Field Induced Electron Transfer Research Articles

Spin-selected electron transfer in liquid–solid contact electrification

Electron transfer has been proven the dominant charge carrier during contact electrification at the liquid–solid interface. However, the effect of electron spin in contact electrification remains to be investigated. This study examines the charge transfer between different liquids and ferrimagnetic solids in a magnetic field, focusing on the contribution of O2 molecules to the liquid–solid contact electrification. The findings reveal that magnetic fields promote electron transfer at the O2-containing liquid–solid interfaces. Moreover, magnetic field-induced electron transfer increases at higher O2 concentrations in the liquids and decreases at elevated temperatures. The results indicate spin-selected electron transfer at liquid–solid interface. External magnetic fields can modulate the spin conversion of the radical pairs at the O2-containing liquid and ferrimagnetic solid interfaces due to the Zeeman interaction, promoting electron transfer. A spin-selected electron transfer model for liquid–solid contact electrification is further proposed based on the radical pair mechanism, in which the HO2 molecules and the free unpaired electrons from the ferrimagnetic solids are considered radical pairs. The spin conversion of the [HO2• •e−] pairs is affected by magnetic fields, rendering the electron transfer magnetic field-sensitive.

Field-induced electron transfer in magnetostrictive material Fe81Ga19

The effect of magnetic fields on the local structure of the Fe81Ga19 alloy was investigated by X-ray absorption fine spectroscopy (XAFS) technique. The results demonstrate that 0.6 T magnetic fields lead to the increasing of the 3d, 4s and 4p electrons of Fe atoms, but the decreasing of the 4p electrons of Ga atoms. The electron transfer from Ga to Fe with applying magnetic fields is revealed. The magnetic fields increase the Fe–Ga bond length. The role of the Fe–Ga bond in determining the magnetostriction is revealed.

Static polarization of the supramolecular dyads of fullerene C60 with porphyrin derivatives

The nonlinear optical properties of four supramolecular dyads consisting of fullerene C 60 non-covalently bonded to porphyrin, porphyrazine, tetrabenzoporphyrin and phthalocyanine were investigated by calculating their electronic polarizability and first- and second-order hyperpolarizabilities using the finite field method and the density functional theory with the Grimme dispersion correction. Large first- and second-order hyperpolarizabilities result in nonlinear dependence of the polarization of dyads on the strength of external electric field. The increase in the size of the π-conjugated electron system of the porphyrin analogs leads to the increase of the polarizability and first- and second-order hyperpolarizabilities of the dyads. The absence of the covalent bonds between the components of the dyads prevents the field-induced electron transfer from porphyrin analogs to fullerene. The main reason for the nonlinear behavior of the polarization of dyads is the mutual polarization of fullerene and porphyrin analogs amplified by the external electric field.

Giant Magnetocapacitance in Magnetic Polypyrrole/Magnetite Nanocomposites under Low Magnetic Field

Electrochemical capacitors have attracted significant attention for their promising potential applications ranging from portable electronic devices to hybrid electrical vehicles and large industrial equipments. Most of the research efforts have been confined within the electrode materials to improve the energy density or power density till now. Here we first report a unique giant magnetocapacitance (GMC, huge capacitance change upon applying a magnetic field) phenomenon in a polymer nanocomposite under a small magnetic field of 1000 G (0.1 T). The capacitance has been increased by 714.0% for the polypyrrole (PPy) nanocomposites with a magnetite (Fe3O4) nanoparticle loading of 40.0 wt%, and the corresponding energy density and power density have been increased by a factor of 19.3 and 1.5, respectively, at a current density of 10 A/g. Two aspects have been proposed to interpret the observed GMC phenomenon. The first is the magnetohydrodynamics (MHD) describing an enhanced movement of the charged electrolyte ions that renders more ions accessible to the electrode materials under both the electric and magnetic fields. The other is the external magnetic field induced electron transfer in the electrode material, where the electrons in the magnetite nanoparticles were transferred to the PPy matrix instead of taking part in the redox reactions, as confirmed by the cyclic voltammetry analysis. Significantly enhanced ion diffusion coefficient and reduced charge transfer resistance have been obtained from electrochemical impedance spectroscopy measurement study and are inferred to be responsible for the superior performances witnessed in the electrode materials under the magnetic field. This observed unique GMC phenomenon provides an innovative alternative approach to substantially enlarge the electrochemical energy storage capacities of the current supercapacitors by just employing a small external magnetic field on the magnetic nanocomposite electrodes. Experimental Magnetite/PPy nanocomposites were synthesized using a facile surface initiated polymerization method as reported before.1 The pure PPy and magnetite/PPy nanocomposites with an initial loading of 10.0, 20.0, 40.0 and 60.0 wt% magnetite nanoparticles were synthesized and denoted as PPy, M-10.0, M-20.0, M-40.0, respectively. About 1 mg magnetite/PPy nanocomposites with different loadings of magnetite nanoparticles were weighed using UMX2 ultra-microbalance and pressed uniformly onto a PELCO Tabs™ double coated carbon conductive tape (6 mm OD), which was adhered to a carbon paper substrate. Electrochemical properties of the nanocomposites were investigated by CV, GCD, and EIS performed on an electrochemical working station VersaSTAT 4 potentiostat (Princeton Applied Research) using a three electrode setup. Results and Discussion The charge-discharge curves of the PPy/magnetite nanocomposites at a current density of 10.0 A/g is shown in Figure 1. The nanocomposites with 10.0 wt% magnetite nanoparticles display the longest discharge time, indicating the largest specific capacitance. When further increasing the magnetite loading, a reduced capacitance was observed and is attributed to the impedance of efficient electron transportation within nanocomposites due to the poor conductivity of the magnetite nanoparticles.1 The magnetic field has a remarkable effect on the nanocomposites. The specific capacitance is calculated to increase by the capacitance is increased by 126.8, 474.9 and 714.0% for the composites with a magnetite nanoparticle loading of 10.0, 20.0 and 40.0 wt%, respectively, at a current density of 10 A/g. The enhanced movement of the charged electrolyte ions under both electric and magnetic field effects,2 Figure 2, is inferred to be responsible for the improved performances. The faster-moving ions are capable of getting accessible to the electrode surfaces much more efficiently for compensating the ions consumed by the redox reactions. Conclusion PPy/magnetite nanocomposites have been investigated for electrochemical capacitor applications under the magnetic field. Both the pure PPy and the PPy/magnetite composites displayed far superior supercapacitive performances. This study provides an innovative alternative approach to substantially enlarge the electrochemical energy storage capacities of the current supercapacitors by just employing a small external magnetic field on the magnetic nanocomposite electrodes. Acknowledgments The financial supports from Seeded Research Enhanced Grant (REG) is kindly acknowledged. Figure 1 Charge-discharge cures of PPy/Magnetite nanocomposites (A) without and (A') with magnetic field at 10 A/g. Figure 2 (a) The movement of charged electrolyte ions under normal condition (without the magnetic field), (b) changed ion movement by MHD, and (c) enhanced ion diffusion by MHD. References (1) J. Guo, Z. Guo, J. Phys. Chem. C, 117, 10191(2013).(2) R. Tacken, L. Janssen, J. Appl. Chem. 25, 1 (1995)

