Electrochemical evaluation of sulfur poisoning in a methane-fuelled solid oxide fuel cell: Effect of current density and sulfur concentration

• Increasing current density does not alleviate poisoning of electrochemical reactions.
• Under internal reforming conditions, deactivation by sulfur is greater at higher current loads.
• At low current loads, anode charge transfer processes are the most sensitive to sulfur.
• At high current loads, anode mass transfer processes are significantly affected by sulfur.
• Gradual deactivation of catalytic reforming results in high fuel utilization at high current loads.

A Ni/ScYSZ based SOFC was tested at 1, 0.5, 0.25, and 0 (OCV) A cm−2 in methane fuel containing 0–100 ppm H2S. Analysis of cell voltage loss during short-term H2S poisoning showed that SOFC performance loss was generally larger at higher current loads. Separating the effect of H2S on catalytic reforming and electrochemical activity by evaluating the relevant area specific resistances and charge transfer processes based on impedance spectroscopy revealed that the poisoning of electrochemical activity was not dependent on current density. Two major anode processes were significantly affected by the presence of H2S in the fuel; the lower frequency mass transfer/fuel reforming processes and higher frequency charge transfer/triple phase boundary (TPB) processes. At high current densities (0.5 and 1 A cm−2), mass transfer/fuel reforming processes were the most sensitive to sulfur poisoning. At OCV, the effect of sulfur was less pronounced on mass transfer/fuel reforming processes but quite significant on the charge transfer/TPB processes. Overall, sulfur related performance loss was more severe at the highest current density (1 A cm−2), due to the deactivation of catalytic fuel reforming reactions in the anode, leading to less available fuel and a higher fuel utilization. All poisoning effects were reversible after removing H2S from the fuel.

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