Effect of NiO/YSZ compositions on the co-sintering process of anode-supported fuel cell

doi:10.1016/j.memsci.2005.03.009

Journal of Membrane Science

Volume 259, Issues 1–2, 15 August 2005, Pages 103-109

https://doi.org/10.1016/j.memsci.2005.03.009 Get rights and content

Abstract

Effect of NiO/YSZ compositions on the co-sintering process of anode-supported fuel cell was researched. The green YSZ layer was fabricated by modifying electrostatic powder coating, and the relative density is about 52%. After co-firing at 1400 °C for 5 h, the sample of YSZ film based on the 1000-NY support (pre-calcinated NiO 60 wt.%, YSZ 40 wt.%) is concave due to the mismatch of shrinkages between the YSZ film and anode support and there exist cracks on the film. Dense YSZ films based on the NY-20P (NiO 48 wt.%, YSZ 32 wt.% and graphite 20 wt.%) support were fabricated after co-firing at 1400 °C for 2 h. The OCV and the peak power density of a single cell with a 15 μm thick YSZ film based on the NY-20P support are 1.09 V and 315 mW/cm² at 800 °C, respectively.

Introduction

Conventional solid oxide fuel cells (SOFCs) based on a thick yttria-stabilized zirconia (YSZ) electrolyte as support are required to operate at high temperature (about 1000 °C) in order to have sufficient ionic conductivity. High temperature operation over a long period will, however, incur many problems such as limited material selection, high material cost and fast performance degradation of cell components [1], [2], [3]. Therefore, it is desirable to reduce the operation temperature of the fuel cell to 600–800 °C in order to reduce cost and improve long-term stability [4]. There are two approaches to overcome this problem, one is to use alternative electrolyte materials with higher ionic conductivity than YSZ, such as doped ceria and doped LaGaO₃ [5], [6], [7], and the other is to reduce the thickness of the YSZ electrolyte [4], [8]. Anode-supported-type SOFC cells are thought to be suitable for cells with low resistance and resultant higher power density; development of this type of cell has been carried out by using fuel electrodes for the cell support [9], [10]. The supporting electrode has not only electro-chemical reactivity and conductivity, but also mechanical strength and lengthy property stability under typical operating conditions.

The sintering temperature for such anode is generally in the range 1350–1400 °C in order to form a dense electrolyte, a good anode and electrolyte interfacial contact and reduce the sintering and grain growth of the Ni phase in the Ni/YSZ anode support desirable porosity of anode. Leng et al. [11] had reported that effect of characteristics of Y₂O₃/ZrO₂ powders on fabrication of anode-supported solid oxide fuel cells. For an anode supported SOFC, the control of the flatness of large-plate cells becomes difficult due to different shrinkages of anode support and electrolyte film at high sintering temperatures. Chen et al. [12] suggests that for a thin-film electrolyte made of nano-sized YSZ powders, it may be possible to sinter an anode-support/electrolyte bilayer at reduced temperatures. In the work, we researched effect of the characteristics of anode support on sintering process of YSZ dense electrolyte and cell properties of a single cell based on anode support with YSZ electrolyte film.

Section snippets

Preparation of powder and anode support

YSZ (Y₂O₃8 mol%) powder produced by co-precipitation, spray drying and calcination process, with particle sizes of 0.2–1.0 μm, and NiO powder prepared by calcining analytical-grade Ni(HCO₃)₂ at 350 °C for 2 h were used in this work. In this study, the four kinds of the powders were used, which include: NiO, pre-calcinated NiO at 1000 °C for 1 h, YSZ and pre-calcinated YSZ at 1000 °C for 1 h. The analytical-grade graphite powder was used for the pore-former. In order to study the effect of the

Shrinkage characteristics of anode cermets

Fig. 2 shows that the shrinkage rates of the anode cermets, YSZ, and NiO were measured after firing at different temperatures. Comparing to the anode cermets, the NiO has the highest shrinkage at 900 °C, which is about 15%. However, the shrinkage rate has a little change from 900 to 1400 °C. The shrinkage rates of the NY and 1000-NY are 23.8 and 15.4%, respectively. Comparing to the NY, the 1000-NY consists of the pre-calcined NiO and YSZ powder. This result indicates the pre-calcined NiO powder

Conclusions

Dense YSZ films based on the NY-20P support after co-firing at 1400 °C for 5 h were fabricated. The relative density of the green YSZ layer fabricating by modifying electrostatic powder coating is about 52% after firing at 900 °C. The shrinkage rates of anode supports depend on the characteristics of NiO and YSZ powders. The pre-calcining NiO and YSZ powder decrease the shrinkage rate of anode supports. Based on the 1000-NY support, the sample is concave toward the YSZ film; at the same time,

Acknowledgements

This work was supported by the Natural Science Foundation of China under contract no. 20271047 and the Ministry of Science and Technology of China under contract nos. G2000026409 and 2001AA323090.

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Effect of NiO/YSZ compositions on the co-sintering process of anode-supported fuel cell

Abstract

Introduction

Section snippets

Preparation of powder and anode support

Shrinkage characteristics of anode cermets

Conclusions

Acknowledgements

Solid State Ionics

Solid State Ionics

J. Alloy Compd.

Solid State Ionics

J. Power Sources

Solid State Ionics

J. Power Sources

Mater. Sci. Eng. A