Polarization Curves of PEMFC and SOFC

The dependence of the cell potential difference on current density is called the cell polarization curve. The experimentally obtained open circnit potential (OCP) in a H2/O2 PEMFC is always below the theoretically calculated OCP, 1.229 V (at 25°C), due to (1) crossover of chemicals through the membrane and (2) a small internal electron current. This parasitic current density (jp) can reduce the OCP down to around 

FIGURE 8.3 Polarization curve of a PEMFC (1) the experimental open circuit potential is less than the theoretical value of 1.229 V (at 25°C) due to permeation of chemicals through membrane, (2) the potential decline due to relatively slow charge transfer cathodic reaction, (3) a linear Ohm s law dependence due to resistance of membrane, (4) the potential drops down due to transport limitation and approaching the limiting current, as shown, of about 1100 mA car.  

When the current density is above 0.8 A cm, the mass transfer processes are dominating, and the cell potential rapidly decreases down to zero. In the middle part of the curve, the internal ohmic resistance of the electrochemical cell is dominating. 

Using the electrochemical thermodynamics and kinetics covered in Chapters 4 and 6, the suggested in [4] equation 

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