Charge Transfer Rate Constant Research Articles

Tailoring Light-Harvesting in Zn-Porphyrin and Carbon Fullerene based Donor-Acceptor Complex through Ethynyl-Extended Donor π-Conjugation.

Organic photovoltaic efficiency though currently limited for practical applications, can be improved by means of various molecular-level modifications. Herein the role of extended donor -conjugation through ethynyl-bridged meso-phenyl/pyridyl on the photoinduced charge-transfer kinetics is studied in noncovalently bound Zn-Porphyrin and carbon-fullerene based donor-acceptor complex using time-dependent optimally tuned range-separated hybrid combined with the kinetic rate theory in polar solvent. Noncovalent dispersive interaction is identified to primarily govern the complex stability. Ethynyl-extended -conjugation results in red-shifted donor-localized Q-band with substantially increased dipole oscillator strength and smaller exciton binding energy, suggesting greater light-harvesting efficiency. However, the low-lying charge-transfer state below to the Q-band is relatively less affected by the ethynyl-extended -conjugation, yielding reduced driving forces for the charge-transfer. Detailed kinetics analysis reveals similar order of charge-transfer rate constants (~1012 s-1) for all donor-acceptor composites studied. Importantly, enhanced light-absorption, smaller exciton binding energy and similar charge-transfer rates together with reduced charge-recombination make these complexes suitable for efficient photoinduced charge-separation. These findings will be helpful to molecularly design the advanced organic donor-acceptor blends for energy efficient photovoltaic applications.

PyCTRAMER: A Python package for charge transfer rate constant of condensed-phase systems from Marcus theory to Fermi's golden rule.

In this work, we introduce PyCTRAMER, a comprehensive Python package designed for calculating charge transfer (CT) rate constants in disordered condensed-phase systems at finite temperatures, such as organic photovoltaic (OPV) materials. PyCTRAMER is a restructured and enriched version of the CTRAMER (Charge-Transfer RAtes from Molecular dynamics, Electronic structure, and Rate theory) package [Tinnin et al. J. Chem. Phys. 154, 214108 (2021)], enabling the computation of the Marcus CT rate constant and the six levels of the linearized semiclassical approximations of Fermi's golden rule (FGR) rate constant. It supports various types of intramolecular and intermolecular CT transitions from the excitonic states to CT state. Integrating quantum chemistry calculations, all-atom molecular dynamics (MD) simulations, spin-boson model construction, and rate constant calculations, PyCTRAMER offers an automatic workflow for handling photoinduced CT processes in explicit solvent environments and interfacial CT in amorphous donor/acceptor blends. The package also provides versatile tools for individual workflow steps, including electronic state analysis, state-specific force field construction, MD simulations, and spin-boson model construction from energy trajectories. We demonstrate the software's capabilities through two examples, highlighting both intramolecular and intermolecular CT processes in prototypical OPV systems.

Theoretical study on the effect of end groups and core ring numbers in non-fullerene acceptors for organic solar cells

Modifying the skeleton, side chains and end groups of non-fullerene acceptors (NFAs) is important approach to improve the photovoltaic performance of organic solar cells. We selected PBDB-T as the donor and INIC, INIC1, INIC2, ITCC, ITCPTC and ITIC as the acceptors in order to study the difference in NFAs. The geometries, electronic structures, excited state properties, excited-state lifetimes and rate constants of charge transfer (CT), charge recombination (CR) and exciton dissociation (ED) processes of the monomers and PBDB-T:NFA complexes have been investigated by means of density functional theory and time-dependent density functional theory. The research reveals that fluorination of end groups, thienyl substitution and increase in the number of central rings result in the decrease in the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Fluorine substitution and increase in central ring numbers cause redshift of the absorption spectrum for NFAs. NFAs with fluorine substitution have a larger maximum electrostatic potential, which facilitates CT at the donor:NFA heterojunction interfaces. Fluorine substitution and thienyl substitution decrease the NFA's CT distances, indicating that both fluorine and thienyl substitutions affect the CT rate. Fluorine substitution, thienyl modification of end groups and increase in central ring numbers also reduce the exciton binding energy, which is beneficial for decreasing CR and improving ED efficiency.

