The effect of fuel composition and temperature on the interaction of H2S with nickel–ceria anodes for Solid Oxide Fuel Cells

The impact of H2S on nickel–gadolinium-doped ceria (Ni–CGO) used as the anode for solid oxide fuel cells has been studied over a range of operating conditions using yttria-stabilised zirconia electrolytes. This included varying the partial pressure of H2S and H2 in the fuel mixture as well as the operating temperature. Electrochemical impedance measurements were made on symmetrical cells under each operating condition and compared with thermodynamic predictions of the state of the material as a function of operating condition. Increasing the H2S concentration (1–3 ppm H2S in moist H2) significantly increased the anode degradation. A decrease in H2 content in the fuel (97–9.7% H2) was found to increase the degree of sulphur interaction with the anodes. Lowering the operating temperature (873–830 K) showed an increase in the detrimental impact of sulphur on the anode. This experimental result was compared to thermodynamic predictions, which show the dependency of Ni–S interaction on pS2 and temperature as well as the effect of ceria–S interaction on pO2 and pS2. The consequence of this study shows that the interaction of sulphur with the anode is strongly dependent on gas composition and operating condition—suggesting that different parts of the anode can be degraded differently, stressing the importance of a well-designed gas flow field and temperature distribution management.