PHOTOOXIDATION REACTION OF WATER ON AN N-TIO2 ELECTRODE - IMPROVEMENT IN EFFICIENCY THROUGH FORMATION OF SURFACE MICROPORES BY PHOTO-ETCHING IN H2SO4

The photocurrent-potential curves and the photoluminescence (PL) peak at 840 nm for n-TiO2 electrodes, in which the n-type semiconductivity is obtained by hydrogen reduction at 550-700 degrees C are investigated in various electrolyte solutions. It is found that a freshly prepared n-TiO2 electrode shows a weak photocurrent and no FL, but both the photocurrent and the PL intensity increase substantially with time when the electrode is illuminated during cyclic potential scans in 0.05 M H2SO4. This is accompanied by the formation of a large number of micropores at the electrode surface. No such activation is observed in 0.1 M HClO4 and 0.5 M Na2SO4, but an n-TiO2 electrode activated by illumination in H2SO4 shows an efficient photocurrent and strong PL in these solutions. It is concluded that the increases in the photocurrent and the PL intensity are caused by the production of an active n-TiO2 surface for the oxygen photoevolution reaction through the formation of surface micropores due to photoetching in H2SO4.