Structural evolution and stability of Sc2(WO4)3 after discharge in a sodium-based electrochemical cell

Sc2(WO4)3, prepared by solid state synthesis and constructed as an electrode, is discharged to different states in half-cell batteries, versus a Na negative electrode. The structural evolution of the Na-containing electrodes is studied with synchrotron powder X-ray diffraction (PXRD) revealing an increase in microstrain and a gradual amorphization taking place with increasing Na content in the electrode. This indicates that a conversion reaction takes place in the electrochemical cell. X-ray absorption spectroscopy (XAS) at the tungsten L3 absorption edge shows a reduction in the tungsten oxidation state. Variable temperature (VT) PXRD shows that the Sc2(WO4)3 electrode remains relatively stable at higher temperatures, while the Na-containing samples undergo a number of phase transitions and/or turn amorphous above ∼400 °C. Although, Sc2(WO4)3 is a negative thermal expansion (NTE) material only a subtle change of the thermal expansion is found below 400 °C for the Na-containing electrodes. This work shows the complexity in employing an electrochemical cell to produce Na-containing Sc2(WO4)3 and the subsequent phase transitions. © 2018 The Royal Society of Chemistry.

Keywords

Electrochemical cells, Electrochemistry, Electrodes, Thermal expansion, Sodium, Sodium compounds, Tungsten, X-ray diffraction, X-ray spectroscopy

Citation

Andersen, H. L., Al Bahri, O. K., Tsarev, S., Johannessen, B., Schulz, B., Liu, J., Brand, H. E. A., Christensen, M. & Sharma, N. (2018). Structural evolution and stability of Sc 2 (WO 4) 3 after discharge in a sodium-based electrochemical cell. Dalton Transactions, 47(4), 1251-1260. doi:10.1039/C7DT04374K