Carbon Microspheres Research Articles

Advances in Carbon Microsphere-Based Nanomaterials for Efficient Electromagnetic Wave Absorption.

Carbon microspheres have indeed shown great promise as effective materials for absorbing electromagnetic waves, particularly in microwave applications. Their unique properties, such as high surface area, porosity, and electronic characteristics, make them ideal candidates for addressing the growing concerns around electromagnetic pollution from electronic devices. By leveraging the properties of these materials, we can work toward creating more efficient and sustainable electromagnetic wave absorption technologies. Recent efforts have focused on synthesizing and investigating carbon microsphere-based electromagnetic wave-absorbing nanomaterials with the ambition of achieving the desired attributes of being thin, light, wide, and robust. This Review first delves into the detailed mechanism of electromagnetic wave absorption, followed by an elucidation of the preparation methods for carbon microsphere-based nanomaterials. Furthermore, it systematically outlines the common methods and strategies employed to improve the microwave absorption capabilities of carbon microspheres, including chemical vapor deposition, emulsion polymerization, hydrothermal methods, and template methods. Lastly, it outlines the challenges encountered by carbon microsphere-based electromagnetic wave absorption nanomaterials and outlines their prospects, mainly morphology change, component hybridization, and elemental doping. This Review aims to provide valuable insights into the creation of carbon microsphere nanomaterials with excellent electromagnetic wave absorption properties.

Sensing of Pb (II) ion by micro and nanocarbon materials- influence of functionality and pi-electron density

In the aspect of pollution due to heavy metal ions, especially Pb (II) ions, there is an urgent need for simple, effective materials and processes for sensing the ions. The present study approaches the sensing of Pb (II) ions by non-metal (O, N and S) doped micro and nanoscale Carbon materials. The unique emission (Fluorescence) properties of the as-prepared doped samples of graphene oxides and Carbon Microspheres were tapped in the selective sensing process of nanomolar to the micromolar concentration of Pb (II) ions. The role-play of Carbon dimensionality, functionality and sp2 Carbon density (pi electron density) in the sensing mechanism was evaluated. The study provided an overview of fundamental aspects of heavy metal ion sensing by Carbon-based nanomaterials (CBNs).

Efficient utilization of lignin heterogeneity: Employing a simple approach to modulate the structure-effect relationship of lignin microspheres for its high-quality applications in supercapacitors

Lignin, an abundant, sustainable, and cost-effective biomass material, is recognized for its high carbon content, making it an ideal candidate for supercapacitors electrode. However, the inhomogeneity of lignin and the amorphous structure of lignin-derived carbon limit its application in energy storage. To effectively address the aforementioned issues, this study initially fractionated alkali lignin (AL) using a green γ-valerolactone/water system to obtain two fractions (L1 and L2) with distinct molecular weights and phenolic hydroxyl contents. The aim of this initiative was to reduce the heterogeneity of the lignin. Subsequently, three groups of lignin microspheres (LMS-AL, LMS-L1 and LMS-L2) with different morphologies were prepared from AL, L1, and L2 using an industrially proven spray-drying technique. This initiative significantly increased the specific surface area of lignin. Ultimately, lignin microspheres were carbonized to prepare carbon microspheres (LMSC-AL, LMSC-L1 and LMSC-L2) that could be used as supercapacitor electrodes. Notably, LMSC-L1 demonstrated superior electrochemical performance, with a specific capacitance of 200 F g−1 at a current density of 1 A g−1, and retaining 93.34 % capacitance after 15,000 charge/discharge cycles. The excellent electrochemical performance of LMSC-L1 is attributed to its elevated specific surface area (388.1 m2 g−1) and substantial porosity (0.238 cm3 g−1). This study also explored practical application, with LMSC-L1 successfully powering LED lights and calculators. Through this research, we have developed a simple method is proposed to modulate the structure of lignin microspheres by leveraging the heterogeneity of lignin itself. Furthermore, we systematically investigated the structure-effect relationship of lignin microspheres and the electrochemical properties of their carbonized microspheres. This work lays a foundational framework for the efficient utilization of lignin in energy storge applications.

