Waste soybean dreg-derived N/O co-doped hierarchical porous carbon for high performance supercapacitor

Acid-modified biomass-based N-doped O-rich hierarchical porous carbon as a high-performance electrode for supercapacitors

In contemporary society, the conversion and efficient utilization of waste biomass and its derivatives are of great significance. Carbonized wood (CW) is an easily accessible and cost-effective green resource, but it has limitations as an electrode material due to its low specific surface area, limited active sites and poor conductivity. Therefore, it is crucial to improve the performance of biomass-based materials by using activation, heteroatom doping and modification methods to enhance the specific surface area and active sites. In this study, we developed acid-modified urea-doped activated carbonized wood (AUACW) with a three-dimensional (3D) porous structure and porosity, achieving a high specific surface area of 1321.3 m2 g-1. In addition, the degree of graphitization (ID/IG = 1.0) provides good conductivity and a large number of active sites, which are conducive to charge transfer and ion diffusion. The increase of nitrogen and oxygen elements enhances the surface wettability of the material and provides additional pseudocapacitance. The specific capacitance of AUACW reaches 435.84 F g-1 at 0.8 A g-1 with a 93.6% capacitance retention after 10 000 cycles in a 1 M KOH electrolyte. More attractively, a symmetrical supercapacitor (SSC) based on AUACW delivers an energy density of 22.61 W h kg-1 at a power density of 533.26 W kg-1. This work demonstrates the promising potential of utilizing waste biomass to develop green and valuable carbon materials for supercapacitors.

Sustainable preparation of high-calorific value and low-N and S energy products through the low-temperature alkali fusion of coal gasification fine ash

Coal gasification fine ash (CGFA) is characterized by high yield, high carbon content, and difficult recovery. This results in waste of coal resources and serious environmental pollution. To address this issue, a novel green deashing process is proposed in this study to modify CGFA into deashed carbon (DAC) with a high calorific value and an ash content of less than 5% through a low-temperature alkaline fusion process. Compared with traditional alkaline fusion (which is carried out at 600-1000 °C), low-temperature alkaline fusion treatment can efficiently remove ash minerals in the temperature range of 300-450 °C, which is beneficial to the efficient recovery of residual carbon in DA, while simultaneously improving the physicochemical properties and energy characteristics of DAC, thereby improving its combustion performance. At an alkali fusion temperature of 350 °C, a NaOH:DA ratio of 4.5:1, and a reaction time of 40 min, the resulting DAC product had ash content of 2.28%, combustible material recovery (CMR) of 82.03%, higher heating value (HHV) of 31.07 MJ kg-1, and SBET of 445.43 m2 g-1. In comparison, it was found that low-temperature alkali fusion significantly improved the deashing of CGFA when compared to existing deashing technologies. These results strongly suggest that this innovative deashing method can modify CGFA into a high-calorific value and low-N and S fuel, thereby providing a cost-effective and sustainable utilization method for CGFA.

Facile synthesis of crumpled nitrogen-doped porous carbon nanosheets with ultrahigh surface area for high-performance supercapacitors

Porous carbon nanosheets are currently considered excellent electrode materials for high-performance supercapacitors. However, their ease of agglomeration and stacking nature reduce the available surface area and limit the electrolyte ion diffusion and transport, thereby leading to low capacitance and poor rate capability. To solve these problems, we report an adenosine blowing and KOH activation combination strategy to prepare crumpled nitrogen-doped porous carbon nanosheets (CNPCNS), which exhibit much higher specific capacitance and rate capability compared to flat microporous carbon nanosheets. The method is simple and capable of one-step scalable production of CNPCNS with ultrathin crumpled nanosheets, ultrahigh specific surface area (SSA), microporous and mesoporous structure and high heteroatom content. The optimized CNPCNS-800 with a thickness of 1.59 nm has an ultrahigh SSA of 2756 m² g^-1, high mesoporosity of 62.9% and high heteroatom content (2.6 at% for N, 5.4 at% for O). Consequently, CNPCNS-800 presents an excellent capacitance, high rate capability and long cycling stability both in 6 M KOH and EMIMBF₄. More importantly, the energy density of the CNPCNS-800-based supercapacitor in EMIMBF₄ can reach up to 94.9 W h kg^-1 at 875 W kg^-1 and is still 61.2 W h kg^-1 at 35 kW kg^-1.

