Method of standard contact porosimetry

To determine the fraction of expanded channels, T and the channel-size distribution must be known. The channel-size distribution gives the fully expanded channel radii and is taken to be the same for different operating conditions and the same as the distribution measured for a liquid-equilibrated membrane. The reasons that this distribution is assumed to be constant are that it should not vary significantly with pressure or temperature xmder typical fuel-cell operating conditions and is used only when there is a separate liquid-water phase. This assumption has been used and proved valid within error tolerances [13, 18, 57]. The pore-size distribution for Nafion has been measured by the method of standard contact porosimetry [29, 58, 59]. In those studies, the distribution included both the channels and the clusters. Since only the channel-size distribution is of interest, only that regime of data is fit using the log-normal distribution [39]. The average channel radius is around 1.5 nm as expected from the physical model and other studies [23, 60, 61). 

MSU. The studies at MSU were supervised by Frumkin much more intently than those at the Institute. On the other hand, Frumkin always thoroughly read all the papers before submitting them for publication. These studies had made fundamental contributions to the theory and practice of electrocatalysis, especially with regard to the dissociative adsorption of organic compounds, the nature of adsorbates, and the rate-determining step of electrooxidation processes. Methods were also developed for optimizing the structure of porous electrodes. The method of standard contact porosimetry was widely used to quantify various materials. Finally, the book by W. Vielstich Brennstojfelemente was translated into Russian with a preface written by Frumkin. 

The method of standard porosimetry (MSP)41-43 was one of the first approaches used to obtain air-water capillary pressure curves for GDMs.16 In this test, a GDM sample is initially saturated with water and contacted with a water-saturated porous disc, which is a standard with known Pc(Sw) behavior. The capillary pressure of the sample-standard system is varied by allowing the liquid to evaporate from the standard and sample while in contact. If the two media can be assumed to be in capillary equilibrium, their capillary pressures are equal. Saturation is determined by measuring the weights of the sample and standard periodically. The capillary pressure of the system is found by reference to the known capillary pressure curve of the standard. This method is limited to scanning... 

Using the standard contact porosimetry method, Gostick et al. (2009) showed that water-air capillary pressure curves of fibrous gas diffudion media depend on sample thickness, clearly demonstrating that finite size effects are important. Compression of the GDM was found to increase the capillary pressures for water injection and decrease the capillary pressures required for water withdrawal. 

Otherwise, the porosity of the electrode needs to be determined by diagnostic methods. So far, several methods have been proposed and implemented to comprehensively characterize porosity, including mercury or gas porosimetry, capillary flow porosimetry, and standard contact porosimetry. 

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