Transfer Redox Research Articles

Discovery of THICZs as Chemical Sensors: Synthesis, Spectrophotometric,Voltammetric and DFT Studies

Absorption spectra of tetrahydro[3,2-b]indolo-carbazoles (THICZs) with various molecular size and alkyl tails have been recorded in various solvents in the range between 200 to 600 nm. The photo physical behaviour of dissolved THICZs depends on the nature of its environment. The solvatochromic behaviours of THICZs and solvent solute interactions can be analysed by means of linear solvation energy relationships concept proposed by Kamlet and Taft. Compound 4 show excellent properties for sensing small molecules. The electrochemical behaviour of some THICZs was investigated at carbon paste electrode where two electrode reactions were involved, irreversible oxidation-one electron transfer and quasi-reversible redox reactions forming phenolic followed by quinolone moiety electro active species. The DFT-calculated molecular orbital energies (B3LYP/6-31G) and HOMO-LUMO gaps for some presented indolocarbazoles have been performed.

A polyimide cathode with superior stability and rate capability for lithium-ion batteries

Organic-based electrode materials for lithium-ion batteries (LIBs) are promising due to their high theoretical capacity, structure versatility and environmental benignity. However, the poor intrinsic electric conductivity of most polymers results in slow reaction kinetics and hinders their application as electrode materials for LIBs. A binder-free self-supporting organic electrode with excellent redox kinetics is herein demonstrated via in situ polymerization of a uniform thin polyimide (PI) layer on a porous and highly conductive carbonized nanofiber (CNF) framework. The PI active material in the porous PI@CNF film has large physical contact area with both the CNF and the electrolyte thus obtains superior electronic and ionic conduction. As a result, the PI@CNF cathode exhibits a discharge capacity of 170 mAh·g−1 at 1 C (175 mA·g−1), remarkable rate-performance (70.5% of 0.5 C capacity can be obtained at a 100 C discharge rate), and superior cycling stability with 81.3% capacity retention after 1,000 cycles at 1 C. Last but not least, a four-electron transfer redox process of the PI polymer was realized for the first time thanks to the excellent redox kinetics of the PI@CNF electrode, showing a discharge capacity exceeding 300 mAh·g−1 at a current of 175 mA·g−1.

Efficient power generating devices utilizing low intensity indoor lights via non-radiative energy transfer mechanism from organic ionic redox couples

Low intensity indoor lightings are often wasted and unutilized, when they could be harvested to produce electrical energy. Unfortunately there is currently no solar cells which could harvest low light intensity efficiently. Therefore, this work reports the synthesis of energy transfer redox couples (ETRCs) that aid in the harvesting of low light intensity for photoelectrochemical cells. Such ETRCs are excellent choices as electrolytes in solid-state photoelectrochemical cells owing to their multifunctional attributes like faster dye regeneration, more efficient light absorption and faster energy transfer kinetics. Electrochemical characterizations reveal that Forster Resonance Energy Transfer (FRET) is occurring between ERTC electrolyte (donor) and the N719 dye (acceptor). Photovoltaic efficiency of the reported device is 28% higher than the conventional silicon solar cells, tested under low light intensity. Additionally, the idiosyncratic design of this device makes it versatile to be used in indoor conditions or can be mounted at a wide range of incidence angle with an ability to retain a high efficiency of 21.08%. Superior ionic-conductivity imparted by the single-component electrolyte provides a platform for future directions in energy harvesting and storage.

Anthraquinone-Based Oligomer as a Long Cycle-Life Organic Electrode Material for Use in Rechargeable Batteries.

An anthraquinone (AQ)-based dimer and trimer linked by a triple bond (-C≡C-) were newly synthesized as active materials for the positive electrode of rechargeable lithium batteries. These synthesized oligomers exhibited an initial discharge capacity of about 200 mAh g-1 with an average voltage of 2.2-2.3 V versus Li(C.E.) . These capacity values are similar to that of the AQ-monomer, reflecting the two-electron transfer redox per AQ unit. Regarding their cycling stability, the capacity of the monomer electrode quickly decreased; however, the electrodes of the prepared oligomers showed an improved cycling performance. In particular, the discharge capacities of the trimer remained almost constant for 100 cycles. A theoretical calculation revealed that the intermolecular binding energy can be increased to the level of a weak covalent bonding by oligomerization, which would be beneficial to suppress the dissolution of the organic active materials into the electrolyte solutions. These results show that the cycle-life of organic active materials can be extended without lowering the discharge capacity by the oligomerization of the redox active molecule unit.

