Photoelectrochemical reduction of carbon dioxide by CdTe based catalyst under visible light

Abstract

The production of useful chemicals by reduction of carbon dioxide takes great interest through sun light due to the global warming issues, and shortage of fossil fuels. For direct CO2 reduction, artificial photosynthesis is potentially the ultimate answer but it has remained unsolved for many years. The catalytic conversion of CO2 to liquid fuels is a critical goal that would positive impact the global carbon balance by recycling CO2 into usable fuels such as methanol, formic acid, methane and carbon monoxide. Although many investigations have been made into such photosynthesis, several problems persist, such as low efficiency, poor stability, and the need for sacrificial materials. If we want to reduce CO2 to other products, we should apply higher potential than the po-tential of reaction in electrochemical test. However, when photo energy is added on electric energy, the overpo-tential, in other words, activation energy is decreased. So we studied the effect and fundamentals of light in elec-trochemical reaction for utilization of carbon dioxide. In general, p-type semiconductors are used for photo-electrochemical reduction of carbon dioxide as a cathode due to effect of unique band bending when semiconductor is in the electrolyte. Cadmium telluride thin film and pyridine as homogeneous catalyst are developed. Because of the 1.5 eV band gap, we could use visible light for photo excitation of electrons under the valence band region. Photoelectrochemical test is conducted in acetate buffer of sodium bicarbonate solution. At first, the current difference between N2 purged and CO2 purged environment was shown, and there was onset potential and current gap between dark condition and irradiated condition in CO2 purged solution. The onset potential obtained under light was increased than the obtained voltage in the absence of light. When pyridine was used, there was no onset potential difference, but photo current is increased about 30 % at -0.6 V. However, the m...