Brønsted acid–base ionic liquids and their use as new materials for anhydrous proton conductors

Abstract

Novel Brønsted acid-base ionic liquids, derived from a simple combination of a wide variety of organic amines with bis(trifluoromethanesulfonyl) amide are electroactive for H2 oxidation and O2 reduction at a Pt electrode under non-humidifying conditions, which shows the prospect of the use of protic ionic liquids as new materials for anhydrous proton conductors at elevated temperatures.

Tunable Wavelength Soft Photoionization of Ionic Liquid Vapors

“…Melting temperatures of room temperature ILs can therefore be much lower compared to those of salts based on atomic ions, such as NaCl, which has a melting temperature of 1074 K. In addition to having low melting temperatures, ILs have a number of unique properties, including excellent solvation ability, extraordinarily low volatility, and high thermal stability. [1][2][3][4][5][6][7][8][9] Since the physical and chemical properties of ILs can be varied by the choices of the cation and anion pair, 1 they can be used for many applications such as fuel cells, [3][4][5] batteries 6,7 and solar cells. 8,9 Furthermore, ILs are also used in ionic propulsion, 10,11 for hypergolic fuels 12 and various chemical extraction applications.…”

Prediction of Macroscopic Properties of Protic Ionic Liquids by Ab Initio Calculations

“…7 This is due to their proton conducting properties, the very low vapor pressure even at temperatures above the boiling point of water, and their wide liquid temperature range (up to 350°C 8 ). Replacing the water-based low-temperature FC systems of today with PIL based electrolytes could thus increase their working temperatures to well above 100°C, reducing the catalyst poisoning problem and subsequently reduced load demands.…”

Design and Materialization of Ionic Liquids Based on an Understanding of Their Fundamental Properties

“…The remarkable changes in conductivity that occur on changing the composition of systems of imidazole or pyrazole and H 2 SO 4 opened a new route to the design of non-aqueous proton conductors. 50 This 43,44 However, in the base-rich conditions, the thermal stability is disappointingly low due to evaporation of the neutral species. 43,47 The thermal stability and electrochemical activity of protic ILs for fuel cell reactions are greatly affected by the chemical structure of protic ILs.…”

“…45 Our initial interest in H + -conducting electrolytes concerned the transport properties of H + in protic ILs. [43][44][45][46][47] At that time, K.-D. Kreuer at the Max Planck Institute for Solid State Research was carrying out pioneering research with non-aqueous proton carriers; [48][49][50][51] his research focused on the autoprotolysis reactions of neutral species such as imidazole and pyrazole, which form proton defects in the systems and accelerate Grotthuss transport. The remarkable changes in conductivity that occur on changing the composition of systems of imidazole or pyrazole and H 2 SO 4 opened a new route to the design of non-aqueous proton conductors.…”

“…Early in our IL studies, we applied protic ILs for use as H + -conducting electrolytes for non-humidified H 2 /O 2 fuel cells operating at temperatures greater than 100°C based on the expectations that cations having active protons (typically ammonium cations) are highly mobile and electrochemically active for use in fuel cell reactions, i.e., the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). 43,44 In the case of acidic aqueous systems (including polymer electrolyte membrane fuel cells), water molecules act as a base, accepting protons to form hydronium cations (H 3 O + ). H + can be conducted through such media by the migration of H 3 O + cations themselves or by proton exchange between H 3 O + and H 2 O, the so-called vehicle and Grotthuss mechanisms, respectively.…”