Photoelectrochemically driven charge transport across free standing TiO2 pigmented organic polymer films

A novel technique is described which facilitates the investigation of photoelectrochemical processes occurring within electrically free standing organic (polymer) films pigmented with metal chalcogenide dispersions. The films are models for delaminated and partially delaminated organic coatings on metallic substrates and consist of polyvinylchloride membranes containing sub-micron dispersions of titanium dioxide used to separate the two compartments of a symmetrical electrochemical cell. Photoelectrochemical charge transport is shown to occur across asymmetrically illuminated membranes in the absence of any externally applied potential gradient. Steady state photocurrents are shown to be strongly dependent of the concentration of dissolved oxygen in the membrane contacting electrolyte. A mechanism is proposed in which the membrane photoresponse results from interparticle electronic charge percolation coupled with an imbalance in the rate of photoanodic and cathodic processes occurring on the illuminated and dark sides of the membrane. It is further argued that this rate imbalance arises from the difference in diffusion length for photogenerated electrons and holes in titanium dioxide.