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A simple B doping strategy to achieve simultaneous optimization of carbon-based multi-scale structures including morphology, crystallinity and doping environment for enhancing the anodic properties of sodium ion batteries.

It is important to study the effect of oxygen-containing functional groups on the competitive adsorption mechanism of benzene and water on the surface of carbon materials, and to directional modification of activated carbon to improve its selective adsorption of benzene in air. In this study, the adsorption characteristics of benzene and water on original and linked ester, carboxyl, hydroxyl, carbon materials linked by ether groups were calculated by quantum chemical simulation based on density functional theory. The types and proportions of weak interactions in the adsorption process were calculated by energy decomposition analysis, and the adsorption mechanism of carbon materials for water and benzene was described. The influence and contribution of oxygen-containing functional groups on the adsorption of benzene and water were further analyzed by van der Waals potential and electrostatic potential, respectively, so as to determine the difference in the adsorption effect of different types of oxygen-containing functional groups on the two molecules. It was found that the carboxyl group has a great influence on the hydrophilicity of carbon materials, and the electrostatic potential distribution before and after linking the carboxyl group changed significantly. Therefore, they can attract each other with water through hydrogen bonds and occupy the surface adsorption sites of carbon materials, thereby inhibiting the adsorption of benzene on carbon materials. On the contrary, due to its hydrophobic properties, the ether group will free up adsorption space for the adsorption of benzene on the surface of the carbon material, which is beneficial to the adsorption of benzene. The adsorption experiments were carried out, and the results were consistent with the simulation. This study provides an idea for preparing efficient carbonaceous adsorbent of benzene and reducing benzene pollution in industry.

Restraining the shuttle effects of lithium polysulfides is the key to improve the cycling reversibility and stability of lithium-sulfur (Li-S) batteries for which design of robust sulfur hosts has been regarded as the most effective strategy. In this work, we report a new type of hybrid sulfur host which is composed of Al2O3 homogenously decorated in nitrogen-rich mesoporous carbon framework (NMC-Al2O3). The NMC-Al2O3 hybrid host features a poly-dispersed spherical morphology and a mesoporous configuration with high surface area and large pore volume that can accommodate a high sulfur content up to 73.5 wt.%. As a result, the fabricated NMC-Al2O3-S cathode exhibits all-round improvements in electrochemical properties in term of capacities (1,212 mAh·g−1 at 0.2 C; 755 mAh·g−1 at 2 C), cycling charge-discharge reversibility (sustainably 100% efficiencies) and stability (1,000 cycles with only 0.023% capacity decay per cycle at 0.5 C). By contrast, the Al2O3-free NMC-S cathode shows both decreased capacities and rapidly descending Coulombic efficiencies during cycling. Density functional theory (DFT) calculations further reveal that the implanted Al2O3 can greatly enhance the chemical adsorption and catalytic conversion for various lithium polysulfides and thereby effectively prevent the polysulfide shuttling and significantly improve the utilizability, reversibility and stability of sulfur cathode.

Porous materials such as activated cokes have been widely utilized in the adsorption removal of atmospheric SO2 emission. Pore configuration of coke is a key factor affecting its SO2 rapid adsorption dynamics, which is critically important for fluidization adsorption craft. Herein, activated coke adsorbents with typically microporous structure and hierarchically porous structure were prepared by a catalytic physical activation method from Chinese large-reserve Zhundong coal, which were used as model adsorbents to investigate the effect of pore configuration on SO2 fluidized adsorption dynamics. SO2 fluidized-state adsorption experiments indicate that hierarchically porous coke has a more rapid initial adsorption dynamic than microporous type coke, and coke with 44.2% meso-/macropores volume shows the highest initial adsorption rate of 7.37 mg g−1·min−1. Additionally, the fitting of Weber-Morris model provides the dominate factors for SO2 adsorption kinetics in each sub-process: SO2 adsorption capacity of microporous-dominated adsorption stages account for 70%–80% of total, and when it comes close to adsorption saturation, the main dominant factor of kinetic becomes the ratio of meso-/macropores volume. This work is of significance for the application of SO2 adsorption craft in fluidized bed and also provides insight into the role of hierarchically porous configuration in gas molecule rapid adsorption.

