Reaction pathways for the highly selective and durable electrochemical CO2 to CO conversion on ZnO supported Ag nanoparticles in KCl electrolyte

Electrochemical CO2 reduction (ECR) is a promising approach for recycling atmospheric CO2 into value-added fuels. However, due to the sluggish ECR, highly effective ctalysts are needed. ZnO supported Ag nanocatalyst (NC) ((ZnO)(3)@Ag) is developed for CO2 to CO conversion where the faradaic efficiency (FE) was similar to 95% in 0.5 M KCl at 1.1 V, and that progressively decreased in 0.1 M KCl (89.7%) and 0.1 M KHCO3 (84.6%). Besides, (ZnO)(3)@Ag NC exhibited unprecedented stability in 0.5 M KCl with only 6.3% decay after 8 h while 14% and 14.3% decay were observed in 0.1 M KCl and 0.1 M KHCO3, respectively. The cross-referencing results of materials analyses and in-situ X-ray absorption spectroscopy suggest that the high CO selectivity of (ZnO)(3)@Ag NC in KCl originates from the synergistic collaboration between ZnO and Ag, where, ZnO supplies electrons to Ag for adsorption/structural rearrangement of CO2 molecule and subsequent desorption of CO. On the other hand, the presence of CO32- ions in KHCO3 hinder the mass transportation (i.e. the adsorption) of CO2, resulting in the decrease in selectivity and stability. Hereby, this study will spark motivation for designing the highly selective and stable ECR catalysts and uncover the mechanistic aspects of ECR.