Environmentally Friendly Water-Based Reduced Graphene Oxide/Cellulose Nanofiber Ink for Supercapacitor Electrode Applications

The agglomeration of reduced graphene oxide (rGO) in water makes the development of rGO inks for supercapacitor printing challenging. Cellulose nanofiber (CNF), a biodegradable and renewable nanomaterial, can act as a nanospacer, preventing the agglomeration and restacking of rGO flakes. In this work, rGO/CNF films were fabricated using an environmentally friendly water-based rGO/CNF ink. In the absence of an additional binder/surfactant, the rGO/CNF films demonstrated remarkably enhanced hydrophilicity while retaining good electrical conductivity. The concentration of CNF was varied to observe the variation in the electrochemical performance. At a current density of 1 mA/cm2, the rGO/CNF-15 film exhibited a maximum areal capacitance of 98.61 mF/cm2, closely matching that of pure rGO films. Because of its excellent electrical performance, ease of manufacturing, and environmental friendliness, this water-based rGO/CNF ink may have promising applications in the printing of supercapacitor electrodes.

Nanocellulose/two dimensional nanomaterials composites for advanced supercapacitor electrodes

With the emerging of the problems of environmental pollution and energy crisis, the development of high-efficiency energy storage technology and green renewable energy is imminent. Supercapacitors have drawn great attention in wearable electronics because of their good performance and portability. Electrodes are the key to fabricate high-performance supercapacitors with good electrochemical properties and flexibility. As a biomass based derived material, nanocellulose has potential application prospects in supercapacitor electrode materials due to its biodegradability, high mechanical strength, strong chemical reactivity, and good mechanical flexibility. In this review, the research progress of nanocellulose/two dimensional nanomaterials composites is summarized for supercapacitors in recent years. First, nanocellulose/MXene composites for supercapacitors are reviewed. Then, nanocellulose/graphene composites for supercapacitors are comprehensively elaborated. Finally, we also introduce the current challenges and development potential of nanocellulose/two dimensional nanomaterials composites in supercapacitors.

Multilayered bacterial cellulose/reduced graphene oxide composite films for self-standing and binder-free electrode application

Multilayered bacterial cellulose (MBC)/reduced graphene oxide (rGO) composite films were fabricated using dyeing method. First, MBC films were constructed by the static culturing of kombucha SCOBY bacterial cellulose in a rectangular plastic mold for 15 days. The MBC formed on the air-liquid interface was collected and employed as the matrix for the preparation of MBC/rGO composite films using dyeing method. As found, the color strength increased with an increase in dyeing cycle due to MBC and GO (rGO precursor) affinity. However, the surface hydrophilicity was found in the opposite direction due to the restacking of hydrophobic rGO nanosheets onto MBC surface after reduction step. SEM images confirmed that MBC/rGO composite films obtained by the dyeing method exhibited the intact multilayer structure. The electrochemical behavior of free-standing and binder-free MBC/rGO electrodes was evaluated. It was found that MBC-1 exhibited the highest specific capacitance value of 192.23 F/g at the current density of 1 A/g (calculated from GCD plots) due to good diffusion of electrolyte arising from surface wettability with current density performance of 66 %. An increase in dyeing cycle (MBC-2, MBC-3, and MBC-4) led to a gradual decrease in the corresponding specific capacitance value due to a gradual increase in the electrolyte resistance derived from an increasing surface hydrophobicity of the composite films. Finally, in all cases, long-term cycle stability of more than 90 % up to 10000 cycles was achievable.

Cellulose-Derived Nanostructures as Sustainable Biomass for Supercapacitors: A Review

Sustainable biomass has attracted a great attention in developing green renewable energy storage devices (e.g., supercapacitors) with low-cost, flexible and lightweight characteristics. Therefore, cellulose has been considered as a suitable candidate to meet the requirements of sustainable energy storage devices due to their most abundant nature, renewability, hydrophilicity, and biodegradability. Particularly, cellulose-derived nanostructures (CNS) are more promising due to their low-density, high surface area, high aspect ratio, and excellent mechanical properties. Recently, various research activities based on CNS and/or various conductive materials have been performed for supercapacitors. In addition, CNS-derived carbon nanofibers prepared by carbonization have also drawn considerable scientific interest because of their high conductivity and rational electrochemical properties. Therefore, CNS or carbonized-CNS based functional materials provide ample opportunities in structure and design engineering approaches for sustainable energy storage devices. In this review, we first provide the introduction and then discuss the fundamentals and technologies of supercapacitors and utilized materials (including cellulose). Next, the efficacy of CNS or carbonized-CNS based materials is discussed. Further, various types of CNS are described and compared. Then, the efficacy of these CNS or carbonized-CNS based materials in developing sustainable energy storage devices is highlighted. Finally, the conclusion and future perspectives are briefly conferred.

