Pseudocapacitive behavior of the Fe2O3 anode and its contribution to high reversible capacity in lithium ion batteries.

Pseudocapacitance, which is the storage of charge based on continuous and fast reversible redox reactions at the surface of electrode materials, is commonly observed for electrodes in lithium ion batteries, especially for transition metal oxide anodes. In this report, bare Fe2O3 of granular morphology (∼30 nm in diameter) with high purity and decent crystallinity as well as recommendable electrochemical performances is fabricated hydrothermally and employed as the subject to clarify pseudocapacitive behavior in transition metal oxide anodes. Electrochemical technologies such as galvanostatic charging/discharging, differential capacity analysis (dQ/dV) and the power law relationship (i = aνb), which can distinguish pseudocapacitive behaviors of an electrode reaction were employed to analyze the electrodes. Reversible capacities of ∼120 mA h g-1 (0.117 F cm-2) for Fe2O3 were found within particular electrochemical windows (2.3-3.0 V, 0.3-0.8 V for discharging and 2.2-3.0 V, 0.3-1.3 V for charging). A new direction of optimizing the capacities, rate and cycling performances for lithium ion batteries is pointed out with connections between the pseudocapacitive behavior and morphologies of surfaces as well as structures of the electrodes.

Synthesis of Hollow Co-Fe Prussian Blue Analogue Cubes by using Silica Spheres as a Sacrificial Template.

Herein, we report a novel method for the formation of hollow Prussian blue analogue (CoFe-PBA) nanocubes, using spherical silica particles as sacrificial templates. In the first step, silica cores are coated by a CoFe-PBA shell and then removed by etching with hydrofluoric acid (HF). The cubic shape of CoFe-PBA is well-retained even after the removal of the silica cores, resulting in the formation of hollow CoFe-PBA cubes. The specific capacity of the hollow CoFe-PBA nanocubes electrodes is about two times higher than that of solid CoFe-PBA nanocubes as storage materials for sodium ions. Such an improvement in the electrochemical properties can be attributed to their hollow internal nanostructure. The hollow architecture can offer a larger interfacial area between the electrolyte and the electrode, leading to an improvement in the electrochemical activity. This strategy can be applied to develop PBAs with hollow interiors for a wide range of applications.

Controlled synthesis of mesoporous nitrogen-doped carbons with highly ordered two-dimensional hexagonal mesostructures and their chemical activation.

Ordered mesoporous nitrogen-doped carbon (OMNC) materials are considered as the most promising material for supercapacitors. In this study, a highly ordered two-dimensional (2D) hexagonal mesostructured polymer was synthesized through a facile assembly of triblock polymer micelles and phenol-melamine/formaldehyde resin via an organic-organic assembly process in aqueous solution. After calcination, the novel OMNC materials with 2D hexagonal mesostructures were obtained. By further KOH activation, the surface area and the porosity of the OMNC significantly improved, and the internal mesoporous structures were maintained. The activated OMNC-800A displayed a specific capacitance as high as 475.75 F g-1 at 0.5 A g-1 with an outstanding cycling stability (over 100% capacitance retention during 2000 cycling tests at 100 mV s-1). These results confirm that the tubular mesochannels inside the OMNC are very beneficial in providing an accessible path for diffusion of the electrolyte, thereby improving the specific capacitance of OMNC at a high current density.

Doped graphene supercapacitors.

Heteroatom-doped graphitic frameworks have received great attention in energy research, since doping endows graphitic structures with a wide spectrum of properties, especially critical for electrochemical supercapacitors, which tend to complement or compete with the current lithium-ion battery technology/devices. This article reviews the latest developments in the chemical modification/doping strategies of graphene and highlights the versatility of such heteroatom-doped graphitic structures. Their role as supercapacitor electrodes is discussed in detail. This review is specifically focused on the concept of material synthesis, techniques for electrode fabrication and metrics of performance, predominantly covering the last four years. Challenges and insights into the future research and perspectives on the development of novel electrode architectures for electrochemical supercapacitors based on doped graphene are also discussed.

Graphene supported non-precious metal-macrocycle catalysts for oxygen reduction reaction in fuel cells.

Fuel cells are promising alternative energy devices owing to their high efficiency and eco-friendliness. While platinum is generally used as a catalyst for the oxygen reduction reaction (ORR) in a typical fuel cell, limited reserves and prohibitively high costs limit its future use. The development of non-precious and durable metal catalysts is being constantly conceived. Graphene has been widely used as a substrate for metal catalysts due to its unique properties, thus improving stability and ORR activities. In this feature, we present an overview on the electrochemical characteristics of graphene supported non-precious metal containing macrocycle catalysts that include metal porphyrin and phthalocyanine derivatives. Suggested research and future development directions are discussed.

Polyaniline-grafted reduced graphene oxide for efficient electrochemical supercapacitors.

An alternative and effective route to prepare conducting polyaniline-grafted reduced graphene oxide (PANi-g-rGO) composite with highly enhanced properties is reported. In order to prepare PANi-g-rGO, amine-protected 4-aminophenol was initially grafted to graphite oxide (GO) via acyl chemistry where a concomitant partial reduction of GO occurred due to the refluxing and exposure of GO to thionyl chloride vapors and heating. Following the deprotection of amine groups, an in situ chemical oxidative grafting of aniline in the presence of an oxidizing agent was carried out to yield highly conducting PANi-g-rGO. Electron microscopic studies demonstrated that the resultant composite has fibrillar morphology with a room-temperature electrical conductivity as high as 8.66 S/cm and capacitance of 250 F/g with good cycling stability.

