Max E. Easton

The Formation of High‐Order Polybromides in a Room‐Temperature Ionic Liquid: From Monoanions ([Br5]− to [Br11]−) to the Isolation of [PC16H36]2[Br24] as Determined by van der Waals Bonding Radii

An unprecedented diversity of high-order bromine catenates (anionic polybromides) was generated in a tetraalkylphosphonium-based room temperature ionic liquid system. Raman spectroscopy was used to identify polybromide monoanions ranging from [Br5 ](-) to [Br11 ](-) in the bulk solution, while single-crystal X-ray diffraction identified extended networks of linked [Br11 ](-) units, forming a previously unknown polymeric [Br24 ](2-) dianion. This represents the largest polybromide species identified to date. In combination with recent work, this suggests that other, higher order molecular polybromide ions might be isolated.

The influence of ionic liquid additives on zinc half-cell electrochemical performance in zinc/bromine flow batteries

Six ionic liquids were assessed for their suitability as alternative bromine-sequestering agents (BSAs) in zinc/bromine redox flow batteries (Zn/Br RFBs) via comparison against conventional BSA, 1-ethyl-1-methylpyrrolidinium bromide ([C2MPyrr]Br). These alternative BSAs included the bromide salts of the following cations: 1-ethyl-1-methylpiperidinium ([C2MPip]+), 1-ethyl-1-methylimidazolium ([C2MIm]+), 1-(2-hydroxyethyl)-3-methylimidazolium ([C2OHMIm]+), 1-ethylpyridinium ([C2Py]+) and 1-(2-hydroxyethyl)pyridinium ([C2OHPy]+). Cyclic and linear sweep voltammetry, as well as electrochemical impedance spectroscopy, were performed to understand the influence of electrolytes containing these ionic liquids on zinc half-cell electrochemical performance. Solutions with [C2Py]Br, [C2MIm]Br and [C2OHPy]Br improved zinc half-cell performance (highest-magnitude current, charge, maximum power and energy) when compared to those utilizing [C2MPyrr]Br. Electrolytes employing these BSAs also reduced the nucleation overpotential of zinc electrodeposition and stripping compared to those using [C2MPyrr]Br. Zinc electrodeposits obtained during charging from electrolytes containing the different BSAs were analyzed via scanning electron microscopy and X-ray diffraction. Scanning electron micrographs showed a strong relationship between the chemical structure of the BSA employed and the crystallinity of zinc electrodeposits, with solutions containing [C2OHMIm]Br, [C2Py]Br and [C2OHPy]Br producing more compact zinc deposits than those with other BSAs. These findings warrant further investigation of BSAs with delocalized cationic charge. While these compounds have been proposed for application in Zn/Br systems, they are also potentially adaptable to other types of RFBs, which employ the Br2/Br− redox couple and use electrolytes containing BSAs.

Zinc bromide in aqueous solutions of ionic liquid bromide salts: the interplay between complexation and electrochemistry

Voltammetric studies of ZnBr2 (50 mM) in aqueous equimolar solutions of ionic liquid bromide salts (1-alkyl-1-methylpyrrolidinium bromide, [CnMPyrr], and tetraalkylammonium bromide, [Nn,n,n,n]Br, 50 mM, where n = 2, 4 or 6) are reported. A simple increase in alkyl chain length of the cation of the bromide salt greatly altered the mechanism of zinc deposition as a result of the complexation of bromozincate anions. The structures of two such bromozincates were isolated and their structures determined by single-crystal X-ray diffraction. These findings provide an additional strategic basis for the design of alternate bromine sequestering agents for aqueous zinc bromide flow cells.

