Abstract
In this paper, the behaviour of silver as cathode conductive material, interconnect wire, and sealing for anode lead connection for microtubular solid oxide fuel cells (µSOFC) is reported. The changes in silver morphology are examined by scanning electron microscopy on cells that had been operated under reformed methane. It is found that using silver in an solid oxide fuel cell (SOFC) stack can improve the cell performance. However, it is also concluded that silver may be responsible for cell degradation. This report brings together and explains all the known problems with application of silver for SOFCs. The results show that silver is unstable in interconnect and in cathode environments. It is found that the process of cell passivation/activation promotes silver migration. The difference in thermal expansion of silver and sealant results in damage to the glass. It is concluded that when silver is exposed to a dual atmosphere condition, high levels of porosity formation is seen in the dense silver interconnect. The relevance of application of silver in SOFC stacks is discussed.
Highlights
Several configurations of solid oxide fuel cells (SOFC) are commercially available; the selection of suitable materials and development techniques is still the subject of current research
Within an SOFC cell, the cathode is a significant contributor to the cell overpotential caused by the slow oxygen reduction reaction [1], which occurs at the electrolyte–cathode–air boundary phase
The silver thermal expansion did not match with the thermal expansion of the other cell materials, and caused damage to the glass sealant
Summary
Several configurations of solid oxide fuel cells (SOFC) are commercially available; the selection of suitable materials and development techniques is still the subject of current research. Key requirements for cathode materials are that they have to be highly conductive for electrons and oxygen ions, and they should maintain thermal stability in SOFC operating temperature. The conductivity of modern cathode materials such as lanthanum strontium manganite (LSM) or lanthanum strontium cobalt ferrite (LSCF) decreases at lower operating temperature. High ohmic losses in the cathode result in reduced cell performance. This can be overcome by the addition of a metal-based current collection layer that enhances the electronic conductivity. The high-conductive layer ensures adhesion and connectivity between the cathode and the interconnect. This reduces the contact resistance of the cathode/interconnect interface
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