Electrochemical Characteristics of Benzanthrone Studied via Cyclic Voltammetry: Charge Transfer Redox Processes

The electrochemical behavior of benzanthrone (BA), a known mutagen and carcinogen, and an environmental pollutant widely found in aerosol particulates, was studied on a platinum electrode using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in 0.15 M tetrabutylammonium hexafluorophosphate-acetonitrile solution. At scan rates < 500 mV/s BA exhibited two well defined cathodic and anodic peaks at -1234.909 ± 5.605 mV, and -1158.9 ± 10.88 mV, respectively. The plot of peak currents (ip) versus ν1/2 scan rates were linear at ν < 200 mV/s and concentrations 0.5-2.0 mM indicating a diffusion controlled one electron transfer reaction. Higher scan rates (500 - 2000 mV/s) exhibited quasi-reversible reactions with ipa/ipc > 1.5. At scan rates > 500 mV/s, a plot of Ip versus ν1/2 deviates from linearity indicating quasi-reversible redox behavior. For all concentrations studied at scan rates < 200 mV/ the Ipa/Ipc ratios were 1.0650 ± 0.0091. The heterogeneous rate constant, k0, of the reversible diffusion-controlled reaction was determined as 3.51 x 10-5 ± 1.18 x 10-5 cm s-1. Via differential pulse voltammetry (DPV) the limit of detection, LOD ( 3s/m), on a bare platinum electrode was determined to be 1.69 x10-4 ± 1.5 x 10-5 M (for ipc) and 3.71 x 10-4 ± 3.56 x10-5 M (for ipa) at 200 mV/s.

Photoredox asymmetric catalytic enantioconvergent substitution of 3-chlorooxindoles.

An enantioconvergent substitution of 3-substituted 3-chlorooxindoles with N-aryl glycines under visible light irradiation is reported. A transition-metal-free cooperative catalysis platform with a dicyanopyrazine-derived chromophore (DPZ) as a photoredox catalyst and a chiral Brønsted acid catalyst is effective for these transformations, which involve a single-electron transfer redox step and an enantioselective radical coupling. A variety of valuable chiral 3-aminomethylene-3-substituted oxindoles can be directly synthesized with high yields and enantioselectivities.

Nickel-Catalyzed Benzylation of Aryl Alkenes with Benzylamines via C-N Bond Activation.

We have developed the first example of nickel-catalyzed Heck-type benzylation of aryl olefins with various benzylamines as benzyl electrophiles, and the benzylic C-N bond cleavage was efficiently promoted by the amine-I2 charge transfer complex (CT complex). The combination of low-cost NiCl2 and I2 has been found to facilitate Heck reaction of tertiary benzylamines and alkenes into various benzyl-substituted alkenes in good to excellent yields. This unconventional Heck reaction is proposed to go through initially the formation of a benzylic radical via oxidative addition of the C-N bond with Ni(0), then capturing by aryl alkene via radical addition, followed by single-electron transfer redox and proton abstraction without oxidant and external base.

Bi- and polynuclear coordination compounds of d-elements as catalysts of homogeneous selective oxidation of thiol groups

This research aims to study the catalytic cycle reactions for homogeneous selective oxidation of thiol RSH groups to RSSR with the participation of coordination compounds for d-element ions-NiII, PdII, Pt II, CuI , CuII. We used the DFT M06, PBE0 / Def2-TZVP methods to build the quantum chemical models of the reactions. We have developed a mechanism for the functioning of the catalytic system in which primary active centers are either binuclear {M(-OH)2M}n+ or polynuclear {M(μ-OH)2M(μ-OH)2M}2+ sites. Catalysts under consideration should retain stable spatial complementarity at all stages of the process. The main interrelated functions of the binuclear catalysts are the spatial approaching of anions RS– in the inner sphere of the bridged coordination compound required for the disulfide (–S–S–) cross-linking and the two-electron redox transfer during the transformation of these anions into disulfide (СH3)2S2