Hybridization of CuFe2O4 by carbon microspheres with improved charge storage characteristics for high energy density solid-state hybrid supercapacitor

The hybrid nanocomposite of Copper Ferrite/Carbon sphere (CuFe2O4/C-sphere NC) has been synthesized and their combined electrochemical activity for supercapacitors is achieved. XRD study reveals the average crystallite size of CuFe2O4/C-sphere NC as 112 nm. CuFe2O4/C-sphere NC provides a huge specific surface area of 532 m2/g. Cyclic voltammetry (CV) analysis exhibits the competitive specific capacity of CuFe2O4/C-sphere NC as 320 C/g at the sweep rate of 10 mV/s. The galvanostatic charge-discharge (GCD) study shows a good specific capacity of 264 C/g at 1 A/g and excellent cyclic stability of 82.4% for 5000 cycles. The CuFe2O4/C-sphere//AC solid-state hybrid supercapacitor provides a high specific capacity of 131 C/g along with remarkable energy density and power density of 40.9 Wh/kg and 11248 W/kg respectively.

Effects of novel carbon sources additives on the solid-state sintering behavior and properties of SiC ceramics

To enhance the density of SiC and improve the purity of the SiC, carbon is frequently used as a sintering additive. SiC ceramics were prepared in this study by using various carbon sources (graphitic carbon microsphere, carbon black, and flake graphite) combined with B4C through spark plasma sintering (SPS) at temperatures ranging from 1800 °C to 1900 °C. Among the above carbon sources, the graphitic carbon microspheres were created by hydrothermal carbonization combined with catalytic graphitization. The influence of the carbon sources on the phase compositions, microstructure, physical properties, and oxidation resistance of the SiC specimens was investigated. The findings revealed that the SiC specimens prepared with graphitic carbon microsphere had a smaller crystallite size than those prepared with other kinds of carbon. The SiC specimens prepared with graphitic carbon microsphere displayed high relative density, hardness, fracture toughness, and remarkable oxidation resistance. This was attributed to the lower oxygen content, better dispersion, and higher chemical reactivity of graphitic carbon spheres. In terms of the oxidation resistance of SiC specimens, factors such as purity (residual carbon) and porosity were found to have a more significant impact than grain size. In general, the use of carbon sources with high reactivity and good dispersion is an effective method in preparing SiC ceramics.

Multi-layered carbon accommodation of MnO2 enabling fast kinetics for highly stable zinc ion batteries

Large-scale durable aqueous zinc ion batteries for stationary storage are realized by spray-coating conductive PEDOT(Poly(3,4-ethylenedioxythiophene)) wrapping MnO2/carbon microspheres hybrid cathode in this work. The porous carbon microspheres with multiple layers deriving from sucrose provide suitable accommodation for MnO2 active materials, exposing more redox active sites and enhancing the contact surface between electrolyte and active materials. As a result, MnO2/microspheres are adhered to the current collector by a conductive PEDOT coating without any binder. The ternary design retards the structural degradation during cycling and shortens the electron and ion transport path, rendering the full batteries high capacity and long cycle stability. The resulting batteries perform the capacity of 277, 227, 110, 85 and 50 mAh/g at 0.2, 0.5, 1, 2 and 5 A/g, respectively. After 3000 cycles the initial capacity retains 86%, and 80% after 5000 cycles. GITT indicates PEDOT wrapping MnO2/microspheres cathode enables better ion intercalating kinetics than conventional MnO2. The work could represent a novel and significant step forward in the studies on the large-scale application of zinc ion batteries.

MoS2 decorated heteroatoms doped carbon microspheres for efficient separation of uranium from wastewater

Uranium serves as a fundamental element for sustainable nuclear reactor energy. Hence, the extraction and enrichment of uranium from radioactive wastewater is of considerable significance for both nuclear power utilization and environmental protection. In this study, carbon microspheres (TAC) doped with nitrogen, phosphorus and sulfur were derived from ternary polyphosphazene. Subsequently, molybdenum disulfide (MoS2) was integrated using hydrothermal method to fabricate the TAC/MoS2 composite, which is designed for the efficient enrichment and separation of uranyl ions. Owing to the unique two-dimensional structure of MoS2 and its strong affinity towards uranyl ions, the adsorption capacity of the composite was significantly enhanced to 399.6 mg/g within 80 min at pH 5 and 298.15 K. Additionally, the composite exhibited commendable thermal stability and hydrophilicity, declaring that it is an outstanding candidate for the efficient enrichment and separation of uranyl ions. Further mechanism studies through XPS analysis and DFT calculations suggested that the vacancies introduced by MoS2 can generate electrostatic interactions and coordination effects with uranyl ions, thereby improving the adsorption performance of the composite. Due to its straightforward preparation process and exceptional adsorption performance, TAC/MoS2 possesses broad application prospects in the extraction of uranium from wastewater.

