Multielectron storage and hydrogen generation with colloidal semiconductors.

Multielectron storage and hydrogen generation by light is achieved in aqueous dispersions of ultrafine TiO(2) particles (120-A diameter) when the amphiphilic viologen derivative N-tetradecyl-N'-methyl-4,4'-dipyridinium dichloride (C(14)MV(2+)) is used as an electron relay. Consecutive reduction of C(14)MV(2+) to the radical ion (C(14)MV(+)) and neutral (C(14)MV(0)) was observed after band-gap excitation of the semiconductor particle. Through surface adsorption of the relay, these electron-transfer reactions can occur very rapidly and are completed within less than 100 musec (pH 11). Two-electron reduction of C(14)MV(2+) can be coupled with H(2) generation in alkaline medium in the presence of Pt catalyst codeposited onto the TiO(2) particle. Electron-relay-free systems are 1/15th as efficient in producing H(2) at the same pH.