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At least 199 records · Page 11

Transition Metal Nitrides as Promising Catalyst Supports for Tuning CO/H 2 Syngas Production from Electrochemical CO 2 Reduction

The electrochemical carbon dioxide reduction reaction (CO 2 RR) to produce synthesis gas (syngas) with tunable CO/H 2 ratios has been studied by supporting Pd catalysts on transition metal nitride (TMN) substrates. Combining experimental measurements and density functional theory (DFT) calculations, Pd-modified niobium nitride (Pd/NbN) is found to generate much higher CO and H 2 partial current densities and greater CO Faradaic efficiency than Pd-modified vanadium nitride (Pd/VN) and commercial Pd/C catalysts. In-situ X-ray diffraction identifies the formation of PdH in Pd/NbN and Pd/C under CO 2 RR conditions, whereas the Pd in Pd/VN is not fully transformed into the active PdH phase. DFT calculations show that the stabilized *HOCO and weakened *CO intermediates on PdH/NbN are critical to achieving higher CO 2 RR activity. This work suggests that NbN is a promising substrate to modify Pd, resulting in an enhanced electrochemical conversion of CO 2 to syngas with a potential reduction in precious metal loading.

25 ENERGY STORAGE↗

Oxophilicity Drives Oxygen Transfer at a Palladium–Silver Interface for Increased CO Oxidation Activity

A single-layer AgO x phase grown on Ag(111) efficiently transfers oxygen to Pd domains at room temperature, rendering the Pd-decorated surface highly reactive toward CO oxidation. Here, oxygen transfer from AgO x to Pd and the surface reactivity toward CO were investigated as a function of the Pd coverage using X-ray photoelectron spectroscopy, surface infrared spectroscopy of adsorbed CO, temperature-programmed reaction spectroscopy, and density functional theory (DFT) calculations. Our results show that all of the oxygen from the AgO x layer (~0.375 monolayer) migrates to the surface of Pd during formation of a nearly complete Pd bilayer at 300 K and that the oxygen coverages generated on Pd increase as the Pd cluster size decreases, reaching values that exceed the oxygen concentration in the AgO x layer by as much as a factor of 2. Experimental measurements and DFT calculations show that preferential binding of oxygen on the edges of the Pd clusters enhances the oxygen coverage on Pd clusters of decreasing size and produces a heterogeneous spatial distribution of oxygen. CO adsorbs in high coverages at 100 K by binding on both the terraces and O-rich edges of the Pd clusters. During subsequent heating, oxidation of the adsorbed CO consumes nearly all of the oxygen that transferred from AgO x to the Pd domains; in contrast, the pure AgO x layer exhibits limited reactivity toward CO adsorbed at 100 K. These results demonstrate that differences in oxophilicity drive facile oxygen transfer from Ag to the edges of Pd nanoclusters and thereby give rise to an efficient pathway for CO oxidation on bimetallic PdAg surfaces. The cooperation between the Pd and Ag domains results in near-interfacial chemistry that may be broadly important in catalysis by bimetallic alloys.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Understanding Cu incorporation in the Cu 2x Hg 2-x GeTe 4 structure using resonant x-ray diffraction

The ability to control carrier concentration based on the extent of Cu solubility in the Cu 2x Hg 2-x GeTe 4 alloy compound (where 0 ≤ x ≤ 1) makes Cu 2x Hg 2-x GeTe 4 an interesting case study in the field of thermoelectrics. While Cu clearly plays a role in this process, it is unknown exactly how Cu incorporates into the Cu 2x Hg 2-x GeTe 4 crystal structure and how this affects the carrier concentration. In this work, we use a combination of resonant energy x-ray diffraction (REXD) experiments and density functional theory (DFT) calculations to elucidate the nature of Cu incorporation into the Cu 2x Hg 2-x GeTe 4 structure. REXD across the Cu k edge facilitates the characterization of Cu incorporation in the Cu 2x Hg 2-x GeTe 4 alloy and enables direct quantification of antisite defects. Here, we find that Cu substitutes for Hg at a 2:1 ratio, wherein Cu annihilates a vacancy and swaps with a Hg atom. DFT calculations confirm this result and further indicate that the incorporation of Cu occurs preferentially on one of the z = 1/4 or z = 3/4 planes before filling the other plane. Furthermore, the amount of Cu Hg antisite defects quantified by REXD was found to be directly proportional to the experimentally measured hole concentration, indicating that the Cu Hg defects are the driving force for tuning carrier concentration in the Cu 2x Hg 2-x GeTe 4 alloy. The link uncovered here between crystal structure, or more specifically antisite defects, and carrier concentration can be extended to similar cation-disordered material systems and will aid the development of improved thermoelectric and other functional materials through defect engineering.