Rectifying behavior of charge transfer complexes of tetrakis(dimethylamino)ethene with acceptor molecules: a theoretical study

The effect of electric field induced electron transfer on the rectification properties of molecular rectifiers based on charge transfer complexes of tetrakis(dimethylamino)ethane (TDAE) with acceptor molecules was explored. The current-voltage curves and the rectification ratios (RR) for two different molecular rectifiers were obtained using a direct ab initio method at M06/LACVP(d) level of theory in the range from -2 to +2 V. The highest RR of 25.7 was determined for the complex of TDAE with 2-nitropyrene-4,5,9,10-tetraone at 0.5 V (D1), while another rectifier [complex of TDAE with 2,7-dimethyl nitropyrene-4,5,9,10-tetraone (D2)] showed a maximum RR of only 2.9 at 0.3 V. The electric field induced electron transfer occurring in D1 creates a one-way conducting channel consisting of two SOMOs involving the entire D1 complex. In the case of D2, no electron transfer occurs at the applied bias voltages due to the relatively high energy difference between HOMO and LUMO.

Electric Field Induced Electron Transfer between a Single-Walled Carbon Nanotube and a Molecularly Doped Hole Transport Layer

In this work, we report a novel, electric field induced hole injection reaction between thin films of single-walled carbon nanotubes (CNT) and a molecularly doped charge (hole) transport layer (CTL) comprising a hole transport molecule (TPD) doped in polycarbonate in the bilayer device configuration. The CNT bilayer device was shown to be able to charge and then discharge in the dark, whereas the controlled bilayer device, constructed by replacing the CNT film with a metal (TiZr) layer, remains charged up after charging. The discharge of the charged CNT bilayer device suggests that hole injection from the CNT film to the CTL (or electron transfer from the CTL to the CNT film) occurs and that the injected holes are neutralized by a series of isoenergetic electron transfer across the CTL. Results show that the rate of the initial discharge increases as the surface conductivity of the CNT film increases. Current–voltage and time-of-flight measurements suggest that the discharge process is limited by the mobility of the CTL when the surface resistivity of the CNT film is ≤250 ohm/sq. For bilayer devices formulated with more resistive CNT films, the discharge process is limited by the hole injection efficiency. Since conductive CNT films are an essentially dense network of carbon nanotubes on Mylar, the decrease in the hole injection efficiency for bilayer devices fabricated from more resistive CNT films can be attributed to the increase in porosity in the CNT network in these films. The increased porosity limits hole injection between the carbon nanotube and the CTL. Since micrometer size pixels of CNT film can be made on a flexible substrate by inkjet printing and a nano imprinting technique, we suggest to couple this electric field induced hole injection reaction with an active-matrix backplane for a novel digital printing application.

