Defect Chemistry and Electrochemical Properties of BaZrO₃ Heavily Doped with Fe

Abstract

To explore a novel concept of bi-percolating mixed conductor of proton and hole for a cathode material of solid oxide fuel cell (SOFC), we have studied a BaZrO3 heavily doped with Fe. The oxygen non-stoichiometry and electrical conductivity of BaZr1- xFexO3-δ with various x values have been prepared and examined by a thermogravimetry and ac two-probe impedance method as a function of temperature and Po2. At high oxygen partial pressures,the dominant charge carrier is estimated as holes, and the hole conductivity that exhibits a nonlinearity against the Fe concentration and marked increase at the percolation threshold is governed by a bond-percolation of Fe-O network. The effect of hydration on the electrical conductivity suggests that BaZr1-xFexO3-δ exhibits a mixed protonic-electronic conducting behavior in humidified conditions at lower temperature range.

Polaronic contributions to oxidation and hole conductivity in acceptor-dopedBaZrO3

“…22 Hole conductivity has been studied experimentally in Fe-doped BaZrO 3 . 60 The analysis presented in these studies suggests that the barrier for long range polaron diffusion is about 1.2 eV at low iron concentrations, where the migration barrier for the self-trapped hole is between 0.4 eV and 0.6 eV and the remaining part is due to ironpolaron association. At higher concentrations on the other hand, the iron ions form a percolation network, which allows polarons to move more freely due to smaller migration barriers in the range of 0 eV to 0.3 eV.…”

Material Discovery and Design Principles for Stable, High Activity Perovskite Cathodes for Solid Oxide Fuel Cells

“…The materials LBF [42] , BFN [43] , and PBFO [44] but with additional dopant elements that we predict will render these new promising materials more stable and/or more conductive than their undoped counterparts. [42,43,[60][61][62][63] All of the materials contained in Figure 3 are intentionally chosen to be metallic, n-type conductors at ORR operating conditions. In addition to the materials in Figure 3, we have made an additional plot of k* versus O p-band center that also includes p-type conductors (see Figure S1 of Section 8 of the SI).…”

Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

“…In the search for higher‐performing PCFC cathode materials, it may prove beneficial to partially substitute the B‐site with redox‐inactive cations such as Zn, Y, and Zr. However, their fraction should not exceed about 30%; otherwise the electronic conductivity becomes too small (e.g., Ba(Zr,Pr)O 3‐ δ , Ba(Zr,Mn)O 3‐ δ , and Ba(Zr,Fe)O 3‐ δ solid solution series). Based on earlier results, the perovskites chosen for this study mainly contain iron on the B‐site and are rich in alkaline earth cations on the A‐site.…”