The effects of dication symmetry on ionic liquid electrolytes in supercapacitors

Molecular Dynamics Simulation of the Influence of External Electric Fields on the Glass Transition Temperature of the Ionic Liquid 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide

We present the results of molecular dynamics simulations of the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C₂C₁im][NTf₂] in the presence of external electric fields (EEFs) of varying strengths to understand the effects of EEFs on the glass transition temperature T_g. We compute T_g with an automated and objective method and observe a depression in T_g when cooling the IL within an EEF above a critical strength. The effect is reversible, and glasses prepared with EEFs recover their original zero-field T_g when heated. By examining the dynamics and structure of the liquid phase, we find that the EEF lowers the activation energy for diffusion, reducing the energetic barrier for movement and consequently T_g. We show that the effect can be leveraged to drive an electrified nonvapor compression refrigeration cycle.

Characterization of the Interface Structure of 1-Ethyl-2,3-alkylimidazolium Bis(trifluoromethylsulfonyl)imide on a Au(111) Surface with Molecular Dynamics Simulations

As a new type of green electrolyte, ionic liquids have been extensively and successfully used in electrochemical systems. It is extremely important to understand the structure and characteristics of their electric double layers. The microscopic structures of room-temperature ionic liquids 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([Emmim]TFSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim]TFSI) were studied on a flat Au(111) surface using molecular dynamics simulations. Since the interactions of [Emmim]TFSI, [Emmim]⁺, and TFSI^- with the Au(111) surface are stronger than those of molecules (or ions) in the [Emim]TFSI system, the linear arrangement of [Emmim]TFSI and the worm-like pattern of the [Emim]TFSI system can be found near the Au(111) surface. Meanwhile, cations are all parallel to the electrode in the [Emmim]TFSI/Au(111) system and tilted toward the surface in the [Emim]TFSI/Au(111) system. TFSI^- presents trans and cis conformations in [Emim]TFSI and [Emmim]TFSI systems adjacent to Au(111), respectively. A Helmholtz-like layer structure with alternating oscillations of anionic and cationic layers can be found in the [Emim]TFSI system, while the molecular layer with cations and anions existing simultaneously can be found in [Emmim]TFSI. Our results confirm that the substitution of hydrogen on C1 by methyl groups in the imidazole ring increases the interaction between the particles. It has also been proved that the change in the anion conformation and cation orientation in the [Emmim]TFSI system can be attributed to the different interaction energies of various particles. The above reasons ultimately make the images on Au(111) different in the two systems. The results provide a new perspective for studying the structure of double layers. They are helpful in deepening the understanding of the interface behavior of ionic liquids and providing a theoretical basis for the design of functional ionic liquids that are suitable for electrochemical equipment.

Organoboron Ionic Liquids as Extractants for Distillation Process of Binary Ethanol + Water Mixtures

Aminoethers of boric acid, which are organoboron ionic liquids, were synthesized by using boric acid, triethanolamine, and triethylene glycol/diethylene glycol. Due to the formation of intermolecular complexes of borates, the structure of aminoethers of boric acid contains ion pairs separated in space, giving these compounds the properties inherent to ionic liquids. It is established that the thermal stability of aminoethers under normal atmospheric conditions increases with an increase in the size of the glycol. According to measurements of fast scanning calorimetry, density, dynamic viscosity, and electrical conductivity, water is involved in the structural organization of aminoethers of boric acid. The impact of the most thermostable organoboron ionic liquids on the phase equilibrium conditions of the vapor–liquid azeotropic ethanol–water mixture is studied. It is shown that the presence of these substances leads to increase in the relative volatility of ethanol. In general, the magnitude of this effect is at the level shown by imidazole ionic liquids, which provide high selectivity in the separation of aqueous alcohol solutions. A large separation factor, high resistance to thermal oxidative degradation processes, accompanied by low cost start reagents, make aminoethers of boric acid on the basis of triethylene glycol a potentially effective extractant for the extractive distillation of water–alcohol mixtures.

Storing Energy in Biodegradable Electrochemical Supercapacitors

The development of green and biodegradable electrical components is one of the main fronts of research to overcome the growing ecological problem related to the issue of electronic waste. At the same time, such devices are highly desirable in biomedical applications such as integrated bioelectronics, for which biocompatibility is also required. Supercapacitors for storage of electrochemical energy, designed only with biodegradable organic matter would contemplate both aspects, that is, they would be ecologically harmless after their service lifetime and would be an important component for applications in biomedical engineering. By means of atomistic simulations of molecular dynamics, we propose a supercapacitor whose electrodes are formed exclusively by self-organizing peptides and whose electrolyte is a green amino acid ionic liquid. Our results indicate that this supercapacitor has a high potential for energy storage with superior performance than conventional supercapacitors. In particular its capacity to store energy was estimated to be almost 20 times greater than an analogue one of planar metallic electrodes.