Anil Suryawanshi

Concurrent synthetic control of dopant (nitrogen) and defect complexes to realize broadband (UV–650 nm) absorption in ZnO nanorods for superior photo-electrochemical performance

We report a facile solution based synthesis protocol to incorporate nitrogen within zinc oxide nanorods with substantially improved visible light harvesting via broadband absorption stretching from UV to deep visible wavelengths (650 nm). We also report a peculiar visible region maximum around 470 nm. Raman and X-ray photoelectron spectroscopy confirm incorporation of nitrogen along with other complex defects such as zinc interstitials and oxygen vacancies. Our N:ZnO appears pale orange as opposed to the pale yellow reported in other works. It exhibits significantly superior photo-electrochemical performance over undoped ZnO. Notably under monochromatic green light illumination (530 nm) N:ZnO shows a photocurrent density of 3.2 μA cm−2, whereas pristine ZnO fails to show any photo-response. The IPCE spectrum of N:ZnO follows the broadband absorption spectrum extending up to an unprecedented value of 650 nm, potentially expanding the scope for using our material in other solar energy harvesting applications.

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.

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.

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.

Mesoscopic magnetic iron oxide spheres for high performance Li-ion battery anode: a new pulsed laser induced reactive micro-bubble synthesis process

Spherical particles of iron oxide (mainly Fe3O4 with a small contribution of α-Fe2O3) having a size of about ∼200 nm are synthesized from bulk commercial α-Fe2O3 powder by a pulsed excimer laser irradiation technique in solution phase. The dispersed α-Fe2O3 powder is subjected to a pulsed excimer laser (248 nm) irradiation at an energy density of ∼214 mJ cm−2 and pulse repetition rate of 10 Hz for 5 h under constant stirring in the presence of aqueous ammonia. It has been observed that the α-Fe2O3 particles get gradually converted into Fe3O4, which can be visualized from the change in the color of the solution from red to dark red, and then finally to a black colored solution. The phase conversion from α-Fe2O3 to Fe3O4 has also been confirmed by various characterizations, such as Raman and Mossbauer spectra. From the Mossbauer spectra at the end of 5 h laser irradiation 87% of Fe3O4 was observed. The detailed mechanism of the formation of these particles has been investigated. The performance of these particles was verified for use as anode materials in Li ion batteries. The iron oxide particles show a capacity of 1100 mA h g−1 at a current density of 100 mA g−1. This capacity is highly stable up to 40 cycles without any significant capacity fading. A coulombic efficiency of 97% has been achieved with high stability and reversibility.

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.

Red Mud and Li‐Ion Batteries: A Magnetic Connection

Exceptional Li-ion battery performance is presented with the oxide component of the anode was extracted from red mud by simple magnetic separation and applied directly without any further processing. The extracted material has γ-Fe2 O3 as the major phase with inter-dispersed phases of Ti, Al, and Si oxides. In a half-cell assembly, the phase displayed a reversible capacity (∼697 mA h g(-1) ) with excellent stability upon cycling. Interestingly, the stability is rendered by the multiphase constitution of the material with the presence of other electrochemically inactive metal oxides, such as Al2 O3 , SiO2 , and Fe2 TiO4 , which could accommodate the strain and facilitate release during the charge-discharge processes in the electrochemically active maghemite component. We fabricated the full-cell assembly with eco-friendly cathode LiMn2 O4 by adjusting the mass loading. Prior to full-cell assembly, an electrochemical pre-lithiation was enforced to overcome the irreversible capacity loss obtained from the anode. The full-cell delivered a capacity of ∼100 mA h g(-1) (based on cathode loading) with capacity retention of ∼61 % after 2000 cycles under ambient conditions.