Highly efficient photoreduction of CO2 to CO: Synergistic optimisation of progressive electron transfer via Fe2+ and oxygen vacancies

The electron transfer in photocatalytic reaction, including electron transfer between the components in the catalyst, electron transfer between reactant molecules and catalysts. Fe2+/Fe3+ and oxygen vacancies (VOs) were simultaneously introduced in Fe-In2O3, the 5 wt% Fe-In2O3 exhibited a 13.7-fold increase in activity (4.80 mmol·g−1·h−1) compared to the In2O3 and a CO selectivity of approximately 84.32 %. Multiple in-situ techniques indicated that the doping of FeOX serves to effectively modulate the concentration of VOs, FeOX and In2O3 form a p-n heterojunction interfacial structure and match energy bands, promoting carrier separation. More importantly, Fe2+, In2+, and VOs serve as electron-donating adsorption sites, increasing the number of electrons received by CO2 and H2O, which causing pre-reduction activation of the reactant molecules. Eventually the dual-reduction reaction of CO2 and H2O were realized, subsequently, CO2 was selectively converted into CO through intermediate species such as formate. This study employs Fe2+ and VOs to synergistic optimize the progressive transfer of photogenerated electrons, and presents a novel approach for elucidating the catalytic mechanism.