High Char Yield Research Articles

Synergistic effects in the co-pyrolysis of thermoset epoxy resin and biomass on kinetics and product distribution

With the rapid growth of wind power, batteries, and aerospace industries, sustainable disposal of thermoset plastics has become a long-term concern. However, pyrolysis, a highly promising solution for this issue, has seen limited studied on thermoset plastics. Drawing inspiration from the synergistic interactions observed between thermoplastics and biomass, this study explored the co-pyrolysis of a thermoset epoxy resin, diglycidyl ether of bisphenol A, cured with 4,4′-Diaminodiphenylmethane, with ash-free biomass pseudo-components (cellulose, lignin, and xylan) using thermogravimetry and Py-GC/MS. The results revealed distinctive synergistic effects in Epoxy-Cellulose and Epoxy-Lignin mixtures, delaying the onset and hastening the conclusion of weight loss. This was accompanied by increased activation energies, assessed through the Friedman and Kissinger-Akahira-Sunose methods, as well as higher char yields. Conversely, in Epoxy-Xylan, synergistic effects led to reduced activation energy across most α values, resulting in a lower onset temperature and a heightened maximum rate of mixture degradation. Regarding product distribution, all three pseudo-components, particularly lignin, enhanced the selectivity of bisphenol A. Additionally, cellulose and xylan altered the kinetics of N–C and C(N)–C(OH) bond cleavage, reducing the amount and altering the distribution of 2-B-N compounds (compounds featuring two benzene rings and nitrogen). Conversely, the presence of resin reduced the volatiles from cellulose and xylan, promoting phenol-type products and –H and alkylene side chains while diminishing guaiacol-type products and alkyl side chains. Three mechanisms were proposed to elucidate these observed synergistic effects: catalytic effects of –OH groups from biomass pseudo-components, hydrogen exchange or hydrogen bonding between resin-derived nitrogen and biomass-derived oxygen-containing functional groups, and radical reactions. These insights into the co-pyrolysis of biomass and cured epoxy resin can inform the selection of suitable feedstocks for various applications.

Highly heat-resistant polymers with good dielectric properties at high frequency derived from a bio-based resveratrol

Starting from a bio-based resveratrol, a new monomer (M1) without oxygen atoms and having thermocrosslinkable benzocyclobutene groups and a double bond has been obtained. Thermally cured M1 displays excellent heat resistance with a 5% weight loss temperature (T5d) of 532 °C, a glass transition temperature (Tg) of higher than 400 °C, a very high char yield of 79% at 1000 °C and a very low coefficient of thermal expansion (CTE) of 18.2 ppm/°C. For comparison, a control monomer (M2) has been prepared by hydrogenating the double bond of M1. Thermally cured M2 exhibits excellent dielectric properties with dielectric constant (Dk) of 2.75 and dielectric loss (Df) of 7 × 10−4 at a high frequency of 5 GHz. These results mean that the double bonds in the molecule endow the polymers with higher thermostability, while the alkyl group makes the Dk and Df polymers decreased. In contrast, the polymers containing oxygen atoms derived from resveratrol (cured M3 and cured M4) exhibit increased Dk and Df, and lowered thermostability. This work provides a helpful way to design the materials with high heat-resistance and low dielectric properties for the application in aerospace and microelectronic industry.

Interlaminar properties, ablation resistance and thermal diffusivity of Carbon/Phenolic Composites (CPCs) derived from optimized high char yield matrices: A comparison with MX-4926 and FM-5014

Carbon/Phenolic Composites (CPCs) are used to manufacture many portions of the nozzle assembly of Solid Rocket Motors (SRMs) which are essential both to preserve the independent access to space as well as for the homeland security. In our research a new family of low cost, high char yield CPCs manufactured using ultra common raw materials - such as T300-like Polyacrylonitrile (PAN) based Carbon Fibers (PAN­CFs) - and having high values of Inter Laminar Shear Strength (ILSS) have been identified. Nanocomposite based CPCs were also produced. The interlaminar properties, ablation resistance and thermal diffusivity of the manufactured CPCs were studied. A unique and comprehensive work of comparison with state-of-the-art CPCs such as MX-4926 and FM-5014 has also been carried out evidencing the merits of the formulations produced in our work.

