Photoresponse of Visible Light Active CM-n-TiO2, HM-n-TiO2, CM-n-Fe2O3, and CM-p-WO3towards Water Splitting Reaction

Yasser A Shaban,Shahed U M Khan

doi:10.1155/2012/749135

Abstract

Photoresponses of visible light active carbon modified titanium oxide (CM-n-TiO2), hydrogen modified titanium oxide (HM-n-TiO2), carbon modified iron oxide (CM-n-Fe2O3), carbon modified tungsten oxide (CM-p-WO3) towards water splitting reaction are reported in this article. Carbon and hydrogen in titanium oxide were found to be responsible for red shift from UV region to visible region which in turn enhanced the photoconversion efficiency by an order of magnitude for water splitting reaction. Photocurrent densities and photoconversion efficiencies of regular n-TiO2and CM-n-TiO2towards water splitting reaction under monochromatic light illumination from a xenon lamp and sunlight were compared and found in reasonable agreement. These oxides were characterized by photocurrent measurements,UV-Visspectra, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) studies and these results are also reported in this article.

Highlights

Sunlight is the unlimited source of clean and renewable energy if it could be efficiently utilized to split water to hydrogen and oxygen
A semiconductor consists of a valence band (VB) and the conduction band CB)
We summarize our studies on thin-film photoelectrodes of the following (i) visible light active carbon-modified titanium oxides (CM-n-TiO2); (ii) visible light active hydrogen modified n-type titanium oxide (HM-n-TiO2) thin films; (iii) carbon-modified iron oxides (CM-n-Fe2O3) thin films; (iv) visible light active carbon-modified p-type tungsten oxides (CM-p-WO3) thin film

Summary

Introduction

Sunlight is the unlimited source of clean and renewable energy if it could be efficiently utilized to split water to hydrogen and oxygen. It was found that carbon modification of n-TiO2 photocatalyst synthesised by thermal oxidation of Ti metal sheet in a natural gas flame lowered the bandgap energy of nTiO2 to 2.32 eV and exhibited water splitting to hydrogen and oxygen with a photoconversion efficiency of 8.35% [1] under artificial light illumination from a Xenon lamp This progress stimulated further investigation into carbon-modified nTiO2 (CM-n-TiO2) as visible light active photocatalysts [43,44,45,46,47,48,49] and as photoelectrodes [14,15,16,17,18,19,20,21,22,23,24, 55,56,57,58,59] for watersplitting reaction with enhanced photoconversion efficiency. Synthesized thin-film photoelectrodes are characterized in terms of bandgap energies, X-ray diffraction pattern, scanning electron micrograms, and carbon contents to correlate with their photoresponse towards water-splitting reaction

Experimental Details and Results

Dependence of Photoconversion Efficiency on Applied

Monochromatic Photocurrent Density-Wavelength

Photocurrent Density-Potential Dependence for Iron

Photoconversion Efficiency-Potential Dependence for