Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

Visualization of Sulfur Chemical State of Cathode Active Materials for Lithium–Sulfur Batteries by Tender X-ray Spectroscopic Ptychography

Abstract: Lithium–Sulfur batteries are rechargeable batteries that have attracted much attention in recent years because of their large theoretical capacity and the low cost of sulfur. However, there is an obstacle to the development of cathode materials for practical use: the reaction and degradation mechanisms during the charge–discharge process are not fully understood. In this study, we demonstrated the visualization of the sulfur chemical state of cathode active materials at a high spatial resolution using tender X-ray spectroscopic ptychography. We measured the sulfurized poly(n-butyl methacrylate) (SPBMA) samples in the form of particles and small pieces of cathode composites at the S K-edge (∼2.47 keV) and successfully visualized the heterogeneous distribution of sulfur chemical state parameters and their trend changes by the charge/discharge processes in them. We found that the distribution of sulfur chemical states in SPBMA particles is heterogeneous and that traces of the discharge reaction exist near the particle surface. We also found that the cathode composites accumulated sulfur oxides, possibly due to side reactions between sulfur and the electrolyte.

Zn1-xCoxO film valence by photoelectron spectroscopy

Abstract: The Co-doped ZnO film was fabricated using a pulsed laser deposition method on a C-sapphire substrate. The structural properties of the Co-doped ZnO film and the chemical states of elements have been studied in this paper. The XRD and HRTEM characterization results show that it is wurtzite structure with the C-axis of the film aligned with that of the substrate without obvious precipitation. Furthermore the experimental results probably reveal the occupation of Co ions at Zn sites in the host lattice. The oxygen ions are lying in metal oxide, which are due to O - Zn(Co) bonds, though a few oxygen deficiencies and oxygen vacancies were also detected. Co ions have replaced part of Zn sites in the host lattice, resulting in Co - O bonds and no obvious precipitate was detected in the film under our experimental conditions. The substituted Co ions are in the 2+ oxidation state. The electronic-structure parameters Δ, U are also induced.

Computer simulation of chemical nucleation

Abstract: The problem of nucleation at chemical instabilities is investigated by means of microscopic computer simulation. The first-order transition of interest involves a new kind of nucleation arising from chemical transformations rather than physical forces. Here it is the chemical state of matter, and not matter itself, which is spatially localized to form the nucleus for transition between different chemical states. First, the concepts of chemical instability, nonequilibrium phase transition, and dissipative structure are reviewed briefly. Then recently developed methods of reactive molecular dynamics are used to study chemical nucleation in a simple model chemical reaction. Finally, the connection of these studies to nucleation and condensation processes involving physical and chemical interactions is explored.

X-ray photoelectron spectroscopy as a tool in the study of nanostructured titanium and commercial PET surfaces in biotechnological applications

Abstract: In this Chapter, two case studies are presented. In the first study, XPS was used to identify the oxidation states of titanium in nanostructured titanium films on titanium surfaces fabricated by different polishing (mechanical and chemical) and sputtering techniques. A layer of titanium dioxide was detected on both substrates, forming a protective passive film. The physiochemical and dielectric properties of this film determine the biocompatibility of titanium when used in the manufacture of medical implants. When formed in aqueous solution, air, or other oxygen-containing environments, the oxide layer is normally only a few nanometres thick and consists essentially of titanium dioxide. However, by varying the sputtering conditions, other chemical states of titanium oxide can be formed, such as Ti2O3 and TiO. Carbon was detected on all surfaces, at various levels ranging from 11% to 30%. Carbon has been shown to be a commonly encountered contaminant in similar studies. In the second study, XPS was used to investigate the bacterial modification of the surfaces of poly(ethylene terephthalate) (PET) bottles exposed to bacterial enrichment culture over a nine month period. Four elements, two carbon species, two oxygen species, and one nitrogen species were detected on the modified surface that were not detected on the reference surface, and two elements present on the reference surface were not detected on the modified surface. As was found in the analysis of the titanium surfaces, some carbon contamination was detected, however as carbon is the primary element in the polymer chains, it is difficult to evaluate the exact nature and extent of contamination.