Sintering Effects on Proton Conductivity of Ta-Doped Ba[sub 2](CaNb)[sub 2]O[sub 6] and its Reactivity with SOFC Cathodes

Abstract

The effect of preparation temperature on electrical conductivity of Ba 2 ͑Ca 0.75 Nb 0.59 Ta 0.66 ͒O 6−␦ , Ba 2 ͑Ca 0.75 Nb 0.66 Ta 0.59 ͒O 6−␦ , and Ba 2 ͑Ca 0.79 Nb 0.66 Ta 0.55 ͒O 6−␦ was investigated in air and humidified N 2 and O 2 . Powder X-ray diffraction ͑PXRD͒ showed the formation of double-perovskite-type structure. Among the compounds investigated, Ba 2 ͑Ca 0.79 Nb 0.66 Ta 0.55 ͒O 6−␦ showed the highest proton conductivity of 3.7 and 5.3 ϫ 10 −4 S/cm at 550°C in wet N 2 , respectively, for a 1400 and 1500°C sintered sample, while no change in conductivity was observed in air. PXRD showed that Ba 2 ͑Ca 0.79 Nb 0.66 Ta 0.55 ͒O 6−␦ is stable against chemical reaction with La 0.8 Sr 0.2 MnO 3 ͑LSM͒ and Sm 0.5 Sr 0.5 CoO 3 ͑SSC͒ electrodes at 800 and 1000°C. Chemical compatibility was further confirmed by energy-dispersive X-ray ͑EDX͒ analysis. The ac impedance employing Pt, LSM, and SSC electrodes on Ba 2 ͑Ca 0.79 Nb 0.66 Ta 0.55 ͒O 6−␦ showed that the area specific polarization resistance ͑ASPR͒ decreased in wet atmospheres compared to that of air. Unlike the oxide ion system, the ASPR was found to be much higher for the presently investigated proton system, suggesting that proton conductivity at the electrolyte and electrode interfaces or water effusion through microspores appears to control the ASPR. Among the electrodes tested, based on ac impedance studies, the LSM appears to be a better electrode compared to SSC for Ta-doped Ba 3 Ca 1+x Nb 2−x O 9−␦ electrolyte.

Electrochemical NOx reduction on an LSM/CGO symmetric cell modified by NOx adsorbents

“…[26][27][28][29][30] Most of the studies on LSM indicate that LSM does not react with the Ba-containing materials. [31][32][33] However, considering the polarization effect, particularly the strong corrosivity of nitrate under polarization and heating, [34][35][36] the reaction between the electrode materials and the Ba compounds is possible. Traulsen et al 12 reported a distinct change in the microstructure on the LSM/CGO cell stacks inltrated with BaO aer the electrochemical test and attributed it to the reaction between BaO and LSM/CGO under the test conditions.…”

Electrical conductivity and chemical stability of perovskite-type BaCe0.8-x Ti x Y0.2O3-δ

“…6). The existence of proton conduction in perovskite-type structures has been well-established in the literature [31][32][33][34][35][36][37][38][39][40][41][52][53][54][55][56][57][58][59][60][61][62][63][64]; therefore, it will not be elaborated in this work. We have investigated the chemical stability of BCTY in CO 2 .…”

“…During the heating and cooling runs, the Arrhenius plots fall on the same line, which verifies the equilibrium conductivity behavior. Several investigators have determined that the increase in electrical conductivity of acceptor-doped perovskites (e.g., ABO 3 A = Sr, Ba; B = Zr, Ce) and related ordered double perovskite-type Ba 3 CaNb 2 O 9 structures in wet atmospheres is primarily a result of proton conduction[52][53][54][55][56][57][58][59][60][61][62][63][64]. Among the samples studied, 5 mol% Ti-doped BaCe 0.75 Ti 0.05 Y 0.2 O 3-δ showed the highest electrical conductivity of 2.52×10 −3 S cm −1 at 650°C in H 2 +3% H 2 O (…”

Electrical transport properties of In-doped Ce1−xInxO2−δ (x = 0.1; 0.2)

“…35 Also, we noticed a similar effect for Ta-doped double perovskite-type Ba 3 CaNb 2 O 9 and In-doped CeO 2 . 27, 30 Hence, only data points in the frequency range from 0.01 Hz to 1 MHz were reported. In general, one would anticipate a minimum of three contributions, for polycrystalline electrolytes, due to bulk, grain-boundary and electrode polarization over the wide range of the investigated frequency.…”