Oxygen-doped carbon materials (OCM) have received a lot of attention for catalyzing the two-electron oxygen reduction reaction (2eORR) towards hydrogen peroxide generation, but the origin of their activity is not well understood. Based on density functional theory calculations, we introduce the Fukui function ( f 0 ), a more comprehensive and accurate method for identifying active sites and systematically investigating the activity of carbon materials doped with typical oxygen functional groups (OGs). According to the results, only ether or carbonyl has the potential to become the activity origin. The 2eORR activities of carbon materials co-doped by different OGs were then investigated, and a significant synergistic effect was discovered between different OGs (particularly between epoxy and other OGs), which might be the real active centers in OCM. To further understand the cause of the activity, the Fundamental Gap (Eg) was introduced to investigate the ability of various OCM to gain and lose electrons. The results show that the decrease in overpotential after oxygen co-doping can be attributed to the decrease in Eg. This work introduces descriptors ( f 0 and Eg) that can aid in the efficient design of catalysts and adds to our understanding of the 2eORR activity origin of OCM.

Catalytic oxidation plays important roles in energy conversion and environment protection. Boron-doped crystalline carbocatalyst has been demonstrated effective; however, the application potential of boron-doped amorphous carbocatalyst remains to be explored. For amorphous carbon material, finite-sized carbon clusters are the basic structural units, which exhibit unique activity due to edge and size effect. Herein, using sulfur dioxide (SO

The mismatch of pollutant concentration and ·OH concentration is the key reason for the inefficient degradation of formaldehyde in the electro-Fenton system. Therefore, formaldehyde and ·OH are adsorbed near the cathode, and the high concentration reaction region is constructed to increase the reaction probability, which is called control of the reaction region. Through nitrogen doping modification of the activated carbon cathode, the adsorption capacity of the modified cathode for formaldehyde and active species, and the selectivity of the two-electron oxygen reduction reaction were deeply analyzed. The results show that the suitable nitrogen doping form of the modified cathode significantly promotes the adsorption capacity of formaldehyde and H

Oxygen-containing groups in carbon materials have been demonstrated to be effective in the anodic sodium-ion storage process; however, the effect of specific oxygen-containing groups on the sodium-...

Low temperature oxidation is the primary source of heat triggering coal spontaneous combustion. Experimental studies have found that adsorbed H2O in coal structure can catalyze low-temperature oxidation. However, the detailed reaction pathways of adsorbed H2O participated low-temperature oxidation process are still unclear. In this work, we for the first time elucidate the catalytic role of adsorbed H2O in coal oxidation process at the molecular level by performing quantum chemistry calculations assisted with differential scanning calorimetry (DSC) experiment validations. Based on computations using composite theoretical method of CBS-QB3 and kinetic analyses, we found that adsorbed H2O can increase the formation of ·OH radicals, which are critical active species for inducing coal low-temperature oxidation. On the one hand, adsorbed H2O molecules are able to increase the formation of aliphatic hydrocarbon radicals, providing more active sites for ·OH radical generation. On the other hand, adsorbed H2O can accelerate the formation of hydroperoxides by playing the “mediator” role in the H transfer from aliphatic structures to peroxyl radicals, providing more “precursors” for ·OH radical generation. DSC experiments using model coal samples with gradient moisture contents and different H2O forms further demonstrate the catalytic role of adsorbed H2O in coal low-temperature oxidation. Results from this study reveal detailed catalytic pathways of adsorbed H2O in ·OH radical formation, providing a more comprehensive understanding on coal low-temperature oxidation theory.

