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[Display omitted] • Solvent-free strategy was developed to synthesize porous carbon (MIC x) doped with rich Faradaic active oxygen (5.8–8.2 atom%). • The resultant MICx owns surface area of 326–427 m2/g and large packing density of 1.12–1.28 g/cm3. • The MICx based electrode achieves superior supercapacitor performances with both high gravimetric and volumetric performances. In the selection of carbon-based electrode materials for supercapacitive energy storage, it is hard to get one that is high in both gravimetric and volumetric performance because there is a trade-off between them. In the presented work, microporous carbon materials denoted herein as MIC x were synthesized through catechol polymerization in the presence of molten FeCl 3. As complexing agent, the iron species coordinate with catechol oligomers, functioning as template as well as catalyst in the synthesis of the microporous carbon. The in situ formation of micropores and carbonaceous skeleton is induced by the carbonyl/hydroxyl redox pairs upon catalytic graphitization during carbonization. The derived nanocarbons have high microporosity (70.6 %–79.2 %) and rich oxygenate functionalities (carbonyl: 3.3–4.0 atom% and hydroxyl: 2.5–4.2 atom%). The FeC x materials are high in faradaic activity. For example, the FeC873-based electrode displays excellent supercapacitor performances: capacitance of 440F/g@1.0 A/g (equivalent to 537F/cm3@1.0 A/g) and 289F/g@20 A/g (equivalent to 353F/cm3@20 A/g), large energy density of 25.5 Wh/kg@900 W/kg (equivalent to 31.1 Wh/L@1098 W/L), and good cycling stability (ca.100 % capacitance retention after 20 000 continual charge/discharge cycles). [ABSTRACT FROM AUTHOR]

[Display omitted] • Expired coffee derived carbons (HCDC) achieves high packing density of 1.81–1.83 cm3/g. • The derived HCDC owns rich nitrogen (4.5 atom%) and oxygenic (12.0 atom%) functionalities. • The HCDC electrode achieves high gravimetric and volumetric capacitance of 312F/g and 567F/cm3. • The HCDC electrode exhibits a high volumetric energy density of 27.8 Wh/L@1820 W/L. Clean production of activated carbon from household expired food provide an alternative way to get value-added product thus benefits waste reutilization and environmental protection. Herein, we fabricated N, O co-doped activated carbons (HCDC) from expired coffee to by a green route of direct water vapor carbonization/activation approach. In our approach, the expired coffee was firstly grinded and then carbonized under water vapor atmosphere. The derived HCDC owns low surface area (172–184 m2/g), large packing density (1.81–1.83 cm3/g), rich redox-active nitrogen (4.5 atom%) and oxygenic (12.0 atom%) functionalities. As electrode for supercapacitor, the HCDC achieves a high gravimetric capacitance of 312F/g at 1.0 A/g (vs 258F/g of commercial AC) and the value can be maintained 223F/g at 20 A/g, showing a high rate capability of 71.5%. Particularly, because of the large packing density, the HCDC exhibits an excellent volumetric supercapacitor performances: ultrahigh volumetric capacitance of 567F/cm3 (vs 165F/cm3 of commercial AC) and large energy density of 27.8 Wh/L@1820 W/L (vs 7.5 Wh/L@576 W/L for commercial AC) and superlong cycling stability with near 100 capacitance retention after continual 30 000 cycles at large current density of 9.0 A/g, suggesting a promising application for practical energy storage devices. [ABSTRACT FROM AUTHOR]

