Dattakumar Mhamane

From graphite oxide to highly water dispersible functionalized graphene by single step plant extract-induced deoxygenation†

We report a single step facile synthesis of highly water dispersible functionalized graphene nanosheets by plant extract-induced deoxygenation of graphite oxide (GO). The results of various characterizations reveal that the properties of such plant extract-converted graphene nanosheets (PCGN) are comparable to chemically converted graphene nanosheets (CCG). These results open a green route to the emerging graphene-based technologies.

Nonaqueous Lithium‐Ion Capacitors with High Energy Densities using Trigol‐Reduced Graphene Oxide Nanosheets as Cathode‐Active Material

One HEC of a material: The use of trigol-reduced graphene oxide nanosheets as cathode material in hybrid lithium-ion electrochemical capacitors (Li-HECs) results in an energy density of 45 Wh kg(-1) ; much enhanced when compared to similar devices. The mass loading of the active materials is optimized, and the devices show good cycling performance. Li-HECs employing these materials outperform other supercapacitors, making them attractive for use in power sources.

Triple nanocomposites of CoMn2O4, Co3O4 and reduced graphene oxide for oxidation of aromatic alcohols

A composite of reduced graphene oxide (RGO) with oxides of manganese and cobalt together was prepared by a solvothermal method. During synthesis, both the reduction of graphene oxide as well as the growth of nanorod shaped CoMn2O4 and Co3O4 occurred simultaneously having a crystallite size of ~8 nm calculated from X-ray diffraction (XRD). The as-obtained triple nanocomposite material designated as RGO–MnCoO exhibited excellent activity for the liquid phase aerobic oxidation of aromatic alcohols under base-free conditions selectively giving the corresponding aldehydes (>85%). RGO loading was varied in the range of 1–10%, among which 1% RGO–MnCoO showed maximum catalytic activity enhancement of 24% as compared to the bare mixed oxide (MnCo-MO) for the oxidation of vanillyl alcohol. HR-TEM of RGO–MnCoO revealed that it was a composite material having uniform nanotubes of ~25 nm length and 6 nm diameter with a fringe pattern showing the (103) and (004) planes and lattice spaces of 0.26 nm and 0.22 nm, respectively, for the spinel CoMn2O4. The detailed studies on the morphology, size and composition of the as-prepared RGO–MnCoO nanocomposite by XRD, XPS, N2-adsorption/desorption and O2-TPD techniques were used to understand the role of RGO in the enhancement of catalytic activity for oxidation reaction.

Silica-assisted bottom-up synthesis of graphene-like high surface area carbon for highly efficient ultracapacitor and Li-ion hybrid capacitor applications

We report a facile bottom-up approach for the synthesis of pure and macro-sized (>500 nm) graphene-like carbon by precisely employing sp2 carbon rich 1,2,4,5-benzene tetracarboxylic acid (BTCA) as a precursor. We also addressed the features, such as high specific surface area (SSA) and sp2 hybridized carbon content, of the BTCA-derived carbon (BTCADC) over conventional top-down processed reduced graphene oxide (RGO). For instance, a two fold enhancement in SSA (960 m2 g−1) and C : O atomic ratio (∼19) was noted for BTCADC when compared to RGO (SSA: 402 m2 g−1 and C : O ratio ∼ 10). The SSA of BTCADC was further extended to 2673 m2 g−1via a chemical activation process (A-BTCADC) along with a high pore volume (2.15 cm3 g−1). Furthermore, we attempted to explain the unsolved issue of carbon layer stacking (π–π stacking) in RGO by precisely adopting a bottom-up approach. From an application point of view, we explored the possibility of using such carbonaceous materials as promising electrodes for both symmetric and Li-ion hybrid supercapacitor configurations in an organic medium. The A-BTCADC based symmetric cell in a 1 M tetraethylammonium tetrafluoroborate (TEA·BF4) in acetonitrile (ACN) electrolyte displayed a specific capacitance (Csp) of 225 F g−1 (at 0.5 A g−1) with a stable cycling profile of up to 10 000 cycles (at 10 A g−1) between 0 and 3 V. This bottom-up approach opens new avenues to extend graphene-based science and technology to the next level.

Hierarchically nanoperforated graphene as a high performance electrode material for ultracapacitors.

High performance is reported for a symmetric ultracapacitor (UC) cell made up of hierarchically perforated graphene nanosheets (HPGN) as an electrode material with excellent values of energy density (68.43 Wh kg⁻¹) and power density (36.31 kW kg⁻¹). Perforations are incorporated in the graphite oxide (GO) and graphene system at room temperature by using silica nanoparticles as template. The symmetric HPGN-based UC cell exhibits excellent specific capacitance (Cs) of 492 F g⁻¹ at 0.1 A g⁻¹ and 200 F g⁻¹ at 20 A g⁻¹ in 1 M H₂SO₄ electrolyte. This performance is further highlighted by galvanostatic charge-discharge study at 2 A g⁻¹ over a large number (1000) of cycles exhibiting 93% retention of the initial Cs. These property features are far superior as compared to those of symmetric UC cells made up of only graphene nanosheets (GNs), i.e. graphene sheets without perforations. The latter exhibit Cs of only 158 F g⁻¹ at 0.1 A g⁻¹ and the cells is not stable at high current density.

