Abstract
The first-order transition from low to superprotonic conducting phase (at 119 < T sp < 145 °C) of a solid solution of CsHSO4 and CsH2PO4 [Cs3(HSO4)2(H2PO4)] was carefully examined by using modulated and conventional differential scanning calorimetric, simultaneous thermogravimetric and differential scanning calorimetric, simultaneous thermogravimetric and mass spectroscopy, impedance spectroscopy, and temperature evolution of X-ray diffraction and scanning electron microscopy. Our results show evidence that at this temperature, the endothermic anomaly associated with the physical transformation is, instead, the response of a chemical-surface thermal decomposition. One of its products is water: part of it is evaporated and part is strongly bonded to the other decomposition products. Given that these are of polymeric nature, they constitute a host matrix that contains liquid water regions. Therefore, as part of liquid water dissolves a superficial portion of salt (providing protons), this system behaves in similar manner to a polymer electrolyte membrane (located over the salt surface) where the proton transport mechanism might include the vehicle type, using H3O+ as a charge carrier. A discussion that favors the non-existence of the superprotonic conducting phase of CsH2PO4 is also presented.
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Acknowledgements
We are grateful to Professor Bengt-Erik Mellander (Department of Applied Physics, Chalmers University of Technology, Gothenburg-Sweden) for the useful discussions about the design of the project that generated, as a product, this contribution.
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Ortiz, E., Piñeres, I. & León, C. On the low- to high proton-conducting transformation of a CsHSO4–CsH2PO4 solid solution and its parents. J Therm Anal Calorim 126, 407–419 (2016). https://doi.org/10.1007/s10973-016-5474-y
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DOI: https://doi.org/10.1007/s10973-016-5474-y