Lewis Acidic Ionic Liquid Research Articles

Simultaneously enhancing mechanical and anti-corrosion properties of aluminum through electrodeposition of supersaturated Al(Fe) solid solutions

The heterogeneous microstructure in bulk aluminum (Al) alloys or coatings, comprising an α-Al solid solution matrix and coarse intermetallic compounds (IMCs), poses a challenge in balancing mechanical and anti-corrosion properties. This challenge is particularly pronounced in Al alloys with high iron (Fe) content. Here, supersaturated Al(Fe) solid solutions with a single phase have been electrodeposited using imidazolium chloroaluminate ionic liquids (ILs). Ferrous chloride (FeCl2) dissolved in Lewis-acidic ILs is assumed to form Cl-bridged [Fe(AlCl4)4]2−, which, together with the well-known Al2Cl7− species, supports the reduction and deposition of Al(Fe) alloy coatings. The supersaturated Fe solutes significantly strengthens the Al matrix, with the hardness of Al(Fe, 6.6 at.%) reaching up to 3.43 GPa, surpassing that of any commercial Al alloys and other binary Al-based solid solutions. Moreover, the Al(Fe) deposits demonstrate superior anti-corrosion performance compared to pure Al. The homogeneous microstructure and extended Fe solubility within Al(Fe) solid solutions inherently contributes to a simultaneous improvements in mechanical and anti-corrosion properties. The nanograined and compact structure also benefit these properties. Accordingly, the combination of electrodeposition techniques and Al(Fe) alloys offers a promising approach for providing effective mechanical and chemical protection on metal surfaces.

Insight into the catalytic behavior of ionic liquids and deactivation suppression technique in naphthalene alkylation

Lewis acidic ionic liquids as catalysts for alkylation reactions exhibited the potential for industrial application. Herein, the catalytic behavior of AlCl3-based ionic liquids with four organic ammonium salts was studied in the alkylation of naphthalene with n-octene for production of lubricating base oil, with special focus on the deactivation and recovery of ionic liquid. The Et3NHCl-AlCl3 ionic liquid exhibited better catalytic performance than others due to its stronger interaction with naphthalene, as evidenced by the adsorption test of naphthalene over ionic liquids. To understand the deactivation mechanism, the deactivated catalysts were extensively characterized by FT-IR and UV–vis. The protonation effect of ionic liquids on polyalkylation products in the presence of HCl was found to aggravate the deactivation of ionic liquid. The negative effect is easily reversed by the decompression treatment on the reaction system before catalyst recovery, this method markedly enhanced the cycling durability of ionic liquids for industrial application.

Clay-supported bio-based Lewis acid ionic liquid as a potent catalyst for the dehydration of fructose to 5-hydroxymthylfurfural

Caffeine and halloysite nanoclay mineral that are bio-based compounds were utilized to synthesize a novel Lewis acid heterogeneous catalyst. To this aim, halloysite was functionalized with 2,4,6-trichloro-1,3,5-triazine and reacted with caffeine, which was then converted to ionic liquid via a reaction with ZnCl2. The catalyst was applied for promoting the dehydration of fructose to 5-hydroxymethylfurfural. To investigate the effects of the reaction variables, response surface methodology was used. The product was achieved in 98.5% in 100 min using a catalyst loading of 30 wt% at 100 °C. Moreover, the catalyst was recyclable up to six runs with slight zinc leaching. Comparison of the catalytic activity of the catalyst with that of halloysite and a control catalyst with one caffeine-based Lewis acid ionic liquid confirmed the superior activity of the former and the important role of 2,4,6-trichloro-1,3,5-triazine for increasing the number of the grafted caffeine and thus the acidic sites of the catalyst. A plausible reaction mechanism was proposed, and the activity of the catalyst for other carbohydrates was also studied. According to the results, this catalyst catalyzed the reaction of other substrates to furnish 5-hydroxymethylfurfural in low to moderate yields. According to the kinetic studies, the activation energy was estimated to be 22.85 kJ/mol.

