Significant Electron Transfer Research Articles

Electrostatic bending and outer-sphere intervalence transfer in a flexible ligand-bridged ruthenium(III)-iron(II) complex

In the mixed-valence complex [RuIII(NH3)5(μ-dpypn)FeII(CN)5] with the flexible bridging ligand 1,3-di(4-pyridyl)propane (dpypn), electrostatic interactions between the {Ru(NH3)5}3+ and {Fe(CN)5}3− moieties drive a strong bending of dpypn and approximation of the RuIII and FeII centers, from which the enhanced electronic coupling between metal ions produces an intense intervalence-transfer absorption in the near-infrared region. Density functional theory calculations corroborate both the electrostatic bending in this heterobinuclear complex and a linear geometry in the homobinuclear counterparts [Ru(NH3)5(μ-dpypn)Ru(NH3)5]5+ and [Fe(CN)5(μ-dpypn)Fe(CN)5]5−, for which no evidence of electronic coupling was found because of the separation between metal centers. Furthermore, the heterobinuclear species formed an inclusion complex with β-cyclodextrin where the imposed linear geometry prevents significant electronic coupling and intervalence charge transfer between the RuIII and FeII centers.

Adsorption mechanisms of metal ions on the potassium dihydrogen phosphate (1 0 0) surface: A density functional theory-based investigation

The adsorption of metal ions (K+, Na+, Ca2+, Cu2+, Al3+, Cr3+) on the (1 0 0) surface of potassium dihydrogen phosphate (KDP) has been studied using density functional theory (DFT). Calculation results show that all the investigated metal ions can be spontaneously adsorbed on the surface with negative adsorption energies. The adsorption stability increases in the order of Na+ < K+ < Cu2+ < Ca2+ < Al3+ < Cr3+, and shows a consistent trend as the adsorbed metal ion valence (monovalent < divalent < trivalent). Three types of stable adsorption configurations are observed, corresponding to three different bonding mechanisms. Na+, K+ and Ca2+ ions with a large radius can form two ionic bonds and one weak covalent bond with the O and H atoms respectively. In addition, the medium-sized ion of Cu2+ forms two covalent bonds with the O and H atoms. Furthermore, Al3+ and Cr3+ ions with the smallest radius form two metal-oxygen and one metal-hydrogen covalent bonds with the surface, making one H–O bond broken. Compared with other metal ions, Al3+ and Cr3+ have the strongest interactions with the surface, which can be explained by the significant electron transfer and more stable covalent bond formations between these two ions and the surface.

The important role of oxygen defect for NO gas-sensing behavior of α-Fe2O3 (0 0 1) surface: Predicted by density functional theory

Using density functional theory (DFT), we investigated and discussed the adsorption characteristics, gas-sensing response and gas-sensing mechanism of NO molecule on α-Fe2O3 (0 0 1) surface with and without oxygen defect (VO). The pure and oxygen-defective α-Fe2O3 (0 0 1) surface exhibited opposite electron transfer. The theoretical results proved that the NO molecule acted as a donor for pure α-Fe2O3 (0 0 1) surface. However, it failed to explain the increasing resistance of n-type metal oxide materials. For oxygen-defective α-Fe2O3 (0 0 1) surface, NO molecule acted as an acceptor. The results leaded to a decreasing electron-carrier concentration, and then resulted in an increasing resistance of oxygen-defective α-Fe2O3 (0 0 1) surface after NO molecule was introduced into. The direction of electron transfer was reversed by oxygen defect. In addition, the VO-NO adsorption configuration induced more stable adsorption structure and more significant electron transfer effects between NO molecule and oxygen-defective α-Fe2O3 (0 0 1) surface. The VO-NO adsorption configuration would have better gas-sensing performance for α-Fe2O3 (0 0 1) surface.

Self-Supported Ternary Ni-S-Se Nanorod Arrays as Highly Active Electrocatalyst for Hydrogen Generation in Both Acidic and Basic Media: Experimental Investigation and DFT Calculation.

