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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Cation Vacancies Enable Anion Redox in Li Cathodes

Conventional Li-ion battery intercalation cathodes leverage charge compensation that is formally associated with redox on the transition metal. Employing the anions in the charge compensation mechanism, so-called anion redox, can yield higher capacities beyond the traditional limitations of intercalation chemistry. Here, we aim to understand the structural considerations that enable anion oxidation and focus on processes that result in structural changes, such as the formation of persulfide bonds. Using a Li-rich metal sulfide as a model system, we present both first-principles simulations and experimental data that show that cation vacancies are required for anion oxidation. First-principles simulations show that the oxidation of sulfide to persulfide only occurs when a neighboring vacancy is present. To experimentally probe the role of vacancies in anion redox processes, we introduce vacancies into the Li 2 TiS 3 phase while maintaining a high valency of Ti. When the cation sublattice is fully occupied and no vacancies can be formed through transition metal oxidation, the material is electrochemically inert. Upon introduction of vacancies, the material can support high degrees of anion redox, even in the absence of transition metal oxidation. The model system offers fundamental insights to deepen our understanding of structure–property relationships that govern reversible anion redox in sulfides and demonstrates that cation vacancies are required for anion oxidation, in which persulfides are formed.

25 ENERGY STORAGE↗
DOE OSTI2026

Room-Temperature Methane Oxidation to Formaldehyde Mediated by CoMoO + Gas-Phase Cations

Formaldehyde (HCHO) is a fundamental chemical feedstock with widespread industrial applications. The direct oxidation of methane by oxygen to formaldehyde (CH 4 + 1/2O 2 → H 2 + HCHO) under mild conditions represents an attractive but challenging transformation, as it requires both activation of the inert C–H bonds of CH 4 and suppression of overoxidation to products such as carbon dioxide. In this work, mass spectrometry experiments combined with theoretical calculations reveal that CoMoO + cations can efficiently mediate this transformation at room temperature. The unique electronic structure of CoMoO + facilitates the formation of a crucial CoMoOCH 2 + intermediate during the reaction with CH 4 and prevents methanol formation. In the subsequent oxidation reaction, the Mo atom in CoMoO + serves as the active site for O 2 adsorption, and both Mo and Co atoms act as electron donors to activate O 2 , leading to the formation of the C–O bond in formaldehyde. This work reports the first gas-phase example of achieving conversion of CH 4 to HCHO and its radical derivatives by O 2 at room temperature using heteronuclear non-noble metal cations. Remarkably, the CoMoOCH 2 + cation maintains high reactivity after adsorbing one or two CH 4 molecules. Finally, these findings provide new mechanistic insights into selective methane activation and conversion.

aldehydes↗
DOE OSTI2014

Effects of ionic liquids on cation dynamics in amorphous polyethylene oxide electrolytes

We perform extensive molecular dynamics simulations of a poly(ethylene oxide)-based polymer electrolyte material containing lithium bis(trifluoromethanesulfonyl)imide salt for a wide temperature regime above and below the experimental crystallization temperature with and without N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (IL). The impact of the IL-concentration on the cation dynamics is studied. The increase of the cation mobility upon addition of IL is significant but temperature-independent. This can be related to distinct variations of the underlying transport properties as expressed within the previously introduced transport model of polymer electrolytes. Even for the largest IL concentration the transport model perfectly predicts the non-trivial time-dependence of the cationic mean square displacement for all temperatures. Finally, we compare our numerical and theoretical findings with the results of recent nuclear magnetic resonance experiments. In this way we can exclusively relate the strong experimentally observed dependence of the low-temperature Li-diffusivity on the IL concentration to the impact of IL on crystallization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Effects of In{sub 3+} substitution on structural properties, cation distribution and Mössbauer spectra of CoFe{sub 2}O{sub 4} ferrite

