Effect of Electrolyte Surface Microstructure on Interfacial Polarization Resistances of Solid Oxide Fuel Cell Cathodes

doi:10.15541/jim20140160

Abstract

Abstract:

The interfacial polarization resistance (R_c) associated with cathode in solid oxide fuel cell (SOFC) is affected by the electrolyte conductivity. In this work, the effect of electrolyte surface microstructure on the cathode performance was demonstrated by analyzing electrochemical impedance spectra of symmetric cells which consist of porous (La_0.85Sr_0.15)_0.9MnO_3-_δ (LSM) and La_0.6Sr_0.4Fe_0.8Co_0.2O_3-_δ (LSCF) electrodes with Sm_0.2Ce_0.8O_2-_δ (SDC) electrolytes. The SDC electrolytes exhibited different surface microstructures, i.e. different grain sizes and grain boundary densities as a result of various sintering conditions. SEM was used to investigate the SDC surface microstructure parameters and the relationships between these parameters and the polarization resistance ware discussed. It is found that R_cis greatly affected by the SDC surface microstructures and decreases with the decrease of grain size, or the increase of grain-boundary density. Moreover, it is demonstrated that the oxygen ion transfer is significantly increased by decreasing grain size for the oxygen reduction at the LSM cathode.

Key words: cathode, interfacial polarization resistance, grain-boundary density, electrolyte microstructure, solidoxide fuel cell

CLC Number:

TQ174

SONG Shu-Xiang, WANG Yun-Long, XIA Chang-Rong. Effect of Electrolyte Surface Microstructure on Interfacial Polarization Resistances of Solid Oxide Fuel Cell Cathodes[J]. Journal of Inorganic Materials, 2014, 29(12): 1253-1256.

Figures/Tables 5

Fig. 1 Surface morphologies of SDC electrolytes sintered under different conditions (a) 1350℃/5 h; (b) 1450℃/5 h; (c)1550℃/5 h; (d)1550℃/15 h

Table 1 Average grain size, grain-boundary density, conductivity at 750℃ for SDC electrolytes sintered at different conditions

Sintering condition	1350℃/5 h	1450℃/5 h	1550℃/5 h	1550℃/15 h
Conductivity/ (S?cm^-1)	0.0380	0.0355	0.0348	0.0305
Grain size/μm	0.83	1.51	4.89	7.49
Grain-boundary density/μm^-1	1.20	0.66	0.23	0.18

Fig. 2 Electro-performance of the symmetrical cells with single phase LSM as the electrodes (a) Impedance spectrum measured at 750℃; (b) Equivalent circuit used to fit the impedance

Fig. 3 Interfacial polarization resistances versus grain size (a) Resistance at various temperatures; (b) Resistance at 750℃ for the high and low frequency arcs

Fig. 4 Electro-performance of symmetrical cells with single phase LSCF as the electrodes (a-b) Impedance spectra at 750℃ for SDC sintered at different conditions and (c) Rc versus grain size of SDC

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