12 research outputs found
Searching for Highly Active Catalysts for Hydrogen Evolution Reaction Based on O‑Terminated MXenes through a Simple Descriptor
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
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
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
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
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 (ÎĽ<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
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
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
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
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
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