The use of non-destructive, high resolution technique namely Mössbauer spectroscopy is discussed in detail for the investigation of structural and magnetic properties of Fe based indium substituted cobalt ferrites. The polycrystalline samples of CoFe{sub 2−x}In{sub x}O{sub 4} (x = 0.2, 0.6) were prepared by double sintering solid state reaction method. To ensure a single phase formation of the as prepared samples the X-ray diffraction (XRD) data of the powdered samples was Rietveld refined using Fd3m space group. An excellent agreement is obtained between the integrated intensity ratios of 57 Fe spectra at A- and B-sites and those calculated on the basis of cation distribution the cation distribution obtained data analysis. The results of Mössbauer spectra and cation distribution are also correlated well with magnetization versus applied field (M-H) study.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Infrared spectroscopy of the acetyl cation and its protonated ketene isomer

[C{sub 2},H{sub 3},O]{sup +} ions are generated with a pulsed discharge in a supersonic expansion containing methyl acetate or acetone. These ions are mass selected and their infrared spectra are recorded via laser photodissociation and the method of argon tagging. Computational chemistry is employed to investigate structural isomers and their spectra. The acetyl cation (CH{sub 3}CO{sup +}) is the global minimum and protonated ketene (CH{sub 2}COH{sup +}) is the next lowest energy isomer (+176.2 kJ/mol). When methyl acetate is employed as the precursor, the infrared spectrum reveals that only the acetyl cation is formed. Partially resolved rotational structure reveals rotation about the C{sub 3} axis. When acetone is used as the precursor, acetyl is still the most abundant cation, but there is also a minor component of protonated ketene. Computations reveal a significant barrier to interconversion between the two isomers (+221 kJ/mol), indicating that protonated ketene must be obtained via kinetic trapping. Both isomers may be present in interstellar environments, and their implications for astrochemistry are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

One-photon mass-analyzed threshold ionization (MATI) spectroscopy of pyridine: Determination of accurate ionization energy and cationic structure

Ionization energies and cationic structures of pyridine were intensively investigated utilizing one-photon mass-analyzed threshold ionization (MATI) spectroscopy with vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The present one-photon high-resolution MATI spectrum of pyridine demonstrated a much finer and richer vibrational structure than that of the previously reported two-photon MATI spectrum. From the MATI spectrum and photoionization efficiency curve, the accurate ionization energy of the ionic ground state of pyridine was confidently determined to be 73 570 ± 6 cm{sup −1} (9.1215 ± 0.0007 eV). The observed spectrum was almost completely assigned by utilizing Franck-Condon factors and vibrational frequencies calculated through adjustments of the geometrical parameters of cationic pyridine at the B3LYP/cc-pVTZ level. A unique feature unveiled through rigorous analysis was the prominent progression of the 10 vibrational mode, which corresponds to in-plane ring bending, and the combination of other totally symmetric fundamentals with the ring bending overtones, which contribute to the geometrical change upon ionization. Notably, the remaining peaks originate from the upper electronic state ({sup 2}A{sub 2}), as predicted by high-resolution photoelectron spectroscopy studies and symmetry-adapted cluster configuration interaction calculations. Based on the quantitatively good agreement between the experimental and calculated results, it was concluded that upon ionization the pyridine cation in the ground electronic state should have a planar structure of C{sub 2v} symmetry through the C-N axis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Electronic spectra of astrophysically interesting cations

The electronic spectra of polyacetylene cations were recorded at 20K in the laboratory in an ion trap instrument. These can then be compared with diffuse interstellar band (DIB) absorptions. Examination of recently published data shows that the attribution of a weak DIB at ∼506.9 nm to diacetylene cation is not justified. Study of the higher excited electronic states of polyacetylene cations shows that their widths can still be sufficiently narrow for consideration as DIB carriers.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Nonadiabatic nuclear dynamics of the ammonia cation studied by surface hopping classical trajectory calculations

