Electrochemical capacitors fill the gap between high energy and high power storage devices. Within this matter EDLCs (Electric Double Layer Capacitors, which store charge electrostatically, are the most studied using carbon based materials. They present excellent performance concerning specific capacitance and cyclability, capable to undergo up to one million of cycles [1]. These materials present a low density, due to the activated carbon, making them unsuitable for applications where a high volumetric capacitance is required. For this special scope alluring high-density polycationic oxides exhibit a reliable advantage over the normal carbon based materials [2].

In this work, several materials of the Fe / W / O system have been investigated. Amongst them, two iron tungstate oxides (FeWO₄ and Fe2WO6) are of peculiar interest. They were successfully synthesized by several techniques, such as ceramic, hydrothermal and polyol-mediated routes [3]. The materials obtained underwent different heat treatments in order to acquire a crystalline structure. Afterwards, the different samples were characterized by X-ray diffraction, Scanning Electron Microscopy, Energy dispersive X-ray spectroscopy, Mössbauer Spectroscopy and surface area measurements, BET. The materials were assembled in a composite electrode to be studied in a three electrode set up in aqueous LiNO3 5M by cyclic voltammetry.

The results showed a compromise between the specific surface area, the particle size, morphology, and crystallization, as well as the mean Fe oxidation state that have a direct impact in the electrochemical performance.

References

[1] P. Simon and Y. Gogotsi, Nature Mater., 2008, 7, 845–854.

[2] O. Crosnier et. al., Curr. Opin. Electrochem., 2018, 9, 87–94.

[3] N. Goubard-Bretesché et. al., Electrochem. Comm., 2015, 57, 61–64.