Anionic Complexes Research Articles

«Green-Ligand» in Metallodrugs Design—Cu(II) Complex with Phytic Acid: Synthetic Approach, EPR-Spectroscopy, and Antimycobacterial Activity

The interaction of sodium phytate hydrate C6H18O24P6·xNa·yH2O (phytNa) with Cu(OAc)2·H2O and 1,10-phenanthroline (phen) led to the anionic tetranuclear complex [Cu4(H2O)4(phen)4(phyt)]·2Na+·2NH4+·32H2O (1), the structure of the latter was determined by X-ray diffraction analysis. The phytate 1 is completely deprotonated; six phosphate− fragments (with atoms P1–P6) are characterized by different spatial arrangements relative to the cyclohexane ring (1a5e conformation), which determines two different types of coordination to the complexing agents—P1 and P3, P4, and P6 have monodentate, while P2 and P5 are bidentately bound to Cu2+ cations. The molecular structure of the anion complex is stabilized by a set of strong intramolecular hydrogen bonds involving coordinated water molecules. Aromatic systems of phen ligands chelating copper ions participate in strong intramolecular and intermolecular π-π interactions, further contributing to their association. At the supramolecular level, endless stacks are formed, in the voids of which sodium and ammonium cations and water molecules are present. The stability of 1 in the presence of human serum albumin (HSA) was investigated using Electron Paramagnetic Resonance (EPR) spectroscopy. Continuous wave (CW) EPR spectra in water/glycerol frozen solution clearly indicate a presence of an exchange-coupled Cu(II)-Cu(II) dimeric unit, as well as a Cu(II) monomer-like signal arising from spins sufficiently distant from each other, with comparable contributions of two types of signals. In the presence of albumin at a 1:1 ratio (1 to albumin), the EPR spectrum changes significantly, primarily due to the reduced contribution of the S = 1 fraction showing dipole–dipole splitting. The biological activity of 1 in vitro against the non-pathogenic (model for Mycobacterium tuberculosis) strain of Mycolicibacterium smegmatis is comparable to the first-line drug for tuberculosis treatment, rifampicin.

Adsorption and Bulk Assembly of Quaternized Hydroxyethylcellulose–Anionic Surfactant Complexes on Negatively Charged Substrates

This study examines the adsorption and bulk assembly behaviour of quaternized hydroxyethylcellulose ethoxylate (QHECE)–sodium dodecyl sulphate (SDS) complexes on negatively charged substrates. Due to its quaternized structure, QHECE, which is used in several industries, including cosmetics, exhibits enhanced electrostatic interactions. The phase behaviour and adsorption mechanisms of QHECE–SDS complexes are investigated using model substrates that mimic the wettability and surface charge of damaged hair fibres. Two preparation methodologies, high-concentration mixing and gradient-free mixing, were employed to examine their impact on the complex equilibrium, phase behaviour, and adsorption properties of the complexes. The measurements of turbidity, electrophoretic mobility, and conductivity demonstrate the existence of nonequilibrium dynamics during the mixing process, which exert a significant influence on the structural and functional characteristics of the complexes. The quartz crystal microbalance with dissipation monitoring (QCM-D) was employed to investigate the adsorption of the complexes onto the substrates. The results demonstrated the critical role of intermediate SDS concentrations in enhancing deposition. The findings emphasise the importance of formulation and preparation protocols in designing stable, high-performance cosmetic products. This research advances our understanding of polyelectrolyte–surfactant interactions and provides insights into optimising QHECE-based formulations.

Molecule-Based Proton-Electron Mixed Conductor with the Highest Ambipolar Conductivity.

