Temperature Effects on the Kinetics of Ferrocene and Cobaltocenium in Methyltriphenylphosphonium Bromide Based Deep Eutectic Solvents

The oxidation of ferrocene (Fc/Fc+) and reduction of cobaltocenium (Cc+/Cc) under different temperatures has been studied by cyclic voltammetry and double potential step chronoamperometry in deep eutectic solvents (DESs) consisting of methyltriphenylphosphonium bromide salt with tri-ethylene glycol, glycerol or ethylene glycol as hydrogen bond donors. The temperature dependence of the measured physical properties of DESs (such as viscosity and conductivity) is discussed in detail. The kinetics of the redox couples are studied using cyclic voltammetry, and the standard heterogeneous electron transfer rate constant, k0 is found to be of the order of 10−5 to 10−4 cms−1 at different temperatures. The diffusion coefficient, D, of Fc and Cc+ is determined to lie between 8.28 × 10−10 to 6.65 × 10−9 cm2 s−1. These results show that both k0 and D increase with temperature in the studied DESs. In addition, better kinetic parameters for the DES with ethylene glycol as hydrogen bond donor means that this could be evaluated favorably as both solvents and electrolytes for redox flow cells

Investigation of ammonium- and phosphonium-based deep eutectic solvents as electrolytes for a non-aqueous all-vanadium redox cell

The charge/discharge characteristics for vanadium acetylacetonate in deep eutectic solvents were evaluated using an H-cell with an anion-exchange membrane separator for the first time. Coulombic (CE) and energy efficiencies (EE) of the electrolyte containing V(acac)3/0.5 M TEABF4 in DES3 (a hydrogen bonded eutectic between choline chloride and ethylene glycol) were obtained as 49-52% and 25-31%, respectively, when charging from 0 to 50% of theoretical maximum state-of-charge for 12 cycles. The low CE may be due to the crossover of the active species through the separator, or to the loss of active vanadium due to a parasitic reaction. However, the CE was similar to that for acetonitrile (CH3CN) indicating the promise of DESs as suitable electrolytes for future evaluation. Charge and discharge voltages are respectively higher and lower than the formal cell potential obtained by voltammetry. Ohmic drop in the DES results from the low conductivity of the electrolyte and the relatively large distance between the two electrodes in the H-cell. Further studies require investigation in a flow cell with analyses of polarization curves and impedance to determine the loss mechanisms in sufficient detail

Surface adsorption of Crizotinib on carbon and boron nitride nanotubes as Anti-Cancer drug Carriers: COSMO-RS and DFT molecular insights

In this study, the adsorption mechanisms and interactions between the anticancer molecule Crizotinib (CZT) on the surfaces of carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) are investigated. The investigations are carried out using the density functional theory (DFT) and the conductor-like screening model for real solvents (COSMO-RS). The quantum molecular descriptors (QMD) are also computed to explain the drug-carrier interaction mechanism and energy of adsorption. The negative adsorption energies of the complex drug-CNT indicate that adsorption is exothermic. The electrophilicity index of the drug-CNT system is five times greater than that of the drug-BNNT, demonstrating the higher stability of the CNTs with respect to BNNT. Moreover, a stronger interaction is observed for CZT-CNT, using the COSMO-RS method. A solvation study in water also reveals that the CZT-CNT complex is more soluble than CZT-BNNT. Finally, a quantum theory of atoms in molecules (QTAIM) analysis is also applied to investigate the nature of the intermolecular interactions. Based on the obtained results, it can be concluded that CNTs are more stable and better carriers than BNNTs when applied for CZT drug delivery in biological media

Investigation of Ammonium-and Phosphonium-Based Deep Eutectic Solvents as Electrolytes for a Non-Aqueous All-Vanadium Redox Cell

