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While manganese-based cathodes have been intensively studied for zinc-ion batteries (ZIBs), the limited rate capability and cycle life have always been a difficult problem to be solved. Here, we report a mixed valent manganese oxide (MnOx) cathode with superior electrochemical performance, which exhibits a high specific capacity of 450 mA h/g at 0.2 C and a satisfactory specific capacity of 158.3 mA h/g at a high rate of 5 C. The mixed cathode system reduces the charge transfer resistance, and show good surface stability and adsorption properties, so it is beneficial for the storage of Zn2+. Meanwhile, coaxial fiber ZIBs (CFZIBs) with splendid flexibility are assembled utilizing the elaborately prepared cathode material. The CFZIBs achieve a reversible capacity of 255.8 mA h/g and the capacity retention rate is as high as 80 % after 1000 bending deformations. This study provides new opportunities for designing ZIBs with high performance and high flexibility.

Molybdenum disulfide (MoS2) has become one of the most promising non-platinum-based electrocatalysts for the hydrogen evolution reaction (HER) because of its unique layered structure. However, the catalytic performance of the thermodynamically stable MoS2 is hindered by its poor conductivity and scarce active sites. We developed a 3D porous N-doped graphene derivative-integrated metal-semiconductor (1T-2H) mixed phase MoS2 (MNG) using urea as a doping reagent. The highly exposed active sites were achieved by inducing the phase transition of MoS2 from 2H phase to 1T phase and the inclusion of highly N-incorporated reduced graphene oxide, both of which were simultaneously realized by optimizing the concentration of the doping reagent. Moreover, the charge/proton transfer was enhanced by the well-designed porous architecture and hydrophilic 1T-MoS2. With these advantages, the optimized MNG-40 catalyst has a small overpotential of 157 mV at a cathodic current density of 10 mA cm-2, a relatively low Tafel slope of 45.8 mV dec-1, and an excellent stability. This work represents a new strategy to design higher-performance HER catalysts and provides new insights into the structural regulation of metal composite transitions.

Owing to the superiority of high-power density and excellent cycling stability, supercapacitors (SCs) have been expected to substitute for secondary batteries as the desired orientation selected for energy storage devices. The incorporation of various heteroatoms into carbon-based materials via surface functionalization or doping technique has been considered as a significant way to ameliorate its properties for SCs application. In this review, a wide variety of fluorine-doped/fluorinated carbon-based materials are put together to overview the development path, preparation route and areas of application in detail. We critically review the optimization effect in electrochemical performance induced by the participation of fluorine element. Moreover, compared with large-scale energy storage devices, miniaturization, flexibility and planarization are an emerging development tendency of SCs. Fluorine-doped/fluorinated carbon-based materials hold great promise in the future.

International audience; In this paper, porous partially fluorinated graphene (PFG) for supercapacitors (SCs) was fabricated by a mild and secure one-pot hydrothermal method utilizing weakly coordinating anion BF4− as the fluorine source. The hydrolysis rate of sodium fluoroborate was adjusted by controlling the reaction temperature and PFG containing semi-ionic Csingle bondF bonds was obtained, where the content of semi-ionic Csingle bondF bonds in PFG can be easily regulated. The final experimental results show that the incorporation of fluorine not only modulates the electrochemical properties of the material, but also creates abundant pores. When assembled in a symmetric supercapacitor, the PFG shows a high specific capacitance of 269.7 F g−1 at 1 A g−1 and a superior rate capability with 89.3% capacitance retained, as the current density is increased from 1 A g−1 even to 20 A g−1. Furthermore, the resultant energy density for PFG is 9.4 Wh kg−1 at a power density of 250.0 W kg−1 (1 A g−1). All these results confirm that as-prepared partially fluorinated graphene is appropriate for the application in SCs and mass production.

In recent years, graphene oxide (GO), prepared by the modified Hummers’ method, and its derivatives have become a focus of research owing to their outstanding physical and chemical properties and low cost. Drawing inspiration from the mussel protein, a facile and environmentally-friendly method was employed to fabricate superhydrophobic/superoleophilic reduced graphene oxide (rGO) derivative. The preparation comprises two steps: coating GO nanosheets with polydopamine (PDA) and subsequent reaction with 1 H ,1 H ,2 H ,2 H -perfluorodecanethiol. Due to the excellent adhesive ability of PDA, the resulting f PDA modified rGO nanosheets (rGO- f PDA) were firmly immobilized onto polyurethane (PU) sponge skeleton by a simple drop-coating method. The as-prepared rGO- f PDA functionalized sponge exhibited superhydrophobic behavior with a water contact angle of 162°±2°, high organic adsorption capacity, recyclability and stable oil/water separation behavior under different acidic/alkaline conditions. Due to its facile fabrication technique and outstanding properties, the superhydrophobic-superoleophilic PU-rGO- f PDA sponge holds great promise as an oil adsorbent for cleaning up large-scale pollution of oil and organic solvents, and dehydrating crude oil.

