Neighboring Ni-Cu dual single-atom sites regulate the local environment of interfacial water for promoting CO2 electroreduction kinetics in CO2-to-CO conversion

Abstract

We develop a Ni-Cu dual single-atom catalyst (DSAC) as a model catalyst to investigate the neighboring synergy in dual single-atom sites for promoting the electrocatalytic carbon dioxide reduction reaction (ECO₂RR) kinetics. Through detailed electrochemical tests, in situ spectroscopic observations and theoretical calculations, we found that during ECO₂RR, the neighboring Ni-Cu dual single-atom sites synergistically weaken the rigidity of the hydrogen-bond networks of interfacial water and optimize the spatial configuration of water molecules surrounding the Ni-Cu dual single-atom sites, which increases the proportion of easily dissociated water species in the interfacial water, thus accelerating the CO₂ protonation kinetics during the conversion of CO₂ to CO. As a result, Ni-Cu DSAC exhibits a 1.5-fold increase and a 15-fold increase in ECO₂RR activity compared to Ni SAC and Cu SAC, respectively. In flow cell electrolyzer, Ni-Cu DSAC achieves almost 100% Faradaic efficiency for CO production (FE_CO) from applied current density of 50 to 400 mA cm⁻², with the optimal full-cell energy efficiency of 61.1% for CO production, reflecting the excellent catalytic performance of neighboring Ni-Cu dual single-atom sites for selective conversion of CO₂ to CO. Benefiting from the efficient suppression of carbonates formation in acidic media, Ni-Cu DSAC achieves an outstanding single-pass carbon efficiency of 67.3% for CO₂-to-CO conversion at 200 mA cm⁻². Additionally, Ni-Cu DSAC also exhibits excellent long-term stability, with less than 10% decay of FE_CO throughout a 170-h continuous electrolysis in strong acid (pH = 1, j = 200 mA cm⁻²).