Journal of Power Sources 157 (2006) 207–211 Short communication Nano-TiO 2 -coated polymer electrolyte membranes for direct methanol fuel cells Zhaolin Liu ∗ , Bing Guo, Junchao Huang, Liang Hong, Ming Han, Leong Ming Gan Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602, Singapore Received 5 May 2005; accepted 27 July 2005 Available online 15 September 2005 Abstract Composite polymer electrolyte membranes with nano-TiO 2 films are fabricated by deposition of titania nanoparticles from a sol solution. Measurements of ion conductivity, methanol permeability and single-cell performance of the modified Nafion membranes are conducted. The TiO 2 films adhere well and are crack-free. The protonic conductivity of the composite membranes decreases with increasing titania content, but methanol permeability is reduced. Preliminary tests on a single-cell of a direct methanol fuel cell (DMFC) indicate that a titania-coated membrane with 0.009 mg cm -2 content gives the highest cell voltage and maximum power density. © 2005 Elsevier B.V. All rights reserved. Keywords: TiO 2 film; Composite membrane; Direct methanol fuel cell; Protonic conductivity; Methanol permeability 1. Introduction The direct methanol fuel cell (DMFC) has potential uses in portable devices and in automobiles, because of its low weight and simple system features. This type of fuel cell does not, how- ever, match the present high performance of hydrogen polymer- electrolyte fuel cells (PEMFCs). One of the main impediments to the practical realization of the DMFC as a power source is cross-over of methanol through the polymer electrolyte mem- brane (PEM). The methanol permeation reduces the fraction of useful methanol since the methanol passed to the cathode is con- verted into carbon dioxide. The formation of a mixed potential at the cathode due to the methanol permeation leads to additional losses so that the cell voltage is lowered and the electric power decreases. Intensive research efforts to decrease the cross-over of methanol are focused mainly on the development of new PEMs [1–5], the development of methanol-tolerant cathode catalysts [6,7], the insertion of catalytically active particles into the PEM [8], the introduction of special coatings with methanol- blocking properties [9,10], surface-modified Nafion membranes ∗ Corresponding author. Tel.: +65 68727532; fax: +65 68720785. E-mail address: zl-liu@imre.a-star.edu.sg (Z. Liu). using plasma etching and palladium-sputtering and Pd-layered Nafion membranes [11–14]. Adjemian et al. [15] and Jung et al. [16] have modified commercial Nafion 115 membranes by a sol–gel reaction with tetraethoxysilane (TEOS) and have applied them to a H 2 /O 2 fuel cell and a DMFC. It was found that silica incorporated into the membrane decreased the proton conductivity of membrane at low temperature (<100 ◦ C). The nano-silica/Nafion composite membranes prepared by plasma- enhanced chemical vapour deposition (PECVD) exhibited a methanol permeability that was reduced by 40%, but had an ion conductivity that was similar to the unmodified Nafion mem- branes [17]. A nanocomposite, re-cast, Nafion hybrid membrane that contains titanium oxide as an inorganic filler has been reported [18]. The introduction of the TiO 2 particles endows the composite membrane with good mechanical and thermal resis- tance and improves the water uptake and ion-exchange capacity in comparison with commercial Nafion membranes. Several physical and chemical techniques such as sputter- ing, chemical vapour deposition (CVD), light-induced CVD, the sol–gel method and spray pyrolysis have been used to prepare thin films of titania. Among these, the relatively simple sol–gel method is the most widely used since it allows easy control over factors like film thickness and porosity [19]. In the present work, a Nafion membrane is coated with nano-TiO 2 by a simple sol–gel procedure. Compared with the commercial Nafion membrane, 0378-7753/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2005.07.070