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 SO₄^2– 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.