S. A. Hashmi

Synthesis of surfactant-free SnS nanorods by a solvothermal route with better electrochemical properties towards supercapacitor applications

We demonstrate a simple, low cost, and eco-friendly synthesis of surfactant free tin monosulfide (SnS) nanorods by a solvothermal route for applications in supercapacitor devices with high specific capacitance. The as-synthesized SnS nanorods, consisting of an intrinsic layered structure, were thoroughly characterised by XRD, TEM, HRTEM, SEM, EDAX and BET techniques to determine their crystal structure, size, morphology and surface area. To explore potential applications for supercapacitors, the nanocrystals were used to fabricate a two electrode system without adding any binder, large area support or conductive filler, and the system was characterised by cyclic voltammograms, galvanostatic charge–discharge and electrochemical impedance spectroscopy measurements in aqueous 2 M Na2SO4 electrolyte. These SnS nanorods exhibit enhanced supercapacitor performance with specific capacitance, energy density and power density values of ∼70 F g−1, 1.49 W h kg−1 and 248.33 W kg−1, respectively, which are found to be two times higher than those of SnS–carbon composites, and thus make SnS nanorods a better alternative source for energy storage devices.

Structural and electrochemical properties of succinonitrile-based gel polymer electrolytes: role of ionic liquid addition.

Experimental studies on the novel compositions of gel polymer electrolytes, comprised of plastic crystal succinonitrile (SN) dispersed with pyrrolidinium and imidazolium-based ionic liquids (ILs) entrapped in a host polymer poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP), are reported. The gel electrolytes are in the form of free-standing films with excellent mechanical, thermal, and electrochemical stability. The introduction of even a small content (~1 wt %) of ionic liquid (1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)imide (BMPTFSI) or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf) in the PVdF-HFP/SN system (1:4 w/w) enhances the electrical conductivity by 4 orders of magnitude, that is, from ~10(-7) to ~10(-3) S cm(-1) at room temperature. The structural changes due to the entrapment of SN or SN/ILs mixtures and ion-SN-polymer interactions are examined by Fourier transform infrared (FTIR)/Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimmetry (DSC). Various physicochemical properties and fast ion conduction in the gel polymer membranes show their promising characteristics as electrolytes in different ionic devices including supercapacitors.

Development of SnS2/RGO nanosheet composite for cost-effective aqueous hybrid supercapacitors

The development of low cost supercapacitor cells with unique capacitive properties is essential for many domestic and industrial purposes. Here we report the first ever application of SnS2-reduced graphene oxide (SnS2/RGO) layered nanocomposite as a superior electrode material for symmetric aqueous hybrid supercapacitors. We synthesized SnS2/RGO nanocomposite comprised of nanosheets of SnS2 and graphene oxide via a one-pot hydrothermal approach. in situ as-synthesized SnS2/RGO is devised for the first time to give high specific capacitance 500 Fg-1, energy density 16.67 Wh kg-1 and power density 488 W kg-1. The cell retains 95% charge/discharge cycle stability up to 1000 cycles. In-short, the SnS2/RGO nanosheet composite presented is a novel and advanced material for application in high stability moderate value hybrid supercapacitors. All the currently available surveys in literature state the potential applicability of SnS2 as the anode material for reversible lithium/sodium ion batteries (LIBs/NIBs) but there is a lack of equivalent studies on electrochemical capacitors. We filled up this knowledge gap by the use of the same material in a cost-effective, highly active hybrid supercapacitor application by utilizing its pseudocapacitance property combined with the layered capacitance property of graphene sheets.

Studies on a proton battery using gel polymer electrolyte

A proton-conducting film of gel polymer electrolyte, poly(vinylidene fluoride hexafluoropropylene)/poly(methyl methacrylate) + ammonium thiocyanate + ethylene carbonate + propylene carbonate, has been prepared by solution casting technique. The ionic conductivity of the film is in the order of approximately 10−3 S cm− 1 at room temperature. A proton battery with the configuration zinc + zinc sulfate heptahydrate | gel electrolyte | lead oxide + vanadium pentoxide has been fabricated using this film as electrolyte and separator between the electrodes. The battery shows an open circuit voltage of 1.45 V and energy density of approximately 10 Wh kg−1at low current drain. The rechargeability of the battery has been observed up to three cycles after which its discharge capacity starts fading.