Relating the microstructural and glass transition temperature evolution of a carbon–carbon composite precursor during pyrolysis using thermomechanical analysis

AbstractPolybenzoxazine thermoset resins exhibit significant potential as precursors for carbon–carbon composites, owing to their high char yield upon pyrolysis. During pyrolysis, the resin is converted to an amorphous carbon‐rich material through a series of mechanisms, resulting in a linear increase of the glass transition temperature (TG) from 133 to 396°C at 0.48 pyrolytic conversion. To better understand this relationship, a non‐isothermal kinetic model was integrated, enabling the prediction of the TG onset, inflection, and endpoint based on the heat treatment protocol (process temperature (TP) vs. time) and the total volume of pyrolytic gases generated. By considering the TG behavior and anticipated gas effects, three distinct mechanisms were identified: (1) gas accumulation and matrix expansion leading to increased sample thickness (TG < TP), (2) crack network formation caused by gas‐pressure‐induced brittle failure (TG > TP), and (3) sample thickness reduction due to gas venting through the crack network (TG < TP). To validate this theory, thermal mechanical analysis was performed during pyrolysis, and changes in thickness (±ΔL/L0) were attributed to gas pressure‐related matrix deformation. Conversely, no change in ΔL/L0 indicated the formation of an interconnected crack network through which gases could vent without building a measurable internal pressure.

Design and synthesis of epoxy prepolymer containing aromatic imide structures for thermoset with excellent thermal, mechanical and dielectric properties

Recently, the development of epoxy thermosets with imide rings has received extensive attention due to their superior integrated properties, especially for thermal, mechanical and dielectric properties, compared to those of commercialized bisphenol A epoxy thermosets, yet remains substantial challenges, such as the high epoxy equivalent weight (EEW) of the epoxy prepolymers and the poor processibility of the epoxy systems. In this work, an imide-containing epoxy prepolymer (BAPT-EP) was facilely synthesized. It had a relatively low EEW of 340 g/equiv. and could be dissolved in hardener methylhexahydrophthalic anhydride (MHHPA) to give a homogeneous BAPT-EP/MHHPA system with good processibility. Thanks to the aromatic imide structures, the cured BAPT-EP/MHHPA showed improved overall properties. In particular, it had a 47.9 °C, 24.7 °C, 29.4%, 77.3% and 10.0% increase in the glass transition temperature, temperature at 5% mass loss, tensile strength, Young’s modulus and tensile toughness, respectively, compared to those of bisphenol A epoxy prepolymer (DGEBA)/MHHPA thermoset. Meanwhile, BAPT-EP/MHHPA thermoset featured good charring ability with a high char yield of 26.4% (800 °C/N2), remarkable dimensional stability with a low coefficient of thermal expansion of 52.5 ppm/°C and good dielectric properties with a low dielectric constant of 3.24 at 100 MHz. This work provides an elegant strategy to prepare high-performance epoxy thermosets with imide structures, which have promising applications in electronics.

Effect of coal tar pitch modification on the structure and char yield of pyrolysis epoxy resin carbons

