The mechanism of Pd/γ-NiOOH 2 nm cubes hydrogen oxidation catalyst for alkaline fuel cell is investigated by operando X-ray absorption spectroscopy.

Most of the recently discovered layered materials such as MoS2 or MoSe2 are n-type, while few materials, such as phosphorene, which suffers from rapid oxidation, are p-type. To form devices such as p-n junctions and heterojunctions, new p-type mono-/few-layers are needed. Here, we report a one-step synthesis of layered, crystalline, p-type copper sulfide by thermal annealing of a standard copper foil in an inert environment using chemical vapor deposition (CVD). Optical spectroscopies (photoluminescence and absorption) show definite correlating features around 2.5 eV. Surface photovoltage spectroscopy shows a photovoltage reduction around the same energy range, which would be expected from a bandgap of a p-type material, and p-type conductivity was also observed using a thermoelectric probe. TEM, XRD, and AFM showed that the synthesized material is layered and has a unique stoichiometry of Cu9S5. Using sonication and dropcasting, we succeeded to isolate few-layers and monolayers. We observed good bulk electrical conductivity and characterized the electrical conductivity of few-layer copper sulfide flakes using peak force tunneling atomic force microscopy (PF-TUNA). We observed an increase in conductivity for increasing number of layers. Given its conductivity and layered morphology, we tested the synthesized Cu9S5 as an electrode for a Li-ion battery. The proposed bottom-up synthesis, which is simple and scalable, allows synthesizing bulk quantities of the p-type layered Cu9S5 which can then be exfoliated (top-down) to deposit monolayer flakes on substrates. Combined with the progress achieved in the preparation of n-type layered materials, this p-type Cu9S5 opens the door to the fabrication of 2D p-n heterojunctions.

The large-scale synthesis of polyhedral Ag nanoparticles (NPs) described here follows a mediated-particle mechanism and the formulation of NPs in high volume fraction ink easily forms highly electrically conductive lines for printed electronics.

Modulation of chiroptics, chiral phenomena of the optical properties, is pivotal in a variety of advanced applications, including chirality-specific biosensing and photonic switches. One of the most effective methods for achieving this control is assembly of the optical moieties into chiral nanostructures. Lipopeptide self-assemblies have been extensively employed as soft templates to organize composites into low-dimensional superstructures due to their rigidity and ease of functionalization. Therefore, an appealing approach is to provide chiroptical control by using lipopeptide self-assemblies as templates to assemble chromophores. Herein, two lipopeptidic molecules, namely, C14-FFK and C14-FK, composed of phenylalanine and lysine residues conjugated to a myristic acid chain, were custom-designed. Spectroscopic and microscopic characterizations indicated that C14-FFK self-assembled to wide, slightly left-handed nanoribbons, while C14-FK formed narrow, intensely right-handed nanofibers. The different chirality was derived from the distinct self-assembly driving forces, especially the molecular bending dimensions. These superstructures presented an ideal capability to serve as soft templates to assemble porphyrin (ZnTPyP) through noncovalent electrostatic attractive interactions, or assemble the phenolic groups through covalent conjugation to peptide backbones. The distinct exciton coupling of the chromophores allowed their achiral optics to become chiral, showing negative Cotton effect when templated by nanoribbons and positive Cotton effect with nanofibers as templates. Following replacement of the lipopeptides with their d-type enantiomers, the handedness of the superstructures and the associated chiroptics were reversed and presented "mirror" symmetric CD signals to their l-type counterparts. These findings may pave the way to the formation of morphologically and chioptically controllable nanomaterials.

We studied the structural transformations from the layered-type to spinel-type ordering upon galvanostatic charging (Li+ extraction) of Li2MnO3 electrodes. We have determined by X-ray, electron diffraction techniques and Raman spectroscopy analyses that these transformations partially occurred even at the initial states-of-charge, at potentials of 4.3–4.5V, and in fully charged (4.7V) and discharged (2.0V) states as well. The above transformations are evident also from the analysis of the intrinsic magnetic properties of Li2MnO3 electrodes that indicate short-range spin correlations typical for the Li2Mn2O4 and LiMn2O4 spinel-type structures, depending on the state of charge and the C-rates used for the cycling.

