Microscopic Investigation of Ethylene Carbonate Interface: A Molecular Dynamics and Vibrational Spectroscopic Study

Ethylene carbonate(EC) liquid and its vapor-liquid interface were investigated using a combination of molecular dynamics(MD)simulation and vibrational IR, Raman and sum frequency generation(SFG)spectroscopies. The MD simulation was performed with a flexible and polarizable model of the EC molecule newly developed for the computation of vibrational spectra. The internal vibration of the model was described on the basis of the harmonic couplings of vibrational modes, including the anharmonicity and Fermi resonance coupling of C=O stretching. The polarizable model was represented by the charge response kernel(CRK),which is based on ab initio molecular orbital calculations and can be readily applied to other systems. The flexible and polarizable model can also accurately reproduce the structural and thermodynamic properties of EC liquid. Meanwhile, a comprehensive set of vibrational spectra of EC liquid, including the IR and Raman spectra of the bulk liquid as well as the SFG spectra of the liquid interface, were experimentally measured and reported. The set of experimental vibrational spectra provided valuable information for validating the model, and the MD simulation using the model comprehensively elucidates the observed vibrational IR, Raman, and SFG spectra of EC liquid. Further MD analysis of the interface region revealed that EC molecules tend to orientate themselves with the C=O bond parallel to the interface. The MD simulation explains the positive Im[χ^((2))](ssp) band of the C=O stretching region in the SFG spectrum in terms of the preferential orientation of EC molecules at the interface. This work also elucidates the distinct lineshapes of the C=O stretching band in the IR, Raman, and SFG spectra. The lineshapes of the C=O band are split by the Fermi resonance of the C=O fundamental and the overtone of skeletal stretching. The Fermi resonance of C=O stretching was fully analyzed using the empirical potential parameter shift analysis(EPSA) method. The apparently different lineshapes of the C=O stretching band in the IR, Raman, and SFG spectra were attributed to the frequency shift of the C=O fundamental in different solvation environments in the bulk liquid and at the interface. This work proposes a systematic procedure for investigating the interface structure and SFG spectra, including general modeling procedure based on ab initio calculations, validation of the model using available experimental data, and simultaneous analysis of molecular orientation and SFG spectra through MD trajectories. The proposed procedure provides microscopic information on the EC interface in this study, and can be further applied to investigate other interface systems, such as liquid-liquid and solid-liquid interfaces.

Selective C3-alkenylation of oxindole with aldehydes using heterogeneous CeO2 catalyst

We report herein that a commercially available CeO2 is an active and reusable catalyst for the C3-selective alkenylation of oxindole with aldehydes under solvent-free conditions. This catalytic method is generally applicable to different aromatic and aliphatic aldehydes, giving 3-alkyledene-oxindoles in high yields(87%–99%) and high stereoselectivities(79%–93% to E-isomers). This is the first example of the catalytic synthesis of 3-alkenyl-oxindoles from oxindole and various aliphatic aldehydes. The Lewis acid-base interaction between Lewis acid sites on CeO2 and benzaldehyde was studied by in situ IR. The structure-activity relationship study using CeO2 catalysts with different sizes suggests that defect-free CeO2 surface is the active site for this reaction.

Doping and alloying in atomically precise gold nanoparticles

The recent success in the synthesis and total structure determination of atomically precise gold nanoparticles has provided exciting opportunities for fundamental studies as well as the development of new applications. These unique nanoparticles are of molecular purity and possess well defined formulas （i.e., specific numbers of metal atoms and ligands）, resembling organic compounds. Crystallization of such molecularly pure nanoparticles into macroscopic single crystals allows for the determination of total structures of nanoparticles （i.e., the arrangement of metal core atoms and surface ligands） by X-ray crystallography. In this perspective article, we summarize recent efforts in doping and alloying gold nanoparticles with other metals, including Pd, Pt, Ag and Cu. With atomically precise gold nanoparticles, a specific number of foreign atoms （e.g., Pd, Pt） can be incorporated into the gold core, whereas a range of Ag and Cu substitutions is observed but, interestingly, the total number of metal atoms in the homogold nanoparticle is preserved. The heteroatom substitution of gold nanoparticles allows one to probe the optical, structural, and electronic properties truly at the single-atom level, and thus provides a wealth of information for understanding the intriguing properties of this new class of nanomaterials.

