Search

Abstract We performed DFT calculations to investigate the role of solvent of the non-aqueous electrolytes for the oxygen reduction reaction (ORR) kinetics in Li-air batteries. The calculated results on structural, thermodynamic and vibrational properties revealed that dimethyl sulfoxide (DMSO) is the most stable solvent among DME, DMSO, and MeCN of non-aqueous electrolytes. The LiCF 3 SO 3 /DMSO electrolyte was primarily assumed to be the most favorable for ORR kinetics from the IR analysis. We calculated thermodynamic properties of the ORR reactions held during the formation of superoxide (O 2 −) ion and the sole discharge products lithium peroxide (Li 2 O 2), and lithium oxide (Li 2 O) to study the ORR kinetics of the stable salt LiCF 3 SO 3 with three solvents namely dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and acetonitrile (MeCN). The thermodynamic properties of the ORR reaction signified the best role of LiCF 3 SO 3 /DMSO electrolyte compared to LiCF 3 SO 3 /DME and LiCF 3 SO 3 /MeCN both in the gas and solution (water) phases. Highlights • The role of solvent of non-aqueous electrolyte in Li-air batteries was studied theoretically. • The LiCF 3 SO 3 /DMSO electrolyte was primarily assumed to be the most favorable for ORR kinetics from the IR analysis. • The thermodynamic properties of the ORR reactions including the (O 2 −) ion and Li 2 O 2 and Li 2 O • Improved ORR kinetics was due to the key role of LiCF 3 SO 3 /DMSO electrolyte compared to LiCF 3 SO 3 /DME and LiCF 3 SO 3 /MeCN. [ABSTRACT FROM AUTHOR]

Abstract Monoclinic clinobisvanite BiVO 4 is one of the most promising photocatalyst due to its stability, low cost, narrow band gap, and suitable valence band maximum (VBM) position. The valence band maximum of about −7.10 eV at vacuum level was observed, which is well below the redox potential of water. However, the conduction band minimum, CBM of about −4.86 eV at vacuum level, which was responsible for its low efficiency. The presence of metal (Bi or V) vacancy changed the charge density and VBM of pristine BiVO 4. Our calculated results revealed that 0.04% of the intrinsic Bi or V defects enhanced p-type conductivity and hence improved photocatalytic activity than O-interstitial in pristine BiVO 4. The optical properties of both pristine and intrinsically defective BiVO 4 were calculated and analyzed with perspective of their photocatalytic properties. Conclusively, the role of Bi or V (metal) vacancies in pristine BiVO 4 was found to be significant than O interstitials in enhancing the photocatalytic properties regarding the solar water splitting. Highlights • The electronic structure of pristine and intrinsically defective BiVO4 was investigated by DFT. • The CBM of BiVO 4 was calculated to be -4.86 eV at vacuum level, which is responsible for its low efficiency. • Bi or V vacancies enhanced p-type conductivity and hence improved photocatalytic activity than O-interstitial in BiVO 4. [ABSTRACT FROM AUTHOR]

Hydrogen storage is indeed fundamental to utilizing H 2 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 (ɛ VB), consequently influencing the hydrogen storage performance of γGy. Our investigation suggests that increased overlap between ɛ VB in Li-loaded graphyne and the effective alignment of H 2 and the supporting structure augments the binding force between Li and H 2 , thereby amplifying the HSC. [Display omitted] • Li-loaded γ-Graphyne stores H 2 via Valence-like interaction. • B- and N-doping can enhance storage capacity of Li-loaded γ-Graphyne. • Valence band center of Li tuned by strain achieve efficient adsorption-desorption. [ABSTRACT FROM AUTHOR]