36 MATERIALS SCIENCE↗

Conversion of CO 2 to Methanol and Ethanol on Pt/CeO x /TiO 2 (110): Enabling Role of Water in C–C Bond Formation

The surface chemistry of alcohol synthesis from CO 2 hydrogenation has been investigated using kinetic testing, ambient pressure x-ray photoelectron spectroscopy (AP-XPS) and DFT calculations over a multicomponent system where Pt and ceria nanoparticles coexisted on a titania template, Pt/CeO x /TiO 2 (110). Due to its high ability to bind and activate CO 2 , not seen for typical Cu-ZnO catalysts, the Pt-CeO x -TiO 2 interface is excellent for the hydrogenation of CO 2 to methanol with some ethanol also being produced (21% selectivity). The results of AP-XPS and DFT calculations indicate that the active state involves a mixture of Ti 4+ /Ti 3+ , Ce 3+ and Pt 0 /Pt + . A fast pathway for the formation of CH 3 O species is only plausible when Ce 3+ and Pt are present. The addition of water to the reaction feed facilitates the first hydrogenation of CO 2 and substantially enhances the surface coverage of C-containing species (CH 3 O, HCOO, CO 3 , CH x ), facilitating the formation of C-C bonds and the production of ethanol (38% selectivity).

36 MATERIALS SCIENCE↗

Bandgap Engineering of Ga 2 O 3 by MOCVD Through Alloying with Indium

Ga 2 O 3 and In 2 O 3 are vital semiconductors with current and future electronic device applications. Here, we study the alloying of In 2 O 3 and Ga 2 O 3 (IGO) and the associated changes in structure, morphology, band gap, and electrical transport properties. Undoped films of IGO were deposited on sapphire substrates with varying indium (In) percentage from zero to 100% by metal-organic chemical vapor deposition (MOCVD). Some films were annealed in H 2 to induce electrical conductivity. The measurements showed the optical band gap decreased by adding In; this was confirmed by density functional (DFT) calculations, which revealed that the nature of the valence band maximum and conduction band minimum strongly relate to the chemistry and that the band gap drops by adding In. The as-grown films were highly resistive except for pure In 2 O 3 , which possesses p-type conductivity, likely arising from In vacancy-related acceptor states. N-type conductivity was induced in all films after H-anneal. DFT calculations revealed that the presence of In decreases the electron effective mass, which is consistent with the electrical transport measurements that showed higher electron mobility for higher In percentage. The work revealed the successful band gap engineering of IGO and the modification of its band structure while maintaining high-quality films by MOCVD.

36 MATERIALS SCIENCE↗

Uncovering the linear boron environment in Na 3 BP 2 through solid-state 11 B NMR spectroscopy

Boron-based compounds exhibit a wide range of structural diversity, with potential applications spanning organic and inorganic chemistry. Herein, we focus on the characterization of the linear boron-phosphorus unit P═B═P in Na 3 BP 2 using solid-state nuclear magnetic resonance (ssNMR) spectroscopy and density functional theory (DFT) calculations. High-resolution 11 B ssNMR spectra were recorded at two fields, and key parameters such as chemical shift anisotropy (CSA), quadrupolar coupling constants (C Q ), and electric field gradient (EFG) tensors were extracted. The 11 B NMR results revealed a distinct chemical environment for the two-coordinate boron atom, with a CSA span (Ω) of 280 ppm and a C Q of 3.0 MHz. These values were further validated through periodic plane-wave DFT calculations, which showed good agreement with experimental results. The obtained spectral parameters are compared to other linear boron units, such as the BO 2 motif, providing a broader context for understanding boron coordination in inorganic compounds. This work expands the body of NMR knowledge on boron-containing materials, particularly for linear boron motifs. The findings contribute to the growing field of boron chemistry and its potential applications in advanced materials.