The Landau–Zener (LZ) type classical-trajectory surface-hopping algorithm is applied to the nonadiabatic nuclear dynamics of the ammonia cation after photoionization of the ground-state neutral molecule to the excited states of the cation. The algorithm employs a recently proposed formula for nonadiabatic LZ transition probabilities derived from the adiabatic potential energy surfaces. The evolution of the populations of the ground state and the two lowest excited adiabatic states is calculated up to 200 fs. The results agree well with quantum simulations available for the first 100 fs based on the same potential energy surfaces. Three different time scales are detected for the nuclear dynamics: Ultrafast Jahn–Teller dynamics between the excited states on a 5 fs time scale; fast transitions between the excited state and the ground state within a time scale of 20 fs; and relatively slow partial conversion of a first-excited-state population to the ground state within a time scale of 100 fs. Beyond 100 fs, the adiabatic electronic populations are nearly constant due to a dynamic equilibrium between the three states. The ultrafast nonradiative decay of the excited-state populations provides a qualitative explanation of the experimental evidence that the ammonia cation is nonfluorescent.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Magnetic moment directions and distributions of cations in Cr (Co) substituted spinel ferrites Ni{sub 0.7}Fe{sub 2.3}O{sub 4}

Powder samples of the spinel ferrites M{sub x}Ni{sub 0.7−x}Fe{sub 2.3}O{sub 4} (M = Cr, Co and 0.0 ≤ x ≤ 0.3) and Cr{sub x}Ni{sub 0.7}Fe{sub 2.3−x}O{sub 4} (0.0 ≤ x ≤ 0.3) were synthesized using the chemical co-precipitation method. The XRD spectra confirmed that the samples had a single-phase cubic spinel structure. Magnetic measurements showed that the magnetic moments (μ{sub exp}) per formula both at 10 K and 300 K increased with Co substitution, while the values of μ{sub exp} decreased with Cr substitution. Applying the assumption that the magnetic moments of Cr{sup 2+} and Cr{sup 3+} lie antiparallel to those of the divalent and trivalent Fe, Co, and Ni cations in the same sublattice of spinel ferrites, these interesting behaviors could be easily interpreted. The cation distributions of the three series of samples were estimated successfully by fitting the dependences of μ{sub exp}, measured at 10 K, on the doping level x, using a quantum-mechanical potential barrier model earlier proposed by our group. The results obtained for the Cr cation distributions at the (A) and [B] sites are very close to those obtained elsewhere using neutron diffraction.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Stable compositions and geometrical structures of titanium oxide cluster cations and anions studied by ion mobility mass spectrometry

Geometrical structures of titanium oxide cluster cations and anions have been investigated by ion mobility mass spectrometry and quantum chemical calculations based on density functional theory. Stable cluster compositions with respect to collision induced dissociation were also determined by changing ion injection energy to an ion drift cell for mobility measurements. The Ti{sub n}O{sub 2n−1}{sup +} cations and Ti{sub n}O{sub 2n}{sup −} anions were predominantly observed at high injection energies, in addition to Ti{sub n}O{sub 2n}{sup +} for cations and Ti{sub n}O{sub 2n+1}{sup −} for anions. Collision cross sections of Ti{sub n}O{sub 2n}{sup +} and Ti{sub n}O{sub 2n+1}{sup −} for n = 1-7, determined by ion mobility mass spectrometry, were compared with those obtained theoretically as orientation-averaged cross sections for the optimized structures by quantum chemical calculations. All of the geometrical structures thus assigned have three-dimensional structures, which are in marked contrast with other oxides of late transition metals. One-oxygen atom dissociation processes from Ti{sub n}O{sub 2n}{sup +} and Ti{sub n}O{sub 2n+1}{sup −} by collisions were also explained by analysis of spin density distributions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Gas-phase reactions of polycyclic aromatic hydrocarbon cations and their nitrogen-containing analogs with H atoms

We have studied the reactions of polycyclic aromatic hydrocarbon cations and their nitrogen-containing analogs with H atoms. Reaction rate constants are measured at 300 K using a flowing afterglow-selected ion flow tube. We have implemented the laser induced acoustic desorption technique to allow the study of large, non-volatile species in the gas phase. The extension of this work from previous studies shows that the reactivity of polycyclic aromatic hydrocarbon cations with H atoms reaches a constant value for large cations. There is a small difference in reactivity when comparing molecules of different size and geometry; however, no difference in reactivity was found when nitrogen was incorporated into the ring.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

A theoretical study on the interstellar synthesis of H{sub 2}NCS{sup +} and HNCSH{sup +} cations

