Photoelectrochemistry of plain and dye-sensitised mesoscopic TiO2 rotating disc electrodes

Abstract

The photoelectrochemical properties of porous pressed TiO2 rotating disc electrode was studied and it is sensitive to UV and visible light. The photocurrent in the UV region of aqueous 0.1 M KCl, 0.1 M NaI acetonitrile, and 0.1 M LiClO4 ethanol solutions were examined. The photocurrent in aqueous solution was found to be much lower than in the rest of the solvents. This is because water is poor hole scavenger in the system. Similarly the effect of rotation speed of the disc, in the presence of air, oxygen, and nitrogen was studied. The photo-currents as function of the thickness of the disc membrane were also studied. The photocurrent is substantially decreased in the presence of air and oxygen. For the relatively thick electrodes the photocurrents were fairly independent of the thickness of the disc membrane and quite unexpectedly even very thick porous electrodes gave good quantum yields. The photocurrent depends on rotation speed of the disc up to about 100 rpm. However, significant photocurrent is still obtained if the solution is purged with nitrogen. This was assigned to the fact that on illumination of the disc electrode some heat is evolved in the solution at the electrode-electrolyte interface. This in turn causes convection. Examination of the action spectra of plain and dye sensitised electrodes revealed the importance of the dye in achievement of photo-response in the visible region for even very thick TiO2 disc electrode.