IDENTIFICATION OF THE MECHANISM IN THE PHOTOELECTROCHEMICAL REDUCTION OF OXYGEN ON THE SURFACE OF A MOLECULAR SEMICONDUCTOR

The rate-limiting step in the photoelectrochemical reduction of oxygen on a molecular semiconductor is found to be the charge transfer at the electrode surface. The electrode consisted of a thin film of phthalocyaninatozinc-(II) in a mixture of poly(vinylidene fluoride) on indium-tin oxide. The current transients as the response upon illumination are analyzed under variation of the light intensity and of the oxygen partial pressure. A model is presented that explains the photoelectrochemical behavior on the basis of oxygen adsorption at the electrode surface according to Langmuir's adsorption isotherm prior to the charge-transfer step. The importance of surface states created by this mechanism for the photoelectrochemical properties of a molecular semiconductor is thereby elucidated.