Lignin Cellulose Nanofibrils as an Electrochemically Functional Component for High-Performance and Flexible Supercapacitor Electrodes

The increasing demand for wearable electronics has driven the development of supercapacitor electrode materials toward enhanced energy density, while being mechanically strong, flexible, as well as environmentally friendly and low-cost. Taking advantage of faradaic reaction of quinone groups in natural lignin that is covalently bound to the high-strength cellulose nanofibrils, the fabrication of a novel class of mechanically strong and flexible thin film electrodes with high energy storage performance is reported. The electrodes were made by growing polyaniline (PANI) on flexible films composed of lignin-containing cellulose nanofibrils (LCNF) and reduced graphene oxide (rGO) nanosheets at various loading levels. The highest specific capacitance was observed for the LCNF/rGO/PANI electrode with 20 wt% rGO nanosheets (475 F g^-1 at 10 mV s^-1 and 733 F g^-1 at 1 mV s^-1 ), which represented a 68 % improvement as compared to a similar electrode made without lignin. In addition, the LCNF/rGO(20)/PANI electrode demonstrated high rate performance and cycle life (87 % after 5000 cycles). These results indicated that LCNF functioned as an electrochemically active multifunctional component to impart the composite electrode with mechanical strength and flexibility and enhanced overall energy storage performance. LCNF/rGO(20)/PANI electrode was further integrated in a flexible supercapacitor device, revealing the excellent promise of LCNF for fabrication of advanced flexible electrodes with reduced cost and environmental footprint and enhanced mechanical and energy storage performances.

Recent advances in bioelectronics chemistry

Research in bioelectronics is highly interdisciplinary, with many new developments being based on techniques from across the physical and life sciences. Advances in our understanding of the fundamental chemistry underlying the materials used in bioelectronic applications have been a crucial component of many recent discoveries. In this review, we highlight ways in which a chemistry-oriented perspective may facilitate novel and deep insights into both the fundamental scientific understanding and the design of materials, which can in turn tune the functionality and biocompatibility of bioelectronic devices. We provide an in-depth examination of several developments in the field, organized by the chemical properties of the materials. We conclude by surveying how some of the latest major topics of chemical research may be further integrated with bioelectronics.

An Overview of Bacterial Cellulose in Flexible Electrochemical Energy Storage

The emerging generation of flexible energy storage devices has accelerated the research pace in terms of new materials, new processing techniques, and new designs that can meet the demands of mechanical stability upon bending or stretching at an acceptable cost, without compromising their electrochemical performance. Among the materials currently explored, biomass-derived materials have received extensive attention, because they are renewable, low in cost, earth-abundant and structurally diverse. This review is focused on fundamentals and applications of the bio-derived material bacterial cellulose (BC) in flexible electrochemical energy storage systems. Specifically, recent advances are summarized in the utilization of BC in stretchable substrates, carbonaceous species, and scaffolds for flexible core component construction. Finally, several perspectives related to BC-based materials for flexible electrochemical energy storages are proposed, aiming to provide possible future research directions in these fields.

Green Synthesis of Free Standing Cellulose/Graphene Oxide/Polyaniline Aerogel Electrode for High-Performance Flexible All-Solid-State Supercapacitors

The cellulose/graphene oxide (GO) networks as the scaffold of free-standing aerogel electrodes are developed by using lithium bromide aqueous solution, as the solvent, to ensure the complete dissolution of cotton linter pulp and well dispersion/reduction of GO nanosheets. Polyaniline (PANI) nanoclusters are then coated onto cellulose/GO networks via in-situ polymerization of aniline monomers. By optimized weight ratio of GO and PANI, the ternary cellulose/GO3.5/PANI aerogel film exhibits well-defined three-dimensional porous structures and high conductivity of 1.15 S/cm, which contributes to its high areal specific capacitance of 1218 mF/cm2 at the current density of 1.0 mA/cm2. Utilizing this cellulose/GO3.5/PANI aerogel film as electrodes in a symmetric configuration supercapacitor can result in an outstanding energy density as high as 258.2 µWh/cm2 at a power density of 1201.4 µW/cm2. Moreover, the device can maintain nearly constant capacitance under different bending deformations, suggesting its promising applications in flexible electronics.

