Further investigation of Ce0.9Sr0.1Cr0.5Fe0.5O3±δ as anode for solid oxide fuel cell fuelled with H2S

Ce0.9Sr0.1Cr0.5Fe0.5O3±δ as a potential anode for solid oxide fuel cell has been described in previous work, such as the conductivities in H2 and H2S, electrochemical properties and longevity of the cell with fuelled 3% H2 or 5% H2S, et al. In the further research, an interesting phenomenon is found that the mass increases when temperature rising over 680 °C in TG–DTA. The reason is the formation of nitrides by the analysis of thermodynamics calculation. Therefore, the synthesized process is optimized to reduce and cool down in 100% H2 for avoiding forming nitrides. Then, the fluorite structure Ce0.9Sr0.1Cr0.5Fe0.5O4±δ (CSCFe) is obtained. Thermal expansion coefficient (TEC) shows that anode CSCFe and electrolyte Ce0.8Sm0.2O1.9 (SDC) have a good matching. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) are used to describe the electron changes of every element in CSCFe before and after cell test. The results indicate that some electrons transfer from Ce3+ to Fe3+, which causes the intensity of EPR weaker, and increases the electron conductivity of CSCFe. After the cell operating in 5% H2S, XPS patterns indicate that some lattice oxygen migrate from the bulk to the surface releasing oxygen vacancies. The triple phase boundary (TPB) of the reaction between H2S and O2− is magnified, and the efficiency of the single cell is enhanced. Compared the electrochemical properties of the cell which fluorite structure Ce0.9Sr0.1Cr0.5Fe0.5O4±δ as anode with previous perovskite structure Ce0.9Sr0.1Cr0.5Fe0.5O3±δ as anode, the results demonstrate that the former is more suitable as anode for SOFC fuelled with H2S due to more content of Ce3+ in the material.

► Fluorite structure CSCFe was obtained after 100% H2 reduction.
► The maximum current density and power density are 87.21 mA/cm2 and 19.23 mW/cm2 for cell test in 5% H2S at 600 °C.
► XPS indicates the electrons easily transfer from Ce3+ to Fe3+ increasing the electronic conduction.
► The formation of oxygen vacancies magnifies the TPB, which enhance the cell efficiency.