Photoelectrochemical properties of sol-gel and particulateTiO2layers

Georg Waldner,Gottfried Grabner,Josef Krýsa,Jaromír Jirkovský

doi:10.1155/s1110662x03000229

Abstract

Polarization curves on irradiatedTiO2layers were measured in various electrolytes, namely sodium hydroxide, sulphuric acid, oxalic acid and potassium oxalate. Photocurrents measured in 0.1M NaOH are very small and decrease with increasing number of Degussa P25TiO2layers. Photocurrents for sol-gelTiO2layers in 0.1M NaOH are about five times higher than for P25TiO2layers and increasing with number of layers. The same holds forNa2SO4, but inH2SO4the difference between P25 and sol-gel diminishes, however the sol-gel layers still show the higher currents. In solutions of oxidizable substrates the trend is inversed: P25 layers show higher currents, with a steep increase with concentration of solute. The shape of the polarization curves was interpreted in terms of response time to irradiation and photocurrent depletion. Degradation experiments demonstrated that the effect (and advantage) of biasing the electrode depends on adsorption properties of substance and surface area of electrode material.

Highlights

The aim of the paper is the comparison of photoelectrochemical properties of various TiO2 layers, namely particulate, sol-gel and thermally produced layers
A possible way to increase the electron-hole separation and to enhance quantum yield is the application of a potential bias
Conventional semiconductor theory essentials postulate the formation of a depletion layer in a doped semiconductor having sufficiently “large particles”

Summary

Introduction

The aim of the paper is the comparison of photoelectrochemical properties of various TiO2 layers, namely particulate, sol-gel and thermally produced layers. The generation of a depletion layer requires the transfer of mobile charge carriers between the semiconductor and the electrolyte. In the absence of a suitable redox couple in the solution, the semiconductor can be polarized by applying an external bias voltage across the junction via an ohmic contact mounted at the backside of the electrode [1]. This photoelectrochemical effect of application of a potential to a TiO2 film was recently illustrated in detail by Butterfield et al [2]. The variety of sol-gel methods is shown in [9]

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Conclusion