EN21.04.05 : Influence of Compressive and Tensile Strain on the Proton-Polaron Driven Proton Transport in Ceramic Electrolyte Membranes

5:00 PM–7:00 PM Apr 4, 2018 (America - Denver)

PCC North, 300 Level, Exhibit Hall C-E

Artur Braun1 Qianli Chen1

1, Empa. Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, , Switzerland

High temperature fuel cells (SOFC) operate at temperatures from 500°C to 1000°C. The electrolytes of these electrochemcial energy converters are thin ceramic metal oxide membranes (zirconia or cerium oxides) membranes in which oxygen ions and vacancies are the electric charge carriers. Their mobility is thermally activated which mandates the high temperature. Under humid atmosphere, numerous metal oxides show proton conductivity at a temperature considerably lower than for oxygen ion conductivity. Yet, fuel cell devleopers hope for substantial improvement of the conductivity to make such electrolyte membranes before they are fit for deployment in SOFC.
We have recently shown that the protons in such ceramic membranes couple to the phonons generated by thermal excitation in a way that they form new quasi-particles which follow characteristically the Holstein polaron concept <!--[endif]---->1, 2. With a suite of analytical techniques we could identify which particular phonon modes propell the protons through the electrolyte membrane during SOFC operation. As these phonon modes scale characteristically with the lattice constant of the proton conductor, we could show that external lattice strain considerable affects the proton conductivity. We have demonstrated this expermentally for compressive strain. Extrapolation of the activation energy to tensile strain in ultrathin membranes suggests that epitxial films with the desirable orientation of lattice planes could further lower the activation energy for proton transport not too distant from the ambient temperature <!--[endif]---->3, 4.<!--![endif]----><!--![endif]---->

1. A. Braun and Q. Chen: Experimental neutron scattering evidence for proton polaron in hydrated metal oxide proton conductors. Nature Communications 8, 15830 (2017).
2. A.L. Samgin: Lattice-assisted proton motion in perovskite oxides. Solid State Ionics 136, 291 (2000).
3. Q. Chen, T.-W. Huang, M. Baldini, A. Hushur, V. Pomjakushin, S. Clark, W.L. Mao, M.H. Manghnani, A. Braun and T. Graule: Effect of Compressive Strain on the Raman Modes of the Dry and Hydrated BaCe0.8Y0.2O3Proton Conductor. The Journal of Physical Chemistry C 115, 24021 (2011).
4. Q.L. Chen, A. Braun, A. Ovalle, C.D. Savaniu, T. Graule and N. Bagdassarov: Hydrostatic pressure decreases the proton mobility in the hydrated BaZr0.9Y0.1O3 proton conductor. Applied Physics Letters 97, 041902 (2010).