Heteroatom-doped carbon materials have been proven to be very effective for gas adsorption. Herein, edge-carboxylated graphene nanoplatelets with gradient oxygen contents and consistent pore structures were used as model adsorbents to independently determine the effects of the oxygen functionalization of carbon materials on the SO2 adsorption. The OGnPs were obtained by employing a simple ball milling method using dry ice by which an oxygen content as high as 14.06 wt% could be achieved, resulting in a 20 times increase in SO2 adsorption capacity as compared to that of oxygen-free graphene nanoplatelets. Both the experiments and density functional theory calculations demonstrated that the enhanced SO2 adsorption on the oxygenated carbon surface had a physisorption nature, which provided new insights into the development of advanced carbon materials with heteroatom doping for gas molecule adsorption.

SO2 oxidation is the rate-determining step during the process of low-temperature SO2 conversion to high-value H2SO4 in porous carbon materials. Non-dissociated O2 molecules and chemisorbed O atoms from O2 dissociation are possible oxidants for SO2 oxidation. While the pathways of oxidation reactions in which chemisorbed O atoms participate have been previously studied via density functional theory calculation, the possible SO2 oxidation pathways by non-dissociated O2 remain to be investigated. Inspired by the mechanism in which a non-dissociated O2 molecule oxidizes other molecules such as CO and NO, we elucidate the detailed pathways for SO2 oxidation by non-dissociated O2 using density functional theory calculation assisted by SO2 removal experiment validation. Computational results show that non-dissociated O2 can be activated at the active sites of porous carbon, generating a C–O–O structure. By low-barrier O transfer processes, the formed C–O–O structure can directly oxidize gaseous SO2 to SO3 without the need of the SO2 chemisorption process. Transient response experiments further validate that the oxidant for SO2 conversion to SO3 in porous carbon materials is non-dissociated O2. This work reveals the role of non-dissociated O2 in directly oxidizing non-chemisorbed SO2 to SO3 at low temperature, providing a new understanding for SO2 conversion to SO3 in porous carbon materials.

Nitrogen-containing functional groups in carbon surface have been demonstrated favorable for SO2 adsorption. While previous literature suggested the SO2 chemisorption nature due to N doping, this work highlights the enhanced physical adsorption interactions between SO2 and nitrogen-containing groups, which are elucidated by density functional theory calculations with the analyses of electrostatic potential, noncovalent interactions, and energy decomposition. The results indicate that for pristine carbon surface, SO2 physisorption mainly occurs on the basal plane due to van der Waals interactions. N doping changes the electron distribution of carbon surfaces, thus altering not only intensity but also types of involved interactions. The quaternary N atoms promote SO2 physisorption mainly by enhancing the van der Waals interactions between the basal plane and SO2 while the improvement of SO2 physisorption by pyridinic and pyrrolic N species should be ascribed to the enhanced electrostatic interactions at edge sites. These results demonstrate that N doping could boost the effective surface for SO2 adsorption by facilitating both van der Waals and electrostatic interactions.

Lithium ion capacitors (LICs) hold potentials to bridge the gap between lithium ion batteries and supercapacitors ; however, the imbalance of electrochemical kinetic and stability between Li + storage anode and capacitive cathode has been the key bottleneck. Herein, we report a high-rate and ultrastable anode for this issue, consisting of boron-doped nanoporous carbon spheres which are synthesized by a continuous spraying-assisted co-assembly process. Experimental and computational investigations as well as the comparison with a nitrogen-rich carbon indicate that boron species enhances ion-surface interactions, electron/ion conductivity and carbon framework cycling firmness, leading to dramatically improved rate and cycling performances, which outperform the extensively explored nitrogen doped carbons and most reported high-rate anode materials . By pairing a coal-derived microporous graphene cathode, we constructed a full-carbon LIC device exhibiting high energy and power densities (207 Wh kg −1 at 511 W kg−1 and still 136 Wh kg−1 at 17.06 kW kg−1), as well as an unprecedented cycling stability with no capacity decay after 15,000 cycles at 2 A g−1. This work not only offers a fundamental basis to understand the enhanced anode performance by doping boron into carbon framework but also provides an effective strategy to circumvent the kinetic and stability discrepancies between anode and cathode for high-performance LICs.