Three alkaline metal carbonates of MgCO 3 , CaCO 3 and BaCO 3 with different morphology, surface basicity and thermal stability were used as templates to find the template effect towards the morphology, oxygen species as well as supercapacitor performance of the derived nanocarbons. [Display omitted] • Three alkaline carbonates were adopted as catalytic templates for the fabrication of nanocarbons. • Residual oxygen and morphology of nanocarbons are greatly influenced by the nature of templates. • Residual oxygen in final products mainly exists in forms of redox-active carbonyl and hydroxyl. • The derived MgC displays superior surface area and supercapacitor performance. Nanocasting techniques are widely adopted for the fabrication of nanocarbons. However, there is little research on the effect of template nature on the physicochemical properties and performances of the nanocarbons. Herein, we investigated how the morphology, oxygen species as well as supercapacitor performance of the derived nanocarbons were governed by the morphology, surface basicity and thermal stability of MgCO 3 , CaCO 3 and BaCO 3 when the alkaline metal carbonates were used as templates. Using MgCO 3 as catalytic template, the MgC973 produced after carbonization at 973 K has ultrathin nanosheet morphology (∼20 nm), large specific surface area (952 m2/g), and superior supercapacitor performances, showing high capacitance of 421F/g@1.0 A/g (maintaining 306F/g@20 A/g), and large energy density of 31.1 Wh/kg@1000 W/kg. The superiority can be ascribed to the ultrathin morphology and thermal instability of the MgCO 3 template, which upon decomposition generates CO 2 and in situ activates the carbon skeleton. Moreover, the surface alkalinity of templates is conducive to the retention of electrochemically active oxygen, and BaC973 is with oxygen content (9.1 atom%) higher than MgC973 (7.9 atom%) and CaC973 (8.8 atom%). The present work provides insightful ideas for the synthesis of unique carbon materials with specific functionalities through the selection of suitable templates. [ABSTRACT FROM AUTHOR]

Carbon-based electrodes are usually poor in volumetric supercapacitor performance in terms of volumetric capacitance (<200 F/cm3) and energy density (usually <10 Wh/L) resulted from low packing density. Herein, we propose a strategy for the preparation of nanocarbon electrodes that are ultrahigh in volumetric supercapacitor performance by creating nanocarbon with high packing density and rich pseudocapacitive nitrogen doping, in which the nitrogen doping is to provide extra capacitance. The derived nanocarbons (ZHNCs) have not only large packing density of 1.14–1.49 g/cm3 and rich nitrogen content (12.3–24.8 atom%), but also homogeneous element distribution. Benefited from the synergetic effect of the above characteristics, the ZHNCs-based electrodes exhibit superior volumetric performances of ultrahigh capacitance of 528 F/cm3 in 1.0 M H 2 SO 4 and 465 F/cm3 in 6.0 M KOH, large energy density of 26.8 Wh/L at 2682 W/L, and impressive cycling stability with about 95% capacitance retention after continual charge/discharge of 20 000 cycles at current density of 20 A/g, indicative of potential applications in the fields of energy storage. [Display omitted] • Nanocarbons (ZHNCs) with high density and rich nitrogen (24.3 atom%) were fabricated. • ZHNCs achieves large gravimetric- (464 F/g) and ultrahigh volumetric capacitances (528 F/cm3). • The ZHNCs based electrode shows a large energy density of 26.8 Wh/L at 2682 W/L. • ZHNCs electrode exhibits superior stability with about 95% capacitance retention after 20 000 cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • An all-solid-state (ASS) strategy without using any solvents and activators was developed. • The ASS strategy derived carbon owns abundant nitrogen species and large packing density. • The resultant product show superior supercapacitor performances with both high gravimetric and volumetric performances. Template synthesis of porous carbon with rich functionalities by a scalable strategy without using any solvents and activators will be a green and promising route. Herein, we reported an all-solid-state synthesis strategy by mixing glucose and graphitic carbon nitride (g -C 3 N 4) by milling and then undergoing a segmented carbonization in which first at low temperature of 573 K to polymerize sucrose onto g -C 3 N 4 , then at high temperature of 973 K to carbonized the composite to obtain a porous carbon (denoted as GNC) with abundant nitrogen species over 20 atom% and large packing density (0.91–1.25 g cm−3). Due to the features of large packing density and rich electrochemically-active N species, as electrode for supercapacitive energy storage, the developed GNC exhibit a comparable energy storage level with both high gravimetric energy density of 26.8 Wh kg−1@1000 W kg−1 and volumetric energy density of 30.8 Wh L−1@1150 W L−1, suggesting a potentiality in energy storage field. Importantly, the present strategy owns characteristics of ease of operation, green and scalable, which would be a promising synthesis route towards the fabrication of functional carbon utilizing in many fields like sorption & separation, catalysis, energy storage and so on. [ABSTRACT FROM AUTHOR]