The Influence of Clustered DNA Damage Containing Iz/Oz and OXOdG on the Charge Transfer through the Double Helix: A Theoretical Study.

The genome-the source of life and platform of evolution-is continuously exposed to harmful factors, both extra- and intra-cellular. Their activity causes different types of DNA damage, with approximately 80 different types of lesions having been identified so far. In this paper, the influence of a clustered DNA damage site containing imidazolone (Iz) or oxazolone (Oz) and 7,8-dihydro-8-oxo-2'-deoxyguanosine (OXOdG) on the charge transfer through the double helix as well as their electronic properties were investigated. To this end, the structures of oligo-Iz, d[A1Iz2A3OXOG4A5]*d[T5C4T3C2T1], and oligo-Oz, d[A1Oz2A3OXOG4A5]*d[T5C4T3C2T1], were optimized at the M06-2X/6-D95**//M06-2X/sto-3G level of theory in the aqueous phase using the ONIOM methodology; all the discussed energies were obtained at the M06-2X/6-31++G** level of theory. The non-equilibrated and equilibrated solvent-solute interactions were taken into consideration. The following results were found: (A) In all the discussed cases, OXOdG showed a higher predisposition to radical cation formation, and B) the excess electron migration toward Iz and Oz was preferred. However, in the case of oligo-Oz, the electron transfer from Oz2 to complementary C4 was noted during vertical to adiabatic anion relaxation, while for oligo-Iz, it was settled exclusively on the Iz2 moiety. The above was reflected in the charge transfer rate constant, vertical/adiabatic ionization potential, and electron affinity energy values, as well as the charge and spin distribution. It can be postulated that imidazolone moiety formation within the CDL ds-oligo structure and its conversion to oxazolone can significantly influence the charge migration process, depending on the C2 carbon hybridization sp2 or sp3. The above can confuse the single DNA damage recognition and removal processes, cause an increase in mutagenesis, and harm the effectiveness of anticancer therapy.

Optimised graphite/carbon black loading of recycled PLA for the production of low-cost conductive filament and its application to the detection of β-estradiol in environmental samples

The production, optimisation, physicochemical, and electroanalytical characterisation of a low-cost electrically conductive additive manufacturing filament made with recycled poly(lactic acid) (rPLA), castor oil, carbon black, and graphite (CB-G/PLA) is reported. Through optimising the carbon black and graphite loading, the best ratio for conductivity, low material cost, and printability was found to be 60% carbon black to 40% graphite. The maximum composition within the rPLA with 10 wt% castor oil was found to be an overall nanocarbon loading of 35 wt% which produced a price of less than £0.01 per electrode whilst still offering excellent low-temperature flexibility and reproducible printing. The additive manufactured electrodes produced from this filament offered excellent electrochemical performance, with a heterogeneous electron (charge) transfer rate constant, k0 calculated to be (2.6 ± 0.1) × 10−3 cm s−1 compared to (0.46 ± 0.03) × 10−3 cm s−1 for the commercial PLA benchmark. The additive manufactured electrodes were applied to the determination of β-estradiol, achieving a sensitivity of 400 nA µM−1, a limit of quantification of 70 nM, and a limit of detection of 21 nM, which compared excellently to other reports in the literature. The system was then applied to the detection of ß-estradiol within four real water samples, including tap, bottled, river, and lake water, where recoveries between 95 and 109% were obtained. Due to the ability to create high-performance filament at a low material cost (£0.06 per gram) and through the use of more sustainable materials such as recycled polymers, bio-based plasticisers, and naturally occurring graphite, additive manufacturing will have a permanent place within the electroanalysis arsenal in the future.Graphical abstract

Synthesis of nanoflakes-covered microparticles of nickel-Application for electrocatalytic oxidation and quantitation of nitrofurazone