Mango-Stone-Derived Nitrogen-Doped Porous Carbon for Supercapacitors

The preparation of N-doped porous carbon (NC-800) is presented via facile mango stone carbonization at 800 °C. The NC-800 material exhibits good cycle stability (the capacity retention is 97.8% after 5000 cycles) and high specific capacitance of 280 F/g at 1 A/g. Furthermore, the assembled symmetric device of NC-800//NCs-800 exhibits about 31.1 Wh/kg of energy density at 800 W/kg in a voltage range of 0-1.6 V. The results of the study suggest that NC-800 may be a promising energy storage material for practical application.

High-yield and nitrogen self-doped hierarchical porous carbon from polyurethane foam for high-performance supercapacitors

Confronted with the environmental pollution and energy crisis issues, upcycling of waste plastics for energy-storage applications has attracted broad interest. Polyurethane (PUR) is a potential candidate for the preparation of N-doped carbon materials. However, its low carbon yield limits the utilization of PUR waste. In this study, PUR foam was converted into N-doped hierarchical porous carbon (NHPC) through an autogenic atmosphere pyrolysis (AAP)-KOH activation approach. An ultra-high carbon yield of 55.0% was achieved through AAP, which is more than 17 times the carbon yield of conventional pyrolysis of PUR. AAP converted 83.2% of C and 61.0% of N in PUR into derived carbon material. The high conversion rate and self-doping effect can increase the environmental and economic benefits of this approach. KOH activation significantly increased the specific surface area of carbon materials to 2057 m² g^-1 and incorporated hierarchical porous structure and O-containing functional groups to the carbon materials. The obtained NHPCs were applied to improve the performance of supercapacitors. The electrochemical measurement revealed that NHPCs exhibited a high specific capacitance of 342 F g^-1 (133 F cm^-3) at 0.5 A g^-1, low resistance, and outstanding cycling stability. The energy density and power density of the supercapacitor were improved to 11.3 W h kg^-1 and 250 W kg^-1, respectively. This research developed a possible solution to plastic pollution and energy shortage.

Hierarchical porous carbon foam electrodes fabricated from waste polyurethane elastomer template for electric double-layer capacitors

Plastic waste has become a major global environmental concern. The utilization of solid waste-derived porous carbon for energy storage has received widespread attention in recent times. Herein, we report the comparison of electrochemical performance of porous carbon foams (CFs) produced from waste polyurethane (PU) elastomer templates via two different activation pathways. Electric double-layer capacitors (EDLCs) fabricated from the carbon foam exhibited a gravimetric capacitance of 74.4 F/g at 0.1 A/g. High packing density due to the presence of carbon spheres in the hierarchical structure offered excellent volumetric capacitance of 134.7 F/cm³ at 0.1 A/g. Besides, the CF-based EDLCs exhibited Coulombic efficiency close to 100% and showed stable cyclic performance for 5000 charge-discharge cycles with good capacitance retention of 97.7% at 3 A/g. Low equivalent series resistance (1.05 Ω) and charge transfer resistance (0.23 Ω) due to the extensive presence of hydroxyl functional groups contributed to attaining high power (48.89 kW/kg). Based on the preferred properties such as high specific surface area, hierarchical pore structure, surface functionalities, low metallic impurities, high conductivity and desirable capacitive behaviour, the CF prepared from waste PU elastomers have shown potential to be adopted as electrodes in EDLCs.

