This chapter gives a brief but broad overview of membrane electrode assemblies (MEAs) used in hydrogen fueled proton exchange membrane fuel cells for automotive applications. MEA construction and subcomponent functional properties are defined, followed by performance, cost, and durability targets for high volume applications. Key performance and durability issues are identified and related to subcomponent technology gaps and needs. Demonstrating fully integrated MEAs having the requisite durability and power requirements at sufficiently low precious group metal catalyst loadings which can be fabricated using six sigma or higher quality manufacturing remains a goal for robust automotive applications.

The nanoscale morphology of highly active Pt3Ni7 nanostructured thin film fuel cell catalysts is linked with catalyst surface area and activity following catalyst pretreatments, conditioning and potential cycling. The significant role of fuel cell conditioning on the structure and composition of these extended surface catalysts is demonstrated by high resolution imaging, elemental mapping and tomography. The dissolution of Ni during fuel cell conditioning leads to highly complex, porous structures which were visualized in 3D by electron tomography. Quantification of the rendered surfaces following catalyst pretreatment, conditioning, and cycling shows the important role pore structure plays in surface area, activity, and durability.

Scanning transmission X-ray microscopy (STXM) has been applied to characterize nano structured thin film (NSTF) catalysts implemented as electrode materials in proton-exchange-membrane (PEM) fuel cells. STXM is used to study all chemical constituents at various stages in the fabrication process, from the perylene red (PR149) starting material, through the formation of the uncoated perylene whiskers, their coated form with Pt-based catalyst, and toward the NSTF anode fully integrated into the catalyst coated membrane (CCM). CCM samples were examined prior to operational testing and after several different accelerated testing protocols: start-up/shut-down (SU/SD), and reversal tests. It was found that, while the perylene support material is present in the pre-test samples, it was completely absent in the post-test samples. We attribute this loss of perylene material to the presence of cracks in the catalyst combined with intensive hydrogenation processes happening at the anode during operation. Despite the loss of the perylene support, the platinum shells forming the NSTF anode catalyst layer performed well during the tests.

Journal Article Fine Tuning Highly Active Pt3Ni7 Nanostructured Thin Films for Fuel Cell Cathodes Get access DA Cullen, DA Cullen Materials Science & Technology Division, ORNL, Oak Ridge, TN 37831-6064 USA Search for other works by this author on: Oxford Academic Google Scholar KL More, KL More Center for Nanophase Materials Sciences, ORNL, Oak Ridge, TN 37831-6064 USA Search for other works by this author on: Oxford Academic Google Scholar M Lopez-Haro, M Lopez-Haro CEA-INAC/UJF-Grenoble 1 UMR-E, SP2M, LEMMA, Minatec, 38054 Grenoble Cedex 9, France Search for other works by this author on: Oxford Academic Google Scholar P Bayle-Guillemaud, P Bayle-Guillemaud CEA-INAC/UJF-Grenoble 1 UMR-E, SP2M, LEMMA, Minatec, 38054 Grenoble Cedex 9, France Search for other works by this author on: Oxford Academic Google Scholar L Guetaz, L Guetaz CEA, LITEN, 38054 Grenoble Cedex 9, France Search for other works by this author on: Oxford Academic Google Scholar MK Debe, MK Debe Fuel Cell Components Program, 3M Co., St. Paul, Minnesota 55144-1000 USA Search for other works by this author on: Oxford Academic Google Scholar DF van der Vliet, DF van der Vliet Fuel Cell Components Program, 3M Co., St. Paul, Minnesota 55144-1000 USA Search for other works by this author on: Oxford Academic Google Scholar AJ Steinbach AJ Steinbach Fuel Cell Components Program, 3M Co., St. Paul, Minnesota 55144-1000 USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 20, Issue S3, 1 August 2014, Pages 418–419, https://doi.org/10.1017/S143192761400381X Published: 27 August 2014

The electrochemical behavior of Pt1-xMnx (0.1 < x < 0.8) catalysts prepared by magnetron sputtering were studied extensively using the rotating disk electrode technique, electron microprobe, X-ray photoelectron spectroscopy and X-ray diffraction. The data suggests that Mn forms an oxide layer at the surface of the catalyst upon contact with air. Mn is preferentially drawn out of the intermixed catalyst into the oxide layer, depleting the core of Mn content. Without significant amounts of Mn present at the core of the catalyst, de-alloying reactions have less effect on the electrochemically active surface area compared to the case of Pt1-xNix, for example. High and low Mn content alloys have about the same Pt-area specific current densities, j(specific), so it is likely that all samples have the same catalytic surface composition, namely Pt. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.019206jes] All rights reserved.

