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A nickel foam-supported Ni(OH) 2 /NiOOH electrode, synthesized in-situ at a specific electrode overpotential, was used to study the oxidation of ammonia in aqueous solution. Results of voltammetric analysis showed the formal potential of Ni(OH) 2 /NiOOH transition at +0.6 V (vs. Hg/HgO, pH 11) at which the current profile was improved by electron transfers of NH 3 in the electrolyte. Selectivity of NH 3 conversion to NO 3 − and N 2 was evaluated by batch constant current experiments. Electrochemical parameters, including solution pH (6–12), temperature (20–40 °C), current density (0.2–3 mA cm −2 ), and initial NH 3 -N concentration (20–450 mg-L −1 ), that may affect ammonia oxidation toward nitrogen selectivity were studied. At constant current density of 1.5 mA cm −2 A, ammonia removal reached 98.5% and NO 3 − was the major product at initial NH 3 -N concentration of 50 mg-L −1 in 7 h. By contrast, N 2 evolution dominated at low current density (<1 mA cm −2 ) and high initial NH 3 -N concentration (i.e., >100 mg-L −1 ). A surface steady-state approach, with NH 3 deprotonation as the rate-limiting step, provided the reaction pathways of NH 3 conversion to molecular nitrogen byproduct. [ABSTRACT FROM AUTHOR]

Direct electrocatalytic oxidation of ammonia was carried out using an open-pore structured nickel foam electrode via electrochemical formation of Ni(OH) 2 /NiOOH nano-flowers (theophrastite phase) on the nickel substrate at specific overpotentials. The electrode surface was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectrometer (RS), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammograms gave information on the nature of electron transfer between nitrogen species and nickel foam electrode and revealed the potential dependence nature of ammonia oxidation over the potential window of +0.7 V to +0.85 V (vs. Hg/HgO). Batch controlled potential experiments using nickel foam as the working anode in a three-electrode system were conducted to study the oxidation of ammonia in solution containing 0.1 M of Na 2 SO 4 electrolyte, at pH 11 and temperature of 25 °C. Based on the current efficiency and reaction kinetics, it was possible to establish the mechanism of selective ammonia conversion to gaseous nitrogen and nitrate. [ABSTRACT FROM AUTHOR]

Graphite-supported α- and β- PbO 2 electrodes (PbO 2 @G) were prepared by electrochemical deposition at appropriate potentials with regard to Pb(II)/PbO 2 redox couple under alkaline and acidic conditions, respectively, for studying the direct electro-oxidation of ammonia in aqueous solutions. Results of surface characterization including scanning electron microscopy (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) indicated the presence of polymorphs of PbO 2 @G. Cyclic voltammetry (CV) of the electrolyte containing NH 3 indicated mediation of electron transfer by PbO 2 . At the onset potential of ca. +1.0 to +1.45 V (vs. Hg/HgO), a pathway of NH 3 oxidation to nitrogen byproducts, namely, N 2 , NO 2 − , and NO 3 − was proposed. The removal efficiency and selective conversion of ammonia (0.1 M Na 2 SO 4 , pH 11, 25 °C) on PbO 2 @G was determined based on controlled potential experiments. [ABSTRACT FROM AUTHOR]

Silicon (Si) has been perceived as a promising next-generation anode material for lithium ion batteries (LIBs) due to its superior theoretical capacity. Despite the natural abundance of this element on Earth, large-scale production of high-purity Si nanomaterials in a green and energy-efficient way is yet to become an industrial reality. Spray-drying methods have been exploited to recover Si particles from low-value sludge produced in the photovoltaic industry, providing a massive and cost-effective Si resource for fabricating anode materials. To address such drawbacks like volume expansion, low electrical and Li + conductivity and unstable solid electrolyte interphase (SEI) formation, the recycled silicon particles have been downsized into nanoscale and shielded by a highly conductive and protective graphene multilayer through high energy ball milling. Cyclic voltammetry and electrochemical impedance spectroscopy measurements have revealed that the graphene wrapping and size reduction approach have significantly improved the electrochemical performance. It delivers an excellent reversible capacity of 1,138 mA h g −1 and a long cycle life with 73% capacity retention over 150 cycles at a high current of 450 mA g −1 . The plentiful waste conversion methodology also provides considerable opportunities for developing additional rechargeable devices, ceramic, powder metallurgy and silane/siloxane products. [ABSTRACT FROM AUTHOR]

The behaviors of lithium ions in a comb-like polymer electrolyte with chelating functional group complexed with LiCF3SO3, LiBr and LiClO4 were characterized by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, AC impedance, and 13C solid-state NMR measurement. The comb-like copolymer was synthesized from poly(ethylene glycol) methyl ether methacrylate (PEGMEM) and (2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) (GMA-IDA). FT-IR spectra reveal the interactions of Li+ ions with both the ether oxygen of the PEGMEM and the nitrogen atom of the GMA-IDA segments. FT-IR spectra also indicate an increasing anion–cation association consistent with increasing LiCF3SO3 concentrations. Moreover, the 13C solid-state NMR spectra for the carbons attached to the ether oxygen atoms exhibited significant line broadening and a slight upfield chemical shift when the dopant was added to the polymer. These findings indicate coordination between the Li cation and the ether oxygens in the PEG segment. Tg and Td of copolymers doped with salts clearly increase, as shown by DSC and TGA measurements. These results indicate the interactions of Li+ with both PEGMEM and GMA-IDA segments form transient cross-links inside the copolymers. The Vogel–Tamman–Fulcher (VTF)-like behavior of conductivity implies the coupling of the charge carriers with the segmental motion of the polymer chain in this study. The maximum conductivity of copolymers relates to the composition of the copolymers and the concentration of doping lithium ions. In summary, the GMA-IDA unit in the copolymer promotes the dissociation of the lithium salt, the mechanical strength and the conductivity of the polyelectrolyte. [Copyright &y& Elsevier]

Novel thermoplastic polyurethanes with chelating groups were synthesized from 4,4′-diphenylmethane diisocyanate (MDI), poly(ethylene glycol) (PEG), and EP-IDA. Differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FT-IR), and impedance spectroscopy (IS) were used to monitor changes in the morphology of these polyurethanes with the concentration of lithium perchlorate (LiClO4) dopants. Adding the salt significantly changes the FTIR spectrum of the polyurethane, indicating an interaction between the lithium cation within the urethane group and the chelating group. The soft segment Tg increases with LiClO4 concentration, as determined by DSC, indicating that solubility of the lithium cation in the host polyurethane increases with the chelating groups. IS shows that the bulk conductivity reaches a maximum as the salt concentration is increased. One of the investigated polyurethane electrolytes has an ionic conductivity as high as ∼10−6 S cm−1 at room temperature. [Copyright &y& Elsevier]