Lewis acid ionic liquid catalysed synthesis of bioderived surfactants from β-pinene

Cationic polymerisation of β-pinene (βP) via earth abundant catalysis has been investigated as a route to low molar mass poly(β-pinene) (PBP) for surfactant applications. As a ‘greener’ alternative to the...

Molecular design and experimental study on the alkylation of benzene with C6 olefin dimer with Lewis acidic monoamine ionic liquids and its sulfonate surfactant properties

Long-chain alkyl benzene (LAB), conventionally manufactured by petrochemical routes, is an important intermediate for the synthesis of high-value chemicals, especially detergents and oil displacement agents. The preparation of LAB from coal-based olefins has attracted extensive research interest. In this work, the alkylation activity of four Lewis acidic monoamine chloroaluminate ionic liquids (LAMCILs), designed by AlCl3 and monoamine hydrochloride with alkyl chains of different lengths, was predicted by quantum chemical calculations using the synthesis of 1-methyl-1-butylheptylbenzene (MBHB) with benzene and C6 olefin dimer as a model reaction. The HOMO*-LUMO* gap indicated that the alkylation activity was enhanced with increasing alkyl chain length of the organic amine molecules in the LAMCILs, in the following order: [n-C6H13NH3]Cl-AlCl3 > [n-C4H9NH3]Cl-AlCl3 > [n-C3H7NH3]Cl-AlCl3 > [C2H5NH3]Cl-AlCl3. These four LAMCILs were successfully synthesized and used to catalyze the alkylation of benzene with the C6 olefin dimer. The experimental results are consistent with the calculated results. The UV/VIS characterization showed that their Hammett acidity function (H0) increased as the alkyl chain of organic monoamine molecules in the LAMCILs extended. Therefore, a two-way correlation between the HOMO*-LUMO* gap, MBHB yield and Hammett acidity function can be established. Furthermore, the effect on the yield of MBHB was investigated by the method of metal chloride modified [n-C4H9NH3]Cl-AlCl3 ionic liquids. The results showed that the CuCl2-modified [n-C4H9NH3]Cl-AlCl3 ionic liquid had better catalytic activity in this study. Under optimal reaction conditions, the conversion of the C6 olefin dimer and selectivity toward MBHB reached 100 % and 91.34 %, respectively. Finally, the surfactant properties of sodium 1-methyl-1-butylheptylbenzene sulfonate (SMBHBS) were examined, and the results indicated that its surfactant properties were basically comparable to those of commercial LAS.

Highly stable Lewis acidic trifloaluminate ionic liquid supported on silica and metallosilicates as an efficient catalyst for continuous flow aminolysis of epoxides

In this work heterogeneous catalysts based on hybrid materials consisted of calcium and/or magnesium silicates and modern task-specific ionic liquids (supported ionic liquid phase material) dedicated particularly for continuous flow synthesis of fine chemicals with liquid reagents were designed. Pure SiO2 (as a reference sample), as well as magnesium (MgO-SiO2) or calcium (CaO-SiO2) silicates were used as supports for Lewis acidic trifloaluminate ionic liquids immobilized via chemical bound. The lowest ionic liquid loading was determined for SiO2 (15.58 wt%) and the highest for CaO-SiO2 (23.70 wt%). Resulted catalysts were used for the optimization of process parameters of the synthesis of β-amino alcohols in batch reactor (molar ratio aniline: styrene oxide 1.1:1; 1 mol% of catalyst, 60 °C). Not only the most active (conversion of styrene oxide 100.0% and selectivity to main product 98.7%) but also stable in 3 cycles of the process was the catalyst based on MgO-SiO2. The activity of poorly recyclable precursor of ionic liquid used as an active phase Al(OTf)3 was also lower (conversion 87.3% and selectivity 94.6%). Substrate scope confirmed the versatility of this method. The key achievement of the research was the confirmation of activity and stability of the most active catalyst in batch process for the aminolysis of epoxide in the presence of heterogeneous catalyst based on MgO-SiO2 in flow system through 72 h (conversion 81.1%, selectivity 95.9%). The proof of concept for the design of this catalytic system for production of selected fine chemicals is shown in this study.

