Which is an Intermediate Species for Photocatalytic Conversion of CO₂ by H₂O as the Electron Donor: CO₂ Molecule, Carbonic Acid, Bicarbonate, or Carbonate Ions?

Abstract

In the photocatalytic conversion of CO2 using H2O as the electron donor, there are four candidates of the intermediate species in the solution: hydrated CO2 molecule (CO2(aq)), carbonic acid (H2CO3), bicarbonate (HCO3 –), and carbonate (CO3 2–) ions. The concentrations of all four species in the system at equilibrium can be controlled by controlling the temperature, pH value, and concentration of the countercation. According to our experiments conducted under different conditions, we narrowed the possible intermediates down to two: CO2(aq) and HCO3 –. The isotopic experiment using 13CO2 and in situ infrared spectroscopy revealed that CO2(aq) reacts with the hydroxyl group anchored on the Ga atom on the surface of ZnGa2O4/Ga2O3 to form bidentate HCO3–Ga, followed by the formation of bidentate HCOO–Ga via monodentate HCO3–Ga. We conclude that bidentate HCOO–Ga is the real intermediate species for the photocatalytic conversion of CO2 by H2O as the electron donor over Ag/ZnGa2O4/Ga2O3 catalyst, and it decomposes into CO as a product.

Enhanced CO evolution for photocatalytic conversion of CO2 by H2O over Ca modified Ga2O3

“…Supplementary Fig. 5 is consistent with our previous results 43,44 . It is worth mentioning that in addition to the presence of intermediate species on the Ga 2 O 3 surface ([δ(OH)-Ga]), the modification by Ca species further increased the amount of intermediate on Ga 2 O 3 _Ca_1.1.…”

Efficient photocatalytic carbon monoxide production from ammonia and carbon dioxide by the aid of artificial photosynthesis

“…Increasing the pH also increases the amount of CO 2 that can be dissolved in the reaction solution. 31 Generally, the formation rate of CO increases with increasing pH, because the reaction rate largely depends on the concentration of substrate. Therefore, the addition of NH 4 HCO 3 contributed to the efficient conversion of CO 2 and the good selectivity toward CO evolution.…”

Utilization of La₂O₃ as a Support of Ga₂O₃ Photocatalyst to Enhance Activity on CO₂ Reduction with Water

“…Entry e shows that without the formation NaLa(CO3)2, Ga2O3/La2O3 did not show catalytic activity. NaHCO3 is essential for the CO2 reduction reaction, because it raised pH of its aqueous solution accompanying the increase of CO2 solubility [33].…”