Proton-electron mixed conductors (PEMCs) are an essential component for potential applications in hydrogen separation and energy conversion devices. However, the exploration of PEMCs with excellent mixed conduction, which is quantified by the ambipolar conductivity, σamb = σeσH/(σe + σH) (σe: electronic conductivity; σH: proton conductivity), is still a great challenge, largely due to the lack of structural characterization of both conducting mechanisms. In this study, we prepared a molecule-based proton-electron mixed-conducting cation radical salt, (ET)4[Pt2(pop)2(Hpop)2]·PhCN (ET: bis(ethylenedithio)tetrathiafulvalene, pop2-: P2H2O52-), by electrocrystallization. The salt shows metallic electronic conduction, which arises from the (ET)2•+ layers, with a high σe value (1-2 S cm-1 at room temperature). The metallic state was corroborated by magnetic susceptibility measurement and band structure calculation. The salt also shows superprotonic conduction (σH = 2.1 × 10-2 S cm-1 at room temperature under dried conditions), which relies on the one-dimensional (1D) hydrogen-bonding network of protonated paddlewheel-type Pt-dimer complex anions, [Pt2(pop)2(Hpop)2]2-. Crystallographic and computational studies revealed the presence of infinite intra- and intermolecular O-H···O hydrogen bonds, which show a double-well-like potential energy curve with a negligible energy barrier in the 1D chain, facilitating Grotthuss-type proton hopping via Lewis basic sites. Among the structurally defined PEMCs, the present salt displays the highest room temperature σamb value of 2.1 × 10-2 S cm-1 even under dried conditions. The σamb value has the same order as those of reported perovskites-type metal oxides at high temperatures and achieves a level that is beneficial for the practical applications.

The Electroactive Species and Electrolyte Solution Chemistry Importance in Non-Aqueous Mg Electrochemical Systems

Abstract The chemistry of the electrolyte solutions that enable reversible Mg deposition is not trivial. Such solutions are currently limited to ethereal solvents and most of them contain chlorides complexes. These ionic complexes have important role in the performance. However, the presence of chlorides in these solutions complicates the cathode side because such solutions are not compatible with the commonly used metallic current collectors for cathodes. Consequently, it is questionable whether it is possible to synthesize fully functional Cl-free electrolyte solutions suitable commercial Mg-ion batteries. Noked et al. reported that by adding DME to the precursor electrolyte [Mg2Cl3*6THF]+ [Ph3AlCl]- in THF, it was possible to create a new electroactive complex Mg salt, namely, [Mg-3.DME]2+ 2[AlPh3Cl]-, which solution performs better than the precursor’s solution. This solution introduces a new case of chlorides free electrolyte solution, with stabilized Mg2+ cations and anions containing chloride ligands which cannot lead to corrosion phenomena. In this work a full evaluation of selected electrolyte solution was carried out, considering rigorously the role of the electroactive species and the anion complexes in the electrochemical process. 
In addition, we study the effect of the anion on the electrochemical performance by comparing this solution with other previously presented solutions.

Synthesis and Redox Chemistry of Co3E4 (E=P, As) Clusters.

The synthesis of the cluster complexes [(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)] (E=P (3), As (4)) starting from the anionic triple-decker complexes [K(18cr6)(dme)2][(Cp'''Co)2(μ,η4:η4-E4)] (E=P (1), As (2)) by electrophilic quenching with the Co dimer [(Cp'''CoCl)2] is reported. Both complexes show a distinct redox chemistry, which was first investigated by cyclic voltammetry. Subsequently, the monoanions [K(L)(sol)n][(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)] (E=P, L=18cr6, sol=dme, n=2 (5), E=As, L=2,2,2-crypt, n=0 (6)), the monocations [(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)][FAl] (E=P (7), As (8)) and the dications [(Cp'''Co)3(μ3,η3:η3:η3-E4)][TEF]2 (E=P (9), As (10)) could be realized experimentally and isolated in moderate to good yields. All compounds were characterized by single crystal X-ray structure analysis, NMR and EPR spectroscopy, mass spectrometry and elemental analysis.

Integrating multiple emission centers for photoluminescence regulation in copper–antimony/bismuth halides

Inserting a CuBr unit into monometallic halides results in heterometallic halides with dual emissions originating from the complex cation and anion unit, which enables wide modulation of emission color and low temperature optical sensing.

