Stack electrical coupling

Thermal and Electrical Coupling in Stacks 335 Stack Current Densities... 

P. Berg, A. Caglar, J. St-Pierre, K. Promislow and B. Wetton, Electrical Coupling in Proton Exchange Membrane Fuel Cell Stacks Mathematical and Computational Modelling, accepted in the IMA J. Appl. Math., March, (2005). 

Kim, G.S., St-Pierre, J., Promislow, K., and Wetton, B. (2005) Electrical coupling in proton exchange membrane fuel cell stacks. J. Power Sources, 152, 210-217. 

Electrical coupling in proton exchange membrane fuel cell stacks mathematical and computational modeling. IMA J. 

So far we have considered electric phenomena in an isothermal stack or thermal phenomena in a stack element with ideally conductive bipolar plates. In reality the electric and thermal phenomena in a stack are coupled. This coupling is due to the strong (exponential) temperature dependence of the electric conductivity of various stack layers and of the half-cell exchange current densities. 

FIGURE 7.4 100-Cell stack voltage distribution model computations for one anomalous bus plate (either stainless steel, nickel, or aluminum) and one copper bus plate, at 300 A. Model curves correspond to inlet, middle, and outlet locations. (Reprinted from Journal of Power Sources, 152, Kim, G. S. et al. Electrical coupling in proton exchange membrane fuel cell stacks. 210-217. Copyright (2005), with permission from Elsevier.)... 

In conclusion, stochastic operating conditions and electrical coupling between cells in the stack will contribute to different degradation rates of the cells. This again means that if the weakest cell limits the hfe of the stack, the EoL of the stack will be reached before the average cell performance reaches EoL conditions. 

Isotachophoresis. In isotachophoresis (ITP), or displacement electrophoresis or multizonal electrophoresis, the sample is inserted between two different buffers (electrolytes) without electroosmotic flow. The electrolytes are chosen so that one (the leading electrolyte) has a higher mobility and the other (the trailing electrolyte) has a lower mobility than the sample ions. An electric field is applied and the ions start to migrate towards the anode (anions) or cathode (cations). The ions separate into zones (bands) determined by their mobilities, after which each band migrates at a steady-state velocity and steady-state stacking of bands is achieved. Note that in ITP, unlike ZE, there is no electroosmotic flow and cations and anions cannot be separated simultaneously. Reference 26 provides a recent example of capillary isotachophoresis/zone electrophoresis coupled with nanoflow ESI-MS. 

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