Detailed Density Functional Theory Research Articles

Experimental and theoretical studies on cobalt ruthenium phosphate structure optimization towards supercapacitor application

Recent studies have given indications that nanoarchitectured binary transition metal phosphates can act as potential supercapacitor (SC) electrode materials due to their exceptional energy storage capacity and remarkable electrochemical stability. However, the highly amorphous nature or broad X-ray diffraction peaks of metal phosphates put a limit on the structural optimization of these materials. We demonstrate a combined experimental and theoretical study leading to an optimized cobalt-ruthenium phosphate (CRP) structure for high-performance SC application. The material structure was optimized by detailed density functional theory (DFT) calculations, including the Bader charge analysis, DOS, and PDOS, revealed the lattice and volume expansion, reduced band gap, and improved conductivity of the cobalt phosphate lattice by including ruthenium in the cobalt phosphate. These predictions are verified with experimental band gap and high-resolution transmission electron microscope plane image indexing. Further, the CRP was developed by potentiostatic deposition onto the carbon cloth substrate. The flexible CRP electrode exhibited a high specific capacitance of 1258 F g−1 (943.5C g−1) in the aqueous 2 M KOH electrolyte. The asymmetric SC device (CRP//activated carbon) has exhibited an excellent specific energy of ∼59 Wh kg−1 at a specific power of ∼751 W kg−1.

Density Functional Theory Investigation of Intermolecular Interactions for Hydrogen-Bonded Deep Eutectic Solvents

Examining the interplay between choline chloride (ChCl) and ethylene glycol (EG) in Deep Eutectic Solvents (DES) assumes a pivotal role in designing innovative solvents. According to the literature, the comprehensive analysis of all possible types of conformers of ChCl and EG-based DES was scarce at different ratios, highlighting a gap in understanding at the atomistic level. In this study, we address this gap through a detailed Density Functional Theory calculation with dispersion correction (DFT+D3). Employing Density Functional Theory (DFT) calculations, our investigation delves into intermolecular relationships within DES, particularly focusing on ChCl and EG-based DES. DFT outcomes highlight the 1:2 ChCl to EG based DES ratio as notably more stable than alternative conformers. Key interactions within this DES conformation include: i) choline-chloride charge centers, ii) choline-EG links, and iii) EG-chloride anion associations. These findings provide valuable insights for crafting advanced solvents with tailored attributes. The intricate intermolecular interplay demonstrated here offers a versatile framework for harnessing DES potential across various domains, from chemical engineering to sustainable technologies.

Tailoring a MOF‐based adsorbent with partitioned aliphatic pore spaces for efficient CH4 purification from natural gas

AbstractSeparation of CH4 from natural gas is an essential but extremely challenging process in the petrochemical industry. Here, we tailored a MOF‐based adsorbent with partitioned aliphatic pore spaces through the simultaneous incorporation of the aliphatic sites and the symmetrically matched partition agent. The resulting adsorbent demonstrates exceptional adsorption capacity for C3H8 and C2H6 compared to CH4, along with remarkably competitive adsorption selectivities for C3H8/CH4 and C2H6/CH4. Breakthrough experiments further support the excellent dynamic separation efficiency of the adsorbent for the purification of CH4 from natural gas. Moreover, detailed density functional theory calculations and molecular simulations elucidate the synergistic interactions between the aliphatic sites and the partitioned pore spaces within the adsorbent, which promote the stronger binding affinities for C3H8 and C2H6 over CH4.

Terahertz Vibrational Dynamics and DFT Calculations for the Quantum Spin Chain Linarite, PbCuSO4(OH)2.

The low-dimensional quantum-magnet, linarite, PbCuS4(OH)2, has been investigated using terahertz (THz) spectroscopy coupled with detailed density functional theory (DFT) calculations in order to explore the effects of the temperature on its lattice vibrations. Linarite is characterized by largely isolated CuO chains propagating along the crystallographic b-axis, which at very low temperatures are responsible for exotic, quasi-1D magnetism in this material. To better understand the synergy between the structural bonds and lattice oscillations that contribute to these chains, polarized THz spectroscopic measurements were performed. Consolidating these results with detailed DFT calculations has revealed that the anisotropic vibrational motion for the THz modes is correlated with extreme motion associated with the crystallographic b-axis. An unexpected feature observed in the infrared spectrum is attributed to subtle lattice distortions which break the centro-symmetry in linarite at high temperatures. This phenomenon has not previously been observed in linarite and likely results from anharmonicity in lattice oscillations.

