Photocatalytic hydrogen evolution from aqueous hydrazine solution over precious-metal/anatase catalysts

Abstract

Aqueous hydrazine solution has been photocatalytically decomposed over precious-metal/anatase catalysts yielding only H2, N2 and NH3. H2/N2(molar ratio of H2 evolved to N2 evolved) is usually ca. 1 and does not depend on the reaction conditions (pH, metal, reactant concentration). However, the value is > 1 when another hole scavenger (CH3OH) is present. N2/NH3 is ca. 0.5 and does not change in the presence of CH3OH. On the basis of these results, the reaction scheme is considered to be as follows: the electrons photoexcited into the conduction band of anatase are consumed through H2 formation and the positive holes generated in the valence band are consumed through the simultaneous formation of N2 and NH3. The dependence of the reaction rate on the concentration of N2H4 and on the metal suggests that the rate-determining step is the formation of H2 over the metal.