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 ∼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.