A Solvent-Free Synthesis of Lignin-Derived Renewable Carbon with Tunable Porosity for Supercapacitor Electrodes

Hierarchical nanoarchitectonics of ordered mesoporous carbon from lignin for high-performance supercapacitors

The synthesis of ordered mesoporous carbons (OMCs) with hierarchical pore structure is significant for supercapacitor applications as electrode material. In this study, the ordered mesoporous carbons with hierarchical pore structure (HOMC) are synthesized via solvent evaporation induced self-assembly (EISA) method using lignin from walnut shell as carbon precursor and Co²⁺ ion as crosslinking agent, followed by removal of metal by diluted acid and chemical activation with KHCO₃. The prepared HOMC material has a large specific surface area of 2033 m² g^-1 and high pore volume of 1.59 cm³ g^-1, and it shows good electrochemical performance as the electrode of supercapacitor with high specific supercapacitances of 286 and 206 F g^-1 in 6 M KOH aqueous solutions at 0.2 and 20 A g^-1, respectively. The assembled HOMC-based symmetric supercapacitors provides a specific energy density of 13.5 Wh kg^-1 at a high power density of 44.3 kW kg^-1 and keep good cycling stability after 5000 cycle tests. The superior electrochemical performance is ascribed to the long range ordered parallel mesoporous channels, hierarchical porous structure, high specific surface area and appropriate microporous/mesoporous ratio. The materials prepared in this study have the potential to be used in the fields of adsorption, energy storage and capacitance deionization.

Three-dimensional hierarchical porous lignin-derived carbon/WO3 for high-performance solid-state planar micro-supercapacitor

The development of advanced energy storage systems, such as rechargeable batteries and supercapacitors (SCs), is one of the great challenges related to energy demand with the rapid development of world economy. Herein, a three-dimensional hierarchical porous lignin-derived carbon/WO₃ (HPC/WO₃) was prepared by carbonization and solvothermal process. This electrode material for supercapacitor can be operated at a wide voltage window range of -0.4 V to 1.0 V. More importantly, 3HPC/WO₃ with ultrahigh mass loading (~3.56 mg cm^-2) has excellent specific capacitance of 432 F g^-1 at 0.5 A g^-1 and cycling stability of 86.6% after 10,000 cycles at 10 A g^-1. The as-assembled asymmetrical supercapacitor shows an energy density of 34.2 W h kg^-1 at a power density of 237 W kg^-1 and energy density of 16 W h kg^-1 at a power density is 14,300 W kg^-1. A solid-state planar micro-supercapacitor (MSC) was fabricated using HPC/WO₃ nanocomposites. Moreover, the calculated specific capacity of MSC was 20 mF cm^-2 in polyvinyl alcohol-sulfuric acid gel electrolyte. Overall, through the reasonable design of HPC/WO₃ nanocomposite materials and the efficient assembly of MSCs, the performance of the device was greatly improved, thus providing a clear strategy for the development of energy storage devices.

Lignin Derived Porous Carbons: Synthesis Methods and Supercapacitor Applications

Lignin, one of the renewable constituents in natural plant biomasses, holds great potential as a sustainable source of functional carbon materials. Tremendous research efforts have been made on lignin-derived carbon electrodes for rechargeable batteries. However, lignin is considered as one of the most promising carbon precursors for the development of high-performance, low-cost porous carbon electrode materials for supercapacitor applications. Yet, these efforts have not been reviewed in detail in the current literature. This review, therefore, offers a basis for the utilization of lignin as a pivotal precursor for the synthesis of porous carbons for use in supercapacitor electrode applications. Lignin chemistry, the synthesis process of lignin-derived porous carbons, and future directions for developing better porous carbon electrode materials from lignin are systematically reviewed. Technological hurdles and approaches that should be prioritized in future research are presented.

Effective fractionation strategy of sugarcane bagasse lignin to fabricate quality lignin-based carbon nanofibers supercapacitors

Lignin is recommended to a tempting alternative precursor of petroleum for fabricating carbon nanofibers (CNFs) due to its high carbon content, low-cost and renewable resources. However, the property of lignin-based carbon nanofibers (LCNFs) is inferior owing to the heterogeneity and 3D-network structure of lignin, which hinders its application in supercapacitors. The latest developments in fractionation technology have shown great potential for overcoming the aforementioned shortcomings. However, most of fractionation methods mainly rely on expensive chemicals and complex reaction process, such as enzymes, multiple solvents, membranes, and dialysis tubes. Herein, we proposed a controllable and effective strategy to fractionate lignin by only changing the ratio of ethanol/water (V/V) as mixture solvent. This gradient extraction method effectively removed the part of lignin with small molecular and branching structure, thus selectively getting the fractionated lignin with high molecular weight, narrow polydispersity index, and good linear structure. Fortunately, when the ratio of ethanol/water was 6:4, the corresponding LCNFs (LCNFs-L60) was obtained with large specific surface area, independent filamentous morphology networks and excellent electrochemical property. Its specific capacitance was up to 405.8 F/g. This way features controllable and sustainable for preparing high-quality LCNFs supercapacitors.

Electrochemical energy storage electrodes from fruit biochar

This review investigates the electrochemical energy storage electrode (EESE) as the most important part of the electrochemical energy storage devices (EES) prepared from fruit-derived carbon. The EES devices include batteries, supercapacitors, and hybrid devices that have various regular and advanced applications. The preparation of EESE from fruit wastes not only reduce the price of the electrode but also lead to enhance the electrochemical properties of the electrode. The astonishing results of fruits biochar at electrochemical analyses guarantee the performance of these electrodes as EESE. Also, using fruit waste as the precursor of the EESE due to protect the environment and reduce environmental pollutions.

