Rate Of Charge Transfer Reaction Research Articles

(Invited) Enhancement of Li-Ion Intercalation Kinetics in High-Concentration Electrolytes

Highly concentrated electrolyte (HCE) solutions containing over 3 mol dm–3 of Li salts have attracted attention recently owing to their unique physicochemical and electrochemical properties such as high thermal and electrochemical stability, unusual Li+ ion transport processes, and good compatibility with next-generation batteries containing Li anodes. Certain HCEs enhance the charge-transfer reaction rate at the electrode/electrolyte interface in Li-ion batteries. The solvation structure of Li+ in HCEs significantly affects the electrochemical interfacial reaction kinetics. In the organic electrolytes of lithium-ion batteries, the desolvation process of Li+ ion at the electrode/electrolyte interface is the rate-limiting process of the charge transfer reaction.1 Our group has found that the rate of charge transfer reaction of Li+ intercalation electrode is affected not only by Li+ solvation structure but also by the activity of Li+ (aLi+)and viscosity in the electrolyte.2 In this study, the charge transfer resistance (Rct) of the LiMn2O4 (LMO)/electrolyte interface in the electrolyte with various Li salt concentrations was evaluated to determine the effect of Li+ activity and viscosity on the charge transfer kinetics. LMO thin-film electrodes were prepared using the polyvinylpyrrolidone (PVP) sol-gel method. The electrochemical measurements of the LMO thin-film electrode were performed using a three-electrode cell. Li metal was employed as both the counter and reference electrodes and a LMO thin film as the working electrode. The mixtures composed of LiN(SO2CF3)2 (LiTFSA) and monoglyme (G1) were used as model electrolytes. Electrochemical impedance spectroscopy (EIS) was conducted at 30 oC and 3.9 VLi to determine Rct. In the range of concentration less than 1.8 mol/L ([LiTFSA]/[G1] =1:4 in molar ratio), Rct decreases with increasing LiTFSA concentration, while it increases at higher than 1.8 mol L-1. The minimum Rct at 1.8 mol L-1 can be attributed to the combined effects of electrolyte viscosity and Li+ activity in the electrolyte. Further results including the reaction kinetics in other electrolytes also will be presented. Acknowledgements: This study was partially supported by the JSPS KAKENHI (Grant No. JP22H00340 and JP 23K17370).

Enhancing the Stability of Lithium Metal Batteries with the Polydopamine-Coated Insulating Scaffold

Lithium metal is the most promising candidate for a high-capacity anode material in Li-ion batteries owing to its high theoretical theoretical capacity (3,860 mAh g-1) and the lowest redox potential (-3.04 V vs S.H.E.).[1] Despite these advantages, the practical application of Li metal anodes (LMAs) is hindered by a number of significant challenges. For instance, LMAs tend to form non-uniform dendrite, continuous dead Li growth, and infinite volume expansion.[2] These issues result in short circuits and continuous consumption of the active material, consequently lowering the Coulombic efficiency (CE) and cycling stability of LMAs.Using a 3D scaffold in the anode is an effective method for to address the issue of infinite volume expansion. The porous structure of the 3D scaffold provides ample space to accommodate Li metal.[3] Among them, electrically insulating scaffolds that do not support electron transport not only promote bottom-up Li deposition behavior but also minimize side reactions between the electrolyte and the scaffold. However, a high current density can lead to the formation of dendritic Li, which can make it challenging to achieve uniform and dense lithium growth on the surface during repeated plating/stripping processes. Therefore, the use of an insulating scaffold requires the introduction of functionalized materials to suppress dendritic formation of Li metal.Furthermore, to achieve further improvements, some studies have investigated the incorporation of polar functional groups into the insulating 3D structure.[4] Notably, these polar functional groups possess the capability to establish strong interactions with Li ions, which can facilitate the uniform distribution of these ions and prevent dendrite formation.[5] In this study, we utilized polydopamine (PDA) which contains polar functional groups such as O-H and N-H2, on a 3D insulating scaffold. These polar functional groups promote increased ionic conductivity and uniform deposition of Li ions by interacting with Li ions through Columbic forces.[6] Consequently, we expected that the advantageous properties of PDA would enhance the charge transfer reaction rate and cycling stability of LMBs.In this study, we aimed to introduce the utilization of a 3D polytetrafluoroethylene (PTFE) scaffold coated with PDA to achieve highly stable and high-energy LMBs. The insulating nature of the PTFE scaffold is expected to facilitate the "bottom-up" formation of Li deposition, while the PDA coating attracts Li ions, enabling homogenization of the Li-ion distribution and uniform growth of Li (Figure 1a). This design aims to simultaneously achieve both high energy density and improved cyclic stability in LMB full cells using our 3D scaffold.To elucidate the enhanced performance of the Lithium Metal Batteries (LMBs) equipped with PDA-coated 3D PTFE scaffold (PD-3P), we conducted a comparative study, including bare Cu foil and the 3D PTFE scaffold (3P) as control groups. Specifically, when tested at a high current density of 1 C with a 3.2 mAh cm-2 NCM, the PD-3P scaffold-based full cell exhibited a stable discharge capacity (Figure 1b).