Nickel microparticles covered with nanoflakes (NMCN) were hydrothermally synthesized in an alkaline solution of acrylamide dissolved in ethylene glycol/ethylenediamine at 200 °C. Structure and morphology of NMCN were characterized by field-emission scanning electron microscopy and X-ray powder diffraction, respectively. NMCN was applied, as an electrode modifier, with a surface concentration of 5.1 × 10−8 mol cm−2, and a detailed study was performed for the kinetics of charge transfer across the modified electrode/electrolyte interface using cyclic voltammetry. For the redox transition of NMCN in an alkaline solution, electron transfer coefficient and apparent charge-transfer rate constant were acquired as 0.65 and 0.6 s−1, respectively. The modified electrode was then applied for a study on the electrocatalytic oxidation of nitrofurazone (NF) on the NMCN surface through an electrochemical-catalytic (EC') mechanism. The oxidation process was followed by a NF diffusion coefficient of 2.9 × 10−6 cm2 s−1 and a catalytic rate constant of 3.0 × 104 cm3 mol−1 s−1. Also, an electron transfer coefficient of 0.40 was attained. The modified electrode was employed as a novel, time-saving, sensitive and simple amperometric sensor for NF, and quantified the drug with a linear range of 30–570 μmol L−1 and a sensitivity of 0.694 ± 0.002 A L mol−1 cm−2. Also, a detection limit of 4.3 μmol L−1 was attained. The sensor was employed for direct assay of NF in the human serum and ointments.

Biogenic synthesis of CuO/ZnO nanocomposite from Bauhinia variegate flower extract for highly sensitive electrochemical detection of vitamin B2

In this study, we report the preparation of bio-inspired binary CuO/ZnO nanocomposite (bb-CuO/ZnO nanocomposite) via the biological route using Bauhinia variegata flower extract following hydrothermal treatment. The prepared bb-CuO/ZnO nanocomposite was electrophoretically deposited (EPD) on indium tin oxide (ITO) substrate to develop bb-CuO/ZnO/ITO biosensing electrode which is employed for the determination of vitamin B2 (Riboflavin) through electrochemical techniques. Physicochemical assets of the prepared bb-CuO/ZnO nanocomposite have been extensively evaluated and make use of different characterization techniques including powder XRD, FT-IR, AFM, SEM, TEM, EDX, XPS, Raman, and TGA. Electrochemical characteristics of the bb-CuO/ZnO/ITO biosensing electrode have been studied towards vitamin B2 determination. Furthermore, different biosensing parameters such as response time, reusability, stability, interference, and real sample analysis were also estimated. From the linear plot of scan rate, charge transfer rate constant (Ks), surface concentration of electrode (γ), and diffusion coefficient (D) have been calculated, and these are found to be 6.56 × 10−1 s−1, 1.21 × 10−7 mol cm−2, and 6.99 × 10−3 cm2 s−1, respectively. This biosensor exhibits the linear range of vitamin B2 detection from 1 to 40 μM, including sensitivity and limit of detection (LOD) of 1.37 × 10−3 mA/μM cm2 and 0.254 μM, respectively. For higher concentration range detection linearity is 50–100 μM, with sensitivity and the LOD of 1.26 × 10−3 mA/μM cm2 and 0.145 μM, respectively. The results indicate that the bio-inspired nanomaterials are promising sustainable biosensing platforms for various food and health-based biosensing devices.

Engineering Metal Halide Perovskite Nanocrystals with BODIPY Dyes for Photosensitization and Photocatalytic Applications.

The sensitization of surface-anchored organic dyes on semiconductor nanocrystals through energy transfer mechanisms has received increasing attention owing to their potential applications in photodynamic therapy, photocatalysis, and photon upconversion. Here, we investigate the sensitization mechanisms through visible-light excitation of two nanohybrids based on CsPbBr3 perovskite nanocrystals (NC) functionalized with borondipyrromethene (BODIPY) dyes, specifically 8-(4-carboxyphenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) and 8-(4-carboxyphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (I2-BDP), named as NC@BDP and NC@I2-BDP, respectively. The ability of I2-BDP dyes to extract hot hole carriers from the perovskite nanocrystals is comprehensively investigated by combining steady-state and time-resolved fluorescence as well as femtosecond transient absorption spectroscopy with spectroelectrochemistry and quantum chemical theoretical calculations, which together provide a complete overview of the phenomena that take place in the nanohybrid. Förster resonance energy transfer (FRET) dominates (82%) the photosensitization of the singlet excited state of BDP in the NC@BDP nanohybrid with a rate constant of 3.8 ± 0.2 × 1010 s-1, while charge transfer (64%) mediated by an ultrafast charge transfer rate constant of 1.00 ± 0.08 × 1012 s-1 from hot states and hole transfer from the band edge is found to be mainly responsible for the photosensitization of the triplet excited state of I2-BDP in the NC@I2-BDP nanohybrid. These findings suggest that the NC@I2-BDP nanohybrid is a unique energy transfer photocatalyst for oxidizing α-terpinene to ascaridole through singlet oxygen formation.