Epoxy resin carbons are of high strength, high temperature resistance, and corrosion resistance, which are widely used as the precursor of carbon composite materials. However, the applications of epoxy resin carbons are greatly limited for the characteristic of non-graphitization and low char yield (22 wt%). In this paper, coal tar pitch was used to modify epoxy resin carbons via a simple heating mixing, pyrolysis and high temperature graphitization. The results show that the coal tar pitch content and heat treatment temperature can improve the ordered graphite carbon content. As the coal tar pitch content increase, the ordered graphite carbon content of modified epoxy resin carbon increase after 3000 °C graphitization for 0.5 h. Particularly, the graphitization degree of epoxy resin carbon and 40 wt% coal tar pitch modified epoxy resin carbon are 8.42 % and 44.21 %, respectively. The grain size (Lc = 13.84 nm) and grain stacking height (La = 7.79 nm) of 40 wt% coal tar pitch modified epoxy resin carbon are bigger than epoxy resin carbon (Lc = 3.44 nm, La = 3.45 nm). The ordered coal tar pitch graphite carbon and disordered epoxy resin amorphous carbon are evenly distributed in the modified epoxy resin carbon, indicating a good comparability of coal tar pitch and epoxy resin. Besides, the entangling carbon ribbon are observed in the epoxy resin carbon after graphitization at 3000 °C. With the coal tar pitch content increasing, the carbon element content and aromatic ring number of modified epoxy resin increased. As the coal tar pitch content increase, the char yield and thermal decomposition temperature of modified epoxy resin gradually increase. The char yield of 50 wt% coal tar pitch modified epoxy resin is 42 wt%, almost double that of epoxy resin (22 wt%). The char yield increased values of modified epoxy resin mainly inherited the high char yield of coal tar pitch (50 wt%) and a small portion of char yield increased value is from the chemical crosslinking weight gain. When the coal tar pitch content is 40 wt%, the chemical crosslinking weight gain reaches the maximum value of 15 wt%. Possible chemical crosslinking reaction can be epoxy group and hydroxyl group of epoxy resin and carboxyl group and phenolic hydroxyl group of coal tar pitch. This study provides some theory foundation for the future application of epoxy resin carbon composite materials.

On the effect of pellet density on biomass pyrolysis in a pressurized fixed bed reactor

In this work, pellets of different densities but the same particle size were prepared from pine wood. The pellets as well as the raw biomass sample, all in form of cubic blocks whose side was 5 mm, were pyrolysed in a pressurised fixed bed reactor at different temperatures (350 and 500 °C) and pressures (1 and 8 bar) to investigate how variation in biomass density affect the product distribution, tar and gas compositions, and char characteristics. More char and less tar were obtained from pellets of higher density at the same pyrolysis conditions. Chars from the pyrolysis of pellets of higher density contain more oxygen and less amount of crystallite clusters, making them more reactive in combustion tests run by thermogravimetric analysis (TGA). Tars were obtained from higher-density pellets in lower yields and were lighter (smaller molecular weight distribution) than those from less dense pellets. At higher temperatures extensive biomass decomposition forms chars with more crystallite clusters and less oxygen, while a higher char yield with less oxygen was obtained at higher pressures, along with smaller amount of a lighter tar. Higher temperature and pressure tend to produce a less reactive char. Through this systematic work, the similarities as well as some key differences between the effect of higher pressure and greater particle density on pyrolysis behavior have been identified.

The effect of heat-treatment temperature (HTT) on the carbon matrix development of both polyarylacetylene-and phenolic-derived carbon–Carbon (C/C) composites

Phenolic resins have been successfully used in the manufacture of C/C Composite hardware. However, they require costly, multiple impregnation–carbonization cycles due to their low char yield. Polyarylacetylene (PAA) resin is a promising alternative carbon precursor that possesses numerous advantages due to its higher char yield and low mass loss. In addition, both thermoset-derived carbons are non-graphitizable and rely on stress graphitization for matrix development, which ultimately dictates composite mechanical performance. The stress graphitization behavior of both composite systems was investigated and related to their mechanical behavior. PAA and phenolic-derived/T50 C/C composites were processed to a series of heat-treatment temperatures (HTTs), (1100°, 1800°, 2800°C) and compared. Increases in localized graphitization as verified by image analysis, AFM, and Raman were observed with increasing HT for both systems, though notably to a much higher degree for the phenolic system. We believe this to be a result of the larger degree of matrix pyrolysis shrinkage experienced at the fiber-matrix interface promoting molecular alignment. The mechanical properties of both composites were strongly affected by the HTT, primarily due to a weakening of the fiber-matrix interface. However, the phenolic-derived composite exhibited a 40% greater increase in fiber strength utilization over the PAA-derived composites after 2800°C, which is attributed to this highly oriented microstructure which contributes favorably to intra-matrix failure and crack deflection. Although there are benefits in utilizing high char yield carbon precursors that reduce manufacturing timelines, one must also account for possible differences in microstructure development when designing these composites for next generation systems.

