Apparent Barrier Research Articles

Mechanism of the Periodic Unsteady-State Water–Gas Shift Reaction on Highly Dispersed Cu-Loaded CeO2 Catalysts

Kinetic analyses of Ce4+ ↔ Ce3+ redox and CO2/H2 formation for the unsteady-state water–gas shift (WGS) reaction under periodic CO ↔ H2O feeds to Cu/CeO2 catalysts are carried out by in situ/operando ultraviolet–vis and infrared studies at 350 °C. Under CO, the Ce4+–OH species are reduced to produce H2, CO2, and Ce3+–□ (oxygen vacancy). Under the subsequent feed of H2O, Ce3+–□ is reoxidized by H2O to yield H2 and Ce4+–OH species. The rates of Ce4+ reduction/Ce3+ reoxidation are close to those of CO2/H2 formation for various Cu/CeO2 catalysts with different Cu loadings, providing quantitative evidence of the redox-based mechanism of the unsteady-state WGS reaction. Ce3+–□ reoxidation by H2O has a lower apparent barrier than the Ce4+–O reduction step. The H2O-promoted desorption of the adsorbed carbonates is responsible for CO2 formation under H2O. The characterization results suggest that the number of interfacial sites between the CeO2 and Cu species increases with decreasing Cu loading. Turnover frequencies per surface Cu site for the Ce4+ ↔ Ce3+ redox reaction and CO2/H2 formation increase with the number of interface sites. An associative redox mechanism based on the redox reaction between the oxidized state (Cu2+–OH adjacent to Ce4+ and Ce4+–OH) and the reduced state (Cu+–□–Ce3+) is proposed as the main catalytic cycle of the unsteady-state WGS reaction.

Aqueous Synthesis of Ultrastable Dual-Color-Emitting Lead-Free Double-Perovskite Cs2SnI6 with a Wide Emission Span Enabled by the Size Effect

Lead-free perovskites are promising materials for the functionalities of optoelectronic devices and systems. In this work, we develop a green-route approach for the synthesis of lead-free double-perovskite Cs2SnI6 powder and nanocrystals (NCs). An environmentally friendly aqueous solution is used to prepare the Cs2SnI6 powder at room temperature, and ultrasonicating the Cs2SnI6 powder in hexane yields the Cs2SnI6 NCs. The photoluminescence (PL) analysis reveals band gaps of 1.3 and 2.8 eV for the Cs2SnI6 powder and NCs, respectively. The Cs2SnI6 powder exhibits a remarkable photothermal effect driven by a laser of 785 nm with electric voltage ranging from 0.31 to 0.36 V, and the PL peak experiences a blueshift of 940 to 934 nm. Increasing temperature from 30 to 90 °C causes a blueshift of the PL peak of the Cs2SnI6 powder with an apparent energy barrier of 1.298 eV for thermal quenching. The Cs2SnI6 NCs exhibit a PL peak centered at 440 nm and a photoluminescence quantum yield of ∼7% at room temperature and have a long-term stability over 50 days. The anomalous behavior of the dual-color emission of the perovskite Cs2SnI6 is likely attributed to the size dependence of the dielectric constant.

Plasma‐catalytic Ammonia Synthesis via Eley‐Rideal Reactions: A Kinetic Analysis

AbstractThe reaction mechanism of plasma‐catalytic ammonia synthesis is not fully understood. MgO supported Ru, Co, Pt, Pd, Cu and Ag catalysts are tested in a DBD plasma at temperature between room temperature and 500 °C and plasma power between 3.8 W and 6.4 W. The resulting ammonia production in the presence of a plasma and a catalyst can be distinguished into (1) temperature‐independent plasma‐based ammonia synthesis, and (2) temperature‐dependent plasma‐catalytic ammonia synthesis. Turn‐over‐frequencies (TOF) are calculated based on the rate of the second pathway and chemisorption data, measuring the number of active sites. Underestimation of TOFs caused by ammonia decomposition was minimized by using exclusively observations at low ammonia concentration. The kinetic results suggest that the Eley‐Rideal reaction between N radicals from the plasma with chemisorbed H atoms is the rate‐determining step for plasma‐catalytic ammonia synthesis on Ru/MgO, Co/MgO, Pt/MgO, Pd/MgO, and Cu/MgO, with apparent activation barriers in the range 18–24 kJ mol−1. In contrast, the apparent activation barrier on Ag/MgO is significant higher at 30 kJ mol−1, suggesting a shift in rate determining step. The low H coverage on Ag may induce a shift to a Langmuir‐Hinshelwood pathway, via adsorption of N radicals on the metal surface.

