Structure-electrochemical performance relationship in Sr2(Fe1-xVx)MoO6 anode.

Structural property is becoming a powerful tool to manipulate oxygen vacancy concentration and electrochemical performance of electrode material. In this work, the structure-electrochemical performance relationship of Sr 2 (Fe 1-x V x)MoO 6 (x = 0, 0.1, 0.2 and 0.25) anode is investigated based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS), BET surface area, DC four-point probe, I–V and electrochemical impedance spectra (EIS). XRD results show that all the compounds are of single phase, the tetragonal to cubic phase transition occurs at x = 0.1, which plays important role in its electrochemical performance. Firstly, the disappeared structural distortion in Sr 2 (Fe 1.8 V 0.2)MoO 6 and Sr 2 (Fe 1.75 V 0.25)MoO 6 anodes benefits electron hopping between Fe–O–Mo–O–Fe, so electron transfer processes (high-frequency semicircle) in their EIS are facilitated. Secondly, both XPS survey and EDS spectrum confirm the change in oxygen content with structural transition, Sr 2 (Fe 1.9 V 0.1)MoO 6 anode own higher concentration of oxygen vacancy, thus the oxygen surface exchange and diffusion process (low-frequency arc) of the corresponding cell is reduced significantly. Consequently, Sr 2 (Fe 1.9 V 0.1)MoO 6 -based cell exhibits the highest power output (810 mW cm−2) at 850 °C. For Sr 2 (Fe 1.8 V 0.2)MoO 6 anode, BET surface area test reveals the slightly higher value, while its lower power density indicates that the influence of oxygen vacancy prevails over that of microstructure. Combining with EIS results, it can be deduced that Sr 2 (Fe 1-x V x)MoO 6 anodes with tetragonal symmetry own higher concentration of oxygen vacancy, thus the expected electrochemical performance is better than that of other cells. Understanding the critical role of structure is important for achieving highly active electrode material. • Electrochemical performance of Sr 2 (Fe 1-x V x)MoO 6 changes significantly with structural transition. • Conductivity of Sr 2 (Fe 0.9 V 0.1)MoO 6 is enhanced significantly by V doping. • Sr 2 (Fe 0.9 V 0.1)MoO 6 anode depicts the best electrochemical performance. [ABSTRACT FROM AUTHOR]