Porous nitrogen-doped graphene for high energy density supercapacitors in an ionic liquid electrolyte

Porous nitrogen-doped graphene (PNG) has been prepared via simple thermal treatment of graphene oxide and urea, and the morphology and structure of the PNG have been characterized by using a range of electron microscopy, X-ray photoelectron spectroscopy, and other techniques. The electrochemical performances of the PNG have been investigated in an ionic liquid electrolyte by cyclic voltammetry and galvanostatic charge-discharge via both three-electrode and two-electrode configurations. The PNG electrode delivers a specific capacitance of 310 F g^?1 at 1 A g^?1 with good cycling stability over 4000 cycles. The high electrochemical performance is ascribed to the porous structure and nitrogen-doping in the PNG. The porous structure enables high specific surface area and rapid ion mobility, contributing to double layer capacitance, while the N-doping enhances electrochemical activity and electric conductivity, contributing to pseudocapacitance. Meanwhile, the ionic liquid electrolyte enables a very wide working voltage of 3 V, leading to a high energy density up to 163.8 W h kg^?1. The fabricated supercapacitor can light up a LED for a long while with low self-discharge, showing good potential for practical application.     

α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films by liquid phase deposition: low-cost option for supercapacitor

In the present study, iron oxide (α-Fe₂O₃) thin films with good adhesion on stainless steel substrates are deposited by liquid phase deposition (LPD) technique, which is additive and binder-free. Iron oxyhydroxide (FeOOH) thin films are formed by means of a ligand-exchange equilibrium reaction of metal-fluoro complex ions and an F^?ions consuming reaction by using boric acid (H₃BO₃) as a scavenging agent. These films are annealed at 500 °C to get α-Fe₂O₃ thin films. The transformation from hydrophobic to hydrophilic nature of the films is observed due to annealing. The films are characterized by different techniques. The α-Fe₂O₃ film is checked for electrochemical supercapacitive performance in Na₂SO₃ solutions of various concentrations. Specific capacitance is calculated from cyclic voltammetry at numerous scan rates (5–200) mV s^?1. The highest obtained value of specific capacitance is 582 F g^?1 at 5 mV s^?1 for 0.5 M Na₂SO₃ electrolyte. The maximum values of specific power and specific energy are 6.9 and 53.4 Wh kg^?1 from the charge-discharge curve at the current density 2 mA cm^?2 in 0.5 M Na₂SO₃ electrolyte.     

Influence of barium titanate nanofiller on PEO/PVdF-HFP blend-based polymer electrolyte membrane for Li-battery applications

Organic-inorganic hybrid membranes based on poly(ethylene oxide) (PEO) 6.25 wt%/poly(vinylidene fluoride hexa fluoro propylene) [P(VdF-HFP)] 18.75 wt% were prepared by using various concentration of nanosized barium titanate (BaTiO₃) filler. Structural characterizations were made by X-ray diffraction and Fourier transform infrared spectroscopy, which indicate the inclusion of BaTiO₃ in to the polymer matrix. Addition of filler creates an effective route of polymer-filler interface and promotes the ionic conductivity of the membranes. From the ionic conductivity results, 6 wt% of BaTiO₃-incorporated composite polymer electrolyte (CPE) showed the highest ionic conductivity (6 × 10^?3 Scm^?1 at room temperature). It is found that the filler content above 6 wt% rendered the membranes less conducting. Morphological images reveal that the ceramic filler was embedded over the membrane. Thermogravimetric and differential thermal analysis (TG-DTA) of the CPE sample with 6 wt% of the BaTiO₃ shows high thermal stability. Electrochemical performance of the composite polymer electrolyte was studied in LiFePO₄/CPE/Li coin cell. Charge-discharge cycle has been performed for the film exhibiting higher conductivity. These properties of the nanocomposite electrolyte are suitable for Li-batteries.     

From current peaks to waves and capacitive currents—on the origins of capacitor-like electrode behavior

Terminology of electrodes and electrode materials used in supercapacitors as well as naming of electrode processes and devices prepared with these electrodes is confusing and rather unregulated. Consequently, misunderstanding in communication about research and development is somehow matched with an incomplete understanding of the reasons of the observed capacitive, pseudocapacitive, or Faradaic behavior. Observed and investigated phenomena relevant for supercapacitor electrodes are briefly reviewed and explained in terms of electrode processes and interfacial phenomena. Further research possibly useful in more fundamental understanding and rational improvement of materials is proposed.     

