Structural And Proton-Dynamics Studies Of The Superprotonic Phase Stability In Phosphate Solid Acids
Abstract
We propose to use x-ray diffraction, neutron scattering, and ac-impedance spectroscopy to study the dehydration and chemical decomposition of phosphate solid acids, and then use this knowledge to improve the stability of their high temperature phases. Our first objective is to determine the microscopic (crystal structure and proton dynamics) and macroscopic (proton conductivity) modifications that accompany the dehydration and chemical decomposition of the superprotonic phases. We will start with CsH2PO4, a solid acid whose high-temperature superprotonic phase is well characterized structurally, by following the evolution of its crystal structure, chemical composition, and proton conductivity upon the relaxation of the high-pressure or high-humidity conditions that prevent superprotonic phase dehydration. We will then carry out similar measurements under ambient pressure and humidity conditions, at the superprotonic transition temperature. Our preliminary data suggest that dehydration might only be partial, so that even after long-term exposure to ambient conditions we expect the sample to be a mixture of superprotonic CsH2PO4 and cesium pyrophosphate (Cs2H2P2O7). We will investigate the thermal stability and proton conductivity of the mixture and determine how they compare to those of superprotonic CsH2PO4. Eventually, we plan similar experiments on RbH2PO4, once the crystal structure of the superprotonic phase of this solid acid is completely elucidated. Our second objective is to synthesize composite materials based on phosphate solid acids and highly dispersed oxides, and to investigate the microscopic structures, proton conduction mechanisms and thermal stability of their superprotonic phases. Our initial approach will be to determine the temperature dependence of the proton conductivity, microscopic structure and proton dynamics, as well as the thermal stability of composites based on CsH2PO4 or RbH2PO4 and different types of silica (SO2). We will investigate the effect of silica content and grain size on the above-mentioned macro and microscopic properties, as well as on the thermal stability of the composite at temperatures where the solid acid component is superprotonic. The main projected outcome of the proposed research is new fundamental knowledge that could lead to overcoming the instability of the superprotonic phases of phosphate solid acids, which is the last barrier to progress toward uncovering their highly-efficient proton transport mechanisms. This is important to the DoD mission, as it will increase the ability to realize the full potential of these materials as new intermediate-temperature fuel cell electrolytes. Our institution’s research programs in functional materials will be strengthened and become more sustainable, enhancing our chance to expand our participation in DoD-sponsored research. Our students will greatly benefit by participating in research important to the defense mission and by receiving unique training opportunities at National Laboratory Synchrotron X-Ray and Neutron Facilities. UTEP – Structural and proton-dynamics studies of superprotonic phase stability in phosphate solid acids
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 11, 2016
- Source ID
- W911NF1510494
Entities
People
- Christian Botez
Organizations
- Army Contracting Command
- Office of the Secretary of Defense
- University of Texas at El Paso