Developing carbon materials featuring both high accessible surface area and high structure stability are desirable to boost the performance of constructed electrochemical electrodes and devices. Herein, we report a new type of microporous carbon (MPC) derived from biomass waste based on a simple high-temperature chemical activation procedure. The optimized MPC-900 possesses microporous structure, high surface area, partially graphitic structure, and particularly low impurity content, which are critical features for enhancing carbon-based electrochemical process. The constructed MPC-900 symmetric supercapacitor exhibits high performances in commercial organic electrolyte such as widened voltage window up to 3 V and thereby high energy/power densities (50.95 Wh kg−1 at 0.44 kW kg−1; 25.3 Wh kg−1 at 21.5 kW kg−1). Furthermore, a simple melt infiltration method has been employed to enclose SnO2 nanocrystals onto the carbon matrix of MPC-900 as a high-performance lithium storage material. The obtained SnO2-MPC composite with ultrafine SnO2 nanocrystals delivers high capacities (1115 mAh g−1 at 0.2 A g−1; 402 mAh g−1 at 10 A g−1) and high-rate cycling lifespan of over 2000 cycles. This work not only develops a microporous carbon with high carbon purity and high surface area, but also provides a general platform for combining electrochemically active materials.

Porous carbons have been widely explored and utilized in the fields of adsorption. Pore structure design is the key for achieving high-capacity and fast adsorption. Herein, we develop a simple and general method for pore regulation of coal-based activated carbons (ACs), which is based on a catalytic physical activation process by using the inherent minerals in coal precursor. By adjusting the inherent mineral distribution in the coal precursors, activated carbons with various pore configurations including microporous structure and hierarchically porous structure can be obtained. More specifically, ZD-HCF-AC from a mineral-free coal precursor shows a microporous structure with a low surface area of 345 m2 g–1, while ZD-AC from mineral-rich coal exhibits a hierarchically porous structure with remarkably improved surface area of 933 m2 g–1. Ca and Mg components in the minerals notably promote the development of mesopore and macropores and lead to the resulting ACs with hierarchical pore structure. The effect...

High-concentration formaldehyde-based wastewater causes a serious hazard to the human body and ecosystem. Electro-Fenton technology can be used for the pre-treatment of high-concentration formaldehyde wastewater, but the uneven distribution of free radicals and formaldehyde affects the degradation efficiency of Electro-Fenton. Oxygen-containing functional groups can enhance the adsorption and enrichment of the pollutants near the cathode, thereby improving the degradation efficiency of Electro-Fenton. In this paper, quantum chemical simulation was adopted to study the effects of different oxygen-containing functional groups on the adsorption of formaldehyde on the carbon surface. The results showed that incorporating oxygen-containing functional groups changed the electronic structure of the carbon surface and affected the interactions between formaldehyde and carbon surface. Only the incorporation of certain oxygen-containing functional groups at the edge of the carbon surface could promote the adsorption of formaldehyde. Edge ether group promoted the basal plane adsorption of formaldehyde on the carbon surface by enhancing dispersion interactions. The edge carboxyl group and edge hydroxyl group influenced the edge adsorption of formaldehyde on carbon surface due to the enhancement of electrostatic interactions. The edge pyrone group promoted the edge adsorption of formaldehyde by influencing the dispersion interactions and electrostatic interactions between formaldehyde and the carbon surface.

