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This paper reports the capacitive behavior of N-enriched carbon nanofiber/MnO 2 /carbon nanofibers with a triple layer structure (N-rich C@MnO 2 @C) prepared by continuous electrospinning. N-functional groups were introduced into the upper (or lower) or middle layer of the triplex and the structures and electrochemical properties of each are compared. N-functional groups introduced into the lower (or upper) layer induce a high surface area, numerous pyrrolic-N, high electrical conductivity, and low contact angle in N-rich C@MnO 2 @C composites. The optimized material provides a specific capacitance of 201 Fg−1 (1 mAcm−2) with more than 84% specific capacitance retention in a symmetric two-electrode cell configuration using a 6 M KOH electrolyte. In addition, it shows a maximum energy density of 24.8 and 13.41 Whkg−1 at power densities of 400 and 10,000 Wkg−1 with excellent cycling stability (95% capacity retention after 10,000 cycles at 1 mAcm−2). An assembled asymmetric device, consisting of optimized N-rich C@MnO 2 @C as the positive electrode and C@MnO 2 @C as a negative electrode, delivers a high energy density of 41 Whkg−1 at a power density of 400 Wkg−1. This material has excellent potential as an electrode for constructing high-voltage asymmetric supercapacitors in aqueous electrolytes. [Display omitted] [ABSTRACT FROM AUTHOR]

When producing hydrogen and carbon black from hydrocarbons using plasma, the economic feasibility must be ensured. In this study, the produced carbon black was heat-treated at various temperatures and applied as a conductive agent in lithium secondary batteries to evaluate its potential. When plasma was discharged into the benzene solution, carbon black particles (primary particles, 20–50 nm) were generated along with hydrogen gas, and were aggregated to grow secondary particles 400–500 nm in size. When carbon black was heat-treated, the crystallinity increased as the heat-treatment temperature increased, and multiple nanoshells in the form of pentagons or hexagons were formed by continuous long multi-graphene. Carbon black produced by heat treatment at 1500 °C showed the highest capacity and excellent charge/discharge characteristics, which was attributed to its high electrical conductivity and specific surface area. The carbon black prepared in this study could be a good candidate to replace commercialised Super-P in the future. [Display omitted] • Plasma was discharged to the benzene to produce hydrogen gas and carbon black particles. • The primary carbon black particles were aggregated to constitute secondary structures. • The heat-treated carbon black has improved electrical conductivity and crystallinity. • The heat-treated carbon black was applied to the conductive agent of the lithium secondary battery. • The capacity and charge/discharge characteristics of carbon black heat treated at 1500 °C were the best. [ABSTRACT FROM AUTHOR]

Triple-layered boron-containing carbon nanofibers (CNFs) with hollow channels (PPMPB) are fabricated via step-by-step electrospinning for high-performance freestanding supercapacitors. Polyacrylonitrile (PAN)-based CNFs in the first layer are chosen as the support layer material because of their excellent chemical stability and electrospinnability. The well-developed hollow channels provided fast ion diffusion in the second layer of PAN/poly(methyl methacrylate) (PMMA)-based CNFs. The surface boron functional groups constituting the third layer contribute to the pseudo-capacitance. The symmetric supercapacitor of the PPMPB electrodes delivers a maximum specific capacitance of 180 Fg−1 at 1 mAcm−2, a high energy density of 22.38 Whkg−1 at a power density of 400 Wkg−1, and an excellent retention rate of 96% after 10,000 cycles in aqueous solution. The excellent electrochemical performance is attributed to the unique sandwich nanostructure with a three-layer structure, in which the factors representing the electrochemical properties of each layer do not interfere with each other. Therefore, a moderate amount of boron and the high surface area of the triple-layer structured PPMPB can be fully utilized as an excellent conductive network and electroactive sites, which is expected in a high-performance supercapacitor electrode. [Display omitted] • Triple-layered boron-containing CNFs were fabricated by step-by-step electrospinning. • The CNFs in the first layer provide active adsorption sites for EDLC. • Hollow core present in the interlayer serves as an excellent conductive network. • A moderate amount of boron in the third layer is utilized as the electroactive site. • Symmetric PPMPB(20) electrode showed good rate capability and long cycle life. [ABSTRACT FROM AUTHOR]

