Ammonia Synthesis via Electrocatalytic Nitrate Reduction Using NiCoO₂ Nanoarrays on a Copper Foam

Ammonia (NH₃) plays a vital role in industrial and agricultural development. The electrocatalytic nitrate reduction reaction (eNO₃RR) is an effective method to produce NH₃ under environmental conditions but also requires considerably active and selective electrocatalysts. Herein, a copper foam was used as a conductive substrate for the electrode materials. Specifically, a Co metal-organic framework (Co-MOF) was in situ grown on the copper foam, etched, and calcined to form NiCoO₂@Cu nanosheets, which were used as cathode electrodes for the eNO₃RR. In 0.1 M Na₂SO₄ with 0.1 M NaNO₃ electrolyte, NiCoO₂@Cu nanosheets realized an NH₃ yield of 5940.73 μg h^-1 cm^-2 at -0.9 V vs reversible hydrogen electrode (RHE), with a Faradaic efficiency of 94.2% at -0.7 V vs RHE. After 33 h of the catalytic reaction, the selectivity of NH₃-N increased to 99.7%. The excellent electrocatalytic performance of NiCoO₂@Cu nanosheets was attributed to the apparent synergistic effect between the Ni atoms and the Co atoms of bimetallic materials. This study shows that the Ni doping of NiCoO₂@Cu nanosheets effectively facilitated the adsorption of NO₃^- on NiCoO₂@Cu, and it promoted the eNO₃RR.