Iron-based Perovskite Material La0.25M0.75FeO3-δ (M=Ca, Sr, Ba): Preparation and Performance as Cathode for Solid Oxide Fuel Cells

doi:10.15541/jim20240500

Abstract

Abstract:

The performance of solid oxide fuel cell (SOFC) is mainly constrained by the cathode's oxygen reduction reaction (ORR), which is crucial for overall cell efficiency. In this study, La_0.25M_0.75FeO_3-_δ (M=Ca, Sr, Ba, abbreviated as LCF, LSF, LBF) perovskite cathodes were synthesized based on tolerance factors and structural design, and effects of Ba, Sr, and Ca doping on electrochemical performance was examined. Different alkaline earth elements have a significant effect on the crystal structure. LBF is Pm-3m cubic phase, LSF is R-3c rhombohedral phase, and LCF is a composite phase of P21ma orthogonal and Pcmn rhombohedral. Difference of crystal structure also leads to various thermal expansion coefficient (TEC) and electrical conductivity. LCF possesses the smallest TEC (1.38×10^-5 K^-1), while LSF possesses the highest conductivity, which reaches 404.4 S·cm^-1 at 550 ℃. All three Fe-based cathodes exhibit excellent stability in air and CO₂ atmospheres, as well as chemical compatibility with electrolytes. In addition, different alkaline earth elements also affect catalytic activity of the material. LSF and LBF have low area specific resistance (ASR). At 800 ℃, their ASR are only 0.022 and 0.027 Ω·cm², which are better than the 0.351 Ω·cm² of LCF. The higher oxygen reduction activity is attributed to its crystal structure, oxygen adsorption and dissociation ability. In view of the advantages and disadvantages of Ba²⁺, Sr²⁺ and Ca²⁺ in cathode performance, medium/high-entropy design can be effectively introduced in A-site in the future to give full play to their respective advantages to obtain SOFC cathode with excellent comprehensive performance.

Key words: solid oxide fuel cell, perovskite, cobalt-free cathode, electrochemical performance

CLC Number:

TM911

YANG Hengqiang, ZHANG Xinyue, MA Yichu, ZHOU Qingjun. Iron-based Perovskite Material La_0.25M_0.75FeO_3-_δ (M=Ca, Sr, Ba): Preparation and Performance as Cathode for Solid Oxide Fuel Cells[J]. Journal of Inorganic Materials, 2025, 40(12): 1365-1372.

Figures/Tables 8

Fig. 1 (a) XRD patterns and (b-d) Rietveld refined XRD patterns of LBF, LSF and LCF samples

Table 1 Lattice parameters of LBF, LSF and LCF powders

Sample	Space group	a/Å	b/Å	c/Å	Volume/Å³	R_wp/%	GOF
LBF	Pm-3m	3.964	3.964	3.964	62.264	8.59	1.28
LSF	R-3c	5.480	5.480	13.428	349.249	8.12	1.62
LCF-1	P21ma	5.450	11.265	5.560	341.347	14.33	2.12
LCF-2	Pcmn	5.425	14.775	5.593	448.293	14.33	2.12

Fig. 2 Stability of LBF, LSF and LCF samples and their compatibility with GDC (a-c) XRD patterns of (a) LBF, (b) LSF and (c) LCF calcined in 5% CO2-air at 800 ℃ for 10 h, and calcined in air at 800 ℃ for 72 h; (d) Thermal expansion curves of LBF, LSF and LCF; (e) XRD patterns of LBF-GDC, LSF-GDC and LCF-GDC calcined at 1100 ℃ for 5 h

Fig. 3 XPS spectra of LBF, LSF and LCF (a-c) O1s and (d-f) Fe2p of (a, d) LBF, (b, e) LSF and (c, f) LCF

Table 2 Binding energies of O1s and Fe2p and the ionic area content percentages in LBF, LSF and LCF samples

Sample	O_ad/eV	O_lat/eV	Fe³⁺/eV	Fe⁴⁺/eV
LBF	531.77(70.40%)	529.13(29.60%)	710.25; 723.25(55.85%)	712.69; 725.57(44.15%)
LSF	531.87(71.67%)	529.03(28.33%)	710.29; 723.59(62.71%)	712.12; 724.95(37.29%)
LCF	531.50(66.93%)	529.15(33.07%)	710.18; 723.17(45.36%)	712.15; 725.40(54.64%)

Fig. 4 Conductivities and Arrhenius curves of LBF, LSF and LCF (a) Temperature dependence of electrical conductivity; (b) Arrhenius curves

Fig. 5 Impedance of symmetric cells for LBF, LSF and LCF (a-c) EIS results of LBF, LSF and LCF cathodes at different temperatures; (d) Equivalent circuit; (e) Corresponding Arrhenius plots of the ASR; (f, g) DRT curves of EIS at 600 and 700 ℃

Fig. 6 Performance of the single cell using LSF cathode (a) I-V and I-P curves at 600-800 ℃; (b) Cross-sectional SEM image of the LSF and GDC after performance test

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