The aim of this study is to develop the templateless fabrication of hierarchical porous carbon nanofiber (CNF)/MnO 2 composites (PMnCD) derived from polyacrylonitrile (PAN)/cyclodextrin (CD) and investigate their morphological and electrochemical properties to determine the different capabilities of inclusion complexes (ICs) formed by α-CD, β-CD and γ-CD. Among the three CD phases, the PMnCD(β) composite using β-CD exhibits a hierarchical porous structure with large specific surface area of 499 m2g-1, and total pore volume of 0.32 cm3g-1, which helps with adsorption efficiency and accumulation of hydrated molecules for double-layer formation. In addition, the numerous mesopores and nitrogen functionalities of the PMnCD(β) composite provide fast diffusion channels for electrolyte ions and higher attractive interactions with electrolyte ions through the pseudocapacitive character. As a result, the PMnCD(β) electrode has a high specific capacitance of 228 Fg-1 at 1 mAcm−2, maximum energy density of 25.3–16.0 Whkg−1 in the power density range of 400-10,000 Wkg-1, and excellent cycling stability of more than 94% after 10000 cycles in aqueous solution, thereby offering potential applications for supercapacitors. Image 1 • Hierarchical porous PMnCD is fabricated by electrospinning without a template. • β-CD stabilizes and encapsulates MnCl 2 through the good size match of β-CD and MnCl 2. • PMnCD(β) shows a large specific surface area for accumulation of ions. • Many mesopores and nitrogen groups of PMnCD(β) provide fast ion diffusion. • Hierarchical porous PMnCD(β) is applied to high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Hierarchically structured carbon nanofiber/graphene/MnO 2 (CGMn) hybrid with oxygen and nitrogen functionalities was fabricated in the form of a web via electrospinning as an electrode material for supercapacitors. The CGMn electrode exhibited a high capacitance (225 Fg −1 at 1 mAcm −2 ), enhanced energy and power efficiency (15.8–13.6 Whkg −1 in the power density range of 197–4000 Wkg −1 ), and excellent capacitance retention (13% of the initial value at a discharge current of 20 mAcm −2 ) in a 6 M KOH aqueous electrolyte, because of the combination of the double-layer capacitance and the pseudocapacitive character associated with the surface redox-type reactions. The porosity and the number of heteroatoms of the CGMn composite were adjusted by changing the PMMA concentration and carbonization temperature. Therefore, the oxygen- and nitrogen-containing hierarchical porous CGMn hybrid prepared by a simple method is a promising candidate as an electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

Abstract: Metallic-impurity-free, nano-sized, short multi-walled carbon nanotubes (MWCNTs) in the form of a tape have been synthesized using stabilized arc discharge under atmospheric conditions. The long, thin tape consisted of crystalline MWCNTs exhibiting indiscernibly blurred interior lattice images and a narrow, hollow core, as well as small and large nanoparticles. The disordered interior regions of the tubes were enlarged into hollow cores by thermal treatment at 2000°C, suggesting that the elongated tubes crystallize via a super-cooling process. The proposed macroscopic model for the growth process of the tubes in the arc resembles the fiber formation of a recently reported electrospinning process; thermally activated carbon ion and vapor create viscous carbon clusters, and the built-up charge in the clusters leads to the elongation into tubules. [Copyright &y& Elsevier]

Abstract: Rubber composite sheets filled with 5wt.% and 30wt.% of highly aligned carbon nanotubes (CNTs) were fabricated through conventional rubber technology. The alignment of CNTs was possibly derived from dragged shear force during the optimized milling process. The selective alignment of CNTs led to enhancements in the elastic modulus, thermal conductivity, electrical conductivity, and electromagnetic shielding property, compared to neat rubber sheet. [Copyright &y& Elsevier]

