Conducted Density Functional Theory Calculations Research Articles

Tailoring hydrogen storage performance in γ-graphyne through valence band modulation of adsorbed Li via doping and strain

Hydrogen storage is indeed fundamental to utilizing H2 effectively, and porous carbon materials have emerged as highly promising supports for this purpose. γ-Graphyne (γGy) possesses abundant chemical bonds, considerable porosity, and exceptional chemical stability, positioning it as a promising candidate for hydrogen storage and transport applications. In this study, we conducted density functional theory calculations to investigate the potential of Li- and Na-loaded γGy as hydrogen storage materials. Our findings reveal that the hydrogen storage capacity (HSC) of Na-loaded γGy falls significantly short of expectations, whereas Li-loaded γGy demonstrates a notably higher HSC. Subsequently, our calculations indicate that B-doping of γGy does not promote favorable HSC, whereas N-doping exhibits a beneficial effect. Furthermore, we observed that tensile strain favors the hydrogen storage properties of 4Li@γGy and 4Li@N-γGy, while compressive strain enhances the hydrogen storage characteristics of 4Li@B-γGy. Notably, we discovered the capacity to adjust the valence band center of Li (ɛVB), consequently influencing the hydrogen storage performance of γGy. Our investigation suggests that increased overlap between ɛVB in Li-loaded graphyne and the effective alignment of H2 and the supporting structure augments the binding force between Li and H2, thereby amplifying the HSC.

Efficient crystal structure materials as reactive sorbent for the CO2 and CH4 adsorption and storage

The efficient dirubidium cobalt bis(dihydrogendiphosphate) dihydrate compound is successfully synthesized in a solution and used as a reactive sorbent for the CO2 and CH4 gases adsorption and storage. A crystal of this Rb2Co(H2P2O7)2·2H2O compound has been isolated and characterized by single X-ray diffraction analysis and was found to crystallize in the triclinic system (P1¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P\\overline{1}$$\\end{document}) with the cell parameters (Å): 6.980(1), 7.370(1), 7.816(1), 81.74(1), 70.35(1), 86.34(1); V = 374.68(9) Å3, Z = 2. The crystal-packing consists of a three-dimensional framework made upon corners and edges sharing of [RbO7], [H2P2O7] and [CoO6] entities, furthermore linked by a network of H-bonds. The UV–Vis spectroscopy revealed usual transitions between the ground state 4T1g and the upper levels 4T2g, 4A2g and 4T1g (P). Moreover, the CO2 and CH4 gases sorption measurements were successfully performed at two different temperatures (25 and 45 °C) and various pressures ranging from vacuum to 50 bar. Our results show that rate of CO2 and CH4 capturing was 3.10 mmol/g and 2.35 mmol/g at temperature 25 °C and pressure 50 bar, respectively. This compound showed a clear potential for CO2/CH4 adsorption and storage thereby paving the way towards its exploration and adaptation for capturing and collecting carbon dioxide and greenhouse gases from the air, and their conversion into hydrocarbon fuels using existing mature technologies. We have also conducted density functional theory calculations to study the CO2 and CH4 adsorption properties of Rb2Co(H2P2O7)2·2H2O. The simulation results show enhanced adsorption of both types of molecules on the surface of the material.

Electrochemical Conversion of High Pressure CO2

The electrochemical reduction of carbon dioxide (CO2R) via an electrochemical process is a strategic approach aimed at completing the carbon cycle for chemical production. Traditionally, this field has predominantly focused on conducting electrolysis on CO2 under standard atmospheric pressure. However, in industrial applications, CO2 is typically pressurized during its capture, transportation, and storage, often existing in a dissolved state. Our research has unveiled a significant discovery: subjecting aqueous CO2 to a pressure of 50 bar alters the CO2R pathways, favoring the formation of formate. This phenomenon is consistently observed across commonly used CO2R catalysts. Through the development of effective techniques for operating under high pressures, including a measurable Raman spectroscopy approach during the ongoing reaction, we have established a connection between the increased preference for formate and the heightened coverage of CO2 on the cathode surface. This collaboration between theoretical models and experimental data strongly supports this mechanism and has led us to enhance the cathode surface of a copper electrode with a proton-resistant layer. This innovation amplifies the selective impact caused by pressure. Furthermore, our research has unveiled the potential to transform gas-phase high-pressure CO2 into ethylene (C2H4) through CO2R. We conducted density functional theory calculations to identify a range of copper alloys that promote C-C dimerization under high pressure, which represents the rate-limiting step for C2H4 production. The theoretical predictions were validated through a combination of electrochemical measurements and operando observations, guiding us in designing a copper-based catalyst for efficient and active conversion of CO2 to C2H4.

