Fuel Cell Membrane Electrode Assemblies with Ultra-Low Pt Nanofiber Electrodes
H2/air fuel cell membrane-electrode-assemblies (MEAs) were fabricated with electrospun particle/polymer nanofiber mat cathodes (0.1 mgPt/cm2 or 0.2 mgPt/cm2 Pt/C, PtCo/C or PtNi/C) and anodes (0.1 mg/cm2 Pt/C), where the binder was a mixture of acid-form perfluorosulfonic acid ionomer (e.g., Nafion) and poly(acrylic acid) (PAA) carrier polymer or sodium-form PFSA with a carrier polymer of either PAA or polyethylene oxide (PEO). For the latter two cases, the water-soluble carrier was removed from the fibers after electrospinning. MEAs with Pt/C anode/cathode catalyst loadings of 0.1 mgPt/cm2 each, an 1100 EW PFSA binder (Nafion dispersion), and a Nafion 211 membrane produced high power at both high and low relative humidity (RH) conditions, e.g., a maximum power density of 919 mW/cm2 at 100% RH and 832 mW/cm2 at 40% RH for a test at 80 °C and 200 kPa abs. The high power at low RH was attributed to nm-size pores within the fibers that trap water via capillary condensation thus maintaining a high proton conductivity of the PFSA binder in the cathode and especially the anode while minimizing/eliminating ionic isolation of catalyst particles in low water content, poorly conductive binder. At the same time, micro-porosity between fibers in the cathode allows for fast removal of electrogenerated water, thus minimizing cathode flooding. Nanofiber MEAs with Pt alloy catalyst cathodes also performed well, where a fibrous PtCo/C catalyst cathode at a loading of 0.1 mg/cm2 produced 20% more power than a conventional powder cathode MEA, e.g., a maximum power density of 1,045 mW/cm2 vs. 869 mW/cm2 at 80 °C, 100% RH, and 200 kPa(abs), and a PtNi/C fiber cathode MEAs prepared with Na+-form Nafion + PEO generated a maximum power of 820 mW/cm2 at 40% RH. Fiber electrode MEAs with a neat Nafion binder (prepared from Na+-form Nafion + PEO or PAA) where the cathode Pt loading was ~0.1 mg/cm2 exhibited a 25% loss in maximum power at 30,000 metal dissolution cycles, as compared to a 12% loss when the cathode binder was H+-form Nafion + PAA. The performance of a fiber mat electrode MEA with Pt/C catalyst (0.2 mg/cm2 cathode loading and 0.1 mg/cm2 anode loading) was excellent. At 80 oC and 200 kPa(abs), the maximum power density was 1104 mW/cm2. The maximum power was independent of feed gas humidity for 40 < RH < 100%. The power loss after a metal dissolution AST (30,000 voltage cycles) was only 13%.
- Research Organization:
- Vanderbilt Univ., Nashville, TN (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Office of Sustainable Transportation. Hydrogen Fuel Cell Technologies Office (HFTO)
- Contributing Organization:
- Vanderbilt University
- DOE Contract Number:
- EE0007653
- OSTI ID:
- 2331465
- Report Number(s):
- DE-EE0007653
- Country of Publication:
- United States
- Language:
- English
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