A New Photovoltaic Effect Observed for Metal‐coated Semiconductor Electrodes and Its Utilization for the Photolysis of Water

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Abstract
The photoelectrochemical behaviors of semiconductor (n‐GaP) electrodes coated with thin, semi‐transparent metal films have been studied. It has been found that the behavior of the n‐GaP electrode coated with gold at a low evaporation speed is quite different from that coated at a high evaporation speed. The former shows oxidation‐reduction waves similar to that of a gold electrode. The photocurrent‐potential curve observed for the latter electrode has an onset potential similar to that of a bare GaP electrode, but its photocurrent is quite steady and the electrode causes no anodic dissolution. A tentative model has been presented to explain the behavior of this new electrode, assuming that the metal film in this case is so coarse that the electrolyte solution can soak into it and reach the surface of the n‐GaP semiconductor.The usefulness of this new electrode is demonstrated by constructing an electrochemical photocell using this electrode, with which water can be photo‐decomposed into oxygen and hydrogen. This photo‐cell works under illumination in the visible region (λ < 550 nm), with the quantum yield of photocurrent of about 20–30% or more under illumination at 420 nm and 0.1 mW/cm2.