Membrane Electrode water clusters

Recently, Dahr [1], Stonehart [2] and Watanabe [3] have made an attempt to reduce the humidification constraints in solid polymer electrolyte fuel cells (SPEFCs) by using modified perfluorosulfonic membranes. A recast Nafion film sandwiched between the two electrodes was first proposed by Dahr [1] for the realization of an internally humidified SPEFC. Stonehart [2] suggested the inclusion of small amounts of silica powder into the recast film in order to retain the electrochemically produeed water inside the membrane. Watanabe et al [3] have tried to exploit the H2/O2 crossover through the membrane to produce a chemical recombination to water on small Pt clusters inside the membrane. All of these membranes were operated with H2/O2 at 80°C and allowed the development of systems without assisted humidification or with near ambient humidification. 

Solid Polymer Electrolyte The most common solid polymer electrolytes consist of a hydrophobic and inert polymer backbone which is sulfonated with hydrophilic acid clusters to provide adequate conductivity as discussed in Chapter 5. In order to ensure adequate performance, some membrane hydration is required. However, excess water in the electrodes can result in electrode flooding, so that a precarious balance must be achieved. Modern perflourosulfonated ionomer electrolytes for H2 PEFCs are 18-25 xm thick with a practical operating temperature limit of 120°C, although PEFC operation is rarely greater than 90°C due to excessive humidity requirements and operational low lifetimes. 

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