Biomass derived hierarchical porous carbon for high-performance O2/N2 adsorption; a new green self-activation approach

Biomass-derived porous carbons are the most common adsorbent materials for O₂/N₂ adsorption because of their excellent textural properties, high surface area, and low expense. A new synthesis method based on a self-activation technique was developed for a new green porous carbon adsorbent. This ecofriendly system was used for the synthesis of hierarchical porous carbons from walnut-shell precursors. The sorbent was successfully synthesized by facile one-step carbonization, with the activating reagents being gases released during the activation. The sample morphology and structure were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, X-ray powder diffraction, thermogravimetric, and differential thermal analysis. The optimal porous carbons were synthesized at 1000 °C, providing a surface area as high as 2042.4 (m² g⁻¹) and micropore volume of about 0.499 (m³ g⁻¹). At 298 °K under 9.5 bar pressure, the potential for O₂/N₂ separation using porous carbon samples was studied, and the sips isotherms with the highest adsorption potential were determined to be 2.94 (mmol g⁻¹) and 2.67 (mmol g⁻¹), respectively. The sample exhibited stable O₂/N₂ separation over ten cycles, showing high reusability for air separation. Finally, the technology described presents a promising strategy for producing eco-friendly porous carbon from a variety of biomass on an industrial scale.

Green porous carbon was synthesized by self-activation methodology with facile one-step carbonization from a walnut-shell precursor for air separation. The adsorption process behavior was surveyed using isotherm, kinetic and thermodynamic models.     

Preparation of cellulose acetate derived carbon nanofibers by ZnCl2 activation as a supercapacitor electrode

Porous carbon nanofibers are fabricated by one-step carbonization and activation of electrospun cellulose acetate (CA) nanofibres. Electrospun CA nanofibers were obtained by the electrospinning of a CA/DMAC/acetone solution, followed by deacetylation in NaOH/ethanol solution. One-step carbonization and activation was achieved by dipping the as-spun fibers in ZnCl₂ solution, followed by one-step high temperature treatment. The effects of the concentration of the dipping solution on the microstructure of the CA-based carbon nanofibers (CACNFs), including the morphology, crystal structure, porous structure, specific surface area and surface chemical properties, have been investigated. The coating of ZnCl₂ effectively improves the thermal stability of electrospun CA nanofibers and obviously enhances the oxygen-containing surface groups of the CACNFs. The CACNFs have a norrow pore size distribution (0.6–1.2 nm) and a high specific surface area (∼1188 m² g⁻¹). Electrochemical performances of the CACNFs were evaluated as supercapacitor electrodes in 6 M KOH solution. The CACNFs demonstrate high specific capacitance (202 F g⁻¹ at 0.1 A g⁻¹) and excellent rate capability (61% of the retention from 0.1 to 20 A g⁻¹). After 5000 cycles of the electrode, the capacitance is maintained at 92%, and the coulombic efficiency is close to 100%, showing high electrochemical stability and reversibility. The renewable features and excellent performance make CACNFs quite a promising alternative to efficient supercapacitor electrodes for energy storage applications.

Porous carbon nanofibers are fabricated by one-step carbonization and activation of electrospun cellulose acetate (CA) nanofibres.     

Facile preparation of 3D porous agar-based heteroatom-doped carbon aerogels for high-energy density supercapacitors

The fabrication of heteroatom-doped porous carbon materials with high electrical conductivity and large specific surface area via an environmentally friendly route is critical and challenging. Herein, nitrogen and oxygen co-doped agar porous carbon (APC) was developed for supercapacitors via a one-step carbonization method with agar as the raw material and ammonia as the activator and nitrogen source. APC outperformed pectin porous carbon, tamarind porous carbon, and the previously reported carbon-based supercapacitors with a high capacitance retention of 72% even from 0.5 A g⁻¹ to 20 A g⁻¹ and excellent cycling stability in 6 M KOH solution (retained after 10 000 cycles) with a rate of over 98.5%. Furthermore, the APC electrode-based symmetric device exhibited an impressive energy density of 20.4 W h kg⁻¹ and an ultra-high power density of 449 W kg⁻¹ in 1 M Na₂SO₄ electrolyte together with excellent cycling stability (103.2% primary capacitance retentivity after 10 000 cycles). This study offers a novel method for the synthesis of nitrogen heteroatom-doped hierarchical porous carbon materials for performance-enhanced energy storage devices.