Repurposing the Industrial Dye Methylene Blue as an Active Component for Redox Flow Batteries

AbstractMethylene blue is a common component of industrial wastewater in the textile industry. The redox properties of this environmentally damaging molecule make it suitable for use in the electrolyte solutions of aqueous redox flow batteries. Here, we carry out electrochemical analyses of aqueous methylene blue solutions to establish the dye as a pH tuneable, two‐electron redox transfer agent with fast transfer kinetics. Galvanostatic charge‐discharge experiments demonstrated ∼100 % coulombic efficiency for 50 cycles over seven days. Cycling performance was dependent on the membrane separator used. Cells containing an AMI‐7001 membrane showed a capacity decay with the state‐of‐charge falling to 56 % due to dye adsorption. Nafion NE1035 showed no adsorption nor membrane crossover. The combination of chemical and redox stability, and fast kinetics motivate the recycling of methylene blue wastewater as the basis for flow battery electrolyte solutions.

How changes in interfacial pH lead to new voltammetric features: the case of the electrochemical oxidation of hydrazine.

The electrochemical oxidation of hydrazine was investigated in strongly and weakly pH buffered solutions to reveal the role of buffer capacity in proton-electron transfer redox reactions. In sufficiently buffered solutions, a single voltammetric feature was observed. However, increasing the hydrazine concentration (or, equivalently, moving to an insufficiently buffered solution) gave rise to a second voltammetric feature. These results are rationalised with a conceptually simple model and finite element simulations. We demonstrate that the new voltammetric feature is caused by a large change in the pH at the electrode surface as the reaction proceeds. Importantly, we show that the occurrence of additional voltammetric features are general for proton-electron transfer reactions in insufficiently buffered solutions, and should not be confused with changes in the reaction mechanism.

Experimental insight into redox transfer by iron- and sulfur-bearing serpentinite dehydration in subduction zones

Dehydration of antigorite in subduction zones releases a large amount of aqueous fluid and volatile elements, which can potentially oxidize the mantle wedge. The redox capacity of three synthetic serpentinites with variable Fetotal, Fe3+ and S− contents is investigated using XANES spectroscopy at both, Fe and S K-edges. Experiments are performed between 450 and 900 °C, at 2 GPa and fO2∼QFM-2; conditions similar to those encountered in subduction zones.Redox reactions in the synthetic serpentinites, which involve Fe and S can be summarized as follows: 1) the reduction of (S−)-pyrite into (S2−)-pyrrhotite (∼450 °C), with ∼4.4 mg/g of the sulfur degassed most likely as H2S, 2) the consumption of magnetite that reacts with antigorite to form Fe-rich olivine (<500 °C), 3) the reduction of (Fe3+)-antigorite into (Fe2+)-antigorite (∼580 °C), occurring about 100 °C below the temperature of antigorite breakdown, 4) the main (Fe2+)-antigorite breakdown that forms olivine and enstatite (∼675 °C), and 5) the decomposition of minor amounts of (Fe2+/3+)-clinochlore (∼800 °C). The bulk Fe3+/Fetotal ratio is found to decrease with run temperature from ∼0.82–0.97 depending on the hydrous starting material, down to 0.1–0.2 in the high-temperature anhydrous assemblages.The evolution of mineral modes and Fe3+/Fetotal with temperature in our synthetic samples shows similar trends to what has been reported in serpentinite rocks collected, for example, along a metamorphic transect in the western Alps. We show that a large amount of O2-equivalent – up to 10 mol/kg of rock – can be generated at temperature around 450 °C due to the presence of oxides and sulfides such as magnetite and pyrite. Owing to the poor capacity of aqueous fluid to transfer redox conditions, we surmise that this O2-equivalent is “consumed” at the scale of the lithospheric-mantle top which is partially serpentinized and therefore bear strong redox gradients.

