ROLE OF OVERLAYER FORMATION IN THE CADMIUM CHALCONIDE/Fe(CN)//6**4** minus **/**3** minus PHOTOELECTROCHEMICAL CELL.

Immersion of n-CdX (X equals S,Se) photoelectrodes in an electrolyte containing Fe(CN)//6**4** minus **/**3** minus causes formation of a left bracket Cd**I**IFe**I**I**/**I**I**I(CN)//6 right bracket **4** minus **/**3** minus surface layer on the electrode which is detectable by diffuse reflectance FTIR and x-ray diffraction analysis. This layer is shown to play an integral role in the interfacial charge transfer process, and is responsible for Gerischer's previous report of partial stabilization of n-CdS by a ferrocyanide electrolyte. It is demonstrated that the heterogeneous interfacial charge transfer rate along with the ability of the surface layer to interact with photogenerated valence band holes and reduced solution species is a strong function of the alkali cations present in the zeolitic surface layer sites.