Thermodynamic instability of positive electrodes (cathodes) in Li-ion batteries in humid air and battery solutions results in capacity fading and batteries degradation, especially at elevated temperatures. In this work, we studied thermal interactions between cathode materials Li2MnO3, xLi2MnO3 .(1 − x)Li(MnNiCo)O2,LiNi0.33Mn0.33Co0.33O2, LiNi0.4Mn0.4Co0.2O2, LiNi0.8Co0.15Al0.05O2 LiMn1.5Ni0.5O4, LiMn(or Fe)PO4, and battery solutions containing ethylene carbonate (EC) or propylene carbonate (PC), dimethyl carbonate (DMC) or ethylmethyl carbonate (EMC) and LiPF6 salt in the temperature range of 40–400 °C. It was found that these materials are stable chemically and well performing in LiPF6-based solutions up to 60 °C. The thermal decomposition of the electrolyte solutions starts >180 °C. The macro-structural transformations of cathode materials upon exothermic reactions were studied by transmission electron microscopy (TEM), X-ray difraction (XRD) and Raman spectroscopy. Differential scanning calorimetry (DSC) studies have shown that the exothermic reactions in the temperature range of 60–140 °C lead to partial decomposition of both the cathode material and electrolyte solution. The systems thus formed consisted of partially decomposed solutions and partially chemically delithiated cathode materials covered by reactions products. Thermal reactions terminate and this system reaches equilibrium at about 120 °C. It remains stable up to the beginning of the solution decomposition at about 180 °C. The increased content of surface Li2CO3 is found to significantly affect the thermal processes at high temperature range due to extensive exothermic decomposition at low temperatures.

We report herein on the study of Li and Mn rich Li-x[MnNiCo]O-2 cathode materials with an emphasis on the effect of AlF3 coating on their electrochemical performance. The initial stoichiometry of these materials was xLi(2)MnO(3)center dot(1-x)LiMnyNizCowO2 where x is in the range 0.4-0.5 and the y:z:w ratio was as we previously reported. Their structure was considered on the basis of two-components model, namely monoclinic Li2MnO3 (C2/m) and rhombohedral LiMO2 (R-3m) (M = Mn, Ni, Co) that are structurally compatible and closely integrated phases. Based on TEM studies we concluded that the coating had a crystalline tetragonal structure t-AlF3 (P4nmm symmetry) and AlF3 nano-crystals were regularly distributed over the particles surface. Amorphous clusters of AlF3 and/or other Al-containing species, like AlFxOy, Al[FOH], etc. may also present, as it follows from solid-state NMR measurements. It was shown that electrodes comprising the AlF3-coated material exhibited higher reversible capacities of similar to 250 mAh/g at a C/5 rate, more stable cycling behavior, higher lithium storage capability at 60 degrees C, and lower impedance measured during Li-deinteraclation comparing to electrodes prepared from the uncoated material. An important finding is that Li-x[MnNiCo]O-2/AlF3 materials revealed much higher thermal stability both in the pristine (lithiated) and cycled (delithiated) states than their uncoated counterparts. (C) 2013 The Electrochemical Society. All rights reserved.

