Direct atomic-level insight into oxygen reduction reaction on size-dependent Pt-based electrocatalysts from density functional theory calculations

Developing novel oxygen reduction reaction(ORR)catalysts with high activity is urgent for proton exchange membrane fuel cells.Herein,we investigated a group of size-dependent Pt-based catalysts as promising ORR catalysts by density functional theory calculations,ranging from single-atom,nanocluster to bulk Pt catalysts.The results showed that the ORR overpotential of these Pt-based catalysts increased when its size enlarged to the nanoparticle scale or reduced to the single-atom scale,and the Pt_(38)cluster had the lowest ORR overpotential(0.46 V)compared with that of Pt_(111)(0.57 V)and single atom Pt(0.7 V).Moreover,we established a volcano curve relationship between the ORR overpotential and binding energy of O*(ΔE_(O*),confirming the intermediate species anchored on Pt38cluster with suitable binding energy located at top of volcano curve.The interaction between intermediate species and Pt-based catalysts were also investigated by the charge distribution and projected density of state and which further confirmed the results of volcano curve.

Integrated separation-electrochemical detection device based on wood column for online identification of enantiomer

Chiral chemicals have attracted significant interest in the pharmaceutical industry,yet the separation methods to get pure enantiomers from racemic mixture are still challenging.To date,the separation of enantiomers still mainly depends on chromatography using high-cost chiral stationary phases.Herein,wood channels were used as the handheld integrated device,and enantiomer separation was simultaneously detected using an electrochemical detector.In this method,a chiral UIO-66(L-UIO-66)modified enantiomer separation zone and carbonized wood based online detection zone are integrated along a single wood column.Based on the in situ separation results from the chronoamperometry data,the wood device shows excellent separation ability for a wide range of electrochemically active enantiomers,including 3,4-dihydroxyphenylalanine,amino acids,ascorbic acid,carnitine,and penicillamine with high chirality purity.The unbiased molecular dynamic simulations indicate that the excellent chiral recognition and separation are attributed to the different barriers from the bound states to the dissociated state of the enantiomers in the homochiral microenvironment of the framework.This integrated enantiomer separation-electrochemical detection device provides a novel,easy,and low-cost platform for the separation of pure enantiomer from racemic mixture.

Quantum Wave Packet Studies on F+HBr Reaction

Time-dependent quantum wave packet calculations were carried out for the F ＋ HBr reaction on the latest London-Erying-Polanyi-Sato potential energy surface constructed by Persky et al. The calculated reaction probabilities dramatically increase near the zero collision energy and then slightly decrease with increasing collision energy, which corresponds well to the behavior of a barrierless reaction. The effects of reagent HBr excitation were examined, it is shown that both the vibrational and the rotational excitations of reagent HBr have a negative effect on the reactivity of F ＋ HBr. The integral cross-section for the ground state of the reagent HBr decreases at a low collision energy and then becomes plat with increasing collision energy, which is reasonable for the feasibility of such an exothermal reaction. The rate constant that was obtained is slightly higher than that obtained in the quasi-classical trajectory calculation.

DFT Investigations About Pyrazine Molecules on Si(100)-2×1 Surface

It is important to understand the interface of aromatic molecules on semiconductor surfaces because of the rich functionality of such molecules on semiconductor surfaces. The chemisorption of pyrazine molecules on the Si （100）- 2×1 surface has been investigated using the B3LYP density functional theory with Si9H12 one-dimer and Si15Hl6 two-dimer cluster models. The calculated results predict that N-dative bonded-state, C2=C5 [E4＋2] and the tight- bridgel,2,5,6 products may coexist on the Si（100）-2 × 1 surface.

Density functional study on structural and electronic properties of bimetallic gold-yttrium clusters: comparison with pure gold and yttrium clusters

Employing first-principles methods, based on the density functional theory, this paper investigates the ground state geometric and electronic properties of pure gold clusters, pure yttrium clusters and gold clusters doped each with one yttrium atom. It is shown that the average bond lengths in the Aun-1Y（n≤9） bimetallic clusters are shorter than those in the corresponding pure gold and yttrium clusters. The most stable isomers of the yttrium-doped gold clusters tend to equally delocalize valence s, p and d electrons of the constituent atoms over the entire structure. The Y atom has maximum number of neighbouring Au atom, which tends to be energetically favourable in the lowest-energy equilibrium structures, because the Au-Y bond is stronger than the Au-Au bond. The three-dimensional isomers of Aun-1Y structures are found in an early appearance starting at n=5 （Au4Y）. Calculated vertical ionization potential and electron affinities as a function of the cluster size show odd-even oscillatory behaviour, and resemble pure gold clusters. However, one of the most striking feature of pure yttrium clusters is the absence of odd-even alternation, in agreement with mass spectrometric observations. The HOMO LUMO gap of Au3Y is the biggest in all the doped Aun-1Y（n≤9） bimetallic clusters.

