Photoelectrochemical and photocatalytic properties of multilayered TiO 2 thin films with a spinodal phase separation str
- PDF / 1,608,459 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 93 Downloads / 203 Views
Multilayered titanium dioxide thin films with a spinodal phase separation structure were prepared by the sol-gel process from sols containing polyoxyethylene(20) nonylphenyl ether (NPE-20), and their photoelectrochemical and photocatalytic properties were investigated. The obtained films showed much higher anodic photocurrent and photocatalytic activity than the dense TiO2 thin film electrodes. We explained these phenomena by the large specific surface area inherent in the spinodal phase separation structure and the higher concentration of Ti3+ species, which were produced by the reducing action of the incorporated organic polymers at sintering temperatures. Ti3+ species in the bulk raise the donor density, and those at the surface provide a larger number of active sites available for photoelectrochemical reaction and photocatalytic reaction.
I. INTRODUCTION
Titanium dioxide is a chemically stable and environmentally friendly semiconductor often used in photocatalytic applications1–3 and has long been believed to be a promising candidate for a photoanode in solar cells.4–8 However, because of its large bandgap energy of about 3.0 eV, TiO2 exhibits a photoresponse only in the ultraviolet (UV) region. Various approaches to this problem have been done; for example, transition metal doping,9,10 metal nanoparticle incorporation,11,12 and dye sensitization4–6 have been attempted to extend the photoresponse to the visible light region. In solar power utilization, the highest energy-conversion efficiency obtained so far is 10–11% under simulated AM (air mass) 1.5 sunlight, which was recorded using photoelectrochemical solar cells consisting of dye-sensitized nanoparticle TiO2 prepared by Grätzel et al.6 However, this value is still less than half the theoretical value and is not large enough for practical application.13 It is thought that one of the reasons for the low energy-conversion efficiency arises from the boundaries between contacting nanoparticles, which should inhibit the migration of the photogenerated electrons to the collector through these nanoparticles.14 In our recent work, we have fabricated anatase TiO2 films with a spinodal phase separated structure (hereafter referred to as SPSS TiO2 thin film) by the sol-gel process.15 We suggested that this morphology was suitable a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0015 J. Mater. Res., Vol. 20, No. 1, Jan 2005
http://journals.cambridge.org
Downloaded: 16 Mar 2015
for a photoelectrochemical electrode in wet-type solar cells. In the current paper, we studied the photoelectrochemical and photocatalytic properties of the SPSS TiO2 thin films in comparison with a dense TiO2 thin film prepared from a sol without the addition of organic polymers. II. EXPERIMENTS A. Sample preparation and characterization
TiO2 film electrodes with the spinodal phase separation structure (SPSS) were prepared from coating solutions consisting of Ti (OC3H7i)4, C2H5OH, H2O, HNO3, and polyoxyethylene(20) nonylpheny
Data Loading...