To store more energy in limited spaces, the volumetric performance of energy storage devices used in electric vehicles and portable electronics has attracted more research attention than their gravimetric performance. Herein, we describe the preparation of N/O co-doped single-walled carbon nanohorns (SWCNH) using chemical vapor deposition with pyridine followed by acid treatment to obtain a supercapacitor electrode material with high specific volumetric capacitance. The synthesized N/O co-doped SWCNH (N and O contents of 6.1 and 9.1 at%, respectively) electrode had a higher bulk density (1.05 g cm−3) than that of the pristine SWCNH electrode (0.86 g cm−3). Moreover, the N/O co-doped SWCNH supercapacitor electrode exhibited drastically increased specific volumetric, gravimetric, and areal capacitances (123 F cm−3, 117 F g−1, and 91.4 μF cm−2, respectively) in 1 M H 2 SO 4 electrolyte, compared with those of a pristine SWCNH electrode (36 F cm−3, 42 F g−1, and 11.4 μF cm−2, respectively). The superior electrochemical performances are associated with enhanced pseudocapacitive contribution and high bulk density of electrode upon N/O co-doping. The simple method described herein for producing SWCNH electrodes with high bulk density and high specific volumetric capacitance should contribute to the development of supercapacitors with high volumetric performance. Image 1 • N/O co-doped SWCNHs are prepared using a straightforward method. • N/O co-doped SWCNHs can be used as active materials in supercapacitor electrodes. • Electrochemical performance of SWCNHs is enhanced by N/O co-doping. • N/O co-doping increases pseudocapacitive contribution and electrode bulk density. [ABSTRACT FROM AUTHOR]

The unitized regenerative fuel cell (URFC) system has attracted significant attention and interests because of its round-trip energy conversion with high energy density. However, the identification of low-cost bipolar (BP) plate with higher corrosion resistance is required to produce a sustainable system. In this work, we investigated the possibilities of using cost-effective lead (Pb) metal-based plate as a BP plate material for URFC system. To further enhance the advantageous properties of Pb plate, silver (Ag) was coated onto the Pb plate. Different types of structural and microstructural analyses (XRD, XPS, SEM, EDAX, and mapping) were conducted to characterize the properties of Pb-based plate and the presence of Ag-coated layer on the surface of Pb plate. When compared with the Pb plate, the Ag-coated Pb plate exhibited a higher water contact angle. The obtained water contact angles of Pb and Ag-coated Pb plates were 77.83° and 92.21°, respectively. The obtained water contact angle of the Ag-coated Pb plate is quite acceptable in the URFC system because it offers exceptional advantages during the URFC operation. Furthermore, the interaction between Pb plate and Ag coated layer resulted in an efficient electrochemical performance. Based on these results, we could conclude that the Pb-based BP plate can be possibly considered for the URFC applications. • The viabilities of cost-effective Pb based plate identified as a BP plate for URFC. • A new kind of BP material for round-trip energy conversion device of URFC system. • The higher water contact angle of Ag–Pb BP plate is more desirable to the URFC. • Ag coating on Pb surface can effectively increase the corrosion resistance. [ABSTRACT FROM AUTHOR]

In the literature, fine structuring and mixing of the radial breathing mode frequencies ( ω RBM ) due to intertube interactions ( Ω int ) for specific inner tubes in free-standing isolated double-walled nanotubes (DWNTs) have been addressed. Questions and arguments related to the Ω int nature and its dependence with the nanotube's growth processes have also been addressed. Later, studies involving bundled (innermost tubes) and isolated (innermost and middle tubes) of triple-walled nanotubes (TWNTs) for diameters between 0.5 and 1.7 nm found no ω RBM fine structuring or mixing but suggested that the Ω int depends on the tube's metallicity. Here, Raman Spectroscopy is combined with transmission electron microscopy (TEM) to show that for bundled DWNTs and TWNTs measured in a broad diameter range (0.5 ≤ d t ≤ 2.8 nm) three effects seem to be fundamental to explain the ω RBM behavior of their constituent tubes: interactions with the external environment, metallicity-independent Ω int and curvature effects due to σ-π bonds re-hybridization. Our results display no evidence of ω RBM mixing but show that Ω int has no apparent dependence with the growth process and that Ω int has the same nature of the tube interactions with the environment. The manuscript also discusses the thus far elusive TWNT outermost tubes ω RBM . Image 1 [ABSTRACT FROM AUTHOR]

