eV Barrier Research Articles

Functionalized Mo2B2 MBenes: Promising anchoring and electrocatalysis materials for Lithium-Sulfur battery

Applications of Li-S batteries are primarily hindered by shuttling effect, poor electronic conductivity of sulfur and inactive decomposition of low-order lithium polysulfide (LiPS). To solve these problems, the anchoring and electrocatalysis properties of two-dimensional transition metal boride (MBene) have been extensively studied to provide general design principles for enhanced electrochemical performance in Li-S batteries. Our results show that direct application of bare Mo2B2 MBene in Li-S battery gives rise to the decomposition of high-order LiPSs, which originates from the excessively strong binding strength between S atoms and surface Mo atoms. Then, we highlight that surface functionalization on Mo2B2 MBene possesses suitable anchoring performance to suppress the shuttling effect. Meanwhile, owing to the excellent electronic conductivity even after the adsorption of LiPS, the functionalized MBenes effectively stimulate the redox electrochemistry in Li-S battery. Finally, accompanied with omnidirectional fast diffusion of Li atom, the functionalized MBene exhibits superior electrocatalysis activity for Li2S decomposition with ultra-low diffusion (0.191 eV) and decomposition (0.441 eV) barriers, improving the capability and coulombic efficiency of Li-S batteries. Our findings pioneer the application of MBenes as anchoring and electrocatalysis materials for Li-S batteries and provide a developed insight on the design of high-performance Li-S battery cathodes.

Mechanistic Aspects of the Photophysics of UVA Filters Based on Meldrum Derivatives.

Skin photoprotection against UVA radiation is crucial, but it is hindered by the sparsity of approved commercial UVA filters. Sinapoyl malate (SM) derivatives are promising candidates for a new class of UVA filters. They have been previously identified as an efficient photoprotective sunscreen in plants due to their fast nonradiative energy dissipation. Combining experimental and computational results, in our previous letter (J. Phys. Chem. Lett. 2021, 12, 337-344) we showed that coumaryl Meldrum (CMe) and sinapoyl Meldrum (SMe) are outstanding candidates for UVA filters in sunscreen formulations. Here, we deliver a comprehensive computational characterization of the excited-state dynamics of these molecules. Using reaction pathways and excited-state dynamics simulations, we could elucidate the photodeactivation mechanism of these molecules. Upon photoexcitation, they follow a two-step logistic decay. First, an ultrafast and efficient relaxation stabilizes the excited state alongside a 90° twisting around the allylic double bond, giving rise to a minimum with a twisted intramolecular excited-state (TICT) character. From this minimum, internal conversion to the ground state occurs after overcoming a 0.2 eV barrier. Minor differences in the nonradiative decay and fluorescence of CMe and SMe are associated with an additional minimum present only in the latter.

NO Binding Energies to and Diffusion Barrier on Pd Obtained with Velocity-Resolved Kinetics.

We report nitric oxide (NO) desorption rates from Pd(111) and Pd(332) surfaces measured with velocity-resolved kinetics. The desorption rates at the surface temperatures from 620 to 800 K span more than 3 orders of magnitude, and competing processes, like dissociation, are absent. Applying transition state theory (TST) to model experimental data leads to the NO binding energy E0 = 1.766 ± 0.024 eV and diffusion barrier DT = 0.29 ± 0.11 eV on the (111) terrace and the stabilization energy for (110)-steps ΔEST = 0.060–0.030+0.015 eV. These parameters provide valuable benchmarks for theory.

Electrical properties of an Ag/ZnS/p–Si heterojunction obtained by sputtered ZnS thin film

ZnS thin films were deposited on both soda-lime glass and p–Si substrates by radio frequency (RF) sputtering of a single ZnS target. The morphological, structural, and optical properties of the films were analyzed. It was seen that the thin films had (111) and (200) orientations of ZnS structure. The particle size distribution of the SEM image showed that the ZnS thin film had a 44.00 ± 0.56 nm average particle size. The optical band gap of ZnS thin films was calculated as 3.7 eV using UV–vis data. The electrical and photoelectrical properties of an Ag/ZnS/p–Si heterojunction were analyzed using current–voltage (I–V) and capacitance–voltage (C–V) measurements. The results showed that the device had 0.694 eV barrier height and 449 Ω series resistance values. In addition, the photodiode of the device was analyzed by I–V measurements under a solar simulator with AM1.5 global filter. Finally, the barrier height value obtained from C–V measurements was compatible with the I–V method.

