Low stoichiometry operation of a proton exchange membrane fuel cell employing the interdigitated flow field – A modeling study

A multiphase fuel cell model based on computational fluid dynamics is used to investigate the possibility of operating a proton exchange membrane fuel cell at low stoichiometric flow ratios (ξ < 1.5) employing the interdigitated flow field design and using completely dry inlet gases. A case study of two different operating temperatures and two different operating pressures is presented. In all cases the cathode side stoichiometric flow ratio was varied from ξc = 1.5 to 1.2, and the anode side varied to as low as ξa = 1.05. It is found that operating at ambient pressure leads to a generally dryer cell, and the only possibility to prevent membrane dry-out is to operate at or below 70 °C. The cell is generally better humidified at an elevated pressure, and here it is found that the cathode channels will become flooded when the operating temperature is too low, e.g. 70 °C, while membrane hydration levels of λ = 7–10 can be achieved at 80 °C. Operation at stoichiometric flow ratios as low as ξ = 1.2 at the cathode side and ξ = 1.05 at the anode side appear feasible. If this can be verified, it would allow open-ended anode operation without recirculation or flow shifting, thus significantly reducing system complexity and cost.

► First multi-phase simulations of an interdigitated flow field including anode, cathode and a detailed membrane model.
► Theoretical proof that water uptake layer (WUL) works.
► Demonstration that fuel cell can operate on completely dry inlet gases at a low stoichiometry employing the WUL.
► Demonstration that anode side can be operated at a very low stoichiometry of 1.05.
► Demonstration that coolant flow should be counter-flow to cathode and co-flow to anode.