Solvent Polarity and Framework Hydrophobicity of Hf-BEA Zeolites Influence Aldol Addition Rates in Organic Media

Solvent identity and pore polarity are known to influence Lewis acidic catalysis in zeolite pores for a variety of liquid-phase chemistries. We investigated how these parameters alter the rates of self-aldol addition of ethyl pyruvate (EP), a model biomass-derived compound, over hydrophobic and hydrophilic Hf-BEA zeolites in both toluene and acetonitrile solvents. Aldol addition rates are of first order across the entire EP activity range (0.02–0.4) for all four systems, consistent with the nucleophilic attack by the enolate as the rate-determining step and a single adsorbed EP as the most abundant reactive intermediate. Apparent first-order rate constants span 2 orders of magnitude across the four systems; at 363 K, the highest rates were observed over hydrophobic Hf-BEA-F in toluene (kapp = 0.36 (mmol) (mmol closed Hf)−1 (s)−1), while the lowest rates were observed in hydrophilic Hf-BEA-OH in an acetonitrile solvent (kapp = 0.0026 (mmol) (mmol closed Hf)−1 (s)−1). Apparent reaction enthalpies and entropies for each system, estimated using non-ideal transition-state theory, revealed that despite the substantial rate constant variation across the four systems, apparent enthalpies for Hf-BEA-F in both solvents and Hf-BEA-OH in acetonitrile were within the error of each other (∼70 kJ mol–1). Reactions performed using Hf-BEA-OH with toluene featured a higher apparent enthalpic barrier of 83.8 kJ mol–1. The differences between the systems are attributed to hydrogen-bonding interactions between the EP molecules and polar silanol nests during catalysis in toluene using Hf-BEA-OH, which hinder EP adsorption to the active site in the hydrophilic framework. These hydrogen-bonding interactions are not present when acetonitrile is used as the solvent, as acetonitrile itself binds to and blocks silanol groups. Equilibrium EP absorption measurements indicate that while both toluene and acetonitrile are present in pores during catalysis, neither solvent forms a tight solvation shell around EP in the pores that must be disrupted prior to EP adsorption. These findings show that aldol addition kinetics are not significantly modified by solvent polarity in hydrophobic frameworks beyond site-blocking effects; however, silanol nests in hydrophilic frameworks significantly alter substrate adsorption to the active site.

Tailoring Active Cu2O/Copper Interface Sites for N‐Formylation of Aliphatic Primary Amines with CO2/H2

AbstractHeterogeneously catalyzed N‐formylation of amines to formamide with CO2/H2 is highly attractive for the valorization of CO2. However, the relationship of the catalytic performance with the catalyst structure is still elusive. Herein, mixed valence catalysts containing Cu2O/Cu interface sites were constructed for this transformation. Both aliphatic primary and secondary amines with diverse structures were efficiently converted into the desired formamides with good to excellent yields. Combined ex and in situ catalyst characterization revealed that the presence of Cu2O/Cu interface sites was vital for the excellent catalytic activity. Density functional theory (DFT) calculations demonstrated that better catalytic activity of Cu2O/Cu(111) than Cu(111) is attributed to the assistance of oxygen at the Cu2O/Cu interface (Ointer) in formation of Ointer‐H moieties, which not only reduce the apparent barrier of HCOOH formation but also benefit the desorption of the desired N‐formylated amine, leading to high activity and selectivity.

Tailoring Active Cu2 O/Copper Interface Sites for N-Formylation of Aliphatic Primary Amines with CO2 /H2.

Heterogeneously catalyzed N-formylation of amines to formamide with CO2 /H2 is highly attractive for the valorization of CO2 . However, the relationship of the catalytic performance with the catalyst structure is still elusive. Herein, mixed valence catalysts containing Cu2 O/Cu interface sites were constructed for this transformation. Both aliphatic primary and secondary amines with diverse structures were efficiently converted into the desired formamides with good to excellent yields. Combined ex and in situ catalyst characterization revealed that the presence of Cu2 O/Cu interface sites was vital for the excellent catalytic activity. Density functional theory (DFT) calculations demonstrated that better catalytic activity of Cu2 O/Cu(111) than Cu(111) is attributed to the assistance of oxygen at the Cu2 O/Cu interface (Ointer ) in formation of Ointer -H moieties, which not only reduce the apparent barrier of HCOOH formation but also benefit the desorption of the desired N-formylated amine, leading to high activity and selectivity.