富勒烯及碳纳米管,实验学家和理论学家的竞技场(英文)

The interplay between experiments and theory has been playing an important role from the very beginning of fullerene and carbon nanotube science. In this talk, we will present our most recent studies on computational fullerene and single-walled carbon nanotube (SWCNT) chemistry.

Heterometallic cluster-based organic frameworks as highly active electrocatalysts for oxygen reduction and oxygen evolution reaction:a density functional theory study

Recently,metal–organic frameworks are one of the potential catalytic materials for electrocatalytic applications.The oxygen reduction reaction and oxygen evolution reaction catalytic activities of heterometallic cluster-based organic frameworks are investigated using density functional theory.Firstly,the catalytic activities of heterometallic clusters are investigated.Among all heterometallic clusters,Fe_(2)Mn–Mn has a minimum overpotential of 0.35 V for oxygen reduction reaction,and Fe_(2)Co–Co possesses the smallest overpotential of 0.32 V for oxygen evolution reaction,respectively 100 and 50 mV lower than those of Pt(111)and RuO_(2)(110)catalysts.The analysis of the potential gap of Fe_(2)M clusters indicates that Fe_(2)Mn,Fe_(2)Co,and Fe_(2)Ni clusters possess good bifunctional catalytic activity.Additionally,the catalytic activity of Fe_(2)Mn and Fe_(2)Co connected through 3,3′,5,5′-azobenzenetetracarboxylate linker to form Fe_(2)M–PCN–Fe_(2)M is explored.Compared with Fe_(2)Mn–PCN–Fe_(2)Mn,Fe_(2)Co–PCN–Fe_(2)Co,and isolated Fe_(2)M clusters,the mixed-metal Fe_(2)Co–PCN–Fe_(2)Mn possesses excellent bifunctional catalytic activity,and the values of potential gap on the Mn and Co sites of Fe_(2)Co–PCN–Fe_(2)Mn are 0.69 and 0.70 V,respectively.Furthermore,the analysis of the electron structure indicates that constructing a mixed-metal cluster can efficiently enhance the electronic properties of the catalyst.In conclusion,the mixed-metal cluster strategy provides a new approach to further design and synthesize high-efficiency bifunctional electrocatalysts.

Macroporous 3D carbon-nitrogen(CN)confined MoO_(x) catalyst for enhanced oxidative desulfurization of dibenzothiophene

Macroporous 3D carbon doped with nitrogen confined Mo catalyst(MoO_(x)@CN)had been prepared by a facile one-step pyrolysis technique using silica as a template and was employed for oxidative desulfurization(ODS)of dibenzothiophene(DBT)in model fuel with H2O_(2) as oxidant.The effect of different ope rating conditions(i.e.,reaction te mperature and time,catalyst dosage,H2O_(2)/DBT(O/S)molar ratio)were also systematic investigated.Under the optimal reaction condition,MoO_(x)@CN catalyst exhibited highly excellent ODS performance toward DBT,the highest sulfur removal efficiency can be up to 99.9%and sulfur content was wiped out from 800 ppm to 10 ppm.Due to the robust 3D structure promoting rapid transfer,in addition to the increased number of active sites induced by the Mo vacancies,the catalyst,prepared using chitosan and ammonium heptamolybdate in a mass ratio of 1:0.5,displayed rapid kinetics and low activation energy in the oxidation of dibenzothiophene.Moreover,it exhibited excellent recyclability after five cycles without any obvious decrease in catalytic activity for the oxidative desulfurization reaction.

Engineering large-scaled electrochromic semiconductor films as reproductive SERS substrates for operando investigation at the solid/liquid interfaces

Although surface-enhanced Raman spectroscopy(SERS)has been applied for gathering fingerprint information,even in single molecule analysis,the decayed Raman signals in aqueous solutions largely obstruct the on-site insight reaction process.In this study,large-scaled semiconductor films with multi-walled(TiO_(2)/WO_(3)/TiO_(2))nanopore distribution are fabricated by combining electrochemical anodization and sputtering technique,and then employed as the SERS substrates for detection of molecules at the solid/liquid interfaces.Given the remarkably improved electrochromic property of the multi-walled film,such SERS substrates were endowed with tunable oxygen vacancy(VO)density and distribution via simply applying electrochemical bias voltage,which enabled one to achieve an enhanced charge transfer efficiency and thus a remarkably increased Raman signal even in solution.The VO-rich SERS substrate is highly repeatable,thus providing a reliable platform for in-situ monitoring of the target molecules or intermediates at the solid/liquid interfaces.

