Symmetry progression and possible polar metallicity in NiPS3 under pressure
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33 ADVANCED PROPULSION SYSTEMS↗
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Electronic band contraction induced low temperature methane activation on metal alloys
The catalytic conversion of methane under mild conditions is an appealing approach to selectively produce value-added products from natural gas. Catalysts which can chemisorb methane can potentially overcome challenges associated with its high stability and achieve facile activation. Although transition metals can activate C–H bonds, chemisorption and low-temperature conversion remain elusive on these surfaces. The broad electronic bands of metals can only weakly interact with the methane orbitals, in contrast to specific transition metal oxide and supported metal cluster surfaces which are now recognized to form methane σ-complexes. Here, we report methane chemisorption can, remarkably, occur on metal surfaces via electronic band contraction and localization from metal alloying. From a broad screening including single atom and intermetallic alloys in various substrates, we find early transition metals as promising metal solutes for methane chemisorption and low-temperature activation. These findings demonstrate a combinatorial diversity of possible candidates in earth abundant metal alloys with this attractive catalytic behavior.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A simple Rice-Ashby ductile–brittle transition temperature (DBTT) model based on dislocation mobility for body-centered cubic complex concentrated alloys
A simple Rice-Ashby type model for ductile–brittle transition temperature (DBTT) of body-centered cubic (bcc) complex concentrated alloys (structures) is presented. The effect of accumulation of dislocation density on DBTT is also analyzed. The model results are compared with experimental yield stress vs. temperature data for four complex concentrated alloys: Nb 45 Ta 25 Ti 15 Hf 15 (NTTH), MoNbTaW, HfNbTaTiZr, NbTiZr and two pure bcc metals, Fe and W. It is shown that the DBTT behavior of these alloys and pure metals are in agreement with the simple ductility model presented in this manuscript. The DBTT model presented in this manuscript along with yield strength models for bcc complex concentrated alloys described in the literature should serve as a useful guide for designing such alloys with good high temperature strength and significant room temperature ductility.
Crack tip processes↗
Ultrafast optical melting of trimer superstructure in layered 1T′-TaTe2
Abstract Quasi-two-dimensional transition-metal dichalcogenides are a key platform for exploring emergent nanoscale phenomena arising from complex interactions. Access to the underlying degrees-of-freedom on their natural time scales motivates the use of advanced ultrafast probes sensitive to self-organised atomic-scale patterns. Here, we report the ultrafast investigation of TaTe 2 , which exhibits unique charge and lattice trimer order characterised by a transition upon cooling from stripe-like chains into a (3 × 3) superstructure of trimer clusters. Utilising MeV-scale ultrafast electron diffraction, we capture the photo-induced TaTe 2 structural dynamics – exposing a rapid ≈ 1.4 ps melting of its low-temperature ordered state followed by recovery via thermalisation into a hot cluster superstructure. Density-functional calculations indicate that the initial quench is triggered by intra-trimer Ta charge transfer which destabilises the clusters, unlike melting of charge density waves in other TaX 2 compounds. Our work paves the way for further exploration and ultimately rapid optical and electronic manipulation of trimer superstructures.
36 MATERIALS SCIENCE↗
Extreme fast charge aging: Correlation between electrode scale and heterogeneous degradation in Ni-rich layered cathodes
Extreme fast charging (XFC) is a key requirement for the adoption of battery-based electric vehicles by the transportation sector. However, XFC has been shown to accelerate degradation, causing the capacity, life, and safety of batteries to deteriorate. There are no systematic studies in the open literature regarding aging modes in Ni-rich Li y Ni 0.a Mn 0.b Co 0.c O 2 (NMCabc) cathodes caused by fast charging. Herein, we report the effects of cathode composition and electrode loading in pouch cells containing NMC532, 622 and 811 paired with graphite and cycled under XFC conditions. The relative anisotropic volume change in the unit cell increases with Ni content in low-loading cells, while it levels up for all three NMC cathodes in high-loading cells because of substantial Li plating. The amounts of lithium plating and heterogeneity on the anode, determined by crystallographic phase quantification, were found to be correlated with electrode loading and cathode heterogeneity. The concentrations of the transition metals deposited on the anodes depend on NMCabc composition in a complex way. More particle cracking and surface degradation was found in NMC811. Here, the findings in this work provide a new understanding of the failure mechanisms and their practical implications for compositional tuning of future high-Ni NMCabc cathode materials during fast charging.