Waste-converted nitrogen and fluorine co-doped porous carbon nanosheets for high performance supercapacitor with ionic liquid electrolyte

In this work, nitrogen and fluorine co-doped porous carbon nanosheets (NFPCNS) were fabricated from pharmaceutical drug residues derived from the fermentation synthesis of lincomycin hydrochloride via high-temperature pyrolysis and subsequent KOH activation without adding any nitrogen and fluorine reagents. The obtained NFPCNS exhibits an optimized integration of three dimensional interconnected nanosheet structure, large specific surface area of 2912 m² g^-1, hierarchical porous structure with large mesopore proportion (S_meso/S_micro = 151.5%, V_meso/V_micro = 248.2%) and high level heteroatom content (13.2 at.% O, 4.3 at.% N and 1.0 at.% F). Therefore, NFPCNS based supercapacitors using 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte exhibit an excellent gravimetric capacitance of 296F g^-1 at 1 A g^-1, good rate capability of 65% at 20 A g^-1 and high energy density of 125 Wh kg^-1. Furthermore, an ultra-high energy density of 173 Wh kg^-1 and a long cycling life with 93% capacitance retention after 2000 cycles has been achieved by NFPCNS based supercapacitors with 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide electrolyte. NFPCNS should be a green and efficient electrode materials for next-generation high-energy supercapacitors.

Facile preparation of flexible binder-free graphene electrodes for high-performance supercapacitors

A facile two-step strategy to prepare flexible graphene electrodes has been developed for supercapacitors using thermal reduction of graphene oxide (GO) and thermally reduced graphene oxide (TRGO) composite films. The tunable porous structure of the GO/TRGO film provided channels to release the high pressure generated by CO₂ gas. The graphene electrode obtained from reduced-GO/TRGO (1 : 1 in mass ratio) film showed great flexibility and high film density (0.52 g cm⁻³). Using the EMI-BF₄ electrolyte with a working voltage of 3.7 V, the as-fabricated free-standing reduced-GO/TRGO (1 : 1) film achieved a great gravimetric capacitance of 180 F g⁻¹ (delivering a gravimetric energy density of 85.6 W h kg⁻¹), a volumetric capacitance of 94 F cm⁻³ (delivering a volumetric energy density of 44.7 W h L⁻¹), and a 92% retention after 10 000 charge/discharge cycles. In addition, the solid state flexible supercapacitor with the free-standing reduced-GO/TRGO (1 : 1) film as the electrodes and the EMI-BF₄/poly (vinylidene fluoride hexafluopropylene) (PVDF-HFP) gel as the electrolyte also demonstrated a high gravimetric capacitance of 146 F g⁻¹ with excellent mechanical flexibility, bending stability, and electrochemical stability. The strategy developed in this study provides great potentials for the synthesis of flexible graphene electrodes for supercapacitors.

A supercapacitor electrode is developed with a free-standing graphene film by a facile two-step strategy. The graphene electrode achieved a gravimetric capacitance of 180 F g⁻¹ and a volumetric capacitance of 94 F cm⁻³.

Zinc-salt assisted synthesis of three-dimensional oxygen and nitrogen co-doped hierarchical micro-meso porous carbon foam for supercapacitors

Nitrogen and oxygen co-doped hierarchical micro-mesoporous carbon foams has been synthesized by pyrolyzation treatment of a preliminary foam containing melamine and formaldehyde as nitrogen, carbon and oxygen precursors and Zn(NO3)2. 6H2O and pluronic F127 as micro-meso pores generators. Several characterizations including thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and Raman spectroscopy, FTIR and X-ray photoelectron spectroscopy, N2 adsorption-desorption, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were performed on the prepared foams. X-ray diffraction patterns, Raman spectra and N2 adsorption-desorption results confirmed that ZnO has pronounced effect on the graphitization of the prepared carbon foam. From X-ray diffraction, thermal gravimetric and N2 adsorption-desorption analysis results it was confirmed that the carbothermal reaction and the elimination of ZnO and also the elimination of pluronic F127 are the main factors for the induction of porosities in the foam structure. The presence of Zn(NO3)2. 6H2O and pluronic F127 in the initial composition of the preliminary foam results in the specific surface area as high as 1176 m2.g-1 and pore volume of 0.68 cm3.g-1. X-ray photoelectron and FTIR spectroscopy analyses results approved the presence of nitrogen (about 1.9 at %) in the form of pyridinic, graphitic and nitrogen oxide and oxygen (about 7.5 at. %) functional groups on the surface of the synthesized carbon foam. Electrochemistry analysis results including cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) and also electrochemical impedance spectroscopy (EIS) analysis illustrated the formation of an electric double layer supercapacitor with the capacitance as high as 137 Fg-1.