Application of functional metal anionic Lewis acid ionic liquids in the alkylation of chlorobenzene/SOCl2.

4,4'-Dichlorodiphenyl sulfoxide is the main raw material for the manufacture of polysulfone, polyether sulfone and other engineering plastics. It is also an intermediate for medicines, dyes and pesticides, which has been widely utilized in engineering plastics, fine chemicals and other fields. The alkylation of chlorobenzene with thionyl chloride can give 4,4'-dichlorodiphenyl sulfoxide as a product using Lewis acidic ionic liquids. In this work, metal-based methylimidazolium ionic liquids were synthesized, which were found to be efficient catalysts for alkylation reactions. The molar ratio of different metal chlorides to 1-butyl-3-methyl imidazole chloride and the influence of different metal chlorine additives on the catalytic Lewis acid center were investigated. The fissionable species of AlCl3 in ionic liquids will enhance the acidity of ionic liquids and, thus, promote the catalytic performance of ionic liquids. Under the optimized reaction conditions, the conversion rate of excess chlorobenzene was 45.3% and the selectivity of 4,4'-dichlorodiphenyl sulfoxide was 31.9%.

One-pot liquefaction of cellulose to ethyl levulinate via 1-sulfonic acid-3-methyl imidazolium trichlorozincate as Brønsted-Lewis catalyst

The direct conversions of cellulose to ethyl levulinate (EL) via Brønsted acidic ionic liquid (BAIL), Lewis acidic ionic liquid (LAIL), and Brønsted-Lewis acidic ionic liquid (BLAIL) conducted in this study is a sustainable approach. Initially, BAIL 1-sulfonic acid-3-methyl imidazolium chloride [SMIM][Cl] was prepared by the mixing of 1-methylimidazole, dry dichloromethane, and chlorosulfonic acid. Then, Lewis acidic site was provided to the BAIL by the addition of zinc chloride (ZnCl2), to synthetize BLAIL 1-sulfonic acid-3-methyl imidazolium trichlorozincate, [SMIM][ZnCl3]. Meanwhile, LAIL 1-butyl-3-methyl imidazolium trichlorozincate [BMIM][ZnCl3] was prepared by the addition of ZnCl2 to a neutral 1-butyl-3-methyl imidazolium chloride [BMIM][Cl]. These three catalysts were then characterized and employed in the one-pot liquefaction process that was conducted in a stainless-steel batch reactor at 180 ˚C for 10 hr, by charging 0.6 g of cellulose, 40 mL of ethanol and 3 g of catalyst. A parameter study, mainly temperature (120–200) °C, time (2–10) hr, and cellulose loading (0.2–1.0) g, were then conducted to determine the selected parameters to obtain high EL yield. Among the employed ionic liquids (ILs), BLAIL [SMIM][ZnCl3] exhibited the highest catalytic activity, which was contributed mainly by its co-existence of Brønsted and Lewis acidic sites as detected in Fourier-Transform Infrared (FTIR) analysis, and its high acidic value. The maximum EL yield (20.27 wt%) was obtained under conditions of 180 °C, 6 hr, 0.6 of cellulose, and 3 g of [SMIM][ZnCl3]. The outcome of this study provides an insight on the potential of novel [SMIM][ZnCl3] in facilitating the direct cellulose ethanolysis to EL.

Ultrafast and selective recycling of poly(p-dioxanone) to monomers by using Brønsted–Lewis acidic ionic liquids as solvents/catalysts

In the [Et3NH][ZnCl3]/pentaerythritol system, poly(p-dioxanone) is almost fully chemically recycled to the high-purityp-dioxanone monomer in several minutes.

Kinetic and thermodynamic studies of HMF-ester synthesis using Brønsted–Lewis acidic ionic liquid catalyst

5-HMF to HMF-ester conversion kinetics.