Probing the catalytic activity of M-N_(4−x)O_(x) embedded graphene for the oxygen reduction reaction by density functional theory

In this work,the detailed oxygen reduction reaction(ORR)catalytic performance of M-N_(4−x)O_(x)(M=Fe,Co,and Ni;x=1−4)has been explored via the detailed density functional theory method.The results suggest that the formation energy of M-N_(4−x)O_(x)shows a good linear relationship with the number of doped O atoms.The adsorption manner of O_(2)on M-N_(4−x)O_(x)changed from end-on(x=1 and 2)to side-on(x=3 and 4),and the adsorption strength gradually increased.Based on the results for binding strength of ORR intermediates and the Gibbs free energy of ORR steps on the studied catalysts,we screened out two highly active ORR catalysts,namely Co-N_(3)O_(1)and Ni-N_(2)O_(2),which possess very small overpotentials of 0.27 and 0.32 V,respectively.Such activities are higher than the precious Pt catalyst.Electronic structure analysis reveals one of the reasons for the higher activity of Co-N_(3)O_(1)and Ni-N_(2)O_(2)is that they have small energy gaps and moderate highest occupied molecular orbital energy levels.Furthermore,the results of the density of states reveal that the O doping can improve the electronic structure of the original catalyst to tune the adsorption of the ORR intermediates.

Ultra-smooth CsPbI_(2)Br film via programmable crystallization process for high-efficiency inorganic perovskite solar cells

CsPbI_(2)Br is an ideal inorganic perovskite material with a reasonable bandgap for solar cell applications because of its advantage of superior thermal and phase stability. However, the performance of CsPbI2Br based solar cells highly relied on the perovskite crystallization process along with the interfacial contact engineering process between CsPbI_(2)Br perovskite and charge-transporting layers. In this work, a programmable crystallization method is developed to obtain ultra-smooth CsPbI_(2)Br perovskite film with a well-engineered contact interface in perovskite solar cells. This method combines a pre-stand-by process with a programmable gradient thermal engineering process, which mediates the crystal growth dynamics process of CsPbI2Br perovskite by controlling the release of dimethyl sulfoxide(DMSO) from its coordinates with the perovskite film, leading to high-quality CsPbI_(2)Br film with large-scale crystalline grains, reduced surface roughness, and low trap density. Fabricated perovskite devices based on CsPbI_(2)Br film obtained by this method deliver power conversion efficiency of 14.55 %;meanwhile, the encapsulated CsPbI_(2)Br perovskite device achieves a maximum efficiency of 15.07 %. This decent solar conversion efficiency demonstrates the effectiveness of the programmable crystallization method used in this work,which shows great potential as a universal approach in obtaining high-quality CsPbI_(2)Br perovskite films for fabricating high-efficiency inorganic perovskite solar cells.

An efficient method for computing excess free energy of liquid

We present a new theoretical method for efficient calculation of free energy of liquid. This interaction entropy method allows one to compute entropy and free energy of liquid from standard single step MD(molecular dynamics) simulation directly in liquid state without the need to perform MD simulations at many intermediate states as required in thermodynamic integration or free energy perturbation methods. In this new approach, one only needs to evaluate the interaction energy of a single(fixed) liquid molecule with the rest of liquid molecules as a function of time from a standard MD simulation of liquid and the fluctuation of distribution of this interaction energy is then used to calculate the interaction entropy of the liquid. Explicit theoretical derivation of this interaction entropy approach is provided and numerical calculations for the benchmark liquid water system were carried out using three different water models. Numerical analysis of the result was performed and comparison of the computational result with experimental data and other theoretical results were provided. Excellent agreement of calculated free energies with the experimental data using TIP4 P model is obtained for liquid water.