A sustainable synthesis of biomass carbon sheets as excellent performance sodium ion batteries anode

Biomass-derived carbon (BMC) materials have attracted much attention due to their high performance and properties of abundant source. Herein, biomass carbon sheets (BMCS) from wheat straws had been successfully synthesized via a facile high temperature carbonization and expansion processes. The morphology of BMCS keeps the natural honeycomb-like shape of the cross section and the hollow tubular array structure of the vertical section with rich pores, which provides low-resistant ion channels to support fast diffusion. The (002) crystal plane reveals that the intercalation distance of carbon sheets is 0.383 nm larger than that graphite (0.335 nm), which benefits the larger sodium ion de/intercalation. By comparing different carbonization temperatures, wheat straws carbonized at 1200 °C (BMCS-1200) with well graphite microcrystallites show more excellent sodium ion storage performance than that of 900 °C (BMC-900). BMCS-1200 shows a stable reversible capacity of 221 mAh g^?1 after 200 cycles at 0.05 A g^?1, while BMC-900 is 162 mAh g^?1 after 100 cycles. And it also exhibits better rate capability (220, 109 mAh g^?1) than that of BMC-900 (125, 77 mAh g^?1) at 0.2 and 1 A g^?1, respectively. Finally, it delivers 89 mAh g^?1 stable capacity after 1400 cycles at 1 A g^?1 to prove its excellent long-term cycling stability.

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Graphical abstract High temperature carbon sheets with well graphite microcrystallites synthesized from wheat straw forexcellent sodium ion storage performance

     

Tin nanoparticles embedded in ordered mesoporous carbon as high-performance anode for sodium-ion batteries

Tin (Sn) has been considered as an attractive anode material for sodium-ion batteries (SIBs) due to its high theoretical capacity (847 mAh g^?1). Nevertheless, its low conductivity and large volume change during cycling essentially prevent the possibility of high capacity and long-term cycle for SIBs. In this work, Sn nanoparticles are well embedded into the highly ordered mesoporous carbon (CMK-3) matrix (Sn@CMK-3) using a facile sonochemical method combined with heat treatment. The resultant Sn@CMK-3 nanohybrid electrode delivers an initial charge capacity of 412 mAh g^?1 at 100 mA g^?1. A reversible capacity of 337 mAh g^?1 is obtained after 200 cycles, indicating the good cycle stability of the nanohybrid structure. The electrode also shows a potential rate capability, which maintains a capacity of 228 mAh g^?1 at 1000 mA g^?1. When the current density returns to 50 mA g^?1, the capacity goes back to 381 mAh g^?1, with a capacity retention of 86.9%. The enhanced sodium storage performance of Sn@CMK-3 nanohybrid can be related to the synergistic effect between CMK-3 and Sn.

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Graphical abstract Sn@CMK-3 nanohybrid with Sn nanoparticles uniformly distributed into the highly ordered mesoporous carbon matrix exhibited good cycling performance and rate capability.

     

Simple chemical route for nanorod-like cobalt oxide films for electrochemical energy storage applications

We used a simple chemical synthesis route to deposit nanorod-like cobalt oxide thin films on different substrates such as stainless steel (ss), indium tin oxide (ITO), and microscopic glass slides. The morphology of the films show that the films were uniformly spread having a nanorod-like structure with the length of the nanorods shortened on ss substrates. The electrochemical properties of the films deposited at different time intervals were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The film deposited after 20 cycles on ss gave the highest specific capacity of 67.6 mAh g^?1 and volumetric capacity of 123 mAh cm^?3 at a scan rate 5 mV s^?1 in comparison to 62.0 mAh g^?1 and 113 mAh cm^?3 obtained, respectively, for its counterpart on ITO. The film electrode deposited after 20 cycles on ITO gave the best rate capability and excellent cyclability with no depreciation after 2000 charge–discharge cycles.     

High-performance supercapacitor electrode based on a nanocomposite of polyaniline and chemically exfoliated MoS<Subscript>2</Subscript> nanosheets

In this study, MoS₂ nanosheets were first prepared by exfoliating its bulk material in HCl/LiNO₃ solution with a yield of 45%, and then a facile strategy was developed to synthesize polyaniline/MoS₂ (PANI/MoS₂) nanocomposite via in situ polymerization. Structural and morphological characterizations of MoS₂ nanosheets and the nanocomposite were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray powder diffraction. The results of SEM illustrated that orderly sawtooth polyaniline (PANI) nanoarrays were formed on the surface of MoS₂ nanosheets. The nanocomposite displayed good electrochemical performance as a supercapacitor electrode material. The specific capacitance reached 560 F/g at a current density of 1.0 A g^?1 in 1.0 M H₂SO₄ solution. Such good performance is because that the MoS₂ nanosheets provided a highly electrolytic accessible surface area for redox-active PANI and a direct path for electrons.