Anion Equilibria and Stability of Quaternary Phosphonium Chloroaluminate Ionic Liquids

The anion equilibria and thermal stability in a series of quaternary trialkyloctylphosphonium chloroaluminate ionic liquids are investigated qualitatively by Raman spectroscopy, broadband dielectric spectroscopy, and nuclear magnetic resonance spectroscopy. Results indicate that Lewis acidic chloroaluminate ionic liquids based upon the phosphonium cation are less stable than those based upon other molecular cations. A slow time-dependent drop in room-temperature dc ionic conductivity as well as a step drop at elevated temperatures is tentatively attributed to a reaction involving the Lewis acidic Al2Cl7 - anion and the phosphonium cations. This reaction results in significant changes in the 1H, 13C, and 31P NMR spectra, but only minor changes in the Raman spectra. Furthermore, extended time at elevated temperatures results in a significant quantity of neutral aluminum chloride sublimating from the liquid. These results demonstrate an unusual reactive instability of phosphonium-based Lewis acidic chloroaluminate ILs.

Bifunctional Ionic Liquid Catalyzed Multicomponent Arylsulfonation of Phenols with Aryl Triazenes and DABSO for the Synthesis of Diaryl Sulfones

AbstractThe bifunctional Lewis acidic ionic liquid (LAIL) catalyzed multicomponent arylsulfonation of phenols with aryl triazenes and DABSO was developed. By using LAILs as redox and Lewis acidic catalysts without any additional promoter or ligand through an N2 extrusion/SO2 insertion sequence, various aryl triazenes were transformed into aryl sulfonyl radicals by coupling with DABSO, and these were then coupled with phenoxy radicals to afford the corresponding diaryl sulfones in good yields. The good functional-group tolerance, gram-scale reaction, and avoidance of the use of SO2 gas further demonstrated the practicality of this arylsulfonation reaction.

(Invited) Aluminum Electrodeposition in AlCl3–1-Ethyl-3-Methylimidazolium Chloride–Urea Melts

Several non-aqueous solvents for aluminum (Al) electrodeposition have been reported so far. Currently most researches on Al electrodeposition are conducted in Lewis acidic chloroaluminate ionic liquids (ILs) and deep eutectic solvents (DESs), which contain AlCl3 over 50 mol% and have a liquid phase at room temperature. Recently these solvents have also drawn attention as electrolytes for Al metal anode anion-rechargeable batteries.1 Only a few years ago, we have reported that Al electrodeposits with unique 2D structure are obtained in a 60.0-40.0 mol% AlCl3–urea DES without any difficulty, but not in the same composition chloroaluminate IL.2 Herein, in order to understand the unique 2D structure fabrication in the AlCl3–urea, we examine Al electrodeposition in the Lewis acidic chloroaluminate ternary melts consisting of AlCl3, 1-ethyl-3-methylimidazolium chloride ([C2mim]Cl), and urea.The preparation and purification processes for AlCl3, [C2mim]Cl, and urea, were identical with those described in previous articles.3 The molar fraction of AlCl3 used in the melts was 60 mol%. The sum of molar fraction for the [C2mim]Cl