Abstract
Understanding the relationship between the acceptor dopant size and proton conductivity in barium zirconate, BaZrO3, is important for maximizing efficiency in this promising fuel cell material. While proton conduction pathways with larger YZr ' and smaller AlZr ' defects have been explored, proton pathways with ScZr ', a defect of comparable size to the replaced ion, have not been investigated using centrality measures, periodic pathway searches, and kinetic Monte Carlo (KMC). Centrality measures in BaSc0.125Zr0.875O3 highlight a trapping region by ScZr ' and scattered high centrality regions on undoped planes. Connected long-range high centrality regions are found mainly in undoped planes for BaAl0.125Zr0.875O3 and in the dopant planes for BaY0.125Zr0.875O3. The best long-range proton conduction periodic pathways in AlZr ' and ScZr ' systems travel between dopant planes, while those for yttrium-doped BaZrO3 remained on dopant planes. KMC trajectories at 1000 K show long-range proton conduction barriers of 0.86 eV, 0.52 eV, and 0.25 eV for AlZr ', ScZr ', and YZr ' systems, respectively. Long-range periodic conduction highway limiting barrier averages correlate well with the connectivity of the most central regions in each system but ignore diffusion around the dopant and through other high centrality regions. BaSc0.125Zr0.875O3 shows an intermediate overall conduction barrier limited by trapping, which earlier experiments and simulations suggest that it can be mitigated with increased oxygen vacancy concentration.
Highlights
Understanding how proton long-range pathways in BaZrO3 are affected by defect size and chemistry is critical for increasing the efficiency of proton conduction
This study suggests that the conduction pathways in the scandium-doped system are significantly different from those of the yttrium-doped system and would perhaps require alternative routes to enhance conduction
kinetic Monte Carlo (KMC) trajectories showed trapping events followed by a long-range motion further away from the trap
Summary
Fuel cells have been of great interest to scientists in recent years as a cleaner energy generation alternative to combustion. Since their discovery in the early 1980s, high-temperature proton conductors, especially perovskite-type oxides, have been among the most promising materials for electrochemical applications. The proton conductivity of the perovskites can be enhanced through acceptor doping and subsequent water exposure, which both fill oxygen vacancies and introduce the protons into the system. Studies have shown that differing dopant defect sizes in perovskites lead to significantly different proton conductivities. Barium zirconate, BaZrO3, has shown one of the highest proton conductivities among perovskites and is the focus of this study.Understanding how proton long-range pathways in BaZrO3 are affected by defect size and chemistry is critical for increasing the efficiency of proton conduction. Fuel cells have been of great interest to scientists in recent years as a cleaner energy generation alternative to combustion.. Fuel cells have been of great interest to scientists in recent years as a cleaner energy generation alternative to combustion.1,2 Since their discovery in the early 1980s, high-temperature proton conductors, especially perovskite-type oxides, have been among the most promising materials for electrochemical applications.. Studies have shown that differing dopant defect sizes in perovskites lead to significantly different proton conductivities..
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