Porter, Andrew P. [Ames Laboratory (AMES), Ames, I↗

Observation of multiple flat bands and Van Hove singularities in the distorted kagome metal NdTi 3 Bi 4

Kagome materials have attracted enormous research interest recently owing to their diverse topological phases and manifestation of electronic correlation. Here, in this study, we present the electronic structure of a distorted ferromagnetic kagome metal, NdTi 3 ⁢Bi 4 , exhibiting a transition temperature of 9 K. Our investigation employs a combination of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations. We discover the presence of two “flat” bands which are found to originate from the kagome structure formed by Ti atoms with a major contribution from Ti 𝑑 𝑥⁢𝑦 and Ti 𝑑 𝑥 2 −𝑦 2 orbitals. We also observed multiple Van Hove singularities (VHSs) in its electronic structure, with one VHS lying near the Fermi level. The ARPES data reveal the existence of Dirac cone at the $\overline{𝐾}$ point, a finding which is corroborated by our DFT calculations. These findings present a detailed electronic structure capable of hosting correlation-driven phenomenon in this novel ferromagnetic kagome metal.

Fermi surface↗

Fathoming the anisotropic magnetoelasticity and magnetocaloric effect in GdNi

Intermetallic GdNi adopts a CrB type of crystal structure (space group Cmcm), and it orders ferromagnetically via a second-order phase transition at 70 K, exhibiting unusually strong spontaneous striction along the three independent crystallographic axes in the ferromagnetically ordered state. Here we introduce a microscopic model to describe anisotropic changes of lattice parameters and elastic contribution to magnetocaloric effect of GdNi. In the model, results of density functional theory (DFT) calculations are used as inputs into a Hamiltonian that includes elastic energy of an anisotropic crystal lattice, exchange interactions, and Zeeman effect. The magnetic and elastic Hamiltonians are coupled through an anisotropic Bean-Rodbell model of magnetoelastic interactions. This coupling gives rise to anisotropic changes in the lattice parameters observed experimentally, and the model reveals good to reasonable agreements between the current theoretical results and earlier experimental data, thus validating the model within the limits of assumptions made. We also show that DFT calculations with 4f electrons of Gd treated as core electrons lead to a more adequate estimate of elastic constants of GdNi in comparison with the LDA + U method where 4f electrons are treated as valence electrons.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Elucidation of Active Sites in Aldol Condensation of Acetone over Single-Facet Dominant Anatase TiO 2 (101) and (001) Catalysts

Aldol condensations of carbonyl compounds for C–C bond formation are a very important class of reactions in organic synthesis and upgrading of biomass-derived feedstocks. However, the atomic level understanding of reaction mechanisms and structure-activity correlation on widely used transition metal oxide catalysts are limited due to the high degree of struc-tural heterogeneity of catalysts such as commercial TiO 2 powders. Here, we provide a deep understanding of the reaction mechanisms, kinetics, and structure–function relationships for vapor phase acetone aldol condensation through the con-trolled synthesis of two catalysts with high surface areas and clean, dominant facets, coupled with detailed characterization and kinetic studies that are further assisted by density functional theory (DFT) calculations. Temperature-dependent diffuse reflectance infrared Fourier transform spectroscopy showed the existence of abundant acetone bonded to surface hydroxyl groups (acetone-O s H) and acetone bonded to Lewis acid sites (acetone-Ti 5c ) on surface of both {101} and {001} facet dom-inant TiO 2 . Intermolecular C–C coupling of enolate intermediate from acetone-Ti 5c and a vicinal acetone-O s H is a kinetically relevant step, which is consistent with kinetic and isotopic studies and DFT calculations. The {001} facet showed a lower apparent activation energy (or higher reactivity) than the {101} facet. This is likely caused by the weaker Lewis acid and Brønsted base strengths of the {001} facet which favors the reprotonation–desorption of the coupled intermediate, making the C–C coupling step more exothermic on the {001} facet and resulting in an earlier transition state with a lower activation barrier. It is also possible that the {001} facet has a smoother surface configuration and less steric hindrance during intermo-lecular C–C bond formation than the {101} facet.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

