Experimental Study of Thermal Conductivity of Catalyst Layer of Polymer Electrolyte Membrane (PEM) Fuel Cells

Efficient operation of a typical automotive PEM fuel cell occurs at a certain range of temperature from 60˚C to 80˚C. At temperatures below 60˚C, the kinetics of the electrochemical reaction slows down, and the electrodes are more prone to being flooded by the liquid water due to the higher possibility of saturation of the produced water at lower temperatures. At temperatures above 80˚C, the membrane dries out, and consequently, ohmic losses attributed to proton transport through the membrane increase. In addition to these performance consequences, PEM fuel cells will face durability issues if they operate outside the mentioned temperature range; breaking down of membrane at high temperatures due to its glass transition at temperatures around 80˚C as well as damage to various components of the fuel cell due to ice expansion during freezing are some of the mentioned durability issues. Therefore, as is clear, water management, thermal control, and degradation minimization are highly and intricately correlated to each other, among which thermal control can be considered as the core controlling factor which directly affects the others. Performing an effective thermal management is hinged on having detailed knowledge about the temperature distribution inside various layers, and the key to finding such information is to have the thermal conductivity of various layers. The thermal conductivity of PEM fuel cell gas diffusion layers (GDL) is well understood, and some experimental data on thermal conductivity of other components have been provided in literature. However, the thermal conductivity of the catalyst layer, where most of the heat generation modes occur, is still unknown. Accordingly, this work is concerned with measurement of this property through two different approaches: the guarded heat flux method and the transient plane source method. In the guarded heat flux method which works based on steady-state measurement of temperature distribution inside the sample, the catalyst samples are placed in between two fluxmeters which introduce a constant heat flow rate through the samples, whereas in the transient plane source method which works based on a transient measurement of temperature inside the sample, two halves of catalyst sandwich the transient plane source sensor.