Elucidating the Transport of Electrons and Molecules in a Solid Electrolyte Interphase Close to Battery Operation Potentials Using a Four-Electrode-Based Generator-Collector Setup.

In lithium-ion batteries, the solid electrolyte interphase (SEI) passivates the anode against reductive decomposition of the electrolyte but allows for electron transfer reactions between anode and redox shuttle molecules, which are added to the electrolyte as an internal overcharge protection. In order to elucidate the origin of these poorly understood passivation properties of the SEI with regard to different molecules, we used a four-electrode-based generator-collector setup to distinguish between electrolyte reduction current and the redox molecule (ferrocenium ion Fc+) reduction current at an SEI-covered glassy carbon electrode. The experiments were carried out in situ during potentiostatic SEI formation close to battery operation potentials. The measured generator and collector currents were used to calculate passivation factors of the SEI with regard to electrolyte reduction and with regard to Fc+ reduction. These passivation factors show huge differences in their absolute values and in their temporal evolution. By making simple assumptions about molecule transport, electron transport, and charge transfer reaction rates in the SEI, distinct passivation mechanisms are identified, strong indication is found for a transition during SEI growth from redox molecule reduction at the electrode | SEI interface to reduction at the SEI | electrolyte interface, and good estimates for the transport coefficients of both electrons and redox molecules are derived. The approach presented here is applicable to any type of electrochemical interphase and should thus also be of interest for interphase characterization in the fields of electrocatalysis and corrosion.

Anionic Effects on Li-Ion Activity and Intercalation Kinetics in Highly Concentrated Electrolytes

Certain highly concentrated electrolytes (HCEs) enhance the charge-transfer reaction rate at the electrode/electrolyte interface in Li-ion batteries. The solvation structure of Li+ in HCEs significantly affects the electrochemical interfacial reaction kinetics.1 However, the effects of different anions on these kinetics have not yet been fully understood. In this study, we investigated the effects of anionic species on the liquid structure and electrochemical reactions of HCEs composed of various Li salts and propylene carbonate (PC).2 Raman spectra revealed that both PC and anions were coordinated to Li+ ions in HCEs and that the concentration of uncoordinated (free) PC changed depending on the anionic species. Consequently, the activity of Li+ in the electrolyte changed depending on the anionic species. The use of Li salts with weakly Lewis basic anions increased the activity of Li+ and decreased the concentration of free PC in HCEs.The activity of Li+ in the electrolyte significantly affected the Li+ intercalation/deintercalation reaction rate of the LiCoO2 thin-film electrode. Electrochemical impedance spectroscopy revealed that the interfacial reaction rate of LiCoO2 was enhanced in the HCEs with anions having weaker Lewis basicity owing to the higher Li+ ion activity. In addition to the Li+ ion activity, the electrolyte viscosity also gives a significant effect on the charge-transfer kinetics at the electrode/electrolyte interface. The effects of salt concentration and anionic species on Li+ ion activity, electrolyte viscosity, and reaction kinetics in the HCEs will be discussed in detail. Acknowledgements : This study was partially supported by the JSPS KAKENHI (Grant No. JP19H05813, JP21H04697, and JP22H00340). References Y. Kondo et al., ACS Appl. Mater. Interfaces 2022, 14, 22706-22718.Y. Ugata et. al., J. Phys. Chem. C 2023, 127, 3977-3987.

