12 research outputs found

    Searching for Highly Active Catalysts for Hydrogen Evolution Reaction Based on O‑Terminated MXenes through a Simple Descriptor

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    An efficient, earth-abundant, and low-cost catalyst for hydrogen evolution reaction (HER) is critical for sustainable hydrogen generation. In this work, we present a density-functional-theory-based screening among two-dimensional (2D) transition metal carbides (MXenes) with a fully O-terminated surface. The catalytic activity of 10 monometal carbides is first investigated, and Ti<sub>2</sub>CO<sub>2</sub> and W<sub>2</sub>CO<sub>2</sub> are found to be highly active catalysts for HER. Then, a volcano plot between the number of electron surface O atoms gains (<i>N</i><sub>e</sub>) and the absolute value of the free energy of hydrogen adsorption (Δ<i>G</i><sub>H</sub>) is established. A simple descriptor, <i>N</i><sub>e</sub>, is thus proposed to evaluate the HER performance of O-terminated MXenes. On this basis, TiVCO<sub>2</sub> is extracted with improved HER performance than Ti<sub>2</sub>CO<sub>2</sub> and W<sub>2</sub>CO<sub>2</sub> among 7 bimetal carbides. Our study provides new possibilities for cost-effective alternatives to Pt for HER, and, more importantly, develops a simple activity descriptor to efficiently search for highly active HER catalysts

    Single Molybdenum Atom Anchored on N‑Doped Carbon as a Promising Electrocatalyst for Nitrogen Reduction into Ammonia at Ambient Conditions

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    Ammonia (NH<sub>3</sub>) is one of the most important industrial chemicals owing to its wide applications in various fields. However, the synthesis of NH<sub>3</sub> at ambient conditions remains a coveted goal for chemists. In this work, we study the potential of the newly synthesized single-atom catalysts, i.e., single metal atoms (Cu, Pd, Pt, and Mo) supported on N-doped carbon for N<sub>2</sub> reduction reaction (NRR) by employing first-principles calculations. It is found that Mo<sub>1</sub>-N<sub>1</sub>C<sub>2</sub> can catalyze NRR through the enzymatic mechanism with an ultralow overpotential of 0.24 V. Most importantly, the removal of the produced NH<sub>3</sub> is rapid with a free-energy uphill of only 0.47 eV for the Mo<sub>1</sub>-N<sub>1</sub>C<sub>2</sub> catalyst, which is much lower than that for ever-reported catalysts with low overpotentials and endows Mo<sub>1</sub>-N<sub>1</sub>C<sub>2</sub> with excellent durability. The coordination effect on activity is further evaluated, showing that the experimentally realized active site, single Mo atom coordinated by one N atom and two C atoms (Mo-N<sub>1</sub>C<sub>2</sub>), possesses the highest catalytic performance. Our study offers new opportunities for advancing electrochemical conversion of N<sub>2</sub> into NH<sub>3</sub> at ambient conditions

    Nanosheet Supported Single-Metal Atom Bifunctional Catalyst for Overall Water Splitting

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    Nanosheet supported single-atom catalysts (SACs) can make full use of metal atoms and yet entail high selectivity and activity, and bifunctional catalysts can enable higher performance while lowering the cost than two separate unifunctional catalysts. Supported single-atom bifunctional catalysts are therefore of great economic interest and scientific importance. Here, on the basis of first-principles computations, we report a design of the first single-atom bifunctional eletrocatalyst, namely, isolated nickel atom supported on β<sub>12</sub> boron monolayer (Ni<sub>1</sub>/β<sub>12</sub>-BM), to achieve overall water splitting. This nanosheet supported SAC exhibits remarkable electrocatalytic performance with the computed overpotential for oxygen/hydrogen evolution reaction being just 0.40/0.06 V. The ab initio molecular dynamics simulation shows that the SAC can survive up to 800 K elevated temperature, while enacting a high energy barrier of 1.68 eV to prevent isolated Ni atoms from clustering. A viable experimental route for the synthesis of Ni<sub>1</sub>/β<sub>12</sub>-BM SAC is demonstrated from computer simulation. The desired nanosheet supported single-atom bifunctional catalysts not only show great potential for achieving overall water splitting but also offer cost-effective opportunities for advancing clean energy technology

    Activating Inert Basal Planes of MoS<sub>2</sub> for Hydrogen Evolution Reaction through the Formation of Different Intrinsic Defects