Exploring the Microstructural Effect of FeCo Alloy on Carbon Microsphere Deposition and Enhanced Electromagnetic Wave Absorption.

The rational design of magnetic carbon composites, encompassing both their composition and microstructure, holds significant potential for achieving exceptional electromagnetic wave-absorbing materials (EAMs). In this study, FeCo@CM composites were efficiently fabricated through an advanced microwave plasma-assisted reduction chemical vapor deposition (MPARCVD) technique, offering high efficiency, low cost, and energy-saving benefits. By depositing graphitized carbon microspheres, the dielectric properties were significantly enhanced, resulting in improved electromagnetic wave absorption performances through optimized impedance matching and a synergistic effect with magnetic loss. A systematic investigation revealed that the laminar-stacked structure of FeCo exhibited superior properties compared to its spherical counterpart, supplying a higher number of exposed edges and enhanced catalytic activity, which facilitated the deposition of uniform and low-defect graphitized carbon microspheres. Consequently, the dielectric loss performance of the FeCo@CM composites was dramatically improved due to increased electrical conductivity and the formation of abundant heterogeneous interfaces. At a 40 wt% filling amount and a frequency of 7.84 GHz, the FeCo@CM composites achieved a minimum reflection loss value of -58.2 dB with an effective absorption bandwidth (fE) of 5.13 GHz. This study presents an effective strategy for developing high-performance EAMs.

N-doped CNTs/CoNi nanochains-carbon hollow microspheres multi-level multi-scale heterogeneous interface structures and microwave absorption properties

Constructing multi-level multi-scale heterogeneous interfaces in magnetic carbon-based composites remains a formidable challenge, requiring rational material combinations to effectively balance dielectric and magnetic losses for achieving high strength and wide frequency wave absorption. Electromagnetic wave (EMW) absorbing materials consisted of cobalt-nickel (CoNi) magnetic nanochain, nitrogen-doped carbon nanotubes (NCNTs) and hollow carbon microspheres were prepared by hydrothermal method without external magnetic field. These composites possessed a unique multi-level multi-scale heterogeneous interface structure that is highly advantageous for efficient absorption of EMWs. The CoNi nanoparticles were self-assembled into uniformly distributed and randomly oriented magnetic nanochains, which were further reassembled with NCNTs and hollow carbon microspheres to form heterogeneous interface structures resembling a rose, chrysanthemum, hedgehog ball, and bauhinia tree. Due to the high-density interface enhancing the loss ability of interface polarization, as well as the higher saturation magnetization, coercivity, and wave absorption ability of the magnetic nanochains compared to the magnetic nanoparticles themselves, the minimum reflection loss achieved is −66.86 dB, and the effective absorption bandwidth achieved is 5.01 GHz, at a content as low as 11 wt%. This study provides a new idea for generating nanochains without magnetic fields and constructing multi-level and multi-scale heterogeneous interface structures to achieve strong absorption and wide effective absorption bandwidth (EAB).

Shungite Paste Electrodes: Basic Characterization and Initial Examples of Applicability in Electroanalysis

This article introduces a new type of carbon paste electrode prepared from black raw shungite. In powdered form, this carbonaceous material was mixed with several nonpolar binders. The resulting shungite pastes were microscopically and electrochemically characterized. Mixtures of several pasting liquids with different contents of shungite powder were tested to select the optimal composition and compared with other types of carbon paste-based electrodes made of graphite and glassy carbon powder. In terms of physical and mechanical properties, shungite paste electrodes (ShPEs) formed a composite mass being like dense pastes from glassy carbon microspheres, having harder consistency than that of traditional graphitic carbon pastes. The respective electrochemical measurements with ShPEs were based on cyclic voltammetry of ferri-/ferro-cyanide redox pairs, allowing us to evaluate some typical parameters such as electrochemically active surface area, double-layer capacitance, potential range in the working media given, heterogeneous rate constant, charge-transfer coefficient, exchange current density, and open-circuit potential. The whole study with ShPEs was then completed with three different examples of possible electroanalytical applications, confirming that the carbon paste-like configuration with powdered shungite represents an environmentally friendly (green) and low-cost electrode material with good stability in mixed aqueous-organic mixtures, and hence with interesting prospects in electroanalysis of biologically active organic compounds. It seems that similar analytical parameters of the already established variants of carbon paste electrodes can also be expected for their shungite analogues.