The charge/discharge characteristics for vanadium acetylacetonate in deep eutectic solvents were evaluated using an H-cell with an anion-exchange membrane separator for the first time. Coulombic (CE) and energy efficiencies (EE) of the electrolyte containing V(acac) 3 /0.5 M TEABF 4 in DES3 (a hydrogen bonded eutectic between choline chloride and ethylene glycol) were obtained as 49-52% and 25-31%, respectively, when charging from 0 to 50% of theoretical maximum state-of-charge for 12 cycles. The low CE may be due to the crossover of the active species through the separator, or to the loss of active vanadium due to a parasitic reaction. However, the CE was similar to that for acetonitrile (CH 3 CN) indicating the promise of DESs as suitable electrolytes for future evaluation. Charge and discharge voltages are respectively higher and lower than the formal cell potential obtained by voltammetry. Ohmic drop in the DES results from the low conductivity of the electrolyte and the relatively large distance between the two electrodes in the H-cell. Further studies require investigation in a flow cell with analyses of polarization curves and impedance to determine the loss mechanisms in sufficient detail. Low energy density is often reported as a barrier in the commercialization of redox flow batteries using current aqueous electrolytes. Non-aqueous electrolytic solvents offer a wide potential window of operation and increase the energy capacity of the system. 2-4 In contrast to organic systems which are either scarce or environmentally unfriendly, ionic liquids (ILs) have emerged as a relatively new class of non-aqueous electrolytes for energy storage applications. • C. ILs have many favorable characteristics, e.g., low volatility, high intrinsic conductivity, large electrochemical window, etc. In addition, ILs can be tuned by combining different cations and anions. However, many reports point out the hazardous toxicity and the poor biodegradability of most ILs. 7 ILs with high purity are also required since impurities, even in trace amounts, affect their physical properties. Additionally, their synthesis is not entirely environmentally friendly since it generally requires a large amount of salts and solvents in order to completely exchange the anions. 10 These drawbacks together with the high price of common ILs unfortunately hamper their industrial applications. Such issues may be overcome by using deep eutectic solvents (DESs). 11,12 A DES is a eutectic mixture of an organic salt (ammonium or phosphonium) and a hydrogen bond donor (HBD), that is made up of different components such as amides, metallic salts, alcohols, carboxylic acids and amines that may be used as complexing agents (typically an H-bond donor). 13,14 DESs have a melting point that is far below that of either individual constituent. The mechanism is that the complexing agent interacts with the anion and increases its effective size. This, in turn, decreases the anionic interaction with the cation thereby reducing the salt-HBD lattice energy and causing a depression in the melting point of the mixture. z E-mail: [email protected] they are simple to synthesize on a large scale. 27 Furthermore, their physicochemical and electrochemical properties (viscosity, conductivity, electrochemical stability, diffusion coefficients, etc.) have been evaluated in a similar manner to that for ILs. The synthesized DESs are applied as electrolytes to determine the effects of the electrode and solvent in our electrochemical system. Ferrocene/ferrocenium (Fc/Fc + ) or cobaltocenium/cobaltocene (Cc + /Cc) redox couples have been investigated as candidates of internal references to provide a known and stable reference point in various DESs. Despite the significance of DESs and their remarkable advantages, their applications in redox flow batteries (RFBs) are limited. The experiments reported here are based on commercially sourced raw materials without additional purification (i.e., these are preliminary experiments that enable an informed decision for choosing appropriate raw materials for preparing DESs for practical experiments with non-aqueous RFB prototypes in future work). The purpose is to prove that a redox battery could be charged/discharged successfully without the need for complex synthesis and purification processes that could possibly lower the economics of the entire process

Investigating the Mechanism and Electrode Kinetics of the Oxygen vertical bar Superoxide (O-2 vertical bar O-2(center dot-)) Couple in Various Room-Temperature Ionic Liquids at Gold and Platinum Electrodes in the Temperature Range 298-318 K

The reduction of oxygen was studied over a range of temperatures (298-318 K) in n -hexyltrietliylammonium bis(trifluorometlianesulfonyl)imide, [N 6,2,2,2] [NTf2], and 1-butyl-2,3-methylimidazorium bis(trifluoromethanesulfonyl)imide, [Qdmim] [NTf2] on both gold and platinum microdisk electrodes, and the mechanism and electrode kinetics of the reaction investigated. Three different models were used to simulate the CVs, based on a simple electron transfer ('E'), an electron transfer coupled with a reversible homogeneous chemical, step ('ECrev') and an electron transfer followed by adsorption of the reduction product ('EC(ads)'), and where appropriate, best fit parameters deduced, including the heterogeneous rate constant, formal electrode potential., transfer coefficient, and homogeneous rate constants for the ECrev mechanism, and adsorption/desorption rate constants for the EC(ads) mechanism. It was concluded from the good simulation fits on gold that a simple E process operates for the reduction of oxygen in [N6,2,2,2][NTf2], and an ECrev process for [Qdmim J[NTf2], with the chemical, step involving the reversible formation of the O2-⋯ [C4dmim] - ion-pair. The E mechanism was found to loosely describe the reduction of oxygen in [N6,2,2,2] [NTf2] on platinum as the simulation fits were reasonable although not perfect, especially for the reverse wave. The electrochemical kinetics are slower on Pt, and observed broadening of the oxidation peak is likely due to the adsorption of superoxide on the electrode surface in a process more complex than simple Langmuirian. In [C 4dmim] [NTf2] the O2- ⋯ predominantly ion-pairs with the solvent rather than adsorbs on the surface, and an EC16V quantitatively describes the reduction of oxygen on Pt also. © 2009 American Chemical Society