Nanometer-size Na cluster formation in micropore of hard carbon as origin of higher-capacity Na-ion battery

Development of high-energy-density anode is crucial for practical application of Na-ion battery as a post Li-ion battery.Hard carbon(HC),though a promising anode candidate,still has bottlenecks of insufficient capacity and unclear microscopic picture.Usage of the micropore has been recently discussed,however,the underlying sodiation mechanism is still controversial.Herein we examined the origin for the high-capacity sodiation of HC,based on density functional theory calculations.We demonstrated that nanometersize Na cluster with 3–6 layers is energetically stable between two sheets of graphene,a model micropore,in addition to the adsorption and intercalation mechanisms.The finding well explains the extended capacity over typical 300 mAhg^(−1),up to 478 mAhg^(−1) recently found in the MgO-templated HC.We also clarified that the MgO-template can produce suitable nanometersize micropores with slightly defective graphitic domains in HC.The present study considerably promotes the atomistic theory of sodiation mechanism and complicated HC science.

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Fundamental knowledge of structure-activity correlations for heterogeneous single-atom catalysts(SACs)is essential in guiding catalytic design.While linear scaling relations are powerful for predicting the performance of traditionalmetal catalysts,they appear to fail with the involvement of SACs.Comparing the catalytic CO oxidation activity of different atomically dispersed metals(3d,4d,and 5d)in conjunction with computational modeling enabled us to establish multiple scaling relations between the activity and simply calculated descriptors.

Efficient Stabilization of Na Storage Reversibility by Ti Integration into O′3-Type NaMnO_(2)

The development of an energy storage system with abundant elements is a key challenge for a sustainable society,and the interest of Na intercalation chemistry is extending throughout the research community.Herein,the impact of Ti integration into NaMnO2 in a binary system of x NaMnO2–(1–x)TiO2(0:5≤x≤1)is systematically examined for rechargeable Na battery applications.Stoichiometric NaMnO2,which is classified as an in-plane distorted O′3-type layered structure,delivers a large initial discharge capacity of approximately 200 mAhg-1,but insufficient capacity retention is observed,most probably associated with dissolution of Mn ions on electrochemical cycles.Ti-substituted samples show highly improved electrode performance as electrode materials.However,the appearance of a sodium-deficient phase,Na4Mn4Ti5O18 with a tunnel-type structure,is observed for Ti-rich phases.Among the samples in this binary system,Na0.8Mn0.8Ti0.2O2(x=0:8),which is a mixture of a partially Ti-substituted O′3-type layered oxide(Na0.88Mn0.88Ti0.12O2)and tunnel-type Na4Mn4Ti5O18 as a minor phase elucidated by Rietveld analysis on both neutron and X-ray diffraction patterns,shows good electrode performance on the basis of energy density and cyclability.Both phases are electrochemically active as evidenced by in situ X-ray diffraction study,and the improvement of reversibility originates from the suppression of Mn dissolution on electrochemical cycles.From these results,the feasibility of Mn-based electrode materials for high-energy rechargeable Na batteries made from only abundant elements is discussed in detail.

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching

Single-atom catalysts(SACs)are promising in some reactions typically promoted by homogeneous catalysts.However,the leaching of active species from the support in liquid-phase reactions hinders their potential applications.Herein,taking the hydroformylation reaction as an example,we report ionic liquid(IL)-induced stabilization of single Rh atoms against leaching.Among the ILs examined.

Structure of polyelectrolyte brushes studied by coarse grain simulations

As an example of a very low friction system,Monte Carlo Brownian dynamics simulations have been used to calculate equilibrium structures of a polyelectrolyte brush grafted onto planes.The polymers were calculated in a semi-flexible coarse-grain model that is appropriate to treat the charge density of the polyion.The effect of linear charge density on the polyionx,the surface negative charge,and added salts were studied.In salt-free solution,scaling theories predicted the structure well in the lowxregion.In the highxregion,additional shrinkage was found from the theories due to counterion condensation.The effect of surface charge showed not only the repulsion of the polyion from the surface but also the shrinkage in the highxregion due to the additional counterions required for electrical neutrality.The addition of salts led to the shrinkage of the brush heights,and in the highxregion,additional extension was found.The computational strategy for calculating the friction dynamics of the system is also discussed.

Corrigendum to“Efficient Stabilization of Na Storage Reversibility by Ti Integration into O′3-Type NaMnO_(2)”

In the article titled“Efficient Stabilization of Na Storage Reversibility by Ti Integration into O′3-Type NaMnO2”[1],there was an error in Figure 4.In panel(a),the“x=0:2”should have read“x=0:8.”This is shown corrected in Figure 4 below。