N and O co-doped agar porous carbon (APC) as electrode materials exhibit excellent performance. A respectable energy density of 20.4 W h kg⁻¹ and an ultra-high power density of 449 W kg⁻¹, as well as excellent cycle stability in 1 M Na₂SO₄ electrolyte.     

Facile synthesis of high-surface-area nanoporous carbon from biomass resources and its application in supercapacitors

It is critical for nanoporous carbons to have a large surface area, and low cost and be readily available for challenging energy and environmental issues. The pursuit of all three characteristics, particularly large surface area, is a formidable challenge because traditional methods to produce porous carbon materials with a high surface area are complicated and expensive, frequently resulting in pollution (commonly from the activation process). Here we report a facile method to synthesize nanoporous carbon materials with a high surface area of up to 1234 m² g⁻¹ and an average pore diameter of 0.88 nm through a simple carbonization procedure with carefully selected carbon precursors (biomass material) and carbonization conditions. It is the high surface area that leads to a high capacitance (up to 213 F g⁻¹ at 0.1 A g⁻¹) and a stable cycle performance (6.6% loss over 12 000 cycles) as shown in a three-electrode cell. Furthermore, the high capacitance (107 F g⁻¹ at 0.1 A g⁻¹) can be obtained in a supercapacitor device. This facile approach may open a door for the preparation of high surface area porous carbons for energy storage.

High-surface-area nanoporous carbon is obtained by direct pyrolysis of biomass resources without an activation process. An electrochemical test shows high capacitance.     

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.

3D porous carbon with ultra-high specific surface area and excellent electrochemical performance is synthesized by a simple activation and carbonization process through adopting biomass yam waste as raw material.     

Self-template/activation nitrogen-doped porous carbon materials derived from lignosulfonate-based ionic liquids for high performance supercapacitors

A simple ion exchange reaction of sodium lignosulfonate (SLS) and 1-allyl-3-methyl imidazolium chloride ([Amim]Cl) produced a new polymeric ionic liquid [Amim]LS and NaCl, and the mixture was successfully used as a precursor to prepare a nitrogen-doped porous carbon material via direct carbonization without any additional activation agent or template. It was believed that the in situ produced NaCl during the precursor synthesis process acted as the self-template and in self-activation. The introduction of imidazolium ionic liquid into the precursor raised the nitrogen content of the obtained carbon material up to 4.68% for a high yield of [Amim]LS-700 carbon material up to 34.6%. The effect of carbonization temperature on the structures and electrochemical properties of the prepared carbon were also studied systematically. It was found that the carbon material exhibits a superior gravimetric capacitance up to 230 F g⁻¹ (0.1 A g⁻¹) at the carbonization temperature of 700 °C, a good energy density of 7.99 W h kg⁻¹ at the power density of 25 W Kg⁻¹, and an excellent cycling stability of 90.3% after 20 000 cycles. This work provides a new path for the value-added utilization of biomass coupled with the field of electrochemical energy storage.

Without any additional template or activation agent, a high N-doped porous carbon was easily prepared by a simple ion exchange reaction and a following carbonization, and showed excellent electrochemical performance as a supercapacitor electrode.     

One-step preparation of N,O co-doped 3D hierarchically porous carbon derived from soybean dregs for high-performance supercapacitors

Hierarchically porous carbon (HPC) material based on environmental friendliness biomass has spurred much attention, due to its high surface area and porous structure. Herein, three-dimensional (3D) N,O co-doped HPC (N–O-HPC) was prepared by using a one-step fabrication process of simultaneously carbonizing and activating soybean dregs and used as an electrode for supercapacitors (SCs). The obtained N–O-HPC with 4.8 at% N and 6.1 at% O exhibits a pretty small charge transfer resistance (0.05 Ω) and a large specific capacitance (408 F g⁻¹ at 1 A g⁻¹), due to its 3D hierarchically porous framework structure with extremely large specific surface area (1688 m² g⁻¹). Moreover, a symmetrical SC assembled with the HPC electrode exhibits an amazingly high energy density (22 W h kg⁻¹ at 450 W kg⁻¹) and a stable long cycling life with only 6% capacitance loss after 5000 cycles in 1 M Na₂SO₄ solution. This work provides a facile, green, and low-cost way to prepare electrode materials for SCs.