[Display omitted] • A solvent-freely polymerizing catechol and paraformaldehyde method was developed. • The present method derived carbon owns high nitrogen functionalties of 21.7 atom%. • The derived carbon achieves high energy density of 34.5 Wh L−1@1370 W/L. Fabrication of nitrogen functionalized carbon with high nitrogen content (over 10 atom%) by a route with simplified and solvent-free procedures would be both economically and environmentally scalable. We demonstrate here a simple solvent-free route towards synthesizing porous carbon doped by nitrogen functionalties (21.7 atom%) involving solid state catalytic polymerization of catechol and paraformaldehyde with g -C 3 N 4 as catalyst. Upon high-temperature treatment, the vaporized catechol and paraformaldehyde would be in situ polymerized on the surface of g -C 3 N 4 forming the composite of g -C 3 N 4 @resin. During the following carbonization process, the resin was carbonized to carbon skeleton, while the g -C 3 N 4 would be decomposed in situ doping the carbon skeleton. In our design, the avoidance of solvents in the whole synthesis procedure and the usage of g -C 3 N 4 in the preparation not only reduces the waste production, but also introduces high nitrogen species (21.7 atom%). As electrode for supercapacitor, the resultant SFC based electrode achieves a large specific capacitance of 391F cm−3@1.0 A/g and high energy density of 34.5 Wh/L@1370 W/L, suggesting a potential as electrode for energy storage. And more, the developed method offers a promising and alternative route for the fabrication of new materials in manner of green and environmentally friendly. [ABSTRACT FROM AUTHOR]

As an industrial material for supercapacitive energy storage, commercial activated carbons (AC) could achieve a satisfactory gravimetric performances by electric double layered capacitance (EDLC) due to their rich microporosity, but the volumetric performances are usually poor resulted from the low packing density. Herein, we presented a strategy to address this tradeoff relationship and to achieve both high gravimetric and volumetric performance by filling the macro/mesoporosity with extra nitrogen doped carbon. The reconstructed activated carbon could inherit most of microporosity from the parent AC, while the macro/mesoporosity of them was greatly decreased, resulting in increase of packing density and the improvement of surface hydrophilicity. Benefited from the increase of packing density and maintenance of microporosity, the resultant activated carbon achieves greatly enhanced energy storage level including three times higher capacitance of 384 F cm−3@ 1.0 A/g (vs 128 F cm−3@ 1.0 A/g for pristine AC), high rate capability of 73.4% (vs 59.2% for pristine AC), larger energy density of 27.5 Wh L−1@ 900 W L−1 (vs 10.0 Wh L−1@747 W L−1). Importantly, the present strategy provides a facile and unique method to process activated carbon, which offers a possibility improving the energy storage level of the commercial activated carbon. [Display omitted] • Commercial activated carbon (AC) was processed by filling the macro/mesoporosity. • The filled AC owns increased packing density and more nitrogen functionalities. • The filled AC achieves greatly enhanced supercapacitor performances. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co 3 O 4 nanoneedle arrays is grafted on V 2 O 5 nanosheet arrays to form VNSAs/CNNAs. • The VNSAs/CNNAs composite shows a high C s value of 1023 F g−1at 5 mV s−1. • The VNSAs/CNNAs composite can work under a large voltage window of 1.6 V. • The VNSAs/CNNAs composite has a high E d value of 127.3 Wh kg−1 at 400 W kg−1. • The high performance is ascribed to the synergistic effect of V 2 O 5 and Co 3 O 4. In this work, two-dimensional V 2 O 5 nanosheet arrays/one-dimensional Co 3 O 4 nanoneedle arrays (2D VNSAs/1D CNNAs) composite is successfully prepared on nickel foam substrate. A variety of structural characterization techniques (SEM, XRD, EDS, TEM, and XPS) show that the as-prepared composite is V 2 O 5 monocrystal with a layered structure grafting by Co 3 O 4 polycrystal with a 1D needle-like structure. The VNSAs/CNNAs composite is used as supercapacitor electrode material. In a three-electrodes system, it shows high specific capacitance (C s) values (1023 F g−1@5 mV s−1 from CV curve and 826 F g−1@0.5 A/g from GCD curve), a high coulombic efficiency (98.6 %@10 A/g), a good cyclic stability (92.7 % after 6000 cycles), a low charge transfer resistance (2.7 Ω), and a fast ionic diffusion rate (2.01 × 10−8 cm2 s−1). In a two-electrodes system, the assembled VNSAs/CNNAs//VNSAs/CNNAs symmetric supercapacitor has C s values of 445 F g−1@5 mV s−1 and 363 F g−1@0.5 A/g. Its cycle stability and rate capability could reach up to 92.3 % and 90.7 % after 6000 cycels, respectively. It also shows a high energy density (E d) of 127.3 Wh kg−1@400 W kg−1 and can retain 72.2 Wh kg−1@8000 W kg−1. The excellent electrochemical properties indicate that VNSAs/CNNAs composite can greatly increase the E d of supercapacitors. [ABSTRACT FROM AUTHOR]

