Co1/3Cu1/3)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.