N,O co-doped 3D HPC derived from soybean dregs was prepared by a one-step method and displays an amazingly high energy density of 22 W h kg⁻¹ (450 W kg⁻¹) using 1 M Na₂SO₄ solution.     

Formation mechanism and characterization of porous biomass carbon for excellent performance lithium-ion batteries

Porous biomass carbon derived from corn stalks was prepared via carbonization and activation of CaCl₂. Combined with its microstructure, the formation mechanism and electrochemical properties were analyzed. The addition of CaCl₂ was the key factor to form the porous structure, and the proportion of CaCl₂ had a significant impact on the pores distribution and electrochemical properties. The resulting sample had a specific surface area of 370.6 m² g⁻¹ and an average pore size of 9.65 nm. The sample was circulated at 0.2C for 100 cycles, the specific discharge capacity was 783 mA h g⁻¹. After 60 cycles at different rates, when the current was restored to 0.2C again, the discharge specific capacity quickly recovered. This showed that the sample had excellent rate performance and cycle stability for lithium-ion batteries.

Porous biomass carbon derived from corn stalks was prepared via carbonization and activation of CaCl₂.     

N-Enriched carbon nanofibers for high energy density supercapacitors and Li-ion batteries

Nitrogen enriched carbon nanofibers have been obtained by one-step carbonization/activation of PAN-based nanofibers with various concentrations of melamine at 800 °C under a N₂ atmosphere. As synthesised carbon nanofibers were directly used as electrodes for symmetric supercapacitors. The obtained PAN-MEL fibers with 5% melamine stabilised at 280 °C and carbonized at 800 °C under a nitrogen atmosphere showed excellent electrochemical performance with a specific capacitance of up to 166 F g⁻¹ at a current density of 1A g⁻¹ using 6 M KOH electrolyte and a capacity retention of 109.7% after 3000 cycles. It shows a 48% increase as compared to pristine carbon nanofibers. Two electrode systems of the CNFM5 sample showed high energy densities of 23.72 to 12.50 W h kg⁻¹ at power densities from 400 to 30 000 W kg⁻¹. When used as an anode for Li-ion battery application the CNFM5 sample showed a high specific capacity up to 435.47 mA h g⁻¹ at 20 mA g⁻¹, good rate capacity and excellent cycling performance (365 mA h g⁻¹ specific capacity even after 200 cycles at 100 mA g⁻¹). The specific capacity obtained for these nitrogen enriched carbon nanofibers is higher than that for pristine carbon nano-fibers.

Nitrogen enriched carbon nanofibers have been obtained by one-step carbonization/activation of PAN-based nanofibers with various concentrations of melamine at 800 °C under a N₂ atmosphere.     

Dicarbonyl-tuned microstructures of hierarchical porous carbons derived from coal-tar pitch for supercapacitor electrodes

A simple and effective template-free method to prepare hierarchical porous carbons (HPCs) has been developed by using low-cost coal-tar pitch as a starting material, anhydrous aluminum chloride as the Friedel–Crafts catalyst, and oxalyl chloride as the cross-linking agent. By a simple controllable Friedel–Crafts reaction, diketone-functionalized coal-tar pitch as the hierarchical porous coal-tar pitch precursor was obtained via a one-step carbonization to provide a well-developed micro–mesoporous network. Nitrogen adsorption and desorption measurements showed that the surface area, pore volume, pore size and pore size distributions of the resulting carbon materials was dependent on the usage of the cross-linking agent. The as-fabricated HPCs have a large Brunauer–Emmett–Teller specific surface area of 1394.6 m² g⁻¹ and exhibit an excellent electrochemical performance with the highest specific capacitance of 317 F g⁻¹ at a current density of 1 A g⁻¹ in a three-electrode system. A symmetric supercapacitor was fabricated from HPC-DK-1.0 in a two-electrode system, which exhibits a high specific capacitance of 276 F g⁻¹ at a current density of 0.25 A g⁻¹, a high rate capability and an excellent cycling stability with a capacitance retention of 92.9% after 10 000 cycles. The one-step carbonization method that produced HPCs for electrical double-layer capacitors represents a new approach for high-performance energy storage.

