Development of new proton conducting chalcogenide based materials for use in intermediate temperature fuel cells

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2005-01-01
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Martindale, Chad
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Steve W. Martin
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Materials Science and Engineering
Materials engineers create new materials and improve existing materials. Everything is limited by the materials that are used to produce it. Materials engineers understand the relationship between the properties of a material and its internal structure — from the macro level down to the atomic level. The better the materials, the better the end result — it’s as simple as that.
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As the world endures higher oil and gas prices, more people in the scientific and industrial communities have turned to fuel cells as a possible alternative. The intermediate temperature fuel cell operating between 100°C and 400°C offers the ability to lower costs through higher efficiencies, cheaper catalysts, and reduced need for expensive scrubbing equipment to remove CO and S impurities. However, there are currently very few known solid-state proton conductors with high conductivities over this temperature range;This work covers the development of two new groups of chalcogenide materials sought to have high proton conductivity over the intermediate temperature range. Anhydrous protonated thioborates based on meta-thioboric acid (HBS 2)3 was the first group of materials explored. Various materials were added to increase the glass forming ability (GeS2, B 2S3) and conductivity (SnI2, GeI2, GeI4). The systems were studied using IR, Raman, NMR, and impedance spectroscopy. A 47% GeI2, + HBS2 sample achieved the highest conductivity of ~10-6 (O CM)-1;The second group of materials was created from the reaction of an alkali metal hydrosulfide (MSH) and metal oxide powder (GeO2, SiO 2, TiO2) in deionized water. The reaction produced a hydrated amorphous material of the general formula MxRSx(OH) 4-x·yH2O;These materials were found to have a conductivity of 10-3 to 10-2 (O cm)-1 over a 100 to 270°C temperature range. The conducting species, mechanism, reaction, and thermal stability were studied by SEM, 1H and 133Cs NMR, and deuterium exchange. The alkali thio-metallates are promising candidates for use in intermediate fuel cells due to their high conductivity and good thermal stability.

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Sat Jan 01 00:00:00 UTC 2005