Avoiding Sabatier’s conflict in bifunctional heterogeneous catalysts for the WGS reaction

Summary A new strategy for designing efficient bifunctional heterogeneous catalysts for the water-gas-shift (WGS) reaction (CO + H2O → CO2 + H2) is presented. We avoid conflicting tasks that require ∗OH or ∗O from dissociated water to adsorb on and then desorb from the substrate of a catalyst. Instead, the CO on metal directly obtains OH from water that is connected by weak hydrogen bonds to the substrate. The task of the substrate is to efficiently channel ∗H on its surface and release them as H2 gas. Experimental and theoretical results show that bifunctional catalysts with weakly reactive substrates have significantly higher CO conversion rates compared with highly reactive substrates that follow either the LH-associative or LH-redox process.

Ru/N-Polar GaN Schottky Diode With Less Than 2 μA/cm² Reverse Current

In this letter, we report the Schottky barrier diode investigation of ruthenium (Ru) deposited by atomic layer deposition on N-polar GaN. The Schottky diodes showed near-ideal thermionic current behavior under forward bias and reverse bias at various temperatures. The barrier height values extracted from both regions agreed well at each temperature and the barrier was extracted to be 0.77 eV at room temperature. The combination of the 0.77 eV barrier and thermionic current characteristic resulted in <; 2 μA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> reverse current at -5 V, which is a record-low value for N-polar GaN Schottky diodes. As a comparison, the Ru on Ga-polar GaN Schottky barrier diode, which has a barrier height of 1.0 eV, exhibited a ~ two-order of magnitude higher leakage than Ru on N-polar GaN at -5 V due to other parasitic leakage mechanisms.

Toward Rapid-Charging Sodium-Ion Batteries using Hybrid-Phase Molybdenum Sulfide Selenide-Based Anodes.

To attain both high energy density and power density in sodium-ion (Na+ ) batteries, the reaction kinetics and structural stability of anodes should be improved by materials optimization. In this work, few-layered molybdenum sulfide selenide (MoSSe) consisting of a mixture of 1T and 2H phases is designed to provide high ionic/electrical conductivities, low Na+ diffusion barrier, and stable Na+ storage. Reduced graphene oxide (rGO) is used as a conductive matrix to form 3D electron transfer paths. The resulting MoSSe@rGO anode exhibits high capacity and rate performance in both organic and solid-state electrolytes. The ultrafast Na+ storage kinetics of the MoSSe@rGO anode is attributed to the surface-dominant reaction process and broad Na+ channels. In situ and ex situ measurements are conducted to reveal the Na+ storage process in MoSSe@rGO. It is found that the MoS and MoSe bonds effectively limit the dissolution of the active materials. The favorable Na+ storage kinetics of the MoSSe@rGO electrode are ascribed to its low adsorption energy of -1.997eV and low diffusion barrier of 0.087eV. These results reveal that anion doping of metal sulfides is a feasible strategy to develop sodium-ion batteries with high energy and power densities and long life-span.

