Electrospun PFSA-Pt/C nanofiber mats have demonstrated promise as electrodes for PEM fuel cells that are highly scalable and show improved performance and durability compared to traditional sprayed electrodes.^1,2 As a result, it is of great interest to understand the underlying mechanisms responsible for these gains, so that these electrode structures may be optimized in order to further increase performance and durability.

Neutron radiography was used to measure water formation through the cross-sections of sprayed gas diffusion electrodes (denoted GDE) and electrospun PFSA-Pt nanofiber electrodes (denoted NF) during operation. Both GDE and NF-containing MEAs were assembled in custom hardware specifically designed for use within the neutron beam and operated in a differential cell configuration at 80°C, with variable RH and current density. Initial polarization results (Figure 1a) demonstrated a lower OCV for the NF electrodes, which were attributed to shorting at the through-holes within the active area, specific to the custom-built imaging hardware. Regardless, the performance of NF electrodes is improved at high (2 A/cm²) current densities. Through-thickness water profiles at 0.2 V (Figure 1b) show that the water concentration is around 2x lower within the MEA and GDLs in the NF-containing MEA compared to the baseline GDE. The lower water contents suggests improved performance in the mass transport region, commensurate with the observed polarization curves. Hardware issues are currently being addressed, and further test results exploring effects of RH, current density, and NF composition, will be discussed.

Acknowledgements

This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium (Fuel Cells Program Manager: Dimitrios Papageorgopoulos and Technical Development Manager: Greg Kleen).

References

1. P. N. Pintauro, “Fuel Cell Membrane-Electrode-Assemblies with Ultra-Low Pt Nanofiber Electrodes,” Fuel Cell R&D Annual Merit Review Proceedings, 2018.
2. Brodt, R. Wycisk, N. Dale, and P. Pintauro, “Power Output and Durability of Nanofiber Fuel Cell Cathodes with PVDF and Nafion/PVDF Binders”, J. Electrochem. Soc., 163, F401-F410 (2016).