25 ENERGY STORAGE↗
Influence of Rare-Earth Ion Radius on Metal–Metal Charge Transfer in Trinuclear Mixed-Valent Complexes
We report the synthesis and characterization of a highly conjugated bisferrocenyl pyrrolediimine ligand, Fc 2 PyrDIH (1), and its trinuclear complexes with rare earth ions—(Fc 2 PyrDI)M(N(TMS) 2 ) 2 (2-M, M = Sc, Y, Lu, La). Crystal structures, NMR spectra, and UV/Vis-NIR data are presented. The latter are in good agreement with DFT calculations, illuminating the impact of the rare earth ionic radius on NIR charge transfer excitations. For [2-Sc] + , the charge transfer is at 11500 cm -1 , while for [2-Y] + only a d-d transition at 8000 cm -1 is observed. Lu has an ionic radius in between Sc and Y, and the [2-Lu] + complex exhibits both transitions. From TDDFT analysis we assign the 11500 cm -1 transition as a mixture of MLCT and MMCT, rather than pure metal-to-metal CT, because it has significant ligand character. Typically, the ferrocenes have high rotational freedom in bis-ferrocenyl mixed valent complexes. However, in the present (Fc 2 PyrDI)M(N(TMS) 2 ) 2 complexes, ligand-ligand repulsions lock the rotational freedom, so that rare earth ionic radius-dependent geometric differences increasingly influence orbital overlap as the ionic radius falls. The Marcus-Hush coupling constant HAB trends as: [2-Sc] + >[2-Lu] + >[2-Y] +
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Charge Transfer Dynamics in Dye-Sensitized Photocatalysts Using Metal Complex Sensitizers with Long-Wavelength Visible Light Absorption Based on Singlet–Triplet Excitation
An Os(II) polypyridyl complex was applied as a photosensitizer in dye-sensitized photocatalyst systems based on Pt-intercalated HCa 2 Nb 3 O 10 and Pt-loaded TiO 2 . The Os(II) complex exhibits a spin-forbidden but partially allowed triplet metal-to-ligand charge transfer ( 3 MLCT) transition, enabling broad visible light absorption up to 800 nm, which surpasses that of conventional Ru(II)-based dyes. Despite its shorter excited-state lifetime compared to Ru(II) complexes, efficient electron injection from the excited Os(II) dye into the semiconductor was confirmed. Under visible-light irradiation, the Os(II)- sensitized photocatalysts showed higher H 2 evolution activity than the Ru(II)-sensitized photocatalysts when sodium ascorbate was used as an electron donor, demonstrating effective utilization of long-wavelength visible light. In contrast, negligible H 2 evolution was observed when NaI was employed as a redox mediator for Z-scheme water splitting. Transient absorption spectroscopy revealed that the lack of activity stemmed from inefficient electron transfer from I − to oxidized Os(II). These findings highlight the importance of selecting appropriate redox mediators to fully exploit long-wavelength dyes for overall water splitting under visible light.
artificial photosynthesis↗
Intentional carbon doping reveals CH as an abundant charged impurity in nominally undoped synthetic WS 2 and WSe 2
Understanding the physical properties and controlling the generation of intrinsic and extrinsic defects is central to the technological adoption of 2D materials in devices. Here we identify a charged carbon-hydrogen complex at a chalcogen site (CH X ) as a common, charged impurity in synthetically grown transition metal dichalcogenides (TMDs). This conclusion is drawn by comparing high resolution scanning probe microscopy measurements of nominally undoped and intentionally carbon doped TMD samples. While CH impurity densities in undoped CVD-grown WS 2 and MOCVD-grown WSe 2 can range anywhere from parts per million to parts per thousand, CH densities in the percentage levels were selectively generated by a post-synthetic methane plasma treatment. Our study indicates that methane plasma treatment is a selective and clean method for the controlled introduction of a charged carbon-hydrogen complex at a surface chalcogen site, adefect that is commonly present in synthetic TMDs.
