Exploring Remedies for PH₃ Poisoning of a Ni-YSZ Anode in Coal-Syngas Fuel

Ni-YSZ cermet is commonly used as the anode of a solid oxide fuel cell (SOFC) because it has excellent electrochemical performance and is a cost effective anode material for coal-syngas fuel. However, coal-syngas contains trace contaminants, such as phosphine (PH₃), hydrogen sulfur (H₂S), arsine (AsH₃) and stibine (SbH₃), and these can cause degradation of the SOFC. Ni-YSZ anode-supported SOFCs were exposed to syngas and H₂ fuel, while co-feeding PH₃ and chlorine Cl₂ impurities under a constant current load at 800°C. The cell degradation was postponed in syngas and highly mitigated in H₂. In another test, a Ni-based filter was used to remove the PH₃ impurity. The results show that the filter can effectively remove 20 ppm PH₃ to a level which does not significantly degrade the SOFC over 400 h. The poisoning effects were evaluated by current-voltage scans and impedance spectroscopy, in addition to thermodynamic and chemical analyses. The post-mortem analyses of the cell and filter were performed by means of XRD and SEM/EDS.