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    Nanoscale molybdenum disulfide (MoS<sub>2</sub>) has attracted ever-growing interest as one of the most promising nonprecious catalysts for hydrogen evolution reaction (HER). However, the active sites of pristine MoS<sub>2</sub> are located at the edges, leaving a large area of basal planes useless. Here, we systematically evaluate the capabilities of 16 kinds of structural defects including point defects (PDs) and grain boundaries (GBs) to activate the basal plane of MoS<sub>2</sub> monolayer. Our first-principle calculations show that six types of defects (i.e., V<sub>s</sub>, V<sub>MoS3</sub>, Mo<sub>S2</sub> PDs; 4|8a, S bridge, and Mo–Mo bond GBs) can greatly improve the HER performance of the in-plane domains of MoS<sub>2</sub>. More importantly, V<sub>s</sub> and Mo<sub>S2</sub> PDs and S bridge and 4|8a GBs exhibit outstanding activity in both Heyrovsky and Tafel reactions as well. Moreover, the different HER activities of defects are well-understood by an amendatory band-center model, which is applicable to a broad class of systems with localized defect states. Our study provides a comprehensive picture of the defect-engineered HER activities of a MoS<sub>2</sub> monolayer and opens a new window for optimizing the HER activity of two-dimensional dichalcogenides for future hydrogen utilization

    Hydrogen Activation on the Promoted and Unpromoted ReS<sub>2</sub> (001) Surfaces under the Sulfidation Conditions: A First-Principles Study

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    Hydrogen activation on the promoted and promoter-free ReS<sub>2</sub>(001) surfaces under the sulfidation conditions is studied by means of periodic density function theory (DFT) calculations within the generalized gradient approximation. First, surface-phase diagrams are investigated by plotting the surface free energy as a function of the chemical potential of S (μ<sub>S</sub>) on the unpromoted and promoted ReS<sub>2</sub> (001) surfaces with different loadings of nickel, cobalt, tungsten, and tantalum. The results show that on the unpromoted surface sulfur coverage of 25% and on the promoted surfaces sulfur coverage of 25% as well as 25% promoter modification are the most stable conditions, respectively, under hydrodesulfurization (HDS) reaction conditions. Second, hydrogen adsorption and dissociation are explored on these preferred surfaces. It is found that hydrogen adsorbs weakly on all the surfaces studied. The physical adsorption character makes its diffusion favorable, resulting in various adsorption sites and dissociation pathways, i.e., dissociation at surface Re or promote atom, at the interlayer, as well as at the adsorbed S atom. Calculated results show that hydrogen dissociation at the surface Re site is always kinetically favorable. All of the studied dopants can largely activate the adsorbed S but display distinct roles toward the activity of the nearest Re atom; i.e., Co/Ni dopant passivates the nearest surface Re while W/Ta activates it. The activity difference is found to be closely associated with the difference in the bond strength of metal–S and the resultant difference in the induced surface geometry. Moreover, promoter effect is localized because it seems nominal when the reaction occurs at a Re atom with one dopant atom separation. The present results provide a rational understanding of the activity difference between the promoter-free and the promoted surfaces, which would be helpful to further understand the mechanism of HDS and to enhance the development of highly active and selective hydrotreating catalysts

    Mechanical Properties, Electronic Structures, and Potential Applications in Lithium Ion Batteries: A First-Principles Study toward SnSe<sub>2</sub> Nanotubes

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    First-principles calculations were carried out to investigate the mechanical and electronic properties as well as the potential application of SnSe<sub>2</sub> nanotubes. It was found that the mechanical properties are closely dependent on diameter and chirality: the Young’s modulus (<i>Y</i>) increases with the enlargement of diameter and converges to the monolayer limit when the diameter reaches a certain degree; with a comparable diameter, the armchair nanotube has a larger Young’s modulus than the zigzag one. The significantly higher Young’s modulus of SnSe<sub>2</sub> nanotubes with the larger diameter demonstrates that the deformation does not easily occur, which is beneficial to the application as anode materials in lithium ion batteries because a large volume expansion during charge–discharge cycling will result in serious pulverization of the electrodes and thus rapid capacity degradation. On the other hand, band structure calculations unveiled that SnSe<sub>2</sub> nanotubes display a diversity of electronic properties, which are also diameter- and chirality-dependent: armchair nanotubes (ANTs) are indirect bandgap semiconductors, and the energy gaps increase monotonously with the increase of tube diameter, while zigzag nanotubes (ZNTs) are metals. The metallic SnSe<sub>2</sub> ZNTs exhibit terrific performance for the adsorption and diffusion of Li atom, thus they are very promising as anode materials in the Li-ion batteries