Water washing regeneration has been applied to recover H2SO4 from desulfurized activated cokes (AC). However, the low regeneration efficiency is the bottleneck which causes inferior cycled desulfurization properties of AC. Herein, we propose that the washing regeneration efficiency can be significantly improved by pore structure regulation of AC. A series of ACs with variable pore configurations were used as model adsorbents to individually investigate the effect of pore structure on the washing-regeneration of desulfurized AC. Cycling desulfurization-regeneration experiments show that the micropore-dominant AC exhibits poor performance of water-washing regeneration. After 10 cycles, the adsorption sulfur capacity of micropore-dominant AC declines to 10.17 mg g−1, only 50% of fresh activated coke. Whereas the hierarchical porous AC containing equivalent volume of micropore and mesopore (0.40 and 0.50 cm3 g−1) has both excellent SO2 removal kinetics and water-washing regeneration performance. Even after 10 cycles, the hierarchical porous AC can still sustain high adsorption sulfur capacity of 70 mg g−1 and excellent water-washing regeneration efficiency of 90%. Molecular dynamic simulations using pore models close to practical AC suggest that the self-diffusion coefficient of H2SO4 in hierarchical pore is about two times of that in micropore, proving the promoting role of hierarchical porous structure in H2SO4 desorption. This work not only reveals the relationship of pore configuration with washing regeneration behavior but also provides a facile pore configuration regulation strategy that can substantially improve AC’s regeneration efficiency, implying great potentials for applying water-washing regeneration in industrial desulfurization process.

Volatile organic compounds (VOCs) adsorption by carbonaceous materials is one of the most promising technologies for their efficient abatement, which requires the construction of both suitable porous structures and functional groups. In this work, nitrogen-doped hierarchical porous bio-char (NHWC) was prepared via a facile catalytic activation process, in which NH3·H2O was used as activation agent to introduce nitrogen dopants and trace CaCl2 acted as catalyst for hierarchical pore formation. VOCs dynamic adsorption experiments indicated that the prepared NHWC exhibits excellent dichloromethane and toluene adsorption properties. Particularly, the combined adsorption capacities of dichloromethane and toluene in NHWC are 54.9 and 308 mg g−1, respectively, much higher than those in microporous bio-char, indicating the significant role of hierarchical porosity in multiple VOCs molecules combined adsorption. Control experiments using the prepared model carbon materials indicate that the excellent combined adsorption performance originates from both nitrogen dopants and hierarchical porous structure. Density functional theory calculations further reveal that the introduced nitrogen functional groups enhance the van der Waals interactions between VOCs molecules and carbon surface, thereby improving the combined adsorption of VOCs. This work provides a new strategy of optimizing the pore structure and surface chemistry of bio-char.

Electrochemical oxygen reduction has been regarded as a promising choice to enable H2O2 on-site production and utilization wherein the exploration of high-efficiency yet cost-effective catalysts is the key. Here, we demonstrate a low-cost activated coke (AC) electrocatalyst with size-tailored amorphous carbon clusters doped by oxygen groups, prepared through a facile CO2 assisted mechanochemistry approach, to deliver among the highest performances reported in a typical alkaline system, including high activity (onset potential of 0.83 V), high H2O2 selectivity (∼90 %) and long-term stability. A series of control experiments, structural characterizations before and after electrochemical tests and density functional theory calculations provide a new insight into the coupling role of carbon cluster size and oxygen doping in H2O2 electrochemical production process, that is, size-reduced amorphous carbon lattices with abundant edges contribute to the high activity, while the basal carbon atoms in ether-doped small-size carbon plane are the most active sites towards H2O2 selectivity.

Low desorption efficiency and inferior adsorbate recovery rate during conductive-heating regeneration have always been the key issues facing activated carbon-based SO2 removal technology, which commonly leads to a short cycling life of an adsorbent. Herein, microwave heating was employed to regenerate desulfurized activated coke, which demonstrates great improvements in regeneration efficiency and cycling desulfurization performances. Compared with the long-time conductive-heating process (30 min), microwave heating shows a more rapid heating rate with just 4 min to achieve complete regeneration. After 10 desulfurization–regeneration cycles, microwave regenerated activated coke (MG-AC) can still maintain a high SO2 removal capacity of 94 mg g–1, more than double than that of thermal regenerated AC (TG-AC). Physicochemical structures analyses confirm that microwave heating selectively activates the adsorbate H2SO4 molecules and thus promotes the porosity development and selective removal of oxygen-containi...