A stable and conductive phthalocyanine-porphyrin two-dimensional carbon-rich conjugation frameworks for highly selective electroreduction of carbon dioxide to dimethyl carbonate

Electrocatalytic reduction of carbon dioxide (CO2RR) to long-chain chemicals, such as dimethyl carbonate (DMC), is considered an effective strategy for addressing excessive CO2 emissions. However, the underlying reaction mechanism remains unclear. In this work, based on phthalocyanine-porphyrin 2D CCFs, a tandem catalyst composed of Fe and other transition metals (TMs) co-embedded in rectangular extended Pc and TM-embedded in porphyrins is proposed. Among various catalysts, the Fe-Sc-Pc-Co-TPP-CCF catalyst stands out due to its unique catalytic sites that can efficiently convert both C1 and C2 intermediates simultaneously. This catalyst exhibits superior CO2 adsorption capacity and excellent catalytic activity, which can be attributed to the ability of the d orbitals of both Fe and TMs to accept lone pairs and feedback electrons from CO2. Additionally, the synergistic effect between the two different metals enhances the adsorption and activation of CO2 molecules. The detailed process of CO2 reduction to DMC on the Fe-Sc-Pc-Co-TPP-CCF catalyst was systematically investigated, and it was identified that the direct coupling of CO2 and methanol to form DMC is the optimal pathway. To evaluate the catalytic performance of the catalyst, we conducted density functional theory calculations. The results show that the Fe-Sc-Pc-Co-TPP-CCF catalyst exhibits an inhibitory effect on competing reactions of CO2RR, such as proton-coupling reaction and HER. Combined with DFT calculations, the reaction mechanism at the phthalocyanine-porphyrin 2D CCFs was systematically studied, providing novel insights into the potential pathway for the chemical conversion of CO2 into long-chain chemicals.

First principles analysis on void-reduction mechanism and impact of oxygen in nitrogen-doped CZ-Si crystal

During silicon (Si) crystal growth with the Czochralski method, nitrogen (N) doping at a concentration of about 1013–1015 atoms/cm3 decreases the size of void defects. This is related to the trapping of vacancies (Vs) by N atoms. The effect by N-doping is weakened with an increase in oxygen (O) concentration. The stable structures and formation processes of N-V and N-O-V complexes were investigated systematically by conducting density functional theory calculations, and the void-reduction mechanism by N-doping and the impact of O atoms were clarified. The results indicate that two interstitial N atoms form N2 which reacts with Vs to change its structure to N2-V and N2-V2. The dissociation of a V from stable N-V complexes requires a large amount of energy. Furthermore, the stabilized O atoms around the N atoms in N-O-V complexes restrict the movement of Si atoms. The energy required for a V to dissociate from N-O-V complexes is reduced, resulting in an increase in the number of free Vs. This is the reason O atoms weaken the void-reduction effect by N-doping.

Unusual High Hardness and Load-Dependent Mechanical Characteristics of Hydrogenated Carbon-Nitrogen Hybrid Films.