Characterization of Eumelanin as an Additive in High‐Temperature Phthalonitrile‐Based Resin Blends

AbstractBio‐manufactured eumelanin is investigated as a sustainable high‐char carbon additive for use with moldable high temperature resins. Blends of Bisphenol A poly‐ether‐ether‐ketone (PEEK)‐based phthalonitrile (PN) with 0–30 wt% melanin are prepared and characterized for their compositional, thermal, and mechanical properties. Although the char yield increases from 10 to 30 wt% melanin loading, the presence of melanin decreases the thermal stability compared to PN resin alone. Despite this, the melanin‐PN resins still maintain a very high char yield (>64%) up to 1000 °C under nitrogen. Rheology, thermal analysis, and mechanical measurements suggest off‐gassing of the melanin and increased crosslinking between the melanin and PN, leading to a lower flexural strength resin with higher additive loadings. Spectroscopic studies suggest possible interaction between melanin and PN during co‐curing, which ultimately can affect the processing and final properties of melanin‐additive composite materials.

Strategies for preventing gelation in preparation of hyperbranched benzoxazines with high performance

The gelation of linear oligomeric benzoxazine precursors (OBPs) and high-molecular-weight benzoxazine precursors (HMWBPs) have been noticed and addressed by various effective actions, while no similar reports on hyperbranched benzoxazoles have been available. A series of hyperbranched benzoxazines were synthesized by A2 + B3 method using 1,3-bis(3-aminopropyl)tetramethyldisiloxane (BATSi) and 1,1,1-tris(4-hydroxyphenyl)ethane (THPE) and paraformaldehyde, namely HB-TSis, to examine the conditions for preventing gelation. We found that in most cases, increasing the feeding molar ratio of -OH to NH2 group, prolonging the reaction time and increasing the reactant concentration were all favorable for the formation of soluble HB-TSis. Except when the molar ratio of -OH to NH2 was 2:3, a lower reactant concentration was more likely to avoid gel formation. A sufficiently high vacuum degree during drying was reported for the first time as a factor affecting the gelation of polybenzoxazine precursors. In addition, gelation-free HB-TSis exhibited high degrees of branching (DBs) and weight-average molecular weight (Mw) in the range of 0.58–0.69 and 6100–10,100 Da, respectively. Their cured resins, poly(HB-TSi)s, both perform well in terms of thermal stability with high char yield (Yc) varying from 37.9 to 56.2%, and flame retardancy with low the heat release capacity (HRC) varying from 49.9 to 81.9 J/(g K), which are capable of being applied as nonignitable materials.

Molecular design of soluble poly(amide-imide) with high char yield for flame retardant epoxy resin

