Investigating the Cycling Stability of Fe2WO6 Pseudocapacitive Electrode Materials

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.

Cationic Ordering, Solid Solution Domain, and Diffuse Reflectance in Fe2WO6 Polymorphs

“…The Rietveld refinement in the Pbcn space group, including a minor contribution (below 0.5%) from hematite (H peaks), is shown in Figure together with the cell parameters and crystallographic parameters; a crystallographic information file is provided in the Supporting Information. A Rietveld refinement based on laboratory X-ray data, very recently reported for a sample prepared by a polyol solution route, is in good agreement with this structural model . However, the excellent signal-to-noise ratio offered by our synchrotron data reveals that a few very small peaks remain unindexed at d = 5.60, 4.59, and 3.28 Å.…”

“…Historically, the interest in the properties of Fe 2 WO 6 was mostly focused on the magnetism and/or transport properties of its polymorphs, considered in the framework of the AB 2 O 6 structures combining a magnetic cation B with an A cation of high formal charge. − In recent years, the environmentally benign character of iron has spurred the interest for iron-based oxides. Accordingly, Fe 2 WO 6 has become the focus of much more varied investigations regarding the photoelectrochemical activity, − photocatalytic properties, − reversible capacity as a lithium-ion battery electrode, , pseudocapacitance in electrochemical capacitors, magnetodielectric properties, thermoelectric properties, , and biological activity . Indeed, half of the ∼30 papers about Fe 2 WO 6 have been published since 2014, with 9 of them published since 2020.…”

“…Some of them concern the polymorphism of Fe 2 WO 6 . Most of the older literature and all of the recent papers have focused on one polymorph only, usually either the high-temperature γ polymorph − ,,− or the α polymorph obtained by low-temperature solution routes. ,,,, In the early 90s, Walczak et al identified a third polymorph, labeled β, whose synthesis required long heat treatments; shortly afterward, Guskos et al , reported some magnetic and electric transport data for the three polymorphs. To date, their work remains the only comparative study of the α/β/γ polymorphs, and further work is needed to clarify the influence of the synthesis conditions on the polymorphism and on structural properties such as the cationic order/disorder.…”

“…Solution routes are the best choice to prepare single phases of the three polymorphs by the same synthesis technique since the reproducible synthesis of the low-temperature α polymorph by solid-state reaction is difficult. Several solution-based syntheses of mixed iron-tungsten oxides were reported in the literature in recent years, such as spray pyrolysis for the synthesis of thin films , or various (co)­precipitation procedures. − , In the present work, a new procedure was developed based on spray-drying an aqueous solution, followed by combustion and heat treatment of the spray-dried precursor. The spray-drying technique is an industrially upscalable method suitable for the reproducible production of large quantities. , The composition of the solution was optimized so that all counterions decompose during the heat treatment, and citric acid was used as a complexing agent to promote a homogeneous distribution of cations in the precursor powder.…”

Revisiting the five-decade-old structure of the Fe2WO6 powder with incommensurate modulations

“…It showed interesting pseudocapacitive performance in terms of volumetric capacitance thanks to the high density of this oxide and long-term cycling behavior was achieved with such electrode. 14 For this latter purpose, Fe 2 WO 6 sample was prepared using a polyol-mediated route at low temperature (220°C). A temperature-dependent X-ray diffraction study indicated, at 800°C, the formation of a well-crystallized phase whose diffraction peaks were successfully indexed into the cell of the α-PbO 2 structure (a α-PbO2 , b α-PbO2 , c α-PbO2 , Pbcn space group).…”