Region II Ohmic Polarization

solving for surface coverage, we can show, from algebraic manipulation, that 

Physically, this shows the surface coverage fraction is simply the ratio of the adsorption reaction to the total sum of parallel reactions. Then the current density i becomes 

Now we seek to relate this expression to the overpotential required to produce that current density at the electrode of interest, so that we can predict electrode overpotential as a function of current density in a similar fashion as with the BV approach for electron-transfer-limited reactions. The electrochemical reaction rate constant % can be written 

The reaction rates required for solution would be determined from existing literature or from direct experimental results. 

Electronic and Ionic Resistance To solve ohmic resistance problems, some basic tools are required. First, Ohm s law can be written 

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Region II Ohmic Polarization 159 Table 43 Typical Conductivily/Resistivity Values for Selected Fuel Cell Materials... 

The losses in region II are dominated by the ohmic polarization of the fuel cell. This includes all electrical and ionic conduction losses through the electrolyte, catalyst layers, cell interconnects, and contacts. 

Both the first (ohmic) and second (polarization controlled) regions can be noted in Figure 10, reporting the results of typical limiting current measurements performed on an ED stack composed of only 19 cationic membranes (CMV type, see Table II) and model solutions containing 9 and 28 mol of NaCl per m3 for superficial velocities (vs) ranging from 3.4 to 5.9 cm/s (Fidaleo and Moresi, 2005a). 

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