Herein, we report a high performance aqueous supercapacitor which is made of highly nitrogen-doped carbon nanospheres (NRMCs) with unimodal mesoporosity. An aerosol-assisted spraying process is employed to obtain the nano-sized NRMC particles possessing large surface areas, high pore volumes and ultra-high N doping levels (14.51%–20.55%). Evaluated as supercapacitor electrode, the optimized NRMC exhibits excellent performance for aqueous electrical double layer capacitors with high material-level specific capacitance (432 F g−1 at 1 A g−1), excellent rate performance (205 F g−1 at a high current density of 100 A g−1) and high cycling stability. The constructed symmetric supercapacitor delivers high energy densities of 9.2 Wh kg−1 and 4 Wh kg−1 at power densities of 0.11 kW kg−1 and 23.24 kW kg−1, respectively. Moreover, the effect of N specie distribution on the rate performance is also demonstrated, which highlights the important role of tuning the N doping patterns on enhancing the supercapacitive performances of carbon materials.

Heteroatom-doped carbon materials have been proven to be very effective for gas adsorption. Herein, edge-carboxylated graphene nanoplatelets with gradient oxygen contents and consistent pore structures were used as model adsorbents to independently determine the effects of the oxygen functionalization of carbon materials on the SO2 adsorption. The OGnPs were obtained by employing a simple ball milling method using dry ice by which an oxygen content as high as 14.06 wt% could be achieved, resulting in a 20 times increase in SO2 adsorption capacity as compared to that of oxygen-free graphene nanoplatelets. Both the experiments and density functional theory calculations demonstrated that the enhanced SO2 adsorption on the oxygenated carbon surface had a physisorption nature, which provided new insights into the development of advanced carbon materials with heteroatom doping for gas molecule adsorption.

Development of porous carbon with both high surface area and high heteroatom doping has attracted considerable research attention in the fields of gas adsorption and electrochemical energy storage. However, cost-effective and scalable production strategies are still needed to accelerate industrial applications. In this study, we exploit a new type of nitrogen-doped microporous carbon by direct carbonization of abundant and low-cost Chinese Zhundong coal under ammonia atmosphere. As an adsorbent, the CO 2 adsorption capacity of this material can reach 3.71 mmol g −1 at 0 °C and 1 bar with a high CO 2 /N 2 selectivity of 22.83; the SO 2 adsorption capacity reaches 132.5 mg g −1 at room temperature. Used as electrode materials, their specific capacitance is as much as 205 F g −1 for supercapacitors at a low current density of 0.5 A g −1 and maintains 129 F g −1 at 50 A g −1 . The discharge capacity as a sodium ion battery anode at 200 mA g −1 remains 190 mAh g −1 even after 500 cycles. Together with their simple synthesis and inexpensive raw materials, these findings indicated that our N-doped carbon materials have great potential for practical application.

For the aim to give a new insight into the interactions between SO 2 molecule and carbon surface and the effect of acidic oxygen-containing groups, density functional theory and noncovalent interaction analysis in terms of reduced density gradient were employed to investigate both the intensity and type of the interactions. The results indicate that the physisorption of SO 2 molecule mainly occurs on the basal plane of pure carbon surface due to van der Waals interactions, however, when acidic oxygen-containing groups were decorated on the carbon surface, they would facilitate SO 2 adsorption as a result of hydrogen bonding and dipole–dipole interactions. What's more, these groups could not affect the chemisorption of SO 2 remarkably, no matter they are near the adsorption sites or not. In addition, calculation results show that the interactions between SO 2 and acidic oxygen-containing groups are in physisorption nature, which challenges a long-held the viewpoint of irreversible chemisorption. Acidic oxygen-containing groups could boost the effective surface area of carbon by enhancing the physisorption on edge positions.