Solvent tunes the selectivity of alkenes epoxidation over Ti-Beta Zeolite: A systematic kinetic assessment on elementary steps, kinetically relevant and reaction barriers

Alkene epoxidation is a very important reaction process for the selective generation of chiral products, usually performed in some solvent(s) with different polarity, solubility and proton properties. These physical properties are entangled and do not explain very well whether they are mainly against population or stability of the reaction intermediates during catalysis. Here, we investigate how different solvents with known polarity properties (CH3CN, (CH3)2CO, CH3OH, etc.) affect the C6H10 transformation over Ti-Beta catalysts. Combining kinetic measurements, thermodynamic investigations and isotope experiments, the solvent was found not to change the reaction path or mechanism, with C6H10 epoxidation most likely following the Eley-Rideal mechanism and C6H10O hydration following a Langmuir-Hinshelwood mechanism, and both nucleophile and carbonium were found to be involved in the transition state (c.a. SN2 process) of hydration. However, in the epoxidation reaction of C6H10 with CH3CN and (CH3)2CO as solvents, the reaction order of [C6H10] is subtly different and the epoxidation rate increases with increasing volumetric fraction of CH3CN in the binary mixture, which indicates that the solvent affects the concentration of dissolved C6H10 surrounding the active sites and leads to the corresponding differences in activity and product selectivity. Nevertheless, the measured apparent reaction barrier (energy difference between transition state and MASIs) spans the elementary step of solvent modification, thus allowing for the observation of negligible solvent thermodynamic modification. Collectively, these findings provide clear evidence of solvent effects on alkene epoxidation and can be easily extended to some other reactions in solvents.

Climatological diagnostics and subseasonal‐to‐seasonal predictions of Madden–Julian Oscillation events

AbstractThe Madden–Julian Oscillation (MJO) is the dominant mode of tropical intraseasonal variability, which serves as a primary source of subseasonal‐to‐seasonal (S2S) predictability. Noticeably, MJO is not always a regularly recurring cycle but is characterized by discrete episodes. In this study, considering the quasi‐consecutive actives and eastward propagating features, a standard metric is proposed to identify MJO events based on the real‐time multivariate MJO (RMM) index. The re‐identification of historical MJO events reveals that there were 5.4 MJO events each year since 1981, and the average duration of each event is about 31.5 days. More MJO events tend to occur in the boreal winter and spring, with stronger intensity, longer duration and faster propagating speed than those in the boreal summer. Furthermore, MJO events are more likely to initiate in Phases 2 and 5, with a longer lifetime than those initiating in other phases. The amplitude and propagation characteristics of MJO events are strongly modulated by the dominant modes of sea surface temperature interannual variability with a strong regional dependence. Based on hindcast datasets of six S2S models, the prediction skill for the MJO is evaluated in the perspective of individual events. The longest leading time of the skilful prediction for individual MJO events ranges from 11 to 17 days, far below the traditional recognition. This result could be attributed to the apparent prediction barrier of MJO initiation, that is, a rapid decrease in prediction skill when predictions are carried out before the initiation of MJO events. In addition, the prediction skills of MJO events depends on interannual variabilities, with relatively higher skills under the conditions of the El Niño and Indian Ocean basin warming. These findings may shed light on the complexity and challenges of profoundly understanding and skilfully predicting MJO events.

Fusion-fission analysis of C12+Cm248 and O16+Pu244 nuclear reactions across the Coulomb barrier

