Thermodynamic, thermomechanical, and electrochemical evaluation of CsHSO4

A thermodynamic analysis of CsHSO4 in oxygen and hydrogen atmospheres has been carried out. In an oxygen atmosphere, the phase relationship for the dehydration of CsHSO4 as a function of H2O partial pressure was established. It is concluded that CsHSO4 is stable in a humidified oxygen atmosphere, pH2O = 0.03 atm, up to 170 jC. However, in hydrogen atmospheres, it was affirmed that CsHSO4 is reduced to H2S and Cs2SO4. Electromotive force (EMF) measurements in a humidified oxygen concentration cell, pH2O = 0.03 atm confirmed the ionic nature of the charge-carrying species. Upon thermal cycling, the voltage obtained from the high temperature phase (T= 149 jC) remained unchanged for over 85 h of measurement. The volume change upon transformation to the superprotonic phase, as directly measured by high temperature X-ray powder diffraction, is + 0.54%. These results demonstrate not only the stability of CsHSO4 in oxygen but also the viability of solid acid-based electrochemical devices that would likely be subjected to thermal cycling during operation. D 2004 Elsevier B.V. All rights reserved. PACS: 84.60.Dn(Electrochemical conversion and storage: electrochemical cells and batteries; fuel cells); 66.10.Ed(Ionic conduction); 82.60.Hc(Chemical equilibria and equilibrium constants)