Highly Efficient Cobalt Sulfide Heterostructures Fabricated on Nickel Foam Electrodes for Oxygen Evolution Reaction in Alkaline Water Electrolysis Cells

Non-noble metal electrocatalysts for the oxygen evolution reaction (OER) have recently gained particular attention. In the present work, a facile one-step electrodeposition method is applied in situ to synthesize cobalt sulfide nanostructures on nickel foam (NF) electrodes. For the first time, a systematic study is carried out on the impact of the Co/S molar ratio on the structural, morphological, and electrochemical characteristics of Ni-based OER electrodes by employing Co(NO3)2·6 H2O and CH4N2S as Co and S precursors, respectively. The optimum performance was obtained for an equimolar Co:S ratio (1:1), whereas sulfur-rich or Co-rich electrodes resulted in an inferior behavior. In particular, the CoxSy@NF electrode with Co/S (1:1) exhibited the lowest overpotential value at 10 mA cm−2 (0.28 V) and a Tafel slope of 95 mV dec−1, offering, in addition, a high double-layer capacitance (CDL) of 10.7 mF cm−2. Electrochemical impedance spectroscopy (EIS) measurements confirmed the crucial effect of the Co/S ratio on the charge-transfer reaction rate, which is maximized for a Co:S molar ratio of 1:1. Moreover, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) were conducted to gain insights into the impact of the Co/S ratio on the structural and morphological characteristics of the electrodes. Notably, the CoxSy@NF electrocatalyst with an equimolar Co:S ratio presented a 3D flower-like nanosheet morphology, offering an increased electrochemically active surface area (ESCA) and improved OER kinetics.

Physics-Based Model to Represent Membrane-Electrode Assemblies of Solid-Oxide Fuel Cells Based on Gadolinium-Doped Ceria

This paper reports a physics-based model that predicts membrane-electrode assembly (MEA) performance of solid-oxide fuel cells (SOFCs) with Ce0.9Gd0.1O2−δ (GDC10) electrolyte membranes. The paper derives self-consistent thermodynamic and transport properties for GDC1o mobile charged defects (oxide vacancies and reduced-ceria small polarons) by fitting published measurements of oxygen non-stoichiometry and conductivity over ranges of temperature and O2 partial pressures. The button-cell model is applied to evaluate how mixed ionic-electronic conductivity influences the performance of an SOFC MEA with a GDC10 electrolyte sandwiched between a porous, composite Ni-GDC10 anode and a porous, composite cathode of Sm0.5Sr0.5CoO3−δ (i.e., SSC) and GDC10. SSC properties are also derived by fitting published conductivity and oxygen non-stoichiometry measurements. Mixed conductivity of GDC10 and competing charge transfer reactions at both electrodes reduce open circuit voltages due to leakage current and buildup of defect concentrations at electrode-electrolyte interfaces. To fit polarization data, the button-cell model includes heterogeneous reaction rates for defect incorporation on the GDC10 surface along with Butler–Volmer expressions derived for competing charge transfer reaction rates from rigorous analyses assuming rate-limiting, elementary charge transfer reactions for each electrode. The calibrated MEA model can support rigorous SOFC modeling with GDC10 electrolytes over the range of conditions within a fully operating cell.

Anionic Effects on Li-Ion Activity and Li-Ion Intercalation Reaction Kinetics in Highly Concentrated Li Salt/Propylene Carbonate Solutions