The hierarchical porous carbons have an excellent cycling stability with a capacitance retention of 92.9% after 10 000 cycles.     

Hierarchically porous N-doped carbon derived from supramolecular assembled polypyrrole as a high performance supercapacitor electrode material

Rationally designed precursors of N-doped carbon are crucial for high performance carbon materials of supercapacitor electrodes. Herein, we report a scalable preparation of hierarchically structured N-doped carbon of micro/meso porous nanofiber morphology by using a supramolecular assembled polypyrrole as the precursor. The influences of the dose of supramolecular dopant on final products after carbonization and sequential chemical activation were investigated. The interconnected nanofiber backbone allows better electron transport and the optimized hierarchically porous structure of the material exhibits a large specific surface area of 2113.2 m² g⁻¹. The N content of the carbon is as high as 6.49 atom%, which is favorable to improve the supercapacitive performance via additional reversible redox reaction over pure carbon. The hierarchically porous N-doped carbon electrode delivered an outstanding specific capacitance of 435.6 F g⁻¹ at 0.5 A g⁻¹, significantly higher than that of the control sample derived from undoped polypyrrole samples. Moreover, the capacitance retention is as high as 96.1% after 5000 cycles. This precursor''s structural control route is readily applicable to various conducting polymers, and provides a methodology to design carbon materials with advanced structure for developing high-performance supercapacitor electrode materials.

Hierarchically porous N-doped carbon with optimized morphology exhibits an enhanced specific capacitance of 435.6 F g⁻¹ at 0.5 A g⁻¹ and 96.1% capacitance retention after 5000 cycles in 1 M H₂SO₄.     

N-doped pinecone-based carbon with a hierarchical porous pie-like structure: a long-cycle-life anode material for potassium-ion batteries

Pinecone-based biomass carbon (PC) is a potential anode material for potassium-ion batteries because it is abundant, cheap, renewable, and easy to obtain. However, because of inferior kinetics and the effects of volume expansion due to the large radius of the K⁺ ion, it does not meet commercial performance requirements. In this study, nitrogen-doped PC (NPC) was prepared by carbonization in molten ZnCl₂ with urea as a nitrogen source. A strategy based on synergistic effects between N doping and ZnCl₂ molten salt was used to produce a hierarchically porous pie-like NPC with abundant defects and active sites and an enlarged interlayer distance—properties that enhance K⁺ adsorption, promote K⁺ intercalation/diffusion, and reduce the effects of volume expansion. This NPC exhibited a high reversible capacity (283 mA h g⁻¹ at 50 mA g⁻¹) and superior rate performance and cyclic stability (110 mA h g⁻¹ after 1000 cycles at 5 A g⁻¹), demonstrating its potential for use in potassium-ion batteries.

Pinecone-based biomass carbon (PC) is a potential anode material for potassium-ion batteries because it is abundant, cheap, renewable, and easy to obtain.     

One-step production of N–O–P–S co-doped porous carbon from bean worms for supercapacitors with high performance

In recent years, multi-heteroatom-doped hierarchical porous carbons (HPCs) derived from natural potential precursors and synthesized in a simple, efficient and environmentally friendly manner have received extensive attention in many critical technology applications. Herein, bean worms (BWs), a pest in bean fields, were innovatively employed as a precursor via a one-step method to prepare N–O–P–S co-doped porous carbon materials. The pore structure and surface elemental composition of carbon can be modified by adjusting KOH dosage, exhibiting a high surface area (S_BET) of 1967.1 m² g⁻¹ together with many surface functional groups. The BW-based electrodes for supercapacitors were shown to have a good capacitance of up to 371.8 F g⁻¹ in 6 M KOH electrolyte at 0.1 A g⁻¹, and good rate properties with 190 F g⁻¹ at a high current density of 10 A g⁻¹. Furthermore, a symmetric supercapacitor based on the optimal carbon material (BWPC_1/3) was also assembled with a wide voltage window of 2.0 V, demonstrating satisfactory energy density (27.5 W h kg⁻¹ at 200 W kg⁻¹) and electrochemical cycling stability (97.1% retention at 10 A g⁻¹ over 10 000 charge/discharge cycles). The facile strategy proposed in this work provides an attractive way to achieve high-efficiency and scalable production of biomass-derived HPCs for energy storage.