Graphene-wrapped Porous Sb Anodes for Sodium-Ion Batteries by Mechanochemical Compositing and Metallomechanical Reduction of Sb2O3

Antimony metal nanoparticles wrapped with a-few-layer graphene coat (Sb@Gn) were fabricated from their oxide form (Sb2O3) in a micrometer dimension using a novel two-step ball-milling process. The first mechanochemical process was designed to decrease the particle size of Sb2O3 microparticles for ensuring advantages of nano size and to subsequently coat the Sb2O3 nanoparticles with a-few-layer graphene (Sb2O3@Gn). The second metallomechanical ball-milling process reduced the oxide to its metal form (Sb@Gn) by the help of Zn as a metallic reductant. The graphene layer (@Gn) blocked the alloying reaction between Sb and Zn, limiting the size of Sb particles during the metallomechanical reduction step. During reduction, oxygen species were transferred from of Sb2O3 through @Gn to Zn along redox transfer pathways rather than direct mass transfer via unsaturated vacancies in the @Gn. the redox transfer involving oxidation of @Gn by O2− is plausible routes for O2− transfer in the metallomechanical reduction. The Sb@Gn anode exhibited outstanding capacity retention along charge/discharge cycles and improved rate capability in sodium-ion batteries. The @Gn provided conductive pathways to the Sb core and limited size expansion during sodium-lithium alloying.

Characterization and electrochemical properties of graphite felt-based electrode modified using an ionomer impregnation approach for vanadium redox flow battery

Vanadium redox flow battery (VRFB) is a promising electrical energy storage device, particularly for applications with intermittent-type renewable energies. In practical operation, the commonly used graphite felt (GF)-based electrode has to be modified first to generate a hydrophilic environment suitable for redox reactions of vanadium ions to proceed. This study proposes a novel modification approach by impregnation with a Nafion® ionomer solution that significantly improves the wettability and substantially enhances the activity of the GF electrode. Characterizations of modified electrode are carried out using various techniques. The whole-cell cyclic voltammogram obtained is well-defined having a wider electrochemical window and more pronounced redox signals than those of the electrochemically oxidized counterpart. Characterization results indicate that there are no surface functional groups generated other than the sulfonic acid of the coated ionomer, and the applied electric field might have caused improved surface graphitization of the modified GF electrode. Electrochemical test results suggest that the electrode kinetics follows a diffusion-controlled process with simple electron transfer redox reactions proceeding directly through the surface graphitic sites, instead of via generated surface functional groups as the conventionally recognized paradigm. Moreover, the fabricated single-cell VRFB exhibits an excellent cell performance. The related redox reaction mechanisms are proposed.

Rechargeable organic batteries using chloro-substituted naphthazarin derivatives as positive electrode materials

The use of redox active organic compounds as an alternative positive electrode material of rechargeable lithium batteries can be a solution for the resource issues of the current battery system. To satisfy both the high capacity and long cycle life of the batteries using organic active materials, naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) derivatives, which potentially exhibit a four-electron transfer redox reaction, were investigated. While the unsubstituted naphthazarin lithium salt (1), having a high theoretical capacity of up to about 550 mAh g−1, showed only half the expected capacity and a short cycle life as a positive electrode active material, the chloro-substituted ones (1-Cl 2 , 1-Cl 4 ) exhibited improved properties in both their initial capacity utilization and cycle life. In addition, the high stability of a chloro-substituted naphthazarin salt (1-Cl 4 ) was supported by a reversible electrochromic behavior during the redox reaction. The substituent effect of the naphthazarin derivatives on the cycle stability was discussed with respect to the battery performance and electrochromic behavior. Also, a guide for designing a new organic active material which shows a high capacity and long cycle life is suggested.