Mechanical components are exposed to a rigorous environment in a number of applications including engineering, aerospace, and automobiles. Thus, their service lifetime and reliability are always on the verge of risk. Protective coatings with high hardness are required to enhance their service lifetime and minimize the replacement cost and waste burden. Hydrogenated amorphous carbon including nitrogen-incorporated films, that are commonly deposited by plasma-enhanced chemical vapor deposition, are widely used for commercial protective coating applications. However, their mechanical hardness still falls into the moderate hard regime. This needs to be substantially enhanced for advanced applications. Here, we report the synthesis of very hard nanostructured hydrogenated carbon-nitrogen hybrid (n-C:H:N) films. The optimized n-C:H:N film displays a hardness of about 36 GPa, elastic modulus of 360 GPa, and reasonably good elastic recovery (ER) of 62.7%. The mechanical properties of n-C:H:N films are further tailored when nitrogen pressure is tuned during the growth. The realized remarkably improved mechanical properties are correlated with the films' structural properties and experimental growth conditions. We also conducted density functional theory calculations that show the trend for the elastic modulus of the amorphous carbon films with varying nitrogen concentrations matches well with experimentally measured values. Finally, we probed load-dependent mechanical properties of n-C:H:N films and found an anomalous behavior; some of the mechanical parameters, for instance, ER, reveal an irregular trend with indentation load, which we explain in the framework of the film-substrate composite concept. Overall, this work uncovers many unknown and exciting mechanical phenomena that could pave the way for new technological developments.

Structure sensitivity of ceria-supported Au catalysts for CO oxidation

Single-atom catalysis is at the center of the attention of the heterogeneous catalysis community. It remains a challenge to determine the thermodynamic stability of single atoms on an oxide support and compare their activity to that of small clusters and nanoparticles. We conducted density functional theory calculations to compare the stability of Au(CO) complexes on the CeO2(111) terrace and step-edge of CeO2(111) against CeO2(111)-supported nanoparticles. The different single atom Au and Au cluster models were compared for CO oxidation at low temperature. Trapped as dopants substituting for Ce in the surface or in a ceria O vacancy, Au cannot catalyze CO oxidation. Single Au atoms at step-edges represent candidate active sites for low-temperature CO oxidation. The CO oxidation at the interface between Au nanoparticles and CeO2 can directly take place through a Mars-van Krevelen mechanism and account for a promising reactivity when the dislodgment of Au(CO) complex is hindered. The possibility of CO-induced dislodgement of a single Au atom depends critically on the topology of the Au-CeO2 interface.

Solution-Phase Synthesis of PdH0.706 Nanocubes with Enhanced Stability and Activity toward Formic Acid Oxidation.

Palladium is one of the few metals capable of forming hydrides, with the catalytic properties being dependent on the elemental composition and spatial distribution of H atoms in the lattice. Herein, we report a facile method for the complete transformation of Pd nanocubes into a stable phase made of PdH0.706 by treating them with aqueous hydrazine at a concentration as low as 9.2 mM. Using formic acid oxidation (FAO) as a model reaction, we systematically investigated the structure-catalytic property relationship of the resultant nanocubes with different degrees of hydride formation. The current density at 0.4 V was enhanced by four times when the nanocubes were completely converted from Pd to PdH0.706. On the basis of a set of slab models with PdH(100) overlayers on Pd(100), we conducted density functional theory calculations to demonstrate that the degree of hybrid formation could influence both the activity and selectivity toward FAO by modulating the relative stability of formate (HCOO) and carboxyl (COOH) intermediates. This work provides a viable strategy for augmenting the performance of Pd-based catalysts toward various reactions without altering the loading of this scarce metal.

Molecular dynamics study of the penetration resistance of multilayer polymer/ceramic nanocomposites under supersonic projectile impacts

We simulated ballistic impact tests of multilayer polyurea/silicon-carbide (SiC) nanostructures using molecular dynamics (MD). First, we conducted density functional theory calculations to obtain accurate parameters to model the nonbonded interactions of the polyurea/SiC interface and subsequently investigated the influence of interfacial adhesion on the impact response. Our MD simulations demonstrate that the ballistic limit velocity and the specific penetration energy of the polyurea/SiC multilayers are significantly higher than the experimentally measured values of other protective materials. Moreover, we demonstrated that the specific penetration energy of a nanoscale target with a given material composition can be remarkably improved (over 75%) by optimizing the individual layer thickness and their arrangement within the target. Our results reveal a potential bottom-up design pathway for developing superior protective materials for extreme engineering applications.