Magnesium in biogenic aragonite skeletons is widely used to infer the geochemical conditions under which the minerals precipitated. However, because molecular speciation of Mg2+ in the aragonite crystal structure remains uncertain, questions are often posed about the reliability and utility of Mg as a paleoenvironment proxy. In this study, we investigated the Mg2+ coordination in abiogenic aragonite by applying first-principles density functional theory (DFT). We report for the first time a Mg2+-site disordered structure model of aragonite: substituted Mg2+ is five-fold coordinated and induces substantial disorder in the bond distances that depends on the relative positions of Mg2+ sites. Using the site disorder model, DFT qualitatively reproduces the key features of experimental Mg K -edge X-ray absorption near-edge structure (XANES) spectra of aragonite. DFT also resolves a long-standing conflict between experimental and theoretical studies pertaining to the enrichment of 26Mg in aragonite relative to calcite. The Boltzmann-averaged 26Mg/24Mg reduced partition function ratios were calculated in the order of aqueous Mg2+ > Mg-doped aragonite > Mg-doped calcite. The disorder structure model is likely applicable to the substitution of cations with radii smaller than the radius of Ca2+ ions in aragonite. Our study provides atomistic insight into metal substitution effects on the metal content and isotope fractionation in biogenic aragonite, which are critical for developing a reliable paleoenvironment proxy. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) are promising candidates for the replacement of lithium-ion batteries (LIBs) because of sodium's abundant reserves and the lower cost of sodium compared to lithium. This is a topic of interest for developing novel anodes with high storage capacity. Owing to their low cost, high stability, and conductivity, carbon-based materials have been studied extensively. However, sp2-C based carbon materials have low-rate capacities. Intensive density functional theory calculations have been implemented to explore the applicability of α, β, and γ graphyne nanotubes (αGyNTs, βGyNTs, and γGyNTs, respectively) as SIB anodes. Results suggest that (3, 0)-αGyNT, (2, 2)-βGyNT, and (4, 0)-γGyNT have, respectively, maximum Na storage capacities of 1535, 1302, and 1001 mAh/g, which exceeds the largest reported value of carbon materials (N-doped graphene foams with 852.6 mAh/g capacity). It was determined that αGyNTs have the largest storage capacity of the three types because they possess the largest specific surface area. Moreover, the larger pores of αGyNTs and βGyNTs allow easier diffusion and penetration of Na atoms compared to those of γGyNTs, which could result in better rate capacity. [ABSTRACT FROM AUTHOR]

Alcohols mediated 7-hydroxyquinoline (7-HQ) complex has received enormous attractions on the issue of proton transfer reaction in the ground and excited states. In the present paper, concentrating on the ground state proton transfer (GSPT), density functional theory (DFT) calculations were carried out to investigate the intrinsic insight into the reaction mechanism. We found that the GSPT is concerted and asynchronous process and can be accelerated by more acidic alcohol. Such GSPT was initiated by the proton transfer from alcohol to keto group of 7-HQ and finished by the proton transfer from nitrogen to alcohol. Our findings were in agreement with experimental conclusions quite well. Our results would be helpful to understand the proton transfer reaction for 7-HQ and related systems. [ABSTRACT FROM AUTHOR]

Observation of novel linear relationship between Δ G OOH and Δ E H suggests Δ E H as a simple descriptor for rational design of HER/ORR bifunctional graphyne materials. [Display omitted] The high cost and relative scarcity of platinum (Pt) restrict large-scale commercialization of fuel cells, which has spurred researchers to develop low-cost alternatives integrating with high hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) catalytic activity. Herein, we performed density functional theory (DFT) calculations to explore the electrocatalytic activity of graphyne nanotubes (GyNTs). Several GyNTs were found to be potential metal-free electrocatalysts, with both HER and ORR activity superior to Pt. Moreover, we revealed a linear relationship between the Gibbs free energy change of O 2 adsorption (Δ G OOH) and binding energy of H adsorption (Δ E H), which could be attributed to the fact that both the C O bond of OOH adsorption and the C H bond of H adsorption are single bonds. Therefore, Δ E H is proposed as a general descriptor for the rational design of bifunctional graphyne materials toward HERs and ORRs. Our findings provide a simple strategy for the rational design of bifunctional materials. [ABSTRACT FROM AUTHOR]

Abstract DFT calculations are performed to investigate the water oxidation reaction intermediates on Ag 2 M (M = Fe, Co, Ni, Cu), and Pt 3 clusters in alkaline media both in the gas and solution (water) phases in the neutral and charged states. The calculated results revealed that the neutral and anionic clusters were found to be more suitable catalysts than cationic clusters because of weakly bonded water oxidation reaction intermediates. In addition, the calculated structural parameters of the water oxidation intermediates with Ag 2 M (M = Fe, Co, Ni, Cu) clusters revealed that M-OH bond strengths are found to be in the order of Cu < Ni < Co < Fe. Conclusively, Ag 2 Cu cluster was determined to be the best electrocatalyst regarding oxygen evolution reaction via 4e transfer, which is consistent with results on larger Ag 2 M clusters (13 atoms) and periodic Ag-M nanoalloys due to weaker binding energies of the water oxidation intermediates. Highlights • Ag 2 M (M = Fe, Co, Ni, Cu), and Pt 3 clusters were considered as electro-catalysts for OER. • Neutral and anionic clusters were found to be more suitable catalysts than cationic clusters. • M OH bond strengths are found to be in the order of Cu < Ni < Co < Fe. • Ag 2 Cu cluster was determined to be the best electrocatalyst regarding oxygen evolution reaction via 4e transfer. [ABSTRACT FROM AUTHOR]

