Nitrogen-rich accordion-like lignin porous carbon via confined self-assembly template and in-situ mild activation strategy for high-performance supercapacitors

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.

Engineering Alkali Lignin Structure Modification: Enhanced Hard Carbon Electrolyte Interface Toward Practical Sodium Ion Batteries

Hard carbon (HC) exhibits great potential as a promising candidate for sodium-ion batteries owing to its inherent advantages. However, the main challenges in utilizing HC stem from its low initial coulombic efficiency (ICE) and poor rate performance caused by its excessive surface defects. In this study, an effective strategy of employing alkali lignin (AL) is proposed, derived from pulp waste, as a binder for HC to create a uniform and inorganically enriched solid electrolyte interface. AL can modify the surface defects of HC through strong π-π interactions between the aromatic ring of AL and HC, while ingeniously grafting abundant active ─OH and ─COOH groups onto the electrode surface. The strong binder force between AL and electrolyte salts facilitates the formation of an ultra-thin NaF-rich solid electrolyte interface (SEI) layer (10 nm), thereby achieving an exceptional ICE of 91%. Furthermore, owing to its electrochemical activity, AL enables HC anode to exhibit an increasing slope capacity during cycling, compensating for capacity decay at high current densities. Consequently, when assembled into a full battery configuration, excellent rate performance is achieved with a reversible capacity of 282 mAh g-1 even at a current density of 5A g-1.

Phase change material composites based on 3D lignin-derived porous carbon prepared by in-situ activation for efficient solar-driven energy conversion and storage

Utilization of three-dimensional biomass-derived porous carbons can effectively address issues of easy leakage, low thermal conductivity, and weak photothermal conversion of phase change materials (PCMs). This enables the production of high-performance composites for solar-induced energy collection, conversion, and storage. In this study, hierarchical lignin-derived porous carbon (HLPC), microporous lignin-derived porous carbon (MILPC) and mesoporous lignin-derived porous carbon (MELPC) were prepared through high-temperature in-situ activation using lignosulphonate (LS) as a carbon precursor and CaCO3, KOH and ZnCO3 as activators. Carbon-based PCM composites with high performance were obtained by encapsulating paraffin wax (PW) in porous carbon supports. Results demonstrated that PW/HLPC exhibited comprehensive performance superior to other tested PW composites owing to its higher specific surface area (2,358 m2/g), larger pore volume (1.1 cm3/g) and well-interconnected framework structure. Additionally, PW/HLPC displayed relatively high latent heat (123.4 kJ/kg), photothermal conversion and storage efficiency (95 %), and photoelectric conversion performance (174.5 mV). Moreover, PW/HLPC also showed better leak-proof properties at 90 °C. The cycling stability and photothermal conversion performance of PW/HLPC were superior to those of the selected crude biochar-based PW composites. This study highlights the advantages of the prepared PW/HLPC for both the high-value utilization of lignin and its practical applications in solar-induced energy harvest, conversion, and storage.

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.

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.

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.

Scalable synthesis of N, O co-doped hierarchical porous carbon for high energy density supercapacitors

Rational design of hierarchical porous architecture with abundant pseudocapacitive sites is highly desirable for carbon electrode materials. However, the lengthy production process and high economic input limit its broader application. Herein, we successfully prepared N, O co-doped hierarchical porous carbon (NOHC) through hydrothermal carbonization (HTC) of chitin biomass with the assist of NH4Cl and subsequent carbonization with NaNH2. The optimal NOHC600 exhibits a remarkable hierarchical porous structure and an ultrahigh specific surface area (SSA) of 2555 m2 g-1. Furthermore, it showcases a significant content of N, O co-doping, thereby providing abundant defects and additional active sites for ion adsorption. The aforementioned characteristics ensure outstanding capacitance performance of NOHC600. In the three-electrode system, NOHC600 exhibits a remarkable specific capacitance of up to 455 F g-1 at a current density of 0.5 A g-1. The symmetric supercapacitors (SCs) based on NOHC600 achieve an impressive energy density of 30.4 Wh kg-1 at a power density of 180 W kg-1. Moreover, the all-solid-state NOHC600 microsupercapacitors (MSCs) demonstrate an exceptional areal capacitance of 78.2 mF cm-2 and an areal energy density of up to 10.8 μWh cm-2. Accordingly, this facile and scalable strategy shows a great potential for producing high-heteroatom-doped porous carbon materials from chitin biomass, which can be applied in practical energy-related applications.

Preparation and research progress of lignin-based supercapacitor electrode materials

The reserve of lignin in the biological world is the second largest biomass resource after cellulose. Lignin has the characteristics of wide sources, low cost, and rich active components. Due to environmental pollution and energy scarcity, lignin is often used as a substitute good for petrochemical products. Lignin-based functional materials can be prepared by chemical modification or compounding, which are widely used in the fields of energy storage, chemical industry, and medicine. Among them, lignin-based carbon materials have the features of stable chemical properties, large pH application range, ideal electrical conductivity, developed pore size, and high specific surface area, which have great application prospects as supercapacitor materials. This paper mainly introduces the structural properties of lignin, the methods, and mechanisms of carbonization, pore-making, and pore-expansion, as well as the research progress of lignin-based carbon materials for supercapacitors, while looking forward to the future research direction of lignin carbon materials.