Structures and reactivities of the CeO2/Pt(111) reverse catalyst: A DFT+U study

AbstractFor heterogeneous catalysts, the build-up of interface contacts can influence markedly their activities. Being different from the conventional supported metal/oxide catalysts, the reverse type of oxide/metal structures, e.g. the ceria/Pt composite, have emerged as novel catalytic materials in many fields. However, it remains challenging to determine the optimal interface structure and/or the metal-oxide synergistic effect that can boost catalytic activities. In this work, we conducted density functional theory calculations with on-site Coulomb interaction correction to determine the optimal structures and investigate the physical as well as catalytic properties of various CeO2/Pt(111) composites containing CeO2(111) monolayer, bilayer, and trilayer at Pt(111). We found that the interaction strength between CeO2(111) and Pt(111) substrate first reduces as the ceria slab grows from monolayer to bilayer, and then largely gets converged when the trilayer occurs. Such trend was well rationalized by analyzing the number and distances of O–Pt bonds at the interface. Calculated Bader charges uncovered the significant charge redistribution occurring around the interface, whereas the net electron transfer across the interface is non-significant and decreases as ceria thickness increases. Moreover, comparative calculations on oxygen vacancy formation energies clarified that oxygen removal can be promoted on the CeO2/Pt(111) composites, especially at the interface. We finally employed CO oxidation as a model reaction to probe the surface reactivity, and determined an intrinsic activity order of monolayer CeO2(111) > monolayer CeO2(111)/Pt(111) > regular CeO2(111). More importantly, we emphasized the significant role of the moderate ceria-Pt interaction at the interface that endows the CeO2/Pt reverse catalyst both good thermostability and high catalytic activity. The monolayer CeO2(111)/Pt(111) composite was theoretically predicted highly efficient for catalyzing CO oxidation.

Resistivity, Seebeck coefficient, and thermal conductivity of platinum at high pressure and temperature

Platinum (Pt) is one of the most widely used functional materials for high-pressure and high-temperature experiments. Despite the crucial importance of its transport properties, both experimental and theoretical studies are very limited. In this study, we conducted density functional theory calculations on the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of solid face-centered cubic Pt at pressures up to 200 GPa and temperatures up to 4800 K by using the Kubo-Greenwood formula. The thermal lattice displacements were treated within the alloy analogy, which is represented by means of the Korringa-Kohn-Rostoker method with the coherent potential approximation. The electrical resistivity decreases with pressure and increases with temperature. These two conflicting effects yield a constant resistivity of similar to 70 mu Omega cm along the melting curve. Both pressure and temperature effects enhance the thermal conductivity at low temperatures, but the temperature effect becomes weaker at high temperatures. Although the pressure dependence of the Seebeck coefficient is negligibly small at temperatures below similar to 1500 K, it becomes larger at higher temperatures. It requires a calibration of a thermocouple such as Pt-Rh in high-pressure and -temperature experiments.

The investigation of 2D monolayers as potential chelation agents in Alzheimer’s disease

In this study, we conducted density functional theory calculations comparing the binding energy of the copper-amyloid-β complex to the binding energies of potential chelation materials. We used the first-coordination sphere of the truncated high-pH amyloid-β protein subject to computational limits. Binding energy and charge transfer calculations were evaluated for copper’s interaction with potential chelators: monolayer boron nitride, monolayer molybdenum disulfide, and monolayer silicene. Silicene produced the highest binding energies to copper, and the evidence of charge transfer between copper and the monolayer proves that a strong ionic bond is present. Although our three monolayers did not directly present chelation potential, the absolute differences between the binding energies of the silicene binding sites and the amyloid-β binding sites were minimal, proving that further research in silicene chelators may be useful for therapy in Alzheimer’s disease.