A new family of all‐carbon structures is proposed via substituting the sp2 carbon atom in graphene and graphyne with carbon trigons. Owing to the existence of carbon trigons, these porous carbon allotropes are named as trigraphene and trigraphyne. The calculations of geometrical, vibrational, and energetic properties by density functional theory reveal that all these structures are metastable and dynamically stable. It is further disclosed from the electronic band structures that trigraphene and α‐trigraphyne are metal, while β‐trigraphyne and γ‐trigraphyne are semiconductor with indirect band gaps of 0.33 and 0.52 eV, respectively. Our results suggest a strategy to design new carbon materials with desired properties, and these all‐carbon materials would have many interesting applications once obtained. [ABSTRACT FROM AUTHOR]

The inhibition effect of a Schiff base with several functional groups on the corrosion of aluminum in alkaline solution is studied by experimental techniques and density function theory (DFT) calculations. The Schiff base are characterized by 1 HNMR, 13 CNMR, FT-IR, and CHN elemental analysis. In addition, different electrochemical and corrosion techniques such as weight loss, tafel polarization, electrochemical impedance spectroscopy (EIS) and optical microscopy images are performed to analyze the inhibiting performances. In the Tafel measurements the cathodic Tafel slopes values incurred small changes with increasing the inhibitor concentration, which revealed that the inhibitor was adsorbed on the aluminum surface. The inhibition efficiencies are calculated from weight loss measurement and electrochemical tests. The adsorption of the inhibitor onto the aluminum surface follows the Langmuir adsorption isotherm with the free adsorption energy of −8.66 kJ mol −1 . The calculated adsorption energies and the amount of charge transfer obtained by DFT calculation revealed that corrosion inhibition effectively occurs with chemisorption, where new N Al bonds are formed between of N atoms in azo (–N N–) group and Al surface atoms, which is confirmed from ab initio molecular dynamics (AIMD) simulation. [ABSTRACT FROM AUTHOR]

We systematically investigated the tuning of the reduction potentials ( E 0 ) for the first row transition metal (M = Cr, Mn, Fe, Co, Ni) complexes with the functionalized 1,4,7-Triazacyclononane-N,N',N”-triacetate (TCTA) ligands by means of DFT calculations. To predict reliable E 0 , the modified UB3LYP functional and equilibrium concept between high and low spin states were utilized. The functional groups NH 2 , CN, −F, and NO 2 were attached to the carbon atoms carefully selected by considering the LUMO and steric hindrance. Based on firmed accuracy of DFT calculations, finally we obtained the calculated E 0 for a series of complexes. It was found that electron donating group such as NH 2 will cause a negative shift of E 0 while electron withdrawing groups have the opposite effect. The overall trend of the calculated E 0 s according to ligand modifications were predicted to have the order as −NH 2 < Pristine < −F ≈ −CN < −NO 2 . In addition, optimized geometries, LUMO, vertical electron attachment and energy components constituting E 0 were discussed in detail to assist the further understanding for E 0 s. Consequently, we suggested that 16 complexes can play a role as an electrolyte in aqueous redox flow battery. They can be classified into 5 groups having similar E 0 ranges: Group I (- 0.6 V ∼ − 0.7 V), Group II (around 0.0 V), Group III (around 0.3 V), Group IV (0.6 ∼ 0.8 V) and Group V (1.1 ∼ 1.2 V). Especially, it is expected that [MnL F ] , [MnL CN ] and [NiL NH2 ] can be used as promising catholyte candidates possibly possessing high E 0 s which almost reach to the reduction potential limitation 1.25 V in aqueous redox flow battery. Our systematic approach to tune E 0 can be applied to the design of other complexes via rational ligand modification. [ABSTRACT FROM AUTHOR]

[Display omitted] A novel all-carbon material with quasi 2D character, supertetrahedraphene, was proposed using carbon tetrahedron as the starting material. The geometry and electronic properties were investigated via density functional theory (DFT) calculations. Supertetrahedraphene was confirmed to be an energetically meta-stable and dynamically stable semiconductor with an indirect band gap of 2.80 eV. An acetylenic linkage (C C) was inserted to change the height of supertetrahedraphene, resulting in a new sp + sp 3 hybrid system. Insertion of C C can further stabilize supertetrahedraphene and transform it to a semiconductor with direct band gaps. These band gaps steadily decrease as the number of C C increases, and the supertetrahedraphene is predicted to be metallic if the C C is of sufficient length. Our results suggest a strategy to design novel carbon materials with desired properties. [ABSTRACT FROM AUTHOR]