In this study, a novel three-dimensional self-supported ternary NiS-Ni9S8-NiSe nanorod (NR) array cathode has been successfully in situ constructed by a two-step hydrothermal route. When applied to hydrogen evolution, the synthesized NiS-Ni9S8-NiSe-NR electrode demonstrates optimized electrocatalytic activity and long-term durability, only requiring overpotentials as low as 120 and 112 mV to drive 10 mA cm-2 for hydrogen evolution reaction in 0.5 M H2SO4 and 1.0 M KOH, respectively. Density functional theory calculation reveals that after Se doping Se 3d orbitals are bonded to Ni 3d orbitals and S p orbitals near Fermi level, attesting a significant electron transfer between nickel and selenium atoms. The success of enhancing the electrocatalytic performance via introducing the Se dopant holds great promise for the potential optimization of other transition-metal compounds in highly efficient electrochemical water splitting for large-scale hydrogen production.

Theoretically obtained insight into the mechanism and dioxetanone species responsible for the singlet chemiexcitation of Coelenterazine

Coelenterazine is a widespread bioluminescent substrate for a diverse set of marine species. Moreover, its imidazopyrazinone core is present in eight phyla of bioluminescent organisms. Given their very attractive intrinsic properties, these bioluminescent systems have been used in bioimaging, photodynamic therapy of cancer, as gene reporter and in sensing applications, among others. While it is known that bioluminescence results from the thermolysis of high-energy dioxetanones, the mechanism and dioxetanone species responsible for the singlet chemiexcitation of Coelenterazine are not fully understood. The theoretical characterization of the reactions of model Coelenterazine dioxetanones showed that efficient chemiexcitation is caused by a neutral dioxetanone with limited electron and charge transfer, by accessing a region of the PES where ground and excited states are nearly-degenerated. This finding was supported by calculation of equilibrium constants, which showed that only neutral dioxetanone is present in conditions associated with bioluminescence. Moreover, while cationic amino-acids easily protonate amide dioxetanone, anionic ones cannot deprotonate the neutral species. These results indicate that, contrary to existent theories, efficient chemiexcitation can occur with significant electron and/or charge transfer. In fact, these processes can be prejudicial to chemiexcitation, as anionic dioxetanones showed a less efficient chemiexcitation despite the occurrence of significant electron and charge transfer.

A quantitative analysis of light-driven charge transfer processes using voronoi partitioning of time dependent DFT-derived electron densities.

An analytical method is presented that provides quantitative insight into light‐driven electron density rearrangement using the output of standard time‐dependent density functional theory (TD‐DFT) computations on molecular compounds. Using final and initial electron densities for photochemical processes, the subtraction of summed electron density in each atom‐centered Voronoi polyhedron yields the electronic charge difference, Q VECD. This subtractive method can also be used with Bader, Mulliken and Hirshfeld charges. A validation study shows Q VECD to have the most consistent performance across basis sets and good conservation of charge between electronic states. Besides vertical transitions, relaxation processes can be investigated as well. Significant electron transfer is computed for isomerization on the excited state energy surface of azobenzene. A number of linear anilinepyridinium donor‐bridge‐acceptor chromophores was examined using Q VECD to unravel the influence of its pi‐conjugated bridge on charge separation. Finally, the usefulness of the presented method as a tool in optimizing charge transfer is shown for a homologous series of organometallic pigments. The presented work allows facile calculation of a novel, relevant quantity describing charge transfer processes at the atomic level. © 2017 The Authors Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

Phosphorus Nanostripe Arrays on Cu(110): A Case Study to Understand the Substrate Effect on the Phosphorus thin Film Growth

