Investigation on Non-isopotential Phenomenon of Bipolar Plates for Polymer Electrolyte Membrane Fuel Cell Stacks Based on Equivalent Circuit Model

To investigate the non-isopotential phenomenon within bipolar plates for PEM fuel cell stacks, we developed a multi-cell stack equivalent circuit model and related iterative solution algorithms. By fitting the key parameters related to the ohmic resistance and overpotential using the experimental data from a commercial 20-cell stack under drying scenarios, we have found that the air inlet areas of the middle cells suffer the severest membrane dehydration. A sensitivity analysis on the across-plane electron transfer resistance and the average through-plane ohmic resistance has also been conducted to investigate the effects of bipolar plate thinning and drying conditions on the non-isopotential behavior of the fuel cell stack. The results revealed that (a) the non-isopotential phenomenon and interaction between cells become significant as the bipolar plate becomes thinner or the operation condition becomes dryer, and (b) the in-plane distribution of the current density tends to be consistent between cells and the “fluidity” of the current between cells becomes weaker as the bipolar plate becomes thinner or the operation condition becomes wetter. The deeper understanding on the inconsistency of fuel cell stacks could provide guidelines for the relevant performance improvement and durability issues in the future.