A photolytic system comprised of a darkened halfcell and an illuminated halfcell in which oxidation and reduction reactions are made to occur. These halfcells are joined by an electrically conductive element and an ion conducting junction for electron transfer and ion transport. The illuminated halfcell is equipped with a cathode and the darkened halfcell contains an improved anode which exhibits a desirably low overvoltage with respect to the substrate which is sought to be oxidized. Oxidation products are formed at the anode and reduction products are formed at the cathode.