CO2 activation of bamboo residue after hydrothermal treatment and performance as an EDLC electrode

CO₂ activation of the solid residue of bamboo after hydrothermal treatment, which is used for the production of xylo-oligosaccharide, was investigated in detail. The reference temperature for carbonization and CO₂ activation was 800 °C. The activated carbon from a solid residue was demonstrated to have a higher potential for making EDLC electrodes than bamboo activated carbon thanks to its very low ash content (almost 0) and high porosity structure with a BET surface area up to ca. 2150 m² g⁻¹. The electrochemical performance of ELDC electrodes prepared from solid residue-derived activated carbon in 1 M H₂SO₄ aqueous solution was measured and well compared with carbon from bamboo. Through investigation, it is clear that the capacitance of the electrode made from the solid residue has a better capacity than that of raw bamboo.

CO₂ activation was performed on hydrothermally treated bamboo for the preparation of an EDLC electrode.     

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.     

Nitrogen doped hierarchical activated carbons derived from polyacrylonitrile fibers for CO2 adsorption and supercapacitor electrodes

Nitrogen doped hierarchical activated carbons with high surface areas and different pore structures are prepared form polyacrylonitrile fibers through KOH activation by two steps. It is found that the specific surface area and porosity of the activated carbons depend strongly on the activation temperatures. The specific surface area increases from 607 m² g⁻¹ to 3797 m² g⁻¹ when the activation temperature increases from 600 °C to 800 °C, and then decreases to 3379 m² g⁻¹ at 900 °C. It shows that the hierarchical activated carbon prepared at a moderate activation temperature of 700 °C exhibits the largest CO₂ capture amount, i.e., 5.25 and 3.63 mmol g⁻¹ at 273 and 298 K, respectively, under the pressure of 1 bar. The excellent CO₂ capture properties are due to the high specific surface area of 2146 m² g⁻¹ and high nitrogen content (5.2 wt%) of the obtained sample. On the other hand, when used as supercapacitor electrodes, the sample with the activation temperature at 800 °C shows the largest specific capacitance of 302 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH aqueous electrolyte, with an excellent rate capability of 231 F g⁻¹ at 10 A g⁻¹. Furthermore, a nearly linear relationship between nitrogen content in the nitrogen doped activated carbons and specific CO₂ uptake as well as the specific capacitance were first established, indicating nitrogen doping was playing key roles in improving CO₂ adsorption and supercapacitor performance. The experimental results indicate that the thus obtained nitrogen doped hierarchical activated carbons are very promising for reducing CO₂ green house gas by adsorption as well as storing energy as utilized in supercapacitors.

Nitrogen doped activated carbons with high surface area up to 3797 m₂ g⁻¹ exhibit specific capacitance of 231 F g⁻¹ at a current density of 10 A g⁻¹.     

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.     

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.     

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.     

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.     

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.     

Hierarchical porous carbons from carboxylated coal-tar pitch functional poly(acrylic acid) hydrogel networks for supercapacitor electrodes

A gel carbonization strategy for the synthesis of hierarchical porous carbons (HPCs) from carboxylated coal-tar pitches (CCP) functional poly(acrylic acid) (PAA) hydrogel networks for advanced supercapacitor electrodes was reported. The amphiphilic CCP and PAA polymer could be easily self-assembled to gel by the major driving force of hydrogen bonding and π–π stacking. The HPCs containing interconnected macro-/meso-/micropores were fabricated by direct carbonization of the dried hydrogels. The resultant HPCs with a high specific surface area and total pore volume of 1294.6 m² g⁻¹ and 1.34 cm³ g⁻¹ respectively, as a supercapacitor electrode exhibit a high specific capacitance of 292 F g⁻¹ at 1.0 A g⁻¹ in two-electrode system. The electrode also exhibits ultra-long cycle life with a capacitance retention as high as 94.2% after 10 000 cycles, indicating the good electrochemical stability. Furthermore, the concept of such hierarchical architecture and synthesis strategy would expand to other materials for advanced energy storage systems, such as Na-ion batteries and metal oxides for supercapacitors.

As a supercapacitor electrode exhibit a high specific capacitance of 292 F g⁻¹ at 1.0 A g⁻¹.     

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.     

Oxygen and nitrogen enriched pectin-derived micro-meso porous carbon for CO2 uptake

Oxygen and nitrogen enriched micro–meso porous carbon powders have been prepared from pectin and melamine as oxygen and nitrogen containing organic precursors, respectively. The synthesis process has been performed following a solvothermal approach in an alkaline solution during which Pluronic F127 was added to the solution as the soft template. Following the solvothermal treatment, the carbonization process has been performed at 700, 850 and 950 °C. The synthesized porous carbons have been characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherms and Fourier transform infrared spectroscopy (FTIR). The surface area of 499.5 m² g⁻¹, total pore volume of 0.35 cm³ g⁻¹, and a high nitrogen and oxygen content of 9.3 and 29.1 wt% are displayed for the fine sample. The optimal porous carbon had CO₂ adsorption of up to 3.1 mmol g⁻¹ at 273 K at 1 bar owing to abundant basic nitrogen-containing functionalities and the valuable micro–meso porous structure. Despite the absence of any reagent and also having a relatively moderate specific surface area, compared to similar materials, a very high ratio of adsorption capacity to specific surface area (6.2 μmol m⁻²) was observed. The Elovich kinetic model was found to be the best and the physisorption process was reported.

