Amr M. Abdelkader

DC Voltammetry of Electro-deoxidation of Solid Oxides

1. Introduction 28632. Theoretical Considerations 28643. Electro-deoxidation under Controlled Voltage orPotential 28663.1. Earlier Attempts to Describe the ReductionMechanism 28663.2. Three-Phase Interline (3PI) PropagationModels 28673.3. Alkali Ternary Oxides Intermediates 28673.3.1. Niobium Oxide 28673.3.2. Tantalum Oxide 28683.3.3. Chromium Oxide 28683.3.4. Titanium Oxide 28683.3.5. Zirconium Oxide 28703.3.6. Tungsten Oxide 28703.3.7. Aluminum Oxide 28703.4. Electro-deoxidation of Mixed Oxides andOxide Solid Solutions 28713.5. Attempts to Use Inert Anode 28734. Cyclic Voltammetry 28744.1. Understanding the Cathodic ReductionReactions 28744.2. Determining the Optimum Operation Po-tential 28764.3. Exploring the Surface Phenomenon 28774.4. Studying the Complex Side Processes andDetecting the High Temperature Intermedi-ate Phases 28774.5. Providing Direct Insights into the Kinetics ofElectrode Reactions 28785. Electro-deoxidation under Constant CurrentChronopotentiometry 28796. Summary and Future Direction 2882Author Information 2883Corresponding Author 2883Notes 2883Biographies 2883References 2884

Supercapacitance from Cellulose and Carbon Nanotube Nanocomposite Fibers

Multiwalled carbon nanotube (MWNT)/cellulose composite nanofibers have been prepared by electrospinning a MWNT/cellulose acetate blend solution followed by deacetylation. These composite nanofibers were then used as precursors for carbon nanofibers (CNFs). The effect of nanotubes on the stabilization of the precursor and microstructure of the resultant CNFs were investigated using thermogravimetric analysis, transmission electron microscopy and Raman spectroscopy. It is demonstrated that the incorporated MWNTs reduce the activation energy of the oxidative stabilization of cellulose nanofibers from ∼230 to ∼180 kJ mol–1. They also increase the crystallite size, structural order, and electrical conductivity of the activated CNFs (ACNFs). The surface area of the ACNFs increased upon addition of nanotubes which protrude from the fiber leading to a rougher surface. The ACNFs were used as the electrodes of a supercapacitor. The electrochemical capacitance of the ACNF derived from pure cellulose nanofibers is demonstrated to be 105 F g–1 at a current density of 10 A g–1, which increases to 145 F g–1 upon the addition of 6% of MWNTs.

Alkali reduction of graphene oxide in molten halide salts: Production of corrugated graphene derivatives for high-performance supercapacitors

Herein we present a green and facile approach to the successful reduction of graphene oxide (GO) materials using molten halide flux at 370 °C. GO materials have been synthesized using a modified Hummers method and subsequently reduced for periods of up to 8 h. Reduced GO (rGO) flakes have been characterized using X-ray-diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR), all indicating a significantly reduced amount of oxygen-containing functionalities on the rGO materials. Furthermore, impressive electrical conductivities and electrochemical capacitances have been measured for the rGO flakes, which, along with the morphology determined from scanning electron microscopy, highlight the role of surface corrugation in these rGO materials.

Electrochemical synthesis of highly corrugated graphene sheets for high performance supercapacitors

Highly corrugated graphene sheets with low susceptibility to re-stacking were prepared by electrochemical reduction of graphene oxide (GO) in a molten salt bath. Oxygen functional groups were removed by depositing the reducing agent on a GO assembled cathode and also by direct electro-deoxygenation without generating reducing agents. The produced graphene derivative had electrical conductivity as high as 2300 S m−1, and a specific surface area of 565 m2 g−1 making it ideal as a supercapacitor with maximum specific capacitance of 255 F g−1 in 6 M KOH aqueous solution without the need for doping the graphene sheets. Further, the supercapacitor showed excellent cycling stability, retaining 95% of its initial capacitance after 5000 cycles of charge/discharge. Therefore, this material presents great promise for future design and large-scale production of affordable and high performance graphene electrodes for portable energy storage devices.