By using the symmetric-asymmetric Gaussian barrier distribution (SAGBD) model, Wong formula, and coupled channel approach, heavy ion fusion dynamics is investigated for $^{12}\mathrm{C}+^{248}\mathrm{Cm}$ and $^{16}\mathrm{O}+^{244}\mathrm{Pu}$ reactions at energies lying below and near the Coulomb barrier. Coupling of various channels linked with the structure of participants to the relative motion of the collision partners is done by considering a Gaussian type of weight function in the SAGBD model and cross sections are found to be enhanced relative to the calculations obtained by the simple barrier penetration model. In the SAGBD model, the channel coupling effects are calculated in terms of channel coupling parameter ($\ensuremath{\lambda}$) and percentage reduction in the height of apparent fusion barrier with respect to the Coulomb barrier (${V}_{\mathrm{CBRED}}$). The channel coupling parameter estimates the cumulative influence of dominant intrinsic channels, which are responsible for the sub-barrier fusion enhancement. The SAGBD calculations appropriately explain the dynamics of $^{12}\mathrm{C}+^{248}\mathrm{Cm}$ and $^{16}\mathrm{O}+^{244}\mathrm{Pu}$ reactions at energies lying around the Coulomb barrier. The coupled channel analysis of the present reactions is done by using the code ccfull and the coupled channel calculations unambiguously identify the dominant influences of the rotational states up to ${10}^{+}$ spin states of the ground state rotational band of target isotopes in both reactions. In addition, the couplings to higher order deformation, such as ${\ensuremath{\beta}}_{4}$ for target and low lying quantum states of the projectile, are necessarily required to reproduce the experimental data of $^{12}\mathrm{C}+^{248}\mathrm{Cm}$ and $^{16}\mathrm{O}+^{244}\mathrm{Pu}$ reactions. Apart from the fusion analysis, the dynamical cluster-decay model (DCM) is applied to understand the fission dynamics of the $^{260}\mathrm{No}^{*}$ nucleus formed via the above-mentioned reactions. The decay study is carried out at the center-of-mass energies spread, ${E}_{\mathrm{c}.\mathrm{m}.}$ ($\ensuremath{\approx}79$ to 109 MeV) by including the quadrupole deformations (${\ensuremath{\beta}}_{2}$) and optimum orientations (${\ensuremath{\theta}}_{i}^{\mathrm{opt}}$) of the decaying fragments. According to the experimental observation, the noncompound nucleus (nCN) fission component competes with the compound nucleus (CN) fission processes. Consequently, the possibility of nCN contribution is also explored in the decay of the $^{260}\mathrm{No}^{*}$ compound nucleus. With an aim to have a comprehensive analysis of CN and nCN fission mechanisms, the role of the center-of-mass energy (${E}_{\mathrm{c}.\mathrm{m}.}$) and angular momentum ($\ensuremath{\ell}$) is explored in terms of various parameters of DCM such as fragmentation potential, preformation probability, barrier modification, etc.

Molecular Engineering of Silicon Phthalocyanine to Improve the Charge Transport and Ammonia Sensing Properties of Organic Heterojunction Gas Sensors

AbstractNovel organic heterostructures fabricated with a bilayer consisting of an axially substituted silicon phthalocyanine (R2‐SiPc) derivative and lutetium bis‐phthalocyanine (LuPc2) are investigated for their ammonia sensing properties. Surface and microstructure characterization of the heterostructure films reveal either compact or highly porous surface topography in (345F)2‐SiPc and Cl2‐SiPc‐based heterostructures, while electrical characterization reveals a strong influence of the axial substituent in R2‐SiPc on NH3 sensing capabilities. Electrical characterization further demonstrates an apparent energy barrier for interfacial charge transport, which is higher in the (345F)2‐SiPc/LuPc2 heterojunction device. In‐depth charge transport studies by impedance spectroscopy further reveal a resistive interface in (345F)2‐SiPc/LuPc2 and faster bulk and interfacial charge transport in Cl2‐SiPc/LuPc2 heterojunction devices. Different interfacial charge transport capabilities and surface topographies affect NH3 sensing properties of the two heterojunction devices, in which (345F)2‐SiPc/LuPc2 reveals a fast and non‐linear response with a limit of detection (LOD) of 310 ppb, while Cl2‐SiPc/LuPc2 exhibits a slow, and linear response to NH3 with LOD of 100 ppb. Finally, different metrological parameters of the two sensors are correlated to the respective gas‐material interactions, in which adsorption and diffusion regimes are modulated by the surface topography and hydrophobicity of the sensing layer.