Certain highly concentrated electrolytes (HCEs) enhance the charge-transfer reaction rate at the electrode/electrolyte interface in Li-ion batteries. The solvation structure of Li+ in HCEs significantly affects the electrochemical interfacial reaction kinetics. However, the effects of different anions on these kinetics have not yet been fully understood. Therefore, in this study, we investigated the effects of anionic species on the liquid structure and electrochemical reactions of HCEs composed of various Li salts and propylene carbonate (PC). Raman spectra revealed that both PC and anions were coordinated to Li+ ions in HCEs and that the concentration of uncoordinated (free) PC changed depending on the anionic species. Consequently, the activity of Li+ in the electrolyte changed depending on the anionic species. The use of Li salts with weakly Lewis basic anions increased the activity of Li+ and decreased the concentration of free PC in HCEs. The activity of Li+ in the electrolyte significantly affected the Li+ intercalation/deintercalation reaction rate of the LiCoO2 thin-film electrode. Electrochemical impedance spectroscopy revealed that the interfacial reaction rate of LiCoO2 was enhanced in the HCEs with anions having weaker Lewis basicity owing to the higher Li+ ion activity.

Nanosecond protonic programmable resistors for analog deep learning.

Nanoscale ionic programmable resistors for analog deep learning are 1000 times smaller than biological cells, but it is not yet clear how much faster they can be relative to neurons and synapses. Scaling analyses of ionic transport and charge-transfer reaction rates point to operation in the nonlinear regime, where extreme electric fields are present within the solid electrolyte and its interfaces. In this work, we generated silicon-compatible nanoscale protonic programmable resistors with highly desirable characteristics under extreme electric fields. This operation regime enabled controlled shuttling and intercalation of protons in nanoseconds at room temperature in an energy-efficient manner. The devices showed symmetric, linear, and reversible modulation characteristics with many conductance states covering a 20× dynamic range. Thus, the space-time-energy performance of the all-solid-state artificial synapses can greatly exceed that of their biological counterparts.

Reaction Kinetics of Photoelectrochemical CO2 Reduction on a CuBi2O4-Based Photocathode.

The CO2 reduction reaction (CO2RR) is an essential step in natural photosynthesis and artificial photosynthesis to provide carbohydrate foods and hydrocarbon energy in the carbon-neutral cycle. However, the current solar conversion efficiencies and/or product selectivity of the CO2RR are very sluggish due to its complicated multiple-step charge transfer reactions. Here, we systematically investigate the charge transfer reaction rate during CO2 reduction on CuBi2O4 photocathodes, where the surface is modified with 3-aminopropyltriethoxysilane (APTES). We discover that the surface amine group increases the charge separation rate, significantly enhancing the surface charge transfer reaction rate. However, the surface acidity has less influence on the first-order reaction, indicating that a rate-determining step (RDS) exists in the early stage of the photoelectrochemical cell (PEC) processes. Moreover, the intensity-modulated photocurrent spectroscopy (IMPS) confirms that both surface charge transfer and the recombination rate on APTES-coated CuBi2O4 are larger than bare CuBi2O4 while possessing comparable charge transfer efficiencies. Overall, the surface charge transfer reactions under the PEC condition require designing more effective nanostructured photoelectrodes and powerful characterization methods to intrinsically increase the charge separation and transfer rate while reducing the recombination rate.

Investigation of active species in low-pressure capacitively coupled N2/Ar plasmas

In this paper, a self-consistent fluid model is developed focusing on the plasma parameters in capacitively coupled 20% N2–80% Ar discharges. Measurements of ion density are performed with the help of a floating double probe, and the emission intensities from Ar(4p) and N2(B) transitions are detected by an optical emission spectroscopy to estimate their relative densities. The consistency between the numerical and experimental results confirms the reliability of the simulation. Then the plasma characteristics, specifically the reaction mechanisms of active species, are analyzed under various voltages. The increasing voltage leads to a monotonous increase in species density, whereas a less homogeneous radial distribution is observed at a higher voltage. Due to the high concentration of Ar gas, Ar+ becomes the main ion, followed by the N2+ ion. Besides the electron impact ionization of neutrals, the charge transfer processes of Ar+/N2 and N2+/Ar are found to have an impact on the ionic species. The results indicate that adopting the lower charge transfer reaction rate coefficients weakens the Ar+ ion density and yields a higher N2+ ion density. However, the effect on the species spatial distributions and other species densities is limited. As for the excited-state species, the electron impact excitation of background gases remains overwhelming in the formation of Ar(4p), N2(B), and N2(a′), whereas the N2(A) molecules are mainly formed by the decay of N2(B). In addition, the dissociation of N2 collided by excited-state Ar atoms dominates the N generation, which are mostly depleted to produce N+ ions.

