Promoting water dissociation for efficient solar driven CO₂ electroreduction via improving hydroxyl adsorption

Exploring efficient electrocatalysts with fundamental understanding of the reaction mechanism is imperative in CO₂ electroreduction. However, the impact of sluggish water dissociation as proton source and the surface species in reaction are still unclear. Herein, we report a strategy of promoting protonation in CO₂ electroreduction by implementing oxygen vacancy engineering on Bi₂O₂CO₃ over which high Faradaic efficiency of formate (above 90%) and large partial current density (162 mA cm^-2) are achieved. Systematic study reveals that the production rate of formate is mainly hampered by water dissociation, while the introduction of oxygen vacancy accelerates water dissociation kinetics by strengthening hydroxyl adsorption and reduces the energetic span of CO₂ electroreduction. Moreover, CO₃* involved in formate formation as the key surface species is clearly identified by electron spin resonance measurements and designed in situ Raman spectroscopy study combined with isotopic labelling. Coupled with photovoltaic device, the solar to formate energy conversion efficiency reaches as high as 13.3%.