Hydrogen bonding in glassy trehalose-water system: Insights from density functional theory and molecular dynamics simulations.

We report a detailed density functional theory and molecular dynamics study of hydrogen bonding between trehalose and water, with a special emphasis on interactions in the amorphous solid state. For comparison, water-water interactions in water dimers and tetramers are evaluated using quantum calculations. The results show that the hydrogen bonding energy is dependent not only on the geometry (bond length and angle) but also on the local environment of the hydrogen bond. This is seen in quantum calculations of complexes in vacuum as well as in amorphous solid states with periodic boundary conditions. The temperature-induced glass transition in the trehalose-water system was studied using molecular dynamics simulations with varying cooling and heating rates. The obtained parameters of the glass transition are in good agreement with the experiments. Moreover, the dehydration of trehalose in the glassy state was investigated through a gradual dehydration with multiple small steps under isothermal conditions. From these simulations, the values of water sorption energy at different temperatures were obtained. The partial molar enthalpy of mixing of water value of -18 kJ/mol found in calorimetric experiments was accurately reproduced in these simulations. These findings are discussed in light of the hydrogen bonding data in the system. We conclude that the observed exothermic effect is due to different responses of liquid and glassy matrices to perturbations associated with the addition or removal of water molecules.

Atomically Dispersed Gold Nanoclusters and Single Atoms Coexisting Chiral Electrode for High‐Performance Enantioselective Electrosynthesis using H2o as Hydrogen Source

AbstractDeveloping chiral electrode catalysts for enantioselective electrosynthesis is a great challenge, as it requires catalysts that possess both high activity and enantioselectivity. Precise synthesis of nanoclusters and single atoms coexisting chiral catalysts provide a promising pathway for enhancing asymmetric catalytic performance. Herein, chiral electrode catalysts are fabricated comprising gold clusters (R‐AuC) and single atoms (R‐AuS) on graphene oxide (R‐AuC/S@GO) through an assembly‐irradiation strategy. Thereinto, the R‐Aus is in situ generated from R‐AuC under light irradiation. The monoatomization process can be precisely regulated by changing the wavelength of the light, resulting in four Au‐based chiral electrode (R‐Au@GO) catalysts with different ratios of nanoclusters and single atoms. These chiral electrodes are applied in the electrocatalytic enantioselective hydrogenation of methyl benzoylformate (MB) to chiral methyl mandelate (S‐MM), and the R‐AuC/S‐2@GO with ≈26% R‐AuC and 74% R‐AuS achieve the highest catalytic activity (35 µmol cm−2 h−1 productivity) and enantioselectivity [97% enantiomeric excess (ee)]. Detailed experimental analysis and density functional theory calculations reveal that the R‐AuS on GO promotes the in situ generation of H* species, and R‐AuC mainly drives the enantioselective conversion of MB by transferring the H* species to the carbonyl group of MB, ultimately yielding chiral S‐MM.

Metallaantiaromaticity of 10-Platinacorrole Complexes.

The aromaticity of cyclic π-conjugated organometallic compounds is known as metallaaromaticity. π-Conjugated metallacycles, such as metallabenzenes and metallapentalenes, have been investigated in order to understand the involvement of the d electrons from the metal center in the π-conjugated systems of the organic ligands. Here, we report the synthesis of Pd(II) 10-platinacorrole complexes with cyclooctadiene (COD) and norbornadiene (NBD) ligands. While the Pd(II) 10-platinacorrole COD complex adopts a distorted structure without showing appreciable antiaromaticity, the corresponding NBD complex exhibits a distinct antiaromatic character due to its highly planar conformation. Detailed density functional theory (DFT) calculations revealed that two d orbitals are involved in macrocyclic π-conjugation. We furthermore demonstrated that Craig-Möbius antiaromaticity is not present in the studied system. The synthesis of 10-platinacorroles enables a systematic comparison of the antiaromaticity and aromaticity of closely related porphyrin analogues, providing a better understanding of π-conjugation that involves d orbitals.