36 MATERIALS SCIENCE↗
Metallic and complex hydride-based electrochemical storage of energy
Abstract The development of efficient storage systems is one of the keys to the success of the energy transition. There are many ways to store energy, but among them, electrochemical storage is particularly valuable because it can store electrons produced by renewable energies with a very good efficiency. However, the solutions currently available on the market remain unsuitable in terms of storage capacity, recharging kinetics, durability, and cost. Technological breakthroughs are therefore expected to meet the growing need for energy storage. Within the framework of the Hydrogen Technology Collaboration Program—H 2 TCP Task-40, IEA’s expert researchers have developed innovative materials based on hydrides (metallic or complex) offering new solutions in the field of solid electrolytes and anodes for alkaline and ionic batteries. This review presents the state of the art of research in this field, from the most fundamental aspects to the applications in battery prototypes.
Cuevas, Fermin (ORCID:0000000290555880)↗
Advances and Challenges of SCAN and r 2 SCAN Density Functionals in Transition‐Metal Compounds
ABSTRACT Transition‐metal compounds (TMCs) with open‐shell d ‐electrons are characterized by a complex interplay of lattice, charge, orbital, and spin degrees of freedom, giving rise to various fascinating applications. Often exhibiting exotic properties, these compounds are commonly classified as correlated systems due to strong inter‐electronic interactions called Hubbard U . This inherent complexity presents significant challenges to Kohn‐Sham density functional theory (KS‐DFT), the most widely used electronic structure method in condensed matter physics and materials science. While KS‐DFT is, in principle, exact for the ground‐state total energy, its exchange‐correlation energy must be approximated in practice. The mean‐field nature of KS implementations, combined with the limitations of current exchange‐correlation density functional approximations, has led to the perception that DFT is inadequate for correlated systems, particularly TMCs. Consequently, a common workaround involves augmenting DFT with an on‐site Hubbard‐like U correction. In recent years, the strongly constrained and appropriately normed (SCAN) density functional, along with its refined variant r 2 SCAN, has achieved remarkable progress in accurately describing the structural, energetic, electronic, magnetic, and vibrational properties of TMCs, challenging the traditional perception of DFT's limitations. This review explores the design principles of SCAN and r 2 SCAN, highlights their key advancements in studying TMCs, explains the mechanisms driving these improvements, and addresses the remaining challenges in this evolving field.
Zhang, Yubo [Minjiang Collaborative Center for The↗
A Spectroscopic and Computational Evaluation of Uranyl Oxo Engagement with Transition Metal Cations
Here, we report the synthesis and characterization of five novel Cd 2+ /UO 2 2+ heterometallic complexes that feature Cd-oxo distances ranging from 78 to 171% of the sum of the van der Waals radii for these atoms. This work marks an extension of our previously reported Pb 2+ /UO 2 2+ and Ag + /UO 2 2+ complexes, yet with much more pronounced structural and spectroscopic effects resulting from Cd-oxo interactions. We observe a major shift in the U═O symmetric stretch and significant uranyl bond length asymmetry. The ρbcp values calculated using Quantum Theory of Atoms in Molecules (QTAIM) support the asymmetry displayed in the structural data and indicate a decrease in covalent character in U═O bonds with close Cd-oxo contacts, more so than in related compounds containing Pb 2+ and Ag + . Second-order perturbation theory (SOPT) analysis reveals that O sp x → Cd s is the most significant orbital overlap and U═O bonding and antibonding orbitals also contribute to the interaction (U═O σ/π → Cd d and Cd s → U═O σ/π*). The overall stabilization energies for these interactions were lower than those in previously reported Pb 2+ cations, yet larger than related Ag + compounds. Analysis of the equatorial coordination sphere of the Cd 2+ /UO 2 2+ compounds (along with Pb 2+ /UO 2 2+ complexes) reveals that 7-coordinate uranium favors closer, stronger M n+ -oxo contacts. These results indicate that U═O bond strength tuning is possible with judicious choice of metal cations for oxo interactions and equatorial ligand coordination.