Oxidative Degradation ofl-Isoleucine by Au3+Complexes in Weakly Acid Medium: A Kinetic and Mechanistic Investigation

Oxidative degradation of l-isoleucine (Ileu) by Au3+ complexes has been studied spectrophotometrically in weakly acid medium (acetic acid–sodium acetate buffer, pH range 3.72–4.80) in the temperature range 288–308 K. The reaction is first order with respect to AuIII but complex order (<1) with respect to isoleucine. Ionic strength has no significant effect on the reaction kinetics. Both H+ and Cl− ions have been found to show inhibiting effect on the reaction rate. Decreasing solvent polarity exerts an adverse effect on the reaction. Au3+ complexes react with the zwitterion form of isoleucine in a one-step two-electron transfer redox process. The reaction passes through intermediate formation of iminic cation, which hydrolyzes to produce 2-methyl butanal, identified by 1H NMR. The activation parameters ΔH≠ and ΔS≠ related to the rate-limiting step of the reaction are evaluated. The derived rate law is in excellent agreement with the experimental results. The kinetic and activation parameters of this investigation have been compared and analyzed with those of the oxidation of l-leucine by gold(III).

Efficient electron transfer kuramite Cu3SnS4 nanosheet thin film towards platinum-free cathode in dye-sensitized solar cells

The density-functional theory calculations in this work clearly revealed that the kuramite-structure Cu3SnS4 material possessing the metallic characteristic, result in the higher charge transfer between I3− ions and the Cu3SnS4 surfaces, and the rapid redox transfer reaction of I3−/I− in dye-sensitized solar cells system. Then, a feasible and mild solution method was proposed to in-situ synthesize Cu-rich kuramite-structure Cu3SnS4 thin film on FTO substrate, and the acquired thin film was used directly as counter electrode to assemble dye-sensitized solar cells without any post-treatments. The obtained-Cu3SnS4 nanosheet film had good bonding strength, expanded surface area, low photoelectron charge transfer resistance at the counter electrode/electrolyte interface, and great catalytic activity toward the reduction of I3−/I− ions. Power conversion efficiency of 7.80% was obtained by utilizing Cu3SnS4 nanosheet as counter electrode, which was superior to that of Pt electrode (6.52%). Our results demonstrate the earth-abundant and low-cost kuramite Cu3SnS4 is an alternative Pt-free counter electrode material in dye-sensitized solar cells.

Rechargaeble Organic Batteries Using Naphthazarin Derivatives: The Effect of Chloro-Substituents on the Battery Performance