Oxygen and nitrogen enriched micro–meso porous carbon powders have been prepared from pectin and melamine as oxygen and nitrogen containing organic precursors, respectively.     

Preparation and lithium storage of core–shell honeycomb-like Co3O4@C microspheres

Core–shell honeycomb-like Co₃O₄@C microspheres were synthesized via a facile solvothermal method and subsequent annealing treatment under an argon atmosphere. Owing to the core–shell honeycomb-like structure, a long cycling life was achieved (a high reversible specific capacity of 318.9 mA h g⁻¹ was maintained at 5C after 1000 cycles). Benefiting from the coated carbon layers, excellent rate capability was realized (a reversible specific capacity as high as 332.6 mA h g⁻¹ was still retained at 10C). The design of core–shell honeycomb-like microspheres provides a new idea for the development of anode materials for high-performance lithium-ion batteries.

The reversible specific capacity of CSHCo₃O₄@C microspheres was as high as 332.6 mA h g⁻¹ at 10C, which was significantly higher than that of SCo₃O₄ microspheres (68.7 mA h g⁻¹).     

The development of activated carbon from corncob for CO2 capture

The accumulation and incineration of crop waste pollutes the environment and releases a large amount of CO₂. In this study, corncob crop waste was directly activated using solid KOH in an inert atmosphere to prepare porous activated carbon (AC) to capture CO₂, and to introduce N-containing functional groups that favour CO₂ adsorption, urea was mixed with corncob and KOH to prepare N-doped AC. The physical and chemical properties of the AC were characterized, and the effects of the mass ratio of KOH and urea to corncob, the activation temperature and time as well as regeneration were investigated to explore the optimal preparation process. The pores in the AC are mainly micropores, with the specific surface area and pore volume reaching 926.07 m² g⁻¹ and 0.40 cm³ g⁻¹ for KOH-activated corncob and 1096.70 m² g⁻¹ and 0.48 cm³ g⁻¹ after N-doping; the C–O plus O–H ratio and the –NH– ratio, which favour CO₂ adsorption in N-doped AC were 6.04 and 1.92%, respectively. The maximum adsorption capacities for KOH-activated corncob before and after N-doping were 3.49 and 4.58 mmol g⁻¹, respectively, at 20 °C and remained at 3.44 and 4.52 mmol g⁻¹ after ten regenerations. The prepared corncob-based AC showed good application prospects for CO₂ capture.

The accumulation and incineration of crop waste pollutes the environment and releases a large amount of CO₂.     

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.     

Self-assembled hierarchical porous NiMn2O4 microspheres as high performance Li-ion battery anodes

Hierarchical structured porous NiMn₂O₄ microspheres assembled with nanorods are synthesized through a simple hydrothermal method followed by calcination in air. As anode materials for lithium ion batteries (LIBs), the NiMn₂O₄ microspheres exhibit a high specific capacity. The initial discharge capacity is 1126 mA h g⁻¹. After 1000 cycles, the NiMn₂O₄ demonstrates a reversible capacity of 900 mA h g⁻¹ at a current density of 500 mA g⁻¹. In particular, the porous NiMn₂O₄ microspheres still could deliver a remarkable discharge capacity of 490 mA h g⁻¹ even at a high current density of 2 A g⁻¹, indicating their potential application in Li-ion batteries. This excellent electrochemical performance is ascribed to the unique hierarchical porous structure which can provide sufficient contact for the transfer of Li⁺ ion and area for the volume change of the electrolyte leading to enhanced Li⁺ mobility.

Hierarchical structured porous NiMn₂O₄ microspheres assembled with nanorods are synthesized through a simple hydrothermal method followed by calcination in air.     

Enhanced photocatalytic reduction of CO2 to CO over BiOBr assisted by phenolic resin-based activated carbon spheres

Photocatalytic reduction of CO₂ using solar energy to decrease CO₂ emission is a promising clean renewable fuel production technology. Recently, Bi-based semiconductors with excellent photocatalytic activity and carbon-based carriers with large specific surface areas and strong CO₂ adsorption capacity have attracted extensive attention. In this study, activated carbon spheres (ACSs) were obtained via carbonization and steam activation of phenolic resin-based carbon spheres at 850 °C synthesized by suspension polymerization. Then, the BiOBr/ACSs sample was successfully prepared via a simple impregnation method. The as-prepared samples were characterized by XRD, SEM, EDX, DRS, PL, EIS, XPS, BET, CO₂ adsorption isotherm and CO₂-TPD. The BiOBr and BiOBr/ACSs samples exhibited high CO selectivity for photocatalytic CO₂ reduction, and BiOBr/ACSs achieved a rather higher photocatalytic activity (23.74 μmol g⁻¹ h⁻¹) than BiOBr (2.39 μmol g⁻¹ h⁻¹) under simulated sunlight irradiation. Moreover, the analysis of the obtained results indicates that in this photocatalyst system, due to their higher micropore surface area and larger micropore volume, ACSs provide enough physical adsorption sites for CO₂ adsorption, and the intrinsic structure of ACSs can offer effective electron transfer ability for a fast and efficient separation of photo-induced electron–hole pairs. Finally, a possible enhanced photocatalytic mechanism of BiOBr/ACSs was investigated and proposed. Our findings should provide new and important research ideas for the construction of highly efficient photocatalyst systems for the reduction of CO₂ to solar fuels and chemicals.

