A series of electroactive spinel compounds, LiMn2CurO4 (0.1 x a 0.5), has been studied by crystallographic, spectroscopic, and electrochemical methods and by electron microscopy. These LiMn2_Cu04 spinels are nearly identical in structure to cubic LiMn2O4 and successfully undergo reversible Li intercalation. The electrochemical data show a remarkable reversible electrochemical process at 4.9 V which is attributed to the oxidation of Cu2 to Cu. The inclusion of Cu in the spinel structure enhances the electrochemical stability of these materials upon cycling. The initial capacity of LiMn2Cu04 spinels decreases with increasing x from 130 mAh/g in LiMn2O4 (x = 0) to 70 mAh/g in "LiMn1 ,Cu1504" (x = 0.5). The data also show slight shifts to higher voltage for the delithiation reaction that normally occurs at 4.1 V in standard Li1Mn204 electrodes (1 x 0) corresponding to the oxidation of MnS* to Mn44. Although the powder X-ray diffraction pattern of "LiMn1 5Cu04" shows a single-phase spinel product, neutron diffraction data show a small but significant quantity of an impurity phase, the composition and structure of which could not be identified. X-ray absorption spectroscopy was used to gather information about the oxidation states of the manganese and copper ions. The composition of the spinel component in the LiMn1 -Cu0 504 was determined from X-ray diffraction and X-ray absorption near-edge spectroscopy to be Li1 01Mn, 67Cu0 3204, suggesting to a best approximation that the impurity in the sample was a lithium-copper-oxide phase. The substitution of manganese by copper enhances the reactivity of the spinel structure toward hydrogen: the compounds are more easily reduced at moderate temperature (-200°C) than LiMn2O4.
We report a two-to threefold enhancement of CO tolerance in a proton exchange membrane (PEM) fuel cell, exhibited by carbon supported nanocrystalline PtMo/C as compared to the current state of the art PtRu/C electrocatalysts. The bulk of these nanocrystals were comprised of Pt alloyed with Mo in the ratio 8.7:1.3 as shown by both X-ray diffraction and in situ extended X-ray absorption fine structure measurements. Rotating disk electrode measurements and cyclic voltammetry in a PEM fuel cell indicate the onset of CO oxidation at potentials as low as 0.1 V. Further, the oxidation of CO exhibits two distinct peaks, indicating redox behavior involving oxyhydroxides of Mo. This is supported by in situ X-ray absorption near edge structure measurements at the Mo K edge.
FeCo alloy nanoparticles have been prepared by using a two step modified polyol process using Fe͑II͒ chloride and Co acetate tetrahydrate as Fe and Co metal precursors. Tetraethyl silicate, aluminum isopropoxide, and zirconium͑IV͒ acetyl acetonate were used to make amorphous SiO 2 , Al 2 O 3 , and ZrO 2 coatings, respectively. X-ray diffraction studies showed that there are no crystalline peaks corresponding to SiO 2 , Al 2 O 3 , and ZrO 2 because the oxide coatings of the FeCo core are amorphous in nature. The scanning electron micrograph analysis depicted the cubic nature of the particles with mean particle size of about 45 nm. The maximum saturation magnetization of 205 emu/ g was achieved at 300 and 4 K. FeCo nanocomposites were screen printed as films and aligned by using an external magnetic field of 10 kOe. The microwave properties measured by in-plane ferromagnetic resonance at various frequencies indicate a minimum linewidth of Ϸ3700 Oe.
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