Preparation and Oxygen-reduction Mechanism Investigation of Nanostructure LSCF-SDC Composite Cathodes

doi:10.15541/jim20160330

Abstract

Abstract:

The solid oxide fuel cell nanometer composite cathodes were prepared by infiltration of La_0.6Sr_0.4Co_0.8Fe_0.2O_3-_δ(LSCF) precursor solution into porous Ce_0.8Sm_0.2O_1.9(SDC) scaffolds followed by being calcined at 800℃for 4 h. The composition and the microstructure of the cathodes were analysed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Average particle size of the LSCF phase is about 50 nm after being calcined at 800℃ for 4 h. The reduction reaction mechanism of O₂ in the LSCF/SDC cathodes and the influence of LSCF loadings on the cathode properties were studied in terms of frequency response, electrode resistance and reaction order at different oxygen partial pressures p(O₂). Three elementary steps are considered to be involved in the cathodes reaction: (1) absorption and dissociation of molecular O₂; (2) oxygen ion conduction in the bulk cathode; (3) oxygen ion transfer at the cathode-electrolyte interface. The oxygen ion conduction in the bulk cathode is found to be the rate-determining steps in the nano-sized LSCF-SDC composite cathode. The reduction reaction mechanism of O₂ in the cathodes is similar to the samples with different LSCF loadings. The polar resistance of the cathode firstly decreases and then increases with increasing the LSCF loadings. The cathode polar resistance reaches the lowest when the volume fraction of LSCF loadings is 16.5vol%.

Key words: solid oxide fuel cell, infiltration, cathode, nano-structure, oxygen reduction

CLC Number:

TM911

XU Hong-Mei, ZHANG Hua, LI Heng, JIAN Yao-Yong, XIE Wu, WANG Yi-Ping, XU Ming-Ze. Preparation and Oxygen-reduction Mechanism Investigation of Nanostructure LSCF-SDC Composite Cathodes[J]. Journal of Inorganic Materials, 2017, 32(4): 379-385.

Figures/Tables 9

Fig. 1 Cross-sectional SEM image of the tri-layer structures of porous∣dense∣porous SDC sintered at 1450℃ for 4 h

Fig. 2 XRD pattern of the LSCF-SDC nanometer composite cathode heat-treated at 800℃ for 4 h

Fig. 3 SEM images of LSCF-SDC composite cathodes prepared by infiltration different LSCF loadings(a) 8.5vol%; (b) 12.3vol%; (c) 16.5vol%; (d) 20.9vol%; (e) 23.2vol%

Fig. 4 Impedance spectra at 873 K of the composite cathodes infiltrated with 12.3vol% LSCF

Fig. 5 Impedance spectra of cathodes infiltrated with 12.3vol% LSCF as a function of oxygen partial pressure (a) and equivalent circuit (b)

Fig. 6 Po2 dependence of ASR for LSCF-SDC nano-scaled composite cathodes

Table 1 Reaction orders “n” of cathodes infiltrated with different LSCF loadings

Loadings /vol%	n
Loadings /vol%	R_H	R_M	R_L	R_p
8.5	0.06	0.22	0.52	0.2524
12.3	0.01	0.25	0.55	0.2630
16.5	0.01	0.27	0.57	0.2900
20.9	0.02	0.26	0.58	0.2903
23.2	0.01	0.21	0.49	0.2482

Fig. 7 AC impedance spectra measured at 873 K for LSCF- SDC composite cathodes with different LSCF loadings

Fig. 8 LSCF loadings dependence of total cathode polarization resistance (Rp), high-frequency polarization resistance (RH), medium-frequency polarization resistance (RM) and low-frequency polarization resistance (RL) in the impedance spectra of LSCF- SDC composite cathodes

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