Effect of light upon electroreduction of 4,4′-bipyridyl and methyl viologen in aqueous solutions

Abstract

The limiting current for the polarographic electroreduction of 4,4′-bipyridyl or methyl viologen to the corresponding dihydrobipyridyl increases when the electrode is irradiated by light of wavelengths between 300 and 400 nm. This photoeffect is interpreted qualitatively as a catalytic process in the solution surrounding the electrode, consisting of the ejection of an electron from the photoexcited dihydrobipyridyl and the subsequent electroreduction of the radical thus formed back to the dihydrobipyridyl, the net chemical result being the reduction of water by the photoejected electron. At negative potentials an increase in the photocurrent occurs; this is explained by the catalytic electroreduction of water at the electrode surface under the action of atomic hydrogen formed as a secondary product in the photoprocess.