Highly conducting and flexible few-walled carbon nanotube thin film.

We report an effective route to prepare highly conducting and flexible few-walled carbon nanotube (FWNT) thin films. The free-standing thin films were fabricated by functionalizing FWNTs with 4-ethoxybenzoic acid (EBA) via a direct Friedel-Crafts acylation reaction in a nondestructive polyphosphoric acid/phosphorus pentoxide medium. The resulting ethoxybenzoyl-functionalized FWNT (EBA-f-FWNT) was readily dispersible in water. EBA-f-FWNT thin films were formed by a simple suction filtration of the dispersed solution. Electron microscopic studies were employed to characterize the morphologies of the resulting thin films. The obtained results indicate that the structure of FWNTs was not perturbed by the incorporation of EBA moieties, which were uniformly grafted onto FWNTs forming the FWNT networks. Room temperature electrical conductivity of the thin films was obtained using standard four-probe measurements, which revealed a value as high as 29 400 S m(-1), while the tensile strength and modulus of the film were found to be about 80 MPa and 15 GPa, respectively. Cyclic voltammograms revealed a rectangular shape, with superior capacitive behaviors nearing 133 F/g for the thin films, which is very attractive for capacitor applications.

Architectures of bilayered gold nanoparticles on UV cross-linked poly(4-vinylpyridine) thin films.

A generic approach for immobilizing gold nanoparticles (GNPs) and the construction of multilayered gold structures are reported. The process involves the use of UV cross-linked poly(4-vinylpyridine) (P4VP) thin films for the immobilization and construction of multilayered GNP architectures. P4VP thin films were prepared by spin-coating of the polymer solution onto silicon wafer substrates which was then cross-linked via UV exposure. GNPs, about 70 nm were immobilized via electrostatic adsorption onto the P4VP films. Further, these monolayer surfaces containing GNPs were capped with a bifunctional cross-linker, 1,6-hexanedithiol (HDT). To the additional end termini of HDT, a second layer of GNPs (approximately 20 nm) was assembled. The self-assembly of 1,6-hexanedithiol on the immobilized GNPs and the bilayered architectures were investigated by atomic force microscopy (AFM), filed emission scanning electron microscopy (FE-SEM), and UV-Vis absorption spectroscopy.

Novel amino-acid-based polymer/multi-walled carbon nanotube bio-nanocomposites: highly water dispersible carbon nanotubes decorated with gold nanoparticles.

A well-reproducible and completely green route towards highly water dispersible multi-walled carbon nanotubes (MWNT) is achieved by a non-invasive, polymer wrapping technique, where the polymer is adsorbed on the MWNT's surface. Simply mixing an amino-acid-based polymer derivative, namely poly methacryloyl beta-alanine (PMBA) with purified MWNTs in distilled water resulted in the formation of PMBA-MWNT nanocomposite hybrids. Gold nanoparticles (AuNPs) were further anchored on the polymer-wrapped MWNTs, which were previously sonicated in distilled water, via the hydrogen bonding interaction between the carboxylic acid functional groups present in the polymer-modified MWNTs and the citrate-capped AuNPs. The surface morphologies and chemistries of the hybrids decorated with nanoparticles were characterized by transmission electron microscopy (TEM) and UV-visible absorption spectroscopy. Additionally, the composites were also prepared by the in situ free radical polymerization of the monomer, methacryloyl beta-alanine (MBA), with MWNTs. Thus functionalized MWNTs were studied by thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM) and TEM. Both methods were effective in the nanotube functionalization and ensured good dispersion and high stability in water over three months. Due to the presence of the high densities of carboxylic acid functionalities on the surface of CNTs, various colloidal nanocrystals can be attached to MWNTs.

A facile synthesis, antibacterial, and antitubercular studies of some piperidin-4-one and tetrahydropyridine derivatives.

The raise in clinical significance of multidrug-resistant bacterial pathogens has directed us to synthesize 2,6-diarylpiperidin-4-one and Delta(3)-tetrahydropyridin-4-ol based benzimidazole and O-arylsulfonyl derivatives. X-ray crystal structure of tetrahydropyridinol (23) confirmed a change in conformation and orientation of substituents upon amide formation. Antibacterial activities evaluated against a wide number of bacterial pathogens (both sensitive and multidrug-resistant) revealed that 19, 27 against Staphylococcus aureus, 27 against Enterococcus faecalis, and 19, 21, 23, and 27 against Enterococcus faecium are significantly good at lowest MIC(90) (16 microg/mL). Inhibitory power noticed by 23 against Vancomycin-Linezolid-resistant E. faecalis and 27 against Vancomycin-resistant E. faecium are onefold better than the standard Linezolid and Trovafloxacin drugs, respectively. Moreover, antitubercular activity for the selected compounds against Mycobacterium tuberculosis H37Rv revealed that compounds 23, 24, and 27 expressed onefold improved potency compared to the standard Rifampicin drug.

r-2,c-6-Bis(3-methoxy-phen-yl)-t-3,t-5-dimethyl-piperidin-4-one.

In the title compound, C(21)H(25)NO(3), the piperidinone ring adopts a chair conformation with an equatorial orientation of all substituents; the 3-methoxy-phenyl groups make a dihedral angle of 60.26 (15)°. The carbonyl group O atom is disordered over two positions in a 0.643 (3):0.357 (3) ratio. The crystal structure is stabilized by N-H⋯O and C-H⋯O hydrogen bonding.