A two‐parameter equation describing water vapor uptake in perfluorosulfonic acid membranes is derived based on the Flory‐Huggins model combined with a chemical equilibrium constant for proton transfer. Temperature‐dependent expressions for the proton‐transfer equilibrium constant K(T) = 0.0256 × exp[(22.4 kJ/mol)/RT] and the Flory interaction parameter χ(T) = 1.936 − (2.18 kJ/mol)/RT are discussed. Advantages of the new equation include accurate reduction of activity vs. water vapor uptake data for perfluorosulfonic acid membranes with few parameters and a well‐behaved dependence of activity on composition and temperature. Comparisons of model results with water uptake measurements in the literature are given. An explanation for the difference in water uptake by membranes in contact with liquid water and with saturated vapor is proposed based on an interpretation of the temperature dependence of water uptake. © 1999 The Electrochemical Society. All rights reserved.

We recently observed that the activation barriers of O-atom abstraction reactions between metal atoms and N2O, in which both reactants are in their ground electronic states and the atoms contain no valence p electrons, vary systematically with the sums of the metal atom ionization potential and the energy required to promote a valence s electron to the lowest p orbital. It is shown here that this observation can be explained by the assumption that the activated complex results from the resonance interactions of ionic and covalent structures. Activation barriers for 43 reactions are calculated and where experimental measurements are available, are shown to be in good agreement with those. New interpretations are offered for literature data on the Ca and Cr reactions. The resonance treatment leads to a more general relationship in which activation barriers depend simultaneously on ionization potentials, electron affinities, promotion energies, and bond energies of the reactants. A number of further series of reactions, where activation barrier or rate coefficient trends with some of these parameters have been observed, are discussed and seen to be special cases of this formalism. Good agreement is found between the height of the barrier for the N2O+H→N2+OH reaction calculated by the present resonance treatment and an ab initio method.

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