Black phosphorus has attracted significant attention as a new emerging 2D material in recent years. Due to its novel and unique properties, new 2D phosphorus nanostructures have also been predicted by theoretical calculations. However, experimental realization of new phosphorus structures has been rarely reported and remains one major challenge. Therefore, it is crucial to investigate phosphorus growth behaviors on different substrates to unravel the growth mechanism and provides useful guidelines for the selection of suitable substrates to synthesis the desired structure. This study reports a molecular‐beam‐epitaxial growth of phosphorus on Cu(110) by using bulk black phosphorous crystals as precursor, through the combination of in situ low temperature scanning tunneling microscopy (STM), low energy electron diffraction, X‐ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Atomically resolved STM image and the corresponding DFT simulations reveal the formation of phosphorus monomers and dimmers locating in the valley of the Cu(110) surface. XPS and Bader charge analysis confirm a significant electron transfer from the Cu(110) substrate to P atoms on top.

Significant electron transfer in heme catalysis: The case of chlorite dismutase

Electron transfer (ET) is significant in heme catalysis but usually difficult to be characterized. In the present DFT calculations, a transition state for ET has been optimized during the decomposition of peracetic acid (PAA) catalyzed by chlorite dismutase (Cld), using an active-site model based on the X-ray crystal structure of Cld. The Cld-catalyzed PAA reaction is revealed to proceed via a homolytic OO bond cleavage to transiently form compound II (Cpd II) and acetate radical (OAc), and a subsequent fast ET from Cpd II porphyrin to OAc leading to compound I (Cpd I) and acetate anion. The second step of ET is rate-limiting. The results highlight the importance of ET in heme chemistry and imply that the mechanisms of heme enzymes may be masked by fast ET even if a key intermediate has been detected (like Cpd I in this case). The comparison with the Cld-catalyzed chlorite reaction further indicates that a heme enzyme may employ different mechanisms for different substrates.

Defective Hexagonal Boron Nitride Nanosheet on Ni(111) and Cu(111): Stability, Electronic Structures, and Potential Applications.

Defective hexagonal boron nitride nanosheets (h-BNNSs) supported by Ni(111) and Cu(111) surfaces have been systematically studied in this work by first-principles methods. The calculation results show that various defects play an important role in enhancing the stability of h-BNNS/metal heterostructure. Importantly, significant electron transfer through the interface between metal substrate and h-BNNS to the defect sites can make h-BNNS more catalytically active. Using the oxygen reduction reaction (ORR) as a probe, it is shown that the binding energies of O2*, OH*, OOH*, and O* on h-BNNS/Cu(111) with a boron vacancy (VB) are quite similar to those observed on the Pt(111) surface, suggesting inert h-BNNS materials with defects can be functionalized by metal surfaces to become catalytically active for the ORR process. On the other hand, the reaction mechanism of CO oxidation on Ni(111) and Cu(111) supported h-BNNS with VB is systematically investigated. The h-BN/Cu(111) catalyst with a VB precovered by a CO species exhibits catalytic capacity for CO oxidation with a lower energy barrier compared with that on h-BN/Cu(111) without any defect. While on Ni(111) supported h-BNNS with a N vacancy, the defect site turns to be dominated by O2 and the energy barrier is significantly increased, indicating its dependence on the type of defect. This work will provide information for designing h-BN-based catalysts in heterogeneous catalysis.

Effect of Intermetallic Particle Size and Distribution on the Corrosion of an Mg-Al Alloy