Among the most challenging issues in technologies for electrochemical energy conversion are the insufficient activity of the catalysts for the oxygen reduction reaction, catalyst degradation and carbon-support corrosion. In an effort to address these barriers, we aimed towards carbon-free multi/bimetallic materials in the form of mesostructured thin films with tailored physical properties. We present here a new class of metallic materials with tunable near-surface composition, morphology and structure that have led to greatly improved affinity for the electrochemical reduction of oxygen. The level of activity for the oxygen reduction reaction established on mesostructured thin-film catalysts exceeds the highest value reported for bulk polycrystalline Pt bimetallic alloys, and is 20-fold more active than the present state-of-the-art Pt/C nanoscale catalyst.

This tutorial reviews the key aspects and literature to date around the nanostructured thin film (NSTF) electrocatalyst technology platform for PEM fuel cells and electrolyzers. The NSTF technology is to date the only practical example of an extended surface area catalyst shown to effectively address several of the performance, cost and durability barriers facing cathode and anode catalysts for fuel cell vehicles. The unique physical characteristics of these ultra-thin, low Pt-loaded electrodes also require alternative solutions for water management and impurity tolerance. We present an overview of the NSTF electrocatalysts' four primary differentiating features, to show how their material and basic geometric and material characteristics translate to functional performance factors. We conclude by briefly recounting the historical origins of the NSTF material with the recommendation that the field of ordered organic molecular solids represents a large opportunity for developing tailored support materials for heterogeneous catalysis.

The principal objectives of the program were development of a durable, low cost, high performance cathode electrode (catalyst and support), that is fully integrated into a fuel cell membrane electrode assembly with gas diffusion media, fabricated by high volume capable processes, and is able to meet or exceed the 2015 DOE targets. Work completed in this contract was an extension of the developments under three preceding cooperative agreements/grants Nos. DE-FC-02-97EE50473, DE-FC-99EE50582 and DE-FC36- 02AL67621 which investigated catalyzed membrane electrode assemblies for PEM fuel cells based on a fundamentally new, nanostructured thin film catalyst and support system, and demonstrated the feasibility for high volume manufacturability.

Water based electrolyzers offer a promising approach for generating hydrogen gas for renewable energy storage. 3M's nanostructured thin film (NSTF) catalyst technology platform has been shown to significantly reduce many of the performance, cost and durability barriers standing in the way of H-2/air PEM fuel cells for vehicles. In this paper we describe results from the first evaluations of low loaded NSTF catalysts in H-2/O-2 electrolyzers at Proton OnSite and Giner, Inc. Over two dozen membrane electrode assemblies comprising nine different NSTF catalyst types were tested in 11 short stack durability tests at Proton OnSite and 14 performance tests in 50 cm(2) single cells at Giner Electrochemical Systems. NSTF catalyst alloys of Pt68Co29Mn3, Pt50Ir50 and Pt50Ir25Ru25, with Pt loadings in the range of 0.1 to 0.2 mg/cm(2), were investigated for beginning-of-life performance and durability up to 4000 hours as both electrolyzer cathodes and anodes. Catalyst composition, deposition and process conditions were found to be important for meeting the performance of standard PGM blacks on electrolyzer anodes while using only 10% as much PGM catalyst. Analyses of MEA's after the durability tests by multiple techniques document changes in catalyst alloy composition, loading, crystallite structure and support stability. (C) 2012 The Electrochemical Society. [DOI:10.1149/2.065206jes] All rights reserved.

