New preparation method for doped polycrystalline titanium(IV) oxide and niobium(V) oxide and their photoelectrochemical properties

Abstract

Doped polycrystalline TiO/sub 2/ and Nb/sub 2/O/sub 5/ have been prepared by a new method and examined as photoanodes. Polycrystalline oxide films on metal substrates which are thick and porous are prepared by anodic oxidation accompanied by sparking in various electrolytes. It was found that cations in the electrolyte are doped into the oxide films during anodic oxidation, which has been proved by ion microprob analysis and mass spectroscopy. Therefore, this is a new easy method of preparing doped polycrystalline TiO/sub 2/ and Nb/sub 2/O/sub 5/. The TiO/sub 2/ film prepared in Na/sub 2/SO/sub 4/ solution at 100 V is a good photoanode, showing a relatively high photocurrent under visible-light illumination. The doping is carried out by addition of the doping ions in saturated Na/sub 2/SO/sub 4/ solution. The Cr-, Ir- and Rh-doped TiO/sub 2/ films exhibit a high visible photocurrent but a low UV photocurrent. The Cr-doped Nb/sub 2/O/sub 5/ films also exhibit similar spectral responses. An increase in the UV photoresponse and a decrease in the visible photoresponse by reduction are observed. The relationship in which the band-gap photocurrents decrease with increasing visible photocurrents is obtained for the doped oxide films. This suggests, with the reduction effects, thatmore » the impurity and the interstitial metal d bands or states bringing about the visible response also act as recombination centers. 6 figures, 2 tables.« less