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Lithium manganese spinel, LiMn 2 O 4 (LMO), is a well-established active material for batteries, in which charge is stored via a two-stage insertion of Li + that manifests with coupled current peaks or voltage plateaus under voltammetric or galvanostatic conditions, respectively. The charge–discharge kinetics for LMO are significantly enhanced when the oxide is expressed in a nanoscale form, for example as an ultrathin coating of nanocrystallites at the surfaces of a 3D carbon substrate, such as fiber paper–supported carbon nanofoams (CNFs). In addition to expressing well-defined “battery-like” Li + -insertion peaks between ∼0.6 and 1 V vs . Ag/AgCl when cycled in aqueous lithium sulfate, LMO@CNF electrodes exhibit a pseudocapacitance envelop at more negative potentials (∼0.2–0.6 V). The pseudocapacitive character of LMO@CNF is further verified when cycled in aqueous sodium sulfate, where a broad capacitance envelop dominates the voltammetric response over the entire potential range at a current density an order of magnitude greater than expected for double-layer capacitance. Thus, the LMO@CNF electrode provides a prime example where multiple distinct charge-storage mechanisms are expressed in a single material. Herein, we apply voltammetry and impedance-based methods to deconvolve the respective contributions of double-layer capacitance, surface-based pseudocapacitance, and battery-like Li + insertion. The use of power-law analysis provides a general assignment of transport dynamics, while projecting impedance data as 3D Bode-style representations provides key mechanistic information regarding the time/frequency–potential response of LMO@CNF electrodes. [ABSTRACT FROM AUTHOR]

We demonstrate that point defects may be introduced into a metal oxide to increase its Li-ion capacity by using various heat treatments to modify the defect structure of polycrystalline V2O5 and then comparing the Li capacity of the materials. The V2O5 that is heated under O2/H2O at 460 °C has a 23% higher Li capacity than the as-received material despite no change to its long-range structure. Other heating conditions lower the Li capacity of the V2O5. We infer that heating under O2/H2O introduces defects, such as cation vacancies associated with lithiated oxygen sites, which can electrochemically exchange Li ions and serve as additional charge-storage sites. This study may also explain how metal oxides synthesized from sol–gels, such as xerogels and aerogels, insert lithium ions without concomitant reduction of transition-metal-ion sites—high-surface-area metal oxides are likely to be nonstoichiometric and rich with surface point defects which can serve as additional charge-storage sites. [Copyright &y& Elsevier]

Abstract: We have redesigned the air cathode for metal–air batteries by adapting fiber-paper-supported carbon nanofoams as the base electrode architecture. Electrocatalytic functionality for the oxygen reduction reaction (ORR) is added into the conductive, ultraporous nanofoam paper by electroless deposition at the carbon walls of conformal nanoscopic coatings of birnessite-like manganese oxide (10–20-nm thick MnO x ) via redox reaction with aqueous permanganate (MnO4 −). We report the ORR activity measured using an air-breathing electroanalytical cell for a series of native and MnO x -functionalized carbon nanofoams in which the size of the pore network is varied from tens to hundreds of nanometers, the thickness of the air cathode is varied, and the degree of hydrophilicity/hydrophobicity of the electrode structure is altered. Technologically relevant ORR activity is obtained at 0.9V vs. Zn for MnOx-functionalized carbon nanofoams that are ≥180-μm thick, have pores on the order of 100–200nm, and are modified with hydrophobic poly(vinylidene difluoride). [Copyright &y& Elsevier]

Abstract: In an adaptation of sol–gel methods recently described for preparing iron oxide (FeO x ) aerogels, we use epichlorohydrin as a proton scavenger to generate mixed metal oxides from ethanol solutions of Mn- and Fe-chloride salts. This reaction forms monolithic gels, which can be processed with supercritical CO2 extraction to form high-surface-area, highly porous Mn–FeO x aerogels. The amorphous as-prepared Mn–FeO x aerogel is transformed into a nanocrystalline form by heating in argon to 300°C. Elemental analysis shows that a Fe:Mn ratio of 2:1 is attained, and the X-ray diffraction pattern for the nanocrystalline aerogel is consistent with that for spinel MnFe2O4, confirming that Mn(II) from the initial sol–gel mixture is incorporated into the crystal structure of the resulting oxide. The nanocrystalline Mn–FeO x aerogel exhibits magnetic properties consistent with a superparamagnetic material, while still retaining the characteristic morphology of an aerogel nanoarchitecture. [Copyright &y& Elsevier]

This study demonstrates that ultrasound rapidly degrades the energetic compounds RDX (cyclo-1,3,5-trinitramine-2,4,6-trimethylene) and ADN (ammonium dinitramide) in aqueous microheterogeneous media. The conditions for effective degradation of these nitramines, as monitored by UV absorption spectroscopy, were determined by varying sonication time, the heterogeneous phase and its suspension density, and the concentration of NaOH. In the presence of 5 mg/ml of aluminum powder and at pH∼12 (10 mM NaOH), 74% of the RDX and 86% of the ammonium dinitramide (ADN) in near-saturated solutions decompose within the first 20 min of sonication (20 kHz; 50 W; ⩽5 °C). Sonication without Al powder and base yields minimal degradation of either RDX and ADN (∼5–10%) or the nitrite/nitrate ions that are expected byproducts during RDX and ADN degradation. Sonication at high pH in the presence of dispersed aluminosilicate zeolite, alumina, or titanium dioxide also yields minimal degradation. Preliminary electrochemical studies and product analyses indicate that in situ ultrasonic generation of metallic aluminum and/or aluminum hydride drives reductive denitration of the nitramines. Sonochemical treatment in the presence of a reductant offers an effective and rapid waste remediation option for energetic waste compounds. [Copyright &y& Elsevier]