Morphology, electronic structure, and CO adsorption of gold supported on well-ordered CeO 2 (111) thin films and CeO x nanoparticles were studied by scanning tunneling microscopy (STM), photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRAS). Ceria nanoparticles grown on crystalline thin silica films possess Ce in both the 3+ and 4+ oxidation states, with the former dominating in smaller particles. Upon deposition on CeO 2 (111) films, most of the Au particles are formed at the step edges. The particles on terraces grow presumably through the decoration of point defects, which are more numerous on reduced surfaces. Combined XPS and IRAS data show that partially charged Au δ+ species are formed by deposition at low temperatures (∼100 K) and low coverages on both ceria supports. Formation of Au δ+ on CeO 2 (111) films is kinetically limited and is attributed to the interaction of the gold ad-atoms with defects. In variance to extended ceria surfaces, where only metallic Au nanoparticles are observed at 300 K, the "cationic" gold species are formed in abundance on nano-CeO x and exhibit enhanced thermal stability. It is shown that nanoceria stabilizes small Au clusters, which may even be incorporated into the ceria nanoparticles at elevated temperatures.

With a remarkably higher theoretical energy density compared to lithium-ion batteries (LIBs) and abundance of elemental sulfur, lithium sulfur (Li-S) batteries have emerged as one of the most promising alternatives among all the post LIB technologies. In particular, the coupling of solid polymer electrolytes (SPEs) with the cell chemistry of Li-S batteries enables a safe and high-capacity electrochemical energy storage system, due to the better processability and less flammability of SPEs compared to liquid electrolytes. However, the practical deployment of all solid-state Li-S batteries (ASSLSBs) containing SPEs is largely hindered by the low accessibility of active materials and side reactions of soluble polysulfide species, resulting in a poor specific capacity and cyclability. In the present work, an ultrahigh performance of ASSLSBs is obtained via an anomalous synergistic effect between (fluorosulfonyl)(trifluoromethanesulfonyl)imide anions inherited from the design of lithium salts in SPEs and the polysulfide species formed during the cycling. The corresponding Li-S cells deliver high specific/areal capacity (1394 mAh g, 1.2 mAh cm), good Coulombic efficiency, and superior rate capability (∼800 mAh g after 60 cycles). These results imply the importance of the molecular structure of lithium salts in ASSLSBs and pave a way for future development of safe and cost-effective Li-S batteries.

Of the various beyond-lithium-ion battery technologies, lithium-sulfur (Li-S) batteries have an appealing theoretical energy density and are being intensely investigated as next-generation rechargeable lithium-metal batteries. However, the stability of the lithium-metal (Li°) anode is among the most urgent challenges that need to be addressed to ensure the long-term stability of Li-S batteries. Herein, we report lithium azide (LiN ) as a novel electrolyte additive for all-solid-state Li-S batteries (ASSLSBs). It results in the formation of a thin, compact and highly conductive passivation layer on the Li° anode, thereby avoiding dendrite formation, and polysulfide shuttling. It greatly enhances the cycling performance, Coulombic and energy efficiencies of ASSLSBs, outperforming the state-of-the-art additive lithium nitrate (LiNO ).

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Supported vanadium oxide catalysts have received considerable attention owing to their high activity for selective oxidation reactions. [1][2][3][4][5] The reactivity has been shown to depend strongly on the oxide support, [2][3][4][5] with reducible oxides (e.g., ceria, titania, and zirconia) exhibiting much higher turnover frequencies for oxidative dehydrogenation (ODH) reactions than irreducible oxides (e.g., silica and alumina). [3,5] Structural characterization of the catalysts has been performed primarily using Raman and UV/Vis spectroscopy (see Ref. [4,6,7] and references therein), as well as X-ray absorption spectroscopy.[8] These results have been used to postulate that vanadia catalysts consist of isolated and polymer structures that wet the supporting oxide (so-called "monolayer catalysts"). To elucidate the surface chemistry of vanadia, different model systems, such as vanadia single crystals [9] and thin films [10] as well as vanadia clusters supported on planar metal oxide substrates, [11][12][13][14][15] have been studied experimentally by surface-science techniques and computational means. [16,17] To rationalize structure-reactivity relationships, welldefined systems are required. Of the reducible metal oxide supports that are known to be highly active in ODH reactions, ceria is particularly suited, because well-ordered thin films can be grown with a known surface termination. [18,19] Previously, the structure and reactivity of vanadia supported on CeO 2 (111) has been studied using photoelectron spectroscopy (PES) and temperature-programmed desorption (TPD). [14,15] However, the atomic structure of ceria-supported vanadia monolayer catalysts has not been resolved.Herein, using a combination of high-resolution scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRAS), and PES with synchrotron radiation, we unambiguously demonstrate the formation of monomeric O=V 5+ O 3 species on the CeO 2 (111) surface at low vanadia loadings. For the first time, we show a direct relationship between the nuclearity of vanadia species (monomeric vs. polymeric) as observed by STM and their vibrational properties. We show that ceria stabilizes the vanadium + 5 oxidation state, leading to partially reduced ceria upon vanadium deposition. These experimental results are fully supported by density functional theory (DFT) calculations. The results indicate that ceria surfaces stabilize small vanadia species, such as monomers and trimers, that sinter into two-dimensional, monolayer islands. Such stabilization probably plays a crucial role in the enhanced activity observed for ceriasupported vanadia in ODH reactions. Indeed, low-nuclearity species revealed reactivities at much lower temperatures [20] than those with higher nuclearity, which in turn show strong similarities to the reactivity of vanadia clusters supported on alumina and silica. [11,13] Figure 1 presents compelling evidence for the presence of vanadia monomers on ceria at low coverage (ca. 0.3 V atoms nm À2 ). The STM image in Fi...

The electrical and optoelectronic properties of materials are determined by the chemical potentials of their constituents. The relative density of point defects is thus controlled, allowing to craft microstructure, trap densities and doping levels. Here, we show that the chemical potentials of chalcogenide materials near the edge of their existence region are not only determined during growth but also at room temperature by post-processing. In particular, we study the generation of anion vacancies, which are critical defects in chalcogenide semiconductors and topological insulators. The example of CuInSe 2 photovoltaic semiconductor reveals that single phase material crosses the phase boundary and forms surface secondary phases upon oxidation, thereby creating anion vacancies. The arising metastable point defect population explains a common root cause of performance losses. This study shows how selective defect annihilation is attained with tailored chemical treatments that mitigate anion vacancy formation and improve the performance of CuInSe 2 solar cells.

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The surface chemistry of the activated carbon supporting material was tailored to investigate the influence of O and N groups as well as O-free Lewis basic sites on the performance...