In recent years, interest in noble metal-free catalysts for the hydrogen evolution reaction (HERs) and supercapacitor (SCs) applications has emerging for altering the high-price of the catalyst and prohibiting the dissolution/phase change of the catalysts in long term performances. In this study, we present a novel noble metal-free electrocatalyst composed of holey carbon nanotubes (h-CNTs) and MXene nanocomposites for electrocatalytic HERs and SCs. By wrapping h-CNTs into the surface of the MXene sheet, we address the limitations of pure MXenes and achieve superior electrochemical performance. Specifically, MXenes containing 20 wt% h-CNTs exhibit a low overpotential of 192 mV versus RHE and a small Tafel slope of 48.95 mV dec−1 at 10 mA cm−2 in 0.5 M H 2 SO 4 with excellent cyclic stability. The presence of C O functional groups and the existence of a holey in CNT probably enhanced the electrocatalytic activity. The excellent wrapping of h-CNTs on MXene efficiently exhibited the HER performances because of their individual effect and the arising of synergy, where the excellent interaction attained between the immobilized atom in the h-CNT and MXene. For SCs, MXenes containing 15 wt% h-CNTs display the highest specific capacitance of 404 F g−1 at 4 A/g with excellent cyclic stability, maintaining 80% capacity after 4000 cycles at 10 A/g at ambient temperature in 2 M KOH. Furthermore, the MXene@h-CNT nanocomposite was subjected to density functional theory (DFT) calculation. Our findings demonstrate that the newly developed nanocomposite offers a promising route to boost HER and SCs performance for a wide range of technological applications. [Display omitted] • Holey carbon nanotubes (h-CNTs) were synthesized by the KOH activation process. • MXene nanosheets were synthesized by the selective etching method. • h-CNTs wrapped on MXene nanocomposites for electrocatalytic HERs and SCs. • MXene@h-CNT exhibited well HER performance 192 mV and a small Tafel slope of 48.95 mV dec−1 at 10 mA cm−2. • MXene@h-CNT exhibited good supercapacitor performance (capacitance of 404 F g−1 at 4 A/g). [ABSTRACT FROM AUTHOR]

Coupling graphene-based materials with SiC nanostructures is one of the most feasible strategies to improve the photocatalytic CO 2 reduction performance. Here, we synthesized the vertical graphene (VG) sheets on the SiC nanowires achieved from rice husks to form the VG@SiC/C composite, in which the VG sheets possess high surface area, excellent electrical conductivity, and chemical stability, and the SiC nanowires have a suitable bandgap for sunlight absorption. The resulting VG@SiC/C composite provides an enhanced photocatalytic reduction of CO 2 to CO and CH 4 , yielding CO and CH 4 evolution yields of 25.5 and 2.3 μmol g−1 h−1, respectively. The achieved CO yield is maximal so far among the SiC-based photocatalysts. The defective VG sheets promote the absorption of sunlight, enhance the CO 2 adsorption and activation, increase the separation of photogenerated electron-hole pairs, improve the activity of photocatalyst, and thereby prompt the photocatalytic reduction of CO 2 to CO with high yield and selectivity. We report that the vertical graphene sheets on the surface of rice-husk-derived SiC/C composite demonstrate the enhanced photocatalytic performance of CO 2 reduction to CO with high yield and selectivity under simulated solar irradiation. [Display omitted] • The VG sheets could be achieved on the surface of rice-husk-derived SiC to form the VG@SiC/C. • The superior photocatalytic CO 2 performance was ascribed to the special structure and features of VG@SiC/C. • The VG can prompt the sunlight absorption, the CO 2 adsorption and activation, and the separation of electron-hole pairs. • The VG@SiC/C showed photocatalytic reduction of CO 2 with a CO yield of 25.5 μmol g−1 h−1 and a selectivity of 91.84%. [ABSTRACT FROM AUTHOR]

