Ionic Liquids–Cobalt(II) Thermochromic Complexes: How the Structure Tunability Affects “Self-Contained” Systems

Floriana Billeci,Natalia V Plechkova,H Q Nimal Gunaratne,Kenneth R Seddon,Peter Licence,Francesca D’Anna

doi:10.1021/acssuschemeng.0c08586

Abstract

With the aim of obtaining thermochromic systems with potential applications in solar energy storage, we evaluated the behavior of some sugar-based ionic liquids (ILs)–Co(NTf2)2 complexes, in IL solution, as a function of temperature. Different structural changes on the cation, the nature of the anion, and the nature of the IL used as the solvent were considered. The analysis of the above factors was carried out through a combined approach of different techniques, that is, variable temperature UV–vis and NMR spectroscopies, conductivity, and thermal gravimetric analysis. The thermochromic systems were analyzed both as solutions and as thin films, and the data collected highlight the defining role played by both the cation structure and the solvent nature in determining their performance. Most of the investigated systems show a chromogenic transition from pink to blue, occurring in a temperature range suitable for practical applications (40–60 °C). Interestingly, when embedded in a polymeric matrix, thin films with high recyclability and long life are also described.

Highlights

The ever-increasing global energy demands, due to expanding developments and increasing populations, have led to serious scrutiny over the depleting energy resources
The schemes generally known as molecular solar thermal systems, for example, phase-changing materials that store energy in the form of lattice energy, represent a promising avenue for harvesting and storing solar energy.[2−4] In this context, photochromic systems where a molecule is converted by photoisomerization into a higher-energy isomer, which is capable of storing the energy until released by a trigger, converting the metastable isomer to the original lightharvesting isomer,[5−9] have played a significant role
The search for new smart materials to be applied in energy saving is a topic of current interest, with the aim to decrease modern societies’ dependency on fossil fuels

Summary

Introduction

The ever-increasing global energy demands, due to expanding developments and increasing populations, have led to serious scrutiny over the depleting energy resources. Global energy demand has focused attention on sustainable energy generation coupled with optimized use of energy and minimized pollution, limiting fossil fuel-based energy consumption to a bare minimum. These aspects have led to an increasing focus on the short-term stored energy resources, which could be derived from wind power, hydropower, solar power, biomass, and so forth. Solar energy is a viable and inexhaustible source of energy[1] for generating power, with the aid of solar cells, and harnessing its heat via efficient storage of sun’s heat using compounds/materials with high heat capacities. The schemes generally known as molecular solar thermal systems, for example, phase-changing materials that store energy in the form of lattice energy, represent a promising avenue for harvesting and storing solar energy.[2−4] In this context, photochromic systems where a molecule is converted by photoisomerization into a higher-energy isomer, which is capable of storing the energy until released by a trigger, converting the metastable isomer to the original lightharvesting isomer,[5−9] have played a significant role

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Conclusion