Durability of solid oxide fuel cells using sulfur containing fuels

The usability of hydrogen and also carbon containing fuels is one of the important advantages of solid oxide fuel cells (SOFCs), which opens the possibility to use fuels derived from conventional sources such as natural gas and from renewable sources such as biogas. Impurities like sulfur compounds are critical in this respect. State-of-the-art Ni/YSZ SOFC anodes suffer from being rather sensitive towards sulfur impurities. In the current study, anode supported SOFCs with Ni/YSZ or Ni/ScYSZ anodes were exposed to H2S in the ppm range both for short periods of 24 h and for a few hundred hours. In a fuel containing significant shares of methane, the reforming activities of the Ni/YSZ and Ni/ScYSZ anodes were severely poisoned already at low H2S concentrations of ∼2 ppm H2S. The poisoning effect on the cell voltage was reversible only to a certain degree after exposure of 500 h in the state-of-the-art cell, due to a loss of percolation of Ni particles in the Ni/YSZ anode layers closest to the electrolyte. Using SOFCs with Ni/ScYSZ anodes improved the H2S tolerance considerably, even at larger H2S concentrations of 10 and 20 ppm over a few hundred hours.

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► Study of H2S poisoning of SOFC with Ni/YSZ or Ni/ScYSZ anodes in CH4–H2O–H2 fuel.
► Similar poisoning of methane reforming activity of both anodes at OCV and 850 °C.
► Two poisoning mechanisms, one fast, reversible (Rp) and one slow, irreversible (Rs).
► Reversible coverage of anode's Ni particles in both anode types by sulfur (Rp).
► Loss of percolation of Ni particles due to H2S & polarization on Ni/YSZ anode (Rs).