Desalination 199 (2006) 283–285
Development and characterization of sulfonated polysulfone membranes for direct methanol fuel cells Francesco Lufrano*, Vincenzo Baglio, Pietro Staiti, Antonino S. Arico’, Vincenzo Antonucci CNR – ITAE, Istituto di Tecnologie Avanzate per l’Energia “Nicola Giordano” Via Salita S. Lucia sopra Contesse n. 5 - 98126 S. Lucia - Messina, Italy email:
[email protected] Received 28 October 2005; accepted 3 March 2006
Abstract The development of a direct methanol fuel cell based on composite polysulfone membranes modified with silica filler is reported. The synthesis of sulfonate polysulfone samples was carried out by a mild sulfonation process using trimethyl silyl chlorosulfonate as sulfonating agent. Composites membranes with 5 wt% of silica filler were prepared and characterized. A composite membrane tested in direct methanol/oxygen fuel cell gave a maximum power density of about 180 mW cm–2 at 120°C. Keywords: Sulfonate polysulfone membrane; Composite membrane; Fuel cell; DMFC
1. Introduction Non-perfluorinated ionomer membranes based on thermostable sulfonated aromatic polymers such as polybenzimidazole, polysulfones, polyethersulfones, polyetherketones have been proposed as alternative materials at the traditional perfluorosulfonic membranes [1,2]. Among them, polysulfones are promising candidates for their low cost, commercial availability and processability and for this, they are under investigation *Corresponding author.
in polymer electrolyte fuel cell technologies [3,4]. In this research, we have used a mild sulfonation process to prepare proton conducting membranes with different sulfonation level to modify a commercial polysulfone polymer. The sulfonated polysulfone (SPSf ) were synthesized using trimethyl silyl chlorosulfonate as sulfonating agent in homogeneous solution of chloroform. The silyl sulfonate polysulfone is modified in sulfonate form by sodium methoxide reagent. A 5% SiO2 filler was added to the polymer in the ionomer form. The proton conducting polymer with a degree of sulfonation, varying
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.03.069
F. Lufrano et al. / Desalination 199 (2006) 283–285
from 50% to 70% was easily obtained by changing the mole ratio between the sulfonating agent and the monomer unit of the polymer. The sulfonate polysulfone membranes were prepared starting from polymer solution in dimethyl acetamide (DMAc) by conventional casting process. The membranes were washed with water, dried and converted in protonic form with HCl before characterizations.
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2. Results and discussion
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Fig. 1. Fuel cell polarization as a function of temperature for composite SPSf membrane.
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Thermal analysis measurements show an increase in glass transition temperature (Tg) for the sulfonated membranes compared to the base polysulfone. Moreover, it is also found an increase in Tg with the increasing degree of sulfonation of the polymer. The thermal stability from thermogravimetry approaches at about 220–250°C, where start the desulfonation process. However, the practical temperature in fuel cells operation could be of 150–160°C. Proton conductivities of the membranes were calculated from resistance measurements from 25°C to 90°C. A value of about 5 ´ 10–2 S ´ cm–1 at 90°C were found rendering these membranes interesting for a possible use in direct methanol fuel cell applications. The effect of cell temperature on fuel cell performance for the composite sulfonated polysulfone membranes based MEAs (membrane and electrode assemblies) in the presence of methanol/O2 and methanol/air was investigated. Fig. 1 shows fuel cell performance as function of temperature in 2M methanol as fuel and oxygen as oxidant for a composite SPSf membrane (EW: 800 g/mol). In Fig. 2, the power density with cell temperature from 90°C to 120°C for composite SPSf membrane is reported. A maximum power density of about 180 mW cm–2 at 120°C was achieved. Further studies are in progress to improve structure, thermal stability, proton conductivity of
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Fig. 2. Power density in 2M methanol/oxygen for composite sulfonated polysulfone membrane.
the polymer, effect of filler as well as the fuel cell performance. References [1]
[2]
Q. Li, R. He, Q.O. Jensen and N.J. Bjerrum, Approaches and recent development of polymer electrolyte membranes for fuel cells operating above 100°C, Chem. Mater., 15 (2003) 4896–4915. W.L. Harrison, M.A. Hickner, Y.S. Kim and J.E. McGrath, Poly(arylene ether sulfone) copolymers and related systems from disulfonated monomer building blocks: Synthesis, characterization, and
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performance – A topical review, Fuel Cells, 5 (2005) 201–212. F. Lufrano, G. Squadrito, A. Patti and E. Passalacqua, Sulfonated polysulfone as promising membranes for polymer electrolyte fuel cells, J. Appl. Polym. Sci., 77 (2000) 1250–1256.
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