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Synthesizing highly crystalline nano-sized ε-VOPO 4 particles is the key to achieve theoretical capacity of 2 Li + intercalation in lithium-ion batteries.
The electrons sublibrary aims to describe electron-atomic cross section data, corresponding to the interaction between electrons and the different atoms. For ENDF/B-VIII.1 we adopted the EPICS2023 EEDL evaluations.
At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (∼73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (∼67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp{sup 3} hybridization to form the σC-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state.
Reactions of the hydrated electron with a wide variety of substrates have been found to exhibit unusually similar activation energies in a manner incompatible with Marcus electron transfer theory. Given the fundamental linear response assumption of Marcus theory, one possible explanation for this apparent failure is that the underlying free energy surfaces governing the reactions are not harmonic, i.e., hydrated electron structural fluctuations exhibit non-Gaussian behavior. In this work, we test this hypothesis by using simulations to calculate the hydrated electron vertical detachment energy distribution. Furthermore, we consider both cavity and non-cavity models for the hydrated electron, between which the actual hydrated electron behavior is expected to lie. Our results identify a possible origin for non-Gaussian behavior of the hydrated electron, but show that it is not of sufficient magnitude to explain the failure of Marcus theory to describe its reactions. Thus, other explanations must be sought.
The development of highly reversible multielectron reaction per redox center in sodium super ionic conductor-structured cathode materials is desired to improve the energy density of sodium-ion batteries. Here, we investigated more than one-electron storage of Na in Na 3 VCr(PO 4 ) 3 . Combining a series of advanced characterization techniques such as ex situ 51 V solid-state nuclear magnetic resonance, X-ray absorption near-edge structure, and in situ X-ray diffraction, we reveal that V 3+ /V 4+ and V 4+ /V 5+ redox couples in the materials can be accessed, leading to a 1.5-electron reaction. It is also found that a light change on the local electronic and structural states or phase change could be observed after the first cycle, resulting in the fast capacity fade at room temperature. As a result, we also showed that the irreversibility of the phase changes could be largely suppressed at low temperature, thus leading to a much improved electrochemical performance.
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Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes.
The radiation-induced decomposition and desorption of nanoscale amorphous solid water (D2O) films adsorbed on -Al2O3(0001) surface was studied at low temperature in ultrahigh vacuum using temperature programmed desorption (TPD) and electron stimulated desorption (ESD) with a mono-energetic, low energy electron source. ESD yields of molecular products ( D2, O2 and D¬2O) and the total sputtering yield increased with increasing D2O coverage up to ~15 water monolayers (i.e. ~15 1015 cm-2) to a coverage-independent level for thicker water films. Experiments with isotopically-layered water films (D2O and H2O) demonstrated that the highest water decomposition yields occurred at the interfaces of the nanoscale water films with the alumina substrate and vacuum. However, the increased reactivity of the water/alumina interface is relatively small compared to the enhancements in the non-thermal reactions previously observed at the water/Pt(111) and water/TiO2(110) interfaces. We propose that the relatively low activity of Al2O3(0001) for the radiation-induced production of molecular hydrogen is associated with lower reactivity of this surface with hydrogen atoms, which are likely precursors for the molecular hydrogen.
Organic radical batteries (ORBs) bearing robust radical polymers as energy storage species, are emerging promisingly with durable high energy and power characteristics by unique tunable redox properties. Here we report the development and application of in situ electrochemical-electron spin resonance (ESR) methodologies to identify the charge transfer mechanism of Poly(2,2,6,6- tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) based organic radical composite cathodes in the charge-discharge process of lithium half cells. The in situ experiments allow each electrochemical state to be associated with the chemical state (or environment) of the radical species upon the cell cycling. In situ ESR spectra of the composite cathode demonstrate a two-electron redox reaction of PTMA. Moreover, two different local environments of radical species are found in the composite electrode that includes both concentrated and isolated radicals. These two types of radicals show similarities during the redox reaction process while behave quite differently in the non-faradic reaction of ion sorption/desorption on the electrode surface.