The corrosion rates for Mg alloys are dependent on their composition. In particular, the corrosion resistance is usually increased if the alloying elements remain in solid solution and decreased if the alloying elements are above the solid solution solubility limit [1, 2]. Al additions up to 4 wt. % reduce the corrosion rate [2, 3]. During heat treatment, intermetallic particle (IMP) [4, 5] sizes increase while the area fraction remains relatively constant [4]. The size and spacing of these particles impacts the corrosion behaviour and will likely alter the cathodic reaction rate and corrosion rate as observed in other alloys systems [6]. In Mg-Al alloys, IMPs are more noble than typical Mg-Al alloy solid solutions [7, 8]. The IMPs function as cathodes when coupled with the α-Mg phase [9]. These IMPs support cathodic reduction reactions at faster rates than high purity Mg [7]. The extent of attack is dependent on the composition of the IMP. For instance, the cathodic activity of Al8Mn5 is much greater than that of Mg12Al17 or Al3Mg2 [10, 11]. However, little is known about how the size and spacing of these particles alters the cathodic rates and subsequently affects the corrosion rate. Mg-Al alloy, AZ31B was heat treated at temperatures ranging from 300 to 450 °C for durations ranging from 240 to 604,800 sec to produce samples varying in particle size and spacing. The corrosion behavior was examined in terms of its instantaneous corrosion rate and cathodic kinetics as a function of IMP size and spacing for a fixed area fraction of IMPs. The corrosion resistance was determined utilizing electrochemical impedance spectroscopy (EIS) [3]. The cathodic reaction rate was determined at -1.8 VSCE after 24 hrs immersed at the open circuit potential in 0.6 M NaCl. There was a decrease in both icorr and ic (Figure 1) with increasing particle size and spacing at a fixed area fraction of IMPs. The fast reactions around IMPs were mapped using Scanning Electrochemical Microscopy [12-15]. A non-aqueous electrolyte, such as ethelyne glycol or methanol mixed with a NaCl, was found to slow the kinetics of Mg corrosion while enabling mapping of active corroding sites [16]. The solution of 50 wt% methanol and 50 wt% H2O was found to give the best results. The mediator, hexaammineruthenium(III), Ru(NH3)6Cl3, has successfully been used to map Mg corrosion and was utilized herein [12]. The reduction of Ru(NH3)6Cl3 occurred at actively corroding sites. The subsequent oxidation of Ru(NH3)6Cl3 at the tip provided an indicator of sites where significant cathodic electron transfer reactions occurred [17]. The evolution of the reactivity of an AZ31B surface with time was mapped in 0.1 M NaCl (Figure 2). The regions of high cathodic reactivity are shown to spread across the surface as a function of exposure time. Acknowledgements This work was funded by the Office of Naval Research Grant N000141210967 with Dr. David A. Shifler.

Experimental and theoretical investigations of the polar intermetallics SrPt3Al2 and Sr2Pd2Al

SrPt3Al2, a CaCu5 relative (P6/mmm; a = 566.29(3), c = 389.39(3) pm; wR2 = 0.0202, 121 F2 values, 9 parameters), and Sr2Pd2Al, isostructural to Ca2Pt2Ge (Fdd2; a = 1041.45(5), b = 1558.24(7), c = 604.37(3) pm; wR2 = 0.0291, 844 F2 values, 25 parameters) have been prepared from the elements. The crystal structures have been investigated by single crystal X-ray diffraction. Structural relaxation confirmed the electronic stability of SrPt3Al2, while orthorhombic Sr2Pd2Al might be a metastable polymorph as it is energetically competitive to its monoclinic variant. Both compounds are predicted to be metallic conductors as their density-of-states (DOS) are non-zero at the Fermi level. COHP bonding analysis coupled with Bader effective charge analysis suggest that the title compounds are polar intermetallic phases in which strong Pt–Al and Pd–Al covalent bonds are present, while a significant electron transfer from Sr atoms to the [Pt3Al2]δ– or [Pd2Al]δ– network is found.

