Role of Bicarbonate Ions in Aqueous Solution as a Carbon Source for Photocatalytic Conversion of CO₂ into CO

Ag/SrNb2O6 nanorods exhibited a high CO formation rate and high selectivity toward CO evolution in aqueous solutions containing bicarbonate ions even without CO2 bubbling. Notably, the formation rate of CO reached as high as 287 μmol h–1 with selectivity toward CO evolution of higher than 94.1% when NH4HCO3 was used as an additive. Both the formation rate of CO and selectivity toward CO evolution increased with the concentration of HCO3–. According to the experimental results and analytical chemistry calculations, it was concluded that CO2(aq) obtained by the dissociation of HCO3– is the actual reactant in the photocatalytic conversion of CO2. In contrast, the HCO3– species in the aqueous solution is beneficial for improving the photocatalytic activity and selectivity toward CO evolution by increasing the adsorption of carbon-related species on the photocatalyst surface and/or suppressing the backward reaction for the photocatalytic conversion of CO2.