Nitrite-Mediated Pulsed Electrocatalytic Nitrate Reduction to Ammonia over Co@Cu NW with Dual Active Sites

Abstract

As a potential alternative to the Haber–Bosch process for ammonia (NH3) synthesis, the electrocatalytic nitrate reduction reaction (NO3RR) has attracted extensive attention. The electrocatalytic conversion of NO3– to NH3 involves a complex 8e– reaction with various byproducts. By decomposing the overall reaction into a 2e– process from NO3– to NO2– and a 6e– process from NO2– to NH3, the two-step reaction can be strategically optimized to achieve efficient tandem catalysis. This work developed a NO2–-mediated pulsed electrocatalytic NO3RR by Co@Cu nanowire (NW) with dual active sites of the Co phase and Cu phase. The Cu phase rapidly accumulates NO2– at low potentials, while the Co phase efficiently converts NO2– to NH3 at high potentials, completing a time-separated tandem catalytic reaction. Ultimately, the Co@Cu NW achieved a maximum NH3 yield rate of 5148.6 μg·h–1·cm–2 and a maximum Faraday efficiency of 88.6% under pulsed potentials of −0.2 and −0.7 V versus the reversible hydrogen electrode in an electrolyte of 0.5 M SO42– and 0.1 M NO3–. Furthermore, in situ reflection absorption imaging and in situ total internal reflection imaging revealed that the pulsed strategy effectively enhances the utilization of NO2– and suppresses competitive hydrogen evolution reaction, thereby improving NO3RR performance.