Temperature-Tunable Operando Nondestructive Detection of Electronic and Geometrical Structures in Battery Electrodes.

Real-time monitoring of the structural evolution of battery materials is crucial for understanding their underlying reaction mechanisms, which cannot be satisfied by the typically used post-mortem analysis. While more and more operando techniques were constructed and employed, they are all based on ambient working conditions that are not generally the case for real-world applications. Indeed, batteries work in an environment where self-heat dissipation increases the surrounding temperature, and extreme temperature applications (<-20 °C or >60 °C) are also frequently proposed. Operando characterization techniques under variable temperatures are therefore highly desired for tracking battery reactions under real-working conditions. Here, we develop a methodology to operando monitor the electronic and geometrical structures of battery materials over a wide range of temperatures based on X-ray spectroscopies. It is substantiated with data collected on a model LiNi0.90Co0.05Mn0.05O2/Si@C pouch cell under operando quick X-ray absorption fine structure spectroscopy, by which we found a temperature-dependent structure evolution behavior that is highly correlated with the electrochemical performance. Our work establishes an exemplary protocol for analyzing battery materials under temperature-variable environments that can be widely used in other related fields.

A Theoretical Study of the Halogen Bond between Heteronuclear Halogen and Benzene.

Halogen bonds play an important role in many fields, such as biological systems, drug design and crystal engineering. In this work, the structural characteristics of the halogen bond between heteronuclear halogen XD (ClF, BrCl, IBr, ICl, BrF and IF) and benzene were studied using density functional theory. The structures of the complexes between heteronuclear halogen and benzene have Cs symmetry. The interaction energies of the complexes between heteronuclear halogen XD (ClF, BrCl, IBr, ICl, BrF and IF) and benzene range from -27.80 to -37.18 kJ/mol, increasing with the increases in the polarity between the atoms of X and D, and are proportional to the angles of a between the Z axis and the covalent bond of heteronuclear halogen. The electron density (ρ) and corresponding Laplacian (∇2ρ) values indicate that the interaction of the heteronuclear halogen and benzene is a typical long-range weak interaction similar to a hydrogen bond. Independent gradient model analysis suggests that the van der Waals is the main interaction between the complexes of heteronuclear halogen and benzene. Symmetry-adapted perturbation theory analysis suggests that the electrostatic interaction is the dominant part in the complexes of C6H6⋯ClF, C6H6⋯ICl, C6H6⋯BrF and C6H6⋯IF, and the dispersion interaction is the main part in the complexes of C6H6⋯BrCl, C6H6⋯IBr.

Dissociative photoionization of ß-pinene: an experimental and theoretical study.

We investigated the photoionization and dissociation photoionization of the ß-pinene molecular using time-of-flight mass spectrometry with a tunable vacuum ultraviolet source in the region from 8.00eV to 15.50eV. The experimental ionization energy (IE) value is 8.60eV using electron impact as the ionization source which is not in good agreement with theoretical value (8.41 eV) with a G3MP2 method. We obtained the accurate IE of ß-pinene (8.45 ± 0.03eV) derived from the efficiency spectrum which is in good agreement with the theoretical value (8.38eV) of the CBS-QB3 method. We elucidated the dissociation pathways of primary fragment ions from the ß-pinene cation on the basis of experimental observations in combination with theoretical calculations. Most of the dissociation pathways occur via a rearrangement reaction prior to dissociation. We also determined the structures of the transition states and intermediates for those isomerization processes.

Measurements of secondary organic aerosol formed from OH-initiated photo-oxidation of isoprene using online photoionization aerosol mass spectrometry.

Isoprene is a significant source of atmospheric organic aerosol; however, the secondary organic aerosol (SOA) formation and involved chemical reaction pathways have remained to be elucidated. Recent works have shown that the photo-oxidation of isoprene leads to form SOA. In this study, the chemical composition of SOA from the OH-initiated photo-oxidation of isoprene, in the absence of seed aerosols, was investigated through the controlled laboratory chamber experiments. Thermal desorption/tunable vacuum-ultraviolet photoionization time-of-flight aerosol mass spectrometry (TD-VUV-TOF-PIAMS) was used in conjunction with the environmental chamber to study SOA formation. The mass spectra obtained at different photon energies and the photoionization efficiency (PIE) spectra of the SOA products can be obtained in real time. Aided by the ionization energies (IE) either from the ab initio calculations or the literatures, a number of SOA products were proposed. In addition to methacrolein, methyl vinyl ketone, and 3-methyl-furan, carbonyls, hydroxycarbonyls, nitrates, hydroxynitrates, and other oxygenated compounds in SOA formed in laboratory photo-oxiadation experiments were identified, some of them were investigated for the first time. Detailed chemical identification of SOA is crucial for understanding the photo-oxidation mechanisms of VOCs and the eventual formation of SOA. Possible reaction mechanisms will be discussed.

