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

Abstract

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.