Effect of hydrogen sulfide on the direct internal reforming of methane in solid oxide fuel cells

Electrochemical full cell evaluation of a Versa Power Systems TSC-2 solid oxide fuel cell was conducted in 1 ppmv hydrogen sulfide (H2S) at 750 °C with 25%, 35% and 50% levels of direct internal reforming (DIR) of methane. It is shown that the addition of H2S significantly degrades both the cell voltage as well as the DIR activity of the cell, as evidenced by gas chromatographic analysis of the cell exhaust gas. With the removal of H2S, the cell voltage recovers, but not to pre-H2S exposure levels. The onset of degradation of electrochemical activity commences before the onset of DIR activity degradation, indicating that H2S penetrates to the Ni-containing anode functional layer before saturation coverage of Ni with sulfur in the support layer. Secondary ion mass spectrometric post-analysis indicated that, while adsorbed sulfur remains on the surface of Ni after recovery for ∼200 h in H2S-free gas, there remains sufficient active Ni surface area in the anode substrate to continue to catalyze the DIR reactions.

The direct internal reforming (DIR) ability of Ni–YSZ (yttria stabilized zirconia) anodes creates fuel flexibility in solid oxide fuel cells (SOFCs), as DIR allows Ni–YSZ anodes to use hydrocarbons directly as a fuel source. Electrochemical full cell evaluation of a Versa Power Systems TSC-2 SOFC was conducted in 1 ppmv hydrogen sulfide (H2S) at 750 °C with 25%, 35% and 50% levels of DIR of methane. The addition of H2S significantly degrades both the cell voltage as well as the DIR activity of the cell. With the removal of H2S, the cell voltage partially recovers to pre-H2S exposure levels, while the DIR activity fully recovers. Secondary time-of-flight mass spectroscopy analysis post-testing indicates that some sulfur remains present on the Ni surface after steady-state recovery.Figure optionsDownload as PowerPoint slide