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

One of the major drawbacks in photoreduction of carbon dioxide (CO 2 ) 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 CO 2 reduction as a solution to this limitation. The twin photoreactor divides the oxygen (O 2 )-generating photocatalyst and the dual-function photocatalyst having both CO 2 reduction and hydrogen (H 2 ) production capabilities in two compartments by a membrane thus preventing the undesired reverse reaction. Herein, the dual-function photocatalyst can hydrogenate CO 2 via the produced H 2 , allowing the overall reaction to be more thermodynamically favorable. The charge balance was accomplished by the aid of IO 3 - /I - redox mediator in the twin photoreactor for shuttling electrons. Two visible-light photocatalysts, Pt/WO 3 (O 2 -generating photocatalyst) and GaN:ZnO-Ni/NiO (both CO 2 -reducing and H 2 -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. ? 2015 Elsevier B.V. All rights reserved.