Effect of ball-milling time and Pd addition on electrochemical hydrogen storage performance of Co2B alloy

The Co2B alloy is synthesized by high temperature solid phase process. 5 wt% Pd is added to the Co2B alloy by ball milling at different milling time in order to enhance discharge performance of the raw alloy. The phase structure and surface morphology of these alloys is characterized by XRD and SEM. The discharge capacities of the alloy milled for 10 min and 30 min are higher than that of the raw alloy. However, the discharge capacity of the alloy milled for 1 h is lower than that of the raw alloy. The result of linear polarization and EIS shows that proper milling time and uniform distribution of palladium on the alloy surface can make the alloy electrode have excellent discharge capacity. Ball milling at appropriate time can make the palladium on the alloy surface uniformly distributed and the alloy particles do not aggregate, which increases the charge-transfer reaction rate and discharge capacity. The experimental results prove that the addition of palladium and proper ball milling can effectively improve the electrochemical hydrogen storage capacity of the Co2B alloy.

Modeling of Sulfation in a Flooded Lead-Acid Battery and Prediction of its Cycle Life

A major cause of failure of a lead acid battery (LAB) is sulfation, i.e. accumulation of lead sulfate in the electrodes over repeated recharging cycles. Charging converts lead sulfate formed during discharge into active materials by reduction of Pb2+ ions. If this is controlled by mass transfer of the ions to the electrochemically active area, charging voltage can far exceed the OCV of a charged battery. Then, charge is partly consumed to electrolyse water, and for evolution of hydrogen and oxygen. It causes sulfation since regeneration of active materials will be incomplete. A mathematical model is developed incorporating resistance to mass transfer of Pb2+ ions into the rate of charge transfer reactions, changes in areas of active materials and sulfate particles, and dependence of electrodes’ resistance on content of lead sulfate. It was used to show that this mechanism of sulfation does lead to failure of flooded LABs because of increased resistance of electrodes, and to predict cycle life. Capacity fade, and increased cycle life when recharging protocol uses lower DoD are other features of degradation which the model predicts. The model also predicts the observed increase in cycle life when conducting additives are added to the negative electrode.

Radical Ions of 3-Styryl-quinoxalin-2-one Derivatives Studied by Pulse Radiolysis in Organic Solvents

The absorption-spectral and kinetic behaviors of radical ions and neutral hydrogenated radicals of seven 3-styryl-quinoxalin-2(1 H)-one (3-SQ) derivatives, one without substituents in the styryl moiety, four others with electron-donating (R = -CH3, -OCH3, and -N(CH3)2) or electron-withdrawing (R = -OCF3) substituents in the para position in their benzene ring, and remaining two with double methoxy substituents (-OCH3), however, at different positions (meta/para and ortho/meta) have been studied by UV-vis spectrophotometric pulse radiolysis in neat acetonitrile saturated with argon (Ar) and oxygen (O2) and in 2-propanol saturated with Ar, at room temperature. In acetonitrile solutions, the radical anions (4R-SQ•-) are characterized by two absorption maxima located at λmax = 470-490 nm and λmax = 510-540 nm, with the respective molar absorption coefficients ε470-490 = 8500-13 100 M-1 cm-1 and ε510-540 = 6100-10 300 M-1 cm-1, depending on the substituent (R). All 4R-SQ•- decay in acetonitrile via first-order kinetics, with the rate constants in the range (1.2-1.5) × 106 s-1. In 2-propanol solutions, they decay predominantly through protonation by the solvent, forming neutral hydrogenated radicals (4R-SQH•), which are characterized by weak absorption bands with λmax = 480-490 nm. Being oxygen-insensitive, the radical cations (4R-SQ•+) are characterized by a strong absorption with λmax = 450-630 nm, depending on the substituent (R). They are formed in a charge-transfer reaction between a radical cation derived from acetonitrile (ACN•+) and substituted 3-styryl-quinoxalin-2-one derivatives (4R-SQ) with a pseudo-first-order rate constant k = (2.7-4.7) × 105 s-1 measured in solutions containing 0.1 mM 4R-3-SQ. The Hammett equation plot gave a very small negative slope (ρ = -0.08), indicating a very weak influence of the substituents in the benzene ring on the rate of charge-transfer reaction. The decay of 4R-SQ•+ in Ar-saturated acetonitrile solutions occurs with a pseudo-first-order rate constant k = (1.6-6.2) × 104 s-1 and, in principle, is not affected by the presence of O2, suggesting charge-spin delocalization over the whole 3-SQ molecule. Most of the radiolytically generated transient spectra are reasonably well-reproduced by semiempirical PM3-ZINDO/S (for 4R-SQ•-) and density functional theory quantum mechanics calculations employing M06-2x hybrid functional together with the def2-TZVP basis set (for 4R-SQ•+).

