Synthesis, Structure, Chemical Stability, and Electrical Properties of Nb-, Zr-, and Nb-Codoped BaCeO₃ Perovskites

Abstract

We report the effect of donor-doped perovskite-type BaCeO(3) on the chemical stability in CO(2) and boiling H(2)O and electrical transport properties in various gas atmospheres that include ambient air, N(2), H(2), and wet and dry H(2). Formation of perovskite-like BaCe(1-x)Nb(x)O(3±δ) and BaCe(0.9-x)Zr(x)Nb(0.1)O(3±δ) (x = 0.1; 0.2) was confirmed using powder X-ray diffraction (XRD) and electron diffraction (ED). The lattice constant was found to decrease with increasing Nb in BaCe(1-x)Nb(x)O(3±δ), which is consistent with Shannon's ionic radius trend. Like BaCeO(3), BaCe(1-x)Nb(x)O(3±δ) was found to be chemically unstable in 50% CO(2) at 700 °C, while Zr doping for Ce improves the structural stability of BaCe(1-x)Nb(x)O(3±δ). AC impedance spectroscopy was used to estimate electrical conductivity, and it was found to vary with the atmospheric conditions and showed mixed ionic and electronic conduction in H(2)-containing atmosphere. Arrhenius-like behavior was observed for BaCe(0.9-x)Zr(x)Nb(0.1)O(3±δ) at 400-700 °C, while Zr-free BaCe(1-x)Nb(x)O(3±δ) exhibits non-Arrhenius behavior at the same temperature range. Among the perovskite-type oxides investigated in the present work, BaCe(0.8)Zr(0.1)Nb(0.1)O(3±δ) showed the highest bulk electrical conductivity of 1.3 × 10(-3) S cm(-1) in wet H(2) at 500 °C, which is comparable to CO(2) and H(2)O unstable high-temperature Y-doped BaCeO(3) proton conductors.

Effect of Zr substitution for Ce in BaCe0.8Gd0.15Pr0.05O3−δ on the chemical stability in CO2 and water, and electrical conductivity

“…27,[39][40][41] Very recently, we demonstrated that Gd+Pr co-doped BCs (BCGP) could achieve electrical conductivities comparable to those of Y-doped BCs, but their stability remained poor under CO 2 , as with the majority of doped BCs. 42,43 Moreover, Gd+Pr have higher electronegativity and ionic radius characteristics than those of Y+Yb (electronegativity of Gd : Pr is 1.2 : 1.13 against the 1.22 : 1.1 of Y : Yb, and ionic radius in the octahedral coordination 93.8 : 99 pm versus 90 : 86 pm respectively). Since Zr is known to increase the stability as in the case of Y doping where only after doping with Zr they achieved significant stability, it is imperative that we continue our pursuit of a chemically stable solid electrolyte for SOFCs without surrendering much proton conductivity by systematically introducing Zr in BCGP.…”

Synthesis and characterisation of ceramic proton conducting perovskite-type multi-element-doped Ba0.5Sr0.5Ce1−−−Zr Gd Y O3−δ (0 < x < 0.5; y = 0, 0.1, 0.15; z = 0.1, 0.2)

“…BaCeO 3 and BaZrO 3 have been extensively studied as electrolytes for proton-conducting solid oxide fuel cells (H-SOFCs) owing to their high H + conductivity [3]. However, BaCeO 3 decompose under water vapor and CO 2 conditions (Equation 1 and 2) [4][5][6][7][8][9]. BaCeO 3 is thermodynamically unstable under CO 2 atmosphere below ~ 1040 o C and under water vapour (P H2O = 0:5 atm) below ~ 404 o C (equation 1) [7][8][9].…”

Effect of Sintering Temperature on Microstructure, Chemical Stability, and Electrical Properties of Transition Metal or Yb-Doped BaZr0.1Ce0.7Y0.1M0.1O3−δ (M = Fe, Ni, Co, and Yb)

“…Acceptor doping of the perovskite creates oxide ion vacancies (V •• o ) in the perovskite structure. Incorporation of H 2 O into these (V •• o ) sites will create mobile proton charge carriers (H + ) (Iwahara et al, 1981). These physical properties make them attractive membranes for proton conducting solid oxide fuel cells (H-SOFCs), H 2 pumps, gas separation, and steam electrolyzers (Schober, 2003).…”

“…To overcome the lower ionic conductivity, acceptor dopants have been introduced to the B-site in order to increase the V •• o and subsequent proton concentration upon H 2 O incorporation into the oxide ion vacancies through reaction (1) (Iwahara et al, 1981;Knight, 1999;Kreuer, 1999;Shimura et al, 2005;Azimova and McIntosh, 2009;Ricote and Bonanos, 2010;Zhao et al, 2010),…”