Molybdenum disulfide (MoS

International audience; MnO2/MnO cathode material with superior Zn2+ storage performance is prepared through a simple physical mixing method. The MnO2/MnO nanocomposite with a mixed mass ratio of 12:1 exhibits the highest specific capacity (364.2 mA.h/g at 0.2C), good cycle performance (170.4 mA.h/g after 100 cycles) and excellent rate performance (205.7 mA.h/g at 2C). Analysis of cyclic voltammetry (CV) data at various scan rates shows that both diffusion-controlled insertion behavior and surface capacitive behavior contribute to the Zn2+ storage performance of MnO2/MnO cathodes. And the capacitive behavior contributes more at high discharge rates, due to the short paths of ion diffusion and the rapid transfer of electrons.

Highlights The traditional and novel etching methods are summarized and compared, especially fluorine-free method. The methods for accelerating exfoliation of Ti3C2Tx are classified.The energy storage mechanisms of Ti3C2Tx in different electrolytes are compared. Based on energy storage mechanisms, the influencing factors of morphology and surface functional groups are discussed.In response to the problems of the Ti3C2Tx, strategies for improving capacitance from structure modulation to composite structure construction are summarized and compared., Ti3C2Tx, a novel two-dimensional layer material, is widely used as electrode materials of supercapacitor due to its good metal conductivity, redox reaction active surface, and so on. However, there are many challenges to be addressed which impede Ti3C2Tx obtaining the ideal specific capacitance, such as restacking, re-crushing, and oxidation of titanium. Recently, many advances have been proposed to enhance capacitance performance of Ti3C2Tx. In this review, recent strategies for improving specific capacitance are summarized and compared, for example, film formation, surface modification, and composite method. Furthermore, in order to comprehend the mechanism of those efforts, this review analyzes the energy storage performance in different electrolytes and influencing factors. This review is expected to predict redouble research direction of Ti3C2Tx materials in supercapacitors.

We have designed and synthesized a unique structured graphene/SnO2 composite, where SnO2 nanoparticles are inserted in between interconnected graphene sheets which form hollow spherical multilayers. The hollow spherical multilayered structure provides much flexibility to accommodate the configuration and volume changes of SnO2 in the material. When it is used as an anode material for lithium-ion batteries, such a novel nanostructure can not only provide a stable conductive matrix and suppress the mechanical stress, but also eliminate the need of any binders for constructing electrodes. Electrochemical tests show that the unique graphene/SnO2 composite electrode as designed could exhibit a large reversible capacity over 1000 mA h g−1 and long cycling life with 88% retention after 100 cycles. These results indicate the great potential of the composite for being used as a high performance anode material for lithium-ion batteries.

Water-enabled crystallization of amorphous anodic SnO2 is reported. After low-temperature water soaking for a short period of time (e.g., 60 °C for 2 h), mesoporous rutile SnO2 with a remarkably increased surface area is achieved (nearly 2-fold that of the as-anodized SnO2 and 3.3 times that of SnO2 annealed at high temperature). Closer examination reveals that the water-crystallized SnO2 possesses a hierarchical nanostructure that features 1D nanochannels (e.g., ∼30 nm in diameter) and thin channel walls (e.g., 20 nm thick) that are comprised of tiny nanoparticles (e.g., ∼4 nm big). The water-crystallized SnO2 directly grown on the copper foil can be directly applied as a novel type of binder-free electrode for sodium-ion storage, delivering a high reversible capacity of 514 mA h g−1 after 100 cycles at a current rate of 0.1C.

Double-layered nanoporous silver is fabricated by dealloying an electrodeposited AgCu double layer with different compositions in each layer. The pore/ligament size and porosity of each layer can be conveniently tailored by controlling the applied voltage profile when electrodepositing the AgCu double-layer precursors. Therefore, nanoporous Ag double layers with a tailor-made porous profile along the film thickness can be easily fabricated. The Ag structures thus obtained are particularly attractive as novel multifunctional enhancement substrates for surface-enhanced Raman spectroscopy (SERS) applications. When a higher porosity is created in the top layer, the double layer can trap more light because of the antireflection effect, enabling stronger SERS enhancement. On the other hand, with smaller pores formed in the top layer, the double layer readily works as a size-screening SERS substrate that can help distinguish SERS signals from a mixture of reagents with different sizes. The theoretical simulation shows good agreement with the experimental observation.