Density functional theory investigations on the mechanisms of homogeneous Sm complex catalyzed CO[formula omitted] cycloaddition with epoxides

Converting excess CO2 into chemically valuable products is a promising routine for sustainable development. Catalyzing epoxides and CO2 cycloaddition reactions homogeneously with rare-earth compounds is an emerging approach. The reaction efficiency can be understood by mechanism study. In this work, we report a detailed density functional theory investigation on a well-designed experimental Sm catalyst. We calibrate the ωB97XD exchange–correlation functional as the best candidate functional for this specific catalytic system. The energetic span of catalytic cycle is approximately 25 kcal mol−1. The rate-determining transition state is the one for ring-closure to generate the product. Two competing paths are revealed. Through both ionic and covalent metal–ligand interactions, the lowering of the epoxide substrate ring-opening step barrier is significant compared with the Sm compound free case. This work demonstrate the values for utilizing modern density functional theory to complement the understandings on the homogeneous rare-earth catalytic processes.

A detailed density functional theory exploration of the photodissociation mechanism of ruthenium complexes for photoactivated chemotherapy.

Polypyridyl Ru(II) complexes have attracted much attention due to their potential as light-activatable anticancer agents in photoactivated chemotherapy (PACT). The action of ruthenium-based PACT compounds relies on the breaking of a coordination bond between the metal center and an organic ligand via a photosubstitution reaction. Here, a detailed computational investigation of the photophysical properties of a novel trisheteroleptic ruthenium complex, [Ru(dpp)(bpy)(mtmp)]2+ (dpp = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2'-bipyridine and mtmp = 2-methylthiomethylpyridine), has been carried out by means of DFT and its time-dependent extension. All the aspects of the mechanism by which, upon light irradiation, the mtmp protecting group is released and the corresponding aquated complex, able to bind to DNA inducing cell death, is formed have been explored in detail. All the involved singlet and triplet states have been fully described, providing the calculation of the corresponding energy barriers. The involvement of solvent molecules in photosubstitution and the role played by pyridyl-thioether chelates as caging groups have been elucidated.

O-Vacancy Mediated Partially Inverted Ferrospinels for Enhanced Activity in the Sulfuric Acid Decomposition for Hydrogen Production.

Understanding the characterization of a tailored Co3O4 spinel with Fe3+ doping poses a challenge due to the surface state complexity in bifunctional catalysts with higher cation diversity. Doping with secondary metal results in a double spinel structure (a hybrid of normal and inverted spinels). This enhances the catalytic properties by generating more active oxygen vacancies. The cobalt-rich (FeCo2O4) hybrid spinel and iron-rich (CoFe2O4) inverted spinel are synthesized using a wet impregnation method, supported over oxidized SiC (SiC-Pretrt) for an improved metal-support interaction. FeCo2O4 on pretreated SiC exhibits the highest catalytic activity (90% conversion at 1173 K) and stability (over 100 h) in sulfuric acid decomposition of the iodine-sulfur process for hydrogen production. This improved performance is attributed to the high electronegativity of Co3+, oxygen vacancies, and strong metal-support interaction. The high electronegativity of Co3+ weakens the S-O bond in M-S-O, enhancing the catalytic activity of the spinels. These results are further corroborated by detailed characterization and density functional theory calculations.

Origin of Stability and Activity Enhancements in Pt-based Oxygen Reduction Reaction Catalysts via Defect-Mediated Dopant Adsorption.