Trigol based reduction of graphite oxide to graphene with enhanced charge storage activity

A triethylene glycol (trigol) based simple approach is reported for the reduction of graphite oxide (GO). This protocol produces high quality graphene which we term as trigol reduced graphene (TRG) and its relevant properties including electrical conductivity and energy storage capacity are comparable to those of graphene obtained by the conventional hydrazine based approach. The achieved specific capacitance for TRG is 130 F g−1 with an energy density value of 18 W h kg−1. This work opens up a new promising synthetic route for the development of graphene and graphene based nanocomposites for various energy related applications.

Rusted iron wire waste into high performance anode (α-Fe2O3) for Li-ion batteries: an efficient waste management approach

Superior Li-storage properties are reported for interconnected α-Fe2O3 derived from iron based wires collected from waste i.e. building supplies or scrap. An interconnected morphology is acquired without the addition of any surfactant or shape controlling agent. We also explore the possibility of employing such a material as a potential low cost conversion type anode for the fabrication of Li-ion cells with a LiMn2O4 cathode. Remarkably, α-Fe2O3 displayed a capacity of ∼1119 mA h g−1 at a current density of 0.05 A g−1 in a half-cell configuration. Good cyclability is also noted, for example α-Fe2O3 delivered ∼800 mA h g−1 after 215 cycles at a current density of 0.2 A g−1. The irreversible capacity loss of the α-Fe2O3 anode has been effectively circumvented by an electrochemical pre-lithiation process and the anode is eventually paired with the eco-friendly cathode, LiMn2O4. The full-cell, LiMn2O4/α-Fe2O3 delivered the initial reversible capacity of ∼737 mA h g−1 with ∼78% retention after 40 cycles. This efficient waste management system with a gram scale synthesis procedure for α-Fe2O3 nanoparticles indeed paved the way for developing high performance Li-ion power packs for high energy requirements.

Surfactant free gram scale synthesis of mesoporous Ni(OH)2–r-GO nanocomposite for high rate pseudocapacitor application

We report a single-step surfactant-free gram scale hydrothermal synthesis of mesoporous Ni(OH)2 nanoparticles and the Ni(OH)2–reduced graphene oxide (Ni(OH)2–r-GO) nanocomposite. Interesting morphological features are noted. These nanomaterials are examined and compared as cathode materials for pseudo-capacitor application through detailed characterizations. A high specific capacitance (Cs) of 1538 F g−1 is observed for Ni(OH)2–r-GO even at a high current density of 40 A g−1, whereas at the same current rate, bare Ni(OH)2 shows Cs of only 936 F g−1.

Non-aqueous energy storage devices using graphene nanosheets synthesized by green route

In this paper we report the use of triethylene glycol reduced graphene oxide (TRGO) as an electrode material for non-aqueous energy storage devices such as supercapacitors and Li-ion batteries. TRGO based non–aqueous symmetric supercapacitor is constructed and shown to deliver maximum energy and power densities of 60.4 Wh kg–1 and 0.15 kW kg–1, respectively. More importantly, symmetric supercapacitor shows an extraordinary cycleability (5000 cycles) with over 80% of capacitance retention. In addition, Li-storage properties of TRGO are also evaluated in half-cell configuration (Li/TRGO) and shown to deliver a reversible capacity of ∼705 mAh g–1 with good cycleability at constant current density of 37 mA g–1. This result clearly suggests that green-synthesized graphene can be effectively used as a prospective electrode material for non-aqueous energy storage systems such as Li-ion batteries and supercapacitors.

Orderly meso-perforated spherical and apple-shaped 3D carbon microstructures for high-energy supercapacitors and high-capacity Li-ion battery anodes

The Stober synthesis, which is composed of two steps of the formation of RF resin spheres in presence of an NH3 catalyst and the carbonization of RF resin spheres under an inert atmosphere, is a well-known approach to the preparation of carbon spheres (CSs). We herein modified the first step of the Stober procedure to introduce morphological and physicochemical changes to CSs. Two different fully perforated 3D carbon-based micromaterials were prepared, namely spherical meso-perforated carbon (SSMPC) and apple-shaped meso-perforated carbon (ASMPC). In the preparation of these materials, we adopted colloidal silica-mediated spray drying method followed by carbonization and silica removal. High specific surface areas and pore volumes were achieved for both ASMPC (1141 m2 g−1 and 3.2 cm3 g−1) and SSMPC (1050 m2 g−1 and 2.1 cm3 g−1). We then evaluated the charge storage properties in organic media from supercapacitor (SC) as well as Li-ion battery (LIB) perspectives. An ASMPC-based symmetric SC was capable of delivering a specific capacitance and energy density of 260 F g−1 and 75.56 W h kg−1, respectively, in addition to an excellent cyclability of 30 000 cycles. In the LIB, ASMPC exhibited a maximum capacity of 1698 mA h g−1 after 175 cycles at 200 mA g−1. We systematically elaborated that inaccessible interior sites of the 3D CSs could become accessible through the introduction of meso-perforations on the periphery and in the interior. We expected that the 3D shape and meso-perforations were responsible for the exceptional performance of CSs in SCs and LIBs.