Defect-rich Cu@CuTCNQ composites for enhanced electrocatalytic nitrate reduction to ammonia

Electrochemical conversion of nitrate (NO3−) pollutants into chemical feedstock and fuel ammonia (NH3) can contribute to sustainable mitigation of the current severe energy and environmental crises. However, the electrocatalytic NO3− reduction to NH3 (NRA) involves a sluggish multielectron and proton transfer process that competes with the hydrogen evolution reaction (HER) in aqueous media, imposing great challenges in developing highly selective catalysts for NRA. In this study, we developed a copper and copper-tetracyanoquinodimethane composite catalyst (Cu@CuTCNQ), which possesses a high density of copper vacancy defects. This catalyst has been proven to be efficient for NRA through an in situ electrochemical reconstruction method. The structural evolution of CuTCNQ during NRA was investigated by in situ Raman spectroscopy, which indicated an accelerated charge transfer from the CuTCNQ substrate to the derived Cu, which facilitated the adsorption activation of NO3−. The obtained Cu@CuTCNQ exhibited an excellent catalytic performance for NRA, with a Faradaic efficiency of 96.4% and productivity of 144.8 μmol h−1 cm−2 at −0.6 V vs. a reversible hydrogen electrode, superior to Cu nanoparticle counterparts and most Cu-based catalysts. Cu vacancy defects and sufficient interfacial charge transfer synergistically optimize the charge distribution of Cu active sites, reduce the energy barrier for NO3− adsorption, and promote deoxidation and hydrogenation processes, thus enhancing NRA and selectivity.