cations↗
Unveiling ultrafast dynamics in bridged bimetallic complexes using optical and X-ray transient absorption spectroscopies
In photosynthetic systems employing multiple transition metal centers, the properties of charge-transfer states are tuned by the coupling between metal centers.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Atomistic Study of the Plastic Deformation of Transition Metals and High Entropy Alloys (Final Report)
The overarching goal of the research performed in the studies supported by the DOE Basic Energy Sciences has been investigation of mechanical properties of materials employed in technologies related to energy production and conversion using atomic level computer modeling. The materials studied are body-centered-cubic (BCC) transition metals, including α-iron, their alloys and most recently also compositionally complex, so called high entropy alloys (HEAs), which are believed to become future materials in high temperature applications. The goal of the research has been to achieve atomic level understanding of the deformation and fracture of these materials starting from the electronic structure, coarse grain the material energetics into potentials describing interaction between atoms and proceed via atomistic modeling and mesoscopic models to investigation of the glide of dislocations and thus advance the theory of plastic deformation of studied materials.
36 MATERIALS SCIENCE↗
Catalytic Dehydrogenation of Alkanes by PCP–Pincer Iridium Complexes Using Proton and Electron Acceptors
Dehydrogenation to give olefins offers the most broadly applicable route to the chemical transformation of alkanes. Furthermore, transition-metal-based catalysts can selectively dehydrogenate alkanes using either olefinic sacrificial acceptors or a purge mechanism to remove H 2 ; both of these approaches have significant practical limitations. Here, we report the use of pincer-ligated iridium complexes to achieve alkane dehydrogenation by proton-coupled electron transfer, using pairs of oxidants and bases as proton and electron acceptors. Up to 97% yield was achieved with respect to oxidant and base, and up to 15 catalytic turnovers with respect to iridium, using t-butoxide as base coupled with various oxidants, including oxidants with very low reduction potentials. Mechanistic studies indicate that (pincer)IrH 2 complexes react with oxidants and base to give the corresponding cationic (pincer)IrH + complex, which is subsequently deprotonated by a second equivalent of base; this affords (pincer)Ir which is known to dehydrogenate alkanes and thereby regenerates (pincer)IrH 2 .
02 PETROLEUM↗
Resolving Chemical and Spatial Heterogeneities at Complex Electrochemical Interfaces in Li-Ion Batteries
The high specific capacities of Ni-rich transition metal oxides have garnered immense interest for improving the energy density of Li-ion batteries (LIBs). Despite the potential of these materials, Ni-rich cathodes suffer from interfacial instabilities that lead to crystallographic rearrangement of the active material surface as well as the formation of a cathode electrolyte interphase (CEI) layer on the composite during electrochemical cycling. While changes in crystallographic structure can be detected with diffraction-based methods, probing the chemistry of the disordered, heterogeneous CEI layer is challenging. In this work, we use a combination of ex situ solid-state nuclear magnetic resonance (SSNMR) spectroscopy and X-ray photoemission electron microscopy (XPEEM) to provide chemical and spatial information, on the nanometer length scale, on the CEI deposited on LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) composite cathode films. XPEEM elemental maps offer insight into the lateral arrangement of the electrolyte decomposition products that comprise the CEI and paramagnetic interactions (assessed with electron paramagnetic resonance (EPR) and relaxation measurements) in 13 C SSNMR provide information on the radial arrangement of the CEI from the NMC811 particles outward. Using this approach, here we find that LiF, Li 2 CO 3 , and carboxy-containing structures are directly appended to NMC811 active particles, whereas soluble species detected during in situ 1 H and 19 F solution NMR experiments (e.g., alkyl carbonates, HF, and vinyl compounds) are randomly deposited on the composite surface. We show that the combined approach of ex situ SSNMR and XPEEM, in conjunction with in situ solution NMR, allows spatially-resolved, molecular-level characterization of paramagnetic surfaces and new insights into electrolyte oxidation mechanisms in porous electrode films.
