Abstract
Urchin-like tungsten oxide (WO3) microspheres self-assembled with nanobelts are deposited on the surface of the hydrophilic carbon cloth (CC) current collector via hydrothermal reaction. The WO3 nanobelts in the urchin-like microspheres are in the hexagonal crystalline phase, and their widths are around 30–50 nm. The resulted hierarchical WO3/CC electrode exhibits a capacitance of 3400 mF/cm2 in H2SO4 electrolyte in the voltage window of −0.5~0.2 V, which makes it an excellent negative electrode for asymmetric supercapacitors. To improve the capacitive performance of the positive electrode and make it comparable with that of the WO3/CC electrode, both the electrode material and the electrolyte have been carefully designed and prepared. Therefore, the hydrophilic CC is further coated with carbon nanotubes (CNTs) to create a hierarchical CNT/CC electrode via a convenient flame synthesis method, and a redox-active electrolyte containing an Fe2+/Fe 3+ couple is introduced into the half-cell system as well. As a result, the high performance of the asymmetric supercapacitor assembled with both the asymmetric electrodes and electrolytes has been realized. It exhibits remarkable energy density as large as 403 μW h/cm2 at 15 mW/cm2 and excellent cyclic stability after 10,000 cycles.
Highlights
Supercapacitors have been considered a new type of energy storage device because of their long cycle life, fast charge and discharge, and excellent power density [1,2], their low energy density severely limits their practical applications
Urchin-like microspheres self-assembled by h-WO3 nanobelts with widths around 30 ~ 50 nm are deposited on the surface of the hydrophilic carbon cloth (CC) through a hydrothermal reaction
MA/cm2) in 1M H2SO4 electrolyte, the resulted hierarchical WO3/CC electrode is directly applied as the negative electrode of the ASC device
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. 3D nanostructures could facilitate the mass transport of the electrochemically active species in the electrode/electrolyte interface and promote the performance of the electrode materials Materials with such hierarchical structures are attracting more and more interest from researchers in the field of energy conversion and storage devices [20,21,22]. Apart from transition metal oxide electrodes that display high electrochemical activity in the negative voltage range and can be used as a perfect negative electrode in asymmetric supercapacitors, the positive electrode needs to be carefully selected and designed to assemble a high-performance energy storage device. Compared with pseudo-capacitance electrode materials, they have better physical and chemical stability, higher electrical conductivity, larger specific surface area [23,24,25], and more importantly, stable electrochemical performance in acid electrolytes in the wide potential window. The performance of the asymmetric supercapacitors assembled with both the hierarchical electrodes and electrolytes will be investigated as well
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