Platinum alloys are highly efficient electrocatalysts for the oxygen reduction reaction (ORR) in acidic conditions. However, these alloys are susceptible to metal loss through leaching and degradation, leading to reduced catalyst stability and activity. Recently, it has been shown that doping with oxophilic elements can significantly alleviate these problems, with a prominent example being Mo-doped Pt alloys. Here, to achieve atomic scale understanding of the exceptional activity and stability of these alloys, we present a detailed density functional theory description of the dopants' structures and impact on electrocatalyst properties. Beginning with the Mo/Pt system, we demonstrate that Mo can be stabilized in the form of low-dimensional oxyhydroxide moieties on Pt defects. The resulting structures enhance stability and activity via distinct physical processes, with the Mo moieties both directly inhibiting Pt dissolution at defects and indirectly enhancing ORR activity by generation of strain fields on surrounding Pt terraces. We then generalize these analyses to other metal dopant elements, and we demonstrate that similar low-dimensional oxyhydroxide structures control the electrocatalytic properties through an intricate interplay of the structures' acid stability, intrinsic activity for the ORR, and ability to induce ORR-promoting strain fields on Pt.

Origin of Stability and Activity Enhancements in Pt‐based Oxygen Reduction Reaction Catalysts via Defect‐Mediated Dopant Adsorption

AbstractPlatinum alloys are highly efficient electrocatalysts for the oxygen reduction reaction (ORR) in acidic conditions. However, these alloys are susceptible to metal loss through leaching and degradation, leading to reduced catalyst stability and activity. Recently, it has been shown that doping with oxophilic elements can significantly alleviate these problems, with a prominent example being Mo‐doped Pt alloys. Here, to achieve atomic scale understanding of the exceptional activity and stability of these alloys, we present a detailed density functional theory description of the dopants’ structures and impact on electrocatalyst properties. Beginning with the Mo/Pt system, we demonstrate that Mo can be stabilized in the form of low‐dimensional oxyhydroxide moieties on Pt defects. The resulting structures enhance stability and activity via distinct physical processes, with the Mo moieties both directly inhibiting Pt dissolution at defects and indirectly enhancing ORR activity by generation of strain fields on surrounding Pt terraces. We then generalize these analyses to other metal dopant elements, and we demonstrate that similar low‐dimensional oxyhydroxide structures control the electrocatalytic properties through an intricate interplay of the structures’ acid stability, intrinsic activity for the ORR, and ability to induce ORR‐promoting strain fields on Pt.

Green synthesis of novel spiropyrazoline-indolinones in neutral deep eutectic solvents and DFT studies

Novel spiropyrazoline-indolinones (4a–t) have been synthesized successfully in neutral deep eutectic solvents by reacting 5-Cl/Br-isatin (1a–b) with aromatic ketones (2a–b) and a variety of substituted hydrazines (3a–e) in good to excellent yields. This eco-friendly straightforward synthetic protocol discloses good functional group compatibility. The conventional synthetic approach was compared with the greener route of microwave-assisted synthesis of spiropyrazolines using ethanol. This approach utilized mild reaction conditions which furnished high yields in short reaction time employing one pot two-step multicomponent. All new compounds were structurally confirmed by detailed spectroscopic analysis and density functional theory calculations. This method provides efficient access to spiropyrazole derivatives using biodegradable and green solvent.

Carrier confinement activated explicit solvent dynamic of CdS/BiVO4/H2O and optimized photocatalytic hydrogen evolution performances

Herein, using an electrophoretic deposition strategy, a S-scheme CdS (cubic)/BiVO4 (monoclinic) heterostructured photocatalyst is fabricated. The as-synthesized photocatalysts exhibit high carrier separation efficiency, prominent hydrogen evolution ability and high stability. The results of the detailed density functional theory (DFT) prove that the photogenerated electrons and holes are located in BiVO4 and CdS components, respectively. Besides, an explicit solvent model based on the electron-enriched region in CdS/BiVO4 heterojunction is designed deliberately to investigate the solid/liquid interface issues. Intriguing findings demonstrate that the surface hydrogen diffusing rate in CdS/BiVO4/H2O is faster than that of BiVO4/H2O and is highly associated with the electron-enrich effect, which has a greater capacity to promote water decomposition, the possibility of proton collision and photocatalytic hydrogen evolution. Notably, the H p orbital can participate in the electron-enrich effect during solvation, thus reforming the orbital energy level and activating the HER of the BiVO4 component in the CdS/BiVO4 system.

