■ Topic : Solid Acid, Its Potential in Fuel Cell Application, and Phase Behavior of a Novel Compound
■ Speaker : Chatr Panithipongwut
■ Affiliation : Chualongkorn University
■ Date : Mar 25 (Wed), 16:00~
■ Venue : Seminar Room 2 (Room No. 2429)
■ Abstract : Several solid acids undergo polymorphic phase transitions at elevated temperatures, 100-300 °C, to their respective superprotonic phases of which proton conductivities increase by 3-4 orders of magnitude. This transition behavior and the transition temperature range along with ease of fabrication and handling make solid acids a potential alternative to the current fuel cell electrolytes. Previously, many simple solid acids were synthesized and characterized, especially to investigate the crystal structures associating with the increases in conductivities and the proton transfer mechanisms. The current studies, nonetheless, focus on syntheses and characterizations of new complex solid acids to understand transition mechanisms and roles of dopant. The system selected to present here is the Rb3H(SO4)2-RbHSO4 pseudo-binary system  of which high-temperature behavior has been examined using high-temperature X-ray diffraction, impedance spectroscopy, and thermal analysis. The finding reveals that Rb3H(SO4)2 does not simply transform to its high-temperature structure, but disproportionates to Rb2SO4 and the high-temperature phase of the new compound Rb5H3(SO4)4, which is a composition between Rb3H(SO4)2 and RbHSO4. Furthermore, it is shown that in fact Rb3H(SO4)2 reacts with RbHSO4 at a temperature between room temperature and 140 °C, giving the low-temperature phase of Rb5H3(SO4)4 before this compound transforms to its high-temperature phase at 185 °C. The continuing works include identifying the crystal structure of the high-temperature Rb5H3(SO4)4, exploring the behavior of the compound at higher temperatures, and completing the phase diagram of Rb3H(SO4)2-RbHSO4 system as well as moving on to other complex solid acids.
 C. Panithipongwut, S.M. Haile,
Solid State Ionics 213 (2012) 53.
 C. Panithipongwut, S.M. Haile, Solid State Ionics 213 (2012) 53.