Photoelectrochemical reduction of carbon dioxide into oxy-hydrocarbon and oxidation of azo dye simultaneously

Date
2011
Authors
Yeh, Yun-Ta
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Publisher
University of Delaware
Abstract
Climate change is caused by greenhouse gases. The increased carbon dioxide (CO2) in the atmosphere is considered the major factor of the climate change. Therefore, it is important to decrease the accumulation the atmospheric carbon dioxide. In this study, in order to save energy and prevent consume “energy” for producing “energy”, the reduction of carbon dioxide was applied in a photoelectrochemical (PEC) system using solar cell and N-doped TiO2 thin film. In both systems, formic acid, formaldehyde, methanol, and methane were produced by the photoelectrochemical reduction of CO2 while hydrogen was form by the water electrolysis. The yields of the products in the 0.1 M KHCO3 aqueous solution were 1.55, 0.62, 2.02, and 2.16 μM for HCOOH, HCOH, CH3OH, and CH4, respectively, for the solar cell system and 2.29, 0.68, 1.91, and 3.94 μM, respectively, for N-doped TiO2 thin film system. In order to save applied energy on hydrogen evolution instead of being used for CO2 reduction, different concentration of methanol-based electrolytes were applied. Methanol electrolytes not only suppressed hydrogen formation, but also increased the yields of the products from photoelectrochemical reduction of CO2. In addition, a differential first-order kinetic model was successfully applied to simulate the photoelectrochemical reduction of CO2 on a copper electrode in KHCO3 aqueous solution at ambient temperature and pressure in both systems. The reaction rate constant for HCOOH, HCOH, CH3OH, and CH4 were 1.30 × 10−8, 4.26 × 10−6, 1.68 × 10−5, and 4.43 × 10−6 s−1/cm2, respectively, for the solar cell system and 9.55×10−9, 4.53 × 10−6, 1.13 × 10−5 and 2.52 × 10−6 s−1/cm2, respectively, for the Ndoped TiO2 thin film system. Furthermore, the degradation of an azo dye, namely, methyl orange (MO) in photocatalytic, electrochemical, and photoelectrochemical processes, was investigated in this study. The degradation of MO was operated simultaneously with the degradation rate of 9.33 × 10−5, 8.31 × 10−5, and 7.13 × 10−5 s−1/cm2 for 0% methanol-based, 20% methanol-based, and 40% methanol-based, respectively, for the solar cell system In addition, the study also investigated the kinetic rate constant of methyl orange via photoelectorchemical, electrochemical and photocatalytic processes using N-doped TiO2 thin film system with the rate constant of 4.32 × 10−6, 4.32 × 10−7, and 1.50 × 10−7 s−1/cm2, respectively, for N-doped TiO2 thin film system.
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