In situ tracking of the nanoscale expansion of porous carbon electrodes

Electrochemical double layer capacitors (EDLC) are rapidly emerging as a promising energy storage technology offering extremely large power densities. Despite significant experimental progress, nanoscale operation mechanisms of the EDLCs remain poorly understood and it is difficult to separate processes at multiple time and length scales involved in operation including that of double layer charging and ionic mass transport. Here we explore the functionality of EDLC microporous carbon electrodes using a combination of classical electrochemical measurements and scanning probe microscopy based dilatometry, thus separating individual stages in charge/discharge processes based on strain generation. These methods allowed us to observe two distinct modes of EDLC charging, one fast charging of the double layer unassociated with strain, and another much slower mass transport related charging exhibiting significant sample volume changes. These studies open the pathway for the exploration of electrochemical systems with multiple processes involved in the charge and discharge, and investigation of the kinetics of those processes

Surface and Void Space Analysis of the Crystal Structures of Two Lithium Bis(pentafluoroethanesulfonyl)imide Salts

Analysis of two crystal structures of lithium bis(pentafluoroethanesulfonyl)imide is presented. Two orientations of the anion, that is a cis and trans orientation, are observed. Both structures exhibit unique interactions leading to the formation of discrete fluorous domains in the solid-state. A notable difference in the F···F interactions is seen when contrasting the two orientations wherein the trans geometry has a higher percentage of fluorine interactions than the cis orientation. The inclusion of water molecules in one of the structures also leads to the formation of a polar domain formed through a series of cyclical hydrogen bonding rings. The two structures allow for a detailed examination of the bond distances and angles involved in the formation of the two structures. Analysis of the void space in the two structures leads to the observation that the trans conformation exhibits notably higher void space as compared with the cis orientation. Hirshfeld surface analysis is used to help rationalize the interactions leading to unique changes in geometries and structure

Surface and Void Space Analysis of the Crystal Structures of Two Lithium Bis(pentafluoroethanesulfonyl)imide Salts

Analysis of two crystal structures of lithium bis(pentafluoroethanesulfonyl)imide is presented. Two orientations of the anion, that is a cis and trans orientation, are observed. Both structures exhibit unique interactions leading to the formation of discrete fluorous domains in the solid-state. A notable difference in the F···F interactions is seen when contrasting the two orientations wherein the trans geometry has a higher percentage of fluorine interactions than the cis orientation. The inclusion of water molecules in one of the structures also leads to the formation of a polar domain formed through a series of cyclical hydrogen bonding rings. The two structures allow for a detailed examination of the bond distances and angles involved in the formation of the two structures. Analysis of the void space in the two structures leads to the observation that the trans conformation exhibits notably higher void space as compared with the cis orientation. Hirshfeld surface analysis is used to help rationalize the interactions leading to unique changes in geometries and structure

Crystal structure of (3-carboxypropyl)triphenylphosphonium hexafluoridophosphate

In the title molecular salt, C22H22O2P+·PF6−, the side chain of the cation adopts an anti–gauche conformation [P—C—C—C and C—C—C—C torsion angles = −179.11 (10) and −77.18 (16)°, respectively]. In the crystal, the cations are linked into carboxylic acid inversion dimers by pairs of O—H...O hydrogen bonds. Weak C—H...F and C—H...(F,F) hydrogen bonds connect the components into a three-dimensional network, but there are no aromatic π–π stacking interactions

Examining the Non-Covalent Interactions for Two Polymorphs of a 2,1,3-benzoxadiazole Derivative

Two polymorphs of a benzoxadiazole derivative were examined to determine the interactions leading to the formation of two distinct crystalline forms. Hirshfeld surface analysis was used to establish and contrast the interactions in the two samples. Fingerprints derived from the surface analysis were used to distinguish and lead the analysis in discovering the different interactions in the two crystals. π interactions, specifically, π-hole interactions with a nitro moiety, were found to play an important role in the formation of the crystal structure. Further, carbonyl interactions and π-stacking contribute to the overall relative stability of the different conformational polymorphs. Calculated energy frameworks were used to help visualize the interactions between molecules in the crystal structure, supported by an understanding of the individual interactions. The experimental data were supplemented with theoretical studies to establish a through understanding of these heterocyclic systems

Bis[2,6-bis(trimethylsilylamino)pyridine-κN1]{[6-bis(trimethylsilylamino)pyridin-2-yl-κN1](trimethylsilyl)azanido-κN}lithium

The title complex, [Li(C11H22N3Si2)(C11H23N3Si2)2], contains a single lithium cation coordinated to three ligands. This is the first reported example of the ligand 2,6-bis(trimethylsilylamino)pyridine supporting a monometallic complex. One ligand is mono-anionic and forms a four-membered chelate ring with the lithium cation via the pyridine and silylamido N atoms. The other two ligands are neutral and bind via the pyridine nitrogen. The lithium cation is coordinated in a tetrahedral environment. No intra- or intermolecular hydrogen bonding is observed in the crystal structure, likely indicating that weak electrostatic interactions are the dominant feature of the crystal packing

Bis[μ-2-(trimethylsilylamido)-6-(trimethylsilylamino)pyridine-κ3N1,N2:N2]bis[(diethyl ether-κO)lithium(I)]

The title complex, [Li2(C11H22N3Si2)2(C4H10O)2], crystallizes in the P-1 space group with one molecule of a centrosymmetric dimeric complex in the unit cell. The lithium cation is coordinated in a bidentate fashion by the pyridyl N atom and a silylamido N atom of one 2,6-bis(trimethylsilylamido)pyridine ligand and by a monodentate, bridging silylamido N atom of another. A diethyl ether molecule completes the tetrahedral coordination environment for each lithium atom. Neither intra- nor intermolecular hydrogen bonding nor π–π stacking are observed in the crystal, likely indicating that weak electrostatic interactions are the dominant feature leading to the supramolecular structure

Molecular Dynamics Simulation Study of the Capacitive Performance of a Binary Mixture of Ionic Liquids near an Onion-like Carbon Electrode

An equimolar mixture of 1-methyl-1-propylpyrrolidinium bis­(trifluoromethylsulfonyl)­imide ([C₃mpy]­[Tf₂N]), 1-methyl-1-butylpiperidinium bis­(trifluoromethylsulfonyl)­imide ([C₄mpip]­[Tf₂N]) was investigated by classic molecular dynamics (MD) simulation. Differential scanning calorimetry (DSC) measurements verified that the binary mixture exhibited lower glass transition temperature than either of the pure room-temperature ionic liquids (RTILs). Moreover, the binary mixture gave rise to higher conductivity than the neat RTILs at lower temperature range. In order to study its capacitive performance in supercapacitors, simulations were performed of the mixture, and the neat RTILs used as electrolytes near an onion-like carbon (OLC) electrode at varying temperatures. The differential capacitance exhibited independence of the electrical potential applied for three electrolytes, which is in agreement with previous work on OLC electrodes in a different RTILs. Positive temperature dependence of the differential capacitance was observed, and it was dominated by the electrical double layer (EDL) thickness, which is for the first time substantiated in MD simulation