Ionic Liquids in Electrochemical Devices and Processes: Managing Interfacial Electrochemistry

Abstract

Many ionic liquids offer a range of properties that make them attractive to the field of electrochemistry; indeed it was electrochemical research and applications that ushered in the modern era of interest in ionic liquids. In parallel with this, a variety of electrochemical devices including solar cells, high energy density batteries, fuel cells, and supercapacitors have become of intense interest as part of various proposed solutions to improve sustainability of energy supply in our societies. Much of our work over the last ten years has been motivated by such applications. Here we summarize the role of ionic liquids in these devices and the insights that the research provides for the broader field of interest of these fascinating liquids.

Spotlight on ionic liquids

“…The realization that task-specific ILs can be created via simple and systematic chemical modifications of the constituent ions takes these systems beyond the promise of designer solvents to highly useful systems for diverse applications including drug delivery and as active pharmaceutical ingredients, [1][2][3] solvents for green processing of otherwise insoluble biomolecules such as cellulose, 4,5 highly energetic materials, 1 and novel electrolytes for energy applications such as batteries, fuel cells, and solar photoelectrochemical cells. [6][7][8][9] Plechkova and Seddon 10 estimated that there may be in excess of 10 6 possible ILs if all currently known IL cations and anions were to be paired, and as many as 10 18 if all ternary systems were to be investigated. The history of ILs predates even the early report of the room temperature IL ethylammonium nitrate by Walden 11 in 1914.…”

Composite polymer electrolytes of sulfonated poly-ether-ether-ketone (SPEEK) with organically functionalized TiO2

“…The current materials research explores different fields: blend of polymers, cross-linked membranes, ionic liquids, block-copolymers, and organic/inorganic hybrids [5][6][7][8][9]. Organic/inorganic hybrids can offer opportunities in many areas and not last in the field of fuel cell materials [10].…”

Properties and Customization of Sensor Materials for Biomedical Applications

“…Hybrid multiwalled carbon nanotubes-ionogel monoliths (from a silica matrix) show a mixed ionic and electronic conductivity, which makes them potential candidates as electrode materials or electron-to-ion transducers in ISEs (96). In some cases, ILs in their solid state have conductivities comparable to the liquid phase, e.g., ethylammonium dicyanamide, which in connection to their plasticity makes them valuable materials as solid-state electrolytes in sensor designing (97). Other properties often mentioned are their low volatility, high ionic density, and conductivity (up to 100 mS cm À1 ), as well as excellent chemical and electrochemical stability (potential windows up to 7 V have been reported) (98).…”

“…For instance, control of the water content during the electropolymerization seems to affect the conductivity of the CP layers. This was observed during the electropolymerization of thiophene in an aqueous electrolyte, and it resulted in the formation of a nonconducting polymer film (97,156). In addition, the choice of IL cation/anion is important as it affects the stabilization of the radical produced during IL electrochemical oxidation and regulates the degree of electrostatic interaction between the anion and the polymer backbone (83,97).…”

“…This was observed during the electropolymerization of thiophene in an aqueous electrolyte, and it resulted in the formation of a nonconducting polymer film (97,156). In addition, the choice of IL cation/anion is important as it affects the stabilization of the radical produced during IL electrochemical oxidation and regulates the degree of electrostatic interaction between the anion and the polymer backbone (83,97). In addition, ILs may affect chemical doping of the polymer film, the polymer film thickness, and film morphology (83).…”