Silicene oxide: a potential Battery500 cathode for sealed non-aqueous lithium–oxygen batteries

The lithium-oxygen battery with high energy density holds a promising roadmap for future Eco society. However, its practical implementation is burdened by the sluggish cathodic kinetics and the severely polarized overpotential as well as the open-cell architecture. In this work, an emerging silicene oxide (SiO) material is predicted and evaluated as a potential cathode for sealed lithium-oxygen battery by first-principles/molecular dynamics simulations. Lithium is revealed to be chemisorbed on the surface of SiO with large binding energies, and afterward a semiconductor-to-metal transition (SMT) occurs in the system. Such an SMT switch can facilitate the charge transport and Li diffusion on the SiO surface (∼0.29 eV barrier), achieving a specific capacity of 609.11 mA h g−1 and an energy density of 359.37 W h kg−1. Moreover, a van der Waals heterostructure consisting of silicene oxide and graphene (Si2O2/G) is established for further improving battery performance. Such a heterostructure exhibits larger Li binding energy and higher open-circuit voltage due to the synergistic effect. Assisted by the solvent effect, the Si2O2 and Si2O2/G cathodes respectively present the energy densities as high as 804.03 W h kg−1 and 564.89 W h kg−1, providing great potentials for the demand of Battery500 consortium. This work proves the potential of Si2O2 as a cathode for sealed lithium-oxygen batteries and opens up interesting possibilities in the rational design of new cathode structures based on two-dimensional (2D) lightweight materials.

C3N monolayer with substitutional doping and strain modulation serving as anode material of lithium-ion batteries

Two-dimensional (2D) materials have been proved to be very promising anode materials of many kinds of batteries, including lithium-ion batteries (LIBs). The graphene-like carbon-nitrides with lightweight nature have received intense attention. The polyaniline (C3N) multilayer has shown its capabilities in LIBs, but C3N monolayer delays its arrival at application owing to too weak lithium (Li) adsorption. In this study, for the first time, the application of C3N monolayer as anode material for LIBs is realized by introducing heteroatom doping (B, O and S) based on first-principles simulations. The O-doped C3N (ON-C3N) offers Li storage capacity of 534.42 mAh g−1, low open circuit voltage (OCV) of 0.02 V, low Li adsorption energy of −3.64 eV and single Li atom migration energy barrier of 0.78 eV. Moreover, SN-C3N can dramatically lower the migration barrier of Li (0.12 eV) with respect to that on pristine C3N (0.41 eV). Further calculations show that the Li adsorption on C3N can be enhanced and migration barrier will decrease through the application of strain. This work demonstrates that heteroatom doping coupled with strain modulation is proved to be an effective and feasible strategy for the design of high-performance carbon-based 2D anode materials of batteries.

Energy Band Alignment of Few-Monolayer WS2 and WSe2 with SiO2 Using Internal Photoemission Spectroscopy

Internal photoemission spectroscopy was used to determine the valence band top energy position in few-monolayer WS2 and WSe2 films directly synthesized on top of the SiO2 insulator. It is found that in WS2 the valence band top edge lies systematically higher (by 0.4–0.7 eV) in energy than that in WSe2. This unexpected trend is seen for several synthesis methods suggesting it to be the intrinsic property of these W-based layered dichalcogenides. At the same time, a change in the WS2 synthesis method from metal sulfurization to chemical vapor deposition leads to a ≈0.3 eV barrier change indicating a non-negligible impact of interface charges or dipoles. The influence of synthesis chemistry on the WSe2/SiO2 interface barrier appears to be marginal at least for the selenization and molecular-beam epitaxy growth methods.

Li-ion transport at the interface between a graphite anode and Li2CO3solid electrolyte interphase:ab initiomolecular dynamics study

Understanding and the control of Li-ion (Li+) transport across the interface between the anode and solid electrolyte interphase (SEI) film or electrolyte is a key issue in battery electrochemistry and interface science. In this study, we investigated the structural, electronic and free energy properties of Li+ migration between a Li-intercalated graphite anode LiCx and Li2CO3 SEI film, by using ab initio molecular dynamics and free energy calculations. We compared three types of graphite edges: H-, OH- and mixed (H, OH, COOH)-terminations, and three cases of transferred Li-ions: Li+ constructing the SEI, excess Li+ and excess Li0 (excess Li+ + e- in anode). After validation of our calculations with Li2CO3 and LiCx bulk systems, we sampled the interfacial structures under thermodynamic equilibrium and demonstrated that the OH- and mixed-terminations had larger binding energies. The calculated free energy profiles of Li+ intercalation from the Li2CO3 SEI to LiC24 showed barriers larger than 1.2 eV irrespective of the terminations and Li+ cases. We also clarified that the charges of Li ions did not change much upon the intercalation. Based on these results and the calculated Li chemical potential, we constructed the probable free energy profile of Li+ between the anode and cathode under charging and discharging. This profile model suggest a possible electric field approximation for the charging stage, and the resultant free energy profiles with such fields gave a ca. 0.5 eV barrier under charging, which was consistent with the experimental values. The present picture will give a crucial insight into Li-ion transport at the battery interfaces.

