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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]

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]

This study aims to optimize the fabrication parameters of nickel‑iron phosphate (NiFe-P) electrode to achieve a high areal capacity electrode for supercapattery. The fabrication of binder-free NiFe-P electrode on nickel foam (NF) employs a one-step hydrothermal synthesis method. Further, central composite design (CCD) under the response surface methodology (RSM) is used to optimize the electrode's performance. The factors evaluated are synthesis temperature (60 to 180 °C), time (6 to 24 h), and the molar ratio of precursor solution (1:3, 1:1, 3:1 of Fe: Ni), whereas the response is the areal capacity of NiFe-P electrode at the scan rate of 3 mV/s in a standard three-electrode cell system. The optimal temperature, time, and molar ratio (Fe:Ni) are determined to be 100 °C, 14 h, and 3:1, respectively. The model is confirmed within the confidence interval and prediction as well as comparable with a 10% percentage error between the experimental and predicted specific capacity. The specific capacity of the optimized electrode is 446 C/g at a scan rate of 3 mV/s using cyclic voltammetry (CV) and 413.75 C/g at a current density of 1 A/g in 1 M KOH using a standard three-electrode cell system. Supercapattery is fabricated by combining NiFe-P and activated carbon electrodes (NiFe-P//AC) as positive and negative electrodes, respectively, to evaluate the two-electrode cell system. The results show the maximum power density of NiFe-P//AC supercapattery is 2250 W/kg at an energy density of 45.6 Wh/kg. Furthermore, the NiFe-P//AC supercapattery demonstrated excellent stability and coulombic efficiency by retaining 87.6% and 98.7% of the initial specific capacity values and coulombic efficiency, respectively. • Binder-free NiFe-P electrode was prepared using hydrothermal synthesis. • The fabrication parameters of the electrode were optimized using DOE. • The electrochemical performance of the electrodes was investigated. • Maximum power density of NiFe-P//AC supercapattery is 2250 W/kg at an energy density of 45.6 Wh/kg. • NiFe-P//AC supercapattery retained 87.6% and 98.7% of the initial specific capacity values and coulombic efficiency. [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]

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] • Ternary metal oxide electrodes are prepared by a feasible green hydrothermal method. • Nanografting effectively increases active interfaces with interpenetrating channels. • These electrodes demonstrate an improved specific capacitance of 788F g−1. • The symmetrical supercapacitors show an energy density of 138 W h kg−1 at 450 W kg−1. • The steadiness of these supercapacitors is retained at 93.5 % after 5000 cycles. Supercapacitors with improved specific capacitance, long cycling life, high power density and energy density are fabricated to close the gap between traditional and emerging energy storage. We develop interactive ternary metal oxides nano-ribbon electrodes used to assemble symmetric supercapacitor. The well-aligned vanadium oxide ribbon arrays act as the matrix, growing from nickel oxide/nickel substrate and then being grafted by manganese oxide nanoparticles. These tri-metallic oxides are formed in a cost-effective and green hydrothermal chemistry. The electrodes composed of ribbon arrays retain their crystallographic structure during charging and discharging processes, enabling steadiness at 83.6 % after 10,000 cycles. These as-prepared electrodes demonstrate a specific capacitance of 788 F g−1 at 5 mV s−1. The symmetrical supercapacitors are assembled using triple component electrodes, achieving a high energy density of 138 W h kg−1 at a power density of 450 W kg−1. These binderless single-cell devices are reported with a simplified design showing 10–20 times higher energy density in comparison with reported results of the V 2 O 5 -MnO 2 system. The nanografting results in reactive interfaces with interpenetrating channels for efficient ion transport and electron conduction. The advances to design nanostructured supercapacitor materials are based on these heterojunction arrays to enhance their supercapacitive performances. [ABSTRACT FROM AUTHOR]