Photocatalytic reduction of CO₂ using solar energy to decrease CO₂ emission is a promising clean renewable fuel production technology.     

High ion adsorption densities of site-selective nitrogen doped carbon sheets prepared from natural lignin

Carbon fibers and sheets were prepared from jet-milled natural chitin and cellulose samples, and from natural lignin sample using ice-templating technique, respectively. Nitrogen doping treatments using melamine were also performed for the carbon fibers and sheets. Electric double layer capacitor (EDLC) electrode properties of the prepared carbon fibers and sheets including the nitrogen doped samples were investigated with aqueous (sulfuric acid) and organic (tetraethylammonium tetrafluoroborate in propylene carbonate) electrolytes. It was found that the nitrogen doped lignin carbon sheets having very small specific surface area of 66 m² g⁻¹ show very high EDLC capacitances of 227 F g⁻¹ and 80 F g⁻¹ determined by charge–discharge measurements at current density of 50 mA g⁻¹ for aqueous and organic electrolytes, respectively. X-ray photoelectron spectroscopy (XPS) measurements revealed that nitrogen atoms of the nitrogen doped lignin carbon sheets exist dominantly in pyridinic sites unlike other chitin and cellulose carbon fibers. We discussed that this site-selective nitrogen doping gives exceptionally high ion adsorption density per unit surface area of the nitrogen doped lignin carbon sheets.

Carbon fibers and sheets were prepared from jet-milled natural chitin and cellulose samples, and from natural lignin sample using ice-templating technique, respectively.     

Functional utilization of biochar derived from Tenebrio molitor feces for CO2 capture and supercapacitor applications

Biochar has attracted great interest in both CO₂ capture and supercapacitor applications due to its unique physicochemical properties and low cost. Fabrication of eco-friendly and cost-effective biochar from high potential biomass Tenebrio molitor feces can not only realize the functional application of waste, but also a potential way of future carbon capture and energy storage technology. In this study, a novel KOH activation waste-fed Tenebrio molitor feces biochar (TMFB) was developed and investigated in terms of CO₂ capture and electrochemical performance. When activated at 700 °C for 1 h, the specific surface area of the feces biochar (TMFB-700A) increased significantly from 232.1 to 2081.8 m² g⁻¹. In addition, well-developed pore distribution facilitates CO₂ capture and electrolyte diffusion. TMFB-700A can quickly adsorb a large amount of CO₂ (3.05 mol kg⁻¹) with excellent recycling performance. TMFB-700A also exhibited promising electrochemical performance (335.8 F g⁻¹ at 0.5 A g⁻¹) and was used as electrode material in a symmetrical supercapacitor. It provided a high energy density of 33.97 W h kg⁻¹ at a power density of 0.25 kW kg⁻¹ with 90.47% capacitance retention after 10 000 charge–discharge cycles. All the results demonstrated that TMFB could be a potential bifunctional material and provided valuable new insights for Tenebrio molitor feces high-value utilization.

Biochar has attracted great interest in both CO₂ capture and supercapacitor applications due to its unique physicochemical properties and low cost.     

Facile fabrication of hierarchical film composed of Co(OH)2@Carbon nanotube core/sheath nanocables and its capacitive performance

A hierarchical film composed of Co(OH)₂@carbon nanotube (CNT) core/sheath nanocables (CCNF) was generated via a simple and rapid electrophoretic deposition method. It is found that the Co(OH)₂ sheath was uniformly anchored on the surface of conductive CNT core. The Co(OH)₂ sheath, with a thickness of ∼20 nm, was composed of numerous very tiny nanoparticles. Such a unique nanostructure endows the CCNF with a high surface area of 126 m² g⁻¹ and a hierarchical porosity, resulting in a large accessible surface area for redox activity. As expected, the CCNF exhibits high specific capacitance and excellent rate performance. Its specific capacitance reached 1215 F g⁻¹ under a low current density of 1 A g⁻¹ and was maintained at 832 F g⁻¹ when the current density was increased 20 times to 20 A g⁻¹. A high capacitance retention of 99.3% was achieved after 10 000 cycles at 1 A g⁻¹. Such intriguing capacitive behavior is attributed to the synergistic effect of the CNT core and the Co(OH)₂ sheath.

A uniform Co(OH)₂ sheath was anchored on the surface of a conductive CNT by a facile strategy, exhibiting comparatively high specific capacitance and outstanding long cycle life stability.