HNCS and NCSH molecules, recently discovered in the interstellar medium, are likely formed via the dissociative recombination of H{sub 2}NCS{sup +} or HNCSH{sup +} isomeric ions. Interstellar synthesis of the latter is discussed on theoretical grounds. The analysis of relevant potential energy surfaces suggests a key role for chemical processes in which CSH{sup +} or HCS{sup +} cations (most likely formed in CS+H{sub 3}{sup +} collisions) react with NH{sub 2} or NH{sub 3}. The astrochemical kinetic database (kida.uva.2011), appended with 7 sulfur-bearing molecules and 48 corresponding reactions, has been applied to model the evolution of HNCS, NCSH, and their cationic precursors in a quiescent molecular cloud. Based on the model and on spectroscopic predictions, for an object like TMC-1, we expect the total intensity of H{sub 2}NCS{sup +} microwave lines to be comparable to that observed for HSCN. Theoretically derived molecular parameters, of interest for radio spectroscopy, are given for the most stable cations sharing the H{sub 2}NCS{sup +} stoichiometry.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

LABORATORY GAS-PHASE DETECTION OF THE CYCLOPROPENYL CATION (c-C{sub 3}H{sub 3} {sup +})

The cyclopropenyl cation (c-C{sub 3}H{sub 3} {sup +}) is the smallest aromatic hydrocarbon molecule and considered to be a pivotal intermediate in ion-molecule reactions in space. An astronomical identification has been prohibited so far, because of a lack of gas-phase data. Here we report the first high resolution infrared laboratory gas-phase spectrum of the ν {sub 4} (C-H asymmetric stretching) fundamental band of c-C{sub 3}H{sub 3} {sup +}. The c-C{sub 3}H{sub 3} {sup +} cations are generated in supersonically expanding planar plasma by discharging a propyne/helium gas pulse, yielding a rotational temperature of ∼35 K. The absorption spectrum is recorded in the 3.19 μm region using sensitive continuous-wave cavity ring-down spectroscopy. The analysis of about 130 ro-vibrational transitions results in precise spectroscopic parameters. These constants allow for an accurate comparison with high-level theoretical predictions, and provide the relevant information needed to search for this astrochemically relevant carbo-cation in space.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ionization of HCCI Neutral and Cations by Strong Laser Fields Simulated With Time Dependent Configuration Interaction

Strong field ionization of neutral iodoacetylene (HCCI) can produce a coherent superposition of the X and A cations. This superposition results in charge migration between the CC π orbital and the iodine π-type lone pair which can be monitored by strong field ionization with short, intense probe pulses. Strong field ionization of the X and A states of HCCI cation was simulated with time-dependent configuration interaction using singly ionized configurations and singly excited, singly ionized configurations (TD-CISD-IP) and an absorbing boundary. Studies with static fields were used to obtain the 3-dimensional angular dependence of instantaneous ionization rates by strong fields and the orbitals involved in producing the cations and dications. The frequency of charge oscillation is determined by the energy separation of the X and A states; this separation can change depending on the direction and strength of the field. Furthermore, fields along the molecular axis can cause extensive mixing between the field-free X and A configurations. For coherent superpositions of the X and A states, the charge oscillations are characterized by two frequencies–the driving frequency of the laser field of the probe pulse and the intrinsic frequency due to the energy separation between the X and A states. For linear and circularly polarized pulses, the ionization rates show marked differences that depend on the polarization direction of the pulse, the carrier envelope phase and initial phase of the superposition. Varying the initial phase of the superposition at the beginning of the probe pulse is analogous to changing the delay between the pump and probe pulses. The charge oscillation in the coherent superposition of the X and A states results in maxima and minima in the ionization yield as a function of the superposition phase

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Towards commercialization of fluorinated cation-disordered rock-salt Li-ion cathodes

Cation-disordered rock-salt cathodes (DRX) are promising materials that could deliver high capacities (>250 mAh g −1 ) with Earth abundant elements and materials. However, their electrochemical performances, other than the capacity, should be improved to be competitive cathodes, and many strategies have been introduced to enhance DRXs. Fluorination has been shown to inhibit oxygen loss and increase power density. Nevertheless, fluorinated cation-disordered rock-salts still suffer from rapid material deterioration and low scalability which limit their practical applications. This mini-review highlights the key challenges for the commercialization of fluorinated cation-disordered rock-salts, discusses the underlying reasons behind material failure and proposes future development directions.