Experimental and Theoretical Elucidation of Electrochemical CO2 Reduction on an Electrodeposited Cu3Sn Alloy

The reaction selectivity of an electrode catalyst can be modulated by regulating its crystal structure, and the modified electrode may show different CO2 reduction selectivity from that of its constituent metal. In this study, we investigated the mechanisms of the electrochemical CO2 reduction on an electrodeposited Cu3Sn alloy by experimental and theoretical analyses. The electrodeposited Cu3Sn alloy electrode showed selectivity for CO production at all the applied potentials, and HCOOH production increased with an increase in the applied potential. In particular, hydrocarbon generation was well suppressed on Cu3Sn(002). To understand this selectivity change in electrochemical CO2 reduction, we conducted density functional theory calculations for the reaction on the Cu3Sn(002) surface. According to the theoretical analysis, the Cu sites in Cu3Sn(002) contributed more to the stabilization of H*, COOH*, and CO* as compared with the Sn sites. Furthermore, the results indicated that Cu3Sn(002) decreased the ...

Millimeter-Scale Single-Crystalline Semiconducting MoTe2 via Solid-to-Solid Phase Transformation.

Among the Mo- and W-based two-dimensional (2D) transition metal dichalcogenides, MoTe2 is particularly interesting for phase-engineering applications, because it has the smallest free energy difference between the semiconducting 2H phase and metallic 1T' phase. In this work, we reveal that, under the proper circumstance, Mo and Te atoms can rearrange themselves to transform from a polycrystalline 1T' phase into a single-crystalline 2H phase in a large scale. We manifest the mechanisms of the solid-to-solid transformation by conducting density functional theory calculations, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The phase transformation is well described by the time-temperature-transformation diagram. By optimizing the kinetic rates of nucleation and crystal growth, we have synthesized a single-crystalline 2H-MoTe2 domain with a diameter of 2.34 mm, a centimeter-scale 2H-MoTe2 thin film with a domain size up to several hundred micrometers, and a seamless 1T'-2H MoTe2 coplanar homojunction. The 1T'-2H MoTe2 homojunction provides an elegant solution for ohmic contact of 2D semiconductors. The controlled solid-to-solid phase transformation in 2D limit provides a new route to realize wafer-scale single-crystalline 2D semiconductor and coplanar heterostructure for 2D circuitry.

First-principles calculations of interaction between solutes and dislocations in tungsten

Changes in mechanical properties due to transmutation products (Re and Os) in W alloys is a central issue for plasma-facing materials in fusion reactors. We conducted density functional theory calculations to investigate the effect of Re, Os, and other 5d solutes on core structure and motion of screw dislocations associated with plastic deformation. Ir, Pt, Au, and Hg solutes show strong attractive interactions with screw dislocations, causing solution strengthening by the pinning mechanism. On the other hand, Hf, Ta, and Re cause softening by facilitating dislocation motion around solutes. This prediction corresponds well with the experimental observation of softening behavior in W-Re alloys.

Adsorption properties of AlN on Si(111) surface: A density functional study

In the process of preparing GaN on Si substrate by MOCVD, an AlN buffer layer is very important. In this study, we conducted density functional theory calculations on the adsorption of AlN molecule on Si(111)-(2 × 2) surface, with the AlN molecule located horizontally or vertically above Si(111) surface at different adsorption sites. The calculations revealed that the lowest adsorption energy was at the N-top-Al-bridge site in the horizontal configuration, with the narrowest band gap, indicating that it was the most preferential adsorption growth status of AlN. In the vertical configurations, N adatom was more reactive and convenient to form bonds with the topmost Si atoms than Al adatom. When the N-end of the AlN molecule was located downward, the hollow site was the preferred adsorption site; when the Al-end was located downward, the bridge site was the most energetically favorable. Moreover, we investigated some electronic properties such as partial density of states, electron density difference, Mulliken populations, etc., revealing the microscale mechanism for AlN adsorption on Si(111) surface and providing theoretical support for adjusting the processing parameters during AlN or GaN production.

