Functional groups in geminal imidazolium ionic compounds and their influence on thermo-physical properties

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Phase Change Materials for Renewable Energy Storage at Intermediate Temperatures

Thermal energy storage technologies utilizing phase change materials (PCMs) that melt in the intermediate temperature range, between 100 and 220 °C, have the potential to mitigate the intermittency issues of wind and solar energy. This technology can take thermal or electrical energy from renewable sources and store it in the form of heat. This is of particular utility when the end use of the energy is also as heat. For this purpose, the material should have a phase change between 100 and 220 °C with a high latent heat of fusion. Although a range of PCMs are known for this temperature range, many of these materials are not practically viable for stability and safety reasons, a perspective not often clear in the primary literature. This review examines the recent development of thermal energy storage materials for application with renewables, the different material classes, their physicochemical properties, and the chemical structural origins of their advantageous thermal properties. Perspectives on further research directions needed to reach the goal of large scale, highly efficient, inexpensive, and reliable intermediate temperature thermal energy storage technologies are also presented.

Guanidinium Organic Salts as Phase-Change Materials for Renewable Energy Storage

A dearth of inexpensive means of energy storage is constraining the expansion of intermittent renewable energy sources such as sun and wind. Thermal energy storage technology utilizing phase-change materials (PCMs) is a promising solution, enabling storage of large quantities of thermal energy at a relatively low cost. Guanidinium mesylate, which melts at 208 °C with latent heat of fusion of ΔH_f =190 J g^-1 is a promising PCM candidate for these applications.^[1] Here, studies on guanidinium organic salts were conducted, including heat capacity, thermal conductivity, advanced thermal stability, long-term cycling, and economic analysis. The data place guanidinium mesylate among the best PCMs operating in the 100-220 °C temperature region in terms of thermal energy storage, with total volumetric energy storage measured as 622 MJ m^-3 (173 kWh m^-3 ). Additionally, it was shown to be stable during cycling, with over 400 cycles performed. Simple economic analysis indicated a cost of 6 USD per MJ of stored thermal energy. This study proves that guanidinium mesylate and potentially other similar salts can be feasible as PCMs for inexpensive energy storage for renewable energy storage applications.

Nanosponges based on self-assembled starfish-shaped cucurbit[6]urils functionalized with imidazolium arms

A new porous material based on the first supramolecular cucurbituril-based nanosponge was synthesized by the functionalization of cucurbit[6]uril with twelve 1-(2-bromoethyl)-3-methyl-1H-imidazol-3-ium arms. The porous structure and the high adsorption capacity were demonstrated through surface area measurements and carbon dioxide adsorption. The new supramolecular sponge showed attractive properties such as (i) a highly porous structure that allowed CO₂ capture, (ii) the possibility to reuse the adsorbed CO₂ for organic synthesis, and (iii) an exciting thermal stability up to around 800 °C, with the potential use of this material in high temperature reactions. Finally, the reuse of CO₂ was successfully investigated in the carboxylation reaction of phenylacetylene.

Pyrazolium Phase-Change Materials for Solar-Thermal Energy Storage

Thermal energy storage technology utilizing phase-change materials (PCMs) can be a promising solution for the intermittency of renewable energy sources. This work describes a novel family of PCMs based on the pyrazolium cation, that operate in the 100-200 °C temperature range, offering safe, inexpensive capacity and low supercooling. Thermal stability and extensive cycling tests of the most promising PCM candidate, pyrazolium mesylate (T_m =168±1 °C, ΔH_f =160 J g^-1 ±5 %, ΔH_total ^v =495 MJ m^-3 ±5 %) show potential for its use in thermal storage applications. Additionally, this work discusses the molecular origins of the high thermal energy storage capacity of these ionic materials based on their crystal structures, revealing the importance of hydrogen bonds in PCM performance.

The Electrochemical Oxidation of Hydroquinone and Catechol through a Novel Poly-geminal Dicationic Ionic Liquid (PGDIL)-TiO2 Composite Film Electrode

A novel poly-geminal dicationic ionic liquid (PGDIL)-TiO₂/Au composite film electrode was successfully prepared by electrochemical polymerization of 1,4-bis(3-(m-aminobenzyl)imidazol-1-yl)butane bis(hexafluorinephosphate) containing polymerizable anilino groups in the electrolyte containing nano-TiO₂. The basic properties of PGDIL-TiO₂/Au composite films were studied by SEM, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry. The SEM results revealed that the PGDIL-TiO₂ powder has a more uniform and smaller particle size than the PGDIL. The cyclic voltammetry results showed that the catalytic effect on electrochemical oxidation of hydroquinone and catechol of the PGDIL-TiO₂ electrode is the best, yet the R_ct of PGDIL-TiO₂ electrode is higher than that of PGDIL and TiO₂ electrode, which is caused by the synergistic effect between TiO₂ and PGDIL. The PGDIL-TiO₂/Au composite electrode presents a good enhancement effect on the reversible electrochemical oxidation of hydroquinone and catechol, and differential pulse voltammetry tests of the hydroquinone and catechol in a certain concentration range revealed that the PGDIL-TiO₂/Au electrode enables a high sensitivity to the differentiation and detection of hydroquinone and catechol. Furthermore, the electrochemical catalytic mechanism of the PGDIL-TiO₂/Au electrode was studied. It was found that the recombination of TiO₂ improved the reversibility and activity of the PGDIL-TiO₂/Au electrode for the electrocatalytic reaction of HQ and CC. The PGDIL-TiO₂/Au electrode is also expected to be used for catalytic oxidation and detection of other organic pollutants containing -OH groups.