Electrospun Particle/Polymer Fiber Electrodes with a Neat Nafion Binder for Hydrogen/Air Fuel Cells
Authors: Waldrop Krysta , Slack John , Gumeci Cenk , Dale Nilesh , Reeves Kimberly Shawn , Cullen David A. , More Karren L. , Pintauro Peter N. 
Published: February 2020

Membrane-electrode-assemblies with electrospun particle/polymer fiber electrodes produce high power at low Pt loading in a proton exchange membrane H2/air fuel cell, with improved cathode durability as compared to conventional sprayed electrodes [1-5]. This boost in performance has been attributed to inter and intra fiber porosity. The increased porosity of a fiber mat cathode allows for facile removal of product water during fuel cell operation. Porosity within a fiber improves access of reactant gases to catalyst sites and may assist in retaining water during low relative humidity fuel cell operation. Additionally, shear mixing of catalyst and binder during the process of creating an electrospun fiber results in a more uniform distribution of ionomer and catalyst with few, if any, polymer or catalyst aggregates. Previous work on fiber electrodes focused on the use of poly(acrylic acid) (PAA) [1-3, 5] or poly(vinylidene fluoride) (PVDF) [4, 5] as a carrier polymer for Nafion perfluorosulfonic acid during electrospinning. In the present work, poly(ethylene oxide) (PEO) was used as the electrospinning carrier polymer for the fabrication of fiber mat cathodes and anodes, with either Pt/C or PtCo/C as the cathode catalyst and Pt/C as the anode catalyst. PEO carrier polymer was washed out of the fiber mat, resulting in a neat Nafion binder. For a fixed cathode and anode Pt loading of 0.1 mg/cm2, fuel cell tests were performed at 80 °C and 200 kPaabs pressure. In this talk, the effect of carrier polymer on fiber morphology will be discussed using STEM-EDX data collected at Oak Ridge National Laboratory. Beginning-of-life fuel cell power output was measured at feed gas relative humidities from 40% to 100%. The fuel cell polarization results, along with cathode ECSA and mass activity data were contrasted with conventional spray electrode MEAs. Fiber electrode MEAs with Pt/C or PtCo/C cathodes produced very high power at high and low feed gas RH. For example, the maximum power for a Pt/C cathode was essentially constant at 830 mW/cm2 ±5% (experimental error) from 40% RH to 100% RH. Additionally, fiber cathode MEAs exhibited better durability in a load cycling accelerated stress test, e.g., fiber electrode MEAs made with a Nafion/PEO electrospinning ink typically retained ~80% of their initial maximum power vs. 70% retention for a sprayed electrode MEA. This talk will focus on: (i) the methods for fiber electrode electrospinning, (ii) the morphology of the resulting fibers, and (iii) contrasting the performance of fiber electrode MEAs with sprayed electrode MEAs.

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). The work at Vanderbilt University was funded under DOE contract No. DE-EE0007653.

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