During thermal treatment of carbon materials, unstable edge sites can easily convert to structurally stable loop structures. Hence, in the present work, carbon edges are physically passivated via high-temperature treatment in the presence of boron atoms to accelerate loop formation. The highly accelerated loop formation, along with stacking multi-layers at the carbon edges, is systematically investigated via high resolution transmission electron micro microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and thermal gravimetric analysis (TGA). The boron-added carbon nanofibers (CNFs) at high temperature exhibit a greatly enhanced electrical conductivity due to the high mobility of boron atoms within the carbon structure. In particular, engineering of the loop structures on the carbon edges can alter the overall electrocatalytic activities of the carbon-based materials, as demonstrated in the reductive conversion of 4-nitrophenol (4-NP) and in the hydrogen evolution reaction (HER). This work not only suggests suitable methods for carbon edge passivation, but also opens up a route towards the advanced design of high-stability carbon materials in various fields. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The effects of two different halogen dopants (bromine and iodine) at different concentrations on the higher frequency modes (the so-called G and G′ bands) of the Raman spectra of double-wall carbon nanotube (DWCNT) “buckypaper” are investigated. The effects of dopants on different DWCNT configurations (metallic inner/semiconducting outer and vice versa) are studied by changing the laser excitation energy. The doping causes the loss of the Breit–Wigner–Fano line shape and the appearance of less metallic behavior. An increase of the relative intensity of the G+ band, which is more sensitive for the outer metallic tubes, is clearly observed with increasing Br2 concentration in the sample. By analysis of the G+ band and the G′ band it is possible to measure the changes in the electron–phonon coupling, due to the charge-transfer between the dopant (Br2 or I2) and the tubes in the DWCNT. The doping effect causes an upshift of the G+ band and a suppression of the contribution of the inner tubes to the G′ band signal and as a consequence, the observed G′ band is dominated by the contribution from the outer tubes. [Copyright &y& Elsevier]

Abstract: The electroactive shape memory of carbon nanotube-filled polyurethane composites, prepared by conventional blending, in situ and cross-linking polymerization, is studied in terms of the dispersion of the tubes. The covalently bonded tubes are homogeneously dispersed within the polyurethane by introducing carboxyl groups on the sidewall of the tubes and selecting a cross-linking polymerization method. The resultant composites, which have 92% shape retention and 95% shape recovery, are expected to be used as preferential materials in various actuators. [Copyright &y& Elsevier]

Abstract: Recent findings of extremely small diameter carbon nanotube and nanowire in the core of a multi-walled carbon nanotube (MWCNT) have attracted interests from broad range of researchers. Direct observation of carbon nanotube is usually done using a transmission electron microscope (TEM). When nanotubes become smaller, it becomes harder to correctly understand the TEM images, not only because of the weak scattering, but also due to the artifact that starts to appear because of the interference effect and the inappropriate defocus condition. In this study, we have shown that the artifact such as ghost fringes due to inappropriate defocus conditions of the TEM appear in the core of an MWCNT, and can be misinterpreted as either carbon nanowire or small carbon nanotube. It is also shown that, in the TEM image, it is hard to distinguish a single-walled nanotube bundle from a double-walled carbon nanotube bundle. Finally, we propose that the cross-sectional observation is necessary for the correct characterization of single- and double-walled carbon nanotube bundles. [Copyright &y& Elsevier]

Abstract: We have evaluated the biological responses to four different types of carbon nanotubes (CNTs), by measuring CD4+ and CD8+ T-cells in peripheral blood, and by the histopathological study on tissues surrounding subcutaneously implanted CNTs for up to 3 months. All mice survived, and no large changes in their weights were observed within our experimental period. After 1 week, only single-walled carbon nanotubes (SWNTs) activated major histocompatibility complex (MHC) class I pathway of antigen–antibody response system (higher CD4+/CD8+ value), resulting in the appearance of an edematous aspect. After 2 weeks, significantly high values in CD4+ and CD4+/CD8+ without change in CD8+ signified an activated MHC class II for all samples. It is worth noting that the toxicological response of CNTs was absolutely lower than that of asbestos. As a result, we envisaged that our result (relatively low toxicity of CNTs) will spur the mass-production, as well widespread application of CNTs in the near future. [Copyright &y& Elsevier]

Here we fabricate high-purity carbon sheets consisting of 250nm nanofibers through the fibre formation of poly (benzimidazol) by electro-spinning and subsequent heat treatment up to 3000°C without the stabilization process (the most time-consuming step). The non-graphitic character of these nanofibers is due to: (1) the low graphitization-ability of the polymer itself, (2) the limited graphitization of the size effect (small diameter) (3) the existence of internal pores formed during the electrospinning process. [Copyright &y& Elsevier]