Electrochemical synthesis and characterization of a NdCo5 permanent magnet

NdCo5 was produced in a simple one-stage process by electro-deoxidising an inexpensive single phase solid oxide solution of Nd2O3 and Co3O4. The reduction was performed in molten CaCl2 at 900 °C and the cell operated at 3.1 V at a cathodic current density of 170 mA cm−2 for 12 hours. The magnetic properties of the product, measured using a vibrating magnetometer, closely matched that of pure and homogenous NdCo5. The reaction mechanism at the cathode is elucidated from partially reduced samples using electron microscopy, X-ray diffraction analysis and conductivity measurements.

Quick one-pot synthesis of amorphous carbon-coated cobalt–ferrite twin elliptical frustums for enhanced lithium storage capability

Hybrid carbon-coated transition metal oxides (TMOs@C) offer enhanced lithium storage capabilities, but the facile formation of TMOs@C nanocomposites remains a great challenge. Herein, we report a novel hierarchical hybrid nanostructure of carbon-coated CoFe2O4 twin elliptical frustums (CoFe2O4@C TEFs) via a quick one-pot refluxing reaction in ethylene glycol (EG) followed by an annealing treatment. When evaluated as an anode in lithium-ion batteries (LIBs), the resultant CoFe2O4@C TEF hybrids demonstrate good electrochemical performance with high reversible specific capacity, excellent rate capability and super-long life cycle. After 600 cycles at a current density of 500 mA g−1, the resultant TEFs still deliver a stable reversible discharge capacity of 875 mA h g−1. This work demonstrates the extensive potential of such simple synthetic methods towards various carbon coated transition metal oxide composites for energy conversion and storage devices.

Few layer graphene–polypropylene nanocomposites: the role of flake diameter

Graphene shows excellent potential as a structural reinforcement in polymer nanocomposites due to its exceptional mechanical properties. We have shown previously that graphene composites can be analysed using conventional composite theory with the graphene flakes acting as short fillers which have a critical length of ∼3 μm which is required for good reinforcement. Herein, polypropylene (PP) nanocomposites were prepared using electrochemically-exfoliated few layer graphene (FLG) with two different flake diameters (5 μm and 20 μm). The crystallization temperature and degree of crystallinity of the PP were found to increase with the loading of FLG, which suggests that the flakes acted as crystallisation nucleation sites. Mechanical testing showed that the 5 μm flakes behaved as short fillers and reinforced the PP matrix poorly. The modulus of the 20 μm flake composites, however, increased linearly with loading up to 20 wt%, without any of the detrimental aggregation effects seen in other graphene systems. The mechanical data were compared with our previous work on other graphene composite systems and the apparent need to balance the degree of functionalization to improve matrix compatibility whilst not encouraging aggregation is discussed.

Electrochemical exfoliation of graphite in quaternary ammonium-based deep eutectic solvents: a route for the mass production of graphane.

We demonstrate a facile and scalable electrochemical approach to exfoliate graphite, which permits in situ hydrogenation of the resultant graphene via a solvated NR(4+) graphite compound in quaternary ammonium-based deep eutectic solvents. Spectroscopic studies reveal the presence of sp(3) C-H bonds in the hydrogenated graphene. The resulting materials consist of micrometre-sized and predominantly monolayer to few layers thick hydrogenated graphenic flakes. A large band gap (∼4 eV) further establishes the high level of hydrogenation. It is also possible to tune the band gap introduced to the graphene by controlling the level of hydrogenation. The mechanism of the exfoliation and hydrogenation is also discussed.

Utilization of Constant Current Chronopotentiometry to Synthesize a Co–Cr Alloy

Co-30 wt % Cr alloy was prepared by electro-deoxidation in molten calcium chloride at 1123 K. Constant current chronopotentiometry was used to prepare the alloy and investigate its mechanism of formation. The sintered starting material consisted of the solid solution Co x Cr y O 4 and some Co 3 O 4 ; the latter decomposes spontaneously to CoO in a low oxygen environment. Electro-deoxidation proceeds by the simultaneous rapid reduction of CoO to Co and the slower reduction of Co x Cr y O 4 to CaCr 2 O 4 and Co. The formation of CaCr 2 O 4 requires calcium ions from the melt, and it was reduced at a higher cathodic potential to Cr, releasing the calcium ions back into the salt. The overall process is under charge-transfer control in the range from 10 to 70 mA cm -2 and mixed control from 70 to 140 mA cm -2 enabling very fast reduction times to be achieved.