PNNL

Abstract

The performance of anode-supported and electrolyte-supported solid oxide fuel cells was investigated in synthetic coal gas containing 0 to 10 ppm arsenic introduced as arsine. Arsenic was found to interact strongly with nickel in the anode, resulting in the formation of nickel-arsenic solid solution, Ni5As2 and Ni11As8, depending on temperature, arsenic concentration, and reaction time. For anode-supported cells, loss of electrical connectivity in the anode support was the principal mode of degradation, as nickel was converted to nickel arsenide phases that migrated to the surface to form large grains. Cell failure occurred well before the entire anode was converted to nickel arsenide, and followed a reciprocal square root of arsenic partial pressure dependence consistent with a diffusion-based rate-limiting step. Failure occurred more quickly with electrolyte-supported cells, which have a substantially smaller nickel inventory. For these cells, time to failure varied linearly with the reciprocal arsenic concentration in coal gas, and occurred when arsenic reached the anode/electrolyte interface. Test performed with nickel/zirconia coupons showed that arsenic was essentially completely captured in a narrow band near the fuel gas inlet.