36 MATERIALS SCIENCE↗
Ground electronic state description of thiourea coordination in homoleptic Zn 2+ , Ni 2+ and Co 2+ complexes using sulfur K -edge X-ray absorption spectroscopy
Sulfur K-edge X-ray absorption spectroscopy (XAS) was employed to experimentally characterize the coordinative bond between the thiourea (TU) or thiocarbamide ligand and transition metal (TM) ions Zn 2+ , Co 2+ and Ni 2+ in distorted tetrahedral and octahedral homoleptic coordination environments. Comparisons of XAS spectra of the free TU ligand and [Zn(TU) 4 ] 2+ , [Co(TU) 4 ] 2+ and [Ni(TU) 6 ] 2+ complexes clearly identify spectral features unique to TM 2+ –S(TU) bonding. Quantitative analysis of pre-edge intensities describes the covalency of Ni 2+ —S(TU) and Co 2+ —S(TU) bonding to be at most 21% and 9% as expressed by the S 3p contributions per TM 3d electron hole. Using relevant Ni 2+ complexes with dithiocarbamate and thioether ligands, we evaluated the empirical S 1s → 3p transition dipole integrals developed for S-donor ligands and their dependence on heteroatom substitutions. With the aid of density functional theory-based ground electronic state calculations, we found evidence for the need of using a transition dipole that is dependent on the presence of conjugated heteroatom (N) substitution in these S-donor ligands.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
Crystal Structure and C–H Bond-Cleaving Reactivity of a Mononuclear Co IV –Dinitrate Complex
High-valent Fe IV =O intermediates with a terminal metal–oxo moiety are key oxidants in many enzymatic and synthetic C–H bond oxidation reactions. While generating stable metal–oxo species for late transition metals remains synthetically challenging, notably, a number of high-valent non-oxo–metal species of late transition metals have been recently described as strong oxidants that activate C–H bonds. In this work, we obtained an unprecedented mononuclear Co IV –dinitrate complex (2) upon one-electron oxidation of its Co(III) precursor supported by a tridentate dianionic N3 ligand. 2 was structurally characterized by X-ray crystallography, showing a square pyramidal geometry with two coordinated nitrate anions. Furthermore, characterization of 2 using combined spectroscopic and computational methods revealed that 2 is a low-spin (S = 1/2) Co(IV) species with the unpaired electron located on the cobalt d z2 orbital, which is well positioned for substrate oxidations. Indeed, while having a high thermal stability, 2 is able to cleave sp 3 C–H bonds up to 87 kcal/mol to afford rate constants and kinetic isotope effects (KIEs) of 2–6 that are comparable to other high-valent metal oxidants. The ability to oxidize strong C–H bonds has yet to be observed for Co IV –O and Co III =O species previously reported. Therefore, 2 represents the first high-valent Co(IV) species that is both structurally characterized by X-ray crystallography and capable of activating strong C–H bonds.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Beyond Graphene: Low-Symmetry and Anisotropic 2D Materials
Low-symmetry 2D materials—such as ReS 2 and ReSe 2 monolayers, black phosphorus monolayers, group-IV monochalcogenide monolayers, borophene, among others—have more complex atomistic structures than the honeycomb lattices of graphene, hexagonal boron nitride, and transition metal dichalcogenides. The reduced symmetries of these emerging materials give rise to inhomogeneous electron, optical, valley, and spin responses, as well as entirely new properties such as ferroelasticity, ferroelectricity, magnetism, spin-wave phenomena, large nonlinear optical properties, photogalvanic effects, and superconductivity. Novel electronic topological properties, nonlinear elastic properties, and structural phase transformations can also take place due to low symmetry. Lastly, the “Beyond Graphene: Low-Symmetry and Anisotropic 2D Materials” Special Topic was assembled to highlight recent experimental and theoretical research on these emerging materials.
2D materials↗