Thermal conductivity in the three layered regions of micro porous layer coated porous transport layers for the PEM fuel cell

Odne S Burheim,Gregory A Crymble,Robert Bock,Nabeel Hussain,Sivakumar Pasupathi,Anton Du Plessis,Stephan Le Roux,Frode Seland,Huaneng Su,Bruno G Pollet

doi:10.1016/j.ijhydene.2015.07.169

Abstract

Thermal conductivity of the polymer electrolyte membrane fuel cell (PEMFC) components has achieved increased attention over the past decade. Despite the fact that the PEMFC itself (between the gas flow plates) is less than a millimetre in thickness, several °C temperature differences can arise inside it during operation. These temperature differences mainly arise across the porous transport layers (PTL) often also referred to as gas diffusion layers (GDL). Several research efforts have led to a good understanding of the thermal conductivity of the PTL; in particular to how this property changes with compression, temperature, PTFE content, different fabrics, and water content. Far less attention has been given to the thermal conductivity of the much thinner layered micro porous layer (MPL) and in particular to the thermal conductivity of the transitional region between the PTL and the MPL.In this study we have used X-ray computer tomography (XCT), scanning electron microscopy (SEM), and thermal conductivity measurements to show that a MPL coated PTL is actually a three layered structure where the PTL is on one side, the MPL on the other, and a composite region consisting of the MPL as a matrix with the PTL fibres in the middle. We have shown that the thermal conductivity of the MPL-PTL-composite region is much larger than for the two others and that temperature differences inside this layer can be neglected compared to the regions where it is MPL-only and PTL-only. We have also shown that the MPL has a significantly lower thermal conductivity than the other two layers. In light of this research, the MPL of the commercial SGL should be integrated into the GDL in order to have lower temperature deviations in the PEMFC. A relevant literature review is included.

Highlights

Hydrogen can be extracted from a wide range of renewable and non-renewable sources and is the chemically bound fuel with the highest available gravimetric energy density
This paper presents an overview of the efforts in determining component throughplane thermal conductivity relevant for stationary PEMFC operation with a particular focus on the micro porous layer (MPL) and its bridge with the porous transport layer (PTL), referred to as the gas diffusion layer (GDL)
Using X-ray computer tomography and scanning electron microscopy, it was possible to study the interfacial region of a micro porous layer (MPL) and a porous transport layer (PTL), in this case the SGL24/25/35-series

Summary

Introduction

Hydrogen can be extracted from a wide range of renewable and non-renewable sources and is the chemically bound fuel with the highest available gravimetric energy density. The PEMFC is typically symmetrical and consists of a catalyst layer (CL), a MPL and a porous transport layer (PTL) situated on each side of a membrane, with the entire assembly enclosed by polarisation plates. The polarisation plates have channels for gas flow and water removal engraved into them. The water typically stems from the reaction in the cathode catalyst layer. From there it must pass through the MPL and the PTL in order to get to the gas flow channels. In addition to supporting the CL, the MPL aids water removal improving the mass transport of the feed gases (oxygen and hydrogen) to the CL

Methods

Findings

Discussion

Conclusion