High Temperature Interactions of Antimony with Nickel
In this chapter, the surface and bulk interactions of antimony with the Ni-based anodes in solid oxide fuel cells (SOFC) will be discussed. High fuel flexibility is a significant advantage of SOFCs, allowing the direct use of fossil and bio fuels without a hydrogen separation unit. Synthesis gas derived from coal and biomass consists of a mixture of hydrogen, carbon monoxide, carbon dioxide, and steam, but finite amounts of tars and trace impurities such as S, Se, P, As, Sb, Cd, Pb, Cl, etc, are also always present. While synthesis gas is commonly treated with a series of chemical processes and scrubbers to remove the impurities, complete purification is not economical. Antimony is widely distributed in coals. During coal gasification antimony is volatilized, such that contact with the SOFC anodes and other SOFC parts, e.g., interconnect, current collecting wires, fuel gas supplying tubing, is most likely. This chapter addresses the following topics: high temperature Ni - Sb interactions; alteration phase, Ni3Sb, Ni5Sb2, NiSb, formation; thermochemical modeling; impact of Sb on the electrocatalytic activity of Ni toward the fuel oxidation and the presence of other impurities (sulfur, in particular); converted anode structural instability during long-term SOFC operation; comparison with nickel heterogeneous catalysts.