On the Behavior of Solid Oxide Fuel Cell Anode Materials in a Hydrogen Sulfide Containing Atmosphere

Abstract

The effect of hydrogen sulfide content in a hydrogenous atmosphere on the structure, physical, and mechanical properties of solid oxide fuel cell (SOFC) anode materials has been studied. A series of specimens of porous nickel and YSZ-Ni cermet have been investigated. In order to obtain the corresponding YSZ-Ni cermet structure, specimens of the YSZ-NiO ceramics were singly reduced in a hydrogenous atmosphere (either Ar-5 vol% H₂ mixture or hydrogen of 99.99 vol% H2 purity) for 4 h at 600°C under the pressure of 0.15 MPa. A part of the specimens of each series was then aged in "hydrogen sulfide in Ar-5 vol% H₂ mixture" atmosphere for 4 h at 600°C. According to a test mode, the atmosphere contained 7 or 18 vol% H₂S. Material microstructure and fracture surface morphology of the specimens as well as the physical and mechanical behaviors were investigated. It was revealed that the atmosphere containing up to 7 vol% H₂S does not affect the strength and electrical conductivity of the YSZ-Ni cermet. Increased content of H₂S (18 vol%) causes some changes in the YSZ-Ni cermet structure. A large number of completely reduced tiny nickel particles is formed. These nickel particles react with hydrogen sulfide. Sulfur is segregated on the boundaries between the zirconia and nickel phases and pores. Finally, multiple breaking of the zirconia-nickel bonds occurs that results in reduced strength of the cermet (by 39% as compared to as-received ceramics).