Region IV Other Polarization Losses

Some fuel cell designs have attempted to boost fuel utilization and reduce system parasitic losses with a dead-ended hydrogen fuel compartment. That is, the hydrogen flow channels have no exit, and fuel is either continuously or sporadically supplied at the consumption rate required for suitable performance. A major drawback of this approach is that inerts and poisons in the flow stream build up in the dead end over time, and at least periodic purging is needed. In low-temperature systems, liquid accumulation is also a common problem, and some flow in the channels is beneficial to remove liquid droplet accumulations [20]. 

Returning to our ultimate goal of being able to analytically describe the fundamental physics of the polarization curve, we now have an expression that includes the starting equilibrium voltage, the departure from this voltage resulting from activation overpotential at each electrode, the ohmic polarization, and concentration polarization  

Only the crossover and shorting polarization losses need to be modeled, which are covered in the next section. 

The final piece of the polarization curve to be modeled is the departure from the expected OCR given by the Nemst equation. For low-temperature PEFCs, the OCV is predicted to be around 1.2 V, but in practice, only about 1.0 V is observed. For a high-temperature SOFC, however, the actual OCV can be very close to the theoretical OCV. For the PEFC, the 0.2 V represents an incredibly significant efficiency loss before any useful current is even drawn. The departure from the theoretical OCV is typically a result of two phenomena  

Crossover of reactants through the electrolyte and subsequent mixed-potential reaction at the opposite electrode 

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