The iron oxide/n-Si heterojunction electrode was studied as a photoanode for a regenerative photoelectrochemical (PEC) cell. The influence of modifying the top layer of the electrode with Pd or RuO2 was investigated. The photocurrent at the heterojunction electrode was produced by the holes which were photo-excited in both iron oxide and n-Si. The addition of Pd or RuO2 on the heterojunction electrode surface enhanced the optical-to-electrical conversion efficiency. The efficiencies for a stable working PEC cell were found to be 1.34% and 1.60% for a Pd-and a RuO2-modified electrode, respectively. This was measured in a 0.2 M KOH solution containing 0.2 M K4[Fe(CN)6] and 0.01 M K3[Fe(CN)6 at a xenon lamp intensity of 55 mW cm-2. The use of iron oxide made the photoanode highly stable, as compared to an electrode such as RuO2/n-Si. From a constant open-circuit voltage independent of the redox potential in 0.2 M KOH, it was concluded that Fermi level pinning occurs at the interface.
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