The graphene material prepared by the chemical reduction method usually has oxygenic functional groups in it and such functional groups often result in interactions between the graphene electrode and the electrolyte in supercapacitors. We have examined the existential form of interactions between graphene as the electrode and three kinds of ionic liquid, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide (EMI-TFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF 4 ), and 1-methyl-1-propylpiperidinium bis (trifluoromethyl sulfonyl) imide (MPPp-TFSI), as the electrolyte of a supercapacitor. Mass spectroscopy (MS) and Fourier transform infrared spectroscopy (FT-IR) analyses confirmed that the residual hydroxyl groups in graphene were transferred to EMI + and TFSI − lost oxygen atoms to graphene, while little reaction took place in BF 4 − or MPPp + , during the process of charging. The chemical reactions are suggested to contribute to the device capacitance while it is also one of the reasons for the decreased electrochemical stability window. In this study the highest energy density achieved using the graphene electrode is 169 Wh kg −1 in MPPp-TFSI electrolyte charged to 4.4 V.

Advanced materials with special wettability have attracted wide attention for their potential application in environmental remediation, catalysis or superfluid now. This contribution reports a straightforward and low-cost high-performance methodology for the preparation of carbon fiber felt with selective superwettability and fire resistance. The functionalized carbon fiber felt (UV-CFF) is prepared by a simple UV-O3 treatment process for the enhancement of its superamphiphilicity in air and superoleophobicity underwater, the underwater contact angles of the organics is over 155°. Subsequently, surface functionalization of UV-CFF with 4-trifluoromethyldiazobenzene hydrochloride is carried out. Its surface could be effectively modified with aryl and carbon–fluorine groups through diazonium chemistry to obtain a superhydrophobic carbon fiber felt (f-CFF) with water contact angle of 152.5 ± 0.8°. Both of the UV-CFF and f-CFF samples exhibits effective oil/water separation behavior. Benefiting from the selective superwettability, the two samples provide the potential to selectively eliminate underwater oily phases and emulsions under different hydraulic pressures. For UV-CFF, its rejection of oil reaches 100%, and the rejection of water for f-CFF reaches 98.21 ± 0.7%. The adsorption capacities of different types of organic solvents for f-CFF is 4–14 g g−1, and its demulsification capacity can reach to 99.9%. Due to its corrosion resistance, facile fabrication technique, cycle stability and flame retardancy, the carbon felts hold great promise for potential applications in environmental remediation of water.

Ionic liquids (ILs) with large electrochemical windows up to 4 V have been employed as the electrolyte to boost the energy density of graphene-based supercapacitors. However, due to the larger molecular size, lower conductivity, and higher viscosity of the IL electrolyte, graphene-based supercapacitors in IL electrolyte usually exhibit low rate capability. To make graphene-based electrodes more compatible with the IL electrolyte, we functionalized chemically reduced graphene oxide with the same IL which is also used as the electrolyte. Electrochemical test results show that the relaxation time and charge transfer resistance at electrode-electrolyte interface for IL modified electrode is one third and one fourth of that for the pristine graphene electrode, respectively, indicating the improved compatibility between the IL modified electrode and the electrolyte. Furthermore, the capacitance retention of the IL modified electrode from current density of 0.5 to 20 A g−1 is 85%, which is much higher than that of the pristine electrode (53%).

Carbon nanotube spaced graphene aerogels have been prepared by a hydrothermal method and used for supercapacitor applications. The specific surface area and specific capacitance can be controlled by tuning the amount of added carbon nanotubes. The as-prepared composite aerogels retain the advantage of aerogel structure in providing macropores to ensure electrodes fast wetted by the electrolyte ions and also possess additional mesopores created by the carbon nanotube spacers for more ion adsorption. Benefited from that, the composite aerogels exhibit significantly enhanced supercapacitor properties in both aqueous and ionic liquid electrolyte. Compared with graphene aerogels, the composite aerogels show a 37% larger specific capacitance of 245.5 F g � 1 at a current density of 2.5 A g � 1 and high rate capability of 197.0 F g � 1 at a high current density of 80 A g � 1 in aqueous electrolyte. Moreover, the composite aerogels deliver a 33% larger specific capacitance of 183.3 F g � 1 at 0.5 A g � 1 and a high energy density of 80 Wh kg � 1 when using an ionic liquid (EMIMBF4) as the electrolyte.

We have designed and synthesized a unique structured graphene/SnO

We have successfully assembled graphene nanosheets into spherical shells using polystyrene spheres as templates. Compared with stacked planar graphene, the as-prepared graphene spherical shells have more free space in between the spheres, which results in a larger accessible surface area for adsorption of electrolyte ions in supercapacitors. Electrochemical tests show that the graphene hollow spheres exhibit a high specific capacitance of 273 F g−1 and excellent electrochemical stability.