The influence of novel bromine sequestration agents on zinc/bromine flow battery performance

This study benchmarks cycle performance of electrolyte solutions containing novel bromine sequestration agents (BSA) in a zinc bromine flow battery. Five alternative BSA candidates – 1-ethyl-1-methylpiperidinium bromide ([C2MPip]Br), 1-ethylpyridinium bromide ([C2Py]Br), 1-(2-hydroxyethyl)-pyridinium bromide ([C2OHPy]Br), 1-ethyl-3-methylimidazolium bromide ([C2MIm]Br) and 1-(2-hydroxyethyl)-3-methylimidazolium bromide ([C2OHMIm]Br) were investigated under operational conditions typical for zinc bromine flow batteries. Results were compared to the conventional BSA, 1-ethyl-1-methylpyrrolidinium bromide ([C2MPyrr]Br). Electrolytes containing the various alternative BSAs were tested at bench scale in a full-cell battery setup under controlled electrolyte flow and temperature. The evaluated performance parameters were: voltaic efficiency, coulombic efficiency, energy efficiency and recoverable charge. A correlation between BSA–bromine bond strength and cycle performance was observed. Performance of the tested electrolytes varied widely, and gains in coulombic efficiency were generally offset by losses in voltaic efficiency. [C2Py]Br and [C2MIm]Br produced cycle performance improvements compared to the other BSAs studied.

Beyond the Halogen Bond: Examining the Limits of Extended Polybromide Networks through Quantum‐Chemical Investigations

The bonding environments of some polybromide monoanions and networks were examined by quantum-chemical methods to investigate electronic interactions between dibromine-dibromine contacts. Examination of thermodynamic parameters and a bond critical point analysis give strong evidence for such bonding modes, which have been previously treated disparately in the literature. The thermodynamic stability of large polybromides up to [Br37 ](-) was also predicted by these methods.

Azolate Anions in Ionic Liquids: Promising and Under-utilized Components of the Ionic Liquid Toolbox

Owing to their ease of synthesis, diffuse positive charge, and chemical stability, 1-alkyl-3-methylimidazolium cations (i.e., [Cn mim]+ ) are one of the most routinely utilized and historically important components in ionic liquid (IL) chemistry. However, while this is a routinely encountered member of the IL family as cations, relatively few workers have explored the versatile chemistry of azoles to allow their use as an anionic component in ILs, as azolates. Azolate anions possess many of the desired properties for IL formation, including a diffuse ionic charge, tailorable asymmetry, and synthetic flexibility, with the added advantages of not relying on halogen atoms for electron-withdrawing effects, as is commonly encountered with IL anions such as hexafluorophosphate. This review explores the 122 azolate-containing ILs known in the literature (prepared from only 39 disparate azolate anions), with a view to highlighting not only their demonstrated utility as an IL component, but the ways in which the larger scientific community may utilize their advantageous properties for new tailored materials.

Zinc Electrodeposition in the Presence of an Aqueous Electrolyte Containing 1-Ethylpyridinium Bromide: Unexpected Oddities*

The reversible electrodeposition of zinc was investigated in an aqueous electrolyte containing zinc bromide (50 mM) and 1-ethylpyridinium bromide ([C2Py]Br, 50 mM) by cyclic voltammetry, chronoamperometry, and scanning electron microscopy. Unusual voltammetric behaviour for the Zn/ZnII redox couple was observed in the presence of [C2Py]Br. Passivation of the redox couple was observed after a single deposition–stripping cycle at switching potentials more negative than −1.25 V versus Ag/AgCl. This unusual behaviour was attributed to the reduction of 1-ethylpyridinium cations to pyridyl radicals and their follow-up reactions, which influenced the zinc electrochemistry. This behaviour was further seen to modify the nucleation process of electrodeposition, which altered the morphology of zinc electrodeposits.

Changing the Action of Iron from Stoichiometric to Electrocatalytic in the Hydrogenation of Ketones in Aqueous Acidic Media

Cyclohexanone, a model compound chosen to conveniently represent small oxygenates present in the aqueous phase of biomass hydrothermal upgrading streams, was hydrogenated in the presence of electrodeposited iron(0) using aqueous formic or sulfuric acid as a hydrogen donor. Under these conditions, zero-valent iron is consumed stoichiometrically and serves as both a formic acid decomposition site and a hydrogen transfer agent. However, the resulting iron(II) can be used to continuously regenerate iron(0) when a potential is applied to the glassy carbon working electrode. Controlled potential electrolysis experiments show a 17% conversion of cyclohexanone (over 1000 seconds) to cyclohexanol with >80% efficiency of iron deposition from an iron(II) sulfate solution containing formic or sulfuric acid. In the absence of electrodeposited iron, formation of cyclohexanol could not be detected.