Interactions Between Fe(III)-Oxides and Fe(III)-Phyllosilicates During Microbial Reduction 1: Synthetic Sediments

ABSTRACTFe(III)-oxides and Fe(III)-bearing phyllosilicates are the two major iron sources utilized as electron acceptors by dissimilatory iron-reducing bacteria (DIRB) in anoxic soils and sediments. Although there have been many studies on microbial Fe(III)-oxide and Fe(III)-phyllosilicate reduction with both natural and specimen materials, no controlled experimental information is available on the interaction between these two phases when both are available for microbial reduction. In this study, the model DIRB Geobacter sulfurreducens was used to examine the pathways of Fe(III) reduction in Fe(III)-oxide stripped subsurface sediment that was coated with different amounts of synthetic high surface area (HSA) goethite. Cryogenic (12K) 57Fe Mössbauer spectroscopy was used to determine changes in the relative abundances of Fe(III)-oxide, Fe(III)-phyllosilicate, and phyllosilicate-associated Fe(II) [Fe(II)-phyllosilicate] in bioreduced samples. Analogous Mössbauer analyses were performed on samples from abiotic Fe(II) sorption experiments in which sediments were exposed to a quantity of exogenous soluble Fe(II) (FeCl2⋅2H2O) comparable to the amount of Fe(II) produced during microbial reduction. A Fe partitioning model was developed to analyze the fate of Fe(II) and assess the potential for abiotic Fe(II)-catalyzed reduction of Fe(III)-phyllosilicates. The microbial reduction experiments indicated that although reduction of Fe(III)-oxide accounted for virtually all of the observed bulk Fe(III) reduction activity, there was no significant abiotic electron transfer between oxide-derived Fe(II) and Fe(III)-phyllosilicatesilicates, with 26–87% of biogenic Fe(II) appearing as sorbed Fe(II) in the Fe(II)-phyllosilicate pool. In contrast, the abiotic Fe(II) sorption experiments showed that 41 and 24% of the added Fe(II) engaged in electron transfer to Fe(III)-phyllosilicate surfaces in synthetic goethite-coated and uncoated sediment. Differences in the rate of Fe(II) addition and system redox potential may account for the microbial and abiotic reaction systems. Our experiments provide new insight into pathways for Fe(III) reduction in mixed Fe(III)-oxide/Fe(III)-phyllosilicate assemblages, and provide key mechanistic insight for interpreting microbial reduction experiments and field data from complex natural soils and sediments.

Tuning the charge states of CrW2O9 clusters deposited on perfect and defective MgO(001) surfaces with different color centers: A comprehensive DFT study

The structures and electronic properties of bimetallic oxide CrW2O9 clusters supported on the perfect and defective MgO(001) surfaces with three different color centers, FS (0), FS (+), and FS (2+) centers, respectively, have been investigated by density functional theory calculations. Our results show that the configurations, adsorption energies, charge transfers, and bonding modes of dispersed CrW2O9 clusters are sensitive to the charge states of the FS centers. Compared with the gas-phase configuration, the CrW2O9 clusters supported on the defective surfaces are distorted dramatically, which exhibit different chain structures. On the perfect MgO surface, the depositions of clusters do not involve obvious charge transfer, while the situation is quite different on the defective MgO(001) surfaces in which significant electron transfer occurs from the surface to the cluster. Interestingly, this effect becomes more remarkable for electron-rich oxygen vacancies (FS (0) center) than that for electron-poor oxygen vacancies (FS (+) and FS (2+) centers). Furthermore, our work reveals a progressive Brønsted acid sites where spin density preferentially localized around the Cr atoms not the W atoms for all kinds of FS-centers, indicating the better catalytic activities can be expected for CrW2O9 cluster on defective MgO(001) surfaces with respect to the W3O9 cluster.

Ba3Pt4Al4-Structure, Properties, and Theoretical and NMR Spectroscopic Investigations of a Complex Platinide Featuring Heterocubane [Pt4Al4] Units.

