[phas-dept] Apr. 30 (Thursday) 4 PM - Physics and Astronomy Colloquium

[Heungman Park]

Spring 2017 Colloquium

Department of Physics & Astronomy

April 20, Thursday, 4-5 PM in Science Building 127

(coffee and cookies will be served at 3:50 PM)

Solid State Physics

Phosphate-based solid acids as functional fuel cell electrolytes
Dr. Cristian Botez

University of Texas at El Paso


[https://lh4.googleusercontent.com/FGDg_k_xfH4vV6fJICcCVu70IJ1g2Q0DtGgqtrM5bIOetcHAdajwGy-BKPwQzpfqM9JlobKEdltXRNVBrx_dnnq6xmXfZqYIPD2EaA1Xw8fn-uAt7G5R8TOKdjYIbeJ3dRIIrYOE]

Dr. Cristian Botez earned BS (1991) in Engineering Physics from the University of Bucharest, Romania, MS (1999) and Ph.D. (2002) degrees in Physics from the University of Missouri. He worked as a postdoctoral researcher at Brookhaven National Laboratory. In 2005, Dr. Botez began his appointment as an assistant professor at the University of Texas at El Paso, where he is currently doing research in solid state physics. More information about Dr. Botez and his research can be found at

https://academics.utep.edu/Default.aspx?tabid=18629


Abstract: Understanding and eventually controlling the atomic-level structures and mechanisms responsible for the macroscopic behavior of functional compounds is one of the main goals of modern materials research. Achieving this goal might enable the “rational design” of functional materials, a dramatic improvement over the current trial-and-error approach. In this context, I will present our experimental work aimed at uncovering the crystal structures and conduction mechanisms responsible for the abrupt, three-order-of-magnitude proton conductivity increase exhibited by certain phosphate-based solid acids above a temperature threshold. This so-called superprotonic behavior allows CsH2PO4 and RbH2PO4 to function as fuel cell electrolytes at temperatures between 150 °C and 350 °C: a remarkable application that attracted significant interest. Yet, prior to our investigations, the nature of the microscopic modifications responsible for the above-mentioned proton conductivity jump had been under debate for almost two decades. We have used laboratory and synchrotron x-rays to carry out time- and temperature-resolved diffraction experiments on samples kept under both ambient- and high-pressure. Our results unequivocally demonstrate that the observed proton conductivity enhancement is due to a monoclinic-to-cubic polymorphic phase transition, and not to chemical decomposition effects induced by dehydration, as previously proposed. In addition, our data show that the cubic modifications of CsH2PO4 and RbH2PO4 are isomorphic, a clear indication that a general (non-cation-specific) proton conduction mechanism is at work in the superprotonic phases of these compounds.

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