Light-Assisted, Aqueous Redox Reactions at Chlorogallium Phthalocyanine Thin-Film Photoconductors: Dependence of the Photopotential on the Formal Potential of the Redox Couple and Evidence for Photoassisted Hydrogen Evolution

Our recent studies have shown that thin films of ordered chlorogallium phthalocyanine (GaPc-Cl) on metal substrates behave as efficient photoconductors in aqueous media, with photopotentials that are dictated by the relative chemical potentials of an electron in the substrate and in the solution redox couple. The magnitudes of the photopotentials are comparable to those seen for photoelectrodes consisting of thin films of a-SiH. When the surface of the phthalocyanine is modified by the addition of submonolayer quantities of platinum, photoassisted hydrogen evolution is observed at an underpotential of 450 mV. The power conversion efficiency of this process is low (less than 0.1%), compared to that seen on other semiconductor materials, but it encourages further development because of the polycrystalline, organic, and potentially more economic nature of the photoelectrodes employed.