Electrolyte supported SOFCs with Ni-YSZ/Ni-GDC bi-layer anodes were operated at 800 degrees C and 900 C with 8% H2O and 10-20 ppm of PH3/syngas to reduce steam-related interference accelerate degradation. Cell power output degraded rapidly within the first 12 h, with even faster degradation at 900 degrees C. Nickel phosphide phases detected in the anode include Ni3P, Ni12P5 and Ni5P2, while CePO4 formed in the catalyst layer. Irrespective of the electrolyte component used, phosphorus penetrated to the anode-electrolyte interface in electrically loaded cells, as well as with Ni-GDC cells in coupon tests. In contaminated bi-layer anodes, phosphorus appeared to concentrate away from the surface, suggesting oxidation of PH3 when steam rich environments were present. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.