Fabrication and electrochemical properties of flexible transparent supercapacitor electrode materials based on cellulose nanofibrils and reduced graphene oxide

Abstract

In this research, flexible transparent supercapacitor electrode materials were fabricated using cellulose nanofibrils (CNFs) and reduced graphene oxide (RGO) via a layer‐by‐layer (LbL) self‐assembly method. First, a transparent film was obtained by vacuum filtration of a CNF suspension, which was isolated from bamboo materials using a combination of 2,2,6,6‐tetramethylpiperidin‐1‐oxyl radical catalytic oxidation and ultrasonic treatment. Subsequently, graphene oxide (GO) was deposited on the surface of the CNF film using Cu2+ as a cross‐linking agent via the LbL self‐assembly technique and then was reduced by L‐ascorbic acid under mild reaction conditions. The degree of reduction of the GO on the CNF film surface was investigated by X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and Fourier transform infrared spectroscopy (FT‐IR); concurrently, the effect of the number of self‐assembly times on the transparency, mechanical properties, and conductivity was also evaluated. The XPS, Raman, and FT‐IR spectral analyses proved that the CNFs/GO composite films were successfully reduced to CNFs/RGO composite films, of which the transparency and mechanical properties decreased with the increase in the number of self‐assembly times, while the conductivity remarkably raised. Based on the analysis of the results, the CNFs/RGO composite film obtained after 18 self‐assembly cycles exhibited excellent transparency, good tensile strength, and a high conductivity. Therefore, the CNFs/RGO composite film was selected to fabricate a supercapacitor electrode material, and the obtained supercapacitor displayed excellent electrochemical properties, in which the areal specific capacitance was 2.25 mF cm−2 at a current density of 0.01 mA cm−2 and the capacitance retention reached 97.3% after 1500 cycles. The presented strategy provides a good reference for the development of transparent and portable energy storage devices.

Advanced Nanocellulose‐Based Composites for Flexible Functional Energy Storage Devices

“…The unique structures and properties of nanocellulose may endow the film composites with good hydrophilic property, mechanical strength, excellent flexibility, as well as optical transparency, depending on the characteristics of the thickness of the as‐obtained films and the nanocellulose‐based‐units. [ 24,101–103 ] Vacuum filtration is among the most widely used methods for the preparation of composite films and can be easily achieved in a laboratory with simple equipment. However, the area of obtained composite films is limited by the filter size.…”

Fabrication and Performance of Self-Supported Flexible Cellulose Nanofibrils/Reduced Graphene Oxide Supercapacitor Electrode Materials

“…Figure 1 illustrates the preparation process of the CNF/RGO composite films. Previous research indicated that it is easier to isolate the CNFs from bamboo materials than other bioresources due to their fewer transverse tissues; also, these CNFs have a higher depth-diameter aspect ratio than those obtained from wood materials, which is better for dispersing carbon-based nanomaterials [31,32,42,43]. Moreover, in this study, we developed a simple method to fabricate the CNF/RGO films, in which the mixture of CNFs and GO was filtrated to form a film with a higher thickness, and then gelled into hydrogel, before finally being dried into a film.…”

“…They are usually extracted from biomass fibers by the combination of 2,2,6,6-tetramethylpiperidin-1-oxyl radical (TEMPO) oxidizing and ultrasonic processing [29,30]. In this process, TEMPO oxides the hydroxyl located in C6 of the cellulose molecule to carboxyl, and the negative charges on the carboxyl are of mutual repulsion, which weakens intermolecular hydrogen bonding, leading to the microfibrils being easily isolated into cellulose nanofibers only under moderate ultrasound treatment [31,32]. As a result, graphene oxide (GO) can be uniformly dispersed in the cellulose nanofibril (CNF) solution under the action of rich carboxyls and hydroxyls [33].…”

A Review on Nanocellulose and Its Application in Supercapacitors

“…Graphene exhibits good conductivity and specific surface area of 2620 m 2 g −1 , making it the preferable carbon material for supercapacitor application, including the graphene derivatives: graphene oxide and reduced graphene oxide. [82] Both, graphene oxide and reduced graphene oxide, tend to agglomerate due to the 𝜋-𝜋 stacking effect of graphene nanosheets. The diffusion of electrolyte ions then becomes constrained, which is not favorable for supercapacitors.…”