    Template-Grown MoS<sub>2</sub> Nanowires Catalyze the Hydrogen Evolution Reaction: Ultralow Kinetic Barriers with High Active Site Density

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    Molybdenum disulfide (MoS<sub>2</sub>) is considered to be one of the most promising low-cost catalysts for the hydrogen evolution reaction (HER). So far, the limited active sites and high kinetic barriers for H<sub>2</sub> evolution still impede its practical application in electrochemical water splitting. In this work, on the basis of comprehensive first-principles calculations, we predict that the recently produced template-grown MoS<sub>2</sub> nanowires (NWs) on Au(755) surfaces have both ultralow kinetic barriers for H<sub>2</sub> evolution and ultrahigh active site density simultaneously. The calculated kinetic barrier of H<sub>2</sub> evolution through the Tafel mechanism is only 0.49 eV on the Mo edges, making the Volmer–Tafel mechanism operative, and the Tafel slope can be as low as 30 mV/dec. Through substitution of the Au(755) substrate with non-noble metals, such as Ni(755) and Cu(755), the activity can be maintained. This work provides a possible way to achieve the ultrahigh HER activity of MoS<sub>2</sub>-based catalysts

    Oxidation Mechanism and Protection Strategy of Ultrathin Indium Selenide: Insight from Theory

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    Ultrathin indium selenide (InSe), as a newly emerging two-dimensional material with high carrier mobility and a broad absorption spectrum, has been the focus of current research. However, the long-term environmental instability of atomically thin InSe seriously limits its practical applications. To develop an effective strategy to protect InSe, it is crucial to reveal the degradation mechanism at the atomic level. By employing density functional theory and ab initio molecular dynamics simulations, we provide an in-depth understanding of the oxidation mechanism of InSe. The defect-free InSe presents excellent stability against oxidation. Nevertheless, the Se vacancies on the surface can react with water and oxygen in air directly and activate the neighboring In–Se bonds on the basal plane for further oxidation, leading to complete degradation of InSe into oxidation products of In<sub>2</sub>O<sub>3</sub> and elemental Se. Furthermore, we propose an efficient strategy to repair the Se vacancies by thiol chemistry. In this way, the repaired surface can resist oxidation from oxygen and retain the original high electron mobility of pristine InSe simultaneously

    Oxidation Mechanism and Protection Strategy of Ultrathin Indium Selenide: Insight from Theory

    No full text
    Ultrathin indium selenide (InSe), as a newly emerging two-dimensional material with high carrier mobility and a broad absorption spectrum, has been the focus of current research. However, the long-term environmental instability of atomically thin InSe seriously limits its practical applications. To develop an effective strategy to protect InSe, it is crucial to reveal the degradation mechanism at the atomic level. By employing density functional theory and ab initio molecular dynamics simulations, we provide an in-depth understanding of the oxidation mechanism of InSe. The defect-free InSe presents excellent stability against oxidation. Nevertheless, the Se vacancies on the surface can react with water and oxygen in air directly and activate the neighboring In–Se bonds on the basal plane for further oxidation, leading to complete degradation of InSe into oxidation products of In<sub>2</sub>O<sub>3</sub> and elemental Se. Furthermore, we propose an efficient strategy to repair the Se vacancies by thiol chemistry. In this way, the repaired surface can resist oxidation from oxygen and retain the original high electron mobility of pristine InSe simultaneously

    Oxidation Mechanism and Protection Strategy of Ultrathin Indium Selenide: Insight from Theory

    No full text
    Ultrathin indium selenide (InSe), as a newly emerging two-dimensional material with high carrier mobility and a broad absorption spectrum, has been the focus of current research. However, the long-term environmental instability of atomically thin InSe seriously limits its practical applications. To develop an effective strategy to protect InSe, it is crucial to reveal the degradation mechanism at the atomic level. By employing density functional theory and ab initio molecular dynamics simulations, we provide an in-depth understanding of the oxidation mechanism of InSe. The defect-free InSe presents excellent stability against oxidation. Nevertheless, the Se vacancies on the surface can react with water and oxygen in air directly and activate the neighboring In–Se bonds on the basal plane for further oxidation, leading to complete degradation of InSe into oxidation products of In<sub>2</sub>O<sub>3</sub> and elemental Se. Furthermore, we propose an efficient strategy to repair the Se vacancies by thiol chemistry. In this way, the repaired surface can resist oxidation from oxygen and retain the original high electron mobility of pristine InSe simultaneously
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