Electrical properties of Cu/Pd2Si Schottky contacts to AlGaN/GaN-on-Si HEMT heterostructures

In this study, we analyze gold-free Cu/Pd2Si Schottky contacts to AlGaN/GaN-on-Si HEMT (high electron mobility transistor) heterostructures. The silicide layers are fabricated through magnetron sputtering deposition using a stoichiometric Pd2Si target and are subjected to post-gate annealing at different temperatures. After annealing at 500 °C the leakage currents of the planar diodes are reduced below 3.2 mA/cm2. The microstructures of the diodes are analyzed through transmission electron microscopy (TEM). The post-gate annealing increases lateral dimensions of silicide grains. The electrical properties of the contacts are determined by performing temperature-dependent current-voltage (I-V-T) measurements. The forward current exhibits a specific voltage dependence, which is interpreted based on the two-diode model, reflecting the properties of the Pd2Si/heterostructure interface along with those of the heterostructure itself. The model is fitted to extract the parameters of the Schottky contacts. The barrier height of 0.91 eV and ideality factor n = 1.5 are obtained after post-gate annealing at 500 °C. The effects of post-gate annealing on the forward conduction and leakage mechanisms are then discussed. A simple method is proposed to estimate the polarization charge density, which is required to calculate the electric fields in the heterostructure in the reverse bias. It is observed that post-gate annealing affects the I-V characteristics, likely by reducing the density of the unintentional donors and trap states, leading to an increase in the apparent barrier height along with a reduction in the density of defects contributing to the leakage current.

The polyoxometalates mediated preparation of phosphate-modified NiMoO4−x with abundant O-vacancies for H2 production via urea electrolysis

It is urgent to develop non-noble metal electrocatalysts with both excellent activity and durable stability for H2 production via water electrolysis. Electric energy is mainly consumed by the sluggish anodic oxygen evolution reaction (OER). The electrocatalytic urea oxidation reaction (UOR) has been regarded as a promising reaction to replace OER because of its small thermodynamic oxidation potential. However, developing a facile and large-scale preparation method for bifunctional hydrogen evolution reaction (HER) and UOR electrocatalysts is still challenging. Herein, phosphate-modified (4.46 atomic%) NiMoO4−x net-like nanostructures are formed on Ni foam (NF) via H3PMo12O40 etching strategy at room temperature (denoted as NF/P-NiMoO4−x). The etched NF can directly serve as HER electrode, and delivers overpotential of 116 mV at current density of 10 mA/cm2 with Tafel slope of 77.5 mV/dec. Furthermore, it displays excellent UOR activity with potential of 1.359 V at current density of 10 mA/cm2 and Tafel slope of 19.3 mV/dec. The apparent activation energy of NF/P-NiMoO4−x is 20.6 kJ/mol, lower than that of NF (37.7 kJ/mol), indicating smaller apparent barrier for CN bond cleavage in urea. The cell voltage of urea electrolysis is around 1.48 V for H2 production to deliver current density of 10 mA/cm2, and better long-term stability for 50 h than that of Ir/C||Pt/C. The etching solution can be recycled for five times by addition of H2O2, turning heteropoly blue into its original state. This work develops a facile and large-scale method to prepare bifunctional HER and UOR electrocatalysts for H2 production in a less-energy saving way via urea electrolysis.

Thermodynamics of high-pressure ice phases explored with atomistic simulations

Most experimentally known high-pressure ice phases have a body-centred cubic (bcc) oxygen lattice. Our large-scale molecular-dynamics simulations with a machine-learning potential indicate that, amongst these bcc ice phases, ices VII, VII′ and X are the same thermodynamic phase under different conditions, whereas superionic ice VII″ has a first-order phase boundary with ice VII′. Moreover, at about 300 GPa, the transformation between ice X and the Pbcm phase has a sharp structural change but no apparent activation barrier, whilst at higher pressures the barrier gradually increases. Our study thus clarifies the phase behaviour of the high-pressure ices and reveals peculiar solid–solid transition mechanisms not known in other systems.

Proton shuttling flattens the energy landscape of nitrite catalytic reduction

Water molecules can enhance or inhibit hydrogenation reactions depending on the nature of the reactive species and active sites. In metal-catalyzed nitrite (NO2–) reduction the presence of protons is essential to complete the reaction in the aqueous phase. By coupling rigorous kinetics studies of nitrite hydrogenation on Pd with kinetic isotope studies and theoretical calculations we have shown that, contrary to previously proposed mechanisms of surface H-insertion on NO*, in aqueous environments the reaction proceeds via H-shuttling in which protons move via the aqueous environment while the electrons reach the NO* through the metal in a concerted fashion. This unique mechanism flattens the energy landscape, which leads to the same apparent activation energy barrier (0.6 eV) for the formation of HNO* and HNOH*. These results are consistent with the hydrogen reaction orders, kinetic isotopic experiments, and micro-kinetic modeling including co-limiting reaction steps for NO* hydrogenation to HNO* and HNOH*. This work provides new insights that will be key in developing more efficient catalysts and processes for catalytic removal of micro-pollutants, such as nitrate and nitrite, in drinking water and more broadly to hydrogenation reactions in aqueous phase.