25 ENERGY STORAGE↗
DOE OSTI2021

Cationic Ordering and Its Influence on the Magnetic Properties of Co-Rich Cobalt Ferrite Thin Films Prepared by Reactive Solid Phase Epitaxy on Nb-Doped SrTiO 3 (001)

Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich Co x Fe 3-x O 4 films with different stoichiometry (x=1.1 and x=1.4) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/Fe 3 O 4 bilayers deposited before on Nb-doped SrTiO 3 (001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of Co 3+ cations in the low-spin state on octahedral sites for the Co 1.4 Fe 1.6 O 4 film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Conformer-Specific Dissociation Dynamics in Dimethyl Methylphosphonate Radical Cation

The dynamics of the dimethyl methylphosphonate (DMMP) radical cation after production by strong field adiabatic ionization have been investigated. Pump-probe experiments using strong field 1300 nm pulses to adiabatically ionize DMMP and a 800 nm non-ionizing probe induce coherent oscillations of the parent ion yield with a period of about 45 fs. The yields of two fragments, PO 2 C 2 H 7 + and PO 2 CH 4 + , oscillate approximately out of phase with the parent ion, but with a slight phase shift relative to each other. We use electronic structure theory and nonadiabatic surface hopping dynamics to understand the underlying dynamics. The results show that while the cation oscillates on the ground state along the P=O bond stretch coordinate, the probe excites population to higher electronic states that can lead to fragments PO 2 C 2 H 7 + and PO 2 CH 4 + . The computational results combined with the experimental observations indicate that the two conformers of DMMP that are populated under experimental conditions exhibit different dynamics after being excited to the higher electronic states of the cation leading to different dissociation products. These results highlight the potential usefulness of these pump-probe measurements as a tool to study conformer-specific dynamics in molecules of biological interest.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Infrared Spectra of Hexa-peri-hexabenzocoronene Cations: HBC{sup +} and HBC{sup 2+}

We present the first infrared (IR) gas-phase spectrum of a large and astronomically relevant polycyclic aromatic hydrocarbon (PAH) cation (C{sub 42}H{sub 18} {sup +}, HBC{sup +}) and its dication (C{sub 42}H{sub 18} {sup 2+}, HBC{sup 2+}). The spectra are recorded via infrared multiphoton dissociation (IRMPD) spectroscopy of ions stored in a quadrupole ion trap, using the intense IR radiation of a free electron laser in the 530–1800 cm{sup −1} (5.6–18.9 μm) range. HBC{sup +} shows main intense absorption peaks at 762 (13.12), 1060 (9.43), 1192 (8.39), 1280 (7.81), 1379 (7.25), and 1530 (6.54) cm{sup −1} (μm), in good agreement with density functional theory calculations after scaling to take the anharmonicities effect into account. HBC{sup 2+} has its main absorption peaks at 660 (15.15), 766 (13.05), 1054 (9.49), 1176 (8.50), 1290 (7.75), 1370 (7.30) and 1530 (6.54) cm{sup −1} (μm). Given the similarity in the cationic and dicationic spectra, we have not identified an obvious diagnostic signature to the presence of multiply charged PAHs in space. While experimental issues associated with the IRMPD technique preclude a detailed comparison with interstellar spectra, we do note that the strong bands of HBC{sup +} and HBC{sup 2+} at ∼6.5, 7.7, 8.4, and 13.1 μm coincide with prominent aromatic infrared bands (AIBs). HBC has only trio CH groups, and the out-of-plane CH bending mode of both HBC cations is measured at 13.1 μm, squarely in the range predicted by theory and as previously found in studies of small (substituted) PAHs. This study therefore supports the use of AIBs observed in the 11–14 μm range as a diagnostic tool for the edge topology of large PAHs in space.

79 ASTRONOMY AND ASTROPHYSICS↗