Bean worms, a pest in bean fields, were innovatively employed as a precursor via a one-step method to prepare N–O–P–S co-doped porous carbon materials.     

Electrospinning preparation of a large surface area,hierarchically porous,and interconnected carbon nanofibrous network using polysulfone as a sacrificial polymer for high performance supercapacitors

Carbon nanofibrous mats (CNFMs) are prepared by electrospinning of blended precursor of polyacrylonitrile and polysulfone (PSF) followed by pre-oxidation stabilization and carbonization. Addition of PSF as a sacrificial polymer leads to CNFMs with high surface area, large numbers of micropores and mesopores, good degree of carbonization, and interconnected fibrous network, due to the high decomposition temperature, release of SO₂ during decomposition, and large amount of carbon residue of PSF during carbonization. The electrochemical characterization shows that the CNFM electrode has a specific capacitance of 272 F g⁻¹ at a current density of 1 A g⁻¹ with 74% of the specific capacitance retained at 50 A g⁻¹ in 2.0 M KOH electrolyte. The CNFM electrodes have excellent cycling durability with 100% capacitance retention after 10 000 cycles.

Carbon nanofibrous mats (CNFMs) are prepared by electrospinning of blended precursor of polyacrylonitrile and polysulfone (PSF) followed by pre-oxidation stabilization and carbonization.     

“Water-in-salt” electrolyte enhanced high voltage aqueous supercapacitor with carbon electrodes derived from biomass waste-ground grain hulls

To design high specific surface area and optimize the pore size distribution of materials, we employ a combination of carbonization and KOH activation to prepare activated carbon derived from ground grain hulls. The resulting carbon material at lower temperature (800, BSAC-A-800) exhibits a porous structure with a high specific surface area of 1037.6 m² g⁻¹ and a pore volume of 0.57 m³ g⁻¹. Due to the synergistic structural characteristics, BSAC-A-800 reveals preferable capacitive performance, showing a specific capacitance as high as 313.3 F g⁻¹ at 0.5 A g⁻¹, good rate performance (above 73%), and particularly stable cycling performance (99.1% capacitance retention after 10 000 cycles at a current density of 10 A g⁻¹). More importantly, the assembled symmetric supercapacitor using a water-in-salt electrolyte (17 m NaClO₄) with high discharge specific capacitance (59 F g⁻¹ at 0.5 A g⁻¹), high energy density (47.2 W h kg⁻¹) and high voltage (2.4 V) represents significant progress towards performance comparable to that of commercial salt-in-water electrolyte supercapacitors (with discharge specific capacitance of 50 F g⁻¹, energy densities of ∼28.1 W h kg⁻¹ and voltages of 2.0 V).

To design high specific surface area and optimize the pore size distribution of materials, we employ a combination of carbonization and KOH activation to prepare activated carbon derived from ground grain hulls.     

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.     

Facile synthesis of Camellia oleifera shell-derived hard carbon as an anode material for lithium-ion batteries

A comparatively facile and ecofriendly process has been developed to synthesize porous carbon materials from Camellia oleifera shells. Potassium carbonate solution (K₂CO₃) impregnation is introduced to modify the functional groups on the surface of Camellia oleifera shells, which may play a role in promoting the development of pore structure during carbonization treatment. Moreover, a small amount of naturally embedded nitrogen and sulfur in the Camellia oleifera shells can also bring about the formation of pores. The Camellia oleifera shell-derived carbon has a large specific surface area of 1479 m² g⁻¹ with a total pore volume of 0.832 cm³ g⁻¹ after being carbonized at 900 °C for 1 h. Furthermore, when used as an anode for lithium-ion batteries, the sample shows superior electrochemical performance with a specific capacity of 483 mA h g⁻¹ after 100 cycles measured at 200 mA g⁻¹ current density. Surprisingly, the specific capacity is even gradually increased with cycling. In addition, this sample exhibits almost 100% retention capacity after 250 cycles at a current density of 200 mA g⁻¹.

