Method of preparing tio.sub.2 thick film photoanodes for

Abstract

Semiconductive photoanodes formed of titanium dioxide (TiO.sub.2) are known for use in photoelectrochemical cells. They have been made by various techniques, including chemical vapor deposition, thermal oxidation or anodic oxidation of thin titanium foils, hot pressing of TiO.sub.2 powder, and plasma spraying. The present invention provides a method for the fabrication of TiO.sub.2 thick film photoanodes, which method is simple, inexpensive and suitable for mass production of large area plates. The method comprises screen printing a film of conductive material on a clean alumina substrate which is then heated to fuse the conductive material into a conductive layer. A first layer of TiO.sub.2 particles in an organic carrier is then screen-printed over the conductive layer, at least 10% of the TiO.sub.2 being of anatase form. The structure is then heated to burn off the organic carrier and to transform at least part of the TiO.sub.2 from anatase form to rutile form, this resulting in good adhesion of the TiO.sub.2 layer to the conductive layer. A second layer of TiO.sub.2 is then screen-printed over the first layer and heated, the second layer being provided in case there should be pinholes in the first layer which would adversely affect the anode structure when submersed in an electrolyte. The resulting structure is then heated in a reducing atmosphere, e.g. anhydrous ammonia or hydrogen, to transform the TiO.sub.2 to TiO.sub.2-x where x is between 0 and 1, to reduce the electrical resistivity of the films.