Ba3Pt4Al4 was prepared from the elements in niobium ampules and crystallizes in an orthorhombic structure, space group Cmcm (oP44, a = 1073.07(3), b = 812.30(3), c = 1182.69(3) pm) isopointal to the Zintl phase A2Zn5As4 (A = K, Rb). The structure features strands of distorted [Pt4Al4] heterocubane-like units connected by condensation over Pt/Al edges. These are arranged in a hexagonal rod packing by further condensation over Pt and Al atoms with the barium atoms located inside cavities of the [Pt4Al4](δ-) framework. Structural relaxation confirmed the electronic stability of the new phase, while band structure calculations indicate metallic behavior. Crystal orbital Hamilton bonding analysis coupled with Bader effective charge analysis suggest a polar intermetallic phase in which strong Al-Pt covalent bonds are present, while a significant electron transfer from Ba to the [Pt4Al4](δ-) network is found. By X-ray photoelectron spectroscopy measurements the Pt 4f5/2 and 4f7/2 energies for Ba3Pt4Al4 were found in the range of those of elemental Pt due to the electron transfer of Ba, while PtAl and PtAl2 show a pronounced shift toward a more cationic platinum state. (27)Al magic-angle spinning NMR investigations verified the two independent crystallographic Al sites with differently distorted tetrahedrally coordinated [AlPt4] units. Peak assignments could be made based on both geometrical considerations and in relation to electric field gradient calculations.

First-principles study of the alkali earth metal atoms adsorption on graphene

Geometries, electronic structures, and magnetic properties for alkali earth metal atoms absorbed graphene have been studied by first-principle calculations. For Be and Mg atoms, the interactions between the adatom and graphene are weak van der Waals interactions. In comparison, Ca, Sr and Ba atoms adsorption on graphene exhibits strong ionic bonding with graphene. We found that these atoms bond to graphene at the hollow site with a significant binding energy and large electron transfer. It is intriguing that these adatoms may induce important changes in both the electronic and magnetic properties of graphene. Semimetal graphene becomes metallic and magnetic due to n-type doping. Detailed analysis shows that the s orbitals of these adatoms should be responsible for the arising of the magnetic moment. We believe that our results are suitable for experimental exploration and useful for graphene-based nanoelectronic and data storage.

Engineering a three-dimensional, photoelectrochemically active p-NiO / i-Sb2S3 junction by atomic layer deposition

A p-NiO/i-Sb2S3 semiconductor junction is created as an array of parallel, coaxially structured, hollow nanocylinders. The preparation bases on two consecutive steps of atomic layer deposition (ALD) onto the pore walls of anodic alumina, used as an inert template. ALD allows for the conformal coating of the deep pores. Characterization by x-ray photoelectron spectroscopy, x-ray diffraction, and transmission electron microscopy demonstrates the high purity, perfect stoichiometry, and nanocrystalline structure of both layers. Annealing the samples increases the crystallite size but disrupts the continuity of the Sb2S3 film. Electrochemical and photoelectrochemical curves evidence the injection of holes from the light absorber Sb2S3 into the p-type NiO, but no significant photoinduced cathodic electron transfer to the electrolyte.

Interaction of aluminum dimer with defective graphene

In the present work, density functional theory (DFT) calculations using cluster and slab models were performed in order to study the adsorption of Al dimer on a monovacancy of graphene. With cluster models, two different approaches were considered for the exchange and correlation functional; namely, the Perdew, Burke and Ernzerhof (PBE) and the Becke, 3-parameter, Lee–Yang–Parr (B3LYP) functionals. Under the slab approximation only PBE was employed. The geometry where two Al atoms are simultaneously adsorbed on both sides of a monovacancy (H3–H3) is the most stable thermodynamically, followed by the structure in which one Al atom resides over the center of a vacancy and the other makes a bridge between two carbon atoms (H3-B). The magnitude of the Al2 adsorption energy is larger than that of an adsorbed Al atom. While the ground states for both free Al2 and isolated defective graphene is predicted to be a triplet, that corresponding to the dimer adsorbed on the monovacancy is calculated to be a singlet. Charge population analysis has shown that a significant electron transfer from Al to the substrate of about 2e is produced. The corresponding density of states (DOS) obtained with periodic conditions indicate that the Al2/defective graphene system at the H3-B geometry with a doping level of about 3% has a nearly zero band gap with almost no states at the Fermi level, unlike the situation where only one Al atom is adsorbed on the monovacancy which present a metal-like behavior.

