Page 254 - Multifunctional Photocatalytic Materials for Energy

Multidimensional TiO 11
2
nanostructured catalysts for

sustainable H generation
2

Jingsheng Cai, Jianying Huang, Mingzheng Ge, Yuekun Lai
Soochow University, Suzhou, PR China

11.1 Introduction

Global environmental pollution and the soon-to-be-exhausted fossil fuels are seen as
two of today's main challenges. Hydrogen is a carbon-neutral energy carrier and is
seen as an alternative to the diminishing fossil fuels; however, bringing this alternative
to fruition will require efficient hydrogen production [1,2]. Catalytic steam reforming,
partial oxidation, and coal gasification are currently the major commercial processes
used to produce hydrogen, but they produce CO 2 emissions and are not environmen-
tally friendly [3,4]. These factors are motivating a search for renewable sources of
clean energy. Photocatalytic water splitting (WS) is considered as a commercial CO 2 -
free and harmless process for producing highly pure hydrogen via splitting water
electrochemically into H 2 and O 2 . The increasing interest in WS has led to an urgent
demand for efficient and stable photocatalysts that will increase the production of
hydrogen [5–9].
Titanium dioxide (TiO 2 ) was first applied in WS by Fujishima et al. in 1972, and
since that time, it has been extensively investigated in photovoltaics [10], photocatal-
ysis [11], solar cells [12,13], energy storage [14,15], biomedical devices [16,17], and
intelligent coatings [18,19]. Nanostructured TiO 2 materials have attracted increasing
attention because of their relatively high conductivity, low cost, environmental safety,
corrosion resistance, and mechanical stability [20]. Most previous investigations fo-
cused on 0D TiO 2 nanoparticles (NPs) that exhibited, for example, excellent perfor-
mances as photocatalysts and sensors because of their large surface area and easy
fabrication process [21,22]. However, inherent defects, such as rapid recombination
of electron-hole pairs, high recycling cost, and slow charge carrier transfer, impede
photocatalytic efficiency. TiO 2 has a hierarchical, dimensional structure, and in recent
years, various dimensions of TiO 2 materials have demonstrated better electron-hole
separation, faster charge carrier transfer, and greater enlargement of active surface
area than the standard TiO 2 NPs, all of which has helped to improve the modifications
of TiO 2 -based materials in photocatalytic activities [23–25]. However, many intrinsic
drawbacks still exist that hinder wide application of TiO 2 in multidimensional nano-
structure forms. Because of the reported recombination of electron-hole pairs gener-
ated from visible light, wide band gap, and low quantum efficiency for photocatalytic
activity, TiO 2 can absorb only UV light, which accounts for < 5% of the entire solar

Multifunctional Photocatalytic Materials for Energy. https://doi.org/10.1016/B978-0-08-101977-1.00012-0
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