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The first metal-free membrane assembly for tubular solid oxide fuel cells efficient in conversion of either sour gas or H2S-containing hydrogen is fabricated and characterized. To achieve high performance, a porous layer of YSZ impregnated with LSBT, LSBT/YSZ (LSBT is La0.4Sr0.5Ba0.1TiO3), was selected as the composite anode material for the fully ceramic SOFC with the established catalyst LSM/YSZ as the cathode. The anode has a high performance and is stable in conversion of sulfur-containing fuels. The tubular fuel cell was characterized electrochemically using impedance spectroscopy (EIS) and potentiodynamic tests performed at 800, 850, and 900 °C with various fuels to determine the effect of H2S content in the following feeds: H2, H2/H2S (5000 ppm), and CH4/H2S (5000 ppm). Encouraging total power densities were obtained: 110, 105, and 41 mW cm−2, respectively using H2/H2S, H2, and dry CH4/H2S at 900 °C, despite high ohmic resistances. [ABSTRACT FROM AUTHOR]

Abstract: The system LSBT/YSZ (LSBT is La0.4Sr0.5Ba0.1TiO3) is a promising combination as an anode material for full ceramic SOFCs. An anode comprising a porous layer of YSZ impregnated with LSBT shows good performance for conversion of high sulfur content fuels. The microstructures within the composite matrix were determined and correlated with the parameters of the production process. The anodes were characterized electrochemically using impedance spectroscopy (EIS) and potentiodynamic tests performed at 850 °C with various fuels to determine the effect of H2S in the feeds: H2, H2/H2S (5000 ppm), CH4, CH4/H2S (5000 ppm). The highest power densities (200 mW cm−2 in H2/H2S) were obtained for LSBT/YSZ composites after impregnation six times with LSBT, corresponding to 12.6 wt% LSBT; further impregnations dramatically decreased performance as a result of restricted access of fuel to active sites. [Copyright &y& Elsevier]

Abstract: Hydrogen sulfide, usually considered to be an anode catalyst poison, strongly promotes methane oxidation over sulfur resistant catalysts. The role of H2S in oxidation of sour CH4 feed over a sulfur resistant SOFC anode catalyst at 850°C has been determined through thermodynamic and experimental studies. The anode material was an intimately mixed 50/50 mass ratio composite of La0.4Sr0.6TiO3−δ and YSZ. The power density improved dramatically from 2mWcm−2 with pure CH4 as fuel to more than 450mWcm−2 for CH4 containing 20% H2S. However, H2S was not the only fuel converted, and its interaction with CH4 was the key factor in enhancement of performance. The anode effluent gas mixture included H2S, SO2, H2 and CS2 consistent with thermodynamic predictions. The role of H2S in the CH4 oxidation mechanism was determined, and showed that CH4 and H2S must be considered together as a fuel and not as two separate fuels. The types of electrochemical reactions that occurred in the fuel cell were strongly dependent on potential. [Copyright &y& Elsevier]

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]

Crystallographic features, physical properties and ionic release from yttria stabilized zirconia (YSZ) in suspension were studied by means of XRD, TEM, light-scattering particle size, BET, ICP and zeta potential analysis. It was found that Zr, Y, Na, and to a lesser extent Ca, Hf and Pd leach from 8 mol% YSZ powder. The impurities present increase the zeta potential of suspensions made from as-received YSZ. A trace amount of tetragonal phase observed in 8 mol% YSZ persists following washing and calcination–milling. Dislocations and crystallographic defects together with fractured crystals which form during milling of the calcined powder should lead to the formation of more broken bonds; as a result the surface of the particles can support higher surface charge density. Washing and calcination–milling lead to a shift of the isoelectric point of 8 mol% YSZ from pH 8.4 to pH 6.3 and 6.8, respectively. Due to higher chemical stability and previously shown positive impacts on microstructure and performance of fuel cells, use of calcined YSZ can be more advantageous than as received powder. [ABSTRACT FROM AUTHOR]