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TITLE Photoelectrocatalytic production of hydrogen from water and conversion of carbon dioxide to useful chemicals.
(Joint Program to Promote Technological Development with the Private Sectors)



Future environmental and energy problems need to be solved under the guideline of environmentally compliant technology which justly includes utilization of mild energy sources such as the sunlight or other light sources left unused. Light energy and water as a hydrogen resource enable processes free from creating additional pollutants unlike those dependent on fossil fuels. We have focused our attention on the use of photocatalysts which can activate under light and catalytically decompose water to produce hydrogen and also convert carbon dioxide to useful chemicals in combination with electrocatalysts.

We have developed a single unit photoelectrocatalysis (SUPEC) system which consists of a highly efficienct thin film anatase titania photocatalyst having a photon-to-current quantum efficiency of 60% and an electrocatalyst. This system can produce hydrogen from water solution at rates of 26 with bias potential between the photocatalyst and the electrocatalyst under light irradiation from a mercury lamp and 0.075 to 0.42 without bias by the sunlight, both in units of l/h/m2-irradiation cross section on the photocatalyst.

We have also developed an electrocatalyst consisting of zinc oxide and copper which when operated in the SUPEC system can stably convert 82% of carbon dioxide to hydrocarbons in terms of current efficiency including 44% for methane and 24% for ethylene without deactivation of the reactions by a special operating method employing a pulsed bias.

We continue to pursue this research and at the same time we are considering possibilities to apply these findings to other environmental problems as well.

Reference: Shinichi Ichikawa and Ryota Doi, Catalysis Today, 27, 271(1996).