Kinetic Understanding of the Enhanced Electroreduction of Nitrate to Ammonia for Co3O4–Modified Cu2+1O Nanowire Electrocatalyst

Electrocatalytic nitrate reduction reaction (NO3−RR) to ammonia (NH3) presents an alternative, sustainable approach to ammonia production. However, the existing catalysts suffer from poor NH3 yield under lower concentrations of NO3−, and the kinetic understanding of bimetal catalysis is lacking. In this study, a Co3O4–modified Cu2+1O nanowire (CoCuNWs) catalyst with a high specific surface area was synthesized to effectively produce NH3 from a 10 mM KNO3 basic solution. CoCuNWs demonstrated a high NH3 yield rate of 0.30 mmol h−1 cm−2 with an NH3 Faradaic efficiency (FE) of 96.7% at −0.2 V vs. RHE, which is 1.5 times higher than the bare Cu2+1O NWs. The synergistic effect between Co3O4 and Cu2+1O significantly enhanced both the nitrate conversion and ammonia yield. Importantly, it is revealed that the surface of CoCuNWs is kinetically more easily saturated with NO3− (NO2−) ions than that of Cu2+1O NWs, as evidenced by both the higher current density and the plateau occurring at higher NOx− concentrations. In addition, CoCuNWs exhibit a higher diffusion coefficient of NO3−, being 1.6 times higher than that of Cu2+1O NWs, which also indicates that the presence of Co3O4 could promote the diffusion and adsorption of NO3− on CoCuNWs. Moreover, the ATR–SEIRAS analysis was applied to illustrate the reduction pathway of NO3− to NH3 on CoCuNWs, which follows the formation of the key intermediate from *NO2−, *NO, *NH2OH to *NH3. This work presents a strategy for constructing dual–metal catalysts for NO3−RR and provides an insight to understand the catalysis from the perspective of the kinetics.