Fluoride Binding in Unlikely Partners: The Formation of Anion-Anion Complexes with [M(EGTA)]⁻ and [M(OBETA)]⁻ (M = Gd3+, Y3+)

Anionic metal complexes (M = Gd3+, Y3+) with two homologous acyclic aminopolycarboxylate ligands, heptadentate (OBETA) and octadentate (EGTA), were prepared and characterized using both relaxometric NMR (for Gd3+) and high-resolution...

Activation of H2O by ThO2- Experimental and Computational Studies.

A synergetic study that utilized anion photoelectron spectroscopy and high-level ab initio calculations has explored the activation of H2O molecules by ThO2- molecular anions. Both experiment and theory found conclusive evidence for said activation. In the experiments, this appeared as a tell-tale directional shift in the spectral profile of the anionic complex that ruled out physisorption, i.e., ThO2-(H2O), and implied chemisorption. In the computations, good agreement was found between the calculated and measured vertical detachment energies, and the atomic connectivity (the structure) of the resulting anionic complex was found to be [OTh(OH)2]-.

Ni(II) and Cu(II) Ion Coordination by the Novel (2E,2′E)-N,N′-(2-Hydroxypropane-1,3-diyl)bis[(2-hydroxyimino)propanamide] Ligand in the Solid State and in Aqueous Medium

In the process of a systematic study of the bis-chelate oxime-amide ligands with different polymethylene spacers and their transition metal complexes, two new Ni(II) and Cu(II) complexes of the mhiea2poh ligand have been isolated, and their molecular and crystal structures determined by single crystal X-ray diffraction. Potentiometric titrations were performed on a range of aqueous solutions in both systems, which allowed the identification of various complex species and afforded their stability constants. ESR spectra of samples with optimised concentrations of complexes in Cu(II)–L–H system were recorded. A distinguishing feature of both systems is the dimerization of anionic pseudo-macrocyclic complexes. The latter is caused either by centrosymmetric hydrogen bonding of the hydroxy group on the propane spacer to the oximato oxygen of the opposing unit or by back-to-back π-stacking of planar complex units. ESR measurements indicated likely coupling of Cu-Cu paramagnetic centres in the dimers.

Mono‐, Di‐, and Trinuclear Complex Anions of RuF5 in Rb[RuF6], Cs[Ru2F11], and [O2][Ru3F16

Herein, we report the synthesis of Rb[RuF6], Cs[Ru2F11], and [O2][Ru3F16] containing mononuclear [RuF6]−, dinuclear [Ru2F11]− and trinuclear [Ru3F16]− anions, respectively, and their characterization by single crystal X‐Ray diffraction. Such a trinuclear anion is described for Ru for the first time. Rb[RuF6] was additionally investigated by Raman spectroscopy while Cs[Ru2F11] was studied by IR and Raman spectroscopy. The fluoride ion affinity of RuF5 and the hypothetic molecules Ru2F10 and Ru3F15 was studied by quantum‐chemical calculations and shown to decrease with increasing nuclearity in contrast to SbxF5∙x species. Intrinsic bond orbital calculations show essentially ionic µ‐F–Ru bonds in the anions [Ru2F11]− and [Ru3F16]−.

A New Bis-Urea Based Cage Receptor for Anions: Synthesis, Solid State Structures and Binding Studies.

The synthesis and characterization of a novel bis-urea-based cage receptor for anions (3S,15S)-3,15,20,25-tetramethyl-1,4,6,12,14,17,20,25-octaazatricyclo[15.5.5.17.11]octacosa-7(28),10-diene-2,5,13,16-tetraone (L) is reported. L is a macro-bicyclic ligand built on the 1,7-dimethyl-1,4,7,10-tetraazacyclododecane scaffold to obtain a cage topology in which two ureido moieties have been inserted as binding sites for anions. L can interact with anion guests (G) via H-bonding; in particular, it binds both spherical (Cl-) and V-shaped anions (AcO-) as well as more complex carboxylate anions, such as the norfloxacin (Nor-). NMR experiments highlight that the interaction between L and G mainly occurs at the ureido moieties. L forms L-G adducts of 1 : 1 ([LG]-) and 1 : 2 ([LG2]2-) stoichiometry with Cl- and AcO-. Otherwise, in the case of Nor- only the formation of the [LG]- complex is observed. L shows higher formation constants values for [LAcO]- (2.9) and [LNor]- (3.6) than [LCl]- suggesting a stronger interaction with the carboxylate anions. In the solid state, three crystal structures of the HL⋅G species were obtained (G=Cl-, AcO-, ClO4 -) highlighting the H-bonding interaction between the chloride, acetate or perchlorate anions and the -NH functions of the ureido fragment. The comparison between the two parent open chain receptors (Lb-c) and L has been reported and discussed.

