Investigation on Structure and Behaviours of Proton Exchange Membrane Materials by TEM

Abstract

H2/O2 fuel cells and direct methanol fuel cells (DMFC) are one of the most promising efficient and environmental friendly energy generation systems because of their low emissions and high working efficiency, which are extensively applied in stationary power, automobiles and portable electrical source[1-2]. The proton exchange membrane (PEM), the key component of fuel cell, acts as a separator to prevent the mixing of the fuel and the oxidant and severs as an electrolyte to transfer protons from the anode to the cathode [3]. The PEM must be satisfied with following peculiarities such as high proton conductivity, low electronic conductivity, long-term chemical stability, good mechanical strength under fuel cell operation conditions and low cost. In the early 1960s, sulfonated polystyrene copolymers membranes were used as the PEM in proton exchange membrane fuel cells (PEMFCs) [4]. However, short lifetime and relatively high price limited their further applications. In the later 1960s, Nafion® perfluorosulfonated membranes produced by DuPont company have been extensively used because of their high conductivity and chemical stability [5-7]. However, there are some drawbacks, such as high methanol permeability, relatively low proton conductivity at high temperature and high price, which baffle their further developing. Recently many researchers have been devoted to developing new hydrocarbon PEM materials that are of good mechanical performance and thermooxidative stability, low price and high proton conductivity. Nowdays, the developed novel polymer electrolyte membranes include sulfonated poly(arylene ether sulfone)s[8-10], sulfonated poly(arylene ether ketone)s[11-15], sulfonated polyimides[16-19], sulfonated polybenzimidazoles[20-22], block sulfonated copolymers and their composite membranes[23-28], etc. Sulfonated polymers may be prepared either by postsulfonation of the polymers or by polycondensation of sulfonated monomer with other non-sulfonated monomers [29]. The postsulfonation polymers were prepared by electrophilic aromatic sulfonation using concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid or