Vertically Oriented Polymer Electrolyte Nanofiber Catalyst Support for Thin Film Proton‐Exchange Membrane Fuel Cell Electrodes

Abstract

Polymer electrolyte fuel cells are highly efficient and offer high power density, but high precious‐metal loading and degradation of carbon‐supported platinum (Pt) catalysts still hinder commercialization. Ionomer binders in conventional electrodes also introduce undesirable, high oxygen‐transport resistance. This paper presents an alternative composite Nafion nanofiber catalyst support electrode, in which the nanofibers provide robust internal proton transport to a conformal Pt catalyst coating without impeding O2 transport. The high‐surface‐area electrodes are prepared by solution casting ionomer onto a sacrificial template to simultaneously fabricate the nanofibers and the membrane. Thin Pt films are deposited on the nanofibers using either physical vapor deposition or chemical vapor deposition. The electrochemical characterization of the nanofiber electrodes demonstrates the high current density and specific activity of this nanofiber approach relative to prior electrodes fabricated by depositing Pt directly onto other Nafion surfaces.

Differences in the Electrochemical Performance of Pt-Based Catalysts Used for Polymer Electrolyte Membrane Fuel Cells in Liquid Half- and Full-Cells

“…Pt-deposited on vertically aligned Nafion nanofibers (Pt/ VANFs) has been proposed on the cathode catalyst layer. 447 VANFs with a high roughness factor was utilized as a catalyst support without the use of a carbon support. The VANFs were prepared using a solution casting method with a sacrificial template.…”

Ionic Conductivity over Metal/Water Interfaces in Ionomer‐Free Fuel Cell Electrodes

“…One such example is 3 M Company's Nanostructured Thin Film (NSTF) electrode, which has Pt or Pt alloy catalyst deposited onto high surface area organic whiskers. Similar structures were adopted by Jiang et al ., using titanium nitride nanorod arrays as the support and platinum‐palladium‐cobalt alloy as the ionomer‐free thin film catalyst, and Komoni Babu et al ., using vertically oriented Nafion® nanofiber as the thin film Pt catalyst support. Although this kind of electrode structure has no ionomer binder, its ionic conductivity has been shown to be sufficient under high RH conditions .…”

Vertically Aligned Titanium Nitride Nanorod Arrays as Supports of Platinum–Palladium–Cobalt Catalysts for Thin‐Film Proton Exchange Membrane Fuel Cell Electrodes

“…[2][3][4][5][6] For the commercial application of fuel cells, the development of an effective membrane electrode assembly (MEA) is significant, because fuel cell performance not only relates to the intrinsic catalytic activity of the as-prepared catalysts, but also depends on the structure of the catalystl ayer formed by thesee lectrocatalysts. [8] The reasons for loss of the electrochemically active surfacea rea (ECSA) of Pt/C can be summarized as follows:1 )loss of platinum nanoparticles from the carbon support, resulting in corrosion of the carbon support;2 )platinum nanoparticle dissolution and Ostwaldr ipening;a nd 3) platinum-nanoparticle aggregation driven by surface-energy minimization. [8] The reasons for loss of the electrochemically active surfacea rea (ECSA) of Pt/C can be summarized as follows:1 )loss of platinum nanoparticles from the carbon support, resulting in corrosion of the carbon support;2 )platinum nanoparticle dissolution and Ostwaldr ipening;a nd 3) platinum-nanoparticle aggregation driven by surface-energy minimization.…”

“…[7] Ac onventional catalytic layer is establishedb yc arbon-supported Ptbased catalysts (Pt/C) and ionomer,w hich resultsi nt he poor durability and high cost of fuel cells. [8] The reasons for loss of the electrochemically active surfacea rea (ECSA) of Pt/C can be summarized as follows:1 )loss of platinum nanoparticles from the carbon support, resulting in corrosion of the carbon support;2 )platinum nanoparticle dissolution and Ostwaldr ipening;a nd 3) platinum-nanoparticle aggregation driven by surface-energy minimization. [2] Although some new oxygen reduction reaction( ORR) electrocatalysts with high activity and high durability have been developed, the most widely used catalyst supports are still high-surface-area carbon materials, which cause as ignificant degradation of as ingle cell or stack performance for carbon corrosion.…”

“…In the proposed electrode, withouta dditional ionomer in the cathode, the water film possibly acted as the proton-conduction pathway.T he proposed benefits of this approacha re as follows:1 )the removal of ionomers or bindersf or better fuel transport;2 )elimination of carbon supports;3 )a thin-film, extended-surface PtPdCo catalyst;and 4) low-tortuosity pathways for transportation. [8] Titanium dioxide NR arrays weref irst hydrothermally grown on carbon paper and then annealed in ammonia gas to convert them into TiNN Rs. The ternary PtPdCo catalysts were sputtered onto the surfaceo fT iN NRsb yu sing physicalv apor deposition (PVD), and annealed in a5 %H 2 /Ar atmosphere to enhancethe crystallization of the catalysts.…”