An overview of the ionic liquids and their hybrids operating in electrochemical cells and capacitors

The present work of review is focused on the recent advancements regarding the exploration of the ionic liquids, ionic liquids with the incorporation of nanoparticles of several materials, and ionic liquid-grafted nanoparticles operating as liquid electrodes in electrochemical cells and capacitors. The ionic liquids are generally synthesized at room temperature and by adding a solution, which can be an acid, a base, or a salt in water, and are composed of organic cations and a great number of charge-delocalized organic/inorganic anions. The electrochemical features such as the electrical conductivity and capacitance of the promising ionic liquids and their hybrids are addressed thoroughly, together with their influencing factors like the nature, concentration, and functionalization of the nanoparticles, type of base fluids, working temperature, and addition of surfactants. Moreover, this overview identifies and discusses the main applications of ionic liquids and their hybrids with nanoparticles in various possible electrochemical device configurations, along with a brief evaluation of the associated feasibility issues. Additionally, this survey of the published scientific papers on the subject enabled the listing and evaluation of the beneficial features related to the usage of these fluids including enhanced electrical conductivity and improved capacitance in comparison with the commonly employed solvents and electrolytes. Finally, it addresses the main problems associated with such types of fluids and outlines the primary prospects for further research and use of ionic liquids and their nanocomposites in different electrochemical technological applications.