We investigated the structural characteristics of Li-rich xLi(2)MnO(3) center dot (1-x)Li[MnyNizCow]O-2 cathode material (x around 0.5, y:z:w around 2:2:1) and its electrochemical performance in lithium cells at 30 and 60 degrees C. It was established that nanoparticles of the xLi(2)MnO(3) center dot (1-x)Li[MnyNizCow]O-2 compound are intergrown on the nano-scale and are built of thin plates of 40-50 angstrom. We demonstrated that xLi(2)MnO(3) center dot u (1-x)Li[MnyNizCow]O-2 electrodes exhibited at 60 degrees C high capacities of similar to 270 and similar to 220 mAh/g at 1C and 2C rates, respectively. They can be cycled effectively at 30 and 60 degrees C providing capacity similar to 250 mAh/g in the initial cycles, but it fades upon prolonged cycling due, to some extent, to increasing the electrode impedance (charge-transfer resistance) especially at the elevated temperature. The effective chemical diffusion coefficient of Li+ in these electrodes measured during charge to 4.7 V by potentiostatic intermittent titration technique (PITT) was found to be similar to 10(-10) cm(2)/s. From convergent beam electron diffraction and Raman spectroscopy studies we established, for the first time, that partial structural transition from layered-type to spinel-type ordering in xLi(2)MnO(3) center dot (1-x)Li[MnyNizCow]O-2 electrodes occurred in the initial charge to 4.7 V and even at the early stages of charging at 4.1 V-4.4 V. The thermal behavior of the xLi(2)MnO(3) center dot (1-x)Li[MnyNizCow]O-2 material and electrodes are also discussed. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.070302jes] All rights reserved.

In this work, we synthesized nano-particles (20–80nm) of Li2MnO3 using the self-combustion reaction and studied the electrochemical activity of electrodes prepared from this nano-material at 30, 45, and 60°C. It was shown that the first Li-extraction from nano-Li2MnO3 occurs at much lower potentials (by 180–360mV) in comparison with micron-sized Li2MnO3 electrodes. This can be associated with the higher surface-to-volume ratio, much shorter the diffusion path and the increased surface concentration of the electrochemically active sites. On the basis of magnetic susceptibility studies of nano-Li2MnO3 we proposed a model of disordered surface layer, containing Mn3+ or Mn2+ ions, both at low spin state, at the surface of these nano-particles. From the results of structural analysis (by X-ray and electron diffraction and vibrational Raman spectroscopy) of galvanostatically cycled nano-Li2MnO3 electrodes in Li-cells we came to a conclusion of partial transition of layered LiMO2 to spinel-type ordering.

In this work, we studied the cycling performance of initially inactive Li2MnO3 electrodes prepared from micron-sized particles, at 30°C and 60°C and possible structural transitions that this material can undergo due to de-lithiation. It was found that being activated at elevated temperatures, Li2MnO3 electrodes demonstrate a steady-state cycling behavior and reasonable capacity retention after aging at 60°C. The main gases evolved during polarization of the Li2MnO3 electrodes are O2 evolved from the structure and CO2 and CO that can be formed due the reaction of oxygen with carbon black. It was found that a transformation of the Li2MnO3 layered structure into a spinel-like phase occurred during the initial charging of the Li2MnO3 electrodes, which were characterized as possessing domains of both layered and spinel-like structures. The results of the structural studies of these electrodes obtained by the X-ray diffraction and transmission electron microscopy were found to be in agreement with their Raman spectroscopic responses. We suggest that the mechanism of the charge compensation during the extraction of lithium at 60°C involves both oxygen removal from the Li2MnO3 structure and the exchange between Li+ and protons formed during the anodic oxidation of ethylene carbonate or dimethyl carbonate solvents in LiPF6 solutions at high potentials (>4.5V). It is assumed that the proton-containing structure Li2−xHx−yMnO3−0.5y is retained in a discharged state of the electrode and may decompose above 500°C with the formation of Li2O and manganese oxides accompanied by the release of water and CO2.

SessionsC698 field E = 1 kV mm -1 , the changes of bond length were (5.2±0.2)10 - Å and (3.0±0.8)10 - Å, respectively.The same measurements on LiH 2 PO 3 (a 1 =11.024, a 2 =5.060, a 3 =5.169,Z=4)[1]are under way and will be compared with the results of LiH 2 PO 4 .This will help to understand the relationship between external deformation and the specific response of chemical bonds in ternary compounds.