Oxygen Exchange Kinetics of (Bi,Sr)(Co,Fe)O_3-δThin-Film Microelectrodes

Abstract

Mixed-conducting (Bi,Sr)(Co,Fe)O 3-δ (BiSCF) perovskites are considered to be promising candidates for the application as cathode materials in solid oxide fuel cells (SOFCs) operating in the intermediate-temperature regime. In this study, the effective rate constants of surface oxygen exchange of both Co-free and Co-containing BiSCF perovskites were measured by electrochemical impedance spectroscopy (EIS) on geometrically well-defined thin-film microelectrodes on Y 2 O 3 -doped ZrO 2 (YSZ) single crystal substrates. Oxygen exchange rate constants in the range of 3.0 × 10 −7 cm s −1 to 2.4 × 10 −6 cm s −1 at 750 • C and an oxygen partial pressure p(O 2 ) of 0.2 bar were obtained, which are higher in particular for Co-containing BiSCF than those of La-containing perovskites. The interrelation between the oxygen exchange rate constant and other material properties was investigated to derive information about the oxygen exchange mechanism. A correlation between the oxygen exchange rate constant and the ionic conductivity from thin-film electrochemical polarization experiments and measurements on bulk samples in the range of 1.4 × 10 −2 S cm −1 to 2.6 × 10 −1 S cm −1 at 650 • C was observed that is similar to the correlation found for Ba-containing perovskites. This suggests oxygen vacancy diffusion to be involved in the rate-determining step (rds) of the oxygen exchange reaction.

Materials Search of Perovskite Cathode in SOFC by Statistical Analysis

“…Such correlation, however, is not valid for the whole of the materials. These are also consistent with the previous studies (13,15,19).…”

Thermodynamic stability of stoichiometric LaFeO3 and BiFeO3: a hybrid DFT study

“…Bismuth ferrate BiFeO3 (BFO) is base for the perovskite solid solutions Bi1-xSrxFeO3-δ and Bi1-xSrxFe1-yCoy O3-δ , which were recently also proposed as promising cathodes for SOFCs. [2][3][4][5] In the same time BFO continues to attract considerable attention due to its multiferroic properties 6 at ambient conditions. It has also been found that photocatalytic 7 and photovoltaic 8 properties of BFO are enhanced due to its ferroelectricity.…”

(Bi,Sr) (Fe1−x,Mx)O3−δ (M = Co, Ni and Mn) Cathode Materials with Mixed Electro-Ionic Conductivity

“…To enhance the conductivity and ORR capability, Co [18,21], Ca [19] and Mn [20] were doped in the BSF perovskite structure. Besides, a higher oxygen exchange rate of pore-free BSF was reported, even higher than that of (La,Sr)FeO 3−δ .…”

“…A new cathode material based on (Bi,Sr)FeO 3 (BSF) was synthesized and reported with interesting conductivity [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. To enhance the conductivity and ORR capability, Co [ 18 , 21 ], Ca [ 19 ] and Mn [ 20 ] were doped in the BSF perovskite structure. Besides, a higher oxygen exchange rate of pore-free BSF was reported, even higher than that of (La,Sr)FeO 3−δ .…”

“…Besides, a higher oxygen exchange rate of pore-free BSF was reported, even higher than that of (La,Sr)FeO 3−δ . The literature [ 21 ] concludes that the BSF structure with large ionic sizes of Bi 3+ and Sr 2+ at A-site, and Fe 3+ in B-site are basically performed favorable oxygen ion conductivity and matched CTE to the Y-doped ZrO 2 electrolyte. The substitution of A and B sites in the perovskite structure also affect the oxygen stoichiometry.…”