Chapal Kumar Das

Synthesis, characterization and electrochemical performance of graphene decorated with 1D NiMoO4·nH2O nanorods

One-dimensional NiMoO4 · nH2O nanorods and their graphene based hybrid composite with good electrochemical properties have been synthesized by a cost effective hydrothermal procedure. The formation of the mixed metal oxide and the composite was confirmed by XRD, XPS and Raman analyses. The morphological characterizations were carried out using FESEM and TEM analyses. The materials were subjected to electrochemical characterization through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) studies with 6 M KOH as the supporting electrolyte. For NiMoO4 · nH2O, a maximum specific capacitance of 161 F g(-1) was obtained at 5 A g(-1) current density, accompanied with an energy density of 4.53 W h kg(-1) at a steady power delivery rate of 1125 W kg(-1). The high utility of the pseudocapacitive NiMoO4 · nH2O was achieved in its graphene based composite, which exhibited a high specific capacitance of 367 F g(-1) at 5 A g(-1) current density and a high energy density of 10.32 W h kg(-1) at a power density of 1125 W kg(-1) accompanied with long term cyclic stability.

Hydrothermal Growth of Hierarchical Ni3S2 and Co3S4 on a Reduced Graphene Oxide Hydrogel@Ni Foam: A High-Energy-Density Aqueous Asymmetric Supercapacitor

Ni foam@reduced graphene oxide (rGO) hydrogel-Ni3S2 and Ni foam@rGO hydrogel-Co3S4 composites have been successfully synthesized with the aid of a two-step hydrothermal protocol, where the rGO hydrogel is sandwiched between the metal sulfide and Ni foam substrate. Sonochemical deposition of exfoliated rGO on Ni foam with subsequent hydrothermal treatment results in the formation of a rGO-hydrogel-coated Ni foam. Then second-time hydrothermal treatment of the dried Ni@rGO substrate with corresponding metal nitrate and sodium sulfide results in individual uniform growth of porous Ni3S2 nanorods and a Co3S4 self-assembled nanosheet on a Ni@rGO substrate. Both Ni@rGO-Ni3S2 and Ni@rGO-Co3S4 have been electrochemically characterized in a 6 M KOH electrolyte, exhibiting high specific capacitance values of 987.8 and 1369 F/g, respectively, at 1.5 A/g accompanied by the respective outstanding cycle stability of 97.9% and 96.6% at 12 A/g over 3000 charge-discharge cycles. An advanced aqueous asymmetric (AAS) supercapacitor has been fabricated by exploiting the as-prepared Ni@rGO-Co3S4 as a positive electrode and Ni@rGO-Ni3S2 as a negative electrode. The as-fabricated AAS has shown promising energy densities of 55.16 and 24.84 Wh/kg at high power densities of 975 and 13000 W/kg, respectively, along with an excellent cycle stability of 96.2% specific capacitance retention over 3000 charge-discharge cycles at 12 A/g. The enhanced specific capacitance, stupendous cycle stability, elevated energy density, and a power density as an AAS of these electrode materials indicate that it could be a potential candidate in the field of supercapacitors.

Graphene decorated with hexagonal shaped M-type ferrite and polyaniline wrapper: a potential candidate for electromagnetic wave absorbing and energy storage device applications

The development of promising microwave absorbing materials is a booming field of research in both the commercial and defense sectors to prevent electromagnetic pollution, and also to enrich the field of stealth technology. Supercapacitors are a symbol of clean energy storage devices. The present work attends to the preparation of hexagonal shaped magnetic M-type hexaferrite, CuFe10Al2O19 (CFA) by a facile chemical co-precipitation method, and the formation of its composites (graphene/CFA) in the presence of acid modified graphene. An in situ approach was employed for the coating of graphene with CFA. Another nanocomposite (graphene/CFA/PANI) was prepared by the wrapping of graphene/CFA with polyaniline (PANI), which was prepared through the in situ chemical oxidation polymerization of aniline. The prepared multifunctional nanocomposites showed an outstanding and improved microwave absorption property (the maximum reflection loss was −63.6 dB at a thickness of 2.5 mm with a broad absorption range) and electrochemical properties (the highest specific capacitance value was 342 F g−1), in contrast to the pristine graphene and CFA. The addition of PANI also improves the microwave absorption and specific capacitance of the nanocomposites. The formation of the multifunctional nanocomposites and their structural characteristics are discussed thoroughly with their impact on the two different fields of applications i.e. microwave absorbing and energy storage device applications individually.

