PtCo/C and Pt/C catalyst powders were incorporated into electrospun nanofiber and conventional sprayed cathode membraneelectrode-assemblies (MEAs) at a fixed electrode loading of 0.1 mg Pt /cm 2 . The binder for PtCo/C nanofiber cathodes and Pt/C nanofiber anodes was a mixture of Nafion and poly(acrylic acid) (PAA), whereas the sprayed electrode MEAs utilized a neat Nafion binder. The structure of electrospun fibers was analyzed by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS), which showed that the fibers were ∼30% porous with a uniform distribution of catalyst and binder in the axial and radial fiber directions. The initial performance of nanofiber MEAs at 80°C was 20% better than the sprayed electrode MEA (a maximum power density of 1,045 mW/cm 2 vs. 869 mW/cm 2 ). The benefit of the nanofiber electrode morphology was most evident at end-of-test (after a metal dissolution accelerated stress test), where power densities dropped by only 8%, after 30,000 square wave voltage cycles (0.6 V to 0.95 V), as compared to a 35% drop in the maximum power for the sprayed electrode MEA. The use of a recovery protocol improved the initial performance of a nanofiber MEA by ∼13%, to 1,070 mW/cm 2 at 0.65 V, and increased the power after a metal dissolution stress test by 5-10% (e.g. 840 mW/cm 2 at 0.65 V after 30,000 voltage cycles). At rated power, the nanofiber MEA generated more than 1,000 mW/cm 2 at 99°C and a pressure of 250 kPa abs. The high performance and durability of PtCo/C nanofiber cathode MEAs is due to the combined effects of a highly active cathode catalyst and the unique nanofiber electrode morphology, where there is a uniform distribution of catalyst and binder (no agglomeration) and short transport pathways across the submicron diameter fibers (which lowers gas transfer resistance and facilitates water removal from the cathode).

Pt–Co truncated octahedral nanocrystals were synthesized and evaluated as a class of highly active and durable catalysts toward oxygen reduction.

Electrospun nanofiber cathode mats were prepared with a metal‐organic framework (MOF)‐derived Fe−N−C catalyst and a blended binder of Nafion and polyvinylidene fluoride (PVDF). The electrodes were incorporated into H2/air fuel cell membrane‐electrode assemblies (MEAs) and compared with conventional sprayed‐cathode MEAs, in terms of power output and durability. The addition of hydrophobic PVDF into the electrode binder of nanofiber and sprayed cathodes produced a stable power output for 300 hours, whereas the sprayed‐electrode MEA with neat Nafion binder exhibited a 63 % power loss. The steady‐state maximum power density output of a PGM‐free nanofiber‐cathode MEA with a 1 : 1 Nafion : PVDF cathode binder at 80 °C and 1 atm backpressure was 154 mW/cm2. MEAs with a nanofiber cathode generated significantly more power than a sprayed cathode and the nanofiber cathodes continued to produce power throughout a carbon‐corrosion voltage cycling accelerated‐stress test. After 50 carbon corrosion‐voltage cycles, the maximum power density rose from 154 to 186 mW/cm2 and then decreased to 106 mW/cm2 at 500 cycles.

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Electrospun nanofiber electrodes for hydrogen/air fuel cells were prepared using poly(ethylene oxide) (PEO) carrier polymer, where previous publications used poly(acrylic acid) (PAA). Electrospinning with PEO carrier is only possible when the ink contains Nafion® in its salt form. Fiber electrodes were evaluated in 5 cm2 membrane-electrode-assemblies (MEAs) and exhibited excellent power at high and low feed gas relative humidities. For example, a nanofiber cathode MEA made from an ink containing Na+-form Nafion, PEO, and Pt/C generated 822 mW/cm2 at maximum power, 40% RH, 80 °C, and 200 kPaabs, whereas PAA-based ink electrode MEAs produced 527 mW/cm2. Changes in PEO molecular weight had no notable impact on fuel cell performance. Different Nafion counter-ions were studied. The use of Cs+-form Nafion resulted in the best MEA performance, producing 919 mW/cm2 at maximum power under full humidification and 800 mW/cm2 at 40% RH.

The impact of polyvinylidene fluoride (PVDF) as a binder component on the durability of Pt/C cathodes in a proton exchange membrane fuel cell membrane-electrode-assembly (MEA) during a carbon corrosion accelerated stress test (AST) was examined using electrochemical fuel cell data and visual inspection/analysis of the cathode morphology via electron-microscopy. Electrospun nanofiber cathode mat MEAs with a Nafion®/PVDF or Nafion/poly(acrylic acid) (PAA) binder or a slurry cathode MEA with neat Nafion or a Nafion/PVDF binder were investigated. The presence of PVDF had profound effects on the structure and chemical/electrochemical properties of a fuel cell cathode; its hydrophobic property slowed the rate of carbon loss and its robust mechanical properties added strength to the binder. Thus, the extent of carbon loss during an AST was inversely proportional to the PVDF content of the binder and there was no observable cathode thinning nor any change in cathode porosity after the AST, when the cathode binder contained at least 50 wt% PVDF. In terms of long-term durability, these beneficial structural effects outweighed the lower Nafion/PVDF binder conductivity and the associated lower initial power output of a Nafion/PVDF cathode MEA. For hydrophilic slurry and nanofiber cathodes with neat Nafion or Nafion/PAA fibers, low power after the carbon corrosion AST was due to greater carbon losses, cathode thinning and the collapse of cathode pores, which dominated MEA performance even though the initial cathode ECSA and mass activity were high for these two MEAs.

Platinum and platinum cobalt alloy catalysts supported on porous carbon were incorporated into electrospun nanofiber and conventional slurry cathodes and then evaluated in hydrogen/air fuel cell membraneelectrode-assemblies (MEAs) at 80 °C. Nanofiber MEAs with PtCo/C and a binder of Nafion and poly(acrylic acid) produced 40% higher power at 0.65 V and 32% higher at peak power, as compared to a slurry cathode MEA with the same catalyst and a neat Nafion binder. The power density of a PtCo/C nanofiber cathode at 0.65 V, 200 kPa absolute pressure, and a catalyst loading of 0.1 mgPt/cm 2 was 785 mW/cm 2 vs. 585 mW/cm 2 for a Pt/C nanofiber cathode MEA. Mass activities were high for the PtCo/C nanofiber cathode, 297 mA/mgPt vs. 180 mA/mgPt for a nanofiber cathode with Pt/C. After a voltage cycling carbon corrosion accelerated stress test (1,000 cycles from 1.0 to 1.5 V), the nanofiber MEAs retained 73% of its maximum power while the conventional slurry cathode MEA retained only 59%.

MEAs with nanofiber mat electrodes containing Pt/C catalyst and Nafion binder were fabricated and evaluated. The electrodes were prepared by electrospinning a solution of catalyst powder, salt-form Nafion (with Na+, Li+, or Cs+ as the sulfonic acid counterion), and a carrier polymer of either polyethylene oxide or poly(acrylic acid). The carrier polymer was extracted prior to MEA testing by a hot water soaking step. The resulting fibers were 15-17% porous, with a core-shell-like morphology (a coating of primarily Nafion on the fiber surface). MEAs with anode/cathode catalyst loadings of 0.1 mgPt/cm2 each and a Nafion 211 membrane produced high power at both high and low relative humidity (RH) conditions in H2/air fuel cell tests, 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 kPaabs. The presence of nm-size pores within the fibers trapped water via capillary condensation during low RH feed gas testing, thus maintaining a high proton conductivity of the Nafion binder in the anode and cathode while minimizing/eliminating ionic isolation of catalyst particles in low water content, poorly conductive binder.