Requirements for the generalization of the ab initio two-state model for external electric field induced electron transfer at electrodes

Abstract This work reports a careful systematic analysis of the validity of the ab initio two-state model for electron transfer between halides and various transition metal single crystal electrodes induced by an external electric field. The surfaces are represented by cluster models and the electron transfer is modeled by compact ab initio wave functions, which are a linear combination of donor–acceptor valence bond structures (DA and D + A − ) written in an appropriate orbital basis. It is found that the two-state model is able to successfully describe the ET for all those adsorbate/surface systems that feature a sufficiently large vertical equilibrium distance (orbitals well localized on the fragments and VB structures properly defined), and that exhibit at least a partially ionic character. The former condition occurs always when the solvent is explicitly taken into account, whereas the latter is fulfilled when not complete charge transfer occurs upon chemisorption.

Electric field induced electron transfer at the adsorbate–surface interface. Effect of the type of metal surface

The ab initio two-state model for electron transfer induced by an external electric field has been applied to the chloride oxidation on Cu, Rh, Pd, Ag, Pt and Au (001) surface models. The two electronic states involved in the model represent physical situations where the electron transferred from the chloride anion to the metal surface lies either on the halide or on the metal substrate. The model assumes that electron transfer takes place when these two states become degenerate and this is achieved by applying an external electric field. Two different situations representing either ultrahigh vacuum or electrochemical conditions have been considered. For the former the present study shows that electric field necessary to achieve degeneracy of the two electronic states is directly related to the metal surface work function whereas for the latter, it is found to be rather insensitive to the metal surface.

Charge carrier photogeneration in oligo(phenylenevinylene) thin films: A quantitative study

We analyze the generation and recombination of charged states in oligo(phenylenevinylene)s at high photoexcitation densities, using femtosecond pump-probe spectroscopy as a direct probe for the time-dependent density of photogenerated singlet, triplet, and doublet states. Pairs of charged states are formed during the exciting laser pulse, partly by a two-photon process. Geminate recombination of these pairs is found in the first ps after formation, after which a nongeminate dispersive mechanism prevails. The application of high electric field strengths opens up an additional channel for charge carrier formation, involving field-induced electron transfer between two singlet excitons. This process is competing with bimolecular singlet exciton annihilation. Field-induced formation of triplet states is governed by nongeminate recombination of field-induced charged states. We give values for cross sections of the photogenerated species, the efficiency of field-induced charge carrier photogeneration and for the early charge carrier mobility.

A Quantum Chemical Model for Electric Field Induced Electron Transfer at Metal Electrodes. Application to Halide Oxidation on Cu(100)

A model based on the use of ab initio quantum chemical explicitly correlated wave functions is proposed to study the electronic transfer reaction between an adsorbate and a metallic electrode. In this model, the effects of the electrode potential are simulated through the application of a uniform external electric field. This field exerts an influence on the relative stability of the two electronic states that are mainly involved in the electron transfer. These electronic states have the transferred electron localized either in the electrode or in the adsorbate. The model has been applied to the electron transfer between halides and a cluster model representation of the Cu(100) single-crystal electrode. A linear correlation between the electric field intensity at which the two electronic states involved in the charge-transfer process become degenerate and the normal reduction electrode potential is found. The existence of this linear correlation indicates that the proposed model contains the essential physics governing the trend of halide oxidation at a metal electrode.

Switching Phenomena in Thin Films of Lead Phthalocyanine

Abstract Further experiments are reported relating to the reported switching phenomenon in lead phthalocyanine thin films including cyclic voltammetry, of both the oxidation and reduction of the thin films on ITO glass, and the influence of vapours on the asymmetry of the current-voltage relationship. The possible mechanisms are reviewed and a mechanism proposed involving a field induced electron transfer to an electron acceptor such as oxygen. The switching may be localised leading ultimately to hot spots and breakdown.

Intervalley Transfer in Uniaxially Strained n-Type Ge

The increase of differential conductivity is observed in strained n-type Ge at 77°K. Samples are subjected to the [111] stress and the electric field (parallel to the stress), up to the value of 1.1×104 kg/cm2 and 9×103 V/cm, respectively. Above 5×103 kg/cm2, differential conductivity clearly increases at about several thousand volts per cm. The phenomenon is due to the field induced electron transfer between strain split <111> valleys: the effective mass in the direction of current of the lower valley is seventeen times as large as that of the three higher valleys. The current density vs. electric field characteristics agree with the calculations based on a simple model. Electron temperature and valley population ratio are estimated from the experimental results.

Investigation of Electron Transfer in Stressed Many-Valley Semiconductors by Optical Anisotropy

A method is proposed for studying electron transfer between stress-split valleys in stressed many valley semiconductors exhibiting bulk negative differential conductivity in strong electric field. Field induced electron transfer causes carrier redistribution which in turn alter the anisotropy of high frequency dielectric constant. Hence, by observing the optical anisotropy in strong field, we can extract valuable information concerning electron transfer. One convenient method is piezobirefringence. Constructing a simple model for electron transfer in stressed many valley semiconductor, we investigate the behavior of optical anisotropy of stressed many valley semiconductor in strong electric field. It is shown that free carrier electro-optic effect in stressed many-valley semiconductors is expected to be strong so that its observation may be a valuable tool for studying electron transfer. With the advent of recent development of laser spectroscopy, this method may be a very efficient method.