Nitrogen and oxygen Co-doped porous carbon derived from yam waste for high-performance supercapacitors

It is a considerable challenge to produce a supercapacitor with inexpensive raw materials and employ a simple process to obtain carbon materials with a high specific surface area, rich pore structure, and appropriate doping of heterogeneous elements. In the current study, yam waste-derived porous carbon was synthesized for the first time by a two-step carbonization and KOH chemical activation process. An ultra-high specific surface area of 2382 m² g^-1 with a pore volume of 1.11 cm³ g^-1 and simultaneous co-doping of O-N was achieved for the optimized sample. Because of these distinct features, the optimized material exhibits a high gravimetric capacitance of 423.23 F g^-1 at 0.5 A g^-1 with an impressive rate capability at 10 A g^-1, and prominent cycling durability with a capacity retention of 96.4% at a high current density of 10 A g^-1 after 10 000 cycles in 6 M KOH in a three-electrode system. Moreover, in 6 M KOH electrolyte, the assembled symmetrical supercapacitor provides a large C of 387.3 F g^-1 at 0.5 A g^-1. It also presents high specific energy of 34.6 W h kg^-1 when the specific power is 200.1 W kg^-1 and a praiseworthy specific energy of 8.3 W h kg^-1 when the specific power is 4000.0 W kg^-1 in 1 M Na₂SO₄ electrolyte. Thus, this study provides reference and guidance for developing high-performance electrode materials for supercapacitors.

Electrochemical properties of an activated carbon xerogel monolith from resorcinol-formaldehyde for supercapacitor electrode applications

Activated carbon xerogel monoliths were prepared from resorcinol and formaldehyde via a catalyst-free and template-free hydrothermal polycondensation reaction, followed by pyrolysis and activation. The ratio of resorcinol (R) to distilled water (W) was varied to afford an interconnected pore structure with controlled pore size, while the pyrolysis temperature was optimized to give high specific surface area. Activation was carried out at 700 °C after soaking the samples in 6 M KOH aqueous solution. The same process, called “heat treatment”, was also carried out without soaking in KOH for comparison. The weight loss upon pyrolysis, activation and heat treatment and the weight gain via KOH soaking were measured. Field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and an N₂ sorption instrument were utilized for characterization. Additionally, electrochemical properties were evaluated using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) with a 3-electrode system, while a 2-electrode system was also employed for selected samples. The highest specific capacitance of 323 F g⁻¹via GCD at 1 A g⁻¹ was obtained at the R/W ratio of 45 and with 500 °C pyrolysis. In addition, this sample also exhibited 89.4% retention at 20 A g⁻¹ in the current density variation and 100% retention in 5000 cycling tests.

A monolithic carbon xerogel electrode for supercapacitors was prepared from resorcinol–formaldehyde, providing a specific capacitance of 323 F g⁻¹via GCD at 1 A g⁻¹ and 100% retention upon 5000 cycling tests.

Promising activated carbon derived from sugarcane tip as electrode material for high-performance supercapacitors

We present a simple, low-cost method for producing activated-carbon materials from sugarcane tips (ST) via two-step pre-carbonization and KOH activation treatment. After optimizing the amount of KOH, the resulting ST-derived activated carbon prepared with a KOH to PC-ST mass ratio of 2 (ACST-2) contained 17.04 wt% oxygen and had a large surface area of 1206.85 m² g^-1, which could be attributed to the large number of micropores in ACST-2. In a three-electrode system, the ACST-2 electrode exhibited a high specific capacitance of 259 F g^-1 at 0.5 A g^-1 and good rate capability with 82.66% retention from 0.5 to 10 A g^-1. In addition, it displayed a high capacitance retention of 89.6% after 5000 cycles at a current density of 3 A g^-1, demonstrating excellent cycling stability. Furthermore, the ACST-2//ACST-2 symmetric supercapacitor could realize a high specific energy density of 7.93 W h kg^-1 at a specific power density of 100 W kg^-1 in 6 M KOH electrolyte. These results demonstrate that sugarcane tips, which are inexpensive and easily accessible agricultural waste, can be used to create a novel biomass precursor for the production of low-cost activated carbon materials for high-performance supercapacitors.