CO 2 -assisted ethane aromatization over zinc and phosphorous modified ZSM-5 catalysts

The tandem reactions of CO 2 -assisted oxidative dehydrogenation and aromatization (CO 2 -ODA) of ethane were investigated over ZSM-5 modified with zinc (Zn) and phosphorus (P) by experimental studies and DFT calculations. The nature of active Zn species and their interaction with P were elucidated for understanding Zn/P-ZSM-5 catalyzed CO 2 -ODA reaction of ethane. Compared to the direct dehydrogenation and aromatization (DDA) reaction, the Zn/P-ZSM-5 catalyst possessed higher ethane conversion, enhanced aromatics yield, and better stability in the CO 2 -ODA reaction. Here, the presence of CO 2 reduced the carbon deposition, stabilized the Zn species, and thereby facilitated the generation of more liquid aromatics in CO 2 -assisted ethane aromatization. In situ characterization and DFT calculations provided insight into the mechanisms of CO 2 -ODA over the Zn/P-ZSM-5 catalyst.

36 MATERIALS SCIENCE↗

Spin-informed universal graph neural networks for simulating magnetic ordering

The screening and discovery of magnetic materials are hindered by the computational cost of first-principles density-functional theory (DFT) calculations required to find the ground state magnetic ordering. Although universal machine-learning interatomic potentials (uMLIPs), also known as atomistic foundation models, offer high-fidelity models of many atomistic systems with significant speedup, they currently lack the inputs required for predicting magnetic ordering. In this work, we present a data-efficient, spin-informed graph neural network framework that incorporates spin degrees of freedom as inputs and preserves physical symmetries, extending the functionality of uMLIPs to simulate magnetic orderings. This framework speeds up DFT calculations through better initial guesses for magnetic moments, determines the ground-state ordering of bulk materials and even generalizes to magnetic ordering in surfaces. Furthermore, we implement a closed-loop anomaly detection approach that effectively addresses the classic "chicken-and-egg" problem of creating a high-quality dataset while developing a uMLIP, unearthing anomalies in large benchmark datasets and boosting model accuracy.

Xu, Wenbin↗

Molecular Level Understanding of Polyethylene Terephthalate (PET) Depolymerization in Base/Alcohol Hybrid Systems

Polyethylene terephthalate (PET) depolymerization in base/alcohol hybrid systems represents a promising low-energy approach for chemically recycling PET waste into valuable monomers. This study investigates the mechanistic pathways of PET depolymerization in NaOH/alcohol solutions, emphasizing the competing roles of hydroxide and alkoxide species. Utilizing a combination of experimental techniques, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations, we explore how factors such as base concentration, alcohol chain length, and pKa values of alcohols influence PET depolymerization efficiency and pathways. Our findings indicate that alkoxide ions (RO⁻) exhibit notably higher reactivity than hydroxide ions (HO⁻), favoring an alcoholysis pathway in the base/alcohol hybrid system. Experimental results across a series of C1 to C5 alcohols show that longer-chain alcohols, particularly 1-butanol, achieve higher PET conversion, although this does not align solely with simple nucleophilicity trends of alkoxides. While DFT calculations reveal comparable activation energies for various alkoxides in PET depolymerization, MD simulations underscore the significant role of alcohol chain length, with longer-chain alcohols forming more stable or frequent interactions with PET. Additionally, the alkoxide concentration, influenced by the alcohol’s pK a , directly impacts PET conversion. These suggest that PET depolymerization is governed by a balance between alkoxide concentration and alkoxide-PET interactions, rather than activation energies or nucleophilicity alone. From a practical perspective, incorporating long-chain alcohols as cosolvents may enhance process efficiency but increases raw material costs by approximately 30%. However, long-chain alcohols present a safer and more sustainable alternative to hazardous cosolvents such as dichloromethane. This work offers a molecular-level understanding of PET depolymerization in base/alcohol systems and provides insights into optimizing these systems for more efficient and sustainable PET recycling processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Hydrogen desorption from the surface and subsurface of cobalt