Rational design of dense microporous carbon derived from coal tar pitch towards high mass loading supercapacitors

The compact carbon materials with huge specific surface area (SSA) and proper pore structure are highly desirable towards high-performance supercapacitors at the cell level. However, to well balance of porosity and density is still an on-going task. Herein, a universal and facile strategy of pre-oxidation-carbonization-activation is employed to prepare the dense microporous carbons from coal tar pitch. The optimized sample POCA800 not only possesses a well-developed porous structure with the SSA of 2142 m² g^-1 and total pore volume (V_t) of 1.540 cm³ g^-1, but also exhibits a high packing density of 0.58 g cm^-3 and proper graphitization. Owing to these advantages, POCA800 electrode at areal mass loading of 10 mg cm^-2 shows a high specific capacitance of 300.8 F g^-1 (174.5 F cm^-3) at 0.5 A g^-1 and good rate performance. The POCA800 based symmetrical supercapacitor with a total mass loading of 20 mg cm^-2 displays a large energy density of 8.07 Wh kg^-1 at 125 W kg^-1 and remarkable cycling durability. It is revealed that the prepared density microporous carbons are promising for practical applications.

Foldable and wearable supercapacitors for powering healthcare monitoring applications with improved performance based on hierarchically co-assembled CoO/NiCo networks

Small-scale and high-performance energy storage devices have drawn tremendous attention with their portable, lightweight, and multi-functionalized features. Here, we present a foldable supercapacitor with affordable flexibility by adopting a developed design and electrode material system as a way to extend usability. Notably, to resolve the limited energy density of conventional capacitors, we successfully synthesize the CoO/NiCo-layered double hydroxide (LDH) core-shell nanostructure on Ni framework as a cathode material. Further, glucose-based activated carbon (GBAC) is utilized for the anode. The CoO/NiCo-LDH electrodes exhibited a high specific capacitance of ∼284.8 mAh g^-1 at 1 A g^-1, and GBAC delivers a high specific capacitance of ∼166 F g^-1 at 1 A g^-1. In the following, the combinatorial integration of these materials enabled the asymmetric supercapacitor (ASC) to increase the energy density by enhancing the capacitance and the voltage window, in which a hydrogel-based electrolyte was facilitated for the foldable and wearable capability. The energy density of the ASC device was ∼24.9 Wh kg^-1 at a power density of ∼779.5 W kg^-1 with a voltage window of ∼1.6 V. As demonstrated, a self-powered energy source was demonstrated by a serially connected multi-ASC device with a help of a commercial solar cell, which was employed for powering wearable healthcare monitoring devices, including personal alarms for patients and recording the human body's electrical signals. The present work offers a viable approach to preparing potential candidates for high-performance electrodes of supercapacitors with deformable configurations to extend the powering capability of other electronic devices with physical functionalities used in wearable electronics.

Morphology engineering of biomass-derived porous carbon from 3D to 2D towards boosting capacitive charge storage capability

Carbon morphology significantly affects the capacitive performance of porous carbons. Biomass-derived porous carbons are usually restricted by inferior capacitive performance owing to their inherently three-dimensional (3D) blocked morphologies. Fabricating two-dimensional (2D) sheet-like morphology is expected to expose more inner space for better electrochemical performance, however, it needs to overcome the self-aggregation of biomass. The comprehensive understanding of how 2D morphology boosts capacitive performance remains challenging. Herein, we provide a morphology-regulating strategy to prepare 2D and 3D porous carbons and investigate the morphology effect on charge storage capability via both experimental data and theoretical simulations. 2D carbon exhibits better capacitance than 3D carbon in both electric double-layer capacitors (254 versus 211F g^-1) and zinc-ion hybrid supercapacitors (320 versus 232F g^-1), because the 2D carbon morphology not only improves the pore accessibility for higher double-layer capacitance, but also facilitates the exposure of active functional groups for more pseudocapacitance. Moreover, 2D morphology shortens pore length, leading to better anti-self-discharge capability. This study is beneficial to understanding the relationship between carbon morphology and capacitive performance and provides a facile strategy to upgrade biomass-derived porous carbons via morphology engineering.

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

Heteroatom-doped porous carbon materials show promise for use as supercapacitor electrodes, but the tradeoff between surface area and the heteroatom dopant levels limits the supercapacitive performance. Here, we modulated the pore structure and surface dopants of N, S co-doped hierarchical porous lignin-derived carbon (NS-HPLC-K) via self-assembly assisted template-coupled activation. The ingenious assembly of lignin micelles and sulfomethylated melamine into a magnesium carbonate basic template greatly promoted the KOH activation process, which endowed the NS-HPLC-K with uniform distributions of activated N/S dopants and highly accessible nanosized pores. The optimized NS-HPLC-K exhibited a three-dimensional hierarchically porous architecture composed of wrinkled nanosheets and a high specific surface area of 2538.3 ± 9.5 m²/g with a rational N content of 3.19 ± 0.01 at.%, which boosted the electrical double-layer capacitance and pseudocapacitance. Consequently, the NS-HPLC-K supercapacitor electrode delivered a superior gravimetric capacitance of 393 F/g at 0.5 A/g. Furthermore, the assembled coin-type supercapacitor showed good energy-power characteristics and cycling stability. This work provides a novel idea for designing eco-friendly porous carbons for use in advanced supercapacitors.