A Computational Study of Nickel Migration in SOFCs Anode Due to Phosphine Induced Degradation and Applied Electrical Current

The poisoning of Solid Oxide Fuel Cells (SOFCs) anode materials by impurities in coal syngas is a significant problem for utilization coal symgas in SOFCs.  One such impurity, phosphine is known to cause catastrophic failure of SOFC anode at ppm level concentrations (below 10 ppm). A significant phenomenon observed in SOFC anodes, made of Ni-YSZ cermets, exposed to phosphine is migration of the nickel from porous matrix to the surface, which is believed to be one of the reasons for performance degradation. The mechanisms responsible for the experimentally observed Nickel migration are not well understood. A possible mechanism, which considers the Nickel diffusion and the formation of secondary phases (Ni-P compounds) as responsible phenomenon of Nickel migration, was proposed by our group. However this consideration does not allow us to predict the experimentally observed effect of the applied current. In this study, a reasonable mechanism is proposed to reveal the effect of electrical current on Nickel migration in SOFCs. The postulation of this mechanism is that the applied electrical current could possibly cause the transport of Nickel by generating an electrical force in the current flow direction. In SOFCs, the electrical current flows from anode/electrolyte interface to anode/fuel interface. Therefore the direction of the Nickel transport is from anode active layer to the anode surface. A transport model for nickel migration is formulated based on these postulations and it is integrated into an existing one dimensional in house code for predicting SOFC anode degradation due to fuel impurities. Simulations show that the proposed mechanism of Ni diffusion driven by secondary phase formation and the electrical force can reveal the experimentally observed accumulation of Ni and secondary phases on the SOFC anode surface when driven by a current and exposed to phosphine.