Electrochemical Behavior of Niobium and Titanium Complexes in Chloride-Fluoride Melts with Addition of Alkaline Earth Metal Cations

The standard rate constants of charge transfer (k s) for the Nb(V)/Nb(IV) redox couple in the NaCl-KCl(equimol.)-NaF(10 wt%)-K2NbF7 melt with addition of alkaline Earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) were determined. It was found that addition of alkaline Earth metal cations resulted in increasing of k s to the certain ratio of Me2+/Nb(V) for the all alkaline Earth metal cations due to substitution of Na+ and K+ cations by Me2+ in the second coordination sphere of niobium complexes that leads to decreasing of niobium fluoride complexes stability. Further addition brought to some decrease of the standard rate constants because the viscosity of melts increasing, which brings to decrease of the diffusion coefficients. The standard rate constants increase with increasing of the ionic potential and reach maximum values for the complexes with outer-sphere magnesium cations. Comparative analysis of the electrochemical behavior of Nb(V)/Nb(IV) and Ti(IV/Ti(III)) redox couples in the NaCl-KCl(equimol.)-NaF(10 wt%) melt without and with addition of alkaline Earth metal cations has been done. It was determined that mechanism of electron transfer from the cathode to niobium and titanium complexes in melts containing alkaline Earth metal cations is the same and has a bridge nature.

Kinetics of electrochemical Eu3+ to Eu2+ reduction in aqueous media

All lanthanides have a stable trivalent oxidation state, but some of them can also occur in the divalent or tetravalent state. Europium is well-known for its divalent oxidation state, which has been investigated in aqueous, organic, and molten salt media. In contrast to other lanthanides, Eu3+ can be easily reduced (Eo=−0.34 V vs. SHE) via chemical, electrochemical or photochemical routes, and Eu2+ is quite stable in a variety of electrolytes, including nitrate salts. To date, the kinetics of the Eu3+/Eu2+ reduction reaction has been investigated only by polarography and chronopotentiometry, most often in perchlorate medium. In this study, the kinetics of the Eu3+/Eu2+ couple were analysed in nitrate, chloride and perchlorate media by cyclic voltammetry and linear sweep voltammetry with a rotating disk electrode (RDE). The diffusion coefficient, charge transfer coefficient and rate constants were calculated based on the Levich and Koutecký-Levich analysis and Tafel plot to gain insight in the electrochemical process and the influence of the electrolyte type on it. Given the pre-existing characterization of this redox couple in perchlorate medium, it is selected as a reference system to both compare the kinetic parameters and to validate whether the methodology can be applied to other electrolytes. The Eu3+ reduction reaction was found to be quasi-reversible in these electrolytes and the calculated kinetic parameters are in line with the previously reported values.

