An Easy and Ecological Method of Obtaining Hydrated and Non-Crystalline WO3−x for Application in Supercapacitors

Abstract

In this work, we report the synthesis of hydrated and non-crystalline WO3 flakes (WO3−x) via an environmentally friendly and facile water-based strategy. This method is described, in the literature, as exfoliation, however, based on the results obtained, we cannot say unequivocally that we have obtained an exfoliated material. Nevertheless, the proposed modification procedure clearly affects the morphology of WO3 and leads to loss of crystallinity of the material. TEM techniques confirmed that the process leads to the formation of WO3 flakes of a few nanometers in thickness. X-ray diffractograms affirmed the poor crystallinity of the flakes, while spectroscopic methods showed that the materials after exfoliation were abundant with the surface groups. The thin film of hydrated and non-crystalline WO3 exhibits a seven times higher specific capacitance (Cs) in an aqueous electrolyte than bulk WO3 and shows an outstanding long-term cycling stability with a capacitance retention of 92% after 1000 chronopotentiometric cycles in the three-electrode system. In the two-electrode system, hydrated WO3−x shows a Cs of 122 F g−1 at a current density of 0.5 A g−1. The developed supercapacitor shows an energy density of 60 Whkg−1 and power density of 803 Wkg−1 with a decrease of 16% in Csp after 10,000 cycles. On the other hand, WO3−x is characterized by inferior properties as an anode material in lithium-ion batteries compared to bulk WO3. Lithium ions intercalate into a WO3 crystal framework and occupy trigonal cavity sites during the electrochemical polarization. If there is no regular layer structure, as in the case of the hydrated and non-crystalline WO3, the insertion of lithium ions between WO3 layers is not possible. Thus, in the case of a non-aqueous electrolyte, the specific capacity of the hydrated and non-crystalline WO3 electrode material is much lower in comparison with the specific capacity of the bulk WO3-based anode material.

An Aqueous Exfoliation of WO3 as a Route for Counterions Fabrication—Improved Photocatalytic and Capacitive Properties of Polyaniline/WO3Composite

“…The XPS spectrum of the W4f region is presented in Figure 3 d. The doublet at 38.1 and 36.1 eV was recorded and ascribed to the binding energies of the W4f 5/2 and W4f 7/2 orbital electrons of W 6+ , respectively. According to our previous report about exfoliated WO 3 , exfoliation procedure leads to the formation of WO 3−x enriched in surface groups, where tungsten occurs in mixed oxidation states (V and VI) [ 29 ]. Here, the reduced form of W was not detected, which is probably the effect of the preparation procedure.…”

“…Thus, it is unlikely that the decrease of capacitance is related to the leach of components from the electrode material. According to the previous paper about electrochemical performance of exfoliated WO 3 , the capacitance retention of inorganic part should be high [ 29 ]. Additionally, when comparing CV curves recorded for PANI/WO 3 electrode before and after 1000 cycles (see Figure S1b ), the disappearance of the peaks related to the oxidation/reduction of polyaniline can be observed.…”

“…The procedure leading to formation of a transparent solution containing hydrated and amorphous WO 3 nanoflakes was described in our previous report [ 29 ]. To sum it up briefly, it is based on a one-stage, environmentally friendly and facile water-based strategy, which is described in the literature as exfoliation.…”

“…GO flakes suspended in water carry a negative surface charge that allows them to act as counter ions during PEDOT (poly(3,4-ethylenedioxythiophene)) and polypyrroleelectropolymerization [ 28 ]. On the other hand, we elaborated the method of WO 3 aqueous exfoliation that leads to the formation of a negatively charged suspension of WO 3−x , abundant with the surface groups [ 29 ]. Based on the idea of using GO as a counterion source, here we performed aniline electropolymerization in the presence of WO 3−x , without the addition of other electrolytes.…”

Highly stable electrochromic cells based on amorphous tungsten oxides prepared using a solution‐annealing process

“…Various transition metal oxides including Ti 2 O 5 , MoO 3 , V 2 O 5 , Nb 2 O 5 , and WO 3 have been used in catalysis and semiconductor applications. Tungsten (W) is the most well‐known TMD material that has been studied for many applications such as gas sensors, 8,9 solar cells, 10,11 supercapacitors, 12,13 batteries, 14,15 and, in particular, electrochromic devices 16,17 . There are numerous facile novels to prepare WO 3 which were reported by previous studies 18,19 .…”