Synthesis and structure of heterometallic multiligand Ge(IV) - 3d-metals complexes with 1-hydroxyethane-1,1-diphosphonic acid and 1,10-phenanthroline

Synthesis methods were developed, five new coordination compounds were isolated and investigated: [M(phen)3]4[Ge6(μ-OH)4(μ-O)2(μ-hedp)6]*хСН3СООНnH2O (M= Fe (1), x= 0, n= 20; Co (2), x= 2, n= 30; Ni (3), x= 2, n= 26), [Cu(phen)2(H2O)]2[Cu(phen)(H2O)3]2[Ge6(μ-OH)4(μ-O)2 (μ-hedp)6]*16H2O (4), [Zn(phen)2(H2O)2]2[Zn(phen)(H2O)4]2[Ge6(μ-OH)4(μ-O)2(μ-hedp)6]*18H2O (5), were Н4hedp - 1-hydroxyethane-1,1-diphosphonic acid, phen - 1,10-phenanthroline. It was found that the complexes belong to the cation-anion type, consisting of the hexanuclear complex anion, in which Ge atoms are connected by three types of bridging ligands (hydroxy-, oxo-, and 1-hydroxyethane-1,1-diphosphonate), and phenanthroline-containing cations of different compositions depending on the 3d-metal. Synthesized substances in crystals are organic-inorganic hybrid ensembles with three-dimensional networks formed by numerous intermolecular hydrogen bonds between complex cations, anions, and water of crystallization molecules.

CHARACTERIZATION OF NEW MIXED AND HYBRID INORGANIC-ORGANIC MATERIALS BASED ON PHOSPHATES BY INFRARED SPECTROSCOPY

In this work we synthesized three inorganic-organic hybrid organic phosphate compounds of current interest due to their fascinating architectures and potential applications in supramolecular chemistry engineeringThese compounds were characterized mainly by elementary analysis and IR spectroscopies. they were synthesized from a reaction carried out in a common organic solvent between the monocyclohexylamine phosphate and〖SnBu〗_2 〖Cl〗_2 〖Y(CH〗_3 〖CO〗_2 )_(3.) or D_y 〖Cl〗_3.. Structures involving complex anions have been proposed. Structures involving complex anions have been proposed. In phosphate compounds, the anion is present in the form of〖HPO〗_4^(2-)and 〖HPO〗_4^(2-)The structures obtained are of the infinite type, monomer or with double metallic components. Phosphato compounds with rare earths gave new monomeric or double metallic component structures. The nine coordination (9) found in one of the metallic components is a coordination that we find with rare earths. The structural study of its complexes has shown that these cordination complexes can present promising catalytic activity for the oxidation and degradation of compounds such as methylene blue.

Physicochemical properties of Na<sub>2</sub>SO<sub>4</sub>-CaSO<sub>4</sub> melts