and urea was 40 mol% and these molar fraction was changed in the range of 0 ~ 40 mol%. The electrochemical measurements were conducted using a three-electrode cell. The working electrode was a Pt disk electrode. An Al plate was used for the counter electrode. The reference electrode was an Al wire immersed directly in the electrolyte. Galvanostatic electrodeposition was conducted using Cu plate electrodes. All the experiments were carried out in an Ar gas-filled glove box with O2 and H2O < 1 ppm. The resulting Al samples were characterized by SEM, EDX, and XRD. Operando digital microscope observation for the Al electrodeposition process was performed using the specially designed two-electrode airtight electrochemical cell.As described in previous article, Al deposition initiates at ca. 0 V (vs. Al(III)/Al) in both 60.0-40.0 mol% AlCl3–[C2mim]Cl IL and 60.0-40.0 mol% AlCl3–urea DES by the following commonly known electrode reaction.2,3 4 [Al2Cl7]− + 3 e− ⇌ Al + 7 [AlCl4]− Typical SEM images of the Al electrodeposits obtained in both electrolytes under the same conditions are exhibited in Fig. 1. In the 60.0-40.0 mol% AlCl3–[C2mim]Cl, dense Al crystals were uniformly electrodeposited on the Cu electrode. Interestingly, in the 60.0-40.0 mol% AlCl3–urea, 2D structured Al deposits, i.e., Al nanoplatelets, were obtained. Such unique Al deposits were yielded at the bath temperature over 313 K, if the applied current density was -5 ~ -20 mA cm-2. EDX analyses of all the electrodeposits revealed that the resultant deposits are pure Al without chloride contamination. XRD measurements strongly suggested that the Al deposits shown in Fig. 1a and 1b are polycrystalline Al and (111)-preferentially oriented Al, respectively. To the best of our knowledge, this anomalous electrodeposition behavior recognized in the 60.0-40.0 mol% AlCl3–urea has not been known in the chloroaluminate IL. Further investigation was conducted by the electrodeposition in the ternary AlCl3–[C2mim]Cl–urea melts under the same condition that can produce Al nanoplatelets in the AlCl3–urea. In the present study, we used three types of melts, 60.0-30.0-10.0 mol%, 60.0-20.0-20.0 mol%, and 60.0-10.0-30.0 mol% AlCl3–[C2mim]Cl–urea. As we expected, the increase in the urea molar faction in the melts provoked the morphology variation in the Al deposits. The 2D structure appeared in only the 60.0-10.0-30.0 mol% AlCl3–[C2mim]Cl–urea, suggesting that the urea is highly involved in the nanoplatelet formation. Because direct observation of the electrodeposition process enables to propose the plausible formation mechanism, the airtight electrochemical cell for operando digital microscope was newly designed. Further insights obtained through the operando observation will be reported in our presentation. References T. Tsuda, in Next Generation Batteries, K. Kanamura, Ed., Springer, Singapore, pp. 565-580 (2021).T. Tsuda, R. Miyakawa, A. Konda, Y. Ikeda, and S. Kuwabata, Program & Book of s (BoA) of 69th Annual ISE Meeting, p. 1512 (2018).T. Tsuda, G. R. Stafford, and C. L. Hussey, J. Electrochem. Soc., 164, H5007 (2017) and references therein. Figure 1

