Debasis Ghosh

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.

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.

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.

Supercapacitor based on H+ and Ni2+ co-doped polyaniline–MWCNTs nanocomposite: synthesis and electrochemical characterization

In the search for promising electrode materials for supercomputer applications, we have synthesized a Ni2+ doped polyaniline, and a nanocomposite based on multiwalled carbon nanotubes (MWCNTs) and a Ni2+ doped polyaniline (PANI) in a HCl medium by an in situ oxidative polymerization. In the HCl medium and in the presence of Ni2+, PANI becomes co-doped with both H+ and Ni2+. The as synthesized materials were characterized by FTIR and Raman spectroscopy and an XRD study. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses confirmed the successful coating of the co-doped PANI on the MWCNT surface. The electrochemical characterizations were carried out by a three electrode system, with 1 M H2SO4 as the electrolyte. The PANI co-doped with H+ and Ni2+exhibited a specific capacitance of 311 F g−1 at a 0.5 A g−1 constant current, which was higher than that of the solely H+ doped PANI, which exhibited a specific capacitance of 265 F g−1 under the same conditions. The incorporation of MWCNTs to the co-doped PANI influenced the specific capacitance to increase to 781 F g−1 at the same constant current density, with a 92% retention of initial specific capacitance over 700 galvanostatic cycles.

High performance supercapacitor electrode material based on vertically aligned PANI grown on reduced graphene oxide/Ni(OH)2 hybrid composite

A simple and cost effective one pot hydrothermal process has been followed for the synthesis of flowery Ni(OH)2, reduced graphene oxide (rGO)/Ni(OH)2 hybrid composite. A ternary composite of rGO/Ni(OH)2/PANI has also been synthesised by in situ oxidative polymerisation of aniline with the binary composite of rGO/Ni(OH)2. A unique morphology of vertically aligned PANI on rGO surface and randomly connected PANI nanowires has been demonstrated following a heterogeneous nucleation on the rGO surface and homogeneous nucleation inside the bulk material. A comparative electrochemical analysis reveals a superior electrochemical behavior of the ternary composite over the rGO–Ni(OH)2, which again shows better electrochemical utility over the virgin Ni(OH)2. The proton insertion/deinsertion reversible pseudocapacitance of Ni(OH)2 combined with the pseudocapacitance of the vertically aligned conducting PANI nanowires and their synergistic effect with in situ reduced graphene oxide results in a high specific capacitance of 514 F g−1 at 2 A g−1 current density accompanied with 94.4% specific capacitance retention after 1000 charge discharge cycles at 5 A g−1 current density.

High Energy Density All Solid State Asymmetric Pseudocapacitors Based on Free Standing Reduced Graphene Oxide-Co3O4 Composite Aerogel Electrodes

Modern flexible consumer electronics require efficient energy storage devices with flexible free-standing electrodes. We report a simple and cost-effective route to a graphene-based composite aerogel encapsulating metal oxide nanoparticles for high energy density, free-standing, binder-free flexible pseudocapacitive electrodes. Hydrothermally synthesized Co3O4 nanoparticles are successfully housed inside the microporous graphene aerogel network during the room temperature interfacial gelation at the Zn surface. The resultant three-dimensional (3D) rGO-Co3O4 composite aerogel shows mesoporous quasiparallel layer stack morphology with a high loading of Co3O4, which offers numerous channels for ion transport and a 3D interconnected network for high electrical conductivity. All solid state asymmetric pseudocapacitors employing the composite aerogel electrodes have demonstrated high areal energy density of 35.92 μWh/cm(2) and power density of 17.79 mW/cm(2) accompanied by excellent cycle life.

Mn3O4 nanoparticles anchored to multiwall carbon nanotubes: a distinctive synergism for high-performance supercapacitors

Modified hydrothermal route (MHT)-evolved Mn3O4 nanoparticles of ∼60 nm diameter were anchored onto a conductive multiwalled carbon nanotubes (MWCNTs) backbone (again under MHT) to produce an energy storage composite. To obtain the benefits of a low cost and stable MWCNT/Mn3O4 composite as a supercapacitor, cyclic voltammetry (CV) and galvanostatic charge–discharge measurements (GCD), as well as cycling stability and electrochemical impedance studies (EIS) have been performed. The electrochemical measurements reveal the suitability of the as-synthesized MWCNT/Mn3O4 composite as an electrode material with a highest specific capacitance of 441 F g−1 at 2 mV s−1 scan rate, which is 1.4 times higher than the specific capacitance (312 F g−1 at a scan rate of 2 mV s−1) of the bare Mn3O4 nanoparticle. MWCNT/Mn3O4 shows an excellent rate capability, outstanding long-term cyclic stability (98% capacity retention after 1000 consecutive cycles) and better power density and energy density. Due to the synergistic effect operating between the pseudocapacitor Mn3O4 nanoparticle and the conductive MWCNT, the capacitive performance of the composite electrode was considerably improved, and we perceive that the composite effect could have benefit in terms of supercapacitor application. These interesting improved material properties of the as-synthesized material indicate that the material is a suitable candidate for use in future energy storage applications.

In Situ Synthesis of Graphene/Amine-Modified Graphene, Polypyrrole Composites in Presence of SrTiO3 for Supercapacitor Applications

Composites based on both unmodified and amine-modified graphene were successfully prepared via in situ oxidative polymerization of pyrrole in presence of SrTiO3. To characterize the graphene/amine-modified graphene-polypyrrole-SrTiO3 composite electrodes, cyclic voltammetry test for measuring specific capacitance, cyclic charge discharge test and an ac impedance test were executed. The composite with unmodified graphene showed better specific capacitance but a little lower cyclability compared to that of modified graphene composite. The presence of SrTiO3 ensures the better thermal stability of the composites compared to that of simple graphene–polypyrrole composite.