Polymer electrolyte fuel cell cathode side impedance

Figure 6.6. Polarization curves of fuel cells with electrodes containing 40 wt% PTFE in the gas diffusion layer. The temperature of the humidifier on the cathode side was maintained at ( ) 65°C and ( ) 80°C. For comparison, the polarization curve of the fuel cell with the electrode containing 30 wt% PTFE in the gas diffusion layer is shown at the cathode humidification temperature of 65°C (A) [5], (Reprinted from Journal of Power Sources, 94(1), Song JM, Cha SY, Lee WM. Optimal composition of polymer electrolyte fuel cell electrodes determined by the AC impedance method, 78-84, 2001, with permission from Elsevier and the authors.)...

Usually, the starting point of model derivation is either a physical description along the channel or across the membrane electrode assembly (MEA). For HT-PEFCs, the interaction of product water and electrolyte deserves special attention. Water is produced on the cathode side of the fuel cell and will either be released to the gas phase or become adsorbed in the electrolyte. As can be derived from electrochemical impedance spectroscopy (EIS) measurements [14], water production and removal are not equally fast Water uptake of the membrane is very fast because the water production takes place inside the electrolyte, whereas the transport of water vapor to the gas channels is difiusion limited. It takes several minutes before a stationary state is reached for a single cell. The electrolyte, which consists of phosphoric add, water, and the membrane polymer, changes composition as a function of temperature and water content [15-18]. As a consequence, the proton conductivity changes as a function of current density [14, 19, 20). 

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