A systematic study considering the microstructural effect of carbon materials on the electrochemical or electrocatalytic performance is essential for developing carbon electrode materials of electric vehicles and smart grids that require durable and robust energy supply. In this study, the edge sites within activated carbons (ACs) were physically modified via thermal treatment to clarify the relationship between the edge density and hydrogen evolution reaction (HER). Moreover, their dominant contribution to the electrochemical performance of lead-carbon batteries was demonstrated. The ACs exhibited decreased defect density and enhanced crystallinity due to the merger of micro-domains during a high-temperature thermal treatment (HTT). In contrast to the specific surface area, the edge area of the ACs, which was quantified via temperature programmed desorption up to 1800 °C, decreased significantly with increasing HTT temperature. We have confirmed a close relationship between the edge densities and HER parameters. The lead-carbon battery unit cell employing HTT1600 with the lowest edge ratio (0.81%) exhibited a higher charging efficiency, higher cycling stability, and lower water loss than the cell employing pristine AC with a high edge ratio (8.42%). The edge ratio of carbon materials can be considered an important parameter in designing electrode materials for electrochemical energy storage. [Display omitted] [ABSTRACT FROM AUTHOR]

Low contact resistance of carbon nanotube (CNT) fibers are fundamental component to improve the electrical transport properties of CNT fibers. To reduce the contact resistance of CNT fibers, we have demonstrated synergistic effect of macroscopic densification in combination with heteroatom doping. Boron and nitrogen atoms were introduced into the hexagonal carbon lattice of the CNTs through judicious combination of high temperature thermal doping and plasma treatment. Chlorosulfonic acid (CSA) was chosen to provide selectively quaternary nitrogen on the sidewall of the CNTs. During this process, densification of the CNT fibers also proceeded, and consequently reduced the hopping or tunneling distance for inter-CNT electron transfer. As a result, we achieved remarkable electrical conductivity of the CNT fibers as high as 5,896 Sm2/kg. The mechanism study by which heterogeneous conduction model proved the decrease of the electrical barrier height of the CNT fibers. These results provide a substantial step towards the use of CNT fibers as conductive materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Despite significant improvements in the synthesis of nitrogen (N)-doped carbon nanotubes (CNTs) and their versatile applications, there has always been a large difficulty in controlling the bonding configuration of N atoms within CNTs. In the current work, we report an effective chemical strategy to synthesize single-walled carbon nanotubes (SWNTs) with 100% of quaternary N via a chlorosulfonic acid(CSA) treatment. In this process, the pyridinic and pyrrolic groups were selectively and completely removed while retaining the quaternary N atoms. The presence of 2.04 at. % of quaternary N atoms within SWNTs was directly identified from a single sharp peak in the N 1s spectra of XPS, and indirectly supported by the downshift of C 1s peak in XPS, the upshift of G'-band in Raman spectroscopy, and the decrease of the work function from 5.46 to 4.59 eV. The doping effect of the quaternary N atoms on the macroscopic properties of SWNT fibers was verified by a large increase in the electrical conductivity from 0.63 to 2.17 MS/m. In perspective, our chemical approach can now be applied to synthesize carbon materials with controlled N functionalities for different applications. Image 1 [ABSTRACT FROM AUTHOR]

