Polymer electrolyte membrane fuel cells (PEMFCs) have gained considerable attention in recent years for application in electric vehicles, portable devices, and cogeneration systems. Large scale commercialization of PEMFCs mainly requires addressing the high cost issues associated with the fuel cell stack in addition to the challenges associated in building H₂ infrastructure. Though, significant amount of research has been carried out in developing low Pt loaded Membrane Electrode Assemblies to meet the 2020 DOE performance targets for automotive applications, there are still challenges associated in meeting durability requirements due to catalyst layer and membrane degradation. It is well documented voltage cycling during start-up/shutdown process leads to Pt dissolution and loss of electrochemical surface area of Pt and thereby affecting the durability. Fuel cells stacks need to be robust against both specific and non-specific failure modes. Specific failure modes of MEA can be predicted by operating conditions/parameters, however non-specific failure mode such as cell reversal is difficult to predict. Though, system level mitigation can be employed to minimize the impact of cell reversal, there is a potential cost trade-off associated with this approach. Ballard¹ was first to develop and report the impact of cell reversal tolerance above sub-zero conditions with and without cell reversal tolerance catalyst in the MEA.

Cell reversals² can occur mainly during reactant starvation and especially during H₂ starvation under freeze start-up operation. This presentation will focus on evaluating the impact of operating parameters on cell reversal under sub-zero conditions and will highlight the mechanism and potential ways to improve cell reversal tolerance under sub-zero conditions. Figure 1 shows the impact of current density on cell reversal tolerance under sub-zero conditions³. As it can be seen, significant reduction in sub-zero reversal tolerance noticed with current density. To the best of our knowledge, we evaluated for the first time, the cell reversal tolerance under sub-zero conditions.

References

1. S.D.Knights, D.P.Wilkinson, S.A. Cambell, J.L.Taylor, J.M. Gascoyne and T.R. Ralph, Solid polymer fuel cell with improved voltage reversal tolerance. US Patent 6936370.
2. C. Qin, J. Wang, D. Yang, B. Li and C. Zhang, Proton Exchange Membrane Fuel Cell Reversal:A Review, Catalysts, 6, 2016, 197.
3. R.Bashyam, J.Bellerive, P.He, Fuel cell system and method of operating fuel cell system, German Patent application DE102016207786A1

Acknowledgement

We thank Volkswagen AG and Audi for funding this work.