Fuel cells powered by hydrogen from secure and renewable sources are the ideal solution for non-polluting vehicles, and extensive research and development on all aspects of this technology over the past fifteen years has delivered prototype cars with impressive performances. But taking the step towards successful commercialization requires oxygen reduction electrocatalysts-crucial components at the heart of fuel cells-that meet exacting performance targets. In addition, these catalyst systems will need to be highly durable, fault-tolerant and amenable to high-volume production with high yields and exceptional quality. Not all the catalyst approaches currently being pursued will meet those demands.

The kinetics of the oxygen reduction reaction (ORR) on nanostructured thin-film (NSTF) ternary PtCoMn catalyst was investigated in 50 cm(2) proton-exchange membrane single cell fixtures. The investigation covered a wide range of oxygen partial pressures (0.2-0.5 atm), temperatures (30-90 degrees C), relative humidities (25-100%), and Pt loadings (0.05-0.2 mg cm(-2)) in the cathode catalyst. The kinetic data were derived from cell polarization curves measured during Galvanodynamic scans from near open-circuit to a high current density and back to near open-circuit. The kinetic data were correlated with a single Tafel equation and a transfer coefficient that is a function of the relative humidity (RH). The correlation indicates a 0.36 order for the O-2 partial pressure, 39.5 kJ mol(-1) activation energy for the temperature dependence, and an additional 0.9 order for RH dependence. The calculated mass activities and specific activities at 0.9 V Ohmic resistance corrected cell voltage, 1 atm H-2 and O-2 partial pressures, 80 degrees C and 100% RH agree well with the measured values of 0.13-0.25 A mg(pt)(-1) and 1.7-2.0 mA cm(pt)(-2) for the cells with different Pt loading. Published by Elsevier B.V.

In an effort to study advanced catalytic materials for the oxygen reduction reaction (ORR), a number of metallic alloy nanostructured thin film (NSTF) catalysts have been characterized by rotating disk electrode (RDE). Optimal loadings for the ORR and activity enhancement compared to conventional carbon supported nanoparticles (Pt/C) were established. The most efficient catalyst was found to be PtNi alloy with 55 wt% of Pt. The enhancement in specific activity is more than one order of magnitude, while the improvement factor in mass activity is 2.5 compared to Pt/C. Further lowering of the platinum to nickel ratio in NSTF catalysts did not lead to increased mass activity values. (C) 2011 Elsevier Ltd. All rights reserved.

Commercialization of automotive fuel cells requires current densities of 1.5 A/cm(2) above 650mV with Pt loadings of 0.125 mg(Pt)/cm(2) or less. Loss of high current density with cathode loadings below 0.2 mg(Pt)/cm(2) in Pt/C electrodes is an issue that current kinetic/transport models are reported inadequate to explain. We show that this effect is much less at a given loading with the NSTF catalyst type electrodes and explain these differences using a model based on elementary kinetic gas theory and known molecule/surface interaction mechanisms that take place in the Knudsen regime. The result is an additional pre-exponential scaling factor f(d(s)) in the Butler-Volmer equation related to a distance metric d(s) describing the catalyst surface area distribution. We approximate this distance metric by the inverse of the surface area per unit volume of the electrode and define and test two possible functional forms for f(d(s)). The preferred form is able to predict the correct heat of enthalpy for O-2 physisorption and the observed ratio of current densities at V(iR-free) = 0.7 V for NSTF compared to Pt/C dispersed electrodes in the 0.05 to 0.15 mg(Pt)/cm(2) range from published data for eleven different catalyst types and cathode loadings below 0.2 mg/cm(2). (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.032201jes]

Three Pt1-xNix catalyst compositions, with high Ni content, were sputter deposited onto 3M Company's Nano-Structured Thin Film catalyst support to determine whether the high oxygen reduction reaction (ORR) activities recently reported are a surface phenomenon or require bulk Ni dissolution. The electrodes with Pt0.27Ni0.73 throughout had the highest mass specific ORR activity of the samples tested. When some of the Pt0.27Ni0.73 was replaced with either Pt or Pt0.75Ni0.25, the mass activity dropped. These results confirmed that continuous high Ni content is required to obtain high mass activity. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3595747] All rights reserved.