Ammonia Synthesis via Electrocatalytic Nitrate Reduction Using NiCoO 2 Nanoarrays on a Copper Foam.

Ammonia (NH ₃ ) plays a vital role in industrial and agricultural development. The electrocatalytic nitrate reduction reaction (eNO ₃ RR) is an effective method to produce NH ₃ 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 NiCoO ₂ @Cu nanosheets, which were used as cathode electrodes for the eNO ₃ RR. In 0.1 M Na ₂ SO ₄ with 0.1 M NaNO ₃ electrolyte, NiCoO ₂ @Cu nanosheets realized an NH ₃ 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 NH ₃ -N increased to 99.7%. The excellent electrocatalytic performance of NiCoO ₂ @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 NiCoO ₂ @Cu nanosheets effectively facilitated the adsorption of NO ₃ ^- on NiCoO ₂ @Cu, and it promoted the eNO ₃ RR.