Ultrasensitive detection of ornidazole–antibiotic drug residues in water using NiMOFs functionalized MWCNT modified electrode

Nitroimidazole-based drugs are widely used as an antibiotic for the treatment of anaerobic bacterial and parasite illnesses. The widespread use of these drugs in animal feed and the consequent environmental pollution have become significant concerns in recent years. Simple, sensitive, and rapid detection of the antibody in various real samples is demanding research interest. Herein, we report a Nickel-metal organic framework functionalized Multiwalled Carbon nanotubes modified glassy carbon electrode (MWCNT@NiMOFs) as an ultrasensitive and rapid voltammetric sensor for the detection of ornidazole (ORDZ) in a neutral pH solution. The MWCNT@NiMOFs were prepared using a microwave-assisted solvothermal technique accompanied by an ultrasonication method. The designed MWCNT@NiMOFs offered a low charge transfer resistance (Rct) of 141 Ω along with excellent electrocatalytic activity, and high current density at the lowered cathodic peak potential (-0.62 V vs Ag/AgCl) for ORDZ detection. The surface adsorption capacity (Γs) in terms of surface excess and heterogeneous charge transfer rate constant (k0) of the MWCNT@NiMOFs were calculated to be 3.29 × 10-9 mol cm−2 and 5.33 × 10-3 cm s−1, respectively. Under an optimal working condition, differential pulse voltammetry measurements of ORDZ have shown concentration linearity in a window, 100 nm to 10 µM range with excellent sensitivity, 5.69 × 10-5A µM−1 cm−2, and detection limit, 26 nM (3.3/s). The designed MWCNT@NiMOFs offered appreciable reproducibility, and repeatability up to 30 days of storage time. The real-time quantitative evaluation of ORDZ in human urine and tap water specimens was done along with ∼ 100 % recovery values. Since the new approach is simple, selective, and separation-free, it can be extendable to a variety of real-time practical applications.

Theoretical Study on Functionalizing A–D–A Type Non‐Fullerene Acceptor by Fused Rings and Side Chains for Organic Solar Cells

AbstractThe modification of fused rings in the central backbone, side chains, and end groups of the non‐fullerene acceptor (NFA) for organic solar cells (OSCs) can modulate properties and photovoltaic performance. In order to investigate the effect of fused rings and side chains on photovoltaic performance, PBDB‐T is selected as electron donor and IDTIC, IDIC, IDIC‐PhC6, IDIC‐C4Ph, 4TIC, ITIC‐OE, IDTTIC, ITC6‐IC, ITIC, and C8‐ITIC are selected as NFAs. Based on quantum chemistry calculations, the geometries, electronic structures, excitation properties, excited‐state lifetimes, and electrostatic potentials (ESPs) of the monomer and the PBDB‐T:NFA complexes are studied, and the rate constants of charge transfer (CT), exciton dissociation (ED) and charge recombination (CR) processes are analyzed. The results show that the increase of fused‐ring in NFA's backbone by substituting phenyl or thienyl with bithiophene can elevate the highest occupied molecular orbital energies, reduce the gap of frontier molecular orbital energies, induce red‐shift of absorption spectrum, increase CT energy, improve CT and ED rates. This work provides a detailed understanding of tuning optoelectronic properties and photovoltaic performance by modifying NFA's side chains and extending backbones.

Enhancing solar energy conversion with nickel/iron oxyhydroxide-modified hematite photoanodes: The role of Fe species in alkaline electrolyte

Hematite photoanodes have shown potential for use in practical applications of photoelectrochemical (PEC) water splitting cells due to their abundance and stability, yet their efficiency needs to be improved. To optimize photoanode performance, co-catalysts such as amorphous nickel/iron oxyhydroxide layers are often deposited on the surface of hematite to enhance activity by catalyzing oxygen evolution. Recent studies have shown that the role of oxyhydroxide layers in changing PEC activity can vary depending on factors such as film morphology, co-catalyst layer thickness, and electrolyte composition. In this study, we investigate the effect of NiOOH and (Ni,Fe)OOH layers on the PEC activity of electrodeposited nanostructured hematite films. Our analysis of charge transfer and recombination rate constants determined from chronoamperometry and electrochemical impedance data suggests that the coatings' role is purely passivating, which is crucial for discontinuous electrodeposited films. Importantly, we show that the passivating properties of these coatings are enhanced by the presence of ppm concentrations of Fe in the electrolyte. We believe that our findings will be useful for further development of hematite photoanodes.

