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

Martindale, Chad
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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.

Materials science and engineering