Article pubs.acs.org/cm
First-Principles Insight into the Hydration Ability and Proton Conduction of the Solid State Proton Conductor, Y and Sn Co-Doped BaZrO3 James A. Dawson,*,† James A. Miller,‡ and Isao Tanaka† †
Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, U.K.
‡
ABSTRACT: Y and Sn co-doped BaZrO3 (BZSY) has recently been shown to exhibit superior hydration ability and improved power output performance compared to those of the traditional solid oxide fuel cell (SOFC) electrolyte, Y-doped BaZrO3. The fact that BZSY is also chemically stable in both H2O and CO2 atmospheres further illustrates the great potential for BZSY as a future electrolyte material in protonconducting SOFCs. In this work, we conducted comprehensive density functional theory calculations to analyze the energetics of hydration and proton migration in BZSY. The energy of hydration is calculated at four different locations in the cell to better assess the specific contributions of each defect type. For all locations tested, hydration is found to be strongly exothermic and is most favorable when Y ions are in the vicinity. The calculated energies of hydration (−1.72 to −1.11 eV) are significantly lower than any previously calculated for acceptordoped BaZrO3-based electrolytes. Nudged elastic band calculations confirm low proton reorientation energies (0.08−0.24 eV) and low intraoctahedral hopping energies (0.21−0.41 eV) and that these diffusion barriers are at minimum when the proton is migrating to an oxygen ion in a YO6 octahedron. Our results show how the synergy of the Sn and Y dopant ions produces the excellent hydration and conduction performance of BZSY and fully support its potential application in next-generation SOFCs. CO2,10,11 which is a major concern for practical usage where long-term operation is a requirement.1 Conversely, acceptordoped BaZrO3 is far more chemically stable12,13 but has low rates of grain growth, which results in high grain boundary concentrations that are damaging to the overall conductivity.12 When substitution at the B-site tetravalent cation with a trivalent dopant cation occurs, the basicity of the system increases and oxygen vacancies are formed to charge compensate. This makes the material more reactive to water and allows the following hydration reaction to occur:
1. INTRODUCTION The requirement for electrolytes for solid oxide fuel cells (SOFCs) with low operating temperatures is essential in reducing the operation cost and degradation of traditional oxygen ion conductors. Conventional SOFCs are based on yttria-stabilized zirconia (YSZ) and normally operate above 800 °C.1,2 With a decrease in the operating temperatures of SOFCs to
