Water Management in Cathode Catalyst Layers of PEM Fuel Cells

Abstract

The cathode catalyst layer ͑CCL͒ is the major competitive ground for electrochemical reaction, reactant transport, and water and heat exchange in a polymer electrolyte fuel cell ͑PEFC͒. Nevertheless, it is often treated as a thin interface. Its pivotal role in the fuel cell water balance is unexplored. Here, the structural picture of CCLs forms the basis for a novel model that links spatial distributions of processes with water handling capabilities and current voltage performance. In the first step, the statistical theory of random composite media is used to relate composition, porous structure, wetting properties, and partial saturation to effective properties. In the second step, these effective properties are used in a macrohomogeneous model of CCL performance. A set of reasonable simplifications leads to a full analytical solution. Results demonstrate that the CCL acts like a watershed in the fuel cell, regulating the balance of opposite water fluxes toward membrane and cathode outlet. Due to a benign porous structure, the CCL represents the prime component for the conversion of liquid to vapor fluxes in PEFCs. Furthermore, the CCL is highlighted as a critical component in view of excessive flooding that could give rise to limiting current behavior.

On the Micro-, Meso-, and Macroporous Structures of Polymer Electrolyte Membrane Fuel Cell Catalyst Layers

“…However, it may be assumed that the micropore-filling process, i.e., the filling of <2 nm pores, occurs in the primary carbon particles, which themselves are ∼30 nm in diameter (8,23). The micropores are thought to exist either between the turbostratic graphite planes of the crystallites or between the edges of two crystallites.…”

A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

“…Reactant transport can be enhanced when the GDL porosity is in the region of around 0.3-0.6 [107,108], and the removal of liquid water to the gas channel can be enhanced with a linearly graded porosity [107]. The use of thinner GDLs can also improve performance by allowing for greater liquid water mass transfer under steady-state conditions [107,109] and greater reactant mass transfer towards the catalyst layer [108]. The permeability of a GDL can vary according to the carbon type [90]; woven and non-woven GDLs have exhibited slightly higher permeabilities than carbon fibre paper GDLs with similar solid volume fractions [110].…”

Modeling Water Management in Polymer-Electrolyte Fuel Cells

“…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.…”