High Performance Supercapacitors Based on Mesopore Structured Multiwalled Carbon Nanotubes

Higher specific capacitance and compressibility nanocellulose based supercapacitor hydrogel electrode assembled by efficient impregnation

The rational and effective combination of different electrochemical substances to prepare high-performance supercapacitor electrodes has been widely studied by researchers. Currently, most work focuses on polymerizing conductive polymers onto the surface of nanocellulose and carbon materials, and then preparing them into supercapacitor electrodes. This method is effective, but the process is cumbersome. Therefore, we propose a simpler and more effective method. A hydrogel was prepared by using TEMPO oxidized cellulose nanofibers (TOCNF)/multi walled carbon nanotubes (MWCNT), and then immersed in aniline and FeCI3 solutions for 24 h to obtain a hydrogel electrode. At a current density of 0.5 mA cm-2, it exhibits an area specific capacitance of 1028 mF cm-2, with a maximum strain of 58 % and a compressive stress of 150 KPa. The assembled symmetrical supercapacitor exhibits a high specific capacitance of 303 mF cm-2 at a current density of 0.5 mA cm-2. The research results indicate that the proposed method is a new feasible approach for developing supercapacitors.

Application of Thermal Response Measurements to Investigate Enhanced Water Adsorption Kinetics in Ball-Milled C2 N-Type Materials

Sorption-based water capture is an attractive solution to provide potable water in arid regions. Heteroatom-decorated microporous carbons with hydrophilic character are promising candidates for water adsorption at low humidity, but the strong affinity between the polar carbon pore walls and water molecules can hinder the water transport within the narrow pore system. To reduce the limitations of mass transfer, C2 N-type carbon materials obtained from the thermal condensation of a molecular hexaazatriphenylene-hexacarbonitrile (HAT-CN) precursor were treated mechanochemically via ball milling. Scanning electron microscopy as well as static light scattering reveal that large pristine C2 N-type particles were split up to a smaller size after ball milling, thus increasing the pore accessibility which consequently leads to faster occupation of the water vapor adsorption sites. The major aim of this work is to demonstrate the applicability of thermal response measurements to track these enhanced kinetics of water adsorption. The adsorption rate constant of a C2 N material condensed at 700 °C remarkably increased from 0.026 s-1 to 0.036 s-1 upon ball milling, while maintaining remarkably high water vapor capacity. This work confirms the advantages of small particle sizes in ultramicroporous materials on their vapor adsorption kinetics. It is demonstrated that thermal response measurements are a valuable and time-saving method to investigate water adsorption kinetics, capacities, and cycling stability.

In Situ Synthesis of CoCeSx Bimetallic Sulfide Nanoparticles on a Bi-Pyrene Terminated Molecular Wire Modified Graphene Surface for Supercapacitors

The excellent electrical conductivity of graphene is due to its highly-conjugated structures. Manipulation of the electronic and mechanical properties of graphene can be achieved by controlling the destruction of its in-sheet conjugation system. Herein, we report the preparation of CoCeS_x -SA@BPMW@RGO through π-π stacking interactions at the molecular level. In this study, sodium alginate was reacted with Co²⁺ and Ce³⁺ , and the composite was loaded onto a graphene surface. The graphene sheets were prepared using a bi-pyrene terminated molecular wire (BPMW) to avoid re-stacking of the grapheme sheets, thereby forming nanoscale spaces between sheets. The angle between the BPMW coplanar pyrene group and the phenyl group was 33.2°, and the graphene layer is supported in an oblique direction. Finally, a three-dimensional porous composite was obtained after annealing and vulcanization. The obtained CoCeS_x -SA@BPMW@RGO exhibited excellent electrical conductivity and remarkable cycle stability. When the current density was 1 A g^-1 , its specific capacitance was as high as 1004 F g^-1 . BPMW modifies graphene through the synergistic effect of π-π stacking interaction and special structure to obtain excellent electrochemical performance. Moreover, a solid-state asymmetric supercapacitor device was fabricated based on the synthesized CoCeS_x -SA@BPMW@RGO hybrid, which exhibited a power density of 979 W kg^-1 at an energy density of 23.96 Wh kg^-1 .