Abstract
The stability upon cycling of Fe2WO6 used as a negative electrode material for electrochemical capacitors was investigated. The material was synthesized using low temperature conditions for the first time (220 °C). The electrochemical study of Fe2WO6 in a 5 M LiNO3 aqueous electrolyte led to a specific and volumetric capacitance of 38 F g−1 and 240 F cm−3 when cycled at 2 mV·s−1, respectively, associated with a minor capacitance loss after 10,000 cycles. In order to investigate this very good cycling stability, both surface and bulk characterization techniques (such as Transmission Electron Microscopy, Mössbauer spectroscopy, and magnetization measurements) were used. Only a slight disordering of the Fe3+ cations was observed in the structure, explaining the good stability of the Fe2WO6 upon cycling. This study adds another pseudocapacitive material to the short list of compounds that exhibit such a behavior up to now.
Highlights
We investigated the possible changes occurring in this electrode material caused by a long-term cycling using several characterization techniques
Fe2 WO6 leads to an amorphous material, unlike some of the other tungstates synthesized by a similar method and already reported in the literature [14,22]
Fe2 WO6 was synthesized for the first time at low temperature (220 ◦ C)
Summary
Most of the current commercial ECs are based on activated carbon electrodes that exhibit specific capacitance in the range 100–200 F g−1 depending on the electrolyte, the pore size distribution, and other parameters [3,4]. They are known as Electric Double Layer Capacitors (EDLCs) and present relatively low volumetric performance due to the low density of the active material (~1 g·cm−3 ). One characteristic of EDLCs is the charge storage mechanism, which processes mainly by electrostatic interactions at the carbon/electrolyte interface, leading to the well-known rectangular signature on the related cyclic voltammograms (CV) [5,6]. The charge storage mechanism in these latter compounds relies upon fast and reversible redox reactions happening at the vicinity of the electrode material, as it has been already demonstrated for several materials such as RuO2 [9], MnO2 [10,11], or
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