Abstract In this study, a noncoplanar diimide diacid monomer (DIDA) was synthesized by direct condensation of trimellitic anhydride (TMA) with m-tolidine. The noncoplanar unit was incorporated into poly(amide-imide)s (PAIs) main chain by Yamazaki-Higashi phosphorylation of DIDA with various aromatic diamines. Encouragingly, all of the PAIs show good solubility in some common solvents such as N,N-Dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), and m-cresol. In addition, the soluble PAIs show good optical transmittances of beyond 85 % at 500 nm due to the decreased crystallization ability. On the other hand, PAIs possess good mechanical properties with tensile strengths of 72–90 MPa and tensile moduli beyond 2 GPa. Meanwhile, the designed PAIs also exhibit excellent thermal properties: their glass transition temperatures (T g) range from 278 to 314 °C, initial decomposition temperatures (5 % weight loss temperatures, T 5wt%) are beyond 470 °C, coefficients of thermal expansion (CTE) are below 10 ppm/°C. The excellent mechanical and thermal properties are due to the strengthened hydrogen bonding interaction among the amide groups. Therefore, it is believed that incorporating noncoplanar unit and amide group into the polymer main chain at the same time can simultaneously improve processability, optical transparency, mechanical and thermal properties. Furthermore, it is worth noting that the char of PAI at 800 °C is as high as 72.5 %, which is one of the highest known values. When PAI was incorporated into epoxy resin, the blend passed UL94 V-0 rating due to the high charring capability of PAI.

Preparation of spherical phenol‐formaldehyde beads from phenol‐liquefied wood and the characteristics of carbonized materials

AbstractIn this study, wood of Cryptomeria japonica D. Don (Japanese fir) was liquefied with phenol as a solvent. Phenol‐liquefied wood was mixed with formalin and spherical phenol‐formaldehyde resin (PF) beads were prepared by a two‐stage suspension polymerization reaction. The influence of the kind and dosage of polyvinyl alcohol (PVA) on the particle size distribution, mechanical strength and thermal properties of spherical PF beads were investigated. The results show that PF beads prepared with partially saponified PVA as a granulating agent are smaller than 75 μm, while the PF beads prepared with fully saponified PVA have larger diameters. However, the average diameter of spherical PF beads decreased with the increase of PVA addition. Thermogravimetric analysis (TGA) indicates that the initial thermal degradation temperature of the PF beads is around 150°C, and the main weight loss occurs between 400 and 600°C. Among them, the PF beads with BF‐04 as the granulating agent have the best heat resistance, and have the highest char yield at 800°C. The Brunauer, Emmett and Teller surface adsorption shows that the internal structure of the carbonized spherical PF beads is microporous pores. Carbonized beads prepared with high PVA adding have large absorption volume.

Production and characterization of activated carbon from pyrolysis biochar of cellulosic cotton-based textile wastes

The increased in the production of textile wastes has been associated to the to the excessive formation of solid wastes resulting to detrimental threat to both human and the environment. Therefore, the upcycling of these wastes materials is in utmost importance. In this study, cotton textile wastes (CTW) undergone slow pyrolysis in a static bed reactor at different temperatures (350 °C − 550 °C), to produce biochar as a precursor for the production of activated carbon (AC). The biochar were then chemically activated using H3PO4 at different impregnation ratios and then heat-treated to obtain the (AC). The produced biochar and AC were characterized using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Results showed that highest char yield (27.64 wt%) was obtained at 450 °C, with a microporosity structure increased as the temperature increases. On the other hand, the micropore volume of AC increases as the impregnation ratio increases. Finally, the AC exhibit an acidic surface with an abundance of oxygen surface groups, making it promising candidates for different applications.

Phthalonitrile functionalized resoles – use of 2,3-dicyanohydroquinone as a versatile monomer for resins with very high thermal stability

In the aerospace industry, composite materials based on high-performance fibers and polymer matrices are widely used. Indeed, they can display very important mechanical and thermal properties with a very large density-to-stiffness balance. Usually, thermal protection systems are made from composite materials containing a char precursor for the polymer matrix. Temperature-resistant organic polymers are still quite rare and generally require very restrictive manufacturing and use processes. Recently, phthalonitriles have gained interest due to their very good thermostability and high char yield. However, phthalonitrile resins are generally solid at room temperature and often have a narrow processing window. In this work, synthesis methods allowing access to phthalonitrile resins were developed from 2,3-dicyanohydroquinone. These methods propose to consider together phenolic chemistry (phenolic reactive positions and aldehyde) and self-crosslinkable phthalonitrile chemistry (hydroxyl-mediated from phenolic and nitriles). It was thus possible to synthesize liquid resins at room temperature, leading to polymeric networks with a very high thermostability (temperature at 5% mass loss > 450 °C and char yield ≈ 70 %).

