Understanding hydrogen sulfide impact on a portable, commercial, propane-powered solid-oxide fuel cell

A portable commercial solid-oxide fuel cell that consisted of 56 stacked cells and used an indirect internal reforming strategy with a rhodium catalyst on an yttria-stabilized zirconia structure for its reformer and a nickel anode on an yttria-stabilized zirconia structure electrolyte was tested with propane fuel intentionally blended with 0 to 15 ppmv H2S. The voltages of cell pairs and stack were recorded during 7-h poison and recovery tests. Results indicated that with higher H2S concentrations, the rate of stack voltage decrease could vary from 181.4 mV/h at 3 ppmv to 432.0 mV/h at 15 ppmv. The voltage losses of individual cell pairs showed a consistent trend as well. Results from recovery tests indicated that a longer recovery time may be necessary at higher H2S concentration. Electrochemical impedance spectroscopy was employed to better understand the role of varying phenomena within the solid-oxide fuel cell. An equivalent circuit model was constructed to fit electrochemical impedance spectral data that was taken at the system level. Effects of individual components within the system (fuel cell, battery, and DC/DC converter), determined by using electrochemical impedance spectra, were then used to deduce the behaviour of the SOFC. A clear charge transfer resistance increase was observed due to H2S poisoning, consistent with the blocking of active sites on the catalyst in the anode layer. The effect was found to be completely reversible by a period of operation with sulfide-free fuel.