Development of hydrophilicity on the proton exchange using sulfonic acid on PEEK in the presence of water: a density functional theory study

The introduction of a protogenic group such as sulfonic acid enables the operation of polymer electrolyte membrane for fuel cells at intermediate temperatures (> 100 °C) and very low humidity. It has been reported that the addition of a strongly acidic sulfonic acid group to hydrophobic polyether ether ketone (PEEK) creates the water permeability and proton transfer. In order to understand how sulfonic acid develops hydrophilicity, we conducted density functional theory calculations to determine the adsorption affinity of water for sulfonated PEEK (SPEEK), which represents the binding energy and band gap between HOMO (highest occupied molecular orbital) of SPEEK and LUMO (lowest unoccupied molecular orbital) of water molecules. Moreover, we designed disulfonated PEEKs (DSPEEK) with cis- and trans-conformations and found that cis-DSPEEK exhibits higher adsorption affinity for water with strong hydrogen bonds. This is attributed to the narrow energy gap of water molecules on cis-DSPEEK. Furthermore, we investigated proton adsorption in the presence of water to determine the effect of hydrophilic environment on the proton exchange in SPEEK. We found that cis-DSPEEK shows high repulsion for hydrogen transfer and moderate adsorption affinity for protons. Theoretical findings confirm that sulfonation ultimately yields hydrophilicity and developed proton transfer ability for PEEK, leading to a suitable structure for preferable proton exchange membrane.

Peptide Release on the Ribosome Involves Substrate-Assisted Base Catalysis

Termination of protein synthesis on the ribosome involves hydrolysis of the ester bond between the P-site tRNA and the nascent peptide chain. This reaction occurs in the peptidyl transferase center and is triggered by the class I release factors RF1 and RF2 in prokaryotes. Peptidyl-tRNA hydrolysis is pH-dependent, and experimental results suggest that an ionizable group with pKa > 9 is involved in the reaction. The nature of this group is, however, unknown. To resolve this problem, we conducted density functional theory calculations using a large cluster model of the peptidyl transferase center. Our calculations reveal that peptidyl-tRNA hydrolysis occurs via a base-catalyzed mechanism with a predicted activation energy of 15.8 kcal mol–1, which is in good agreement with experimental data. In this mechanism, the P-site A76 2′-OH group is deprotonated and acts as the general base by activating the nucleophilic water molecule. The energy cost of deprotonating the 2′-hydroxyl group at pH 7.5 is estimated to ...

The Effect of Solvation on the Radiation Damage Rate Constants for Adenine.

It is well known that water plays an important part in almost all biological systems and that inclusion of solvation effects might therefore be of utmost importance in studies of radiation damage to DNA. In the present investigation, we have studied the effect of different solvation models in calculations of Gibbs free energies and reaction rates for the reaction between the OH radical and the DNA nucleobase adenine by conducting density functional theory calculations at the ωB97X-D/6-311++G(2df,2pd) level with the Eckart tunnelling correction. The solvent, water, was included through either the implicit polarizable continuum model (PCM) or through explicit modelling of micro-solvation by a single water molecule at the site of reaction as well as by the combination of both. Scrutiny of the thermodynamics and kinetics of the individual sub-reactions suggests that the qualitative differences introduced by the solvation models do not significantly alter the conclusions made based solely on simple gas-phase calculations. Abstraction of the amine hydrogen atoms H61 and H62 and addition onto C8 remain the most likely reaction pathways.

The Al(I) molecule, Ph2COAl and its anion

We have formed the Al(I)-containing molecule, benzophenone-aluminum, i.e., Ph2COAl, and studied it by conducting density functional theory calculations on both its neutral and anionic forms and by measuring the photoelectron spectrum of its anion. Our calculations identified two nearly iso-energetic anion isomers, (Ph2COAl)−, the vertical detachment energies (VDE) of which are in excellent agreement with our photoelectron spectrum. Natural population analysis (NPA) of Ph2COAl found the Al moiety to be positively charged by +0.81 e, indicating a strongly ionic bond between Al and Ph2CO, i.e., Ph2CO−Al+.