The analog photography community is well-versed with the fact that silver halides are tunable band gap semiconductors. Thus the photoactivity of AgCl can be tuned from the UV into the visible light region by a process known as self-sensitization, which is due to the formation of Ag clusters during the photoreaction. The formation of these clusters introduces new levels within the forbidden gap that can now be populated by visible light (Fig. 7).
The photocatalytic oxidation of water to O2 on thin nanostructured AgCl layers has been reported.568 In subsequent work by the same group, AgCl photoanodes have been combined with either p-GaInP2569,570 or an amorphous silicon solar cell57i in the cathodic part of an electrochemical cell to split water. Modification of AgCl with gold colloids was found to enhance H2 and O2 production.57^572
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