Critical Role of Water and Oxygen Defects in C–O Scission during CO₂ Reduction on Zn₂GeO₄(010)

Exploration of catalyst structure and environmental sensitivity for C–O bond scission is essential for improving the conversion efficiency because of the inertness of CO₂. We performed density functional theory calculations to understand the influence of the properties of adsorbed water and the reciprocal action with oxygen vacancy on the CO₂ dissociation mechanism on Zn₂GeO₄(010). When a perfect surface was hydrated, the introduction of H₂O was predicted to promote the scission step by two modes based on its appearance, with the greatest enhancement from dissociative adsorbed H₂O. The dissociative H₂O lowers the barrier and reaction energy of CO₂ dissociation through hydrogen bonding to preactivate the C–O bond and assisted scission via a COOH intermediate. The perfect surface with bidentate-binding H₂O was energetically more favorable for CO₂ dissociation than the surface with monodentate-binding H₂O. Direct dissociation was energetically favored by the former, whereas monodentate H₂O facilitated the H-assisted pathway. The defective surface exhibited a higher reactivity for CO₂ decomposition than the perfect surface because the generation of oxygen vacancies could disperse the product location. When the defective surface was hydrated, the reciprocal action for vacancy and surface H₂O on CO₂ dissociation was related to the vacancy type. The presence of H₂O substantially decreased the reaction energy for the direct dissociation of CO₂ on O_2c1- and O_3c2-defect surfaces, which converts the endoergic reaction to an exoergic reaction. However, the increased decomposition barrier made the step kinetically unfavorable and reduced the reaction rate. When H₂O was present on the O_2c2-defect surface, both the barrier and reaction energy for direct dissociation were invariable. This result indicated that the introduction of H₂O had little effect on the kinetics and thermodynamics. Moreover, the H-assisted pathway was suppressed on all hydrated defect surfaces. These results provide a theoretical perspective for the design of highly efficient catalysts