Effect of tungsten doping on strontium ferrite electrode for symmetrical solid oxide electrochemical cell

Abstract

Tungsten-doped strontium ferrite (SrFe1-xWxO3-δ, SFW) is prepared and characterized as the electrode materials for symmetrical solid oxide electrochemical cell. X-ray diffraction refinement reveals the symmetrical structure transform from cubic (pm3¯m) for x = 0.1 to tetragonal (I4/m) when x = 0.2. According to the analysis including electrical conductivity, Hydrogen temperature-programmed reduction (H2-TPR), thermal expansion and X-ray photoelectron spectra (XPS), it suggests that the decrease in conductivity, content of Fe2+ and oxygen vacancy concentration with the increase of W content is attributed to the stronger lattice framework. The oxygen vacancy can be dramatically activated around 600 °C. Using SrFe0.8W0.2O3-δ as the electrodes, symmetrical single cells supported on doped ceria electrolytes can achieve acceptable power density (0.19 W cm−2 at 750 °C) and considerable stability. Meanwhile symmetrical cells with La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte substrates can achieve 0.75 A cm−2 at 800 °C under the voltage of OCV (open circuit voltage) +0.5 V when it is operated in electrolysis mode. SrFe0.8W0.2O3-δ can gain a considerable stability and electrochemical activity under both oxide and reductive atmospheres. Oxygen vacancy formation energy (Evac) and electron density distribution are computed to verify the enhancement on crystal structure stability by doping W. The Evac critically depends on the distance from the W atom.