A prefilter for mitigating PH3 contamination of a Ni-YSZ anode

Ni-YSZ is used as the anode of a solid oxide fuel cell (SOFC) because it has excellent electrochemical performance for operation with coal-derived syngas. However, trace impurities, PH3 H2S AsH3, and Sb in coal-syngas can cause SOFC degradation. Described here is a means of removing PH3 impurity from syngas by using a Ni-based prefilter. In one test, a thin Ni-based filter was set upstream of a Ni-YSZ anode-supported SOFC. The SOFC was exposed to syngas with PH3 under a constant current load at 800 °C. The filter decreased 20 ppm PH3 in the feed to a level which did not degrade the SOFC for over 400 h until the filter became saturated. In another test, both H2S and PH3 were co-fed to the cell with Ni-based and Fe/Ni-based filters. The interaction between these two impurities did not significantly impact the filter performance with respect to PH3 removal for both filter formulations. The cell performance was evaluated by current–voltage measurements and impedance spectroscopy. Post-mortem analyses of the cell and filter were performed by means of XRD, SEM/EDS and XPS. With proper filter design, the Ni-YSZ SOFC can operate on contaminated coal-syngas without degradation over a prescribed period of time.

The images of the central area of (a) the poisoned prefilter surface and (b) the cell with prefilter cross-section. After the cell with prefilter exposed to 20 ppm PH3 for 600 h, the prefilter was penetrated by PH3.Figure optionsDownload as PowerPoint slideHighlights
► A ppm PH3 impurity in syngas can poison a Ni-YSZ anode at SOFC working temperatures.
► Ni and Fe are found to be cost-effective materials for PH3 removal.
► The prefilter can remove 20 ppm PH3 to a level which does not degrade the SOFC.
► Poisoning of a Ni-YSZ anode by phosphorus adsorption is observed.
► H2S co-impurity in syngas does not impede the PH3 removal function of the prefilter.