Hazardous Petroleum Sludge-Derived Nitrogen and Oxygen Co-Doped Carbon Material with Hierarchical Porous Structure for High-Performance All-Solid-State Supercapacitors

Rational design and sustainable preparation of high-performance carbonaceous electrode materials are important to the practical application of supercapacitors. In this work, a cost-effective synthesis strategy for nitrogen and oxygen co-doped porous carbon (NOC) from petroleum sludge waste was developed. The hierarchical porous structure and ultra-high surface area (2514.7 m² g⁻¹) of NOC electrode materials could provide an efficient transport path and capacitance active site for electrolyte ions. The uniform co-doping of N and O heteroatoms brought enhanced wettability, electrical conductivity and probably additional pseudo-capacitance. The as-obtained NOC electrodes exhibited a high specific capacitance (441.2 F g⁻¹ at 0.5 A g⁻¹), outstanding rate capability, and cycling performance with inconspicuous capacitance loss after 10,000 cycles. Further, the assembled all-solid-state MnO₂/NOC asymmetrical supercapacitor device (ASC) could deliver an excellent capacitance of 119.3 F g⁻¹ at 0.2 A g⁻¹ under a wide potential operation window of 0–1.8 V with flexible mechanical stability. This ASC device yielded a superior energy density of 53.7 W h kg⁻¹ at a power density of 180 W kg⁻¹ and a reasonable cycling life. Overall, this sustainable, low-cost and waste-derived porous carbon electrode material might be widely used in the field of energy storage, now and into the foreseeable future.

Construction of hierarchically porous biomass carbon using iodine as pore-making agent for energy storage

High specific surface area, hierarchical porosity, high conductivity and heteroatoms doping have been considered as the dominating factors of high-performance carbon-based supercapacitors. Inspired by the blue phenomenon of combination of starch and iodine, iodine is employed firstly as pore-making agent to create micropores for the starch-derived carbon in this study. Based on this mechanism, the hierarchically porous carbon is synthesized through simple solvent heating and high-temperature (1000 °C) carbonization, which achieves high specific surface area of 2989 m² g^-1 (an increase of 39.7% compared to that without iodine) and low electrical resistivity of 0.21 Ω·cm. The assembled symmetric supercapacitors, combined with dual redox-active electrolyte (Bi³⁺ and Br^-), deliver the specific capacitance of 1216 F g^-1, energy density of 65.4 Wh kg^-1, as well as power density of 787.3 W kg^-1 at 2 A g^-1. In brief, the abundant biomass resource starch is exploited as carbon source, and the iodine sublimation reaction is conducted to provide more micropores to develop high-performance electrodes of supercapacitors.

Nitrogen, sulfur co-doped hierarchical carbon encapsulated in graphene with "sphere-in-layer" interconnection for high-performance supercapacitor

Rational design of electrode with hierarchical charge-transfer structure and good electronic conductivity is important to achieve high specific capacitance and energy density for supercapacitor, but it still remains a challenge. Herein, a nitrogen, sulfur co-doped pollen-derived carbon/graphene (PCG) composite with interconnected "sphere-in-layer" structure was fabricated, in which hierarchically pollen-derived carbon microspheres can serve as "porous spacers" to prevent the agglomeration of graphene nanosheets. The optimized PCG composite prepared with 0.5 wt% of graphene oxide (PCG-0.5) exhibited high specific capacitance (420Fg^-1 at 1Ag^-1), rate performance (280Fg^-1 at 20Ag^-1), and excellent cycling stability with 94% of capacitance retention after 10,000 cycles. The symmetrical device delivered a remarkable energy density of 31.3Whkg^-1 in neutral medium. Moreover, density functional theory calculation revealed that PCG electrode possessed the accelerated charge transfer and enhanced electronic conductivity, thus ensuring a remarkable electrochemical performance. This work may afford an effective strategy for the development of biomass-derived carbon electrodes with novel charge-transfer structure toward supercapacitor applications.

