Composite cathode materials Ag-Ba0.5Sr0.5Co0.8Fe0.2O3 for solid oxide fuel cells

Michał Mosiałek,Maciej Tatko,Małgorzata Zimowska,Aneta Kędra,Magdalena Dudek,Aneta Michna

doi:10.1007/s10008-014-2457-4

Abstract

Silver-Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathodes were prepared in two ways. In the first method, Ag-BSCF composite powder was prepared in ethanol solution, where Ag nanoparticles serving as a component in the preparation of Ag-BSCF composite cathodes had been previously obtained via one-step synthesis in absolute ethanol using a neutral polymer (polyvinylpyrrolidone). To the best of our knowledge, this is the first study to use a Ag sol obtained by the above method for preparation of Ag-BSCF composite powder. Then, a paste containing this powder was screen-printed on a Sm0.2Ce0.8O1.9 electrolyte and sintered at 1,000 °C. In the second technique, an aqueous solution of AgNO3 was added to a previously sintered BSCF cathode, which was then sintered again at 800 °C. The oxygen reduction reaction at the quasi-point BSCF cathode on the Sm0.2Ce0.8O1.9 electrolyte was tested by electrochemical impedance spectroscopy at different oxygen concentrations in three electrode setup. The continuous decrease of polarization resistance was observed under polarization −0.5 V at 600 °C. The comparative studies of both obtained composite Ag-BSCF materials were performed in hydrogen-oxygen IT-SOFC involving samaria-doped ceria as an electrolyte and Ni-Gd0.2Ce0.8O1.9 anode. In both cases, the addition of silver to the cathode caused an increase in current and power density compared with an IT-SOFC built with the same components but involving a monophase BSFC cathode material.

Highlights

Nowadays, efforts in the domain of solid oxide fuel cells (SOFCs) are focused on devices capable of operating within an intermediate temperature (IT) range (500–700 °C)
The method of nitrate decomposition was applied for this purpose: 0.05 mol dm−3 of AgNO3 solution was added by drops, using a suction pipette accurate to 0.01 ml, and poured into the porous BSCF cathode layer placed on a heated hot plate to evaporate water, followed by firing at 800 °C for 6 h
This result correlated quite well with the particle diameters measured in bulk by dynamic light scattering (DLS) (36 and 92 nm) and on the mica surface by scanning electron microscopy (SEM) (31 nm) and presented in “Synthesis of silver nanoparticles and preparation of Ag-BSCF composite powders”

Summary

Introduction

Efforts in the domain of solid oxide fuel cells (SOFCs) are focused on devices capable of operating within an intermediate temperature (IT) range (500–700 °C). Zhang et al [44] prepared a composite Ag-BSCF cathode using a paste containing 14 % silver These authors reported that the introduction of either SDC or Ag into the BSCF cathode lowered the performance of the cells. The Ag-BSCF powder obtained as described in Synthesis of silver nanoparticles and preparation of Ag-BSCF composite powders and an organic vehicle (Fuel Cells Materials) were used to prepare the Ag-BSCF paste, using method (1). The method of nitrate decomposition was applied for this purpose: 0.05 mol dm−3 of AgNO3 solution was added by drops, using a suction pipette accurate to 0.01 ml, and poured into the porous BSCF cathode layer placed on a heated hot plate to evaporate water, followed by firing at 800 °C for 6 h.

Methods

Results and discussion

Conclusions