Electrochemical performance and stability of LSFMn+NiSDC anode in dry methane

SrTiO3-SrVO3 Ceramics for Solid Oxide Fuel Cell Anodes: A Route from Oxidized Precursors

Perovskite-type Sr(Ti,V)O3-δ ceramics are promising anode materials for natural gas- and biogas-fueled solid oxide fuel cells, but the instability of these phases under oxidizing conditions complicates their practical application. The present work explores approaches to the fabrication of strontium titanate-vanadate electrodes from oxidized precursors. Porous ceramics with the nominal composition SrTi1-yVyOz (y = 0.1-0.3) were prepared in air via a solid state reaction route. Thermal processing at temperatures not exceeding 1100 °C yielded composite ceramics comprising perovskite-type SrTiO3, pyrovanadate Sr2V2O7 and orthovanadate Sr3(VO4)2 phases, while increasing firing temperatures to 1250-1440 °C enabled the formation of SrTi1-yVyO3 perovskites. Vanadium was found to substitute into the titanium sublattice predominantly as V4+, even under oxidizing conditions at elevated temperatures. Both perovskite and composite oxidized ceramics exhibit moderate thermal expansion coefficients in air, 11.1-12.1 ppm/K at 30-1000 °C, and insignificant dimensional changes induced by reduction in a 10%H2-N2 atmosphere. The electrical conductivity of reduced perovskite samples remains comparatively low, ~10-1 S/cm at 900 °C, whereas the transformation of oxidized vanadate phases into high-conducting SrVO3-δ perovskites upon reduction results in enhancement in conductivity, which reaches ~3 S/cm at 900 °C in porous composite ceramics with nominal composition SrTi0.7V0.3Oz. The electrical performance of the composite is expected to be further improved by optimization of the processing route and microstructure to facilitate the reduction of the oxidized precursor and attain better percolation of the SrVO3 phase.

Impact of oxygen content on preferred localization of p- and n-type carriers in La0.5Sr0.5Fe1-xMnxO3-δ

The oxygen content in La_0.5Sr_0.5Fe_1-xMn_xO_3-δ, measured by coulometric titration in a wide range of oxygen partial pressure at various temperatures, was used for defect chemistry analysis. The obtained data were well approximated by a model assuming defect formation in La_0.5Sr_0.5Fe_1-xMn_xO_3-δvia Fe³⁺ and Mn³⁺ oxidation reactions and charge disproportionation on Fe³⁺ and Mn³⁺ ions. The partial molar enthalpy and entropy of oxygen in La_0.5Sr_0.5Fe_1-xMn_xO_3-δ obtained by statistical thermodynamic calculations were found to be in satisfactory agreement with those obtained using the Gibbs-Helmholtz equations, thus further confirming the adequacy of the model. The impact of manganese substitution on defect equilibrium in La_0.5Sr_0.5Fe_1-xMn_xO_3-δ was shown to be attributed to a lower enthalpy of Mn³⁺ oxidation reaction (vs. for the oxidation of Fe³⁺) and the charge disproportionation reaction on Mn³⁺ (vs. for that on Fe³⁺). The former makes Mn⁴⁺ ions more resistant to reduction than Fe⁴⁺. The latter favors the presence of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions in oxides in comparable concentrations. The distribution of charge carriers over iron and manganese ions was determined as a function of oxygen content in La_0.5Sr_0.5Fe_1-xMn_xO_3-δ.