Oxygen vacancies in Co3O4 promote CO2 photoreduction

The introduction of oxygen vacancies (OVs) in metal oxides has been proved to be a powerful means for promoting the activation of CO2. However, the lack of effective methods for OVs implantation currently hampers the rational design of highly-active CO2 reduction catalysts. Herein, we reported a novel non-equilibrium photochemical strategy for preparing OV-rich Co3O4 at ambient temperature and pressure. Results confirm that the single isolated OV and Co-OV associates are the predominant defect types within Co3O4 skeleton. Moreover, the OVs concentration in Co3O4 can be tuned over a wide range by merely controlling the light-irradiation time. The experiments and theoretical calculations reveal that the OVs can promote the adsorption/activation of CO2 and water, while considerably lowering the free energy barrier for COOH* formation, thereby accelerating the reaction kinetics. The OV-rich Co3O4 displays a 26.7-fold improvement in CO2 reduction activity over the OV-poor Co3O4. The turnover frequency of Co atoms in OV-rich Co3O4 reaches 3.754 s−1, which is one of the best reported catalysts for CO2 photoreduction to date. Moreover, we also successfully synthesize a series of defect-rich metal oxides and metal sulfides using this photochemical method, such as TiO2, Fe2O3, CuO, Mn3O4, CeO2, V2O5, MoO3, ZrO2, Bi2O3, MoS2, MnS, CdS, NiS2-Ni3S4 and Bi2S3-BiS2, which suggests its universality. We believe this photochemical method developed herein greatly enriches the knowledge for the synthesis of defective nanocrystals under mild synthesis conditions. Importantly, the relationship between the OVs and the CO2 reduction performance has been established by various characterizations, which may guide the design of highly-efficient catalysts for CO2 photofixation.