The influence of coverage on the diffusion of hydrogen into the subsurface of cobalt was studied using density functional theory (DFT) and temperature programmed desorption (TPD). DFT calculations show that as the hydrogen coverage on Co(0001) increases, the barrier for hydrogen diffusion into the bulk decreases by 20%. Additionally, subsurface hydrogen on a hydrogen covered surface was found to be more stable when compared to a clean cobalt surface. To test these theoretical findings experimentally, excited hydrogen was used in an ultra-high vacuum environment to access higher hydrogen coverages. Here, our TPD studies showed that at high hydrogen coverages, a sharp low temperature feature appeared, indicating the stabilization of subsurface hydrogen. Further DFT calculations indicate that this sharp low temperature feature results from associative hydrogen desorption from a hydrogen saturated surface with a population of subsurface hydrogen. Microkinetic modelling was used to model the TPD spectra for hydrogen desporption from cobalt with and without subsurface hydrogen, showing reasonable agreement with experiment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

High-pressure structural behavior and elastic properties of U3Si5: A combined synchrotron XRD and DFT study

We present an integrated experimental and theoretical study of the structural behavior of U 3 Si 5 at highpressure conditions using angle-dispersive synchrotron X-ray diffraction (XRD) in a diamond anvil cell (DAC) and density functional theory (DFT) calculations. On increasing pressure, the ambient hexagonal structure of U 3 Si 5 with space group P6/mmm remains stable up to 16.7 GPa, the maximum pressure tested with DAC. The bulk modulus and the a- and c-axial moduli of U 3 Si 5 were experimentally determined to be 126 ± 4 GPa, 173 ± 8 GPa and 79.7 ± 4.3 GPa, respectively. Thus an anisotropy in the axial compressibility of U 3 Si 5 is observed with its c-axis being more compressible than the a-axis. Our DFT calculation results are in general agreement with the experimental values, including reproducing the compressibility anisotropy. A comparison of the bulk modulus of U 3 Si 5 to those of other U-Si compounds reveals a general trend that the bulk modulus of U-Si decreases with increasing U/(U+Si) ratio.

36 MATERIALS SCIENCE↗

Hourglass-type bulk Ni 3 d band and Ce 4 f Kondo resonance states in the potential topological Kondo semimetal CeNiSn via angle-resolved photoemission spectroscopy

The electronic structure of CeNiSn, which is a potential topological Kondo insulator and a Dirac nodal-loop semimetal, has been investigated by employing temperature (T) dependent angle-resolved photoemission spectroscopy (ARPES). The Fermi surfaces (FSs) and the band structures of CeNiSn for three orthogonal crystallographic planes are measured, in which both the very dispersive bands and the flat bands are observed, having mainly the Ni 3d character and the Ce 4f character, respectively. The measured FSs and ARPES bands agree reasonably well with the density functional theory (DFT) calculations. The Fermi-edge (E F ) photon energy (hν) map along k b (=k (010) ) shows that the metallic E F -crossing states on the (010) surface have the three-dimensional character, suggesting that the observed E F -crossing metallic states do not correspond to the topological surface states of the two-dimensional character. On the other hand, albeit weak, the features of the hourglass-type bulk band crossings are observed along SXS, with the energies and the slopes being similar to those predicted by the DFT calculations, supporting the Dirac semimetallic nature of CeNiSn. In T-dependent ARPES, the Ce 4f Kondo resonance states are clearly revealed at low T, which become much suppressed above ~80 K. This feature is consistent with the Kondo temperature of CeNiSn, estimated from its ρ(T) data. This work demonstrates the importance of the coherent Kondo states in determining the topological properties of CeNiSn.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

