Conversion of carbohydrate into hydrogen fuel by a photocatalytic process

Abstract

Attempts have been made to find green plants which produce low-molecular weight hydrocarbons^1,2 and to find seaweeds which produce hydrogen from water utilizing solar energy^3,4. These attempts are aimed at finding methods of making use of the photosynthetic process in plants for direct production. Most green plants, however, synthesize carbohydrates, such as sugar, starch and/or cellulose, from water and carbon dioxide. The C₄ plants⁵, such as corns and sugar cane, grow rapidly, utilizing solar energy with ∼1% efficiency for the fixation of CO₂. This value is 10 times larger than that of the average efficiency of photosynthesis of plants, 0.1%. However, the carbohydrates produced by these plants cannot be used directly as fuel. Here we show a new route for the conversion of carbohydrates into hydrogen (a clean fuel in the hydrogen energy system), taking advantage of the photocatalytic process. We found that the irradiation of the carbohydrates, not only sugar or starch but also cellulose, in the presence of water and a RuO₂/TiO₂/Pt photocatalyst powder leads to the efficient production of hydrogen gas.