Local Electron Environment Regulation of Spinel CoMn2O4 Induced Effective Reactant Adsorption and Transformation of Lattice Oxygen for Toluene Oxidation.

In contrast to numerous studies on oxygen species, the interaction of volatile organic compounds (VOCs) with oxides is also critical to the catalytic reaction but has hardly been considered. Herein, we develop a highly efficient Pt atom doped spinel CoMn2O4 (Pt-CoMn) for oxidation of toluene at low temperature, and the toluene conversion rate increased by 18.3 times (129.7 versus 7.1 × 10-11 mol/(m2·s)) at 160 °C compared to that of CoMn2O4. Detailed characterizations and density functional theory calculations reveal that the local electron environment of the Co sites is changed after Pt doping, and the formed electron-deficient Co sites in turn strengthen the interaction with toluene. Adsorbed toluene will react with lattice oxygen in Pt-CoMn and CoMn catalysts and convert into benzoate intermediates, and the consumption rate of benzoate is closely related to the activation of gaseous oxygen. Significantly, the abundant bulk defects of Pt-CoMn help to open the reaction channel in the CoMn spinel, which acts as an oxygen pump to promote the transformation of bulk lattice oxygen into surface lattice oxygen at lower temperatures, thus accelerating the conversion rate of benzoate intermediates into CO2 and enhancing low-temperature combustion of toluene. Pt-CoMn developed here emphasizes the regulation of VOCs adsorption strength and lattice oxygen transformation processes on CoMn2O4 by adjusting the local electron environment, which will provide new guidance for the design of efficient oxide catalysts for catalytic oxidation.

Optimizing the cask effect in multicomponent natural gas purification to provide high methane productivity

AbstractThe efficient separation of CH4 from natural gas containing C2H6 and C3H8 impurities is an important topic. Previous work on the separation of CH4/C2H6/C3H8 mixtures often focuses on the C3H8/CH4 selectivity, inadvertently sidelining the critical importance of C2H6/CH4 selectivity. This oversight results in reduced CH₄ productivity and compromised separation efficiency, a phenomenon often termed as the “cask effect.” Herein, we fine‐tune the interrelationship between thermodynamics and kinetics, targeting enhanced CH4 production. A synergistic thermodynamic–kinetic C3H8/CH4 and C2H6/CH4 selectivity is achieved using dynamic breakthrough experiments, underpinned by the stable metal–organic framework TIFSIX‐Cu‐TPA. The CH4 productivity in TIFSIX‐Cu‐TPA is up to 5 mmol g−1, surpassing most of the popular materials. Detailed density functional theory and molecular dynamics computational insights reveal a counteractive thermodynamic–kinetic relationship, proving pivotal for the simultaneous breakthrough of C2H6 and C3H8 under optimal conditions. Moreover, precise adsorption sites of C2H6 and C3H8 are clearly determined through in situ single‐crystal structures.

Synergistic effect of platinum single atoms and nanoclusters for preferential oxidation of carbon monoxide in hydrogen-rich stream

Despite the maximum atom-utilization efficiency and remarkable activity of single-atom catalysts, further improvement of catalytic activity can be obtained by the synergistic effect of single atoms and nanoclusters in some catalytic systems. Herein, CeFeOx-supported Pt single atoms coupling with subnanometric clusters (Pt1-Ptn) structures are developed via a facile strategy. They are applied as the highly efficient catalysts for the preferential oxidation of CO in H2-rich stream (CO-PROX), which achieve complete elimination of CO at low temperature of 50 °C, with a wide operating temperature window and extraordinary stability for over 500 h without noticeable deactivation. The exceptional performance is attributed to the synergistic effect of distinctive Pt1-Ptn structures, which couple the benefits of Pt single atoms and subnanometric clusters in a remarkable way. The disadvantages of single Pt species catalysts, such as sensibility to strong adsorption of CO or reduced lattice oxygen reactivity due to excessive coordination, can be well mitigated. The results of detailed characterizations and density functional theory calculations confirm that the unique structures possess moderate adsorption strength for CO and create abundant active interfacial oxygen species, because of the absence of bulk metallic Pt0 and appropriate coordination to lattice oxygen, which synergistically facilitate the catalytic performance.

