Absorption, Desorption, and Transport of Water in Polymer Electrolyte Membranes for Fuel Cells

Abstract

The transport of water vapor through a Nafion membrane includes absorption of water at one membrane/gas diffusion layer interface, water transport in the membrane, and desorption of water at another interface. Based on the structure of the membrane, a model for the water transport through the membrane is presented. It was assumed that the mass-transfer coefficients for the absorption and desorption of water and the water diffusion coefficient were dependent on the volume fraction of water ͑ f V ͒ in the membrane. These parameters were determined from steady-state water transport flux through the membranes at different water activity gradients. The results show that the mass-transfer coefficient for the absorption of water ͑k a = 3.53 ϫ 10 −5 fv m/s, 353 K͒ is much lower than that for the desorption of water ͑k d = 1.42 ϫ 10 −4 fv m/s, 353 K͒. The parameters k a and k d describe the nonequilibrium water uptake of the membrane on operating conditions. Using these obtained parameters, the simulation results agree well with experimental data under many different conditions, including thickness of the membrane, water vapor/liquid water, temperature, and flow rate.

Preparation of Polybenzimidazole-Based Membranes and Their Potential Applications in the Fuel Cell System

“…In a separate study, we evaluated the stability, water uptake, and dimensional change of s-OPBI ( Figure 6). The proton conductivity of the s-OPBI membrane relatively increased as the water uptake increased (i.e., a 24-h sulfonated membrane), indicating a possible relationship between these two properties [19,29]. More thorough studies are under way to fully understand this relationship.…”

Transient non-isothermal model of a polymer electrolyte fuel cell

“…From the experimental and numerical results in [42], we can approximate the coefficients of absorption and desorption as follows…”

Macroscopic Modeling of Polymer-Electrolyte Membranes

“…While the polynomial fit is not rigorous, it does allow ease of use in modeling, especially when one might have to take the derivative of the curve (see section 4.3). A problem with the fit is that it does not take into account the observed lower uptake at higher temperatures (see for example references [146][147][148]), although this can be done with other curve fits or by extrapolating the curve if some data points are known at higher temperatures [149]. Finally, there are some models that use the same approach except use a fourth-order polynomial [86,133].…”