The Selectivity of Electrode Reactions in Semiconductor Electrodes

Abstract

Electrode processes at illuminated semiconductor photoanodes were investigated by a rotating ring disk electrode with as a disk. The collection efficiency in a solution was found to be larger than the theoretical collection efficiency . When the light intensity was kept constant, the collection efficiency increased with lowering band bending and exceeded with the ring potential being −0.4V vs. SCE at . A large collection efficiency observed was ascribed to electrons and holes that can have different reaction pathways, in which cathodic reaction by electrons and anodic reaction by holes can take place independently and simultaneously without recombination. As a result, the disk current decreases because the hole flux is counterbalanced by the electron flux, but the oxidation product to be detected at the ring electrode remains constant. Consequently, the collection efficiency defined by the ratio of the ring current to the disk current can be much larger than . It is pointed out that the electron transfer near the flatband potential does not necessarily mean an electron‐hole recombination, which is believed to determine the current‐potential characteristics in the electrolyte‐semiconductor interface, as well as the metal‐semiconductor interface. On the basis of a model developed herein, the transfer coefficient for electrons was determined to be 0.88 for the electrode reaction of