PEM Conductivity Simply a Function of Composition

It is possible to derive a simple expression for the PEM conductivity based on these essential principles of PEM structure and functioning. As demonstrated below, this simple treatment is possible within the limits of high water content. Assuming 100% dissociation of sulfonic acid sites and assuming further that all protons acquire a bulk-like proton mobility as in free liquid water, the proton conductivity is 

This expression radically simplifies structural effects on proton charge density and proton mobility. It serves as a springboard for detailed treatments of these effects in subsequent sections. 

The proton charge density in the ideal case of complete acid dissociation is 

In a random porous network with fixed geometry and topology, the structure-based factor/(Xw) exhibits a percolation-type dependence on Xw.  

The mobility of protons in bulk water at infinite dilution and 25°C is = 3.63 10 cm s (Adamson, 1979 Meiboom, 1961). DuPont Nafion PFSA-type membranes (NRE211 and NRE 212) have lEC 1 mmol g i and 2g cm , corresponding to a maximum proton charge density of = 

---

The section PEM Conductivity Simply a Function of Composition in Chapter 2 presents a rudimentary conductivity model, based on Equation 2.1. Local variations of proton density and mobility in pores render the simple factorized form of Equation 2.1 inapplicable at the pore level. In the case of a cylindrical pore of length Lp, radius Rp, with uniform surface charge density at the pore walls, the conductance Epore is given by an integral expression... 

The simplest approximation to describe the operation of a PEM was discussed in the section PEM Conductivity Simply a Function of Composition It involves the following basic instructions ... 

---