Vacuum ultraviolet photoionization and dissociative photoionization of toluene: Experimental and theoretical insights.

The photoionization and dissociative photoionization of toluene have been studied using synchrotron radiation vacuum ultraviolet light with photon energy in the range of 8.50-25.50 eV. The ionization energies (8.82 eV) and double ionization energies (23.80 eV) of toluene as well as the appearance energies for its major fragments C7H7+ (11.17/10.71 eV), C6H5+ (13.73 eV), C5H6+ (13.58/12.50 eV), C5H5+ (16.23 eV), C4H5+ (15.64 eV), C4H4+ (16.10 eV) and C4H3+ (17.11 eV) are determined, respectively by using photoionization efficiency spectrometry. With the help of experimental and theoretical results, seven dissociative photoionization channels have been proposed: C7H7+ + H, C6H5+ + CH3, C5H6+ + C2H2, C5H5+ + C2H2 + H, C4H5+ + C3H3, C4H4+ + C3H4 and C4H3+ + C3H4 + H. In addition, the geometries of the intermediates, transition states and products involved in these photoionization and dissociative photoionization processes have been performed at the B3LYP/6-311++G(d, p) level. The mechanisms of dissociative photoionization of toluene and the intermediates and transition states involved are discussed in detail. Generally speaking, the experimental results are in agreement with theoretical calculations in this work and published literature results. Especially the mechanisms of dissociative photoionization to C4H5+, C4H4+ and C4H3+ were discussed for the first time in this work. This investigation may provide useful information on understanding the photoionization and dissociative photoionization of toluene.

Recent advances in different-dimension electrocatalysts for carbon dioxide reduction.

Greenhouse effect and energy crisis require the recycling use of carbon dioxide (CO2) in atmosphere. The electrocatalytic reduction of CO2 transformed to value-added chemicals with sustainable energy derived electric energy provides a feasible way to address these energy and environment problems; however, developing the electrocatalysts with highly active, selective and durability is still a significant challenge for electrocatalytic CO2 reduction reaction (CO2RR). The nanostructured electrocatalysts have been extensively researched as promising catalysts to speed up CO2 conversion. Here, we summarized the recent advances in different-dimension nanostructured electrocatalysts for CO2RR, tried to give a picture on how do different dimension catalysts work, and discussed the challenges and perspectives for achieving high CO2RR electrocatalysts.

Vacuum ultraviolet photoionization mass spectrometric study of cyclohexene.

In this work, photoionization and dissociation of cyclohexene have been studied by means of coupling a reflectron time-of-flight mass spectrometer with the tunable vacuum ultraviolet (VUV) synchrotron radiation. The adiabatic ionization energy of cyclohexene as well as the appearance energies of its fragment ions C6 H9 (+) , C6 H7 (+) , C5 H7 (+) , C5 H5 (+) , C4 H6 (+) , C4 H5 (+) , C3 H5 (+) and C3 H3 (+) were derived from the onset of the photoionization efficiency (PIE) curves. The optimized structures for the transition states and intermediates on the ground state potential energy surfaces related to photodissociation of cyclohexene were characterized at the ωB97X-D/6-31+g(d,p) level. The coupled cluster method, CCSD(T)/cc-pVTZ, was employed to calculate the corresponding energies with the zero-point energy corrections by the ωB97X-D/6-31+g(d,p) approach. Combining experimental and theoretical results, possible formation pathways of the fragment ions were proposed and discussed in detail. The retro-Cope rearrangement was found to play a crucial role in the formation of C4 H6 (+) , C4 H5 (+) and C3 H5 (+) . Intramolecular hydrogen migrations were observed as dominant processes in most of the fragmentation pathways of cyclohexene. The present research provides a clear picture of the photoionization and dissociation processes of cyclohexene in the 8- to 15.5-eV photon energy region.