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We demonstrate electrochemical cycling-induced reduction of MoO3 to monoclinic molybdenum dioxide and molybdenum sub-oxides (MoO3-x), which exhibit excellent electrochemical hydrogen evolution reaction (HER) activity. The conversion of MoO3 during cycling was probed; after 250 cycles, the redox peaks were found to diminish with an onset potential shift and increased HER current density. At 400 cycles, the insertion/deinsertion processes observed in the initial cycles are completely absent and the HER current density is enhanced to the maximum. The effect of MoO3 morphology and size on the electrochemical reduction of MoO3 was also studied.

For the first time, we are reporting the synthesis of Au100-xPtx nanoporous materials in the size range of 7-10 nm through the galvanic replacement of Ag by Pt from Au100-xAg2x spherical nano-alloys (x = 20, 15, 10 and 5) in an aqueous medium. The galvanic replacement reaction follows the 'Volmer-Weber' growth mode, resulting in the formation of surface bound platinum islands on a nanoporous gold surface. The high angle annular dark field image and low angle X-ray diffraction studies confirm the presence of nanoporous Au100-xPtx NPs. The electrochemical studies using the Au85Pt15/C catalyst show excellent methanol tolerance behaviour and better performance towards oxygen reduction reaction (ORR) in terms of high mass activity, mass-specific activity and figure of merit (FOM) when compared to HiSPEC Pt/C commercial catalyst. Preliminary studies on a full cell using nanoporous Au85Pt15/C (loading 1.0 mg cm(-2)) as the cathode material and Pt-Ru/C (loading: 0.5 mg cm(-2)) as the anode material performed better (38 mW cm(-2)) than the HiSPEC Pt/C cathode material (16 mW cm(-2)).

Hexagonal BiPO4·xH2O and Bi0.95Eu0.05PO4·xH2O nanoparticles were synthesized by a polyol-mediated method employing diethylene glycol. The powder X-ray diffraction revealed the phase purity and isostructural nature of both undoped and Eu3+-doped BiPO4. The monoclinic Bi0.95Eu0.05PO4 was obtained by heating the hexagonal Bi0.95Eu0.05PO4·xH2O at 600 °C. The microscopical characterization revealed the formation of nanocrystalline materials. Water molecules present in the bismuth precursor favoured the formation of hexagonal phase at low temperature. The role of DEG molecules in arresting the particle growth during the phase transformation of Bi0.95Eu0.05PO4 from hexagonal to monoclinic was observed. The synthesized materials were characterized using different spectroscopic techniques such as FT-IR, Raman, 31P MAS-NMR, DRUV-Vis and PL. The difference in the crystal structures and symmetries is clearly reflected in the spectral results of hexagonal and monoclinic Bi0.95Eu0.05PO4. The structure-property relations were studied to derive its importance from both fundamental and technological aspects.

Divalent europium-activated alkaline-earth-metal chlorophosphate luminophores (MCAP:Eu 2+ ; M=Ca, Sr, Ba) have been prepared by self-propagating high-temperature (SPHT) synthesis in one pot employing the corresponding nitrates/chlorides, urea and diammonium hydrogen phosphate. The synthesized materials have been characterized by X-ray diffraction, photoluminescent emission spectroscopy, thermogravimetry, scanning electron microscopy and particle size analysis. The formation of chloroapatite depends on the nature of acid used in the combustion mixture. The photoluminescent emission efficiency and particle size distribution are found to depend on the amount of metal chloride used and on the sintering temperature. The results obtained are discussed with respect to the processing method employed.

Recently there has been a considerable focus on the synthesis of nitrogen functionalized graphene for energy storage and conversion. Herein, we report a simple, economical and facile process for the synthesis of nitrogen containing graphene composite which can be scaled up for mass production by using a nitrogen containing organic compound, ethylenediaminetetraacetic acid (EDTA) and graphene oxide as precursors. From the XRD studies, the increase in the interlayer distance between the graphene sheets confirms the functionalization of graphene sheets and the FT-IR spectroscopic analysis revealed the presence of N-containing functional groups in N-doped graphene sheets. XPS analysis confirms the chemical nature of N-containing functional groups, and TG analysis showed the amount of EDTA loaded on the graphene sheets. This composite exhibits a large specific capacitance of 290 F g−1 at 0.1 A g−1 with a capacitance retention of 67% and 58% at high current densities of 10 and 20 A g−1, respectively, thereby showing superior rate capability. In addition, it showed long-term electrochemical stability through 6000 charge–discharge cycles even at a high current density of 5 A g−1 with a specific capacitance loss of 2%.

Mn3O4-reduced graphene oxide (RGO) nanocomposites were prepared by chemical decomposition of the manganese hexacyanoferrate (MnHCF) complex directly on the graphene surface. XRD studies revealed the formation of crystalline hausmannite Mn3O4 nanocubes in the as-prepared nanocomposites without any heat treatment. The FE-SEM images showed the formation of Mn3O4 nanocubes on the graphene surface in the as-prepared nanocomposites. HR-TEM studies confirmed the homogeneous dispersion of ∼25 nm Mn3O4 nanocubes on graphene nanosheets. The amount of Mn3O4 nanocubes and graphene in the nanocomposites was estimated using TGA analysis from room temperature to 800 °C in air. The FT-IR and Raman spectroscopic analysis confirmed the functional groups in the nanocomposites and defects in graphene nanosheets in the nanocomposites. Cyclic voltammetry and galvanostatic charge-discharge experiments demonstrated a high specific capacitance of 131 F g(-1) in 1 M Na2SO4 electrolyte at a current density of 0.5 A g(-1) for the RGM-0.5 nanocomposite. A capacitance retention of 99% was observed for 500 charge-discharge cycles at a current density of 5 A g(-1), which conformed the excellent stability of the RGM electrodes. The prepared Mn3O4-RGO nanocomposites are promising for electrochemical energy storage.

A graded nano-alloy of Au100−xPtx (x = 7, 15, 23, 32, 40, 51, 62, 73 and 86) nanoparticles (NPs) formed by co-reduction of HAuCl4 and H2PtCl6 and the details are presented in this work. Au100−xPtx NPs were characterized using surface plasmon resonance (SPR) absorption spectroscopy and transmission electron microscopy (TEM). The NPs were dispersed in Vulcan carbon (Au100−xPtx/C) and annealed at 250, 400, 600 and 800 °C. The as-formed and annealed materials were characterized using TEM, high resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (XRD), cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The CV studies indicate excess Pt on the surface, which is corroborated by XPS and HR-TEM results. The XRD data show that Vegard's law is obeyed by the as-formed material and the materials annealed at 250 and 400 °C, indicating that these materials are not nano-alloys. The studies clearly indicate that the formation of Au100−xPtx NPs is kinetically controlled rather than being controlled by the thermodynamic stability. The results demonstrate the formation of graded alloys of Au100−xPtx NPs. Pt excess in the graded nano-alloy is reflected favourably in the electrochemical oxidation of small organics. In the methanol oxidation reaction (MOR), the peak current value per mg of Pt increases as a function of x, reaches a maximum value at x = 23 and the ratio of forward current to reverse current for MOR reached an unprecedented value of 6.7, which shows the catalyst’s stability against poisoning by carbonaceous intermediates.

Bulk-synthesized silicon carbide, hitherto considered inactive for electrochemical lithium insertion, is demonstrated as a potential high-capacity, long-cycling anode material for lithium-ion batteries. In this study, we show that cubic (3C polytype) nano SiC, prepared by a chemical vapour deposition (CVD) method, delivers a reversible lithium insertion capacity of about 1200 mA h g−1 over 200 cycles.