Intriguing electronic and optical properties of M2CX2 (M = Mo, W; X = O, F) MXenes and their van der Waals heterostructures

M2CX2 (M = Mo,W; X = O,F) MXenes and their van der Waals heterostructures are investigated by first-principle calculations. Phonon spectrum has shown that Mo2CO2/W2CO2 and Mo2CF2/W2CO2 heterostructures and corresponding monolayers are dynamically stable. W2CO2 exhibits the properties of topological insulator and Mo2CO2 is narrow band gap semiconductor, while Mo(W)2CF2 are metals. Mo2CO2/W2CO2 heterostructure indicates a possible topological feature similar to corresponding monolayers and reveals type-II band alignment. Mo2CF2/W2CO2 heterostructure generating n-type Schottky contact with 0.139 eV barrier height. Large absorption in the visible region is observed for Mo2CO2 and blue shift is noticed for W2CO2 and W2CO2/Mo2CO2heterostructure, especially the part contributed by Mo2CO2.

First-Principles Investigations of Single Metal Atoms (Sc, Ti, V, Cr, Mn, and Ni) Embedded in Hexagonal Boron Nitride Nanosheets for the Catalysis of CO Oxidation

We evaluated isolated transition metal atoms (Sc, Ti, V, Cr, Mn, and Ni) embedded in hexagonal-BN as novel single atom catalysts for CO oxidation. We predicted that embedded Ni atoms should have superior performance for this task. Ti, V, and Mn bind CO2 too strongly and so the reaction will not proceed smoothly. We studied the detailed reaction processes for Sc, Cr, and Ni. The Langmuir–Hinshelwood (LH), Eley–Rideal (ER), and the new termolecular Eley–Rideal (TER) processes for CO oxidation were investigated. Sc was not effective. Cr primarily used the ER process, although the barrier was relatively large at 1.30 eV. Ni was the best of the group, with a 0.44 eV barrier for LH, and a 0.47 eV barrier for TER. Therefore, we predicted that the LH and TER processes could operate at relatively low temperatures between 300 and 500 K.

DFT study on the oxygen titanium porphyrin as sustainable cyclic catalyst for water splitting

With global resource shortage and deterioration of ecological environment, the research and development of clean and renewable energy is of vital importance. Using first-principles calculations, we firstly study water splitting catalyzed by metal based biomolecule porphyrin (MPP) (M = Mg, Ba, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn). Among all the systems, after releasing electron, TiPP is the most effective catalyst for H2O splitting. TiPP and the remainder O atom form the very stable structure OTiPP. The H2O + OTiPP can release electron with the 6.76 eV potential barrier. The releasing electron process of porphyrin can be easily realized under the effect of solar energy by experiment study. After releasing electron, OTiPP can effectively catalyze the dissociation of H+ from H2O in an exothermic process. The desorption of O atom is an endothermic process with 0.72 eV barrier. The H2O + OTiPP system can readily return to its original state OTiPP, in other word, the OTiPP can be a sustainable cycling catalyst for water splitting under the effect of potential barrier transfer. The whole catalytic process is remarkable clean without any pollution. This method may open up new avenues for the development of future clean energy and extraordinary biomimetic photosynthesizers.

Nanoscale Investigation of Defects and Oxidation of HfSe2.