Intrinsically flame-retardant vanillin-based PU networks with self-healing and reprocessing performances

Conventional polyurethane (PU) networks fabricated from nonrenewable fossil resources are difficult to be recycled, reprocessed, and reshaped because of the permanent covalent cross-linked networks, and the flammability of PU networks limits their wide application. Herein, the novel polyols were synthesized from renewable vanillin and then reacted with hexamethylene diisocyanate (HDI) trimer to obtain versatile bio-based PU networks with dynamic disulfide and imine bonds for the first time. Obtain malleable PU networks that possess excellent reprocessability and self-healing performance, as well as superior fire resistance. The vanillin-based PU networks show a high T5d of ∼180 °C, high char yield of 23% at 800 °C, fast stress relaxation of ∼38 s at 80 °C, excellent scratch self-healing performance with approximately 100% healing efficiency at 120 °C for 90 min, outstanding flame retardancy with high LOI of ∼30% and UL-94 V0 rating. Additionally, the vanillin-based PU networks display excellent malleability with the activation energy (Ea) of 30.2–54.8 kJ•mol−1 due to dual dynamic bonds in the networks, which can be recycled in 60 min at 120 °C by hot pressing. Moreover, the vanillin-based PU networks with Schiff base can be degraded rapidly in the mixture of HCl and THF. Briefly, produced PU networks from abundant and renewable resources are significant examples to foster the development of versatile PU network materials.

Ferrocenecarboxaldehyde modified terephthalaldehyde-phenolic resin: A comprehensive study on the synthesis, curing behavior, and pyrolysis process

To meet the demand for high performance carbon-based materials, catalytic graphitization particles are widely used to improve the thermal stability and char yields of conventional phenolic resins. The direct addition of inorganic particles may cause significant phase separation and reduce the crosslinking density of phenolic resins. In the study, a non-hazardous aromatic dialdehyde, terephthalaldehyde (TPA), was utilized to synthesize a formaldehyde-free phenolic resin (PTPA). A high char yield ferrocenecarboxaldehyde modified terephthalaldehyde-phenolic resin (Fc-PTPA) with a value of 76.0% at 800 °C was obtained by co-curing ferrocenecarboxaldehyde (Fc) and PTPA. The curing process of Fc-PTPA and the carbide structural evolution during pyrolysis were studied. The results show that Fc could act in the second stage of curing which led to an increase in the crosslinking density of resin. The generated Fe3C during the pyrolysis of Fc-PTPA contributed to form a more ordered carbide structure which was an important reason for the improvement in the thermal properties and char yields.

One-Pot Synthesis of Polymers Containing PC Bonds in the Main Chain.

Placement of phosphorus in the polymer main chain leads to organophosphorus polymers with potentially unique chemical and physical properties. Herein, it is demonstrated that the Abramov phosphonylation reaction can be extended to the synthesis of such polymers, by reacting di- or tricarbaldehydes with phosphinic acid (PA) in the presence of N,O-bis(trimethylsilyl)acetamide (BSA). This technique affords polymers with main chain PC bonds, wherein phosphorus (V), aromatic rings, and hydroxymethylene moieties are linked by bis(α-hydroxymethylene)phosphinic acid (BHMPA) units. The resulting polymers are water soluble, display resilience against acid- and base-catalyzed hydrolysis, and exhibit superior thermal stability with high char yield in air (≈83%) and nitrogen (≈76%) atmosphere.