Low-energy (100 eV) electron-stimulated reactions in layered H{sub 2}O/CO/H{sub 2}O ices are investigated. For CO layers buried in amorphous solid water (ASW) films at depths of 50 monolayers (ML) or less from the vacuum interface, both oxidation and reduction reactions are observed. However, for CO buried more deeply in ASW films, only the reduction of CO to methanol is observed. Experiments with layered films of H{sub 2}O and D{sub 2}O show that the hydrogen atoms participating in the reduction of the buried CO originate in the region that is 10–50 ML below the surface of the ASW films and subsequently diffuse through the film. For deeply buried CO layers, the CO reduction reactions quickly increase with temperature above ∼60 K. We present a simple chemical kinetic model that treats the diffusion of hydrogen atoms in the ASW and sequential hydrogenation of the CO to methanol to account for the observations.
Using temperature programmed desorption (TPD) and photon stimulated desorption (PSD), we show that coadsorbates of varying binding energies on the rutile TiO2(110) surface exert a commensurate inhibiting influence on the hole-mediated photodesorption of adsorbed O2. A variety of coadsorbates (Ar, Kr, Xe, N2, CO, CO2, CH4, N2O, acetone, methanol or water) were shown to quench O2 photoactivity, with the extent correlating with the coadsorbate’s gas phase basicity, which in turn determines the strength of the coadsorbate-Ti4+ bond. Coadsorbed rare gases inhibited the photodesorption of O2 by ~10-25%, whereas strongly bound species (water, methanol and acetone) nearly completely inhibited O2 PSD. We suggest that coadsorption of these molecules inhibit the arrival probability of holes to the surface. Band bending effects, which vary with the extent of charge transfer between the coadsorbate and the TiO2(110) surface, are not expected to be significant in the cases of the rare gases and physisorbed species. These results indicate that neutral coadsorbates can exert a significant influence on charge transfer events by altering the interfacial dipole in the vicinity of the target molecule. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The work was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for DOE by Battelle under Contract DE-AC05-76RL01830.
Electron transfer near an electrode immersed in ionic fluids is studied using the linear response approximation, namely, mean value of the vertical energy gap can be used to evaluate the reorganization energy, and hence any linear response model that can treat Coulomb interactions successfully can be used for the reorganization energy calculation. Specifically, a molecular Debye-Hückel theory is used to calculate the reorganization energy of electron transfer reactions in an electric cell. Applications to electron transfer near an electrode in molten salts show that the reorganization energies from our molecular Debye-Hückel theory agree well with the results from MD simulations.
Our current research program examines the photon- and electron-initiated reaction mechanisms, half-collision dynamics, and other nonequilibrium-excited dynamics effects, occurring with excitation of adsorbates on well-characterized metal-oxide of metalchalcogenide surfaces, both in single-crystal and in nanocrystalline forms. The program has made extensive use of STM methods, collaborations with the Nanoprobing SPLEEM system at Brookhaven National Lab, and XPS methods. As our current program terminates, it brings to an end a sustained and major effort to understand reactions and electronic structure on materials of interest for photochemistry on precision surfaces. The last two close-out years of our program allowed us to complete our STM surface studies, interact with scientists at BNL on programs useful for two dimensional (2D) materials, and initiate a new effort in ultrafast two-photon photoemission spectroscopy. Our work has then shown how nanoscale stressed surface regions on sold crystal surfaces (typically TiO 2 ) lead to enhanced reactivity of adsorbate molecules – a result of much importance for nanocatalysis. In addition we have developed several new surface and near-surface probing methods – these, also, are of general use to the community. Finally due to the pervasive interest in DOE labs in these materials, we have exploited our earlier synchrotron-based understanding of the electronic structure in (2D) materials to begin a study of surface chemical reactions in these same materials and their corresponding molecular dynamics. These efforts are described briefly below and in the references or DOE publications presented in the publications section of this report. We are pleased to have been able to contribute so many publications in the last two years of this many year DOE program. We also wish to thank DOE for the sustained funding that has made this program such a success.