The aim of the work was to study the properties of melts of the Na2SO4–CaSO4 system, which are best suited for practical application in metallurgy, for example, for improving the operation of industrial furnaces. In addition, information on the properties of this system is of interest for applied chemistry of molten salts, for example, for cleaning gases, metal and ceramic surfaces of structural elements. The properties of melts of binary sulfate systems, necessary for selecting application parameters, have not been studied sufficiently. The most important for practice are density, surface tension and dynamic viscosity. The work uses modern experimental research methods: maximum pressure in an argon bubble blown into the melt through a capillary to determine the density and surface tension, and the vibration method – for dynamic viscosity. The temperature and concentration ranges of measurements were 1050–1200°C and 0–60 mol. %. For the entire studied range of melt compositions, linear dependences of density and surface tension on temperature were obtained. Dynamic viscosity obeys an exponential dependence. As a result of statistical processing of the experimental data, general equations of polytherms of density, surface tension and viscosity were derived. Analysis of the experimental results showed that the values of density, surface tension and viscosity have deviations from additivity, which reflects a change in the structure of sodium sulfate – calcium sulfate melts with an increase in the concentration of CaSO4. Comparison of the obtained experimental data with those already known for binary carbonate melts indicated changes in the structure of the melts, in particular, the formation in the volume, in addition to the Na+ and Ca2+ cations and the SO42- anion, of complex anions [NaSO4]- predominantly on the surface and [Ca(SO4)]n- predominantly in the volume.

Chalcogen Bonds Enable Efficient Photoreduction of Sulfur-Containing Heterocycles.

Chalcogen bonding interactions have attracted significant attention in a broad chemistry community, with a particular focus on their ability to stabilise the key transition states in various organic synthetic routes. In this work, we demonstrate that they can also be harnessed in selective photoredox reactions, which cannot be otherwise achieved with alternative approaches to photoreduction. We demonstrate this concept through the photoreduction of the sulfur-containing DNA nucleoside precursor thioanhydrouridine to 2'-deoxy-thiouridine, revealing the previously unrecognized role of bisulfide in this process. Based on quantum chemical simulations, we identify a stable chalcogen-bonding complex of the hydrosulfide anion and thionhydrouridine (HS-⋅⋅⋅S contacts), which enables directional photoinduced electron transfer, resulting in the formation of non-canonical DNA nucleoside. We also disprove the possibility that photoreduction of thioanhydronucleosides could be initiated by hydrated electrons generated from irradiated bisulfide anions which do not interact with the chromophore. Finally, we show that selective photoreduction mediated by chalcogen bonds can only occur for chromophores, which exhibit sufficiently long excited-state lifetimes in the locally-excited states to undergo transition to the productive charge transfer state. These findings can be further used in the design of similar photoredox reactions which can employ the potential of chalcogen bonding interactions.

An advanced separation method for the acquisition of 212Pb/212Bi from natural thorium

212Pb/212Bi hold significant potential for targeted cancer therapy; however, their supply remains severely limited. The extraction of 212Pb/212Bi from natural thorium is expected to fundamentally address this issue. This study proposes and verifies a new, efficient and low-cost method for separating 212Pb/212Bi from natural 232Th by investigating the separation behavior and mechanism of a silica-supported anion exchange resin (SiPyR-N4) toward multiple types of metal cations in hydrochloric solution. The experimental results demonstrated that SiPyR-N4 was successfully prepared with a uniform shape, porous structure, and containing quaternary amines. SiPyR-N4 showed extremely high selectivity for Pb2+ and Bi3+, but no affinity for Th4+, La3+, and Ba2+. The adsorption speed was more than six times as fast as traditional resins, providing significant advantages in the separation of short-lived nuclides. The hot separation experiment suggested that 212Pb and 212Bi were successfully isolated from natural 232Th by using natural thorium as the raw material, and the long-lived nuclides were removed completely. The selective separation mechanism was attributed to Pb2+ and Bi3+ forming anionic complexes in the hydrochloric acid medium, while Th4+, Ra2+, and Ac3+ did not form such complexes. Pb2+ and Bi3+ were bound to the active sites via chloride bridges, with [PbCl3]− and [BiCl6]3− serving as the main adsorbed species. This study is the first to report the direct and selective separation of 212Pb and 212Bi from 232Th decay chains using non-crown ether materials, and it provides an excellent material candidate for the separation of short-lived nuclides, showing significant application potential in the future.