Designed for Circularity: Chemically Recyclable and Enzymatically Degradable Biorenewable Schiff Base Polyester-Imines

Bio-based plastics potentially have several positive impacts on the environment; however, in order to make a real difference, they need to have managed and sustainable end of life. This means they should from the start be designed for chemical, mechanical, and/or organic (biological) recycling. Development of energy-efficient and selective chemical recycling processes is a necessary part in reaching truly circular plastic flows. Polyesters are generally well suited for chemical recycling due to the presence of reversible ester bonds. Utilization of dynamic covalent chemistry to include a second, even more easily reversed bond, such as Schiff base (SB, imine bond), could further facilitate chemical recycling, enabling depolymerization back to monomeric products under mild conditions. Here, we present the synthesis of three vanillin-derived SB monomers SBM1, SBM2, and SBM3 and the corresponding polymers SBP3a–b, SBP4a–b, and SBP5a–b. Three different diamines and two potentially bio-sourced diesters were utilized to yield altogether six different polyester-imines with different aliphatic/aromatic contents. All the obtained SB-based polyesters were thermally stable at ∼290–330 °C and had a high char yield during the pyrolysis, which may indicate inherent flame resistance. All the polyesters were amorphous with glass transition temperatures from 36 to 76 °C. The chemical recyclability and hydrolytic degradation of the synthesized polyesters was evaluated by using real-time 1H NMR spectroscopy. Finally, the susceptibility of the synthesized polyester-imines to enzymatic degradation by PETase was demonstrated. The experimental results were further supported by induced-fit docking experiments to theoretically evaluate the potential productive binding of the produced polyester-imines and intermediates thereof to the active site of PETase.

Pyrolysis mechanism of composite binder composed of coal tar pitch and phenolic resin for carbon materials

The composite binder consisting of coal tar pitch (CTP) and phenolic resin (PR) has both low viscosity and high char yield, and it has great potential in the preparation of advanced carbon materials. However, the lack of understanding of its synergetic behavior and mechanism hinders the optimization of the preparation process. In this work, the co-pyrolysis of CTP and PR was systematically investigated. The char yield of the composite binder was confirmed to be remarkably higher than the weighted average of the two single binders. Furthermore, the calculated activation energy for the pyrolysis of the composite binder was higher than that of CTP and PR after 400 °C. The interaction and structure evolution mechanisms of composite binder were clarified. Specifically, the ortho-position of the phenoxy carbon in CTP cross-link with the para-position of the phenoxy carbon in PR by the methylene bridge, and the free polycyclic aromatic hydrocarbons stack onto the as-crosslinked polycyclic aromatics driven by the pancake bonds.

Synergistic effect of CO2 and H2O co-activation of Zhundong coal at a low burn-off rate on high performance supercapacitor

This study presents porous activated carbons, prepared by the physical activation of high-alkali Zhundong coal with CO2, H2O, or CO2/H2O, as supercapacitor electrode materials. The synergistic effect between CO2 and H2O activation on the specific capacitance, morphology, pore and physicochemical structure, and supercapacitor performance of activated carbons was systematically investigated for the first time. A hierarchical porous structure is formed in carbon co-activated by CO2 and H2O at 800 °C (TCC/H-800), which also has a rich graphite microcrystalline structure, long-range ordered graphite network, abundant oxygen- and nitrogen-containing functional groups and high char yield (about 70 wt%), all of which are desirable properties. Moreover, the TCC/H-800 electrode shows better electrochemical performance than electrodes based on carbon activated by CO2 or H2O alone, and has an ideal coulombic efficiency (98.95% after 2000 cycles at 5 A g−1) and a good specific capacitance. The symmetrical TCC/H-800 supercapacitor reaches a 155.1 F g−1 specific capacitance at 0.5 A g−1. Meanwhile, its energy density is 21.54 Wh kg−1 at 500.00 W kg−1, with 92.97% of the initial discharge capacity retains after 10,000 cycles. Coal-based porous carbon activated by CO2 and H2O synergistically has the advantages of low losses and low pollution.