Solid State Flexible Asymmetric Supercapacitor Based on Carbon Fiber Supported Hierarchical Co(OH)xCO3 and Ni(OH)2

Conducting flexible carbon fiber (CF) cloth was used as a substrate for the hydrothermal growth of nickel hydroxide (Ni(OH)2) and cobalt hydroxy carbonate [Co(OH)xCO3] with unique hierarchical flowery architecture and then was used as a flexible supercapacitor electrode. In a three-electrode configuration in 6 M KOH aqueous electrolyte, the CF-Ni(OH)2 and CF-Co(OH)xCO3 electrode showed the maximum specific capacitance of 789 F/g and 550 F/g, respectively, at 2A/g current accompanied by outstanding cycle stability by retaining 99.9% and 99.5% specific capacitance over 1500 consecutive charge-discharge cycles at 5 A/g. However, the low cell voltage (0.4 V) restricted the respective specific energy to 4.38 and 3.05 Wh/kg at a specific power of 100 W/kg. To overcome the issue, two solid state flexible asymmetric supercapacitors were fabricated using the CF-Ni(OH)2 and CF-Co(OH)xCO3 as the anode and sonochemically deposited CNT over carbon fiber as the cathode material in PVA-KOH gel electrolyte. The as-fabricated flexible supercapacitors CF-Ni(OH)2//CF-CNT and CF-Co(OH)xCO3//CF-CNT were able to deliver high specific energy of 41.1 and 33.48 Wh/kg, respectively, at high specific power of 1.4 kW/kg accompanied by excellent cycle stability (retaining 98% and 97.6% specific capacitance, respectively, over 3000 charge-discharge cycle at 5 A/g).

Polyaniline-wrapped 1D CoMoO4·0.75H2O nanorods as electrode materials for supercapacitor energy storage applications

In this study, a simple and cost effective one-pot hydrothermal process has been carried out for the synthesis of 1D CoMoO4·0.75H2O nanorods. A binary composite of CoMoO4·0.75H2O/PANI has also been synthesized by the in situ oxidative polymerization of aniline with virgin CoMoO4·0.75H2O. Two types of PANI morphologies have been demonstrated: amorphous nanodimensional PANI uniformly coated on CoMoO4·0.75H2O nanorods, and interconnected hollow spheres like PANI inside the bulk material. The prepared CoMoO4·0.75H2O/PANI composite was characterized by X-ray diffraction analysis and Fourier transform infrared spectroscopy for the phase and formation, respectively. The surface morphology was investigated by using FESEM and TEM, which revealed the formation of the CoMoO4·0.75H2O/PANI composite. The electrochemical characterization of the pseudocapacitive CoMoO4·0.75H2O and CoMoO4·0.75H2O/PANI composites in 1 M Na2SO4 showed the highest specific capacitances of 285 F g−1 and 380 F g−1, respectively, at a current density of 1 A g−1. The cyclic stability test demonstrated the specific capacitance retention of about 90.4% after 1000 consecutive charge–discharge cycles at a constant current density of 1 A g−1, which is also higher than that of virgin CoMoO4·0.75H2O—86.3% retention of specific capacitance.

Modified graphene/polyaniline nanocomposites for supercapacitor application

AbstractThis work explored the effect of graphene surface modification on the electrochemical performance of polyaniline-based nanocomposite. The surface modification of graphene was confirmed by Fourier transform infrared spectroscopy. Field emission scanning electron microscopy and high-resolution transmission electron microscopy showed uniform polyaniline coating of the modified graphene. The specific capacitance of the graphene/polyaniline composite was 242 F/g, but it decreased to 193 F/g after graphene modification. However, the capacitance retention increased from 86% to 89% after 500 cycles due to the graphene modification. The thermal stability of the composite also increased after the graphene modification.

