Carbonised Human Hair Incorporated in Agar/KGM Bioscaffold for Tissue Engineering Application: Fabrication and Characterisation

Carbon derived from biomass waste usage is rising in various fields of application due to its availability, cost-effectiveness, and sustainability, but it remains limited in tissue engineering applications. Carbon derived from human hair waste was selected to fabricate a carbon-based bioscaffold (CHAK) due to its ease of collection and inexpensive synthesis procedure. The CHAK was fabricated via gelation, rapid freezing, and ethanol immersion and characterised based on their morphology, porosity, Fourier transforms infrared (FTIR), tensile strength, swelling ability, degradability, electrical conductivity, and biocompatibility using Wharton’s jelly-derived mesenchymal stem cells (WJMSCs). The addition of carbon reduced the porosity of the bioscaffold. Via FTIR analysis, the combination of carbon, agar, and KGM was compatible. Among the CHAK, the 3HC bioscaffold displayed the highest tensile strength (62.35 ± 29.12 kPa). The CHAK also showed excellent swelling and water uptake capability. All bioscaffolds demonstrated a slow degradability rate (<50%) after 28 days of incubation, while the electrical conductivity analysis showed that the 3AHC bioscaffold had the highest conductivity compared to other CHAK bioscaffolds. Our findings also showed that the CHAK bioscaffolds were biocompatible with WJMSCs. These findings showed that the CHAK bioscaffolds have potential as bioscaffolds for tissue engineering applications.

Lignocellulosic Biomass-Derived Carbon Electrodes for Flexible Supercapacitors: An Overview

With the increasing demand for high-performance electronic devices in smart textiles, various types of flexible/wearable electronic device (i.e., supercapacitors, batteries, fuel cells, etc.) have emerged regularly. As one of the most promising wearable devices, flexible supercapacitors from a variety of electrode materials have been developed. In particular, carbon materials from lignocellulosic biomass precursor have the characteristics of low cost, natural abundance, high specific surface area, excellent electrochemical stability, etc. Moreover, their chemical structures usually contain a large number of heteroatomic groups, which greatly contribute to the capacitive performance of the corresponding flexible supercapacitors. This review summarizes the working mechanism, configuration of flexible electrodes, conversion of lignocellulosic biomass-derived carbon electrodes, and their corresponding electrochemical properties in flexible/wearable supercapacitors. Technology challenges and future research trends will also be provided.

Controlled preparation of interconnected 3D hierarchical porous carbons from bacterial cellulose-based composite monoliths for supercapacitors

The controlled design and synthesis of porous carbons with anticipated microstructures and morphologies, and a high specific surface area (SSA) have been focused on for supercapacitor development. Here, hierarchical porous carbons (HPCs) with an interconnected three-dimensional morphology derived from a natural-based bacterial cellulose (BC) composite have been successfully prepared by thermally induced phase separation of poly(ethylene-co-vinyl alcohol) (EVOH) and subsequent carbonization/activation. The SSA and porous architectures can be controlled by fine-tuning the preparation conditions such as the precursor morphology and structure, activator dosage and activation temperature, and the relationships between the super-capacitive properties and the SSA and pore size distribution have been further investigated. The obtained porous carbon material possesses a hierarchical porous structure with moderate micropores, favorable mesopores, interconnected macropores, a high SSA of 2161 m² g^-1 and a maximum oxygen-dopant content of 9.99%, enabling an increase in the active materials utilization efficiency and wettability. Due to the synergistic effects of these features, the obtained porous carbon electrode used in a supercapacitor shows a high specific capacitance of 420 F g^-1 at 0.5 A g^-1, excellent rate performance with 75% capacitance retention at 20 A g^-1, and good cycling stability with ∼96.1% retention even after 10 000 continuous charge-discharge cycles at 5 A g^-1. Additionally, the assembled supercapacitor based on porous carbon displays a moderate energy density of 20 W h kg^-1. The good electrochemical performance and facile effective synthesis of bio-derived carbon materials with tunable porous structures indicate promising applications in supercapacitors.

Self-Assembled Dipeptide Aerogels with Tunable Wettability

Constructing supramolecular materials with tunable properties and functions is a great challenge due to the complex competition between multiple assembly pathways. Herein, we report that dipeptides can self-assemble into aerogels with entirely different surface wettability through precisely controlling the assembly pathways. Charged groups or aromatic residues are selectively exposed on the surface of their nanoscale building blocks which results either in a superhydrophilic or highly hydrophobic surface. With this special property, single component dipeptide aerogels can play diverse roles in medical care applications. This study suggests great promise in the synthesis of supramolecular materials with different targeted functions from the same molecular unit.