Electrodeposition for Metal Recovery from Spent Batteries: Strategies for Improving Selectivity

Selective recovery of critical metals such as cobalt and nickel at a molecular level is crucial for the sustainable recycling of Li-ion batteries. However, the similarity in reduction potentials between these metals presents a significant challenge for achieving selectivity during electrodeposition, particularly for elements like cobalt and nickel (with E°Co = −0.277 V and E°Ni = −0.250 V vs SHE). In this presentation, we introduce a key strategy aimed at controlling selectivity toward either cobalt or nickel during potential-dependent electrodeposition. Initially, manipulating the electrolyte composition to introduce an excess of chloride ions enables precise control over speciation, leading to the distinct formation of anionic cobalt chloride complexes (CoCl42-) while keeping nickel predominantly in its cationic form ([Ni(H2O)5Cl]+) within an aqueous electrolyte. This forms the basis for potential-dependent selectivity. Additionally, regulating the interfacial charge density through electrode functionalization further fine-tunes selectivity by controlling the diffusion coefficient of the target ions. Moreover, we demonstrate the effectiveness of temperature-dependent control in achieving selectivity, resulting in a Ni/Co ratio exceeding 100. Unlike traditional selective electrodeposition methods, where the extended enrichment of one metal on the solid surface adversely impacts dynamic selectivity due to concentration change in the bulk electrolyte, our innovative approach guarantees high-purity and high-recovery metal extraction even during prolonged electrodeposition. This study presents a hopeful prospect for selective electrodeposition as a proficient separation method in battery recycling procedures.

Development of Europium-Doped Barium Fluorochloride Translucent Ceramic Scintillators

In solid-state ionizing radiation detectors, there are two main types of approaches: direct conversion and indirect conversion. The former generally uses semiconductor detectors (e.g., Si photodiodes) that convert radiation directly into electronic signals. The latter, on the other hand, uses phosphors and converts radiation into low-energy photons, which are then detected with a photodetector. Such phosphors are divided into scintillators and storage phosphors. Scintillators emit photons when electrons and holes generated by ionizing radiation recombine at emission centers. These are widely used in security, medical imaging, and basic physics. In storage phosphors, electrons and holes generated by ionizing radiation are temporarily captured in the trapping levels. When the storage phosphors are externally stimulated, these captured electrons and holes are re-excited and recombine at emission centers. Storage phosphors are used as personal dosimeters and imaging plates.In general, the requirements for scintillators are high light yield (LY), short decay time constants, large effective atomic number (Z eff), low afterglow levels, and chemical stability. The search for scintillators has a long history, but no material has been developed that fulfills all the required properties. Therefore, various scintillators with different chemical compositions have been developed, and scintillators have been selected and used for different measurement applications.Single crystals have been the most commonly used scintillator material form because of their high light transfer efficiency at emission wavelengths. However, these are problematic because of the long time and high cost required for their preparation. To solve the problems that single crystals have, translucent ceramics have attracted attention in recent years. Ceramics are synthesized by solid-phase reactions, which generally take a shorter time and cost less than single crystals grown by melt growth techniques. In this context, our group has successfully developed translucent ceramic scintillators with high luminescence efficiency. We reported that Y3Al5O12:Ce [1] and Lu3Al5O12:Ce [2] translucent ceramics showed higher LYs than single crystals of the same composition. Since translucent ceramics have only recently begun to be developed, only a few materials have been fabricated.In this study, we developed BaFCl:Eu in translucent ceramic form. Ba-based complex anions have been actively studied as scintillators and dosimetric materials because of their high luminescence intensity and high Z eff (~50). In particular, BaFCl:Eu is known to have an emission wavelength suitable for general photodetectors (~380 nm), a relatively fast decay time constant (~5 μs), and chemical stability [3]. These properties are suitable for scintillators to detect X- and γ-rays. BaFCl:Eu has been fabricated in opaque ceramics and studied in detail with dosimetric properties, but there are still no reports of BaFCl:Eu translucent ceramics. In this study, BaFCl translucent ceramics doped with 0.01, 0.1, 0.5, and 1.0% Eu were synthesized by the spark plasma sintering method. The optical and scintillation properties of the fabricated samples were investigated, and their potential as scintillators was examined.Photoluminescence (PL) emission spectra and X-ray-induced scintillation spectra of the BaFCl:Eu translucent ceramics were measured, both of which were dominated by an emission peak at 390 nm. According to the report [3], this emission peak was suggested to originate from the 5d–4f transition of Eu2+. Pulse height spectra were measured to determine a scintillation light yield, which was 15,000 ph/MeV at a maximum. This value is about twice that of commercially used Gd2SiO5:Ce (8,000 ph/MeV, [4]).We will present a detailed attribution of the luminescence in BaFCl:Eu translucent ceramics and the concentration dependence of the samples.<reference>[1] T. Yanagida et al., IEEE Trans. Nucl. Sci., 52, 1836 (2005).[2] T. Yanagida et al., Radiat. Meas., 46, 1503 (2011).[3] M. Ignatovych et al., Radiat. Prot. Dosimetry, 84, 185 (1999).[4] I. G. Valais et al., IEEE Trans. Nucl. Sci., 54, 11 (2007).