One of the recent requirements for the current rechargeable lithium battery systems is to reduce the amount of minor metal-based materials, especially from the positive-electrode. Our strategy to confront this issue is to replace the rare-metal oxides-based positive-electrode with redox active organic ones. So far, we have demonstrated that a series of low-molecular-weight quinone derivatives, which undergo multi-electron redox reactions, can be an alternative material category [1‒3]. To increase the discharge capacity of such organic compounds, we focused our attention on the naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) skeleton as a new redox unit. This skeleton can exhibit a four-electron transfer redox reaction, which should lead to a large capacity of up to 550 mAh/g. This paper compares the battery performance of the electrodes incorporating the lithium salt of the naphthazarin skeleton (1)and some analogues carrying two or four peripheral chloro-substituents (1-Cl2 , 1-Cl4 ) (Fig. 1a). 5,8-Dihydroxy-1,4-naphthoquinone and 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone were purchased. 2,3,6,7-Tetrachloro-5,8-dihydroxy-1,4-naphthoquinone was synthesized by the chlorination of 2,3,6,7-tetrachloro-1,4,5,8-naphthodiquinone using sulfuryl chloride. The active material salts, 1, 1-Cl2 , and 1-Cl4 , were prepared by neutralizing the above-mentioned naphthazarin derivatives with lithium hydroxide. Their electrochemical properties as the positive-electrode active materials were evaluated in a coin-type half-cell using a metallic lithium sheet negative electrode and the electrolyte solution of tetraglyme/lithium bis(trifluoromethanesulfonyl)amide equimolar mixture. Figure 1b shows the discharge curves of the prepared electrodes after the initial charge. In this figure, the capacities are expressed in the percentage of the theoretical values (1: 531; 1-Cl2 : 396; 1-Cl4 : 316 mAh/g) which assumes each four-electron transfer reactions. All discharge curves have complicated forms composed of some plateau potential regions, reflecting their multi-electron transfer reactions during the discharge processes. While the electrode of 1 was only about 50% of the theoretical value, the electrodes of 1-Cl2 and 1-Cl4 showed higher values of 88 and 87%, respectively. The actual specific discharge capacities of the electrodes of 1, 1-Cl2 , and 1-Cl4 were 259, 349, and 274 mAh/g, respectively. We consider that this difference in the initial utilization ratio results from the fact that the solubility of the charged (oxidized) state of 1 in the electrolyte solution might be higher than those of the chloro-substituted 1-Cl2 and 1-Cl4 . In the cycle test, the discharge capacity of the electrode using 1 quickly dropped upon cycling; it decreased to 13% of the theoretical value after 20 cycles as shown in Fig. 1c. On the other hand, the electrodes usingchloro-substituted ones exhibited better performance; the electrodes of 1-Cl2 and 1-Cl4 respectively maintained 28 and 57% of the theoretical value after 20 cycles. In addition to the battery tests, a potentiostatic polarization measurement combined with a UV-Vis spectroscopic apparatus was applied to solutions of 1, 1-Cl2 , and 1-Cl4 in a dimethyl sulfoxide/lithium bis(trifluoromethanesulfonyl)amide system. The measurement revealed that the solution state of the unsubstituted 1 is less stable than those of the chloro-substituted 1-Cl2 and 1-Cl4 during their redox reactions, and 1-Cl4 was most stable among them. As is often the case, the discharge capacity of low-molecular-weight organic active materials tend to decrease upon cycling. One of the reasons of this capacity decay is suggested to be the loss of the active materials from the electrodes by the dissolution of the organic molecules in the electrolyte solutions. In this study, there seems a correlation between the electrochemical stability of the monomer state and the cycle-life performance, i.e., higher the electrochemical stability, the longer the cycle-life. The chloro substituent is considered to work as a protecting group to suppress the undesired side reactions during the redox reaction. This study suggests that both enhancing the chemical durability and suppressing the solubility in the electrolyte solution are important to design a long cycle-life organic active material.

Room Temperature, Hybrid Na-Based Flow Batteries with Organic Catholytes and Multi-Electron Transfer Redox Reactions

Redox flow batteries (RFBs) have attracted significant interest lately for use in grid-scale electrochemical energy storage. One of the most studied RFB systems is the all vanadium RFB. Due to a phenomena known as crossover, RFBs suffer from rapid capacity decay in which the catholyte and anolyte become mixed during cycles. In addition, the energy density of RFBs is low. To increase the cell voltage and thus energy density, organic electrolytes can be used to replace aqueous electrolytes. However, to date the organic electrolyte based RFBs have not offered higher energy densities due to the low solubility of ions in electrolytes. Recently, we have introduced a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane. This new type of room temperature flow batteries address low energy density and crossover issues simultaneously. In this study we have investigated the redox reaction mechanism of an organic catholyte made of vanadium acetylacetonate, V(acac)3, in acetonitrile solvent. We demonstrate that with the newly invented HNFB the V(acac)3 catholyte can provide multi-electron transfer redox reactions per vanadium ion to enhance the energy density of the HNFB while possessing tolerance to the impurity water in the system. In conventional RFBs the impurity water reacts with oxidized V(acac)3 to become vanadyl acetylacentonate, VO(acac)2, leading to gradual degradation of the cell. This study, for the first time, shows that the reaction between the impurity water and oxidized V(acac)3 can be utilized as an energy storage mechanism enabled by HNFBs to enhance the energy density of the cell.

