Photo‐ and Electrochemical Reactions of Excited Dyes at Metal‐Electrodes

Abstract

AbstractThe spectral sensitization of metal electrodes in dye solutions was studied. Illuminating the interface by light absorbed only by the dye an anodic photocurrent was observed if the leuco‐form of the dye or another reducing agent was added to the electrolyte. It could be shown that the mechanism consists of two different processes. In a pure photochemical reaction the excited dye is reduced to its semireduced form which then is oxidized electrochemically (anodic photocurrent). According to kinetic investigations the photochemical step occurs within the bulk of the solution. The density of the photocurrent is mainly determined by the life time of the semireduced species which diffuses towards the electrode. Small anodic photocurrents were also observed with dye solutions free from any reducing agent, provided that no oxygen is present whereas a saturation of the solution by oxygen led to a cathodic photocurrent. In these cases the formation of radicals is also responsible for the electrode processes. The reaction mechanisms are discussed in detail and the results compared with those obtained with semiconductors.