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Research Papers

# Modeling of Polymer Electrolyte Membrane Fuel Cell Stack End Plates

[+] Author and Article Information
Suvi Karvonen

Laboratory of Advanced Energy Systems,  Helsinki University of Technology, P.O. BOX 2200, FIN-02015 TKK, Finland

Tero Hottinen

Wärtsilä Finland Oyj, Tekniikantie 14, 02150 Espoo, Finland

Jari Ihonen, Heidi Uusalo

VTT Technical Research Centre of Finland, P.O. Box 1601, FI-02044 VTT, Finland

J. Fuel Cell Sci. Technol 5(4), 041009 (Sep 09, 2008) (9 pages) doi:10.1115/1.2930775 History: Received October 31, 2006; Revised October 19, 2007; Published September 09, 2008

## Abstract

Good thermal and electric contacts of gas diffusion layers (GDLs) with electrode surface and flow-field plates are important for the performance of a polymer electrolyte membrane fuel cell (PEMFC). These contacts are dependent on the compression pressure applied on the GDL surface. The compression also affects the GDL porosity and permeability, and consequently has an impact on the mass transfer in the GDL. Thus, the compression pressure distribution on the GDL can have a significant effect on the performance and lifetime of a PEMFC stack. Typically, fuel cell stacks are assembled between two end plates, which function as the supporting structure for the unit cells. The rigidity of the stack end plates is crucial to the pressure distribution. In this work, the compression on the GDL with different end plate structures was studied with finite element modeling. The modeling results show that more uniform pressure distributions can be reached if ribbed-plate structures are used instead of the traditional flat plates. Two different materials, steel and aluminum, were compared as end plate materials. With a ribbed aluminum end plate structure and a certain clamping pressure distribution, it was possible to achieve nearly uniform pressure distribution within $10–15bars$. The modeling results were verified with pressure-sensitive film experiments.

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## Figures

Figure 1

A cross-sectional schematic of the unit cell components in (a) a real stack and (b) the approximative model

Figure 2

A top (x,y-plane) view of the flat end plate structure. The dimensions are in millimeters.

Figure 3

Schematic representations of three different rib structures: (a) the two-rib, (b) the ten-rib, and (c) the edge-supported ten-rib structures.

Figure 4

The clamping pressure isobars on the GDL surface of the original flat plate with 1kN load at each bolt. The pressure values are in bars. The origin (lower right corner) corresponds to the point of symmetry.

Figure 5

The diagonal GDL pressure values of the flat plate structure with 1kN load at each bolt

Figure 6

A schematic of the ten-rib structures for (a) steel and (b) aluminum. The dimensions are in millimeters.

Figure 7

The diagonal GDL pressure values of the studied steel and aluminum structures with 1kN load at each bolt

Figure 8

The clamping pressure isobars on the GDL surface of the 7cm aluminum rib structure with 1kN load at each bolt. The pressure values are in bars.

Figure 9

The diagonal GDL pressure values of the structures with optimized bolt loads. The first load value refers to the corner bolt, the second to the bolts next to the corner, and the last to the bolts at the middle of the edges.

Figure 10

Pressure isobars on the GDL: (a) 4cm steel ribs, (b) 5cm aluminum ribs, (c) 6cm aluminum ribs, and (d) 7cm aluminum ribs. The pressure values are in bars.

Figure 11

The pressure isobars of the 7cm aluminum ribs on the three GDL surfaces: (a) top (outermost), (b) middle, and (c) bottom (closest to z-symmetry boundary, i.e., middle of the stack)

Figure 12

The five-cell stack measurement results: (a) corresponds to the pressure on the middle cell in the stack with the original flat end plates and (b) to the 6cm rib aluminum plates. The color bar values show the pressure value in relation to the average clamping pressure.

Figure 13

The single cell measurement results: (a) original flat plates with homogeneous clamping, (b) 6cm rib aluminum plates with homogeneous clamping, and (c) 6cm rib aluminum plates with optimized clamping distribution. The color bar values show the pressure value in relation to the average clamping pressure.

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