Investigation of Discharge Products of Mg-Air Battery with Non-Aqueous Ether-Based Electrolytes

Introduction Metal-air batteries are expected as one of the post lithium ion batteries. Many researchers have focused on strategies enabling the use of high energy cathode such as O2 and Li metal anode, e.g. Li-air batteries. However lithium metal leads to some problems such as low safety due to a formation of lithium metal dendrite. Recently, it has been claimed that multi valence metal anodes such as magnesium metal realize higher energy density of battery. They may offer large specific/volumetric energy density as a negative electrode owing to two electron transfer redox by Mg2+. In addition, large natural abundance of Mg resources and its chemically stable nature allows a utilization to battery. Despite such remarkable potential, cycling behavior of Mg metal anode coupled with air cathode (O2and oxide anions) has been unexplored yet, and reaction products with superoxide anions and Mg ions is still unknown. Here, we studied the reaction mechanism of Mg with superoxide anions in non-aqueous ether-based electrolytes by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) to investigate the discharge product and electrochemical behavior during oxygen reduction reaction with superoxide anions and Mg ions. Experimental Triglyme (G3), Magnesium bis(trifluoromethane sulfonyl)imide (Mg(TFSI)2) and tetraethylammonium bis(trifluoromethane sulfonyl)imide (TEATFSI) were purchased and used as received. The electrolyte solutions were prepared by mixing salts and G3 in the Ar-filled glove box, and the molar ratio of salt toward G3 was fixed at 1/5. Cyclic voltammetry was performed with a typical three-electrode cell in which a glassy carbon (GC) disk (3 mm) and a platinum wire were used as a working electrode and a counter electrode, respectively. A reference electrode was fabricated by soaking Ag wire in (0.01 M AgNO3 + 0.1 M Mg(TFSI)2)/G3, confined in a glass tube with a liquid junction of a Vycol glass. Mg(TFSI)2/G3 (1:5 in mol) and TEATFSI/G3 (1:5 in mol) solutions were saturated with O2 by bubbling for 1h before measurements. The CV measurements of GC electrode at a scan rate of 50 mV s−1 were performed in two electrolytes (Mg(TFSI)2/G3 and TEATFSI/G3) solutions, to clarify the role of Mg2+ ion during charge and discharge reactions. The surface of GC electrode after cathodic polarization at a constant voltage of −1.35 V vs. Ag/Ag+was subsequently characterized by XPS. R esults and Discussion Figure 1 shows the cyclic voltammograms of GC electrode in two electrolytes (Mg(TFSI)2/G3 and TEATFSI/G3) . The electrochemical response of GC electrode strongly depends on the constituent cation in the electrolytes. For TEATFSI electrolyte, redox couple of oxygen, e.g. O2 + e− → O2 − at −1.3 V vs. Ag/Ag+ and O2 − → O2 + e− at −1.2 V vs. Ag/Ag+, were clearly observed, indicating sufficient stability of TEA+ cation (and also TFSI− anion) made capable to be cycled with superoxide O2 − anion. In contrast, no anodic current was found before oxidative decomposition of the electrolyte (at +1.5 V vs. Ag/Ag+) for the Mg(TFSI)2/G3 electrolyte while the reduction of O2 to O2 − would be took place. XPS spectra suggest the formation of MgO and MgF2 on the working GC electrode during cathodic scan. As MgO and MgF2 are difficult to be decomposed electrochemically because of their high stability. Precipitates disturb favorable electrochemical reaction of oxygen with Mg, thereby poor cycling ability was observed. Reference [1] Catalytic Cycle Employing a TEMPO−Anion omplex to Obtain a Secondary Mg−O2 Battery Figure 1

Principles of formation of catalytic systems for oxidation of aliphatic thiols based on d-element complexes

Mechanism of catalytic selective oxidation of aliphatic thiols RSH into disulfides R2S2 has been suggested basing on quantum-chemical DFT simulation (M06/Def2-TZVP) of coordination compounds of d-elements and using the principle of complementarity. The active center of the catalytic system is a binuclear fragment {M(m-OH)2M′}n+ formed due to hydrolysis of the starting mononuclear d-element compound. The catalysts based on Pd(II) and Pt(II) binuclear active centers are spatially similar throughout the process. The chief interrelated functions of the binuclear catalysts are spatial approaching of two thiolate anions RS– in the inner sphere of the bridged coordination compound required for the disulfide (–S–S–) cross-linking and providing for two-electron redox transfer during the transformation of these anions into disulfide (СH3)2S2.