"Water-in-Sugar" Electrolytes Enable Ultrafast and Stable Electrochemical Naked Proton Storage.

Proton is an ideal charge carrier for rechargeable batteries due to its small ionic radius, ultrafast diffusion kinetics and wide availability. However, in commonly used acid electrolytes, the co-interaction of polarized water and proton (namely hydronium) with electrode materials often causes electrode structural distortions. The hydronium adsorption on electrode surfaces also facilitates hydrogen evolution as an unwanted side reaction. Here, a "water-in-sugar" electrolyte with high concentration of glucose dissolved in acid to enable the naked proton intercalation, as well as an extended 3.9 V working potential window, is shown. A glucose-derived organic thin film is formed on electrode surface upon cycling. Molecular dynamics simulations reveal the significant decrease of free water in bulk electrolytes, while density functional theory calculations indicate that glucose preferentially binds to the electrode surface which can inhibit water adsorption. The scarcity of free water and the protective organic film work in synergy to suppress water interactions with the electrode surface, which enables the naked proton (de)intercalation. The "water-in-sugar" electrolyte significantly enhances a MoO3 electrode for stable cycling over 100 000 times. This facile electrolyte approach opens new avenues to aqueous electrochemistry and energy storage devices.

Synthetic Bilayers on Mica from Self-Assembly of Hydrogen-Bonded Triazines.

This study describes organic thin films prepared under a range of conditions from a model series of bis-N-alkyl chloro-triazines functionalized with short alkyl chains from ethyl to hexyl. The pure films were characterized using atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). When cast on mica, these compounds assemble as crystalline sheets made up of a synthetic bilayer along the crystallographic ab-plane with an internal hydrogen-bonded domain between external alkyl chains. These micron-scale surfaces stack along the c-axis, and increasing the alkyl chain length results in changes to the crystal morphology from needles to nanoscale plates. Thicker films produce nanoscale, pyramidal stacks of bilayers. Compared to atomically flat mica, a rougher, unetched silicon substrate produced irregular domains in the secondary bilayer. Films of mixtures comprising the ethyl derivative with butyl, pentyl, or hexyl derivative were imaged using time-of-flight secondary-ion mass spectrometry (ToF-SIMS) that indicated a trend toward a constant stoichiometry with increasing alkyl chain length. AFM of mixed films on mica showed single bilayers of height <2 nm, with an acceptable correlation to the XRD measurements, supporting a constant stoichiometry. These materials permit easy modification of mica to a micron-scale, atomically flat hydrophobic surface, and the use of mixtures with different alkyl chain lengths suggests a method to improve the quality of functional organic thin films.