Redox electroactive group-modified carbon cloth as flexible electrode for high performance solid-state supercapacitors

One-Step Electrodeposition of Polyaniline Nanorods on Carbon Cloth for High-Performance Flexible Supercapacitors

The electrochemical performance of the carbon cloth (CC)-based electrodes is determined by the kind, content, morphology, and size of the modified pseudocapacitive materials, as well as the interaction with CC. Also, such structural parameters were mainly dependent on the deposition condition. More uniform polyaniline (PANI) could be obtained by electrochemical polymerization in comparison to chemical oxidation polymerization. However, two steps of electrodeposition were usually needed for nucleation and growth. Here, based on the comprehensive optimization of the electrodeposition condition, well-defined PANI nanorods anchored on the functionalized carbon cloth (FCC) as flexible electrodes (FCC@PANI) were synthesized by a facile one-step electrochemical polymerization. Compared with the FCC electrode, the resultant FCC@PANI-4 sample possessed good cycling stability (98.3% capacitance retention after 10,000 cycles), higher specific capacitances of 2312 mF cm-2 (1.0 mA cm-2) and 107 F g-1 (1.0 A g-1) with the boosting ratio in the areal specific capacitance (CA), and mass specific capacitances (Cm) of 169 and 181%, respectively. The improvement in both specific capacitance and cycling stability was obtained by the strong interaction between the FCC and the modified PANI nanorods with enhanced utilization efficiency of electroactive materials. Furthermore, the symmetric solid-state device assembled using the FCC@PANI-4 electrode delivered a maximum energy density of 0.079 mWh cm-2 at a power density of 0.363 mW cm-2.

COF-Based Electrodes with Vertically Supported Tentacle Array for Ultrahigh Stability Flexible Energy Storage

As an emerging porous crystal polymer, covalent organic frameworks (COFs) possess unique characteristics, such as high porosity, excellent stability, diverse topologies, designable open channels, and functional tunability. However, limited by the solid powder form, most COFs display low active site utilization and weak binding force with the current collector. In this pioneering research, we integrate redox-active COFs onto carbon fiber surfaces (AC-COFs) via strong covalent bridging. The 2,6-diaminoanthraquinone (DAAQ) pillars embedded on the carbon fiber surface are the key to precisely controlling the growth direction of COFs. The obtained tentacle-like array vertically supported on the surface of the carbon fiber can effectively induce charge transfer and prevent COFs from aggregating/collapsing. The strong covalent coupling and increase of accessible active sites contributed to the high specific capacitance of AC-COFs electrode (1034 mF cm^-2). In addition, the COF-based flexible electrode retains an initial capacitance of 98% after 20000 charge-discharge cycles. The flexible all-solid-state symmetric supercapacitor is assembled by PVA/H₂SO₄ gel electrolyte with an areal capacitance of 715 mF cm^-2. Besides, a red LED can be easily powered by three-bending AC-COFs//AC-COFs devices. The innovative synthesis strategy opens up new opportunities to develop high-performance flexible energy storage devices based on COFs.

High Performance Asymmetric Supercapacitor Based on Hierarchical Carbon Cloth In Situ Deposited with h-WO3 Nanobelts as Negative Electrode and Carbon Nanotubes as Positive Electrode

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.