(Invited) Cathode Active Materials for Aluminum Metal Anode Rechargeable Batteries

Aluminum (Al) metal anode secondary batteries are a battery system that has been attracting attention in recent years. This is not only because Al resources are abundant, but also because Al metal can be used with a large charge-discharge capacity. The electrolytes include Lewis acidic AlCl3-based organic ionic liquids (AlCl3–1-ethyl-3-methylimidazolium chloride ([C2mim]Cl) etc.) and inorganic ones (AlCl3–NaCl, AlCl3–NaCl–KCl etc.), in which the aluminum metal anode reaction proceeds with low overvoltage and high coulombic efficiency. It is known that the Al metal anode reaction proceeds according to equation [1].4[Al2Cl7]− + 3e− ⇌ Al + 7[AlCl4]− [1]The ionic species that make up these electrolytes depend on the type of salt combined with AlCl3, but, in many cases, are [C2mim]+, alkali metal cations (Li(I), Na(I), K(I)), [AlCl4]−, and [Al2Cl7]−. The two chloroaluminate complex anion species are directly involved in the favorable metal anode reaction.1 However, as described below, the type of cation also would be indirectly involved in battery reactions.Aluminum metal anode secondary battery began to attract attention after a paper by Lin et al. published in Nature.2 They reported that by using three-dimensional graphical foam as the cathode active material, an Al metal anode secondary battery system with excellent cycle and rate characteristics could be constructed. Since that report, Al metal anode secondary batteries with various graphite-based cathode active materials have been reported. Similarly, non-graphite materials are also being considered for application as cathode active materials of the Al batteries. In this lecture, mainly based on our research results, I will outline the characteristics of graphite-based and non-graphite-based cathode active materials for Al metal anode secondary batteries. Graphite-based cathode active materials- The reaction of graphite-based positive electrodes used in Al metal anode secondary batteries is described by equation [2], and no matter what graphite material is used, the reaction itself remains the same. nC (graphite) + [AlCl4]− ⇌ C n [AlCl4] + e− [2]However, electrode performances such as charge-discharge capacity and rate characteristics vary greatly depending on not only the shape of the active material but also the presence or absence and type of conductive additive used when making the composite cathode. Figure 1 shows the charge-discharge behaviors of some composite cathodes when graphene nanoplatelets and polysulfone were used as the cathode active material and the binder, respectively, under different usage conditions of conductive additives.3 The performance alters depending on the type of conductive additive used, and we have succeeded in obtaining extremely good rate characteristics. On the other hand, when expanded graphite sheets are used as the cathode active material, the rate characteristics are not so great, but the capacity increases,4 and a value of about 130 mAh g− 1 can be obtained when the inorganic AlCl3–NaCl–KCl IL electrolyte is employed.5 We guess this unexpected result would be caused by the presence of Na(I) and K(I) in the electrolyte. Non-graphite-based cathode active materials- Carbon materials other than graphite-based ones, e.g., activated carbon fiber cloth, can also be employed as cathode active materials. But, because charge-discharge reactions proceed through electrochemical adsorption/desorption reactions of anionic species (including anionic species newly generated in electrode reactions), no clear plateau voltage appears and energy storage performance is not enough, like EDLCs.6 In recent years, the exploration for cathode active materials for the purpose of increasing the cathode capacity has become active. Our laboratory is investigating cathode active materials with sulfur, focusing on the fact that it is a cheap and abundant resource. Among these, materials in which sulfur is doped into the carbon skeleton, such as sulfur-modified polyethylene glycol (SPEG)7 and sulfur-modified polyacrylonitrile (SPAN)8, are promising materials, because they can greatly increase charge-discharge capacity compared to conventional graphite-based materials. However, unfortunately this characteristic can only be exhibited by the inorganic IL electrolyte, and the reason for this is not clear at present. References T. Tsuda, G. R. Stafford, and C. L. Hussey, J. Electrochem. Soc., 164, H5007 (2017) and references therein.M. C. Lin, M. Angell, H. J. Dai, et al., Nature, 520, 324 (2015).T. Tsuda, Y. Uemura, et al., Electrochemistry, 86(2), 72 (2018).Y. Uemura, T. Tsuda, et al., Electrochemistry, 92(4), 043012 (2024).C.-Y. Chen, T. Tsuda, S. Kuwabata, and C. L. Hussey, Chem. Commun., 54, 4164 (2018).T. Tsuda, M. Ishikawa, S. Kuwabata, et al., J. Electrochem. Soc., 161, A908 (2014).T. Tsuda, H. Senoh, S. Kuwabata, et al., Chem. Commun., 58, 1518 (2022).T. Tsuda, Y. Tsuji, S. Kuwabata, H. Senoh, et al., Meeting s of 242nd Meeting, L02-2126 (2022). Figure 1