Extended Plateau Capacity of Hard Carbon Anode for High Energy Lithium-Ion Batteries.

Hard carbon materials have shown promising potential for sodium-ion storage due to accommodating larger sodium ions. However, as for lithium-ion storage, the challenge lies in tuning the high lithiation plateau capacities, which impacts the overall energy density. Here, hard carbon microspheres (HCM) are prepared by tailoring the cross-linked polysaccharide, establishing a comprehensive methodology to obtain high-performance lithium-ion batteries (LIBs) with long plateau capacities. The "adsorption-intercalation mechanism" for lithium storage is revealed combining in situ Raman characterization and ex situ nuclear magnetic resonance spectroscopy. The optimized HCM possesses reduced defect content, enriched graphitic microcrystalline, and low specific surface area, which is beneficial for fast lithium storage. Therefore, HCM demonstrates a high reversible capacity of 537mAhg-1 with a significant low-voltage plateau capacity ratio of 55%, high initial Coulombic efficiency, and outstanding rate performance (152mAhg-1 at 10Ag-1). Moreover, the full cell (HCM||LiCoO2) delivers outstanding fast-charging capability (4min charge to 80% at 10C) and impressive energy density of 393Whkg-1. Additionally, 80% reversible capacity can be delivered under -40°C with competitive cycling stability. This work provides in-depth insights into the rational design of hard carbon structures with extended low-voltage plateau capacity for high energy LIBs.

Iron nanowire/carbon microsphere composite flexible fabric strain sensor for human motion monitoring

People pay more and more attention to sports and health, especially the goal of sports recovery and scientific sports is more and more clear. In order to avoid human injury caused by unreasonable sports, it is necessary to carry out real-time detection of human motion state. In this paper, the motion state of human body was taken as the test object, a flexible strain sensitive material combining iron nanowires and carbon microspheres was proposed, and polyester fabric was introduced as the sensor substrate to construct a sandwich structure flexible fabric strain sensor. Then a mechanical test platform was built to carry out mechanical property testing and practical application verification research. The mechanical test results show that the iron nanowires/carbon microspheres flexible fabric strain sensor has good linearity, the response time is 42 ms, and the hysteresis error is approximately 8.7 %. Finally, the flexible fabric strain sensor is fixed on the part of the human body that needs to be detected, and the electrical signal curve of the response is output by the electrochemical workstation. Through the analysis of the response curve, it can be seen that the iron nanowires/carbon microspheres flexible fabric strain sensor prepared in this paper has great potential in human movement health monitoring.

Fabrication of close-contact S-scheme Cr2Bi3O11-Bi2O3/Fe3O4@porous carbon microspheres based on in-situ reaction: Enhanced photo-Fenton wastewater treatment

Low photo-induced carrier recombination rate, exceptional light absorption, and advantageous recycling performance are crucial attributes of semiconductor photocatalyst for wastewater purification. Herein, based on in-situ reaction, close-contact S-scheme bismuth chromate/bismuth oxide/ferroferric oxide@porous carbon microspheres (Cr2Bi3O11-Bi2O3/Fe3O4@PCs) (F-CBFP) was fabricated using alginates as precursor. Due to the abundance of functional groups on the porous carbon (PCs), Bi2O3 and Cr2Bi3O11 nanoparticles (NPs) are in situ deposited onto the highly conductive 3D magnetic porous Fe3O4@PCs microsphere surface, which not only form tight interfacial contacts and reduces interfacial potential barriers but also prevent agglomeration or shedding of the NPs during photocatalytic reactions. Moreover, density functional theory (DFT) calculations further confirm that the formation of a robust built-in electric field (BIEF) within F-CBFP prompts photo-induced electrons in the conduction band (CB) of Bi2O3 to combine with holes in the valence band (VB) of Cr2Bi3O11, effectively constructing a S-scheme heterojunction system. Also, Fe3O4 can act as a Fenton catalyst, activating the H2O2 generated by Cr2Bi3O11 under illumination. In wastewater treatment, the obtained F-CBFP shows remarkable photo-Fenton degradation (towards methyl orange (97.8 %, 60 min) and tetracycline hydrochloride (95.3 %, 100 min)) and disinfection performance (100 % E. coli inactivation), and exceptional cyclic stability.