HfSe2 is a very good candidate for a transition metal dichalcogenide-based field-effect transistor owing to its moderate band gap of about 1 eV and its high-κ dielectric native oxide. Unfortunately, the experimentally determined charge carrier mobility is about 3 orders of magnitude lower than the theoretically predicted value. This strong deviation calls for a detailed investigation of the physical and electronic properties of HfSe2. Here, we have studied the structure, density, and density of states of several types of defects that are abundant on the HfSe2 surface using scanning tunneling microscopy and spectroscopy. Compared to MoS2 and WSe2, HfSe2 exhibits similar type of defects, albeit with a substantially higher density of 9 × 1011 cm–2. The most abundant defect is a subsurface defect, which shows up as a dim feature in scanning tunneling microscopy images. These dim dark defects have a substantially larger band gap (1.25 eV) than the pristine surface (1 eV), suggesting a substitution of the Hf atom by another atom. The high density of defects on the HfSe2 surface leads to very low Schottky barrier heights. Conductive atomic force microscopy measurements reveal a very small dependence of the Schottky barrier height on the work function of the metals, suggesting a strong Fermi-level pinning. We attribute the observed Fermi-level pinning (pinning factor ∼0.1) to surface distortions and Se/Hf defects. In addition, we have also studied the HfSe2 surface after the exposure to air by scanning tunneling microscopy and conductive atomic force microscopy. Partly oxidized layers with band gaps of 2 eV and Schottky barrier heights of ∼0.6 eV were readily found on the surface. Our experiments reveal that HfSe2 is very air-sensitive, implying that capping or encapsulating of HfSe2, in order to protect it against oxidation, is a necessity for technological applications.

Insight into the formation mechanism of C[sbnd]C chain in ethanol synthesis at the interface of partially hydroxylated γ-Al2O3 (110D) surface and polyethylene glycol solvent

A detailed reaction network has been constructed for ethanol synthesis at the interface of partially hydroxylated γ-Al2O3 (110D) surface and polyethylene glycol (PEG) solvent using periodic density functional theory calculations, which provides a first glimpse into the plausible reaction mechanism for ethanol synthesis. The formation of key intermediate CH3 is the rate determining step of the overall process, accompanied with a reaction barrier of 1.29 eV. Based on thermodynamic, kinetic data and Bader charge analyses, we confirm that the methyl carbonylation is responsible for the initial CC bond formation, which needs to overcome a 0.96 eV barrier and is exothermic by1.67 eV. The hydroxyl coverage conditions formed by dissociative adsorbed H2O govern the key active sites on the γ-Al2O3 (110D) surface which in turn has a significant role in determining the dominant reaction mechanism. Meanwhile, the absence of PEG solvent also affects the optimal reaction route of ethanol synthesis and the essential reason is the existence of fairly strong hydrogen bonds. Our findings manifest the interface located between partially hydroxylated γ-Al2O3 (110D) surface and PEG solvent possesses decent catalytic performance for ethanol synthesis and facilitates providing new strategy to tune and design promising CuZnAl catalysts for ethanol synthesis.

Perovskite/p-Si photodiode with ultra-thin metal cathode

Perovskites have attracted great interest because they provide promising improvement for solar cells. Yet, the perovskites have not been extensively used by the researchers for diode applications. In this study, both Al/p-type Si and Al/perovskite/p-type Si devices have been obtained. We used a facile and cost-effective way of making perovskite thin film layer between the ultra-thin metal and semiconductor as an interfacial layer by spin coating technique as well distributed film. In order to keep costs low, aluminum was chosen as the cathode material. The Al/p-type Si and Al/perovskite/p-type Si devices have exhibited good rectifying properties and calculated rectifying ratio of the devices are 2.39 × 103 and 4.56 × 104 at 1 V, respectively. Photodiode properties of the device have been illustrated and discussed in the details by calculating some diode parameters. While the Al/p-type Si device has 1.53 ideality factor value and 0.72 eV barrier height, the ideality factor and barrier height values of Al/perovskite/p-type Si device have been obtained as 2.12 and 0.87 eV, respectively under dark condition. The solar cell efficiency and fill factor values of the Al/perovskite/p-type Si device are 7.44 × 10−3 and 23.7, respectively. Such devices can find applications as rectifiers and photodiodes in industry.

