(Invited) Performance of Nanofiber Meas in a Hydrogen/Air Fuel Cell with Low Relative Humidity Feed Gases

Abstract

Membrane-electrode-assemblies (MEAs) with particle/polymer nanofiber mat electrodes produce high power and exhibit excellent durability at low platinum loadings in a H2/air proton exchange membrane fuel cell [1-4]. The morphology of an electrospun mat electrode is well-suited for fuel cell applications due to: (1) a high interfacial electrode area, with both inter- and intra-fiber porosity which improves oxygen access to catalytic sites while providing pathways for proton transport, electron conduction, and the removal of product water and (2) a well-dispersed mixture of catalyst and binder along the fiber length and cross-section with a conformal coating of binder on catalyst particles (a consequence of shear mixing, rapid solvent evaporation, and fiber elongation during electrospinning). The focus of this talk is on the design and fabrication of nanofiber-based MEAs (anode, cathode, and membrane) that produce high power at both high and low relative humidity (RH) feed gas conditions. Procedures for electrospinning fiber mat electrodes with low EW PFSA binders will be described and the effect of electrode binder type on power output will be presented. As an example, one nanofiber-based MEA had a 20 μm thick composite membrane (725 EW PFSA with reinforcing PVDF fibers), a 725 EW PFSA binder for the anode and cathode, a Pt/C anode at 0.10 mg/cm2, and a PtCo/C cathode at 0.10 mg/cm2. The measured maximum power density for this MEA in a H2/air fuel cell at 200 kPa pressure, 80oC, and 125/500 sccm H2/air flow rates was 940 mW/cm2 at 100% RH, 924 mW/cm2 at 30% RH, and 804 mW/cm2 at 20% RH. Acknowledgments This work was funded by the Fuel Cell Consortium for Performance and Durability, DOE-EERE FC-PAD Project DE-EE0007653. The authors thank Mike Yandrasits at 3M Co. for providing the 725 EW PFSA ionomer used in the experiments. References Zhang and P. N. Pintauro, ChemSusChem, 4, 1753-1757 (2011).Brodt, R. Wycisk, and P. N. Pintauro, J. Electrochem. Soc., 160, F744-F749 (2013).Brodt, T. Han, N. Dale, E. Niangar, R. Wycisk, and P. Pintauro, J. Electrochem. Soc., 162, F84-F91 (2015).Brodt, R. Wycisk, N. Dale, and P. Pintauro, J. Electrochem. Soc., 163, F401-F410 (2016).