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 O2c1- and O3c2-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 O2c2-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.