Nanocellulose, a Versatile Green Platform: From Biosources to Materials and Their Applications

With increasing environmental and ecological concerns due to the use of petroleum-based chemicals and products, the synthesis of fine chemicals and functional materials from natural resources is of great public value. Nanocellulose may prove to be one of the most promising green materials of modern times due to its intrinsic properties, renewability, and abundance. In this review, we present nanocellulose-based materials from sourcing, synthesis, and surface modification of nanocellulose, to materials formation and applications. Nanocellulose can be sourced from biomass, plants, or bacteria, relying on fairly simple, scalable, and efficient isolation techniques. Mechanical, chemical, and enzymatic treatments, or a combination of these, can be used to extract nanocellulose from natural sources. The properties of nanocellulose are dependent on the source, the isolation technique, and potential subsequent surface transformations. Nanocellulose surface modification techniques are typically used to introduce either charged or hydrophobic moieties, and include amidation, esterification, etherification, silylation, polymerization, urethanization, sulfonation, and phosphorylation. Nanocellulose has excellent strength, high Young's modulus, biocompatibility, and tunable self-assembly, thixotropic, and photonic properties, which are essential for the applications of this material. Nanocellulose participates in the fabrication of a large range of nanomaterials and nanocomposites, including those based on polymers, metals, metal oxides, and carbon. In particular, nanocellulose complements organic-based materials, where it imparts its mechanical properties to the composite. Nanocellulose is a promising material whenever material strength, flexibility, and/or specific nanostructuration are required. Applications include functional paper, optoelectronics, and antibacterial coatings, packaging, mechanically reinforced polymer composites, tissue scaffolds, drug delivery, biosensors, energy storage, catalysis, environmental remediation, and electrochemically controlled separation. Phosphorylated nanocellulose is a particularly interesting material, spanning a surprising set of applications in various dimensions including bone scaffolds, adsorbents, and flame retardants and as a support for the heterogenization of homogeneous catalysts.

Nanocellulose: a promising nanomaterial for advanced electrochemical energy storage

Nanocellulose has emerged as a sustainable and promising nanomaterial owing to its unique structures, superb properties, and natural abundance. Here, we present a comprehensive review of the current research activities that center on the development of nanocellulose for advanced electrochemical energy storage. We begin with a brief introduction of the structural features of cellulose nanofibers within the cell walls of cellulose resources. We then focus on a variety of processes that have been explored to fabricate nanocellulose with various structures and surface chemical properties. Next, we highlight a number of energy storage systems that utilize nanocellulose-derived materials, including supercapacitors, lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries. In this section, the main focus is on the integration of nanocellulose with other active materials, developing films/aerogel as flexible substrates, and the pyrolyzation of nanocellulose to carbon materials and their functionalization by activation, heteroatom-doping, and hybridization with other active materials. Finally, we present our perspectives on several issues that need further exploration in this active research field in the future.

Layer-by-Layer Assembled Bacterial Cellulose/Graphene Oxide Hydrogels with Extremely Enhanced Mechanical Properties

Uniform dispersion of two-dimensional (2D) graphene materials in polymer matrices remains challenging. In this work, a novel layer-by-layer assembly strategy was developed to prepare a sophisticated nanostructure with highly dispersed 2D graphene oxide in a three-dimensional matrix consisting of one-dimensional bacterial cellulose (BC) nanofibers. This method is a breakthrough, with respect to the conventional static culture method for BC that involves multiple in situ layer-by-layer assembly steps at the interface between previously grown BC and the culture medium. In the as-prepared BC/GO nanocomposites, the GO nanosheets are mechanically bundled and chemically bonded with BC nanofibers via hydrogen bonding, forming an intriguing nanostructure. The sophisticated nanostructure of the BC/GO leads to greatly enhanced mechanical properties compared to those of bare BC. This strategy is versatile, facile, scalable, and can be promising for the development of high-performance BC-based nanocomposite hydrogels.

Preparation of three-dimensional compressible MnO2@carbon nanotube sponges with enhanced supercapacitor performance

Fabrication of highly durable and compressible electrode materials for supercapacitors has been vital to promote the use of elastic electronics and deformation-tolerant devices.