Engineering the Schottky Interface of 3.3 kV SiC JBS Diodes Using a P<sub>2</sub>O<sub>5</sub> Surface Passivation Treatment

A systematic study is presented into the impact of a P2O5 surface passivation treatment, carried out prior to the deposition of a high refactory metal contact to 3.3 kV JBS diodes. Electrical results from Mo, W and Nb diodes reveal that those diodes that undergo the treatment have a major leakage current reduction, most significantly by 3.5 orders of magnitude to 1.5×10-6 A.cm-2 for treated W diodes. When applied to fully optimized 3.3 kV Mo/SiC JBS diodes, the P2O5 surface passivation treatment reduces the apparent barrier height, as well as the leakage current. SIMS analysis reveals that during the treatment, phosphorous diffuses into the top 10 nm of the SiC, achieving a peak density of 1019 cm-3, while XPS results suggest some of this diffuses into the contact metal during the contact anneal, altering the SBH. TCAD simulations help give more insight into band diagram changes at the Schottky interface, where the partial activation of the phosphorous ions is shown to alter the Schottky barrier, promoting a thermionic field emission conduction, effectively lowering the barrier height at the interface in Mo/4H-SiC diodes.

GENETIC VARIABILITY IN Sechium spp. (Cucurbitaceae) EVALUATED WITH AFLP MARKERS

There are few studies in Mexico aimed at evaluating the genetic variability of Sechium spp. Despite certain biological variants are reported with very high potential to develop antineoplastic supplements to treat public health conditions. Using the Amplified Fragment Length Polymorphism (AFLP) technique, the genetic variability of a sample of 95 accessions of three species of Sechium (S. edule, S. chinantlense, S. compositum) was evaluated, with leaf DNA from the Banco Nacional de Germoplasma de Sechium edule en Mexico. Four combinations of AFPL were applied (EcoRI + ACC/MseI + CAC, EcoRI + ACC/MseI + CAT, EcoRI + ACC/MseI + CGC, and EcoRI + ACC/MseI + CGG). DNA samples were classified into three groups based on the flavour of the fruit (sweet, neutral, bitter). An average of 47.91% polymorphism, 0.16 heterozygosity, 32.83 number of polymorphic bands, and a zero Wright fixation index (Fst) was obtained. The evidence showed that the domesticated accessions (sweet, neutral) were separated from the bitter-taste genotypes. A monophyletic tree was generated with the genetic distance matrix and the neighbour-joining methodology. Analyses showed S. edule as the root taxon, deriving S. compositum and S. chinantlense as subgroups, and suggesting that there is not enough differentiation to treat them as separate species. The evaluated sample showed that there is no apparent reproductive barrier for genetic cross breeding. Genotypes behaved as a complex with evolutive dynamism; that genetic complexity would allow the design of new variants.

Heterojunction Engineering and Ideal Factor Optimization Toward Efficient MINP Perovskite Solar Cells

AbstractThe pursuit of high power conversion efficiency (PCE) and cost‐effective perovskite solar cells (PSCs) has spawned many innovative device structure designs. Compared with the traditional NIP type PSCs, electron transport layer (ETL) free PSCs have attracted growing attention due to their enormous potential in large area, low‐cost flexible application. However, there is still a lack of in‐depth understanding of the energy level arrangement indium tin oxide (ITO)/perovskite interface, resulting in poor device performance. Here, a metal/insulator/n‐type perovskite/p‐type spiro‐MeOTAD (MINP) structure is proposed to elaborate on the influence of the apparent work function and contact barrier change of the metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) junction on the carrier transfer and collection. Common and easily available 5‐amino‐valeric acid is inserted into the ITO/perovskite interface to form an insulating dipole layer and to ensure quasi‐ohmic contact at the front interface. Consequently, the device changes from Schottky/PN cascade heterojunction type to a single PN heterojunction device with its ideal factor decreasing from 3.35 to 2.05. Accordingly, the champion device achieves 19.37% PCE with significantly increased Voc and FF compared to the pristine device. This work provides a facile and effective method to improve the application potential of novel ETL‐free PSCs.