Reversible absorption of NF3 with high solubility in Lewis acidic ionic liquids

It is urgent to find a way to capture Nitrogen trifluoride (NF3) with the increasing emissions during the expansion of the electronic industry. Due to the strong electron − withdrawing of F atom, the interactions between NF3 and most compounds are quite weak, making the capture of NF3 full of challenges. Herein, a pioneering attempt was made to capture NF3 in Lewis acidic ionic liquids (LAILs). Impressively, under the condition of 313.2 K and 1.0 bar, [Omim][Fe2Cl7] LAILs exhibited high NF3 solubility (0.1801 mol/mol), which is 64 and 180 times higher than that of [Emim][Ac] and [Bmim][PF6] respectively. The interaction mechanism between LAILs and NF3 was proposed with its reversible regeneration, which has been confirmed by FT − IR, Raman, and theoretical calculations. This work reveals a novel insight into industrial prospects and applications of NF3 capture.

4-Methylpyridinium chloride ionic liquid grafted on Mn@zeolite-Y: Design, fabrication and performance as a novel multi-functional nanocatalyst in the four-component synthesis of pyrazolophthalazine-diones

In this work, 4-methylpyridinium chloride (4-MePy-Cl) ionic liquid grafted on nanoporous Mn/zeolite-Y was synthesized in several steps. First, Mn@zeolite-Y nanostructure was prepared by the metal exchange reaction of manganese (II) chloride with zeolite-NaY. This nanomaterial was then reacted consecutively with trimethoxysilylpropyl chloride and 4-methylpyridine to obtain multi-functional 4-MePy-Cl ionic liquid manganese nanocomposite (Mn/4-MePy-IL@ZY) for the first time. The structure of this nanoporous compound was confirmed using different characterization techniques such as FT-IR, FE-SEM, EDX, XRD, N 2 adsorption-desorption (BET), and TGA analyses. To evaluate the catalytic performance, the catalyst obtained was successfully employed as a multi-functional and efficient nanocatalyst in the facile synthesis of 3-amino-1-aryl-5,10-dioxo-pyrazolo [(Jagadeesan, 2016; Srilakshmi and Saraf, 2018) 1,21,2-b]phthalazine-2-carbonitriles through the four-component reaction of phthalic anhydride, hydrazine hydrate, malononitrile and arylaldehydes under mild reaction conditions with excellent yields. One of the obvious advantages of this nanocatalyst is the presence of Lewis acid (Mn 2+ ) and basic ionic liquid (4-MePy-Cl) sites on a nanoporous solid surface (multi-functional), which can be very useful and important in multi-component syntheses. • Designing new multi-functional nano-system of zeolitic micro-mesoporous is noteworthy advantage. • The Mn/4-MePy-IL@zeolite-Y acts as catalyst in the four-component synthesis of pyrazolophthalazines under green conditions. • Multi-functional nanocatalysts can be very useful and important in multi-component syntheses. • This procedure is eco-friendly, economically viable and versatile.

Novel hydrolytically stable Lewis acidic ionic liquid catalyst system for polybutylene succinate (PBS) synthesis

A new Lewis acidic ionic liquid catalyst system with improved catalytic activity and hydrolytic stability has been developed for the synthesis of poly(butylene succinate). Improved thermal stability of the final polymer is an added advantage of our new catalyst system.

Encapsulated Lewis acidic ionic liquids by halloysite using as efficient catalyst for CO2 conversion

A type of clay-supported catalysts were developed for conversion of CO2 by encapsulating ZnBr2-based Lewis acidic ionic liquids (ZnBr2/IL) in halloysite (Hal) via a one-step strategy. The Lewis acidic ionic liquid was loaded within enlarged lumens of Hal via acid treatment, and the mesoporous structure was found to benefit for CO2 storage/conversion. The composite ZnBr2/IL@P-Hal was found to have an adsorption capacity (6.43 cm3/g) of CO2 via adsorption/desorption isotherm measurements. The composite ZnBr2/IL@P-Hal showed excellent catalytic performance (TOF value was 1747.7 h−1) for coupling of CO2 with epoxides to produce propylene carbonate under the lack of any cocatalyst. Kinetic investigations indicated the reaction followed an order of one, with respect to catalyst ZnBr2/IL@P-Hal. The overall pathway of CO2 cycloaddition was theoretically validated via DFT calculations. These experimental and computational efforts deepen comprehension of the rational design of clay-based catalysts for CO2 cycloaddition, further elucidated halloysite was a promising support.

Bismuth-rich bimetallic clusters (CuBi8)3+ and [MBi10]4+ (M = Pd, Pt) from ionothermal synthesis

Abstract The reaction of Bi, BiBr3, and CuBr in the Lewis-acidic ionic liquid [BMIm]Br·4AlBr3 (BMIm = 1-n-butyl-3-limidazolium) at 180 °C yielded air-sensitive, shiny black crystals of (CuBi8)[AlBr4]2[Al2Br7]. Crystals of [MBi10][AlCl4]4 (M = Pd, Pt) were obtained by reacting Bi, BiCl3, and MCl2 under similar conditions. The structures have been determined by X-ray diffraction on single-crystals and were found to be very similar to that of the known analogues with other halogens, although not isostructural. In crystals of the complex salts, polyhedral bimetallic clusters (CuBi8)3+ or [MBi10]4+ are embedded in matrices of halogenidoaluminate anions. The heteroatomic nido-cluster (CuBi8)3+ consists of a (Bi8)2+ square antiprism η4-coordinating a copper(I) cation. In the cluster cation [MBi10]4+, the metal atoms M center a pentagonal antiprism of bismuth atoms.

Cost-Effective Processing of Carbon-Rich Materials in Ionic Liquids: An Expeditious Approach to Biofuels.