Carbon black–clay hybrid nanocomposites based upon EPDM elastomer

The present study explored the effect of nanoclay on the properties of the ethylene–propylene–diene rubber (EPDM)/carbon black (CB) composites. The nanocomposites were prepared with 40 wt% loading of fillers, where the nanoclay percentage was kept constant at 3 wt%. As the modified nanoclay contains the polar groups and the EPDM matrix is nonpolar, a polar rubber oil extended carboxylated styrene butadiene rubber (XSBR), was used during the preparation of nanocomposites to improve the compatibility. Primarily the nanoclay was dispersed in XSBR by solution mixing followed by ultrasonication. After that EPDM-based, CB–clay hybrid nanocomposites, were prepared in a laboratory scale two roll mill. The dispersion of the different nanoclay in the EPDM matrix was observed by wide-angle X-ray diffraction (WAXD) and high resolution transmission electron microscopy. It was found that the mechanical properties of the hybrid nanocomposites were highly influenced by the dispersion and exfoliation of the nanoclays in the EPDM matrix. Thermo gravimetric analysis, scanning electron microscopy and dynamic mechanical thermal analysis was carried out for each nanocomposite. Among all the nanocomposites studied, the thermal and mechanical properties of Cloisite 30B filled EPDM/CB nanocomposite were found to be highest.

Recycling natural rubber vulcanizates through mechanochemical devulcanization

Sulfur-cured gum natural rubber vulcanizates were devulcanized using two different concentrations of diallyl disulfide. The devulcanization process was performed at 110 °C for 10 min in an open two-roll cracker-cummixing mill. Natural rubber vulcanizates having various sulfur/accelerator ratios were used to study the cleavage of monosulfide, disulfide, and polysulfide bonds. The properties of devulcanized natural rubber increased upon increasing the disulfide concentration and the mechanical properties of the revulcanized natural rubber increased upon decreasing the sulfur content in the original rubber vulcanizates. The scorch time and the maximum state of cure both increased when the ground vulcanizates were treated with higher amounts of disulfide. TGA and DMA were conducted to study the effects of the devulcanization on the thermal stability and theTg behavior of the vulcanizates. SEM analysis was conducted to study how the failure mechanism was affected by the devulcanization process. It was possible to recover 70–80% of the original gum rubber properties by using this process. From IR spectroscopic analysis, we observed that the oxidation of the main chains did not occur during high-temperature milling.

Effect of cure systems on shrinkability of polyolefin–EPDM blends

Effects of cure systems on shrinkability of polyolefin and EPDM blends have been studied as a function of cure time and amount of elastomers added. During measurement one of the parameters is kept constant while the other varies. The shrinkability of the blends increases with the increase in cure time when elastomer content is fixed. Similarly, at constant cure time higher loading of elastomer increases the shrinkability of the blends. Samples stretched under high temperature show higher shrinkability than those stretched under room temperature. Dicumylperoxide (DCP) is a more effective curing agent for making a particular set of blends more shrinkable than the sulfur. The changing morphological pattern with DCP-cured shrunk samples from those of sulfur cured samples is corroborated by the SEM studies where the elastomer phase appears to be globular in nature. The crystallinity of the blend depends on the dose and type of the elastomer used in polyolefin. The curing efficiency of the elastomerphase depends on the polyolefin used as blend partner.

One pot synthesis of ilmenite-type NiMnO3-"nitrogen-doped" graphene nanocomposite as next generation supercapacitors.

NiMnO3-nitrogen doped graphene composite has been synthesized by a simple hydrothermal method and its supercapacitor performance investigated. The composite exhibits a specific capacitance of 750.2 F g(-1) in 1 M Na2SO4 at a scan rate of 1 mV s(-1). Nitrogen insertion inside the carbon lattice plays a crucial role in the enhancement of the overall specific capacitance and its long-term stability. This reproducible and superior performance of NiMnO3-nitrogen doped graphene composite make it attractive as a candidate for energy storage materials.