The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ{sub 0}=ℏω{sub 0}/k{sub B}T where ω{sub 0} is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ{sub 0} < 1 − 3) and for low (ξ{sub 0}≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T→ 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems.
Electronically non-adiabatic effects play an important role in many chemical reactions. However, how these effects manifest in cold and ultracold chemistry remains largely unexplored. Here for the first time we present from first principles the non-adiabatic quantum dynamics of the reactive scattering between ultracold alkali-metal LiNa molecules and Li atoms. We show that non-adiabatic dynamics induces quantum interference effects that dramatically alter the ultracold rotationally resolved reaction rate coefficients. The interference effect arises from the conical intersection between the ground and an excited electronic state that is energetically accessible even for ultracold collisions. These unique interference effects might be exploited for quantum control applications such as a quantum molecular switch. The non-adiabatic dynamics are based on full-dimensional ab initio potential energy surfaces for the two electronic states that includes the non-adiabatic couplings and an accurate treatment of the long-range interactions. A statistical analysis of rotational populations of the Li2 product reveals a Poisson distribution implying the underlying classical dynamics are chaotic. The Poisson distribution is robust and amenable to experimental verification and appears to be a universal property of ultracold reactions involving alkali metal dimers.
Proton-coupled electron transfer (PCET) reactions mediate essential biological energy-conversion processes, yet dynamical experiments that distinguish concerted electron/proton motion from sequential electron-transfer/proton-transfer pathways are unprecedented on ultrafast time scales. Here we report a tightly coupled donor–spacer–acceptor assembly, NDI-Sp-PhOH/BI, that enables direct interrogation of light-triggered and ultrafast PCET dynamics. Photoexcitation of the naphthalene diimide chromophore drives charge separation forming NDI radical anion and benzimidazolium phenoxy radical (PhO●/BIH+) products with a 440 fs time constant, followed by thermal charge recombination on a 5 ps time scale. Transient visible/near-infrared and mid-infrared spectroscopies independently track electron and proton motion and reveal coincident formation and decay of the charge-separated PCET products, excluding detectable phenol radical cation or phenoxide intermediates expected for sequential electron transfer-proton transfer (ET-PT) pathways. Surface-hopping quasiclassical trajectory simulations demonstrate rapid proton relocation coupled to evolution from locally excited to charge-transfer states, congruent with a concerted mechanism. These combined spectroscopic and computational results establish NDI-Sp-PhOH/BI as an archetype for ultrafast, concerted PCET occurring with unit quantum yield; further, because this platform provides distinct electronic and vibrational spectroscopic handles in its ground, electronically excited, and charge-separated states, it provides new opportunities to characterize mechanistic crossover in biomimetic PCET systems.
The photosynthetic protein complex, photosystem II (PSII), conducts the light-driven water-splitting reaction with unrivaled efficiency. Proton-coupled electron transfer (PCET) reactions at the redox-active tyrosine residues are thought to play a critical role in the water-splitting chemistry. Addressing the fundamental question as to why the tyrosine residue, Y Z , is kinetically competent in comparison with a symmetrically placed tyrosine residue, Y D , is important for the elucidation of the mechanism of PCET in the water-splitting reaction of PSII. Here, using all-quantum-mechanical calculations we study PCET at the Y Z and Y D residues of PSII. We find that when Y Z is in its protein matrix under physiological conditions, the HOMO of Y Z constitutes the HOMO of the whole system. In contrast, the HOMO of Y D is buried under the electronic states localized elsewhere in the protein matrix and PCET at YD requires the transfer of the phenolic proton, which elevates the HOMO of Y D to being the HOMO of the whole system. This leads to the oxidation of Y D albeit on a slower timescale. Our study reveals that the key differences in the electronic structure of Y Z and Y D is primarily determined by the protonation state of the respective hydrogen-bonding partners, D1-His190 and D2-His189, or more generally by the H-bonding network of the protein matrix.