Photoelectrochemical Behavior of Chlorophyll a-Lipid Films on a Platinum Electrode in an Aqueous Electrolyte

The photoelectrochemical behavior of chlorophyll a-lipid mixed monolayers coated on a platinum electrode by the Langmuir-Blodgett technique was investigated under potentiostatic conditions in an aqueous electrolyte in the absence of redox agents. Under illumination, cathodic photocurrents were observed at electrodes coated with a sufficient number of monolayers. The quantum efficiency of the photocurrent was estimated to be about 10−4, much lower than that obtainable for dye-sensitized photocurrent on semiconductor electrode. The cathodic photocurrent increased with lowering in the pH of electrolyte. The possibility of the photoreduction of water by excited triplet chlorophyll a is discussed on the basis of observed pH dependence and correlation of the redox potentials involved.