Investigations on Poly(ethylene oxide) + NH4PF6 Solid Polymer Electrolyte System

The authors report experimental investigation on a solid polymer electrolyte PEO + NH4PF6. The solid thin films of different compositions of PEO + NH4PF6 complex were synthesized using solution cast technique and characterized. Complexation between polymer and the salt has been established using X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, and thermogravimetric analysis. Ion transport in the polymer material has been studied by electrical conductivity measurements with composition, temperature, and humidity; by total ionic transference number measurement; and by dielectric measurements. The maximum room temperature (∼29°C) conductivity of the material has been found to be 1.04 × 10−6 S cm−1 for at RH = 60%. The conductivity shows strong humidity dependence. The temperature dependence of the conductivity shows the Arrhenius behavior. The total ionic transference number of the electrolyte material has been found to be between 0.94 and 0.97.

A free-standing, flexible PEDOT:PSS film and its nanocomposites with graphene nanoplatelets as electrodes for quasi-solid-state supercapacitors

Research and development on all-solid-state, flexible supercapacitors is the prime concern of the scientific community these days due to their various advantages including their easy transportability, miniaturization, and compactness in different appliances. We report the novel configuration of all-solid symmetrical supercapacitors employing free-standing, flexible films of poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) and its nanocomposite electrodes with graphene nanoplatelets (GNPs), separated by ionic liquid (IL) (1-ethyl 3-methylimidazolium trifluoromethanesulfonate (EMITf))-based gel polymer electrolyte (GPE) films. The free-standing and flexible form of PEDOT:PSS/GNP nanocomposite films have been prepared via simple mixing of the two counterparts. Scanning electron microscopy, x-ray diffraction, Raman analysis, and thermal and mechanical characterizations have been performed to ascertain the suitability of pristine and nanocomposite PEDOT:PSS films as potential supercapacitor electrodes. The GPE film, comprising of a solution of NH4CF3SO3 (NH4-triflate or NH4Tf) in IL, entrapped in poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP), is a promising electrolyte due to its high ionic conductivity and sufficient electrochemical stability window. The supercapacitor with a PEDOT:PSS nanocomposite containing ∼3.8 wt.% of GNP has been found to give an optimum specific capacitance of ∼106 F g-1 (evaluated from electrochemical impedance spectroscopy), and specific energy and power of ∼6.95 Wh kg-1 and 2.58 kW kg-1, respectively (evaluated from galvanostatic charge-discharge). More importantly, the capacitors demonstrate stable performance for more than 2000 charge-discharge cycles, with only ∼10% initial fading in capacitance. Interestingly, the PEDOT:PSS/GNP nanocomposite-based solid-state supercapacitors with the IL-incorporated GPE have shown comparable (even better) performance than other reported PEDOT:PSS-based supercapacitors.

Nanofiller-incorporated porous polymer electrolyte for electrochemical energy storage devices

We report the poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP)-based microporous polymer membranes, prepared by phase inversion technique, incorporated with different amounts of nanosized zirconium dioxide (ZrO2) filler. Scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermal studies confirm the role of ZrO2 nanofiller to modify the polymer structure, pore geometry and crystallinity. The nanofillers interact with the PVdF-HFP chains via surface groups and electrostatic interactions, and their incorporation led to an increase in crystalline content of the membrane and ionic conductivity (when activated with a liquid electrolyte (LE)). A possible mechanism for the increase in crystallinity in the polymer due to interaction with nanofiller particles has also been presented. The optimized membrane has been saturated with an LE sodium perchlorate-ethylene carbonate:propylene carbonate for use as a separator/electrolyte in electrical double-layer capacitor (EDLC). The cells fabricated with the nanofiller-incorporated membrane show better performance in terms of specific electrode capacitance, specific energy and specific power (approximately 76 F g−1, approximately 20.9 Wh kg−1 and 2.62 kW kg−1) than the cells using the membrane devoid of nanofillers (approximately 61 F g−1, approximately 17.3 Wh kg−1 and approximately 3.16 kW kg−1), respectively. The EDLC shows approximately 85% retention in specific capacitance for 10,000 charge–discharge cycles.

Performance of electrical double layer capacitors fabricated with gel polymer electrolytes containing Li+ and K+-salts: A comparison

The comparative performance of the solid-state electrical double layer capacitors (EDLCs) based on the multiwalled carbon nanotube (MWCNT) electrodes and poly (vinaylidinefluoride-co-hexafluoropropyline) (PVdF-HFP) based gel polymer electrolytes (GPEs) containing potassium and lithium salts have been studied. The room temperature ionic conductivity of the GPEs have been found to be ∼3.8×10−3 and 5.9×10−3 S cm−1 for lithium and potassium based systems. The performance of EDLC cells studied by impedance spectroscopy, cyclic voltammetry and constant current charge-discharge techniques, indicate that the EDLC with potassium salt containing GPE shows excellent performance almost equivalent to the EDLC with Li-salt-based GPE.