[en] Copper powder was introduced into the lithium sulfur battery system to capture intermediate polysulfides and Cu_xS (x = 1 or 2) species was generated depending on the chain length of polysulfides. This phenomenon was verified by X-ray absorption near edge structure technique. The results indicated that copper can be oxidized to CuS by Li_2S_x (x ≥ 6), and a mixture of Cu_2S and CuS was obtained when x ranges from 3 to 6. While Cu_2S is eventually formed in the presence of Li_2S_3. After several cycles activation, the polysulfide-shuttle effect and self-discharge phenomenon which hinder the application of lithium sulfur batteries are found nearly eliminated Further experiments demonstrated that in the case of Cu_2S generation, a high specific sulfur capacity of 1300 mAh g"–"1 could be delivered, corresponding to 77.6% sulfur utilization, while the Coulombic efficiency approximates around 100%. As a result, self-discharge experiment further demonstrated that polysulfides almost disappear in the electrolyte, which verified the polysulfide-capture capability of copper.

[en] Highlights: • Various engine oils formulated differently were dosed into a GDI engine to examine ash formation process. • Successfully obtained stand-alone ash particles in the size range of sub-20-nm from a gasoline direct injection engine. • There found Ca, P and C elements in raw ash particles, regardless of particle size and engine oil formulation.. • XANES analysis proposes that raw ash particles contain Ca₅(OH)(PO₄)₂, Ca₃(PO₄)₂ and Zn₃(PO₄)₂ as major chemicals. Engine oil-derived ash particles emitted from internal combustion (IC) engines are unwanted by-products, after oil is involved in in-cylinder combustion process. Since they typically come out together with particulate emissions, no detail has been reported about their early-stage particles other than agglomerated particles loaded on aftertreatment catalysts and filters. To better understand ash formation process during the combustion process, differently formulated engine oils were dosed into a fuel system of a gasoline direct injection (GDI) engine that produces low soot mass emissions at normal operating conditions to increase the chances to find stand-alone ash particles separated from soot aggregates in the sub-20-nm size range. In addition to them, ash/soot aggregates in the larger size range were examined using scanning transmission electron microscopy (STEM)-X-ray electron dispersive spectroscopy (XEDS) to present elemental information at different sizes of particles from various oil formulations. The STEM-XEDS results showed that regardless of formulated oil type and particle size, Ca, P and C were always contained, while Zn was occasionally found on relatively large particles, suggesting that these elements get together from an early stage of particle formation. The S, Ca and P K-edge X-ray absorption near edge structure (XANES) analyses were performed for bulk soot containing raw ash. The linear combination approach & cross-checking among XANES results proposed that Ca₅(OH)(PO₄)₂, Ca₃(PO₄)₂ and Zn₃(PO₄)₂ are potentially major chemical compounds in raw ash particles, when combined with the STEM-XEDS results. Despite many reports that CaSO₄ is a major ash chemical when ash found in DPF/GFP systems was examined, it was observed to be rarely present in raw ashes using the S K-edge XANES analysis, suggesting ash transformation.

[en] Uniformly dispersed Pd nanoparticles on ZnO-passivated porous carbon were synthesized via an atomic layer deposition (ALD) technique, which was tested as a cathode material in a rechargeable Li-O_2 battery, showing a highly active catalytic effect toward the electrochemical reactions—in particular, the oxygen evolution reaction. Transmission electron microscopy (TEM) showed discrete crystalline nanoparticles decorating the surface of the ZnO-passivated porous carbon support in which the size could be controlled in the range of 3–6 nm, depending on the number of Pd ALD cycles performed. X-ray absorption spectroscopy (XAS) at the Pd K-edge revealed that the carbon-supported Pd existed in a mixed phase of metallic palladium and palladium oxide. The ZnO-passivated layer effectively blocks the defect sites on the carbon surface, minimizing the electrolyte decomposition. Our results suggest that ALD is a promising technique for tailoring the surface composition and structure of nanoporous supports for Li-O_2 batteries. (paper)

[en] Full, reversible intercalation of two Li"+ has not yet been achieved in promising VOPO_4 electrodes. A pronounced Li"+ gradient has been reported in the low voltage window (i.e., second lithium reaction) that is thought to originate from disrupted kinetics in the high voltage regime (i.e., first lithium reaction). Here, we employ a combination of hard and soft x–ray photoelectron and absorption spectroscopy techniques to depth profile solid state synthesized LiVOPO_4 cycled within the low voltage window only. Analysis of the vanadium environment revealed no evidence of a Li"+ gradient, which combined with almost full theoretical capacity confirms that disrupted kinetics in the high voltage window are responsible for hindering full two lithium insertion. Furthermore, we argue that the uniform Li"+ intercalation is a prerequisite for the formation of intermediate phases Li_1_._5_0VOPO_4 and Li_1_._7_5VOPO_4. The evolution from LiVOPO_4 to Li_2VOPO_4 via the intermediate phases is confirmed by direct comparison between O K–edge absorption spectroscopy and density functional theory.

[en] Highlights: • Sub-Å TEM imaging of the tunneled structure of α-MnO₂ stabilized by K⁺. • Na⁺ insertion/extraction inside single α-MnO₂ nanowire is dynamically tracked. • Mn valence evolution during (de)sodiation is dynamically quantified. • Direct comparison between sodiation- and lithiation-resulted tunnel instability. In this report, the electrochemical sodiation and desodiation in single crystalline alpha-MnO₂ nanowires are studied dynamically at both single particle level using in situ transmission electron microscopy (TEM) and bulk level using in situ synchrotron X-ray. The TEM results suggest that the first sodiation process starts with tunnel-based Na⁺ intercalation, experiences the formation of Na_0.5MnO₂ as a result of tunnel degradation, and ends with the Mn₂O₃ phase. The inserted Na⁺ can be partially extracted out of the sodiated products, and the following cycles are dominated by the reversible conversion reaction between Na_0.5MnO₂ and Mn₂O₃. The Mn valence evolution inside a cycling coin using alpha-MnO₂ nanowire electrode also exhibits partially reversible characteristic, agreeing well with the in situ TEM analysis. The sodiation is compared with lithiation in the same alpha-MnO₂ nanowires. Both Na⁺ and Li⁺ interact with the tunneled structure via a similar tunnel-driven intercalation mechanism before Mn⁴⁺ is reduced to Mn^3.5+. For the following deep insertion, the tunnels survive up to LiMnO₂ (Mn³⁺) during lithiation, while the sodiation proceeds via a different mechanism that involves obvious phase transition and fast tunnel degradation after Mn’s valence is below 3.5+. The difference in charge carrier insertion mechanisms can be ascribed to the strong interaction between the tunnel frame and inserted Na⁺ possessing a larger ionic size than inserted Li⁺.