In this paper, porous NiO nanoflake arrays@V 2 O 5 nanoparticles (PNFAs@VNPs) composite is fabricated on Ni foam through a facile hydrothermal process. The PNFAs@VNPs composite has an ordered array structure, a large active surface, and favorable physical stability. Based on the CV profile, the specific capacitance can achieve 950 F g−1 and remain stable at 95.8 % of the original value after 5000 loops. When the PNFAs@VNPs composite is assembled into a symmetric supercapacitor, the energy density can reach 67.0 W h kg−1 at a power density of 550 W kg−1. Even if the power density rises to 11,000 W kg−1, the energy density can still be held at 25.3 W h kg−1. The high supercapacitive property of the PNFAs@VNPs composite is owed to the synergic action of the PNFAs and VNPs. The PNFAs@VNPs composite with the advantages of battery-type and capacitive-type pseudocapacitances has higher charge transfer dynamics, making it a potential supercapacitive electrode material. [Display omitted] • Porous NiO nanoflake arrays (PNFAs) is successfully prepared on nickel foam. • V 2 O 5 nanoparticles (VNPs) are loaded on the PNFAs to form a hierarchical structure. • The PNFAs@VNPs has the advantages of Faraday and intercalation type pseudocapacitor. • The PNFAs@VNPs shows a specific capacitance of 950 F g−1at 5 mV s−1. • The PNFAs@VNPs supercapacitor has an energy density of 67.0 W h kg−1 at 550 W kg−1. [ABSTRACT FROM AUTHOR]

V 2 O 5 nanobelt arrays (VNBAs) is fabricated on Ni foam by using an easy hydrothermal route and then NiO nanosheet arrays (NNSAs) is grown on VNBAs by using a simple chemical bath deposition approach to form VNBAs/NNSAs composite. It is found that the monocrystalline VNBAs with a lamellar structure is uniformly distributed on nickel foam and the polystalline NNSAs with a close packed structure is closely covered on the VNBAs. CV, GCD, EIS and CA electrochemical techniques are used to test the supercapacitive properties of the VNBAs/NNSAs composite. The single electrode displays a high specific capacity of 875 F g−1, a good cycling stability of 96.1%, a small charge transfer resistance of 1.32 Ω and a rapid ion diffusivity of 2.5 × 10−8 cm2 s−1. The symmetric supercapacitor combined by the VNBAs/NNSAs displays a large energy density of 120.1 W h kg−1 at 400 W kg−1 and it retains 68.3 W h kg−1 at 8000 W kg−1. The VNBAs/NNSAs composite with high electrochemical performance is a potential supercapacitor electrode material. [Display omitted] • The V 2 O 5 nanobelt arrays (VNBAs) is successfully prepared on a nickel foam. • The NiO nanosheet arrays (NNSAs) is compounded on the VNBAs to form a hierarchy. • The VNBAs/NNSAs shows a high specific capacitance of 875 F g−1 at 5 mV s−1. • The VNBAs/NNSAs has an energy density of 120.1 W h kg−1 at 400 W kg−1. • The high performance of the VNBAs/NNSAs are ascribed to its synergistic effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • V 2 O 5 nanobelt arrays@RuO 2 nanosheet arrays (VNBs@RNSs) is prepared on a nickel foam. • The VNBs@RNSs electrode shows a specific capacitance of 971F g−1 at 5 mV s−1. • The VNBs@RNSs supercapacitor has an energy density of 174.2 W h kg−1 at 450 W kg−1. • The cyclic steadiness of the supercapacitor is retained at 80.4% after 10,000 cycles. • The high performance of VNBs@RNSs is ascribed to their synergistic effect. V 2 O 5 nanobelt arrays (VNBs) are directly synthesized on porous nickel as the primary structure, and then the VNBs are completely covered by RuO 2 nanosheets (RNSs) as the secondary structure to create a core–shell heterojunction. The as-prepared VNBs@RNSs core–shell heterojunction is systematically researched through SEM, EDS, XRD, XPS and TEM, and the growth process is investigated in detail by sampling at different time. The VNBs@RNSs has a superb specific capacitive value of 971F g−1 at a voltage scanning speed of 5 mV s−1, a better cyclic steadiness of 80.4 % after recycling 10,000 times, a small charge transferring resistance value of 1.8 Ω and a fast effective diffusion coefficient of 1.01 × 10−8 cm2 s−1 calculated by CV, GCD, AC impedance and CA electrochemical techniques in a three-electrode testing system. A symmetrical electrochemical capacitor assembled by the as-prepared VNBs@RNSs electrode material has a superior energy density of 174.2 W h kg−1 at a power density of 450 W kg−1 and still retains 95.9 W h kg−1 at 9000 W kg−1 in a two-electrode testing system. The improved supercapacitive performance makes the VNBs@RNSs as a superior electrode material for supercapacitor. [ABSTRACT FROM AUTHOR]

