Polymer electrolyte membranes that conduct hydroxide ions have potential use in fuel cells. A variety of polystyrenebased quaternary ammonium hydroxides have been reported as anion exchange fuel cell membranes. However, the hydrolytic stability and conductivity of the commercially available membranes are not adequate to meet the requirements of fuel cell applications. When compared with commercially available membranes, polystyrene-imidazolium alkaline membrane electrolytes are more stable and more highly conducting. At the time of this reporting, this has been the first such usage for imidazolium-based polymeric materials for fuel cells.
Imidazolium salts are known to be electrochemically stable over wide potential ranges. By controlling the relative ratio of imidazolium groups in polystyrene-imidazolium salts, their physiochemical properties could be modulated.
Alkaline anion exchange membranes based on polystyrene-imidazolium hydroxide materials have been developed. The first step was to synthesize the poly(styrene-co-(1-((4-vinyl)methyl)-3- methylimidazolium) chloride through a free-radical polymerization. Casting of this material followed by in situ treatment of the membranes with sodium hydroxide solutions provided the corresponding hydroxide salts. Various ratios of the monomers 4-chloromoethylvinylbenzine (CMVB) and vinylbenzine (VB) provided various compositions of the polymer. The preferred material, due to the relative ease of casting the film, and its relatively low hygroscopic nature, was a 2:1 ratio of CMVB to VB.
Testing confirmed that at room temperature, the new membranes outperformed commercially available membranes by a large margin. With fuel cells now in use at NASA and in transportation, and with defense potential, any improvement to fuel cell efficiency is a significant development.
This work was done by Sri R. Narayan and Shiao-Ping S. Yen of Caltech, and Prakash V. Reddy and Nanditha Nair of Missouri University of Science and Technology for NASA’s Jet Propulsion Laboratory. NPO-46457
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Imidazolium-Based Polymeric Materials as Alkaline Anion-Exchange Fuel Cell Membranes
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Overview
The document titled "Imidazolium-Based Polymeric Materials as Alkaline Anion-Exchange Fuel Cell Membranes" presents research conducted by scientists at NASA's Jet Propulsion Laboratory and Missouri University of Science and Technology. It focuses on the development of novel polymeric materials that serve as alkaline anion-exchange membranes, which are crucial for the advancement of polymer electrolyte fuel cells.
The research highlights the synthesis of polymers using varying ratios of 4-chloromoethylvinylbenzene (CMVB) and vinylbenzene (VB). The specific ratios explored were 1:1, 1:2, and 2:1, with the 2:1 composition emerging as the most favorable due to its ease of film casting and lower hygroscopic nature. These polymers were subsequently treated with sodium hydroxide to produce hydroxide salts, enhancing their functionality as membranes.
Conductivity measurements were a key focus of the study, comparing the in-house prepared membranes with commercial membranes from Tokuyama Corporation. The results indicated that the polystyrene-imidazolium membrane exhibited a conductivity of 0.059 S/cm, which is significantly higher—17 times—than that of the commercial AMS membrane, which had a conductivity of only 0.003 S/cm. This substantial difference underscores the potential of the newly developed membranes for improved performance in fuel cell applications.
The document emphasizes the stability and hydroxide ion conductivity of the imidazolium-based membranes, positioning them as superior candidates for use in alkaline fuel cells. The research is part of a broader effort to enhance energy solutions through innovative materials, with implications for various technological and commercial applications.
Overall, the findings suggest that imidazolium-based polymeric materials could play a pivotal role in the future of fuel cell technology, offering enhanced performance characteristics that could lead to more efficient and effective energy systems. The research was conducted under the auspices of NASA, highlighting the agency's commitment to advancing scientific knowledge and technology in the field of energy.
