Journal of Membrane Science 323 (2008) 148–152 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Performance of H 2 /O 2 fuel cell using membrane electrolyte of phosphotungstic acid-modified 3-glycidoxypropyl-trimethoxysilanes Takayuki Inoue, Thanganathan Uma, Masayuki Nogami ∗ Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa, Nagoya, 466-8555, Japan article info Article history: Received 28 February 2008 Received in revised form 4 June 2008 Accepted 7 June 2008 Available online 20 June 2008 Keywords: H 2 /O 2 fuel cell Organic–inorganic composite Electrolyte Sol–gel abstract Proton-conducting membranes based on phosphotungstic acid (PWA) and 3-glycidoxypropyl- trimethoxysilane (GPTMS) was investigated as the electrolyte for low temperature H 2 /O 2 fuel cell. Parameters determining the conductivity and elastic modulus of the membranes were characterized by thermogravimetry/differential thermal analysis and infrared spectroscopic measurements. The compos- ite containing 5% of PWA exhibited an elastic modulus below 100MPa at room temperature and a high proton conductivity of 1.0 × 10 -2 S/cm at 80 ◦ C and 100% RH. Low elastic modulus of the membrane was found to be useful for both the reduction of the membrane thickness and the better contact with the electrodes. The performance of the membrane electrode assemblies (MEA) was systematically studied as an effect of preparation conditions. A maximum power density of 45 mW/cm 2 and the current den- sity of 175 mA/cm 2 at 0.2 V were achieved at 90 ◦ C and 100% RH for the membrane of 5PWA·95GPTMS composition and 0.2 mm thickness. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Proton-exchange membrane fuel cells convert chemical energy directly to electrical energy using electrodes and a proton- conducting electrolyte and have much attention from the energy and environmental viewpoints [1,2]. There are a number of fuel cell design parameters with various subjects, usually categorized into two types based on their operating temperature and the electrolytes employed. Our research interesting is to develop a new solid type electrolyte-based fuel cells operating at room temperature. For this purpose, membranes with high proton con- ductivity and high thermal and chemical stabilities are necessary as the electrolytes. A series of perfluorosulfonate ionomers such as Nafion ® are used in actual cells as the electrolytes with high pro- ton conductivity [3–6]. Despite their high conductivities around room temperature, they still have some problems for practical use because of high cost and thermal degradation. Particularly, the decreased conductivity at temperatures higher than ∼80 ◦ C limits their practical use. On the other hand, recently, inorganic materials have attracted a lot of interest due to their thermal and chemi- cal stabilities. Many researchers have diverted their interest to the synthesis of proton-conducting inorganic materials. ∗ Corresponding author. Tel.: +81 52 735 5285; fax: +81 52 735 5285. E-mail address: nogami@nitech.ac.jp (M. Nogami). We were the first to report on the preparation of porous P 2 O 5 –SiO 2 glasses, which displayed a conductivity of ∼10 -2 S/cm at room temperature [7–9]. These glasses were applied to the elec- trolyte of hydrogen/oxygen fuel cell, exhibiting power densities of order of ∼10 mW/cm 2 at room temperature. More recently, we used heteropolyacidic compounds to complex with the P 2 O 5 –SiO 2 glasses as the fuel cell electrolytes [10–14]. Heteropolyacid such as H 3 W 12 PO 40 ·nH 2 O (phosphotungstic acid, PWA, n ∼ 29) has a Keggin structure and has attracted a lot of interest due to its high protonic conductivity of 10 -1 S/cm in the crystalline state [15]. The proton conductivities of these glass membranes increased up to ∼10 -1 S/cm at 90 ◦ C and 30% RH, and the power density was 23 mW/cm 2 at 30 ◦ C [14]. These inorganic materi- als are more favorable than polymers as the electrolytes due to their higher thermal stability. Nevertheless, no fuel cell has been exhibited high power densities expected from these high conductivities of electrolytes. One problem is the high resis- tivities occurred between the electrolyte and electrodes. High elastic modulus of the inorganic compounds impedes good con- tact with the electrodes, resulting into the decreased performance of the cell. New type electrolytes having both the thermal and mechanical flexible properties would be applicable for practi- cal use in the fuel cells. One is the using of organic compounds with elasticity. Among them, 3-glycidoxypropyl-trimethoxysilane ((OCH 3 ) 3 Si(CH 2 ) 3 OCH 2 CHOCH 2 , GPTMS) GPTNS has been used as precursor of proton conductive organic–inorganic hybrid membranes[16–19]. Three methoxy groups in GPTMS are expected 0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2008.06.030