Temperature-Invariant Superelastic and Fatigue Resistant Carbon Nanofiber Aerogels

Superelastic and fatigue-resistant materials that can work over a wide temperature range are highly desired for diverse applications. A morphology-retained and scalable carbonization method is reported to thermally convert a structural biological material (i.e., bacterial cellulose) into graphitic carbon nanofiber aerogel by engineering the pyrolysis chemistry. The prepared carbon aerogel perfectly inherits the hierarchical structures of bacterial cellulose from macroscopic to microscopic scales, resulting in remarkable thermomechanical properties. In particular, it maintains superelasticity without plastic deformation even after 2 × 10⁶ compressive cycles and exhibits exceptional temperature-invariant superelasticity and fatigue resistance over a wide temperature range at least from -100 to 500 °C. This aerogel shows unique advantages over polymeric foams, metallic foams, and ceramic foams in terms of thermomechanical stability and fatigue resistance, with the realization of scalable synthesis and the economic advantage of biological materials.

Poly(Ionic Liquid)-Derived Graphitic Nanoporous Carbon Membrane Enables Superior Supercapacitive Energy Storage

High energy/power density, capacitance, and long-life cycles are urgently demanded for energy storage electrodes. Porous carbons as benchmark commercial electrode materials are underscored by their (electro)chemical stability and wide accessibility, yet are often constrained by moderate performances associated with their powdery status. Here via controlled vacuum pyrolysis of a poly(ionic liquid) membrane template, advantageous features including good conductivity (132 S cm^-1 at 298 K), interconnected hierarchical pores, large specific surface area (1501 m² g^-1), and heteroatom doping are realized in a single carbon membrane electrode. The structure synergy at multiple length scales enables large areal capacitances both for a basic aqueous electrolyte (3.1 F cm^-2) and for a symmetric all-solid-state supercapacitor (1.0 F cm^-2), together with superior energy densities (1.72 and 0.14 mW h cm^-2, respectively) without employing a current collector. In addition, theoretical calculations verify a synergistic heteroatom co-doping effect beneficial to the supercapacitive performance. This membrane electrode is scalable and compatible for device fabrication, highlighting the great promise of a poly(ionic liquid) for designing graphitic nanoporous carbon membranes in advanced energy storage.

Supramolecular Self-Assembly of 3D Conductive Cellulose Nanofiber Aerogels for Flexible Supercapacitors and Ultrasensitive Sensors

Nature employs supramolecular self-assembly to organize many molecularly complex structures. Based on this, we now report for the first time the supramolecular self-assembly of 3D lightweight nanocellulose aerogels using carboxylated ginger cellulose nanofibers and polyaniline (PANI) in a green aqueous medium. A possible supramolecular self-assembly of the 3D conductive supramolecular aerogel (SA) was provided, which also possessed mechanical flexibility, shape recovery capabilities, and a porous networked microstructure to support the conductive PANI chains. The lightweight conductive SA with hierarchically porous 3D structures (porosity of 96.90%) exhibited a high conductivity of 0.372 mS/cm and a larger area-normalized capacitance (C_s) of 59.26 mF/cm², which is 20 times higher than other 3D chemically cross-linked nanocellulose aerogels, fast charge-discharge performance, and excellent capacitance retention. Combining the flexible SA solid electrolyte with low-cost nonwoven polypropylene and PVA/H₂SO₄ yielded a high normalized capacitance (C_m) of 291.01 F/g without the use of adhesive that was typically required for flexible energy storage devices. Furthermore, the supramolecular conductive aerogel could be used as a universal sensitive sensor for toxic gas, field sobriety tests, and health monitoring devices by utilizing the electrode material in lightweight supercapacitor and wearable flexible devices.

Superelastic Hard Carbon Nanofiber Aerogels

Superelastic carbon aerogels have been widely explored by graphitic carbons and soft carbons. These soft aerogels usually have delicate microstructures with good fatigue resistance but ultralow strength. Hard carbon aerogels show great advantages in mechanical strength and structural stability due to the sp³ -C-induced turbostratic "house-of-cards" structure. However, it is still a challenge to fabricate superelastic hard carbon-based aerogels. Through rational nanofibrous structural design, the traditional rigid phenolic resin can be converted into superelastic hard carbon aerogels. The hard carbon nanofibers and abundant welded junctions endow the hard carbon aerogels with robust and stable mechanical performance, including superelasticity, high strength, extremely fast recovery speed (860 mm s^-1 ), low energy-loss coefficient (<0.16), long cycle lifespan, and heat/cold-endurance. These emerging hard carbon nanofiber aerogels hold a great promise in the application of piezoresistive stress sensors with high stability and wide detection range (50 kPa), as well as stretchable or bendable conductors.

