Symmetrical gas supply

Figure 5.17c shows the equivalent circuit of the PEM fuel cell symmetrical gas supply arrangement. Fitting the spectra of the symmetrical cells for both the anode and the cathode, as seen in Figure 5.17c, Rctanode and Rct,catho

Figure 5.17. Equivalent circuit of a PEM fuel cell, with a and b H2/02 gas supply, and c symmetrical gas supply [19]. (With kind permission from Springer Science+Business Media Journal of Applied Electrochemistry, Characterization of membrane electrode assemblies in polymer electrolyte fuel cells using a.c. impedance spectroscopy, 32, 2002, 859-63, Wagner N, Figure 3, 2002 Springer.)...

Figure 4.5.57. Bode diagram of the measured impedance spectra, PEFC (Nation-impregnated electrodes) at 80°C, at pH2 and PO2 = 2 bar absolute, symmetrical gas supply, at open cell potential.

The equivalent circuit for a complete PEM fuel cell can be applied initially to a "symmetrical" gas supply while varying current densities. At low current densities (< 400 mA/cm ) the mass-transport limitations are very minor, and a simple Nyquist diagram with two relaxation times emerges. The overall impedance is dominated primarily by the cathodic process, with resulting higher cathodic overpotentials. The equivalent circuit is represented by two parallel combinations of charge-transfer resistances R and doublelayer capacitors C 20 pF/cm for the anode and cathode processes. The... 

---