Thermodynamic Insights of Base Flipping in TNA Duplex: Force Fields, Salt Concentrations, and Free-Energy Simulation Methods

Threofuranosyl nucleic acid(TNA)is an analogue of DNA with a shift in the internucleotide linkages from the wild-type 5’-to-3’direction to 3’-to-2.’This alteration leads to higher chemical stability,less reactive groups,and lower conformational flexibility.Experimental observations indicate that these characteristic changes are attributable to a minimal perturbation of the interaction network,but the thermodynamic stability of the duplex remains unaltered in the TNA mutation.We applied the equilibrium and nonequilibrium free-energy simulations employing three popular assisted model building with energy refinement(AMBER)force fields for nucleotides to investigate this mutation-dependent behavior in the base flipping from T(DNA)residue to the T-to-TFT mutation(TNA)computationally.The force fields were performed similarly,as described in the base-paired state.However,after exploring the high-energy regions with free-energy simulations,we observed that these three force fields behaved differently.Previous reports conclude that the net-neutral and excess-salt simulations provided similar results.Nonetheless,our free-energy simulation indicated that the presence of excess salt affected the thermodynamic stability.The free-energy barrier along the base-flipping pathway was generally elevated upon the addition of excess salts,but the relative height of the free-energy barriers in DNA and TNA duplexes did not change significantly.This phenomenon emphasizes the importance of adding sufficient salts in the simulation scheme to reproduce the experimental condition.

缺陷富集型钌基电催化剂在强碱和强酸析氢反应中的高质量比活性研究

合理的设计策略以提高贵金属电催化剂在析氢反应(HER)中的利用率,对于简化HER的工艺流程,促进未来能源循环经济的发展至关重要.本文在约2.4 nm的Ru纳米颗粒上设计了大量的缺陷,使其在苛刻的酸性和碱性电解质中具有超高质量比反应活性.在过电势为100 m V时,所制备的缺陷富集型Ru基电催化剂DR-Ru表现出超高的HER翻转频率(碱性:16.4 s^(-1);酸性:20.6 s^(-1))和超低的过电势(碱性:η10=28.2 m V;酸性:η10=25.1 mV),明显优于其他Ru基电催化剂.此外,低配位的Ru活性位和表面部分晶格氧削弱了DR-Ru的Ru–H结合能,促进了酸性HER进行;同时有利于H2O分子分解,缓解了碱性HER过程中水分子的解离迟滞,导致其具有与酸性HER相当的高质量比活性.

Insights into the selective catalytic reduction of NO by NH_3 over Mn_3O_4(110):a DFT study coupled with microkinetic analysis

Nitric oxide(NO_x), as one of the main pollutants, can contribute to a series of environmental problems, and to date the selective catalytic reduction(SCR) of NO_x with NH_3 in the presence of excess of O_2 over the catalysts has served as one of the most effective methods, in which Mn-based catalysts have been widely studied owing to their excellent low-temperature activity toward NH3-SCR. However, the related structure-activity relation was not satisfactorily explored at the atomic level. By virtue of DFT+U calculations together with microkinetic analysis, we systemically investigate the selective catalytic reduction process of NO with NH_3 over Mn_3 O_4(110), and identify the crucial thermodynamic and kinetic factors that limit the catalytic activity and selectivity.It is found that NH3 prefers to adsorb on the Lewis acid site and then dehydrogenates into NH_2~* assisted by either the two-or three-fold lattice oxygen; NH_2~* would then react with the gaseous NO to form an important intermediate NH_2 NO that prefers to convert into N_2 O rather than N_2 after the sequential dehydrogenation, while the residual H atoms interact with O_2 and left the surface in the form of H_2 O. The rate-determining step is proposed to be the coupling reaction between NH_2~* and gaseous NO.Regarding the complex surface structure of Mn_3 O_4(110),the main active sites are quantitatively revealed to be O_(3 c) and Mn_(4 c).

Imitating trumpet shells: Mbius container molecules

Mbius container molecules C64H8,C60N4H4,and C58N6H2 with topological one-sided characteristics were constructed at the first time by imitating natural trumpet shells.The structure is an open cage with an inner hexagonal bridge.The bridge joints the outer and inner surfaces of the cage to form a new one-sided Mbius structure.The optimized structures of the three molecules in the singlet(the ground state),triplet and quintet states are obtained using the density functional theory(B3LYP).For the ground state structures of the three Mbius molecules,their oxidizabilities are weaker than that of the C60 and reducibilities are close to that of the stable C80 cage and slightly stronger than that of the C60.These may show that the unusual Mbius structures have some stability.Their potential properties were predicted,for example,the special aromaticity of the bridge ring due to the unique interaction between the bridge and the cage wall.These findings enlarge the knowledge of Mbius molecules. The idea of bionic and topological imitating in chemistry may promote the design of new complex-shaped nano-molecules and molecular devices.