Disruption of extended defects in solid oxide fuel cell anodes for methane oxidation

Abstract

Point defects largely govern the electrochemical properties of oxides: at low defect concentrations, conductivity increases with concentration; however, at higher concentrations, defect–defect interactions start to dominate1,2. Thus, in searching for electrochemically active materials for fuel cell anodes, high defect concentration is generally avoided. Here we describe an oxide anode formed from lanthanum-substituted strontium titanate (La-SrTiO3) in which we control the oxygen stoichiometry in order to break down the extended defect intergrowth regions and create phases with considerable disordered oxygen defects. We substitute Ti in these phases with Ga and Mn to induce redox activity and allow more flexible coordination. The material demonstrates impressive fuel cell performance using wet hydrogen at 950 °C. It is also important for fuel cell technology to achieve efficient electrode operation with different hydrocarbon fuels3,4, although such fuels are more demanding than pure hydrogen. The best anode materials to date—Ni-YSZ (yttria-stabilized zirconia) cermets5—suffer some disadvantages related to low tolerance to sulphur6, carbon build-up when using hydrocarbon fuels7 (though device modifications and lower temperature operation can avoid this8,9) and volume instability on redox cycling. Our anode material is very active for methane oxidation at high temperatures, with open circuit voltages in excess of 1.2 V. The materials design concept that we use here could lead to devices that enable more-efficient energy extraction from fossil fuels and carbon-neutral fuels.

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Figure 1: Relation between microstructure, composition and conductivity of the ‘La 4 Sr n -4 Ti n O 3 n +2 ’ series.
Figure 2: Polarization measurements on LSTMG/YSZ with varying temperatures and atmospheres.
Figure 3: Performance plots in different atmospheres.
Figure 4: Electrode interface.

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Acknowledgements

This work was funded partly by a EU Marie Curie Fellowship and by EPSRC.

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Correspondence to John T. S. Irvine.

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Ruiz-Morales, J., Canales-Vázquez, J., Savaniu, C. et al. Disruption of extended defects in solid oxide fuel cell anodes for methane oxidation. Nature 439, 568–571 (2006). https://doi.org/10.1038/nature04438

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