This work presents a cost-effective approach for processing of renewable carbon-rich biomass using pyridinium-based Lewis acidic ionic liquids (LAILs). Rice husk as carbon-rich lignocellulosic waste was pretreated with a series of neutral and Lewis acidic ionic liquids to yield valuable intermediate platform monosaccharides. Novelty in the work lies in direct conversion of lignocellulosic carbohydrates into reducing sugars without their further conversion into 5-hydroxymethylfurfural or any other platform chemicals that are fermentation inhibitors for bioethanol production. The unconverted cellulose-rich material (CRM) is regenerated as a delignified material by the simultaneous addition of antisolvents. CRM and recovered lignin obtained after pretreatment were analyzed via scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy. The process was optimized with respect to a high yield of platform sugars and the quantity as well as quality of recovered CRM and lignin contents. Various reaction parameters involving the molecular structure of ionic liquids (ILs), Lewis acidic strength of ILs, biomass loading into IL, time, temperature, and biomass particle size were screened thoroughly. From all of the tested ILs, unsymmetrical 3-methylpyridinium IL having N-octyl substitution and chloroaluminate anion showed a greater conversion efficiency at 100 °C for 1.5 h. FTIR and SEM analyses of recovered CRM justify >90% lignin removal from rice husk. From all of the removed lignin, 60 wt % of original lignin content was recovered. The Lewis acidic system possessed recycling ability up to 3 times for subsequent treatment of rice husk without a significant loss of efficiency.

Electrochemical Complexation of Polyatomic Aluminum Cations in Quinone-Type Organic Battery Electrodes Revealed By Solid-State NMR

Rechargeable aluminum batteries represent a significant area of opportunity for beyond-lithium-ion energy storage due to the high theoretical capacity (2980 mA∙h∙g-1, 8046 mA∙h∙mL-1), large earth abundance (8.23 wt.%), low cost, and safety of aluminum metal. Due to the stable native oxide layer that forms on aluminum, very few electrolytes are able to reversibly plate and strip aluminum at room temperature. Lewis acidic chloroaluminate ionic liquid electrolytes have demonstrated success in this regard; however, any cathode materials must also be (electro)chemical stable in this electrolyte. Electrode materials based on organic molecules have garnered attention due to their tunable structures and properties, enabling optimization for specific energy storage systems. Furthermore, diverse functional groups enable a range of possible charge storage mechanisms, many of which have yet to be explored in these systems. Like aluminum, organic materials are highly abundant and can be derived from various sources without geopolitical constraints. However, few Al-organic battery studies exist, and none so far have performed mechanistic analyses based on experimental data to identify conclusively the electroactive ions and their binding sites.Here, we present a rigorous analysis of charge storage mechanisms in quinone-type organic molecules for the first time, established through multi-dimensional solid-state nuclear magnetic resonance (ssNMR) spectroscopy in concert with quantum chemical calculations and electrochemical measurements. Indanthrone quinone (INDQ) is investigated for the first time as a model system due to its two distinct quinone functionalities and low solubility in many solvents. Through-space 27Al{1H} and 13C{1H} dipolar-mediated ssNMR techniques are used to establish the sub-nanometer proximities between polyatomic aluminum cations and specific moieties in the organic frameworks. Furthermore, dipolar-mediated ssNMR measurements are sensitive to both molecular dynamics and internuclear distances, which enables us to selectively filter out signals from residual liquid electrolyte, eliminating the need for solvent rinsing that can perturb the sample. Al-INDQ cells achieve reversible capacities of up to 240 mA∙h∙g-1 and maintain capacities >100 mA∙h∙g-1 at rates up to 2400 mA∙g-1. The enolization reaction and charge-balancing AlCl2 + cation complexation was established via dipolar-mediated ssNMR, findings that are corroborated through density functional theory (DFT) calculations. Other quinone-based organic structures with modified structures and compositions were also investigated using similar methods and will briefly be compared to INDQ. In aggregate, the quinone-based model systems serve as a basis to better understand how different functional groups, heteroatoms, and organic structures affect the electrochemical properties of rechargeable Al-organic batteries. The results yield strategies towards creating ‘designer’ organic electrode materials for rechargeable aluminum batteries.