Improved contacting by the use of silver in solid oxide fuel cells up to an operating temperature of 800 °C

Abstract

In the following, a contacting variant for solid oxide fuel cells will be presented in which the conductivity of the interconnect is ensured by contact elements made of fine silver. To this end, the interconnect has holes through which the contact elements of fine silver (99.9 wt% Ag) are introduced and then pressed. This pressing process and the thermal expansion of the silver during heating leads to a gastight joint. The silver penetrations are additionally soldered to render them capable of withstanding temperature cycling. Contact resistance measurements and corrosion studies at 800 °C in air or Ar/4 vol.% H₂/3 vol.% H₂O demonstrate the functionality of the contacting variant under the described conditions. The experimental results indicate that contacting by means of silver contact elements ensures long-term stability up to operating temperatures of 800 °C. Current transmission via the silver contact elements means that a large number of materials are conceivable as the interconnect material. In the following application, an FeCrAl steel (1.4767, Aluchrom Y Hf—trade name Krupp Thyssen Nirosta) with 5.7 wt.% aluminium was used. At the operating temperature, a dense aluminium oxide layer forms on its surface which prevents the vaporization, for example of chromium oxide species, during fuel cell operation.