"Waste to Wealth": Lignin as a Renewable Building Block for Energy Harvesting/Storage and Environmental Remediation

Lignin is the second most earth-abundant biopolymer having aromatic unit structures, but it has received less attention than other natural biomaterials. Recent advances in the development of lignin-based materials, such as mesoporous carbon, flexible thin films, and fiber matrix, have found their way into applications to photovoltaic devices, energy-storage systems, mechanical energy harvesters, and catalytic components. In this Review, we summarize and suggest another dimension of lignin valorization as a building block for the synthesis of functional materials in the fields of energy and environmental applications. We cover lignin-based materials in the photovoltaic and artificial photosynthesis for solar energy conversion applications. The most recent technological evolution in lignin-based triboelectric nanogenerators is summarized from its fundamental properties to practical implementations. Lignin-derived catalysts for solar-to-heat conversion and oxygen reduction are discussed. For energy-storage applications, we describe the utilization of lignin-based materials in lithium-ion rechargeable batteries and supercapacitors (e.g., electrodes, binders, and separators). We also summarize the use of lignin-based materials as heavy-metal adsorbents for environmental remediation. This Review paves the way to future potentials and opportunities of lignin as a renewable material for energy and environmental applications.

Self-Supported, Sulfate-Functionalized Nickel Hydroxide Nanoplates with Enhanced Wettability and Conductivity for Use in High-Performance Supercapacitors

Nickel hydroxide is promising for use in supercapacitor applications because of its low cost and tunable electrochemical properties, but its performance is usually restricted by insufficient conductivity and surface reactivity. In this work, sulfate-functionalized Ni(OH)₂ (SNO) nanoplates were grown in situ on nickel foam (NF) by a green and facile one-step hydrothermal treatment of NF without the need for an external Ni source or surfactant addition. The resulting material showed a 9.3 times higher areal capacity and 1.8 times higher rate capability than the sulfate-free control and retained 81.3 % capacity after 5000 cycles. If used as the positive electrode in a hybrid supercapacitor, the SNO/NF//activated carbon system achieved >95 % Coulombic efficiency, a maximum energy density of 3.59 Wh m^-2 , and a maximum power density of 44.63 Wm^-2 , which surpass those achievable by most known Ni-based supercapacitors. Detailed material characterization and DFT calculations revealed that the introduction of sulfate expanded the layer spacing of Ni(OH)₂ and improved the electrical conductivity and wettability to favor more efficient electrolyte diffusion, charge transfer, and reactant adsorption. The high loading of reactive components and inherited porous structure also contributed to the superior capacitive performance of the SNO/NF electrodes. Therefore, SNO/NF holds great potential for commercialized supercapacitor applications.

Polyhydroxyalkanoate-Modified Bacterium Regulates Biomass Structure and Promotes Synthesis of Carbon Materials for High-Performance Supercapacitors

Biomass-derived carbons have been extensively explored as electrode materials in supercapacitors. However, the type of biomass selected and its specific structure affects the synthesis of the advanced biomass-derived carbon materials. A green and facile method for the synthesis of carbon material with nanoscale and microscale porous structures for supercapacitors has been developed, based on regulating the original cell structure of the bacterial strain. The cell structure is modified in situ by regulating the accumulation of polyhydroxyalkanoate under controlled cultivation conditions. The novel bacterial in situ modification and nitrogen doping endow this hierarchically derived carbon material with improved performance. This material exhibits an extremely high specific capacitance (420 F g^-1 at 1 A g^-1 ) and long cycling stability (97 % capacitance retention after 10 000 cycles at 5 A g^-1 ) in aqueous electrolytes. More importantly, the symmetric supercapacitor delivers a superior energy density of 60.76 Wh kg^-1 at 625 W kg^-1 in an ionic liquid electrolyte system. Moreover, all components in the synthesis are low in cost, environmentally friendly, and biocompatible. With these unique features, the bacterial self-modification mode opens new avenues into the design and production of a wide range of hierarchical structures.

Transforming lignin into porous graphene via direct laser writing for solid-state supercapacitors

Cost-effective valorization of lignin into carbon-based electrode materials remains a challenge. Here we reported a facile and ultrafast laser writing technique to convert lignin into porous graphene as active electrode material for solid-state supercapacitors (SCs). During laser writing, alkaline lignin experienced graphitization. By controlling laser parameters such as power the porous structure and graphitization degree can be well modulated. Graphene obtained at 80% of laser power setting (LIG-80) had higher graphene quality and more porous structure than that obtained at the lower power levels (i.e., 50%, 70%). TEM images revealed that LIG-80 had few-layer graphene structure with fringe-like patterns. LIG-80 proved to be an active electrode material for SCs with a specific capacitance as high as 25.44 mF cm⁻² in a H₂SO₄/PVA gel electrolyte, which is comparable or even superior to SCs based on pristine LIG obtained from other carbon precursors. Taken together, our proposed technical route for lignin-based LIG and subsequent application in SCs would not only open a new avenue to lignin valorization, but also produce porous graphene from a renewable carbon precursor for energy storage applications.

Direct laser writing transforms alkaline lignin into porous graphene for solid-state supercapacitors with high electrochemical performance.