Novel in situ method (vacuum assisted electroless plating) modified porous cathode for solid oxide fuel cells

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Abstract

A novel in situ method – vacuum assisted electroless plating (VA–EP) is developed to modify the porous structure of various materials. The advantage of this method is it can form a metal network based on the already-given structure. We utilize this method to deposit silver (VA–EPA) in porous perovskite cathode Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) for an intermediate temperature solid oxide fuel cell (IT–SOFC) in the present research. The results of investigation show the performance of the modified cathode (VA–EPA–BSCF) enhances greatly, for example, the polarization resistance of VA–EPA–BSCF decreases by 60% at 600 °C compared to BSCF.

Introduction

Electroless plating (EP) is widely used in many areas, such as magnetic disk-drive heads, NMR microcoils, and micro/nanoelectronic devices [1]. It has been successfully used to deposit metals on variety of surface (e.g., Si/SiO2, glass [2], polyimide [3]), both two-dimensional (2D) and three-dimensional (3D) films [4]. Besides that, the most important characteristic for electroless plating is its in situ feature [4], [5]. Here, a novel modified EP method named vacuum assisted electroless plating (VA–EP) is presented to deposit metals into the micro-porous structure, which is operated under a vacuum condition (<20 kPa). Air within the micro-porous of the sample is deflated before dropping into the solution, which enables the immersed solution to infilter into the micro-porous structure easily to form a homogeneous deposition, preventing the surface from covering with the excess deposition. This method focuses on modifying the already-given micro-porous structure. Most important, the convenient and economic character of this method is obvious in preparing catalyst in a porous support.

To demonstrate the advantage of VA–EP, the mixed ionic/electronic conductors (MIECs) Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is selected as the already-given porous support, which is an excellent cathode material for IT–SOFCs [6], [7]. We expect the deposition of silver into BSCF (VA–EPA–BSCF) can further improve the electrochemical performance by means of enhancing the electronic conductivity, as well as the catalysis ability of oxygen reaction.

Section snippets

Sample preparation

Detailed synthesis of BSCF, electrolyte material Ce0.8Sm0.2O1.9 (SDC) and anode materials Ni–SDC powders for this investigation were available elsewhere [8], [9], [10]. Then a half cell with symmetric cathodes (0.28 cm2) was prepared with BSCF fabricated on both sides of the SDC electrolyte disk (sintered at 1400 °C for 4 h) and sintered at 1000 °C for 4 h. The cathode (0.20 cm2) fabricated on an anode supported cell was sintered at 1000 °C for 4 h as well. Formaldehyde and ammonia were used as

Microstructure characterization

Fig. 1a shows a cross-sectional morphology of the symmetrical cell, in which fine BSCF particles are fabricated in a porous structure and adheres well to the dense electrolyte SDC. Fig. 1b shows the BSCF particles have a diameter of 1 μm by average. Fig. 1c and d reveal BSCF cathode modified by the VA–EPA method. Both of the cathodes have a thickness of 12 μm. A homogeneous, slim and translucent silver network throughout the porous BSCF layer can be seen, which meet our expectation compared with

Conclusions

The novel vacuum assisted electroless plating method successfully introduced homogeneous silver network into the porous BSCF cathode. The XPS results showed the silver had different chemical states in the original and inner surface. Both the impedance spectra results and the maximum power densities indicated the VA–EPA–BSCF cathode exhibited much better performance than the pure BSCF one. More important, this modification method would be a promising one for other porous materials in other

Acknowledgements

The authors gratefully acknowledge the financial supports from the Ministry of Science and Technology of China under contract no. 2007AA05Z139. The authors were also grateful to Dianlong Wang and Hua Jin (Harbin Institute of Technology) for their friendly help.

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