Nanostructured amorphous and anatase TiO2 are both considered as high rate Li-insertion/extraction electrode materials. To clarify which phase is more desirable for lithium ion batteries with both high power and high density, we compare the electrochemical properties of anatase and amorphous TiO2 by using anodic TiO2 nanotube arrays (ATNTAs) as electrodes. With the same morphological features, the rate capacity of nanostructured amorphous TiO2 is higher than that of nanostructured anatase TiO2 due to the higher Li-diffusion coefficient of amorphous TiO2 as proved by the electrochemical impedance spectra of an amorphous and an anatase ATNTA electrode. The electrochemical impedance spectra also prove that the electronic conductivity of amorphous TiO2 is lower than that of anatase TiO2. These results are helpful in the structural and componential design of all TiO2 mesoporous structures as anode material in lithium ion batteries. Moreover, all the advantages of the amorphous ATNTA electrode including high rate capacity, desirable cycling performance and the simplicity of its fabrication process indicate that amorphous ATNTA is potentially useful as the anode for lithium ion batteries with both high power and high energy density.

Bimetallic and multi-component catalysts often exhibit superior activity and selectivity compared with their single-component counterparts. To investigate the origin of the composition dependence observed in the catalytic activities of CoPd bimetallic catalysts, the compositional and structural evolution of monodisperse CoPd alloy nanoparticles (NPs) were followed under catalytic CO oxidation conditions using ambient pressure X-ray spectroscopy (AP-XPS) and transmission electron microscopy (TEM). It was found that the catalysis process induced a reconstruction of the catalysts, leaving CoO x on the NP surface. The synergy between Pd and CoO x coexisting on the surface promotes the catalytic activity of the bimetallic catalysts. Such synergistic effects can be optimized by tuning the Co/Pd ratios in the NP synthesis and reach a maximum at compositions near Co 0.26 Pd 0.74 , which exhibits the lowest temperature for complete CO conversion. Our combined AP-XPS and TEM studies provide a direct observation of the bimetallic NPs surface evolution under catalytic conditions and its correlation to catalytic properties. Recent advances in in situ/operando surface characterization 28-32 have made it possible to study catalyst surfaces and their interaction with gas-phase reactants under reaction conditions. One example is the development of ambient-pressure x-ray photoelectron spectroscopy (AP-XPS), which makes this traditionally vacuum-requiring surface analysis tool operational under reactant gases up to Torr pressures. 28,33 Herein, we combined an in situ AP-XPS investigation of monodisperse CoPd NPs under CO oxidation conditions with in situ and ex situ (scanning) transmission electron microscopy [(S)TEM] and electron energy loss spectroscopy (EELS), as well as ex situ x-ray absorption spectroscopy. This integrated study reveals the surface/structure evolution and bimetallic synergy of NP catalysts in action. We observed that the atomic surface composition of the CoPd alloy NPs transformed during the oxidation/reduction pre-treatments. At 200 and 300°C, exposure to CO drives Pd atoms to migrate to the surface, whereas O 2 exposure does the opposite. Such reversible reactant-driven surface segregation however, becomes less prominent with increasing Co content and is eventually negligible in the case of Co 0.52 Pd 0.48 NPs, where the NPs with highest Co content the surface becomes completely covered by CoO x as corroborated by STEM-EELS mapping. The observed segregation behavior in CoPd NPs suggested that Pd and CoO x coexist on the catalyst surface both exposed to the reactant gases, at least for NPs Co content below 50%. The Pd/CoO x coexistence contributes to the promotion of the CO oxidation kinetics. This mechanism explains the trend of the catalytic properties of five NP catalysts of different compositions from pure Pd to Co 0.52 Pd 0.49 , among which the Co 0.26 Pd 0.74 shows the lowest temperature for complete conversion of CO to CO 2. This work highlights the benefits of using well

A carbon-free nanocomposite consisting of MoO nanoparticles embedded between MoSe nanosheets, named MoO@MoSe, has been synthesized and demonstrated excellent electrochemical properties for lithium ion batteries. In such a composite, MoSe nanosheets provide a flexible substrate for MoO nanoparticles; while MoO nanoparticles act as spacers to retain the desired active surface to electrolyte and also introduce metallic conduction. In addition, the heterojunctions at the interface between MoSe and MoO introduce a self-built electric field to promote the lithiation/delithiation process. As a result, such lamellar composite has a long cycling stability with a reversible capacity of 520.4 mA h g at a current density of 2000 mA g after 400 cycles and excellent rate performance, which are attributed to the synergistic combination of the two components in nanoscale.

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