An adequate understanding of the conductivity of polyperfluorosulfonic acid (PFSA) membranes as a function of water content, or relative humidity, and temperature is necessary for an analysis of the functioning of proton-exchange membrane (PEM) fuel cells. Although much work has been done toward elucidating the microstructure and conduction mechanism in PFSA, a satisfactory theoretical model with a minimum of fitted parameters is not yet available. Such a model is developed here for the conduction of protons in hydrated Nafion ® or like membranes based on the dusty-fluid model for transport and the percolation model for structural aspects. Further, thermodynamics of dissociation of the acid groups in the presence of polar solvents such as water is included. The sorption of solvent from vapor is modeled using a finite-layer Brunauer-Emmett-Teller (BET) model. With the only fitted parameters employed being the BET constants, determined independently, and the ratio of diffusion coefficients representing the interaction of the protonated solvent molecules with solvent and that with the membrane, the model provides excellent correlation with a variety of experimental data.

The feasibility of using nonvolatile molten and solid acidic electrolyte impregnated ion-exchange membranes in higher temperature proton-exchange membrane fuel cells (PEMFC5) to alleviate their water dependence is investigated. Higher temperature PEMFC operation reduces CO poisoning as well as passivation of the Pt electrocatalyst by other condensable species. Further, higher temperature operation could eventually allow direct use of low-temperature reformable fuels such as methanol in the PEMFC. The methodology proposed here involves supporting an appropriate acidic solid, melt, or solution of low volatility within the pores of Nation® so as to enhance its protonic conductivity at higher temperatures and lower humidity levels. Preliminary experimental results reported here for a PEM fuel cell operating at temperatures of 110 to 120°C based on Nafion supported solutions of heteropolyacid indicate the feasibility of the technique.•• 0 densable species would be reduced, and it would also alleviate the water management problems in PEMFCs. This is the broad objective of this work.Before discussing the rationale behind the proposed methodology, it is useful to reflect briefly on the proton transport mechanism in conventional ion-exchange membranes. Aspects of proton transport in polymer ion-exchange membranes have been discussed by other authors based on transport and spectroscopic studies.713Yeager8 and Gierke and Hsu9 describe a structural three-zone pore model, namely, (i) a low dielectric constant region consisting of the hydrophobic fluorocarbon polymer matrix, (ii) a high dielectric constant inverted micellular region containing ion clusters including the sulfonate exchange sites, counterions, and sorbed water, and (iii) the interfacial region consisting mostly of the pendant side chains of the sulfonate groups and a small amount of water. In fully hydrated Nation®, these clusters are -4 nm in diameter, shrinking to -1.9 nm at low water concentrations.910 The interconnection of such spherical micelles within the membrane pores by channels creates a network for ion transport.'°F igure 1 shows the schematic diagram of a pore within an ionexchange membrane in which the interconnected cellular geometry of the ion-cluster network is approximated by straight-cylindrical geometry. The anionic groups (-SO) are tethered to the pore sur-

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The development and feasibility of a novel fuel cell for simultaneously generating electricity and homogeneously catalyzed acetaldehyde from ethanol are reported. The fuel cell is based on the supported molten-salt electrocatalysis technique that allows use of homogeneous (liquid-phase) catalysts in fuel cells for the first time. The electrocatalytic reaction combines the chemistry of the Wacker process conventionally used for acetaldehyde production from the partial oxidation of ethylene and that of the Veba-Chemie method. Nafion membranes impregnated with different electrolytic materials were used in the fuel cell as electrolytes to allow operation at reaction temperatures up to 165°C. Results obtained are com~arable to those revorted in the literature on ~a r t i a l oxidation of ethylene to acetaldehyde in a fuel cell based on con-ven6onal heterogeneok electrocatalysts.