Comparative study of the anchorage and the catalytic properties of nanoporous TiO2 films modified with ruthenium (II) and rhenium (I) carbonyl complexes

In this article we study the anchoring of cis-[Ru(bpyC4pyr)(CO)2(CH3CN)2]2+, cis-[Ru(bpy)2(CO)2]2+ and cis-[Ru(bpyac)(CO)2Cl2], onto nanoporous TiO2 employing electropolymerization, electrostatic interaction and chemical bonding. Also, the [Re(bpyac)(CO)3Cl] rhenium(I) complex for chemical anchorage was analyzed. The characterization of TiO2/Ru(II) and TiO2/Re(I) nanocomposite films was performed by field emission scanning electron microscopy (FESEM), electron dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. In addition, for the more stable nanocomposites obtained, the catalytic properties (solar energy conversion and CO2 reduction) were evaluated. The efficiency improvement in redox process derived from the (photo)electrochemical evidence indicates that modified nanoporous TiO2 structures enhance the rate of charge transfer reactions.

Unravelling the Role of an Aqueous Environment on the Electronic Structure and Ionization of Phenol Using Photoelectron Spectroscopy.

Water is the predominant medium for chemistry and biology, yet its role in determining how molecules respond to ultraviolet light is not well understood at the molecular level. Here, we combine gas-phase and liquid-microjet photoelectron spectroscopy to investigate how an aqueous environment influences the electronic structure and relaxation dynamics of phenol, a ubiquitous motif in many biologically relevant chromophores. The vertical ionization energies of electronically excited states are important quantities that govern the rates of charge-transfer reactions, and, in phenol, the vertical ionization energy of the first electronically excited state is found to be lowered by around 0.8 eV in aqueous solution. The initial relaxation dynamics following photoexcitation with ultraviolet light appear to be remarkably similar in the gas-phase and aqueous solution; however, in aqueous solution, we find evidence to suggest that solvated electrons are formed on an ultrafast time scale following photoexcitation just above the conical intersection between the first two excited electronic states.

Reduced Graphene Oxide Coating with Anticorrosion and Electrochemical Property-Enhancing Effects Applied in Hydrogen Storage System.

Low-capacity retention is the most prominent problem of the magnesium nickel alloy (Mg2Ni), which prevents it from being commercially applied. Here, we propose a practical method for enhancing the cycle stability of the Mg2Ni alloy. Reduced graphene oxide (rGO) possesses a graphene-based structure, which could provide high-quality barriers that block the hydroxyl in the aqueous electrolyte; it also possesses good hydrophilicity. rGO has been successfully coated on the amorphous-structured Mg2Ni alloy via electrostatic assembly to form the rGO-encapsulated Mg2Ni alloy composite (rGO/Mg2Ni). The experimental results show that ζ potentials of rGO and the modified Mg2Ni alloy are totally opposite in water, with values of -11.0 and +22.4 mV, respectively. The crumpled structure of rGO sheets and the contents of the carbon element on the surface of the alloy are measured using scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometry. The Tafel polarization test indicates that the rGO/Mg2Ni system exhibits a much higher anticorrosion ability against the alkaline solution during charging/discharging. As a result, high-capacity retentions of 94% (557 mAh g-1) at the 10th cycle and 60% (358 mAh g-1) at the 50th cycle have been achieved, which are much higher than the results on Mg2Ni capacity retention combined with the absolute value reported so far to our knowledge. In addition, both the charge-transfer reaction rate and the hydrogen diffusion rate are proven to be boosted with the rGO encapsulation. Overall, this work demonstrates the effective anticorrosion and electrochemical property-enhancing effects of rGO coating and shows its applicability in the Mg-based hydrogen storage system.

