PHOTOOXIDATION REACTION OF WATER ON AN N-TIO2 ELECTRODE - IMPROVEMENTIN 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 investigate d in various electrolyte solutions. It is found that a freshly prepare d n-TiO2 electrode shows a weak photocurrent and no FL, but both the p hotocurrent 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 micro pores 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 illumin ation 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 surf ace for the oxygen photoevolution reaction through the formation of su rface micropores due to photoetching in H2SO4.