Boosting capacitive performance of N, S co-doped hierarchical porous lignin-derived carbon via self-assembly assisted template-coupled activation

In-situ engineering of centralized mesopores and edge nitrogen for porous carbons toward zinc ion hybrid capacitors

Porous carbons with large surface area (>3000 m2/g) and heteroatom dopants have shown great promise as electrode materials for zinc ion hybrid capacitors. Centralized mesopores are effective to accelerate kinetics, and edge nitrogen can efficiently enhance pseudocapacitive capability. It is a great challenge to engineer centralized mesopores and edge nitrogen in large-surface-area porous carbons. Herein, a strategy of melamine-boosted K2CO3 activation is proposed to prepare edge-nitrogen-doped hierarchical porous carbons (ENHPCs). KOCN generated by K2CO3 reacting cyano groups (-CN) couples with K2CO3 activation engineers large-surface-area porous carbon. KCN in-situ generated by KOCN etching carbon atoms plays a template role in constructing centralized mesopores. Edge-nitrogen skeleton is formed by g-C3N4 losing -CN, and then in-situ integrated into porous carbon skeleton. The efficiency of melamine-boosted K2CO3 activation reaches the highest at a melamine/lignin mass ratio of 0.5, where the optimized ENHPCs (ENHPC-0.5) have a large surface area of 3122 m2/g, a mesopore architecture (2.8 nm) with a mesoporosity of 60.5 % and a moderate edge-N content of 1.9 at.%. ENHPC-0.5 cathode displays a high capacitance of 350F/g at 0.1 A/g, an excellent rate capability of 129F/g at 20 A/g and a robust cycling life. This work provides a novel strategy to prepare heteroatom-doped high-surface-area porous carbons for zinc ion hybrid capacitors.

Heteropoly acid-assisted carboxymethyl cellulose-soft template self-assembly synthesis of three-dimensional hybrid layered porous carbon for supercapacitors

This study introduces an innovative, environmentally friendly method for controlling the morphology, size, spatial structure and activity of three-dimensional hybrid layered porous carbon (HLPC). The hydrothermal reaction is carried out in a microreactor through a synergistic interaction between triblock copolymer (F127) and ammonium molybdate phosphate (APMo). Carboxymethyl cellulose undergoes acid-catalyzed hydrolysis and self-assembles into HLPC at the interface between the microreactor and the solution. The structural integrities and dimensional attributes of HLPC are modulated by adjusting the hydrothermal time to allow for swelling, tearing or further development. The addition of varying amounts of APMo allows customization of HLPC's spatial structures, such as layered, curled or folded configurations. HLPC demonstrates efficient ion storage and transmission channels, a hydrophilic surface, high reactivity and robust electrochemical performance. When tested in a 6 mol·L-1 KOH electrolyte, HLPC achieved a specific capacitance of 318 F·g-1 at a current density of 0.5 A·g-1 and maintained a retention of 96 % after 10,000 charging/discharging cycles at 10 A·g-1. Additionally, the symmetrical supercapacitor with HLPC in an ionic liquid electrolyte (1-butyl-3-methylimidazolium tetrafluoroborate) exhibited a specific capacitance of 102 F·g-1 at 0.1 A·g-1 and an energy density of 31.88 W·h·kg-1.

Structural Regulation and Performance Enhancement of Carbon-Based Supercapacitors: Insights into Electrode Material Engineering

The development of carbon-based supercapacitors is pivotal for advancing high energy and power density applications. This review provides a comprehensive analysis of structural regulation and performance enhancement strategies in carbon-based supercapacitors, focusing on electrode material engineering. Key areas explored include pore structure optimization, heteroatom doping, intrinsic defect engineering, and surface/interface modifications. These strategies significantly enhance electrochemical performance through increasing surface area, improving conductivity, facilitating charge transfer, introducing additional pseudocapacitive reactions, and optimizing the density of states at the Fermi level, among other mechanisms. After introducing these fundamental concepts, the review details various preparation methods and their effects on supercapacitor performance, highlighting the interplay between material structure and electrochemical properties. Challenges in scaling advanced fabrication techniques and ensuring the long-term stability of functionalized materials are discussed. Additionally, future research directions are proposed, emphasizing the development of cost-effective, scalable methods and interdisciplinary approaches to design next-generation supercapacitors, thereby meeting the growing demand for efficient and sustainable energy storage solutions.

Preparation of nitrogen-doped lignin porous carbon using low dosage KHCO3 for efficient methylene blue adsorption: Activation mechanism and adsorption performance

The previous requirement for activation of porous carbon adsorbents commonly exceeded several times the mass of the carbon precursor. Therefore, it was crucial to develop cost-effective and efficient carbon adsorbent materials for long-term environmental remediation. In this study, biorefinery lignin was utilized to fabricate porous carbon with an ultrahigh specific surface area (3423 m2 g-1) and pore volume (1.52 cm3 g-1) by employing melamine as the nitrogen source and a low dosage of KHCO3 as the activator. Multiple activations during the carbonization process contributed to the exceptional characteristics of the porous carbon, including well-developed pore structure, high specific surface area, and reasonable nitrogen doping. The porous carbon demonstrated remarkable adsorption capabilities with a maximum methylene blue (MB) adsorption capacity of 1457 mg g-1. Structural characterization conducted before and after adsorption revealed that electrostatic interactions, pore filling, hydrogen bonding, and π-π stacking were among the main mechanisms employed by lignin porous carbon for effective MB adsorption. The proposed method is a simple, green, highly efficient, and environmentally friendly approach that can be applied to treat lignin from various industrial sources. It provides valuable insights into the development of advanced carbon materials suitable for adsorption and capacitor applications.

