Dioxido De Titanio

International Journal of Hydrogen Energy 32 (2007) 2609 – 2629
www.elsevier.com/locate/ijhydene

Titanium dioxide for solar-hydrogen I. Functional properties
J. Nowotny ∗ , T. Bak, M.K. Nowotny, L.R. Sheppard
Centre for Materials Research in Energy Conversion, School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia
Available online 28 November2006

Abstract
The present work considers the concept of photoelectrochemical generation of hydrogen through water splitting using solar energy (solarhydrogen). The focus is on functional material properties that are essential for the performance of photoelectrochemical cell for solar-hydrogen.
The performance of the cell is discussed in terms of the energy conversion efficiency (ECE). It isargued that TiO2 and TiO2 -based materials
are the most promising candidates for photoelectrodes for solar-hydrogen. The modification of TiO2 in order to achieve desired performance
parameters is discussed in terms of the electronic structure, concentration of charge carriers and segregation-induced surface properties, which are
critical to the ECE. Challenges to the development of abi-photoelectrode cell, equipped with both n-type and p-type TiO2 , forming photoanode
and photocathode, respectively, are discussed. The research strategies and pressing issues related to the optimization of key functional properties
necessary for the commercialization of solar-hydrogen are outlined. It is shown that defect chemistry is the most appropriate framework for
tailoring the functionalproperties of TiO2 -based oxide systems in order to obtain high-performance photoelectrodes. The present work provides
an overview of the research progress on solar-hydrogen.
2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Keywords: Titanium dioxide; Water splitting; Photoelectrochemical cell

1. Introduction
The world is rapidly running out offossil fuels. As a matter of considerable urgency, technologies for the generation of
new types of energy must be developed. There is a growing
consensus that hydrogen has the potential to supplement and
ultimately replace fossil fuels for the production of fuel [1]. At
the same time there is a growing consensus that the emission
of greenhouse gases must be reduced in order to address globalwarming which has become increasingly obvious and problematic [2–4]. Therefore, there is an urgent need to develop both
renewable and clean sources of energy, such as solar energy
[5–8].
Hydrogen generated from the splitting of water using solar energy, termed solar-hydrogen, represents a sustainable fuel
that is environmentally safe [9]. Awareness is growing that
solar-hydrogen has the capacityto provide global energy security, at potentially very low cost, and to reduce global warming.
The present work was performed as within the research and development
program on solar-hydrogen.
∗ Corresponding author. Tel.: +61 2 9385 6465; fax: +61 2 9385 6467.
E-mail address: j.nowotny@unsw.edu.au (J. Nowotny).

The benefits of solar-hydrogen technologies include:
• Solar-hydrogen isenvironmentally friendly in terms of both
production and utilization.
• Solar-hydrogen will assist in reducing the levels of greenhouse gases, pollutant gases and acid rains.
• Solar-hydrogen will reduce the world’s reliance on fossil
fuels.
• Solar-hydrogen will allow producers to export solar energy.
• Large areas of the globe, where sunlight and water are abundant, are ideally placed tocommercialize solar-hydrogen.
The advantages of solar-hydrogen technologies over other
hydrogen-generation technologies include:
• The fuel may be generated anywhere.
• The process is sustainable (requires supplies of only solar
energy and water).
• The hydrogen-generating device does not have any moving
parts, so maintenance is minimal.
• The associated infrastructure is simple.
• The process...