Nafion

About: Nafion is a research topic. Over the lifetime, 9110 publications have been published within this topic receiving 320865 citations.

Durability of PEFCs at High Humidity Conditions

Abstract: This work addresses issues of long-term durability of hydrogen-air polymer electrolyte fuel cells (PEFCs). The chromium in a Pt 3 Cr binary alloy catalyst has been found to migrate from cathode to anode during the course of life testing when operating within the oversaturated, or high-humidity, gas feed regime (one or both inlet feeds with a dew point equal to or higher than cell operating temperature) above 1 A/cm 2 current density. Other major factors such as membrane degradation, dissolution of catalyst-layer recast ionomer, catalyst oxidation, and catalyst agglomeration/growth have been identified as simultaneous, gradual processes that can lead to long-term PEFC failure. In situ cyclic voltammetry measurement of electrochemically active catalyst surface area shows a continuous decrease, revealing that catalyst agglomeration and/or growth may be a major cause of membrane electrode assembly degradation during middle-term life tests (i.e., operation times up to about 2000 h) under high-humidity conditions. Membrane and/or recast ionomer degradation was confirmed by the presence of fluoride and sulfate anions in the cathode outlet water. Scanning and transmission electron microscopy observation of a tested MEA suggest the loss of carbon-supported catalyst clusters and possible dissolution of recast Nafion ionomer.

Water-sorption and transport properties of Nafion 117 H

Abstract: The density and dimensional changes of Nafion 117 H have been measured as a function of the water content. Swelling of Nafion commences at N (≡ mol ratio water to hydrogen ion) ∼ 1.9. Some anisotropy of dimensional changes was observed. Water-sorption isotherms obey Henry's Law with a nonzero intercept indicating some water retention. The diffusion coefficient of water in Nafion and the electrical conductivity of Nafion are strong functions of the water content. The latter is exploited for the development of a humidity sensor. © 1993 John Wiley & Sons, Inc.

Aromatic Poly(ether ketone)s with Pendant Sulfonic Acid Phenyl Groups Prepared by a Mild Sulfonation Method for Proton Exchange Membranes

Abstract: The sulfonation selectivity of seven poly(ether ether ketone)s (PEEKs) was investigated, and several possessed targeted single- or double-substituted sites per repeated unit on pendant phenyl groups via the postsulfonation approach. The presence of the various pendant groups enabled postsulfonation to occur under mild reaction conditions, in much shorter times than required for the sulfonation of commercial PEEK. A series of poly(ether ketone)s (PEKs) with ion exchange capacity of 2.23−0.84 mequiv/g could be realized by controlling the length of unsulfonated segments of both homopolymers and copolymers. These side-group sulfonation polymers had excellent mechanical properties, good thermal and oxidative stability, and good dimensional stability in hot water. The methanol permeability values of Me-SPEEKK, Me-SPEEKDK, Ph-SPEEKK, and Ph-SPEEKDK at room temperature were in the range 3.31 × 10-7−9.55 × 10-8 cm2/s, which is several times lower than that of Nafion 117. Me-SPEEKK and Ph-SPEEKK also exhibited high...