Ionic Liquid As an Electrolyte Solvent for Proton Rechargeable Batteries

The diversity of carrier ions in electrochemical devices has attracted much attention to the use of protons.1−3 However, the narrow potential window of acid-based aqueous solutions typically used as proton conductors limits the operation of active materials.4 In this work, we examined the applicability of ionic liquids consisting of bis(trifluoromethanesulfonyl)amide (TFSA−) combined with N-propyl-N-methylpyrrolidinium (Pyr1,3 +) or 1-ethyl-3-methylimidazolium (EMI+), as the electrolytes. Raman spectroscopic measurements revealed that protons undergo coordination by TFSA− to form anionic complex of [H(TFSA) x ]1–x (Figure 1a). The addition of HTFSA narrowed the electrochemical windows compared with those of neat ionic liquids. However, the electrolytes allowed electrochemical H-adsorption/desorption on Pt (working electrode) within the electrochemical windows, which was investigated using quartz crystal microbalance technique. The ionic liquid electrolytes of [HTFSA]0.1[Cation-TFSA]0.9 were applied to rutile TiO2 composite electrodes. Comparing the charge/discharge property in an aqueous electrolyte, ionic liquid decreased the irreversible H2 evolution and the resulting non-electrochemical H+-extraction to show a reversible capacity of ca. 190 mA h g–1 at the first cycle (Figure 1b).AcknowledgementThis work was supported by a Grant-in-Aid for Scientific Research (B) (24K01601) from the Japan Society for the Promotion of Science (JSPS).References Wang, Y. Xie, K. Tang, C. Wang, C. Yan, Angew. Chem. Int. Ed., 57 (2018) 11569.B. Mitchell, W. C. Lo, A. Genc, J. LeBeau, V. Augustyn, Chem. Mater., 29 (2017) 3928.Makivić, J.-Y. Cho, K. D. Harris, J.-M. Tarascon, B. Limoges, V. Balland, Chem. Mater., 33 (2021) 3436.Shimizu, D. Nishida, A. Kikuchi, S. Arai, J. Phys. Chem. C, 127 (2023) 17677. Figure 1