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Platinum electrocatalysts supported on high surface area and Vulcan carbon blacks (Pt/HSC, Pt/V) were characterized in rotating disk electrode (RDE) setups for electrochemical area (ECA) and oxygen reduction reaction (ORR) area specific activity (SA) and mass specific activity (MA) at 0.9 V. Films fabricated using several ink formulations and film-drying techniques were characterized for a statistically significant number of independent samples. The highest quality Pt/HSC films exhibited MA 870 ± 91 mA/mgPt and SA 864 ± 56 µA/cm²Pt while Pt/V had MA 706 ± 42 mA/mgpt and SA 1120 ± 70 µA/cm²pt when measured in 0.1 M HClO4, 20 mV/s, 100 kPa O2 and 23 ± 2°C. An enhancement factor of 2.8 in the measured SA was observable on eliminating Nafion ionomer and employing extremely thin, uniform films (~4.5 µg/cm²Pt) of Pt/HSC. The ECA for Pt/HSC (99 ± 7 m²/gPt) and Pt/V (65 ± 5 m/gPt) were statistically invariant and insensitive to film uniformity/thickness/fabrication technique; accordingly, enhancements in MA are wholly attributable to increases in SA. impedance measurements coupled with scanning electron microscopy were used to de-convolute the losses within the catalyst layer and ascribed to the catalyst layer resistance, oxygen diffusion, and sulfonate anion adsorption/blocking. The ramifications of these results for proton exchange membrane fuel cells have also been examined. [ABSTRACT FROM AUTHOR]

Using cyclic voltammetry as a quick ex situ screening tool, the impact of the extracted solution and the individual leachable constituents from prospective balance of plant component materials on the performance and recoverability of the platinum catalyst were evaluated. Taking an extract from Zytel HTN51G35HSLR (polyphthalamide) as an example, the major leachable organic components are caprolactam and 1,6-hexanediol. While these organic compounds by themselves do poison the Pt catalyst to some extent, such influence is mostly recoverable by means of potential holding and potential cycling. The extracted solution, however, shows a more drastic poisoning effect and it was not recoverable. Therefore, the non-recoverable poisoning effect observed for the extracted solution is not from the two organic species studied. This demonstrates the complexity of such a contaminant study. Inorganic compounds that are known poisons (like sulfur) even in very low concentration may have a more dominant effect on the Pt catalyst and the recoverability. [ABSTRACT FROM AUTHOR]

Platinum-based catalytic materials have received significant attention, particularly in the shape and size control of faceted materials for . More recently, there has been a rapid increase in the number of reports of successful preparations in this field; however, a fundamental understanding of controlled growth towards catalytic material design is essential for future implementation and broad application. In this review, we provide an overview of the recent findings reported since 2009, focusing on methods for shape control as well as the effects of exposed surface facets on select . Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Membrane-electrode interfacial resistance and deterioration over time was investigated using a series of sulfonated poly (arylene ether) membranes and Nafion. Dimensional mismatch due to swelling/deswelling, wetting/adhesion and water transport mismatch between the electrodes and the polymer electrolyte membrane were all investigated as potential root causes of membrane- electrode interfacial resistance and durability. The data presented from a large number of diverse polymers strongly support dimensional mismatch as the primary cause of interfacial failure. Extended direct methanol fuel cell life tests, up to 3000 h, showed high performance and good durability for membranes with low water uptake. Polymer electrolyte membranes with ∼35 vol % water uptake were the best in this study. However, a low water uptake coating layer greatly improved the performance and durability of a higher water uptake polymer electrolyte membrane. This study demonstrates the potential importance of the membrane-electrode interface on fuel cell performance and durability and provides a basis for implementing polymer electrolyte membranes effectively in high performance polymer electrolyte fuel cells (PEFCs). [ABSTRACT FROM AUTHOR]

The impact of the membrane-electrode interface on fuel cell durability was investigated in polymer electrolyte fuel cells (PEFCs). Cells using disulfonated poly (arylene ether) copolymer (BPSH) membranes exhibited greater performance loss than a cell using Nafion after 700 h of direct methanol fuel cell (DMFC) testing. Additionally, the performance loss and cell resistance within the BPSH family of copolymers increased with increasing degree of disulfonation. Membrane characterization using H NMR, potentiometric titration, intrinsic viscosity, water uptake, and proton conductivity showed minimal impact from chemical/physical changes. Fuel cell performance degradation scaled well with initial membrane-electrode interfacial resistance, suggesting that the membrane-electrode interface was an important contributor to DMFC durability. These results are of particular interest for alternative proton exchange membranes where interfacial compatibility with electrodes is a critical, unresolved issue. [ABSTRACT FROM AUTHOR]

Direct methanol fuel cell (DMFC) performance of sulfonated (arylene ether ether nitrile) (m-SPAEEN) copolymers is reported. Low water absorption of m-SPAEEN copolymers enabled increased proton-exchange concentrations in the hydrated polymer matrix, resulting in more desirable membrane properties for DMFC applications. The membrane electrode assemblies (MEAs) using m-SPAEENs showed improved cell properties which could not be obtained by the MEAs using sulfonated polysulfone or Nafion. The DMFC performance using an optimized m-SPAEEN membrane exceeded those of the other membrane systems. For example, 265 mA/cm2 was obtained for an MEA using m-SPAEEN, compared to 230 and 195 mA/cm2 for MEAs using sulfonated polysulfone and Nafion membranes, respectively, at 0.5 V, measured under identical conditions. In the comparative evaluations, membrane thickness was selected to give methanol crossover limiting currents that were similar for each of the polymer electrolyte types. Stable cell performance during extended operation (>100 h) suggested that interfacial compatibility between m-SPAEEN and Nafion-bonded electrodes was good. [ABSTRACT FROM AUTHOR]