Biomimetic CaCO3 microspheres as a promising delivery system for catalase: Immobilization, kinetic studies and potential perspectives in oxidative stress diseases

Oxidative stress is implicated in the pathophysiology of several illnesses. Catalase (CAT), an antioxidant enzyme, remains a prime target for oxidative stress related therapies. Unfortunately, the labile nature, difficulty in recovering and reusing, and insufficient delivery systems limit its use in therapy. This study used a simple biomineralization process for the synthesis of vaterite porous calcium carbonate (CaCO3) microspheres (MS) for the development of cross-linked immobilized (CAT-MS). Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), particle size analysis, and zeta-potential measurements were used for CaCO3-MS characterization. CAT was immobilized efficiently with a high immobilization yield (99 %). The immobilized enzyme had a higher Km than free CAT with a 1.7 fold increase in Vmax and Kcat. CAT-MS displayed a longer half-life, efficient reusability, enhanced storage stability, and excellent stability against various denaturants compared to free CAT. Furthermore, CAT-MS demonstrated negligible cytotoxicity in the fibroblast cell line (BJ1), where CAT-MS recorded higher cell viability than free CAT, (p< 0.05) indicating exceptional biocompatibility. This study raises the potential of an eco-friendly approach that enforces wide and safe catalase application in intracellular therapy for treating oxidative stress-associated diseases.

Nitrogen-doped hollow carbon sphere composite Mn3O4 as an advanced host for lithium-sulfur battery

As the most promising advanced energy storage system, lithium-sulfur batteries (LSBs) are highly favored by the researchers because of their advantages of high energy density (2500 W h kg−1), low cost and non-pollution. However, the low conductivity, volume expansion of sulfur, and shuttle effect are still the great hindrance to the practical application of LSBs. Herein, the above problems can be addressed through the following strategies: (1) Hollow carbon microspheres with high specific surface area were constructed as sulfur hosts to increase sulfur loading while also being able to enhance the physical adsorption of polysulfides; (2) the loading of Mn3O4 particles on the basis of hollow carbon microspheres facilitates the capture and adsorption of polysulfides; (3) the hollow carbon sphere structure as a conductive network can provide more pathways for rapid electrical/ionic transport and also accelerate electrolyte wetting. Moreover, the thinner shell of hollow carbon microsphere is conducive to ion diffusion and speed up the reaction rate. Thus, the NHCS/Mn3O4/S composites exhibit a high discharge specific capacity of 1010.3 mAh g−1 at first and still maintained a reversible capacity of 269.2 mAh g−1 after 500 cycles. This work presents a facile sustainable and efficient synergistic strategy for the development of advanced LSBs.

Study on the characteristics of microwave pyrolysis of pine wood catalyzed by bimetallic catalysts prepared with microwave-assisted hydrothermal char

Bimetallic hydrothermal char catalysts (Co-Ni/MHC, Fe-Co/MHC, Fe-Ni/MHC) were prepared through ionic hydrothermal methods and microwave high-temperature activation. During catalyst preparation, different metals synergistically promoted the formation of ordered carbon structures such as carbon nanotubes and carbon microspheres, respectively. Serving both as microwave absorbers and catalysts for the microwave pyrolysis of pine wood, the bimetallic catalysts exhibited distinct advantageous characteristics. Fe-Ni/MHC exhibited excellent microwave absorption properties and was able to assist the PW to heat up rapidly at a rate of 6.17 °C/s, benefiting from which PW achieved a high bio-oil yield of 44.0 % in the microwave-assisted catalytic pyrolysis process. Using Co-Ni/MHC as a catalyst resulted in bio-oil with up to 42.7 % styrene content and had good catalytic effects on the formation of CO and H2. This study provides a scientific reference for the application of hydrothermal treatment and microwave-assisted pyrolysis in biomass pyrolysis technology.

