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We studied the potential and time-dependent changes in the electric double layer (EDL) structure of an imidazolium-based room temperature ionic liquid (RTIL) electrolyte at an epitaxial graphene (EG) surface. We used in situ X-ray reflectivity (XR) to determine the EDL structure at static potentials, during cyclic voltammetry (CV) and potential step measurements. The static potential structures were also investigated with fully atomistic molecular dynamics (MD) simulations. Combined XR and MD results show that the EDL structure has alternating anion/cation layers within the first nanometer of the interface and that these structures are distinct at the most positive and negative static potentials (1.0 and −0.4 V, respectively) applied in this study. The dynamical response of the EDL to potential steps has a slow component (>10 s) and the RTIL structure shows hysteresis during CV scans (e.g., at 100 mV/s scan rate). Our results reveal that both the slow kinetics and hysteresis are due to the reorganization of the distinct EDL structures found at the extreme potentials.

The performance of supercapacitors is determined by the electrical double layers (EDLs) formed at electrolyte/electrode interfaces. To understand the energy storage mechanism underlying supercapacitors, molecular dynamics (MD) simulations were used to study the capacitive behavior of carbon-based supercapacitors with room-temperature ionic liquid (RTIL) electrolytes. The performance of porous supercapacitors was found to be correlated with the ion/pore size and applied voltage. Supercapacitors composed of RTILs on the outer, positively curved surfaces of onionlike carbons (OLCs) or carbon nanotubes (CNTs) exhibited significant effects on capacitance and the distinctive feature that differential capacitance varies only weakly with voltage. Investigations of temperature influence revealed a positive temperature dependence of capacitance for OLC-based supercapacitors and a weak dependence of capacitance on temperature for CNT-based supercapacitors, in line with experimental observations. Molecular insights into RTIL-based supercapacitors, reviewed in this Perspective, could facilitate the design and development of a new generation of energy storage devices.

Although gold nanorods (GNRs) have been prepared with a wide range of methods for their uses as novel diagnostic and therapeutic agents, the synthesis of monodispersed GNRs with high yields and size tunability still requires further improvements. We report on a simple one-pot method for preparing highly monodispersed GNRs using phenols (e.g., hydroquinone, 1,2,3-trihydroxybenzene, and 1,2,4-trihydroxybenzene) as the reducing agent and NaBH 4 as the initiating reactant. Finetuning of the LSPR peak position of phenols-reduced GNRs from 550 to 1150 nm is accomplished by regulating the silver ion concentrations. The size of GNRs produced via phenols reduction can also be controlled by changing the NaBH 4 concentration. By systematically optimizing the concentrations of the reagents involved in the one-pot synthesis of GNRs, the yield (in many cases exceeding 90%) is significantly higher than that prepared with the commonly used reductant (e.g., ascorbic acid). The improved efficiency and controllability cut down the cost and time involved in GNRs production.

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Lithium (Li)‐metal batteries (LMBs) with high‐voltage cathodes and limited Li‐metal anodes are crucial to realizing high‐energy storage. However, functional electrolytes that are compatible with both high‐voltage cathodes and Li anodes are required for their developments. In this study, the use of a moderate‐concentration LiPF6 and LiNO3 dual‐salt electrolyte composed of ester and ether co‐solvents (fluoroethylene carbonate/dimethoxyethane, FEC/DME), which forms a unique Li+ solvation with aggregated dual anions, that is, PF6− and NO3−, is proposed to stabilize high‐voltage LMBs. Mechanistic studies reveal that such a solvation sheath improves the Li plating/stripping kinetics and induces the generation of a solid electrolyte interphase (SEI) layer with gradient heterostructure and high Young's modulus on the anode, and a thin and robust cathode electrolyte interface (CEI) film. Therefore, this novel electrolyte enables colossal Li deposits with a high Coulombic efficiency (≈98.9%) for 450 cycles at 0.5 mA cm−2. The as‐assembled LiǁLiNi0.85Co0.10Al0.05O2 full batteries deliver an excellent lifespan and capacity retention at 4.3 V with a rigid negative‐to‐positive capacity ratio. This electrolyte system with a dual‐anion‐aggregated solvation structure provides insights into the interfacial chemistries through solvation regulation for high‐voltage LMBs.

Molecular dynamics (MD) simulations of supercapacitors with single-walled carbon nanotube (SWCNT) electrodes in roomtemperature ionic liquids were performed to investigate the influences of the applied electrical potential, the radius/curvature of SWCNTs, and temperature on their capacitive behavior. It is found that (1) SWCNTsbased supercapacitors exhibit a near-flat capacitance−potential curve, (2) the capacitance increases as the tube radius decreases, and (3) the capacitance depends little on the temperature. We report the first MD study showing the influence of the electrode curvature on the capacitance−potential curve and negligible dependence of temperature on capacitance of tubular electrode. The latter is in good agreement with recent experimental findings and is attributed to the similarity of the electrical double layer (EDL) microstructure with temperature varying from 260 to 400 K. The electrode curvature effect is explained by the dominance of charge overscreening and increased ion density per unit area of electrode surface.

The dynamic and structural properties of a room-temperature ionic liquid (RTIL) 1-butyl-3-methyl-imidazolium(trifluoromethanesulfonimide) ([C4mim][Tf2N]) confined in silica and carbon mesopores were investigated by molecular dynamics (MD) simulations and nuclear magnetic resonance (NMR) experiments. The complex interfacial microstructures of confined [C4mim][Tf2N] are attributed to the distinctive surface features of the silica mesopore. The temperature-dependent diffusion coefficients of [C4mim][Tf2N] confined in the silica or carbon mesopore exhibit divergent behavior. The loading fraction (f = 1.0, 0.5, and 0.25) has a large effect on the magnitude of the diffusion coefficient in the silica pore and displays weaker temperature dependence as the loading fraction decreases. The diffusion coefficients of mesoporous carbon-confined [C4mim][Tf2N] are relatively insensitive to the loading faction and exhibit a temperature dependence that is similar to the bulk dependence at all loading levels. Such phenomena can be attributed to the unique surface heterogeneity, dissimilar interfacial microstructures, and interaction potential profile of RTILs near silica and carbon walls.