Proton exchange membrane fuel cells permeability

V. Gurau, M. J. Bluemle, E. S. De Castro, et al. Characterization of transport properties in gas diffusion layers for proton exchange membrane fuel cells. 2. Absolute permeability. Journal of Power Sources 165 (2007) 793-802. 

Proton exchange membrane fuel cells (PEMFCs) work with a polymer electrolyte in the form of a thin, permeable sheet. The PEMFCs, otherwise known as polymer electrolyte fuel cells (PEFC), are of particular importance for the use in mobile and small/medium-sized stationary applications (Pehnt, 2001). The PEM fuel cells are considered to be the most promising fuel cell for power generation (Kazim, 2000). 

Among a series of other materials, PPS has been tested as proton exchange membrane material, because of its promising properties. Heterogeneous membranes based on medium-sulfonated PPS are made by dispersing the PPS in a poly(olefin) matrix. A commercial fuel cell has been used for membrane testing. It turned out that membranes with high amounts of sulfonated particles are almost as conductive as Nafion 17. However, these membranes exhibit considerably lower diffusive permeabilities to methanol. Further, the membranes are less oxidatively stable. 

Fuel cells are often named for either the fuel or the electrolyte used. In the hydro-gen-PEM fuel cell (the acronym PEM stands for either proton-exchange membrane or polymer-electrolyte membrane), the anode and cathode are separated by a membrane, which is permeable to protons but not to electrons ( FIGURE 20.21). The membrane therefore acts as a salt bridge. The electrodes are typically made from graphite. 

The states of methanol in proton exchange membranes are considered to have a significant influence on the permeability of methanol in direct methanol fuel cell membranes [102]. 

Partially disulfonated hydroquinone-based PAES random copolymers have been synthesized and characterized for application as proton exchange membranes [128]. A copolymer with a 25% degree of disulfonafion showed the best balance between water uptake and proton conductivity. The copolymers showed substantially reduced methanol permeability compared with Nafion and a satisfactory performance of direct methanol fuel cell applications. 

Sulfonated Pis with a high proton conductivity and low methanol permeability were tested for their performance as proton exchange membranes in direct methanol fuel cells [58]. The proton to methanol transport selectivity of the membranes correlates well with the self-diffusion coefficients of water in the membranes. The membranes show an improved fuel cell device performance, however the high interfacial resistance between the membranes and electrodes... 

The proton-exchange membrane (PEM) fuel cell uses a thin, permeable polymeric membrane as the electrolyte. The membrane is very small and hght and in order to catalyse the reaction, platinum electrodes are used on either side of the membrane. Within the PEM fuel cell unit, hydrogen molecules are supplied at the anode and split into hydrogen... 

Sulfonated polyimides (SPI, Fig. 11.11) are potential candidates for proton exchange membranes and direct methanol fuel cells (DMFC) because the polyimide forms a network structure to control methanol permeability, and if sulfonic acid groups are introduced in the polymer chain, then it becomes hydrophilic and facilitates proton conduction. Polyimide is mechanically and thermally stable and chemically resistant [77]. 

Voltanunetric and chronoamperometric techniques are widely used recently to determine the methanol permeability through proton exchange membranes intended for nse in direct methanol fuel cell [36]. These techniques can be used with either a real fuel cell or a simulated one (diffusion cell). It is expected that the only electron transfer reaction that can occur at the working electrode surface, within the potential range or potential value under consideration, is the methanol oxidation. 

Methods of preparation of various functional fluoropolymers suitable for fuel cell applications have been discussed by Ameduri and coworkers [ 120]. They claimed that in spite of the high cost of Nafion and its permeability to methanol, it still remains the fluorinated polymer of choice for the preparation of the proton exchange membranes for PCs. 

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