Structure sensitivity in the photocatalytic reduction of CO2 with Co3O4 catalysts

[Display omitted] •The moderate-strength CO2 adsorption sites related to surface cobalt atoms determine the catalytic activity and CO selectivity in CO2-to-CO reaction.•The CO evolution activity and CO selectivity of Co3O4 catalysts are controlled by the surface atomic arrangement of Co2+ and Co3+.•The Co3O4 with rich exposure of Co2+ exhibits high activity and CO selectivity owing to a combination of improved separation of charge carriers, O-defects that promote the adsorption and activation of CO2, as well as the Co2+ site that facilitate the desorption of CO product. Transition metal oxides (TMOs) have been proposed as potential candidates for CO2 photoreduction (CO2RR). Nonetheless, they often exhibit low efficiency and poor selectivity. Understanding how structural surface features influence photocatalytic reactions is crucial for the development of efficient catalysts. Unfortunately, the intricate structure of TMOs often hinders the thorough understanding of their structure–activity relationships. In this study, three spinel Co3O4 nanocrystals with different planes are used as model catalysts to systematically investigate the structure sensitivity for CO2RR. According to both experimental results and theoretical calculations, Co3O4 with a higher exposure of Co2+ is more effective in the photoreduction of CO2 to CO. This can be attributed to a combination of factors including improved separation of charge carriers, O-defects that promote CO2 activation and the Co2+ sites that facilitate the desorption of CO product. Moreover, the CO2RR performance over Co3O4 catalysts can be controlled by the surface atomic arrangement of Co2+ and Co3+, which through affecting a tradeoff between activating the CO2 reactant and releasing the CO product. Therefore, the proper control of Co2+/Co3+ ratio on the surface of Co3O4 can optimize the reaction performance. This study provides guidance for designing highly active and cost-effective TMO-based catalysts for CO2RR.