Facile construction of hierarchically porous carbon nanofiber aerogel for high-performance supercapacitor

Hierarchical porous carbon derived from jujube fruits as sustainable and ultrahigh capacitance material for advanced supercapacitors

Herein, we propose a new highly porous natural carbon material from renewable and inexpensive jujube fruits as a carbon source applied in supercapacitors. The combination of pre-carbonization and chemical activation approaches is employed to product hierarchical porous carbon from natural jujube fruits. The specific surface area of the prepared porous carbon is increased from 85.4 to 1135 m² g^-1 after the completion of NaOH activation at an optimized condition, which is beneficial to enhancing electrochemical performance of supercapacitors. A 3-electrode configuration was utilized to explore the electrochemical ability of porous carbon in 6 M KOH electrolyte. The acquired results demonstrate that porous carbon displays the specific capacitance of 587, 460 and 324 F g^-1 at 0.1, 1 and 100 A g^-1, respectively, which is confirmed by its admirable capacitance and rate behaviors. The porous carbon also shows a wonderful durability with a capacitance retention of 92.2% after 130,000 cycles at 50 A g^-1. Moreover, the assembled symmetrical coin-like supercapacitors with wide potential window of 2.5 V in 1 M Et₄NBF₄/AN organic electrolyte offer a high energy density of 23.7 Wh kg^-1 at 0.629 kW kg^-1 with remaining 94% capacitance over 10,000 cycles at 30 A g^-1, indicating its practical application prospect. As a result, the present study proves the natural jujube fruits is a promising sustainable carbon source for making more economical and efficient electrode material of high performance supercapacitors.

Advances in Manufacturing Composite Carbon Nanofiber-Based Aerogels

This article provides an overview on manufacturing composite carbon nanofiber-based aerogels through freeze casting technology. As known, freeze casting is a relatively new manufacturing technique for generating highly porous structures. During the process, deep cooling is used first to rapidly solidify a well-dispersed slurry. Then, vacuum drying is conducted to sublimate the solvent. This allows the creation of highly porous materials. Although the freeze casting technique was initially developed for porous ceramics processing, it has found various applications, especially for making aerogels. Aerogels are highly porous materials with extremely high volume of free spaces, which contributes to the characteristics of high porosity, ultralight, large specific surface area, huge interface area, and in addition, super low thermal conductivity. Recently, carbon nanofiber aerogels have been studied to achieve exceptional properties of high stiffness, flame-retardant and thermal-insulating. The freeze casting technology has been reported for preparing carbon nanofiber composite aerogels for energy storage, energy conversion, water purification, catalysis, fire prevention etc. This review deals with freeze casting carbon nanofiber composite materials consisting of functional nanoparticles with exceptional properties. The content of this review article is organized as follows. The first part will introduce the general freeze casting manufacturing technology of aerogels with the emphasis on how to use the technology to make nanoparticle-containing composite carbon nanofiber aerogels. Then, modeling and characterization of the freeze cast particle-containing carbon nanofibers will be presented with an emphasis on modeling the thermal conductivity and electrical conductivity of the carbon nanofiber network aerogels. After that, the applications of the carbon nanofiber aerogels will be described. Examples of energy converters, supercapacitors, secondary battery electrodes, dye absorbents, sensors, and catalysts made from composite carbon nanofiber aerogels will be shown. Finally, the perspectives to future work will be presented.