Bio-waste Camellia oleifera shells (COS) are converted into porous carbon by a two-step method.     

Catalytic graphitization assisted synthesis of Fe3C/Fe/graphitic carbon with advanced pseudocapacitance

We report an environmentally friendly strategy for the synthesis of Fe₃C/Fe/graphitic carbon based on hydrothermal carbonization and graphitization of carbon spheres with potassium ferrate (K₂FeO₄) at 800 °C. The obtained sample consisting of Fe₃C/Fe nanoparticles and graphitic carbon (FC-1-8) delivered an enhanced pseudocapacitance of 428.0 F g⁻¹ at a current density of 1 A g⁻¹. After removal of the Fe₃C/Fe electroactive materials, the graphitic carbon (FC-1-8-HCl) possessed a large specific surface area (SSA) up to 2813.6 m² g⁻¹ with a capacity of 243.3 F g⁻¹ at 1 A g⁻¹, far outweighing the other amorphous carbon electrodes of FC-0-8 (carbon spheres annealed at 800 °C without the treatment of K₂FeO₄). The graphitic material with a porous structure could offer more electroactive sites and improved conductivity of the sample. This method provided guidelines for the synthesis of superior performance supercapacitors with synchronous graphitic carbon and electroactive species.

We report an environmentally friendly strategy for the synthesis of Fe₃C/Fe/graphitic carbon based on hydrothermal carbonization and graphitization of carbon spheres with potassium ferrate (K₂FeO₄) at 800 °C.     

Mesopore-dominant nitrogen-doped carbon with a large defect degree and high conductivity via inherent hydroxyapatite-induced self-activation for lithium-ion batteries

In this study, N-doped mesopore-dominant carbon (NMC) materials were prepared using bio-waste tortoise shells as a carbon source via a one-step self-activation process. With intrinsic hydroxyapatites (HAPs) as natural templates to fulfill the synchronous carbonization and activation of the precursor, this highly efficient and time-saving method provides N-doped carbon materials that represent a large mesopore volume proportion of 74.59%, a high conductivity of 4382 m S⁻¹, as well as larger defects, as demonstrated by Raman and XRD studies. These features make the NMC exhibit a high reversible lithium-storage capacity of 970 mA h g⁻¹ at 0.1 A g⁻¹, a strong rate capability of 818 mA h g⁻¹ at 2 A g⁻¹, and a good capacity of 831 mA h g⁻¹ after 500 cycles at 1 A g⁻¹. This study provides a highly efficient and feasible method to prepare renewable biomass-derived carbons as advanced electrode materials for the application of energy storage.

A hydroxyapatite-induced self-activation method has been used to prepare nitrogen-doped mesopore-dominant carbon. The carbon has abundant macro/mesopores, high conductivity, and favorable defects and exhibited high-performance in LIBs.     

Formation of nickel–cobalt sulphide@graphene composites with enhanced electrochemical capacitive properties

Here, nickel–cobalt sulphide particles embedded in graphene layers (porous Ni–Co–S@G), were successfully prepared by one-step annealing of metallocene/metal–organic framework (MOF) hybrids involving simultaneous carbonization and sulfidation. Benefiting from the porous structure, highly conductive graphene layers and large loading of super-capacitive Ni–Co–S, the obtained Ni–Co–S@G composites exhibited excellent electrochemical performance with a specific capacitance of 1463 F g⁻¹ at a current density of 1 A g⁻¹. A flexible solid-state asymmetric supercapacitor (ASC), assembled with Ni–Co–S@G and active carbon, demonstrated a high energy density of 51.0 W h kg⁻¹ at a power density of 650.3 W kg⁻¹. It is noteworthy that the ASC offered robust flexibility and excellent performance that was maintained when the devices were bent at various angles. The results indicate that the as-prepared materials could potentially be applied in high-performance electrochemical capacitors.

Ni–Co–S@graphene composites, derived from a metallocene/MOF precursor, presents high energy density and excellent cycling stability.