Membrane catalyst material/PFSA

Membrane. Perfluorosulfonic acid (PFSA) is the most commonly used membrane material [4], PFSA membranes are relatively strong and stable in both oxidative and reductive environments, since the structure of PFSA is based on a PTFE backbone. The conductivity of a well-humidified PFSA membrane can be as high as 0.2s cm. As is well known, fuel cell operation at elevated temperatures can increase the rates of reaction, reduce problems related to catalyst poisoning, reduce the use of expensive catalysts, and minimize problems due to electrode flooding. Unfortunately, a PFSA membrane must be kept hydrated to retain its proton conductivity. Moreover, a PFSA membrane is alcohol permeable if it is used in DAFCs. Because of the disadvantages of PFSA membranes, many alternatives have been proposed [106]. Five categories of membranes are classified (1) perfluorinated, (2) partially fluorinated, (3) non-fluorinated, (4) non-fluorinated composite, and (5) others. 

Typically, the membranes for low-temperature PEM fuel cells are made of perfluoiocaibon-sulfonic acid ionomers (PFSA). The best material known is Nafion produced by DuPont, though similar materials have been developed for commercial or development purposes by other manufacturers such as Asahi Glass (Flemion) or As Chemical (Aciplex). In the electrode part, the catalyst is generally dispersed as small particles on a conductive support (carbon powders). Despite many attempts to develop a non-noble-metal catalyst, platinum remains the best known electrocatalyst for ORR in PEM fuel cells. The most extensive limitations to large-scale commercial use of these materials arise from the fact that... 

The principle of operation is shown in Fig. 2. Chlorine gas is produced at the anode (especially optimized dimensionally stable anode) with an anolyte feed concentration of 14 wt % HCl. Anode and cathode are separated by a cation exchange membrane (perfluorosulfonic acid polymer, PFSA, e.g., Nafion of DuPont). The ODC is based on a conductive carbon cloth which operates simultaneously as a gas diffusion layer because a suitable material is incorporated. The oxygen reduction reaction (5) takes place in three-phase boundaries of a thin, porous catalyst layer on the surface. 

The CL should keep the phase equilibrium with other PEM materials [13], The CLs applied onto both sides of the PEM are highly intercoimected with the membrane by their content of proton-conducting PFSA ionomer. The typical MEA structures show strains of PFSA ionomer running through the CLs, connecting catalyst particles to the membrane on the ionic conductor level. These strains form an ionic connection to the membrane not only for mobile protons, but also for all species which can enter the pores within these materials. In the normal case, the phase equilibrium at the interface between the CLs and the PEM material is always assumed to be established. 

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