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For solid oxide fuel cell with La 0.4 Ce 0.6 O 1.8 –La 0.4 Sr 0.6 TiO 3±δ (LDC-L4ST) impregnated anodes, the electrochemical oxidation rates of H 2 and CH 4 were significantly improved when H 2 S (0.5%) was present in the feeds as evidenced by the substantially decreased polarization resistance and the improved power density of the cell although H 2 S did not predominantly function as a fuel. Conductivity measurements of various anode component materials implied that the addition of H 2 S into the feeds increased their conductivities. More importantly, from the mass spectroscopic analysis of the anode gas effluents and the thermodynamic calculations, direct evidences of H 2 S caused SOFC performance improvement have been confirmed, three distinct regions for the electrochemical oxidation pathways of 0.5% H 2 S–CH 4 vs. overpotential ( η ) were proposed to explain the effect. The chemisorbed S species, together with LDC-L4ST, behaved as an effective catalyst promoting CH 4 oxidations via COS and CS 2 intermediates. The addition of LDC in the anode enhanced this synergic effect and further increased CH 4 electrochemical conversion as well as coking resistance in comparison of the L4ST anode. [ABSTRACT FROM AUTHOR]

Abstract: The performance of La0.4Sr0.6TiO3±δ -Y0.2Ce0.8O2−δ (LST-YDC) composite anodes in solid oxide fuel cells significantly improved when 0.5% H2S was present in syngas (40% H2, 60% CO) or hydrogen. However, electrochemical impedance spectroscopy measurements at OCV showed that polarization resistance of the cell increased when the concentration of H2S exceeded 0.5%. Gas chromatographic and mass spectrometric analyses revealed that the rate of electrochemical oxidation of all fuel components improved when H2S was present in the fuel. Electrochemical stability tests performed under potentiostatic conditions showed that there was no power degradation caused by the presence of H2S in different feeds, and that there was power enhancement when 0.5% H2S was present. [Copyright &y& Elsevier]

The ideal solid oxide fuel cells (SOFCs) can be powered by readily available hydrocarbon fuels containing impurities. While this is commonly recognized as a key advantage of SOFC, it also, together with the elevated operating temperature, becomes the main barrier impeding the in-situ or operando investigations of the anode surface chemistry. Here, using a well-designed quenching experiment, we managed to characterize the near-surface structure of La 0.4 Sr 0.6 TiO 3+δ (LST) anode in SOFCs fuelled by H 2 S-containing methane. This new method enabled us to clearly observe the surface amorphization and sulfidation of LST under simulated SOFC operating conditions. The ∼1 nm-thick two dimensional sulfur-adsorbed layer was on top of the disordered LST, containing –S, –SH and elemental sulfur species. In SOFC test, such “poisoned” anode showed increased performances: a ten-fold enhanced power density enhancement (up to 30 mW cm −2 ) and an improved open circuit voltage (from 0.69 V to 1.17 V). Moreover, its anodic polarization resistance in methane decreased to 21.53 Ω cm 2 , a difference of 95% compared with the sulfur-free anode. Control experiments confirmed that once the adsorbed sulfur species were removed electrochemically, methane conversion slowed down simultaneously till full stop. [ABSTRACT FROM AUTHOR]