Studying the optoelectronic properties and emission quenching dynamics of poly‐TPD by incorporating ZnO nanoparticles and multiwalled carbon nanotubes

AbstractIn this study, the optoelectronic properties and emission dynamic quenching of poly‐TPD were investigated upon incorporating ZnO nanoparticles and multiwalled carbon nanotubes (MWCNTs). A solution blending method was utilized to successfully prepare poly‐TPD incorporated with various contents of ZnO/MWCNT nanocomposites. The optoelectronic properties of the nanocomposites were analyzed using UV–Vis and photoluminescence spectrophotometry. The incorporation of the nanocomposites resulted in a decrease in transmittance, reflectance, and absorption edge, indicating a reduction in the poly‐TPD's bandgap. Parameters such as extinction coefficient, Urbach energy, and charge carrier density also decreased with addition of the nanocomposites, suggesting increased scattering, disorder, and the presence of defect states. The decrease in bandgap from 2.970 to 2.852 eV with increasing the nanocomposite content confirmed the emergence of new electronic states. Furthermore, the nature of the transitions changed from direct allowed for pure poly‐TPD to direct forbidden upon incorporation of the nanocomposites. The inclusion of the nanocomposites also led to a decrease in refractive index and fluorescence intensity. The observed fluorescence quenching primarily exhibited dynamic characteristics, with a Stern–Volmer constant of 5.14 L/g and quenching rate constants surpassing the minimum threshold for efficient quenching. The increase in charge transfer rate constants with the nanocomposite content indicated enhanced quenching efficiency and charge transfer, likely due to the increased surface area and presence of defects. These findings suggest that poly‐TPD incorporated with ZnO/MWCNT nanocomposites displays promising properties for applications in optoelectronic devices.

Spin-dependent charge transmission through chiral 2T3N self-assembled monolayer on Au.

A gold surface is functionalized by chemisorption of the enantiopure N,N'-bis-[2,2';5',2″]tert-thiophene-5-yl methylcyclohexane-1,2-diamine (2T3N), a chiral oligothiophene derivative, via overnight incubation in a 2T3N ethanol solution. The Au|2T3N interface is characterized by x-ray photoelectron circular dichroism and comparing x-ray photoemission spectroscopy and electro-desorption results. Charge transmission at the Au|2T3N| solution interface is characterized by recording the cyclic voltammetry of the Fe(III)/Fe(II) reversible redox couple, finding a charge transfer rate constant, k°, variation from 1 × 10-1 to 3.3 × 10-2 cm s-1, when comparing the bare Au and the Au|2T3N interfaces, respectively. The "anomalous" high value of k° found for the chiral Au|2T3N interface can be rationalized on the basis of the chiral-induced spin selectivity effect, as further proved by magnetic-conductive atomic force microscopy measurements at room temperature. A spin polarization of about 30% is found.

Bulk embedding of Ti-defected TiO2 nano-heterointerfaces in hematite photoanode for boosted photoelectrochemical water splitting

The practical application of the most promising α-Fe2O3 photoanode in solar hydrogen generation is facing an awkward challenge arising from its poor bulk carrier transport. Present work demonstrates the acceleration of the carrier transport via embedding the p-type Ti-defected TiO2 (TiO2-VTi) nanocrystals in the n-type Fe2O3 photoanode matrix, which results in significantly improved photoelectrochemical performance. By embedding sub-5 nm TiO2-VTi nanocrystals in the bulk of α-Fe2O3 photoanode, numerous p-n nano-heterointerfaces were constructed for the first time in Fe2O3 photoanode matrix. The formed p-n nano-heterointerfaces lead to 10 times enhancement of charge transfer rate constant (ktran), and 1.5 times reduction of the charge recombination rate constant (krec), which is due to the formation of the built-in electric fields and effective carrier transport and separation at the p-n nano-heterointerfaces of TiO2-VTi/Fe2O3. Such strategy leads to the Fe2O3 photoanode with a reduction of photogenerated carrier transport time by 3 times, resulting in an excellent photocurrent density as high as 1.45 mA cm−2 at 1.23 VRHE, 5 times higher than that of pristine hematite (0.27 mA cm−2). We thus believe that our study opens up a route to regulate hematite or even metal-oxide semiconductor chemical/physical features via p-n nano-heterostructure embedding.