A theory for the coexistence of coiled and stretched configurational phases in the extensional flow of entangled polymer melts.

It has recently been demonstrated via nonequilibrium molecular dynamics (NEMD) simulation [M. H. Nafar Sefiddashti, B. J. Edwards, and B. Khomami, J. Chem. Phys. 148, 141103 (2018); Phys. Rev. Lett. 121, 247802 (2018)] that the extensional flow of entangled polymer melts can engender, within a definite strain-rate regime [expressed in terms of the Deborah number (De) based on the Rouse time], the coexistence of separate domains consisting primarily of either coiled or stretched chain-like macromolecules. This flow-induced phase separation results in bimodal configurational distributions, where transitions of individual molecules between the coiled and stretched states occur very slowly by hopping over an apparent energy activation barrier. We demonstrate that the qualitative aspects of this phenomenon can be described via the single-mode Rolie-Poly model including Convective Constraint Release (CCR) and finite extensibility of the chain-like macromolecules. This analysis reveals the physical mechanism for the configurational coexistence, namely, the nonlinear rate of change of the average entropic restoring force of a given entangled chain with extension. Under conditions of significant flow-induced disentanglement, the rate of change of the effective restoring force initially decreases with extension (effective spring softening) and then increases (hardens) as the maximum chain length is approached. When balanced by flow-induced chain stretching, we find that there can be two configuration states within the same De regime, as covered by the NEMD simulations; therefore, a region of conformational coexistence can indeed exist. However, we demonstrate that this coexistence of configurational microstates is only possible when the magnitude of the CCR parameters is consistent with the rate of flow-induced disentanglement, as observed in the NEMD simulations.

Revisited the mechanism of cobalt(III) catalyzed cyanation of arenes and heteroarenes: A DFT study

Transition metal catalyzed cyanation of arenes and heteroarenes by CH activation is an attractive process for functionalization of aromatic system. One such reaction under the catalysis of cobalt complex using N-cyano-N-phenyl-p-toluenesulfonamide as a cyanating reagent was studied theoretically. Metal mediated cyanation of aromatic ring involving one and more acetic acid have been explored. Our finding reveals that during the metal mediated activation of CH bond, presence of two acetic acid, increase the activation energy of the proton abstraction step. Comparison of the energy profile diagrams for single and double acetic acid mediated steps shows that the pathway, assisted by single acetic acid, is energetically more favorable. The calculated apparent activation barrier of the reaction is also consistent with the experimental report and it also shows high temperature (120 °C) has been needed to carry out the reaction.

SNP detection and population structure evaluation of Salix gordejevii Y. L. Chang et Skv. in Hunshandake Sandland, Inner Mongolia, China.

Single nucleotide polymorphisms (SNPs) are the most abundant and richest form of genomic polymorphism and, hence, are highly favorable markers for genetic map construction and genome-wide association studies. Based on the DNA specific-locus amplified fragment sequencing (SLAF-seq) for large-scale SNP detection, the genetic diversity and population structure of Salix gordejevii Y. L. Chang et Skv., a valuable sand-fixing shrub, was assessed in 199 accessions from 20 populations in Hunshandake Sandland of northern China. A total of 623.15M reads resulted in 30.49 × sequencing depth on average and a mean Q30 of 95.70%, and 2,287,715 SNPs in 178,509 polymorphic SLAF tags were obtained. By discarding minor allele frequency > 0.05 and integrity > 0.8, a total of 93,600 SNPs were retained for population genetic analyses, which revealed that 199 individuals could be divided into six groups based on cross-validation errors. However, this grouping pattern did not match the geographical distribution, indicating that there is no apparent geographic barrier in the blank areas where S. gordejevii was not distributed in Hunshandake Sandland. In addition, the physical distance of linkage disequilibrium decay in the analyzed S. gordejevii individuals was 18.5kb when r 2 = 0.1. The linkage disequilibrium decay distances for different chromosomes varied from 4.6kb (chromosome 16) to 37.8kb (chromosome 3). The obtained SNPs offer suitable marker resources for further genetic and genomic studies and will benefit S. gordejevii breeding programs.