Co-doping mechanism of biomass-derived nitrogen-boron porous carbon and its applications in energy storage and environmental purification

In this paper, we aim to design and synthesize a low-cost, multifunctional and efficient electrode and adsorbent material (nitrogen doped and nitrogen-boron co-doped) by combinatorial doping of heteroatoms using cherry blossoms (Prunus yedoensis) as biomass feedstock. The differences in morphology and structure of the two materials due to the doping of boron atoms were analyzed. Among them, the nitrogen-boron co-doped porous carbon NBKCC had a hierarchical porous structure with a shape similar to that of carbon microspheres and a specific surface area as high as 1184 m2/g. In the three-electrode system, the specific capacitance of the assembled electrodes was 337.5 F/g (current density: 0.5 A/g). In the NBKCC symmetric capacitor test, the energy density could reach 15.1 Wh/kg at a power density of 420.5 W/kg. After 10,000 charge/discharge cycles, the capacitance retention was 96.98 % (5 A/g), which showed good stability. In addition, we evaluated the adsorption capacity of carbon microspheres for malachite green, rhodamine B, and methylene blue. Among them, the maximum adsorption of malachite green in a single system was 572.4 mg/g. Based on this, we demonstrated the feasibility and preparation of porous carbon materials by combinatorial doping with heteroatoms using biomass waste cherry blossoms as carbon substrates.

(1 1 1) Facet-dominant peracetic acid activation by octahedral CoO anchored hollow carbon microspheres for tetracycline degradation

Peracetic acid (PAA), an environmental friendly disinfectant, has attracted increasing interest in applications on advanced oxidation processes for treating emerging pollutants. Herein, octahedral cobalt oxide anchored on cation exchange resin (CER)-derived hollow carbon microspheres were fabricated via a facile strategy and employed as the heterogeneous catalyst for PAA activation to degrade tetracycline (TC) antibiotic. Calcination temperature was demonstrated to play a significant role in resulted structure and composition, physicochemical properties and catalytic activities of the cobalt-based compounds/carbon composites. With the optimal catalyst which was calcined at 600 °C, namely the Co@CER-600, complete elimination of TC was achieved within 10 min in Co@CER-600/PAA system. The determination of reactive oxygen species (ROS) indicated that both non-radical (singlet oxygen) and radical (superoxide radical) mechanisms were evidenced in Co@CER-600/PAA system. Particularly, it is notable that the extensively exposed (111) facet in octahedral CoO was confirmed to show remarkable PAA activation activity, therefore promoted the ROS generation process. Considering that facet engineering is a novel whilst important strategy for catalyst regulation, the proposed (111) facet-dominant octahedral CoO anchored hollow carbon microspheres might suggest new inspirations for catalyst design in PAA-based AOPs toward antibiotic contamination remediation.

Ion-crosslink alginate emulsion droplets toward synthesis of porous carbon microspheres as anodes for lithium-ion batteries

Porous carbon microsphere (PCM) is an important anode material for lithium-ion batteries; however, the preparation of PCM at large scale is still complex, sometimes even needing sophisticated instruments. Herein, we developed a water-in-oil (W/O) phase-separation strategy to prepare PCM in terms of simple and low-cost manner. As-prepared PCM has a large surface area of 182 m2/g, and abundant mesopores, which benefits the penetration of Li+-carrying electrolyte into the electrode. Therefore, the optimized PCM electrode shows a high-rate capability (408 mA h g−1 at 2 A/g). This work broadens a new vision in preparing PCM for energy-storage/-conversion applications.

Hydrothermal preparation of N and O-rich porous carbon microspheres and their capacitance properties

In this paper, N and O-rich porous activated carbon (N-O/AC) microsphere with various pore sizes was prepared by thermal and KOH activation of g-C3N4@graphene oxide (CN@GO) microsphere. CN@GO microsphere was pre-prepared through a hydrothermal method directly from glucose and melamine, which resulted into high content and uniform doping of O and N in the final product. CN@GO microsphere was composed of GO/CN/GO sandwich nanochips, forming a porous structure with various pore sizes. The obtained N-O/AC has high energy density (33.19 Wh/kg) and high power density (499.93 W/kg), in company with excellent cyclic stability (remaining 98.64 % after 1000 cycles). The N-O/AC derived from the hydrothermal method provides a low-cost way of constructing porous carbon matrix composites with pseudo-capacitance.