Charge Transfer Kinetics of the Ti(IV)/Ti(III) Redox Couple in the Cesium Chloride-Cesium Fluoride Melt with Addition of Alkaline Earth Metal Cations

The electrochemical behavior of the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt%)-K2TiF6 melt was studied by cyclic voltammetry. The diffusion coefficients of the Ti(IV) complexes were calculated using the Randles-Sevcik equation. The standard rate constants of charge transfer for the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt%)-K2TiF6 melt without and with additions of alkaline Earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) were determined. It was found that the rate constants of charge transfer increase with increasing ionic potential of the addition, reaching a maximum value for complexes with outer-sphere cations of magnesium, and this dependence is rectilinear. The activation energies of the charge transfer process in melts with additions of alkaline Earth metal cations were calculated and these values are significantly lower than the activation energy of the initial system CsCl-CsF(10 wt%)-K2TiF6. The kinetic parameters of the Ti(IV)/Ti(III) redox couple in chloride-fluoride melts with different second coordination sphere composition of the complexes were compared.

Electrochemistry of Neodymium in an Equimolar NaCl-KCl Melt without and with Addition of Fluoride Ions

Abstract The paper presents the results of neodymium electrochemical behavior in chloride and chloride-fluoride melts. It was shown that the process of neodymium electroreduction in the NaCl-KCl-NdCl3 melt proceeds in two stages. By diagnostic criteria of voltammetry it was established that the discharge process of Nd(III) to Nd(II) at a sweep rate in the range of 0.6 ≤  ≤ 1.0 V s-1 is not complicated by disproportionation reaction. In this study diffusion coefficients, activation energy of diffusion for Nd(III) chloride complexes and standard rate constants of charge transfer for the Nd(III)/Nd(II) redox couple in the NaCl-KCl melt were determined. The nature of the working electrode on the standard rate constants of charge transfer for the Nd(III)/Nd(II) redox couple has been studied by cyclic voltammetry and electrochemical impedance spectroscopy. The formal redox potentials E*Nd(III)/Nd(II) in the NaCl-KCl melt were obtained from the cyclic voltammetry data. It was shown that the addition of fluorine anions into the NaCl-KCl-NdCl3 melt leads to stabilization of the higher oxidation state of neodymium in chloride-fluoride melts and the intermediate oxidation state Nd(II) does not exist in these melts.

Effect of external electric fields in the charge transfer rates of donor-acceptor dyads: A straightforward computational evaluation.

We present a straightforward and low-cost computational protocol to estimate the variation of the charge transfer rate constant, kCT, in a molecular donor-acceptor caused by an external electric field. The proposed protocol also allows for determining the strength and direction of the field that maximize the kCT. The application of this external electric field results in up to a >4000-fold increase in the kCT for one of the systems studied. Our method allows the identification of field-induced charge-transfer processes that would not occur without the perturbation caused by an external electric field. In addition, the proposed protocol can be used to predict the effect on the kCT due to the presence of charged functional groups, which may allow for the rational design of more efficient donor-acceptor dyads.

Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts

The electrochemical behavior of trichloride ytterbium in NaCl-KCl, KCl, and CsCl melts was studied in the temperature range 973–1173 K by different electrochemical methods. The diffusion coefficients (D) of Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The formal redox potentials E * Yb(III)/Yb(II) in alkali chloride melts were obtained by the cyclic voltammetry and the Gibbs free energy for the reaction: YbCl2(sol.) + 1/2 Cl2(g.) ↔YbCl3(sol.) in alkali chloride melts was calculated. The electrochemical behavior of the Yb(III)/Yb(II) redox couple in the NaCl-KCl- NaF (5 wt%) melt was studied. A comparative analysis of electrochemical behavior of ytterbium chloride complexes in the NaCl-KCl melt and ytterbium fluoride complexes in the NaCl-KCl- NaF (5 wt%) melt was performed. It was shown that the formation of the stronger fluoride complexes reduced diffusion coefficients, standard rate constants of charge transfer for the Yb(III)/Yb(II) redox couple, and shifted the formal standard redox potentials to more electronegative values.