Compression of a cell during assembly mainly influences the cathode-side carbon-based porous transport layer (PTL). The compression of this PTL is directly related to the contact pressure on the active cell area via the material properties of the material used. Higher compression of the PTL material leads to an increased contact pressure on the land areas of the flow field structure. Stähler et al. [1] showed that with increasing compression, the cell performance improved but the hydrogen permeation from the anode to the cathode side also increased.

The contact pressure distribution on the active area was investigated in a series of tests with different cathode PTL materials. For this purpose, carbon paper with a high bending stiffness and carbon fleece with a low bending stiffness were used.

The influence of different compressions of the PTL materials on the cell performance is shown in Figure 1 a) and b). The associated local pressure distribution was determined using pressure sensitive foils. Exemplary pressure distributions for a compression of 30% are shown in figure 1 c) and d). In addition to the expected dependence on compression and the associated contact pressure, the cell performance also showed a dependence on the pressure distribution on the active cell area and therefore the mechanical properties of the PTL material used in the tests. A possible explanation for this is the better electrical contacting of the membrane below the channel surface and a better utilization of the catalyst surface. The pressure distribution also showed an influence on the hydrogen permeation through the membrane.

References

[1] M. Stähler, A. Stähler, F. Scheepers, M. Carmo, W. Lehnert, and D. Stolten, “Impact of porous transport layer compression on hydrogen permeation in PEM water electrolysis,” International Journal of Hydrogen Energy, vol. 45, no. 7, pp. 4008–4014, 2020, doi: 10.1016/j.ijhydene.2019.12.016.