High Stability/Catalytic Activity Co-based Perovskite as SOFC Anode: In-situ Preparation by Fuel Reducing Method

doi:10.15541/jim20240025

Abstract

Abstract:

Taking inspiration from the in-situ reduction technique employed for exsolved nano-metal as anodes in solid oxide fuel cells (SOFCs), this study utilized Sr₂V_0.1Co_0.9MoO₆, which was synthesized in an ambient air environment, with perovskites of other phases to co-fire with the electrolyte under atmospheric conditions for direct fabrication of a single cell. By this way, the procedure of subjecting the cell to harsh preparative conditions in a reducing/inert atmosphere to prevent its anodic oxidation can be circumvented. After preparation of the anode precursor on the electrolyte sheet, we adopted a simple process of in-situ reduction at 750 ℃ for 4 h on the fuel side to achieve formation of a pure phase Sr₂V_0.1Co_0.9MoO₆ (R-SVCMO) as anode. The results demonstrate a significant reduction in the activation energy of R-SVCMO, accompanied by an increase in conductivity from 2.7 to 21.6 S•cm^-1. Moreover, when employing R-SVCMO as anode in a single cell with H₂ and wet CH₄ as fuel gases, the maximum power density (P_max) at 850 ℃ can reach up to 862 and 514 mW·cm^-2, respectively, showcasing exceptional catalytic performance. The anodes before and after reduction exhibit average thermal expansion coefficient (TEC) of 1.15×10^-5 and 1.23×10^-5 K^-1, respectively, within the temperature range of 100-850 ℃, comparable to those observed in conventional SOFC electrolytes. Therefore, the reduction process does not induce any volumetric changes in the anode layer, significantly enhancing its structural stability. Meanwhile, degradation rate of only 0.13% is occurred. It is worth noting that this R-SVCMO synthesis method can result in remarkable long-term stability and high catalytic activity as an anode material. The obtained R-SVCMO can achieve a 60% catalytic efficiency for wet CH₄ and last for 1450 h. Based on this R-SVCMO, the single cell can maintain stability for 450 h at 0.7 V. In conclusion, this study demonstrates an effective way of employing an in-situ fuel reduction method to prepare a single cell with exceptional electrochemical performance and structural stability.

Key words: solid oxide fuel cell, fuel reducing method, high stable anode, methane fuel

CLC Number:

TM911

PAN Jianlong, MA Guanjun, SONG Lemei, HUAN Yu, WEI Tao. High Stability/Catalytic Activity Co-based Perovskite as SOFC Anode: In-situ Preparation by Fuel Reducing Method[J]. Journal of Inorganic Materials, 2024, 39(8): 911-919.

Figures/Tables 18

Fig. 1 XRD patterns of SCMO and SVCMO before and after calcination under different conditions (a) SCMO powders before and after H2 reduction at 750 ℃ for 4 h; (b) SVCMO powders before and after H2 reduction at different temperatures for 4 and 72 h; (c) Enlarged patterns of 2θ=26°-30° in (b)

Table 1 Lattice parameters of SCMO and R-SVCMO obtained by XRD Rietveld refinement

Parameter	SCMO	R-SVCMO
Space group	I4/m	I4/m
a=b/Å	5.6374	5.6218
c/Å	7.9128	7.8823
α/(º)	90	90
β/(º)	90	90
γ/(º)	90	90
Sr-O/Å	2.8130	2.8071
Co-O/Å	2.0765	2.0532
V-O/Å	—	1.7758
Mo-O/Å	1.8945	1.9191

Fig. 2 Microstructure of R-SVCMO sample (a) TEM image; (b) HRTEM image and (c) corresponding SAED pattern; (d) STEM image and corresponding EDX elemental mappings

Fig. 3 Thermal expansion of different materials (a) Thermal expansion (ΔL/L0) curves of electrolyte LSGM, anodes SCMO and R-SVCMO from room temperature to 850 ℃; (b) TEC curves of SCMO, SVCMO and R-SVCMO in the range of 100−850 ℃; (c) Comparison of TEC of SCMO, SVCMO and R-SVCMO with conventional electrolytes and other perovskite anode materials[7⇓-9,11,14 -15,17,26]

Fig. 4 XPS spectra for SCMO and R-SVCMO (a) Co2p, (b) Mo3d, (d) O1s XPS spectra for SCMO and R-SVCMO; (c) V2p XPS spectrum for R-SVCMO

Table 2 Area content percentages of Mo and Co elements in different valences, and different O types for SCMO and R-SVCMO samples based on XPS data

Sample	Valence ratio/%
	Mo		O			Co
	Mo⁵⁺	Mo⁶⁺	O_latt.	O_ad.	H₂O	Co²⁺	Co³⁺
SCMO	34.1	65.9	31.4	60.5	8.2	74.0	26.0
R-SVCMO	58.5	41.5	31.1	65.5	3.4	62.9	37.1

Fig. 5 Conductivity and H2-TPR curves for SCMO and R-SVCMO in testing H2 (a) Temperature dependence of conductivity curves; (b) Arrhenius curves; (c) H2-TPR curves; Colorful figures are available on website

Fig. 6 Electrochemical performance of single cells with SCMO and R-SVCMO as anode materials (a, b) I-V-P curves for single cells with (a) SCMO and (b) R-SVCMO as anodes obtained under H2 at different temperatures; (c, d) Electrochemical Impedance spectra for (c) SCMO and (d) R-SVCMO single cells under H2 at different temperatures; (e) Durability of single cells with SCMO and R-SVCMO as anodes under 0.7 V at 750 ℃; Colorful figures are available on website

Fig. 7 Electrochemical performance of single cells or symmetric cells with SCMO and R-SVCMO as anodes or symmetric electrodes (a) EIS and (b) DRT spectra of SCMO and R-SVCMO symmetric cells under H2 at different temperatures; (c) I-V-P curves and (d) DRT spectra of R-SVCMO single cell under different H2 partial pressures at 750 ℃; Colorful figures are available on website

Fig. 8 Electrochemical performance of single cells with SCMO and R-SVCMO as anodes in CH4 atmosphere (a, b) I-V-P curves of (a) SCMO and (b) R-SVCMO based SOFC with humidified CH4 as fuel gas at different temperatures; (c, d) EIS spectra of (c) SCMO and (d) R-SVCMO based SOFC in humidified CH4 at different temperatures; (e) CH4 conversion rate of R-SVCMO catalyst for CH4 reforming and R-SVCMO based single cell working at 0.7 V under humidified CH4 at 750 ℃ as a function of testing time; Colorful figures are available on website

Fig. S1 ietveld refined XRD patterns of (a) SCMO and (b) R-SVCMO

Fig. S2 XRD patterns of SVCMO and D-SVCMO composite anodes

Fig. S3 O1s XPS spectra for SVCMO and SCMO samples

Fig. S4 XRD patterns of SVCMO and LSGM after co-firing in air for 5 h

Fig. S5 XRD patterns of SVCMO and SDC after co-firing in air for 5 h

Fig. S6 XRD pattern of LSCF

Fig. S7 SEM image of the single cell with R-SVCMO anode

Fig. S8 Equivalent circuit for the fitting EIS of different cells

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