Hydrogen evolution from water using solid carbon and light energy

Abstract

Using solar energy to decompose water and produce hydrogen for use in hydrogen energy systems has attracted much attention. Some semiconductors (such as TiO₂ and SrTiO₃) can decompose water to produce hydrogen and oxygen using the energy¹ of light and the decomposition of water using powdered semiconductors has been reported^2,3. One problem with powdered semiconductors is that when H₂O decomposes into H₂ and O₂ in one cell an explosive gas is produced. Furthermore, although Schrauzer and Guth reported² that traces of H₂ and O₂ were detected after the decomposition of water gas on TiO₂, the reverse reaction will increase simultaneously as product is evolved. Hydrogen evolution stopped after a few hours. Hence the hydrogen or oxygen produced should be converted to more stable gaseous chemical species. The use of solid carbon is an interesting problem in relation to coal gasification and we have now examined the photocatalytic decomposition of water on TiO₂ using solid carbon. We found that reactions (1) and (2) occur producing hydrogen gas from water vapour and solid carbon when mixed powders of TiO₂, RuO₂ and active carbon exposed to water vapour at room temperature ∼80 °C are illuminated. The free energies are increased by 63 and 92 kJ mol⁻¹ respectively, utilising light energy.