Photoelectrochemistry of microcrystalline chlorophyll a films

Thin films of microcrystalline chlorophyll a in contact with electrolytes have been studied. It is shown that the electrode acts as a photocathode, as indicated by the dependence of photoeffect on electrode potential and redox potential of electrolyte. Impedance measurements at low frequencies show that a space charge is formed at the electrode/electrolyte interface. The chlorophyll photocathode is in principle capable of reducing water to hydrogen, even though a very high overpotential kinetically blocks this. All these photoelectrochemical properties are compatible with the picture of the organic photoelectrode as a p-type semiconductor.