Enhanced electrochemical kinetics of magnesium-based hydrogen storage alloy by mechanical milling with graphite

Magnesium nickel alloy (Mg2Ni) which used as the negative electrode material in the nickel-metal hydride (Ni/MH) secondary battery is modified by graphite via mechanical milling. The effects of graphite on the Mg2Ni are systematically investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and a series of electrochemical tests. The results show that the cycle stability of the Mg2Ni alloy is improved with the addition of 10 wt.% graphite and the discharge capacity at the 20th cycle increase from 116.9 mA g−1 to 178.5 mA g−1. The Tafel polarization test indicates better corrosion resistance of the Mg2Ni/graphite composite. Meanwhile, the results of electrochemical tests indicate that both the charge-transfer reaction rate on the surface of the alloy and the hydrogen diffusion rate inside the bulk of alloy are boosted with the introduction of graphite.

Spectral broadening and red edge excitation effect in liquid and viscous solutions of DMABN

Effect of intensity redistribution of two fluorescence bands of N,N'-Dimethylaminobenzonitrile in polar solutions of the different viscosity was studied using selective UV irradiation over the red edge of the main absorption band. The effect being depends on temperature and viscosity, indicated eloquently strong inhomogeneous spectral broadening appearing at the red edge excitation. The conformational broadening exists for electronic transitions in the range of the local excited short wavelength band with weak change of electric dipole moments of the solutes. It was found that the spectral conformational broadening may exists independently on the orientational broadening which is due to the change of solute electric dipole moments in polar media and of thermal environmental fluctuations. When different conformers are excited into upper singlet levels, there is no fast dissipation of excitation energy over different conformational sublevels compared to the charge transfer reaction rates. In this case fluorescence and the charge transfer reaction occur from Franck-Condon sublevels with different rates.

Electron transfer dynamics in fuel producing photosystems

An often overlooked aspect of solar fuel production is the inherent mismatch between bulk charge carrier lifetimes and rates of charge transfer reactions. Considering water oxidation, interfacial charge transfer occurs on the millisecond to second timescales while bulk charge carrier lifetimes of metal oxides are typically in the fast picosecond–nanosecond regime. For charge transfer to efficiently compete with charge recombination, strategies that substantially increase the charge carrier lifetime need to be applied. In this chapter, we discuss the magnitude of the kinetic mismatch, overview common effective charge separation strategies that address this mismatch and highlight recent developments in our understanding of these processes. We also touch upon recent advances in determining the chemical nature of key reaction intermediates.

A 3D Continuum-Kinetic Monte Carlo Simulation Study of Early Stages of Nucleation and Growth in Ni Electrodeposition

A 3D continuum code coupled with a kinetic Monte Carlo module has been developed for the simulation of Ni electrocrystallization in the initial stages of nucleation and growth. Mass transfer in solution was controlled by a finite-difference code which is distributed over an irregular nanoscale grid system in vertical direction to the substrate. Deposition events such as surface diffusion, chemisorption and crystallization in the system were considered in a KMC module that processes the output of a diffusion-controlled scheme in probability functions to model electrodeposition process on surface. Electrochemical data of this simulation was simultaneously generated according to analytical electrochemical equations to study nucleation and growth mechanism. In spite of minor dissimilarities at current transient coordinates, a reasonable agreement could be noticed between electroanalytical simulation data and experimental results, both of which showed that under presumed conditions nickel electrodeposition is prone to a progressive nucleation mechanism at initial seconds. A similar result has been achieved from the juxtaposition of experimental morphological studies and simulated snapshots. It was found that a balance between surface diffusion and charge transfer reaction rate is a critical factor in dominant nucleation mechanism and deviation from the equilibrium could remarkably alter the nucleation regime and also nanostructure of the deposit.