Tracking the Micro-Heterogeneity and Hydrogen-Bonding Interactions in Hydroxyl-Functionalized Ionic Liquid Solutions: A Combined Experimental and Computational Study

Diverse Applications of Two-Dimensional Correlation Spectroscopy (2D-COS)

This second of the two-part series of a comprehensive survey review provides the diverse applications of two-dimensional correlation spectroscopy (2D-COS) covering different probes, perturbations, and systems in the last two years. Infrared spectroscopy has maintained its top popularity in 2D-COS over the past two years. Fluorescence spectroscopy is the second most frequently used analytical method, which has been heavily applied to the analysis of heavy metal binding, environmental, and solution systems. Various other analytical methods including laser-induced breakdown spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, capillary electrophoresis, seismologic, and so on, have also been reported. In the last two years, concentration, composition, and pH are the main effects of perturbation used in the 2D-COS fields, as well as temperature. Environmental science is especially heavily studied using 2D-COS. This comprehensive survey review shows that 2D-COS undergoes continuous evolution and growth, marked by novel developments and successful applications across diverse scientific fields.

In Situ Species Analysis of a Lithium-Ion Battery Electrolyte Containing LiTFSI and Propylene Carbonate

In this study, we analyzed the species in a model electrolyte consisting of a lithium salt, lithium bis(trifluoromethane sulfone)imide (LiTFSI), and a widely used neutral solvent propylene carbonate (PC) with excess infrared (IR) spectroscopy, ab initio molecular dynamics simulations (AIMD), and quantum chemical calculations. Complexing species including the charged ones [Li+(PC)4, TFSI-, TFSI-(PC), TFSI-(PC)2, and Li(TFSI)2-] are identified in the electrolyte. Quantum chemical calculations show strong Li+···O(PC) interaction, which suggests that Li+ would transport in the mode of solvation-carriage. However, the interaction energy of each hydrogen bond in TFSI-(PC) is very weak, suggesting that TFSI- would transport in hopping mode. In addition, the concentration dependences of the relative population of the species were also derived, providing a scenario for the dissolving process of the salt in PC. These in-depth studies provide physical insights into the structural and interactive properties of the electrolyte of lithium-ion batteries.

Electron Density Learning of Z-Bonds in Ionic Liquids and Its Application

Ionic liquids (ILs) exhibit fascinating properties due to special Z-bonds and have been widely used in electrochemical systems. The local Z-bond networks potentially cause a discrepancy in electrochemical properties. Understanding the correlations between the Z-bond energy (EZ-bond) and the electrochemical properties is helpful to identify appropriate ILs. It is difficult to estimate the correlations from single density functional theory calculations or molecular dynamic simulations. In this work, a machine learning model targeting the electronic density (ρBCP) of Z-bonds has been trained successfully, as expected for use in systems above the nanoscale size. The connection between the EZ-bond and the electrochemical potential window in ILs@TiO2, as well as that between the EZ-bond and the charge carrier mobility in ILs-PEDOT:Tos@SiO2, was separately investigated. This study highlights an efficient model for predicting ρBCP in nanoscale systems and anticipates exploring the connection between Z-bonds and the electrochemical properties of IL-based systems.

Work function regulation of surface-engineered Ti2CT2 MXenes for efficient electrochemical nitrogen reduction reaction

Electrochemical conversion of nitrogen to ammonia is a promising method in modern agriculture and industry due to its suitability and feasibility under mild conditions. Therefore, seeking electrocatalysts and understanding the catalytic mechanisms are of great importance. In this work, by combining the concept of the synergetic effect of the terminal vacancy and transition metal active center, we studied the whole catalytic mechanism of defective Ti₂CT₂ MXenes with functional groups (T = O, F, H, OH) by employing first-principles calculations. It is demonstrated that the electron transfer behavior of 2D transition metal carbides can be tuned by modifying the surface functional groups. Herein, the rarely investigated work function regulation is proved to effectively alter the electron transfer ability, thus the binding strength of key intermediates on the surface can be optimized. Besides, Ti₂CO₂ with an oxygen vacancy is identified as a promising candidate through a distal mechanism, where the calculated electronic properties reveal that the introduction of in-gap states is responsible for activating N₂ with physical adsorption. In addition, obvious orbital splitting of the σ and π* orbitals of N₂ is observed due to the hybridization of frontier orbitals. The symmetry matching rule of the frontier orbitals of π* 2p and the σ 2p orbitals of N with Ti d orbitals further illustrates the "acceptance-donation" interaction. These theoretical insights highlight the underlying mechanism of the synergetic effect of surficial vacancy and exposed transition metal atoms, and provide an alternative view of designing efficient NRR electrocatalysts.

Generalized Excess Spectroscopy

With a clear enhancement of the apparent resolution of experimentally determined spectra, excess spectroscopy has been developed as a powerful tool to study solution structures and molecular interactions. In the standard procedure of the method, excess spectra are calculated based on the ideal spectra constructed using two pure compounds. This limits the applications of the method when the pure compounds are unstable or their physical state is different from that of the mixtures. To overcome the problem or to extend the application, we propose generalized excess spectroscopy in this work, where the ideal spectrum is evaluated from the spectra of reference mixtures. After deducing the working equations, we performed digital simulation and then applied the novel approach to a binary system consisting of tert-butanol and carbon tetrachloride. Both results illustrated the feasibility and universality of the method.