In silico discovery of active, stable, CO-tolerant and cost-effective electrocatalysts for hydrogen evolution and oxidation

Various databases of density functional theory (DFT) calculations for materials and adsorption properties are currently available. Using the Materials Project and GASpy databases of material stability and binding energies (H* and CO*), respectively, we evaluate multiple aspects of catalysts to discover active, stable, CO-tolerant, and cost-effective hydrogen evolution and oxidation catalysts. Finally, we suggest a few candidate materials for future experimental validations. We highlight that the stability analysis is easily obtainable but provides invaluable information to assess thermodynamic and electrochemical stability, bridging the gap between simulations and experiments. Furthermore, it reduces the number of expensive DFT calculations required to predict catalytic activities of surfaces by filtering out unstable materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Anion Vacancies Coupling with Heterostructures Enable Advanced Aerogel Cathode for Ultrafast Aqueous Zinc‐Ion Storage

As a potential cathode material, manganese-based sulfide has recently attracted increasing interest due to its many advantages in aqueous zinc-ion storage. Unfortunately, some challenges such as sluggish kinetics, unstable structure, and controversial phase transition mechanism during the energy storage process hinder its practical application. Herein, inspired by density functional theory (DFT) calculations, a novel 3D sulfur vacancy-rich and heterostructured MnS/MXene aerogel is designed, and used as a cathode for aqueous Zn-ion batteries/hybrid capacitors (ZIBs/ZICs) for the first time. Thanks to the synergistic modification strategy of sulfur vacancies and heterostructures, the as-constructed MnS/MXene//Zn ZIBs exhibit significantly enhanced electrochemical properties, especially outstanding rate capability and cyclic stability. More encouragingly, the as-assembled MnS/MXene//porous carbon (PC) ZICs exhibit an ultrahigh energy density, a high power density, and a splendid cycling lifespan. Most notably, systematic kinetic analyses, ex situ characterizations, and DFT calculations illustrate that MnS/MXene first irreversibly converts into MnO x @ZnMnO 3 /MXene, and then undergoes a reversible conversion from MnO x @ZnMnO 3 /MXene to MnOOH@ZnMn 2 O 4 /MXene, accompanied by the co-insertion/extraction of H + and Zn 2+ . Further, the synergistic modification strategy of sulfur vacancies and heterostructures and the thorough mechanistic study proposed in this work offer valuable guidance for designing and exploiting high-performance cathodes in aqueous zinc-based energy storage devices.

25 ENERGY STORAGE↗

Long-Lived Excited State in a Solubilized Graphene Nanoribbon

Graphene nanoribbons have excellent light-absorbing properties, but often exhibit short excited-state lifetimes that prevent their applications in photocatalysis. Here, we report a long-lived charge-transfer triplet excited state in a well solubilized, chlorinated graphene nanoribbon (Cl-GNR) with edges modified by bipyrimidine (bpm) moieties. The photophysical behavior of Cl-GNR was observed and characterized by steady-state UV-vis absorption and emission spectroscopy, transient absorption spectroscopy on the ps-ms timescale, and density functional theory (DFT) calculations. In this work, both the Cl-GNR and its monomeric subunit, chlorinated graphene quantum dot (Cl-GQD), were synthesized using bottom-up techniques to produce the H- analogs of the compounds followed by edge-chlorination to achieve soluble products. The absorption spectra of Cl-GQD and Cl-GNR appear in the UV-vis range with lowest-energy peaks at 375 and 600 nm, respectively. The excitons in Cl-GNR were found to exhibit charge-transfer character with the bpm edges serving as electron acceptors. DFT calculations indicate that the excitons are relatively localized, spreading over at most two monomeric units of the GNR. Transient absorption spectroscopy shows that singlet excited states of Cl-GQD and Cl-GNR undergo intersystem crossing with ~300 ps lifetime to form triplet states that last for 15.7 μs (Cl-GQD) and 106 μs (Cl-GNR). These properties, combined with the ability of the bpm sites to coordinate transition metals, make Cl-GNRs promising light-harvesting motifs for photocatalytic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