Coal-fired organic pollutant emission is regarded as an important precursor to regional air pollution. Adsorption using activated coke has the potential to achieve the simultaneous removal of multiple gas pollutants such as SO2, NOx and the volatile organic compounds (VOCs) in organic pollutants, for which developing low-cost activated coke adsorbents with suitable pore configuration is the key. In this work, we propose a green and facile trace potassium assisted catalytic activation strategy to prepared coal-based activated cokes with simultaneously large surface areas, hierarchical pore topology and high production yield. By simply adjusting the type of potassium species and amounts added, potassium induced catalytic activities for the reaction between CO2 and coal framework can be controlled, thus yielding two types of activated cokes, namely microporous and hierarchically porous activated cokes. Evaluated as adsorbents, the optimized hierarchically porous KP_AC_2 shows outstanding toluene capacities in both single adsorption (300.3 mg·g−1) and combined adsorption (262.5 mg·g−1) cases. Moreover, KP_AC_2 also exhibits good SO2 and NO adsorption properties in combined adsorption cases due to the hierarchical storage of various adsorbates. Furthermore, the effects of H2O, O2 and temperature are investigated, providing guidelines for actual flue gas government. This work provides a green, low-cost and scalable method for preparing activated coke adsorbents used in combined adsorption of SO2, NO and VOCs, which hold potentials to replace the traditional physical or chemical activation craft and is promising in the field of coal-fired flue gas purification.

During the adsorption process of multi-water molecules, two types of hydrogen bonds are gradually formed in lignite. One type of hydrogen bonds exists between H2O molecules and oxygen-containing functional groups, wheras the other exists between different H2O molecules. As reported by previous studies, strength distributions of the above two types of hydrogen bonding networks are heterogeneous, however, the change rules of the hydrogen bonding network as well as its heterogeneity from the adsorption of single water molecule to multi-water molecules remain to be investigated. In this work, we quantitatively analyzed the change of hydrogen bonding networks during the adsorption of multi-water molecules in lignite. Analysis of Atoms in Molecules (AIM) and density functional theory (DFT) calculation were performed to calculate the hydrogen bond energy. Using the standard deviation of hydrogen bond energy as an indicator, we found that the heterogeneities of hydrogen bonding networks in lignite are enhanced with the proceeding of H2O molecule adsorption, which can be mainly ascribed to the adsorption of multi-water molecules near carboxyl group. Specifically, from the adsorption of three to four H2O molecules, the standard deviation of hydrogen bond energy between carboxyl group and H2O molecules increases about 1.5 times (from 14 kJ/mol to 35 kJ/mol), whereas that of hydrogen bond energy between different H2O molecules decreases from 16 kJ/mol to 9 kJ/mol. Based on the above findings, gradient dewatering strategy is proposed for the removal of adsorbed H2O molecules in lignite.

Aiming to enhancing porosity development and reducing the dosage of activation agents in preparation of activated carbon, a novel green and efficient strategy of trace K2CO3 induced catalytic activation was proposed. In the design, adding small amount of K2CO3 (less than 2% weight ratio of precursor) can significantly reduce the reaction barrier between coal framework and CO2 molecules, thus enhancing pore formation of as-obtained activated carbons. The resulting Ca_AC-1 has short range ordered microcrystalline structure and developed pore structure, even superior to the activated carbon from chemical activation with large dosage of K2CO3 (three times weight ratio of carbon precursor). Evaluated as CO2 adsorbent, Ca_AC-1 a high CO2 adsorption capacity and adsorption-regeneration cycling stability. More importantly, Ca_AC-1 with optimized pore and crystalline structure can deliver excellent supercapacitive performances in term of high energy and power densities (26–35 Wh/kg at 0.338–6.25 kW/kg in organic system) as well as 100% cycling stability. Both experiment and density functional theory (DFT) calculations demonstrate that C-O-K structure can be regenerated in CO2 activation, leading to continuously catalytic effects despite low-dose K2CO3 addition. Combining the low-cost sources, simple preparation procedures and good application performances, the resulting activated carbon holds great potentials for scalable production and applications. Such strategy can also be extented for developing high-performance activated carbons from various kinds of solid carbon sources.