Lignin-Derived Activated Carbon as Electrode Material for High-Performance Supercapacitor

Utilizing lignin-derived activated carbon in supercapacitors has emerged as a promising approach to alleviating environmental pollution and promoting the high-value utilization of byproducts in the papermaking industry. In this study, activated carbons (LACs) were prepared using a simple one-step KOH activation approach and by employing enzymatic hydrolysis lignin (EHL). The impact of the KOH activation parameters on the microstructure and capacitive performance of the LACs was investigated by varying the KOH/EHL ratio and activation temperature. The optimized sample LAC800-4 showed an interconnected porous structure with a high surface area of 2285 m2/g, abundant micropores, and a small number of mesopores, which makes it a suitable electrode material for supercapacitors. The sample LAC800-4 demonstrated a high specific capacitance of 291.3 F/g in a three-electrode system. Under a symmetrical supercapacitor electrode system, the specific capacitance of the LAC800-4 electrode reached 186.8 F/g at 0.5 A/g. After 10,000 cycles at 20 A/g, the capacitance retention rate remained at 96.1%. The symmetrical supercapacitor also demonstrated a superior energy density of 6.5 Wh/kg. This work provides valuable insights into the transformation of low-value natural biomass derivatives into environmentally friendly, high-performing supercapacitor electrode materials.

Thiocyanogen-modulated N, S Co-doped lignin hierarchical porous carbons for high-performance aqueous supercapacitors

Constructing heteroatom-doped porous carbons with distinct charge storage properties is significant for high-energy-density supercapacitors, yet it remains a formidable challenge. Herein, we employed a thiocyanogen-modulated alkali activation strategy to synthesize N and S co-doped lignin hierarchical porous carbon (NSLHPC). In this process, thiocyanogen serves as a surface modulation mediator to substitute oxygen with nitrogen and sulfur species, while the combination of KOH activation and MgO template generates numerous nanopores within the carbon structure. The three-dimensional interconnected nanosheet architecture facilitates rapid ion transfer and enhances accessibility to active sites. Density functional theory (DFT) calculations demonstrate that introducing N and S heteroatoms through oxygen substitution reduces the adsorption energy barrier of Zn2+. Consequently, the optimized NSLHPC exhibits a remarkable specific capacitance of 438F/g at 0.5 A/g in 6 M KOH, delivering an energy density of 10.4 Wh/kg in the symmetric supercapacitor and an impressive energy density of 104.9 Wh/kg in the zinc-ion hybrid capacitor. The NSLHPC cathode also shows an excellent lifespan with capacitance retention of 99.0 % and Columbic efficiency of 100 % over 10,000 cycles. This study presents innovative strategies for engineering high-performance porous carbon electrode materials by emphasizing pore structure modulation and N, S co-doping as crucial approaches.

High-performance electrode materials of heteroatom-doped lignin-based carbon materials for supercapacitor applications

Supercapacitors are the preferred option for supporting renewable energy sources owing to many benefits, including fast charging, long life, high energy and power density, and saving energy. While electrode materials with environmentally friendly preparation, high performance, and low cost are important research directions of supercapacitors. At present, the growing global population and the increasingly pressing issue of environmental pollution have drawn the focus of numerous researchers worldwide to the development and utilization of renewable biomass resources. Lignin, a renewable aromatic polymer, has reserves second only to cellulose in nature. Ten million tonnes of industrial lignin are produced in pulp and paper mills annually, most of which are disposed of as waste or burned for fuel, seriously depleting natural resources and polluting the environment. One practical strategy to accomplish sustainable development is to employ lignin resources to create high-value materials. Based on the high carbon content and rich functional groups of lignin, the lignin-based carbon materials generated after carbonization treatment display specific electrochemical properties as electrode materials. Nevertheless, low electrochemical activity of untreated lignin precludes it from achieving its full potential for application in energy storage. Heteroatom doping is a common modification method that aims to improve the electrochemical performance of the electrode materials by optimizing the structure of the lignin, improving its pore structure and increasing the number of active sites on its surface. This paper aims to establish theoretical foundations for design, preparation, and optimizing the performance of heteroatom-doped lignin-based carbon materials, as well as for developing high-value-added lignin materials. The most reported the mechanism of supercapacitors, the doping process involving various types of heteroatoms, and the analysis of how heteroatoms affect the performance of lignin-based carbon materials are also detailed in this review.

