Hierarchical porous carbon/Kraft lignin composite with significantly improved superior pseudocapacitive behavior

Preparation of Symmetrical Capacitors from Lignin-Derived Phenol and PANI Composites with Good Electrical Conductivity

As a natural polymer, lignin is only less abundant in nature than cellulose. It has the form of an aromatic macromolecule, with benzene propane monomers connected by molecular bonds such as C-C and C-O-C. One method to accomplish high-value lignin conversion is degradation. The use of deep eutectic solvents (DESs) to degrade lignin is a simple, efficient and environmentally friendly degradation method. After degradation, the lignin is broken due to β-O-4 to produce phenolic aromatic monomers. In this work, lignin degradation products were evaluated as additives for the preparation of polyaniline conductive polymers, which not only avoids solvent waste but also achieves a high-value use of lignin. The morphological and structural characteristics of the LDP/PANI composites were investigated using ¹H NMR, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and elemental analysis. The LDP/PANI nanocomposite provides a specific capacitance of 416.6 F/g at 1 A/g and can be used as a lignin-based supercapacitor with good conductivity. Assembled as a symmetrical supercapacitor device, it provides an energy density of 57.86 Wh/kg, an excellent power density of 952.43 W/kg and, better still, a sustained cycling stability. Thus, the combination of polyaniline and lignin degradate, which is environmentally friendly, amplifies the capacitive function on the basis of polyaniline.

Bio-Based Carbon Materials for High-Performance Supercapacitors

Lignin, one of the components of natural plant biomass, is a rich source of carbon and has excellent potential as a valuable, sustainable source of carbon material. Low-cost lignosulfonate (LS) doped with polyaniline (PANI) has been used as a precursor to produce porous carbon. LS has a highly dispersed and sparse microstructure and can be accidentally doped with S atoms. N and S double-doped carbon can be directly synthesized with abundant mesopores and high surface area in a lamellar network using PANI as another doping source. This study explored the optimal conditions of LS/PANI material with different amounts of lignosulfonate and different carbonization temperatures. When the amount of lignosulfonate was 4 g and the carbonization temperature was 700 °C, graded porous carbon was obtained, and the electrochemical performance was the best. At 0.5 A/g, the specific capacitance reached 333.50 F/g (three-electrode system) and 242.20 F/g (two-electrode system). After 5000 charge/discharge cycles at 5 A/g, the material maintained good cycling stability and achieved a capacitance retention rate of 95.14% (three-electrode system) and 97.04% (two-electrode system). The energy and power densities of the SNC700 samples were 8.33 Wh/kg and 62.5 W/kg at 0.25 A/g, respectively, values that meet the requirements of today's commercially available supercapacitor electrode materials, further demonstrating their good practicality. This paper provides an efficient double-doping method to prepare layered structures. Porous carbon is used for electrochemical energy storage devices.

Porous Carbon Composite Generated from Silk Fibroins and Graphene for Supercapacitors

Hierarchical porous heteroatom-doped carbon composites were developed by carbonization followed by KOH activation process, with natural silkworm cocoon and chemical exfoliated graphene sheets as starting materials. The introduction of graphene sheets offers more hierarchical micro/meso porosities, a low charge-transfer resistance, and a large BET surface area of ∼1281.8 m² g^-1, which are responsible for the fast charge/discharge kinetics and the high rate capability compared with those of single silk fibroins-derived carbon materials. The silk fiber provides a high level of heteroatom functionalities (∼2.54% N and ∼21.3% O), which are desirable for high faradaic pseudocapacitance. The as-prepared carbon composite exhibited a high specific capacitance of 290 F g^-1 with good rate capability and cycling stability. The symmetric supercapacitors yielded a high value of energy density of 12.9 W h kg^-1 at a power density of 95 W kg^-1 with a 1.45 V voltage range in 1 M KOH aqueous electrolytes.

Lignin-Derived Quinone Redox Moieties for Bio-Based Supercapacitors

Because of their rapid charging and discharging, high power densities, and excellent cycling life stabilities, supercapacitors have great potential for use in electric vehicles, portable electronics, and for grid frequency modulation. The growing need for supercapacitors that are both efficient and ecologically friendly has generated curiosity in developing sustainable biomass-based electrode materials and electrolytes. Lignin, an aromatic polymer with remarkable electroactive redox characteristics and a large number of active functional groups, is one such candidate for use in renewable supercapacitors. Because its chemical structure features an abundance of quinone groups, lignin undergoes various surface redox processes, storing and releasing both electrons and protons. Accordingly, lignin and its derivatives have been tested as electroactive materials in supercapacitors. This review discusses recent examples of supercapacitors incorporating electrode materials and electrolytes derived from lignin, focusing on the pseudocapacitance provided by the quinone moieties, with the goal of encouraging the use of lignin as a raw material for high-value applications. Employing lignin and its derivatives as active materials in supercapacitor electrodes and as a redox additive in electrolytes has the potential to minimize environmental pollution and energy scarcity while also providing economic benefits.

Lignin-Based/Polypyrrole Carbon Nanofiber Electrode With Enhanced Electrochemical Properties by Electrospun Method

Tailoring the structure and properties of lignin is an important step toward electrochemical applications. In this study, lignin/polypyrrole (PPy) composite electrode films with microporous and mesoporous structures were designed effectively by electrostatic spinning, carbonization, and in situ polymerization methods. The lignin can not only reduce the cost of carbon fiber but also increase the specific surface area of composite films due to the removal of carbonyl and phenolic functional groups of lignin during carbonization. Besides, the compact three-dimensional (3D) conductive network structures were constructed with PPy particles densely coated on the lignin nanofibers, which was helpful to improve the conductivity and fast electron transfer during the charging and discharging processes. The synthesized lignin carbon fibers/PPy anode materials had good electrochemical performance in 1 M H2SO4 electrolyte. The results showed that, at a current density of 1 A g−1, the lignin carbon nanofibers/PPy (LCNFs/PPy) had a larger specific capacitance of 213.7 F g−1 than carbon nanofibers (CNFs), lignin carbon nanofibers (LCNFs), and lignin/PPy fiber (LPAN/PPy). In addition, the specific surface area of LCNFs/PPy reached 872.60 m2 g−1 and the average pore size decreased to 2.50 nm after being coated by PPy. Therefore, the independent non-binder and self-supporting conductive film is expected to be a promising electrode material for supercapacitors with high performance.

Inorganic salt-induced synthesis of lignin derived hierarchical porous carbon with self-embedded quantum dots and ultrahigh mesoporosity for supercapacitors

Lignin-based hierarchical porous carbon with self-embedded carbon quantum dots for supercapacitor electrodes.