The successful operation of a photogalvanic cell for solar energy conversion requires that the illuminated electrode should discriminate between the two redox couples in solution. In the case of the iron‐thionine system the electrode must oxidize photogenerated leucothionine but not reduce the photogenerated Fe(III). Modified electrodes with coatings of thionine of up to 20 monolayers can be prepared on Pt and . These electrodes have been investigated using ring disk, cyclic voltammetry, XPES, and spectroelectrochemical measurements. Results for the modified electrode kinetics are presented for the following systems: thionine, disulfonated thionine, Fe(III), , , Ce(IV), quinone, and N,N,N′,N′‐tetramethyl‐p‐phenylenediamine. The results for the Fe(III) and thionine systems show that this modified electrode is suitable for the iron‐thionine photogalvanic cell.