Nitrogen-functionalization of carbon materials for supercapacitor: Combining with nanostructure directly is superior to doping amorphous element

Just how heteroatomic functionalization enhances electrochemical capacity of carbon materials is a recent and widely studied field in scientific research. However, there is no consensus on whether combining with heteroatom-bearing nanostructures directly or doping amorphous elements is more advantageous. Herein, two kinds of porous carbon nanosheets were prepared from coal tar pitch through anchoring graphitic carbon nitride (PCNs/GCNs-5) or doping amorphous nitrogen element (PCNs/N). The structural characteristics and electrochemical properties of the two PCNs were revealed and compared carefully. It can be found that the amorphous nitrogen of PCNs/N will have a grievous impact on its carbon skeleton network, resulting in reduced stability in charge and discharge process, while the structural collapse of carbon network could be avoided in PCNs/GCNs-5 by the heteroatoms in the form of nanostructure. Particularly, PCNs/GCNs-5 exhibits extremely high specific capacity of 388 F g-1 at 1 A g-1, and splendid the capacitance retention rate of 98% after 10,000 cycles of charge and discharge, which are overmatch than the amorphous nitrogen doped carbon materials reported recently and PCNs/N. The combining strategy with nanostructure will inspire the design of carbon materials towards high-performance supercapacitor.

MnO2 porous carbon composite from cellulose enabling high gravimetric/volumetric performance for supercapacitor

Preparing electrode material integrated with high gravimetric/volumetric capacitance and fast electron/ion transfer is crucial for the practical application. Owing to the structural contradiction, it is a big challenge to construct electrode material with high packing density, sufficient ion transport channels, and fast electronic transfer pathways. Herein, MnO2 porous carbon composite with abundant porous structure and 3D carbon skeleton was facilely fabricated from Linum usitatissimum. L stems via NaOH activation and MnO2 introduction. The in-situ introduced MnO2 not only increases the packing density and the electrical conductivity of the porous carbon but also provides more active sites for oxidation reactions. These unique characteristics endow the resultant MnO2 porous carbon composite with remarkable gravimetric capacitance of 549 F g-1, volumetric capacitance of 378 F cm-3, and capacitance retention of 54.9 %. Giving the simple process and low cost, this work might offer a new approach for structural design and the practical application of high-performance electrode materials.

Preparation of spherical porous carbon from lignin-derived phenolic resin and its application in supercapacitor electrodes

Lignin is the most abundant aromatic biomass resource in nature and is the main by-product of paper industry and biorefinery industry, which has the characteristics of abundant source, renewable and low cost. Deep eutectic solvents (DES) are a nascent environmentally friendly solvent option that is gaining traction. DES composed of p-toluenesulfonic acid and choline chloride is used for batch treatment of alkaline lignin, and the bio-oil obtained is ternary polymerized with formaldehyde and phenol to obtain lignin phenolic resin. The porous carbon material is produced through a two-step carbonization process, utilizing phenolic resin derived from lignin as the primary source of carbon. The morphology and composition of the carbon were analyzed by SEM, TEM, XRD, TGA, XPS and Raman spectroscopy, the specific surface area and pore size distribution were analyzed by BET. The results showed that the specific surface area of the lignin-based phenolic resin was significantly higher than that of the pure phenolic resin carbon, and the porous carbon material that was acquired demonstrated a specific surface area of as much as 1026 m2/g. In the three-electrode system, the specific capacitance of DLPFC can reach 245.8 F/g (0.25 A/g), with a very small decrease in the value of specific capacitance at 10,000 cycles, with a retention of 97.62% (10 A/g). The porous carbon demonstrated a specific capacitance of 112.4 F/g at a current density of 0.5 A/g, and the capacitance retention rate could still reach 98.8% after 5000 charge/discharge cycles, with high cycling stability (in the two-electrode system). The prepared symmetrical supercapacitors exhibited high energy density and power density of 3.9 Wh/kg and 125.0 W/kg. The results suggest a new idea of high value-added application of lignin phenolic resin for high-performance supercapacitor electrodes.

Recent advances in biopolymers-based carbon materials for supercapacitors

Supercapacitors as potential candidates for novel green energy storage devices demonstrate a promising future in promoting sustainable energy supply, but their development is impeded by limited energy density, which can be addressed by developing high-capacitance electrode materials with efforts. Carbon materials derived from biopolymers have received much attention for their abundant reserves and environmentally sustainable nature, rendering them ideal for supercapacitor electrodes. However, the limited capacitance has hindered their widespread application, resulting in the proposal of various strategies to enhance the capacity properties of carbon electrodes. This paper critically reviewed the recent research progress of biopolymers-based carbon electrodes. The advances in biopolymers-based carbon electrodes for supercapacitors are presented, followed by the strategies to improve the capacitance of carbon electrodes which include pore engineering, doping engineering and composite engineering. Furthermore, this review is summarized and the challenges of biopolymer-derived carbon electrodes are discussed. The purpose of this review is to promote the widespread application of biopolymers in the domain of supercapacitors.