Hierarchically porous carbon derived from potassium-citrate-loaded poplar catkin for high performance supercapacitors

A simple one-step preparation of biomass derived carbon materials with hierarchical pore structure for supercapacitor application is proposed. Briefly, potassium citrate is loaded onto poplar catkin, a forestry and agricultural residue, for carbonization at different temperature (750-900 ℃). With the confined effect of poplar catkin and pore-forming role of potassium compounds, interconnected carbon networks combining of macropores, small mesopores and micropores are obtained. The product carbonized at 850 ℃ (S-850) processes large surface area of 2186 m²/g with two main micropore ranges distributed in 0.5-0.7 nm and 0.7-1.5 nm, and the sample of S-900 processes relatively high electrical conductivity because of the high degree of graphitization. The electrodes based on these carbon materials show main electrical double-layer capacitors with small part of pseudo-capacitors due to O-doping. The S-850 sample displays superior specific capacity at low charge-discharge current density while the electrode based on S-900 shows high specific capacity under high current density. The symmetrical devices based on S-850 give a superb stability and high energy and power densities in alkaline electrolyte. Within a voltage window of 1.4 V, the device can deliver a 13.3 Wh/kg energy density at a power density of 720 W/kg and maintain 7.8 Wh/kg at 14040 W/kg.

Insulation board-derived N/O self-doped porous carbon as an electrode material for high-performance symmetric supercapacitors

A high-efficient and low-cost supercapacitor electrode material was sustainably prepared using white waste pollutant as the starting material.

Electrochemical properties of kenaf-based activated carbon monolith for supercapacitor electrode applications

Activated carbon monoliths of kenaf (ACMKs) were prepared by moulding kenaf fibers into a column-shape monolith and then carrying out pyrolysis at 500, 600, 700 or 800 °C, followed by activation with KOH at 700 °C. Then, the sample was characterized using thermogravimetric analyzer (TGA), field-emission scanning electron microscopy (FE-SEM), field-emission transmission electron microscopy (FE-TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD) and N₂ sorption instruments. The prepared ACMK was subjected to electrochemical property evaluation via cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS). The GCD study using a three-electrode system showed that the specific capacitance decreased with higher pyrolysis temperature (PYT) with the ACMK pyrolyzed at 500 °C (ACMK-500) exhibiting the highest specific capacitance of 217 F g⁻¹. A two-electrode system provided 95.9% retention upon a 5000 cycle test as well as the specific capacitance of 212 F g⁻¹, being converted to an energy density of 6 W h kg⁻¹ at a power density of 215 W kg⁻¹.

Monolithic carbon from kenaf-based fiber for supercapacitor electrode application provided a specific capacitance of 212 F g⁻¹via GCD at 1 A g⁻¹, converting to an energy density of 6 W h kg⁻¹ at the power density of 215 W kg⁻¹ as well as 95.9% retention upon 5000 cycling test.

Bacterial cellulose-derived carbon nanofibers as both anode and cathode for hybrid sodium ion capacitor

Hybrid ion capacitors (HICs) based on insertion reactions have attracted considerable attention due to their energy density being much higher than that of the electrical double-layer capacitors (EDLCs). However, the development of hybrid ion capacitors with high energy density at high power density is a big challenge due to the mismatch of charge storage capacities and electrode kinetics between the battery-type anode and capacitor-type cathode. In this work, N and O dual doped carbon nanofibers (N,O-CNFs) were combined with carbon nanotubes (CNTs) to compose a complex carbon anode. N,O dual doping effectively tuned the functional group and surface activity of the CNFs while the integration of CNTs increased the extent of graphitization and electrical conductivity. The carbon cathode with high specific surface area and high capacity was obtained by the activation of CNFs (A-CNFs). Finally, a hybrid sodium ion capacitor was constructed by the double carbon electrode, which showed a superior electrochemical capacitive performance. The as-assembled HIC device delivers a maximum energy density of 59.2 W h kg⁻¹ at a power density of 275 W kg⁻¹, with a high energy density of 38.7 W h kg⁻¹ at a power density of 5500 W kg⁻¹.

A hybrid sodium ion capacitor is constructed by the double carbon electrode, whose precursors are both from nanofibers of bacterial cellulose, showing a superior electrochemical capacitive performance.