Nanocellulose-Enabled, All-Nanofiber, High-Performance Supercapacitor

Nanocellulose has been used as a sustainable nanomaterial for constructing advanced electrochemical energy-storage systems with renewability, lightweight, flexibility, high performance, and satisfying safety. Here, we demonstrate a high-performance all-nanofiber asymmetric supercapacitor (ASC) assembled using a forest-based, nanocellulose-derived hierarchical porous carbon (nanocellulose carbon, HPC) anode, a mesoporous nanocellulose membrane separator (nanocellulose separator), and a NiCo₂O₄ cathode with nanocellulose carbon as the support matrix (nanocellulose cathode, HPC/NiCo₂O₄). HPC has a three-dimensional porous structure comprising interconnected nanofibers with an ultrahigh surface area of 2046 m² g^-1. When integrated with the mesoporous feature of the nanocellulose membrane separator, these properties facilitate the quick delivery of both ions and electrons even with a thick (up to several hundreds of micrometers) and highly loaded (5.8 mg cm^-2) ASC design. Consequently, the all-nanofiber ASC demonstrates a high electrochemical performance (64.83 F g^-1 (10.84 F cm^-3) at 0.25 A g^-1 and 32.78 F g^-1 or 5.48 F cm^-3 at 4 A g^-1) that surpasses most cellulose-based ASCs ever reported. Moreover, the nanocellulose components promise renewability, low cost, and biodegradability, thereby presenting a promising direction toward high-power, environmentally friendly, and renewable energy-storage devices.

Nanocellulose toward Advanced Energy Storage Devices: Structure and Electrochemistry

Cellulose is the most abundant biopolymer on Earth and has long been used as a sustainable building block of conventional paper. Note that nanocellulose accounts for nearly 40% of wood's weight and can be extracted using well-developed methods. Due to its appealing mechanical and electrochemical properties, including high specific modulus (∼100 GPa/(g/cm³)), excellent stability in most solvents, and stability over a wide electrochemical window, nanocellulose has been widely used as a separator, electrolyte, binder, and substrate material for energy storage. Additionally, nanocellulose-derived carbon materials have also drawn increasing scientific interest in sustainable energy storage due to their low-cost and raw-material abundance, high conductivity, and rational electrochemical performance. The inexpensive and environmentally friendly nature of nanocellulose and its derivatives as well as simple fabrication techniques make nanocellulose-based energy storage devices promising candidates for the future of "green" and renewable electronics. For nanocellulose-based energy storage, structure engineering and design play a vital role in achieving desired electrochemical properties and performances. Thus, it is important to identify suitable structure and design engineering strategies and to better understand their relationship. In this Account, we review recent developments in nanocellulose-based energy storage. Due to the limited space, we will mainly focus on structure design and engineering strategies in macrofiber, paper, and three-dimensional (3D) structured electrochemical energy storage (EES) devices and highlight progress made in our group. We first present the structure and properties of nanocellulose, with a particular discussion of nanocellulose from wood materials. We then go on to discuss studies on nanocellulose-based macrofiber, paper, and 3D wood- and other aerogel-based EES devices. Within this discussion, we highlight the use of natural nanocellulose as a flexible substrate for a macrofiber supercapacitor and an excellent electrolyte reservoir for a breathable textile lithium-oxygen battery. Paper batteries and supercapacitors using nanocellulose as a green dispersant, nanocellulose-based paper as a flexible substrate, and nanocellulose as separator and electrolyte are also examined. We highlight recent progress on wood-based batteries and supercapacitors, focusing on the advantages of wood materials for energy storage, the structure design and engineering strategies, and their microstructure and electrochemical properties. We discuss the influence of structure (particularly pores) on the electrochemical performance of the energy storage devices. By taking advantage of the straight, nature-made channels in wood materials, ultrathick, highly loaded, and low-tortuosity energy storage devices are demonstrated. Finally, we offer concluding remarks on the challenges and directions of future research in the field of nanocellulose-based energy storage devices.