Photocatalytic water splitting and hydrogenation of CO2 in a novel twin photoreactor with IO3−/I− shuttle redox mediator

•A twin photoreactor system improves significantly the photo quantum efficiency.•GaN:ZnO–Ni/NiO hydrogenates CO2 via the H2-generating from water splitting.•Pt/WO3, known as the O2-generating photocatalyst, produces O2 simultaneously.•The charge balance is accomplished by the aid of IO3−/I− redox mediator.

One of the major drawbacks in photoreduction of carbon dioxide (CO2) into hydrocarbons is the high thermodynamic barrier involved, resulting in low photoreduction quantum efficiency (PQE). A novel twin photoreactor system has been developed to enhance the PQE of CO2 reduction as a solution to this limitation. The twin photoreactor divides the oxygen (O2)-generating photocatalyst and the dual-function photocatalyst having both CO2 reduction and hydrogen (H2) production capabilities in two compartments by a membrane thus preventing the undesired reverse reaction. Herein, the dual-function photocatalyst can hydrogenate CO2 via the produced H2, allowing the overall reaction to be more thermodynamically favorable. The charge balance was accomplished by the aid of IO3−/I− redox mediator in the twin photoreactor for shuttling electrons. Two visible-light photocatalysts, Pt/WO3 (O2-generating photocatalyst) and GaN:ZnO–Ni/NiO (both CO2-reducing and H2-generating photocatalysts) were used. We found out that through the application of the twin photoreactor system under artificial sunlight (AM1.5G 300 W Xenon lamp), the PQE was enhanced more than 4-folds in comparison with that in the single photoreactor, an increase from 0.015% to 0.070%. A possible enhancing mechanism for twin photoreactor, in compare with the conventional single photoreactor, is also proposed based on the knowledge of species present during the photocatalytic reaction.

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