Sonochemical assisted fabrication of 3D hierarchical porous carbon for high-performance symmetric supercapacitor

A scalable fabrication of 3D hierarchical porous carbon structure (3D-HPC) has been achieved via a simple sonochemical route at different pyrolysis temperatures. It is worth noting that all the 3D-HPC samples possess oxygen-functional groups after activation by KOH and self-doped by nitrogen, which are beneficial to improving their surface wettability as well as increasing the electro-active surface area between the electrode and the surrounding electrolyte, consequently enhancing their electrochemical performance. Remarkably, the resulting carbon sample pyrolyzed at 850 °C (AC-850) possesses a maximum doping level of 2.75 at% and a high surface area of 1376.19 m² g^-1, which exhibits high electrochemical performance with high capacitance up to 269.19 F g^-1 at a current density of 2 A g^-1. Moreover remarkably, the AC-850-based symmetric supercapacitor delivers a high energy density of 21.4 Wh kg^-1 at a power density of 531.2 W kg^-1 with excellent rate performance and superior cycling stability (94.7% retention over 5000 cycles). The present approach is very suitable for large scale production of high-quality porous carbon materials at low cost, which can be used in different aspects, such as energy storage, gas storage, environmental remediation, and so on.

One-pot synthesis of unique skin-tissue-bone structured porous carbons for enhanced supercapacitor performance

Introduction of hierarchical porous structure and heteroatom in porous carbons are always effective approaches to improve the capacitive performance for supercapacitor. However, it is still a challenge to achieve the desired structure characteristics by a convenient one-step synthesis. Herein, C₁₆mimPF₆, an ionic liquid, was introduced in the self-assembly process of poly-benzoxazine to obtain a unique skin-tissue-bone structured hierarchical porous carbon with homogeneous N, P co-doping after carbonization. As the key component, C₁₆mimPF₆ works not only as a structure-directing agent to form a hierarchical structure through microphase separation mechanism, thereby promoting the transfer of ion and electron, but also as a heteroatom precursor to contribute an additional pseudocapacitance by doping phosphorus atoms on carbon matrix. The obtained porous carbon displays a high gravimetric capacitance (C_g) of 209 F g^-1 (especially in the carbons prepared without corrosive activation step), a good volumetric capacitance (C_v) of 132 F cm^-3 and an excellent area-normalized capacitance (C_a) of 35 μF cm^-2. Overall, this work opens a new way to design the polymer-derived carbons with easy heteroatoms doping and hierarchical porous structure.

3D flower-like CoNi2S4/polyaniline with high performance for glycerol electrooxidation in an alkaline medium

Schematic of the fabrication of CoNi₂S₄/PANI.

N, O and P co-doped honeycomb-like hierarchical porous carbon derived from Sophora japonica for high performance supercapacitors

Novel N, O and P co-doped honeycomb-like hierarchically porous carbon (N-O-P-HHPC) materials with a large specific surface area from Sophora japonica were prepared via a one-step activation and carbonization method and used as an electrode for supercapacitors. The results indicate that as-prepared N-P-HHPC with a large specific surface area (2068.9 m² g⁻¹) and N (1.5 atomic%), O (8.4 atomic%) and P (0.4 atomic%) co-doping has a high specific capacitance of 386 F g⁻¹ at 1 A g⁻¹. Moreover, a 1.8 V symmetrical SC was assembled from the N-O-P-HHPC-3 electrode using 1 M Na₂SO₄ gel electrolyte, presenting a high energy density (28.4 W h kg⁻¹ at 449.9 W kg⁻¹) and a long life cycling stability with only 7.3% capacitance loss after 10 000 cycles. Furthermore, the coin-type symmetrical SC using EMIMBF4 as electrolyte presents an ultrahigh energy density (80.8 W h kg⁻¹ at 1500 W kg⁻¹). When the two coin-type symmetrical SCs are connected in series, eight red light-emitting diodes (LEDs) and a small display screen can be powered. These results demonstrate as-prepared N, O and P co-doped HHPC is a considerable candidate as a carbon electrode for energy storage devices.

N, O and P co-doped honeycomb-like hierarchical porous carbon (N-P-HHPC-3) derived from Sophora japonica displays an ultrahigh energy density (80.8 W h kg⁻¹ at 1500 W kg⁻¹) and outstanding long-term stability.