The influence of dissolved sulfide ion and the ferri/ferrocyanide redox system on the photoelectrochemical behavior of iron oxide has been investigated. Particular attention was given to transient behavior and to clark current phenomena. An interpretation of the results is given in terms of a back-reaction of photogenerated species with conduction band electrons via surface s~ates.

The solution was next purified by preliminary electrolysis for 40 hr under conditions similar to those of the electrolysis itself, and the Tafel straight line was again determined. This is shown in Fig. lb. In this case the slope is ca. 110-120 mV, pointing to the purity of the solution.The results of electrolysis of the preelectrolyzed solution fully satisfied Faraday's law. ConclusionsIt was concluded that the probable cause of the anomalies described by Palit is that he did not take into account all of the electrode processes which take place, and that the impurities adsorbed on the surface of the Pt during electrolysis inhibit certain steps of the anode process. A larger amount of H202 may thus accumulate in the anode space; part of it may diffuse into the cathode space, where it decomposes or is electrolytically reduced.The effect of the micro local galvanic cells on the surface cannot be regarded as decisive, for it is not probable that there would be a large number of cathodic surface cells on the anode with potentials 1.6-2.0V more negative than that of the bulk of the surface, and vice versa.for the valuable discussions constantly provided during the evaluation of the results.

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