The effects of water and microstructure on the performance of polymer electrolyte fuel cells

Abstract

In this paper, we present a comprehensive non-isothermal, one-dimensional model of the cathode side of a Polymer Electrolyte Fuel Cell. We explicitly include the catalyst layer, gas diffusion layer and the membrane. The catalyst layer and gas diffusion layer are characterized by several measurable microstructural parameters. We model all three phases of water, with a view to capturing the effect that each has on the performance of the cell. A comparison with experiment is presented, demonstrating excellent agreement, particularly with regard to the effects of water activity in the channels and how it impacts flooding and membrane hydration. We present several results pertaining to the effects of water on the current density (or cell voltage), demonstrating the role of micro-structure, liquid water removal from the channel, water activity, membrane and gas diffusion layer thickness and channel temperature. These results provide an indication of the changes that are required to achieve optimal performance through improved water management and MEA-component design. Moreover, with its level of detail, the model we develop forms an excellent basis for a multi-dimensional model of the entire membrane electrode assembly.

Modeling Water Management in Polymer-Electrolyte Fuel Cells

“…One of the most detailed applications of this model is that of Shah et al 133 In their model, they account for such impacts as membrane swelling, inactive catalyst in the agglomerate pores, surface films of both ionomer and water if the vapor phase is saturated, and the number and dispersion of agglomerates. Furthermore, they do everything in a geometrically and material-balance consistent manner.…”

“…136 Recent models mainly examine distributions of platinum, Nafion ® , operational changes, and material properties such as agglomerate wettability and CL thickness. 133,[137][138][139][140] While most of the models deal with experimentally-based values, some look at possible structures that are more ordered and perhaps experimentally unobtainable currently.…”

Transient non-isothermal model of a polymer electrolyte fuel cell

“…In the present case, a one-dimensional formulation, based largely on our earlier work in [25], is shown to be sufficient to qualitatively capture observed behaviour -by comparison with [22,24] -and predict performance. Efforts to extend the model to two and three dimensions are ongoing.…”

Reliability of the spherical agglomerate models for catalyst layer in polymer electrolyte membrane fuel cells

“…It is hence interesting to see if, for a given catalyst layer, an effective single diameter exists with which the spherical agglomerate model can effectively describe the average oxygen reduction rate across a range of overpotentials. In the literature, such effective diameters vary widely in the range from 200 nm to 6000 nm (Shah et al, 2006;Siegel et al, 2003). These are considerably higher than the diameter estimated from the images of real catalyst layers, which is approximately 100 nm .…”

“…This partly explained why the diameter reported in the literature for the spherical agglomerate model varies so widely in the range from 200 nm to 6000 nm (Shah et al, 2006;Siegel et al, 2003), much larger than the average agglomerate diameter estimated from experiments . This implicates that the spherical agglomerate models must be used with great care in catalyst layer design, especially for catalyst layers that will work at high overpotential, as a wrong interpretation of the agglomerate size in a design could lead to wrong results for catalyst loading and ionomer content.…”