Next Generation Superprotonic Solid Acids

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARYThe goal of this research is to advance the science of solid acid proton conductors, where solid acid compounds can be described generically as MnHm(XO4)p with M = alkali metal, alkaline earth, or even rare earth, and X = S, P, Si, Se, As or Ge. A major part of the effort will focus on exploratory synthesis to develop new compounds with the desired characteristics of insolubility in water, stability against chemical reduction, and high (or super-) protonic conductivity even at room temperature. A superprotonic conductor exhibits rapid reorientation of XO4 anion groups as the mechanism of proton transport. Hydrothermal and related synthesis routes will be utilized to prepare hypothesized phosphate and silicate analogs to known sulfate (and selenate) solid acids with high conductivity. The decomposition/dehydration behavior of new and known superprotonic solid acids will further be determined via thermal gravimetric analysis under high (up to 0.6 atm) water partial pressures to temperatures of 300 °C. From these studies not only can fuel cell operation conditions be established, but also fundamental thermodynamic quantities (formation enthalpies and entropies). These terms can, in turn, be used to systematically evaluate the role of hydrogen bond formation on compound stabilization. Simultaneously, a novel electrochemical test configuration will be employed to probe electrochemical reaction pathways on metal electrodes used with solid acid fuel cells, with the ultimate goal of eliminating Pt. NON-TECHNICAL SUMMARYThe goals of this research are to (1) develop new proton conducting materials for fuel cell applications and (2) understand fuel cell reaction pathways so as to ultimately eliminate precious metals from fuel cell designs. The significance of successful disovery of electrolyte materials with the characteristics targetted in this work on energy technologies cannot be overstated. Solid acid fuel cells (SAFCs) operate in a temperature regime (150-300°C) that is unexplored and as such create opportunities for new modes of fuel cell operation. Ultimately, Pt-free fuel cell systems without the extreme temperatures of solid oxide fuel cells may be possible. Commercial development of SAFCs is moving rapidly (under the auspices of the spin-off Superprotonic, Inc.), however, next-generation, truly robust materials are required in order to fully realize the potential benefits of solid acid electrolytes. In addition to new materials development, these comprehensive studies will help to clarify the chemical and structural bases for superprotonic transitions and the overall role of hydrogen bonds in stabilizing compounds. The breadth of tools to be utilized, the relative ease with which the materials can be synthesized, and the high level of public interest in energy technologies, renders this an ideal system for training future leaders in materials chemistry and its application to societally relevant problems. Such training will be specifically achieved through participation in this research by undegraduate, graduate and post-doctoral researchers, as well as through outreach activities for K-12 students.