서강대학교

초록/요약

In this study, zinc oxide covered with zinc telluride (ZnO/ZnTe, ZO@ZT) photocathode was used to produce liquid solar fuels by CO2 reduction via PEC system. Photocathode needs to meet several criteria such as multi-electron shuttling function and optimum conduction band energy level for reduction potential tuning with reduced graphene oxide (rGO), CO2 activation to have lower activation energy of CO2 reduction reaction to have a large kinetic constant for the product formation with polypyrrole (PPy) and one pot reaction of proton coupled electron transport reaction for the CO2 reduction with Nafion coating. ZO@ZT photocathode was fabricated by anion exchange reactions based on the difference of solubility product constants (Ksp) for ZnO and ZnTe. rGO/ZnO@ZnTe (R/ZO@ZT) photocathode was fabricated by spin coating method. Photocurrent was increased with R/ZO@ZT photocathode under CO2 purged electrolyte because of multi-electron shuttling function of rGO. Also, photoelectrochemical CO2 reduction reaction product of R/ZO@ZT photocathode showed higher product concentration and product selectivity in comparison with ZO@ZT photocathode. PPy was coated on the surface of R/ZO@ZT by spin coating for CO2 activation by complexation with CO2 molecules. Finally, Nafion was coated on the surface of PPy/R/ZO@ZT by spin-coating for the efficient proton transport through Nafion. To prevent re-oxidation of CO2 reduction product by photo-generated hole on the surface of cathode, both photoelectrochemical compartments were separated by Nafion membrane between cathode and anode. To compare the effect of re-oxidation of alcohol products, solar light illumination was carried out with only photoanode and both photoanode and cathode. The quantitative analysis showed that the single illumination on BiVO4 photoanode with R/ZO@ZT cathode produced 99.94 μM of ethanol for 6 hrs, on the other hand, double simultaneous illumination on both BiVO4 photoanode and R/ZO@ZT cathode produced 3.58 μM of ethanol for 6 hours. This might be due to re-oxidation of produced ethanol on the photocathode surface.