[Display omitted] • V 2 O 5 nanobelt arrays@RuO 2 nanosheet arrays (VNBs@RNSs) is prepared on a nickel foam. • The VNBs@RNSs electrode shows a specific capacitance of 971F g−1 at 5 mV s−1. • The VNBs@RNSs supercapacitor has an energy density of 174.2 W h kg−1 at 450 W kg−1. • The cyclic steadiness of the supercapacitor is retained at 80.4% after 10,000 cycles. • The high performance of VNBs@RNSs is ascribed to their synergistic effect. V 2 O 5 nanobelt arrays (VNBs) are directly synthesized on porous nickel as the primary structure, and then the VNBs are completely covered by RuO 2 nanosheets (RNSs) as the secondary structure to create a core–shell heterojunction. The as-prepared VNBs@RNSs core–shell heterojunction is systematically researched through SEM, EDS, XRD, XPS and TEM, and the growth process is investigated in detail by sampling at different time. The VNBs@RNSs has a superb specific capacitive value of 971F g−1 at a voltage scanning speed of 5 mV s−1, a better cyclic steadiness of 80.4 % after recycling 10,000 times, a small charge transferring resistance value of 1.8 Ω and a fast effective diffusion coefficient of 1.01 × 10−8 cm2 s−1 calculated by CV, GCD, AC impedance and CA electrochemical techniques in a three-electrode testing system. A symmetrical electrochemical capacitor assembled by the as-prepared VNBs@RNSs electrode material has a superior energy density of 174.2 W h kg−1 at a power density of 450 W kg−1 and still retains 95.9 W h kg−1 at 9000 W kg−1 in a two-electrode testing system. The improved supercapacitive performance makes the VNBs@RNSs as a superior electrode material for supercapacitor. [ABSTRACT FROM AUTHOR]

In this paper, four NiO nano-arrays with different morphology on nickel foam were synthesized by a hydrothermal approach. It is found that the porous single crystal NiO nanoflake array (PNFA) holds superior electrochemical properties, better than the other three samples. The specific capacitance of the PNFA obtained from the cyclic voltammetry curve was 716 F g−1 and that derived from the galvanostatic charge-discharge curve was 589 F g−1 in three-electrode system. The cycling stability of the PNFA could retain as high as 92.4% after 5000 cycles. When the PNFA was assembled into a symmetric supercapacitor, the PNFA//PNFA device exhibited an energy density of 39.3 W h kg−1 (at 550 W kg−1) and could retain 13.2 W h kg−1 (at 11,000 W kg−1) in two-electrode system. Furthermore, the SEM, XRD, TEM and XPS results prove that the PNFA is a special porous single crystal structure, which combines the advantages of the cross-linked single crystal structure for facilitating electron transfer and the porous structure providing more interfaces for insertion/exit of electrolyte ions from the active material. It indicates that the PNFA is a potential electrode material for supercapacitors. [Display omitted] • Porous single crystal NiO nanoflake array (PNFA) is directly grown on nickel foam. • The PNFA is prepared by a facile hydrothermal method following an annealing process. • The PNFA combines the advantages of porous material and single crystal material. • The PNFA shows a specific capacitance of 716 F g−1 at a scan rate of 5 mV/s. • The PNFA//PNFA supercapacitor has an energy density of 39.3 W h kg−1 at 550 W kg−1. [ABSTRACT FROM AUTHOR]