A comparative study of H2S poisoning on electrode behavior of Ni/YSZ and Ni/GDC anodes of solid oxide fuel cells

The effect of sulfur poisoning on the activity and performance of Ni/Y2O3–ZrO2 (Ni/YSZ) and Ni/Gd2O3–CeO2 (Ni/GDC) cermet anodes of solid oxide fuel cells has been examined by polarization and electrochemical impedance spectroscopy (EIS) measurements at 800 °C. The anodes are alternately polarized in pure H2 and H2S-containing H2 fuels with H2S concentration gradually increased from 5 ppm to 700 ppm at 200 mA cm−2 for 2 h. The results show that the anode potential of Ni/YSZ electrodes measured in pure H2 decreases from 0.61 V to 0.34 V after exposure to H2S-containing H2 fuels with H2S concentration increased from 5 to 700 ppm. On the other hand, the anode potential of Ni/GDC electrodes measured in pure H2 decreases from 0.78 V to 0.72 V under identical test conditions. The degradation in performance for the hydrogen oxidation in H2S-containing H2 fuels is substantially smaller on Ni/GDC anodes, as compared to that on Ni/YSZ anodes. Similar trend is also observed for the change of the electrode polarization resistance for the hydrogen oxidation reaction on the Ni/YSZ and Ni/GDC anodes after exposure to H2S-containing H2 fuels. The SEM results indicate the structure modification of Ni/YSZ anodes only occurs on Ni particles, and in the case of Ni/GDC anodes, structural modification on both Ni and GDC phases occurs. The mixed ionic and electronic conductivity of GDC phase could be the primary reason for the high sulfur tolerance of the Ni/GDC cermet anodes.