CeNCl‐CeO2 Heterojunction‐Modified Ni Catalysts for Efficient Electroreduction of CO2 to CO

AbstractRenewable‐electricity‐powered electrochemical CO2 reduction (CO2RR) is considered one of the most promising ways to convert exhaust CO2 into value‐added chemicals and fuels. Among various CO2RR products, CO is of great significance since it can be directly used as feedstock to produce chemical products through the Fischer–Tropsch process. However, the CO2‐to‐CO electrocatalytic process is often accompanied by a kinetically competing side reaction: H2 evolution reaction (HER). Designing electrocatalysts with tunable electronic structures is an attractive strategy to enhance CO selectivity. In this work, a CeNCl‐CeO2 heterojunction‐modified Ni catalyst is successfully synthesized with high CO2RR catalytic performance by the impregnation‐calcination method. Benefiting from the strong electron interaction between the CeNCl‐CeO2 heterojunction and Ni nanoparticles (NPs), the catalytic performance is greatly improved. Maximal CO Faradaic efficiency (FE) is up to 90% at −0.8 V (vs RHE), plus good stability close to 12 h. Detailed electrochemical tests and density functional theory (DFT) calculation results reveal that the introduction of the CeNCl‐CeO2 heterojunction tunes the electronic structure of Ni NPs. The positively charged Ni center leads to an enhanced local electronic structure, thus promoting the activation of CO2 and the adsorption of *COOH.

Stereoselectivity control in Rh-catalyzed β-OH elimination for chiral allene formation

Stereoselectivity control and understanding in the metal-catalyzed reactions are fundamental issues in catalysis. Here we report sterically controlled rhodium-catalyzed SN2’-type substitution reactions of optically active tertiary propargylic alcohols with arylmetallic species affording the non-readily available enantioenriched tetrasubstituted allenes via either exclusive syn- or anti-β-OH elimination, respectively, under two sets of different reaction parameters. Detailed mechanistic experiments and density functional theory (DFT) studies reveal that the exclusive anti-Rh(I)-OH elimination is dictated by the simultaneous aid of in situ generated boric acid and ambient water, which act as the shuttle in the hydroxy relay to facilitate the Rh(I)-OH elimination process via a unique ten-membered cyclic transition state (anti-TS2_u). By contrast, the syn-Rh(III)-OH elimination in C–H bond activation-based allenylation reaction is controlled by a four-membered cyclic transition state (syn-TS3) due to the steric surroundings around the Rh(III) center preventing the approach of the other assisting molecules. Under the guidance of these mechanistic understandings, a stereodivergent protocol to construct the enantiomer of optically active tetrasubstituted allenes from the same starting materials is successfully developed.

Mechanism and Origins of Regio- and Stereoselective Alkylboration of Endocyclic Olefins Enabled by Nickel Catalysis.

The Ni-catalyzed alkylboration of endocyclic olefins is a stereo- and regioselective approach for the synthesis of boron-containing compounds. We report a detailed density functional theory (DFT) study to elucidate the mechanism and origins of the stereo-, chemo-, and regioselectivity of alkylboration of endocyclic olefins enabled by nickel catalysis. The alkylboration proceeds via the migratory insertion of alkenes, β-H elimination of the Ni(II) complex, subsequent migratory insertion leading to a new Ni(II) complex, combined with an alkyl radical, and reductive eliminations. The electronic effects of the endocyclic olefins synergistically control the regioselectivity toward the C1- and C2-position boration. In C1-position boration, a more electron-deficient carbon atom tends to combine with an electron-rich -Bpin group and leads to C1-position boration products. The stereoselectivity is influenced by the solvent effect, and the interaction between the substrate and Ni-catalyzed groups, the low-polarity solvent 1,4-dioxane, and a favorable steric hindrance effect result in the cis-alkylboration product. Chemoselectivity toward 1,3-alkylboration results from the steric hindrance effects of the -Bpin group.