Electronic Structures and Nanofilm Growth of 2,7-Dioctyl[1]Benzothieno[3,2-b]Benzothiophene on Black Phosphorus.

The interfacial electronic structure and morphology of nanofilm of 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on black phosphorus (BP) was investigated with photoemission spectroscopy (PES) and atomic force microscopy (AFM). The heterojunction of C8-BTBT/BP is a straddling one with a hole injection barrier of 1.41 eV and electron injection barrier of 2.43 eV from BP to C8-BTBT. There is a 0.18 eV interface dipole pointing from BP to C8-BTBT, which means a relative weak interaction of substrate BP and the C8-BTBT molecules. Volmer-Weber growth mode of C8-BTBT nanofilm on BP was confirmed and the C8-BTBT molecules adopt standing up configuration.

Catalytic activity of γ-AlOOH (0 0 1) surface in syngas conversion: Probing into the mechanism of carbon chain growth

Identifying the exact mechanism of CC chain formation in syngas conversion to C2 oxygenate is a significant yet challenging issue. Based on a detailed density functional theory study, we find for the first time that γ-AlOOH (0 0 1) surface not only has specific activity for the carbon chain growth but also prefers an unconventional route for syngas conversion to ethanol. Our results reveal that the optimal route starts with CO hydrogenation to CHO, followed by reacting with CO to form key intermediate CH and release CO2, then the initial CC chain is formed via CO insertion into CH along with conquering a 0.76 eV barrier and exothermic by 1.90 eV, finally CHCO undergoes successive hydrogenation to produce ethanol in which the step of CH formation is identified as the rate-determining step of the overall process. In addition, as determined from the Bader charge analysis, carbon chain growth proceeding by CO insertion into CH is more facile. Moreover, the arising of CO2 during the process of syngas conversion to ethanol is inevitable, which is well consistent with our previous experiments. Notably, compared to our previously reported γ-AlOOH (1 0 0) surface, the γ-AlOOH (0 0 1) surface is inclined to trigger syngas conversion because the more saturated adsorption sites on the γ-AlOOH (0 0 1) surface lower the barriers associated with corresponding steps by weakening the absorption of key intermediates with suitable binding energy. The insights might be valuable for rational tailoring and designing of better, stable catalysts with superior reactivity involved in syngas conversion.

Atomic-Scale Core/Shell Structure Engineering Induces Precise Tensile Strain to Boost Hydrogen Evolution Catalysis.

Tuning surface strain is a new strategy for boosting catalytic activity to achieve sustainable energy supplies; however, correlating the surface strain with catalytic performance is scarce because such mechanistic studies strongly require the capability of tailoring surface strain on catalysts as precisely as possible. Herein, a conceptual strategy of precisely tuning tensile surface strain on Co9 S8 /MoS2 core/shell nanocrystals for boosting the hydrogen evolution reaction (HER) activity by controlling the MoS2 shell numbers is demonstrated. It is found that the tensile surface strain of Co9 S8 /MoS2 core/shell nanocrystals can be precisely tuned from 3.5% to 0% by changing the MoS2 shell layer from 5L to 1L, in which the strained Co9 S8 /1L MoS2 (3.5%) exhibits the best HER performance with an overpotential of only 97 mV (10 mA cm-2 ) and a Tafel slope of 71 mV dec-1 . The density functional theory calculation reveals that the Co9 S8 /1L MoS2 core/shell nanostructure yields the lowest hydrogen adsorption energy (∆EH ) of -1.03 eV and transition state energy barrier (∆E2H* ) of 0.29 eV (MoS2 , ∆EH = -0.86 eV and ∆E2H* = 0.49 eV), which are the key in boosting HER activity by stabilizing the HER intermediate, seizing H ions, and releasing H2 gas.