Page 135 - Introduction to Transfer Phenomena in PEM Fuel Cells

124 Introduction to Transfer Phenomena in PEM Fuel Cells
Moreover, this coefficient has recently been measured at around 1.07 in
the studies [YE 07, LIU 07] for a Gore® membrane.
3.7. Conclusion
The equations describing the mass transfer in the different layers of a
PEMFC are presented in this chapter. Stefan–Maxwell and Darcy models are
useful for visualizing the diffusion of gaseous mixtures in the diffusion
layers and the convective motion of the gas mixtures in the flux channels and
the diffusion layers, respectively. The kinetic law of Butler–Volmer deals
with the electrical representation of the electrochemical reactions that take
place in the reaction layers.

The study of the mass transfer of different species involved in the fuel
cell as well as the management of different flows are essential for its proper
functioning, and consequently for a longer lifetime. Indeed, it should be
supplied continuously with fuel (hydrogen) and oxidant (oxygen) to ensure
the production of electricity. On the contrary, the products of the reaction at
the heart of the fuel cell should also be continuously released as the
mismanagement of the mass flows can lead to significantly lower
performance in the fuel cell.

The flow of water in the membrane can describe the behavior of the fuel
cell, which is why it contributes to the performance of a fuel cell. Two main
descriptions (models) of this phenomenon have been described: porous
medium model and phenomenological model. The transport of water in the
membrane strongly depends on the overall thermoelectric behavior of the
system. Maintaining a good membrane water content can guarantee good ion
conductivity and consequently a good electrical performance of the PEMFC.