In response to the demand for clean, renewable energy sources and storage technologies, innovative materials and combinations have been developed at reasonable prices as effective electrode materials. Current research and development of carbon-based metal-free catalysts have opened up new research areas for bifunctional electrocatalysts for overall water splitting. Herein, we developed N-self-doped defect-rich porous carbon nanosheets derived from platycladus orientalis tree-cone biomass for overall water splitting. The developed N-self-doped defect-rich porous carbon nanosheets have large surface areas (3369 m2/g), high pore volumes (2.1 cm3 g−1), and high electrical conductivities (12.69 S/cm). N-self-doped defect-rich porous carbon nanosheet framework was employed in water splitting as a dual function in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Electrodes fabricated from the KOH-II ABC nanosheets show excellent OER and HER performances in the 0.5 M H 2 SO 4 solution. The current density of 10 mA cm−2 is reached at a low overpotential of 90 mV for OER and 188 mV for HER. In addition, KOH-II ABC nanosheets also show a remarkable performance on overall water splitting, which only required a cell voltage of 1.49 V to reach current densities of 10 mA cm−2 in 0.5 M H 2 SO 4 solution. The presence of defects in the carbon nanosheets, higher specific surface area, excellent electrochemical active surface area and N doping effectively enhance the reaction kinetics for attaining efficient OER and HER performances. This facile approach to preparing biomass-derived N-doped defect-rich porous carbon materials empowers next-generation green fuel conversion technologies for carbon neutrality. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of this study was to compare the effectiveness of carbon black, single-walled carbon nanotubes (SWCNTs), and double-walled carbon nanotubes (DWCNTs) as conducting agents for lithium iron phosphate (LFP) cathodes. A water-based slurry system was employed by incorporating SWCNTs and DWCNTs with polyvinylpyrrolidone (PVP) as a dispersing agent and binder. Both SWCNTs and DWCNTs exhibited remarkable wrapping ability on the surface of LFP particles, affecting the electrical conductivity and physical properties (including adhesion and cohesion strengths) of the electrode, and then influencing the electrochemical performance of the cathode. Notably, the DWCNTs outperformed the SWCNTs as conducting agents, demonstrating higher electrical conductivity and adhesion/cohesion strengths, as well as improved rate performances. This can be attributed to the higher aspect ratio, better crystallinity, and superior mechanical strength of the DWCNTs. In situ Raman measurements conducted during the charge–discharge process showed significant changes in the Raman peaks. SWCNTs exhibited complete suppression of Raman signals upon lithiation, while DWCNTs displayed the unique ability of retaining the Raman peaks originating from the inner nanotubes, indicating the protective function of the outer tubes. These findings highlight the promising potential of the incorporation of SWCNTs and DWCNTs into cathodes, as their exceptional wrapping ability distinguishes them from multi-walled carbon nanotubes and carbon black. In particular, owing to their high aspect ratio and superior wrapping capabilities, the DWCNTs are expected to serve as effective conducting agents for advanced lithium-ion batteries. [Display omitted] [ABSTRACT FROM AUTHOR]

Vertical graphene (VG) sheets, which consist of few-layer graphene vertically aligned on the substrate with three-dimensionally interconnected porous network, make them become one of the most promising energy storage electrodes, especially for SCs. Nevertheless, the intrinsic hydrophobic nature of pristine VG sheets severely limited its application in aqueous SCs. Here, electrochemical oxidation strategy is adopted to increase the hydrophilicity of VG sheets by introducing oxygen functional groups so that the aqueous electrolyte can fully be in contact with the VG sheets to improve charge storage performance. Our work demonstrated that the introduction of oxygen functional groups not only greatly improved the hydrophilicity but also generated a pseudocapacitance to increase the specific capacitance. The resulting capacitance of electrochemically oxidized VG for 7 min (denoted as EOVG-7) exhibited three orders of magnitude higher (1605 mF/cm2) compared to pristine VG sheets. Through assembled two EOVG-7 electrodes, a symmetric supercapacitor demonstrated high specific capacitance of 307.5 mF/cm2, high energy density of 138.3 μWh/cm2 as well as excellent cyclic stability (84% capacitance retention after 10000 cycles). This strategy provides a promising way for designing and engineering carbon-based aqueous supercapacitors with high performance. The electrochemical oxidation strategy is adopted to increase the hydrophilicity of VG sheets by introducing oxygen functional groups so that the aqueous electrolyte can fully be in contact with the VG sheets to enhance electrochemical charge storage performance. The introduction of oxygen functional groups not only greatly improved the hydrophilicity but also generated a pseudocapacitance to increase the specific capacitance, further improve the energy density. [Display omitted] • Electrochemical oxidation method can significantly increase the functional groups on the surface of VG. • The hydrophilicity and additional pseudocapacitance are generated on surface-functionalized VG. • The optimized oxygen functional groups of VG surface can improve capacitance. • The symmetric SC shows excellent energy density (138.3 μWh/cm2), long-term cycle stability (84 %) and voltage of 1.8 V. [ABSTRACT FROM AUTHOR]