Iron oxide/n-Si heterojunction electrodes modified by an outer Pd layer were studied for its utility as an efficient photoanode. The addition of an evaporated Pd layer on the electrode greatly enhanced the photocurrent and shifted the onset potential from 0.5V (Hg-HgO) to the more cathodic side in a 0.2M KOH solution. A 100Å Pd layer showed the most cathodic onset potential of-0.36V (Hg-HgO). The unmodified iron oxide/n-Si electrode gave a relatively broad spectral photoresponse with the maximum region lying between 550 and 700 nm. With the addition of the Pd layer the quantum efficiency of spectral photoresponse from 400 to 800 nm became 20% higher. The addition of methanol enhanced the photocurrent up to 1.25 times at 0.6M concentration on the unmodified electrode, whereas on the Pd-modified electrode, the photocurrent decreased slightly by the addition of methanol. These phenomena are discussed in terms of various mechanisms for methanol oxidation.
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