Evidence of a graphene-like Sn-sheet on a Au(111) substrate: electronic structure and transport properties from first principles calculations.

Two dimensional nanostructures of group IV elements have attracted a great deal of attention because of their fundamental and technological applications. A graphene-like single layer of tin atoms, commonly called stanene, has recently been predicted to behave like a quantum spin Hall insulator. Here we report the atomic structure, stability and electron transport properties of stanene stabilized on a gold substrate. The optimization of geometry and electronic structure was carried out using a plane-wave based pseudo-potential approach. This work is divided into three parts: (i) the nature of chemical interaction between tin atoms and the gold support, (ii) the geometrical shape and electronic structure of the tin layer on the gold support and (iii) the electron transport behavior of the gold supported tin layer. The results show that tin atoms bind to the gold support through strong chemical bonds and significant electronic charge transfer occurs from tin to the gold support. Remarkably, for a layer of tin atoms, while a buckled structure is preferred in the free state, a planar graphene-like atomic arrangement is stabilized on the gold support. This structural change corroborates the metal-like band structure of the planar stanene in comparison to the semi-metallic buckled configuration. The tunneling current of the supported tin layer shows Ohmic-like behavior and the calculated STM pattern of the supported tin layer shows distinct images of 'holes', characteristic of the hexagonal lattice.

Electron transfer kinetics on mono- and multilayer graphene.

Understanding of the electrochemical properties of graphene, especially the electron transfer kinetics of a redox reaction between the graphene surface and a molecule, in comparison to graphite or other carbon-based materials, is essential for its potential in energy conversion and storage to be realized. Here we use voltammetric determination of the electron transfer rate for three redox mediators, ferricyanide, hexaammineruthenium, and hexachloroiridate (Fe(CN)(6)(3-), Ru(NH3)(6)(3+), and IrCl(6)(2-), respectively), to measure the reactivity of graphene samples prepared by mechanical exfoliation of natural graphite. Electron transfer rates are measured for varied number of graphene layers (1 to ca. 1000 layers) using microscopic droplets. The basal planes of mono- and multilayer graphene, supported on an insulating Si/SiO(2) substrate, exhibit significant electron transfer activity and changes in kinetics are observed for all three mediators. No significant trend in kinetics with flake thickness is discernible for each mediator; however, a large variation in kinetics is observed across the basal plane of the same flakes, indicating that local surface conditions affect the electrochemical performance. This is confirmed by in situ graphite exfoliation, which reveals significant deterioration of initially, near-reversible kinetics for Ru(NH3)(6)(3+) when comparing the atmosphere-aged and freshly exfoliated graphite surfaces.

The potential application of phosphorene as an anode material in Li-ion batteries

The capacity and stability of the constituent electrodes critically determine the performance of Li-ion batteries (LIBs). In this study, density functional theory is employed to explore the potential application of the recently synthesized two dimensional phosphorene as an electrode material in LIBs. Our results show that Li atoms can bind strongly with the phosphorene monolayer and double layer with significant electron transfer. Besides, the structure of phosphorene is not influenced much by lithiation and the volume change is only 0.2%. After lithiation, a semiconductor-to-conductor transition is observed. The diffusion barrier values of Li are calculated to be 0.76 and 0.72 eV on monolayer and double layer phosphorene, respectively. We further demonstrate that the theoretical specific capacity of the phosphorene monolayer is 432.79 mA h g−1, which is larger than those of other commercial anode materials. The influence of Si and S implantation is also examined and our results indicate that Si-doped phosphorene greatly improves the binding of Li atoms, while the diffusion barrier is not affected. Our findings show that the high capacity, low open circuit voltage, small volume change and electrical conductivity of lithiated phosphorene make it a good candidate for application as an electrode material in batteries.