서강대학교

초록/요약

In this study, BiVO4 photoanode was used to produce the large production of electrons and protons by water splitting reaction utilizing solar energy. The CuInS2 (CIS) thin film was used as base photocathode material and modified by functional layers of g-C3N4 nano-sheet and Nafion to enhance CO2 reduction into solar liquid fuel products via photoelectrochemical (PEC) process. The thickness of g-C3N4 nano-sheet and Nafion was optimized to have the highest efficiency of photoelectrochemical CO2 reduction into liquid fuels. Photocathode needs to have conditions such as multi-electron shuttling for highly reduced product formation and CO2 activation for lowering activation energy of CO2 reduction reaction, which was done with g-C3N4 nano-sheet. It should also have one-pot reaction to have multiple proton-coupled multiple electron transfer reaction for CO2 reduction, which was done with Nafion layer. The structural, optical, electrochemical and photoelectrochemical properties of the fabricated hybrid composite film of g-C3N4 nano-sheet/CuInS2 were investigated by using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and photoluminescence (TR-PL) to get the optimum thickness of g-C3N4 nano-sheet for the highest efficiency of CO2 reduction by multi-electron shuttling process, reduction potential tuning and CO2 activation and photoelectrochemical reactivity was investigated with cyclic voltammogram (CV). Then, exact decreased values of reaction over-potential and activation energy are calculated from tafel plot and Arrhenius plot from EIS with different temperature. Nafion layer was coated on the surface of g-C3N4 nano-sheet/CuInS2 cathode. The fabricated hybrid composite thin film of Nafion/g-C3N4 nano-sheet/CuInS2 was studied to optimize the parameters for the highest efficiency of CO2 reduction into liquid solar fuel products by using electrochemical and photoelectrochemical methods like LSV, CV and I-t curve for current density measurement for one-pot reaction function. Each photoelectrochemical CO2 reduction experiment was carried out and CO2-• radical was confirmed with electron paramagnetic resonance (EPR). the quantitative analysis showed that BiVO4 photoanode//Nafion(300 nm)/g-C3N4 nano-sheet(100 nm)/CIS photocathode system produced 493 μM of ethanol for one hour as the highest solar to fuel efficiency.