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1.
J Phys Chem Lett ; 12(41): 10190-10196, 2021 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-34644080

RESUMO

Two-dimensional (2D) photocatalytic material is a vital project for modern solar energy conversion and storage. Despite a vast family of potential 2D photocatalysts that is demonstrated, their commercial applications are severely limited because of fast photogenerated electron-hole recombination. Here, based on first-principles, we propose a general paradigm to boost the separation of photoexcited charge carriers in 2D photocatalysts by stacking engineering. Taking the emerging water splitting photocatalyst MoSi2N4 as an example, we show that specific interlayer stacking-induced electric polarization plays a significant role in altering the electronic properties and thus the suppressed recombination rate of photoexcited carriers. Moreover, we find that the catalytic performance can be further controlled by vertical strain. These generalized findings not only highlight the importance of stacking-induced electric polarization but also offer new prospects for the design and application of 2D photocatalysts.

2.
J Phys Chem Lett ; 12(36): 8847-8854, 2021 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-34494851

RESUMO

Designing efficient organic photovoltaic (OPV) materials purposefully is still challenging and time-consuming. It is of paramount importance in material development to identify basic functional units that play the key roles in material performance and subsequently establish the substructure-property relationship. Herein, we describe an automatic design framework based on an in-house designed La FREMD Fingerprint and machine learning (ML) algorithms for highly efficient OPV donor molecules. The key building blocks are identified, and a library consisting of 18 960 new molecules is generated within this framework. Through investigating the chemical structures of materials with different performance, a guidance on designing efficient OPV materials is proposed. Furthermore, the most promising candidates exhibit a predicted power conversion efficiency (PCE) value of over 15% when combined with acceptor Y6. Density functional theory (DFT) studies show these candidate materials possess exceptional potential for efficient charge carrier transport. The proposed framework demonstrates the ability to design new materials based on the substructure-property relationship built by ML, which provides an alternative methodology for applying ML in new material discovery.

3.
Phys Chem Chem Phys ; 23(35): 19627-19635, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34524282

RESUMO

Layered biaxial hyperbolic molybdenum trioxide (α-MoO3) with weak van der Waals (vdW) interlayer bonding recently received extensive attention due to its anisotropic dielectric response to infrared (IR) radiation, which couples to the lattice vibrations and allows for manipulating the radiative energy transport. However, the understanding of IR-active phonon modes and dielectric function of it has not yet been fully achieved. Here, by utilizing mode-level first-principles analysis based on density functional theory (DFT), the phonon modes contributing to the IR dielectric response of α-MoO3 are fully determined. The anisotropic IR-active modes are identified from lattice vibration analysis, allowing for a clear evaluation of the IR absorption contribution from the weak or strong IR phonon modes. By further employing anharmonic-lattice dynamics calculations, the damping of the corresponding IR modes is directly obtained. This approach enables predictions of IR optical properties without any fitting or assumed parameters. Our predictions bridge the scientific gap of comprehensively understanding the unreported IR-active phonon modes of α-MoO3 and overall agree well with available experimental data, placing our DFT-based method at a privileged stage for accurately predicting the IR optical properties of α-MoO3. These comprehensive understandings of the IR phonons and dielectric properties of α-MoO3 pave the way for nanophotonic devices with tunable functionalities and enable design of α-MoO3 for advanced optical devices.

4.
J Hazard Mater ; 422: 126761, 2021 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-34418836

RESUMO

Carbon and its analogous nanomaterials are beneficial for toxic gas sensors since they are used to increase the electrochemically active surface region and improve the transmission of electrons. The present article addresses a detailed investigation on the potential of the monolayer PC3 compound as a possible sensor material for environmentally toxic nitrogen-containing gases (NCGs), namely NH3, NO, and NO2. The entire work is carried out under the frameworks of density functional theory, ab-initio molecular dynamics simulations, and non-equilibrium Green's function approaches. The monolayer-gas interactions are studied with the van der Waals dispersion correction. The stability of pristine monolayer PC3 is confirmed through dynamical, mechanical, and thermal analyses. The mobility and relaxation time of 2D PC3 sensor material with NCGs are obtained in the range of 101-104 cm2 V-1 s-1 and 101-103 fs for armchair and zigzag directions, respectively. Out of six possible adsorption sites for toxic gases on the PC3 surface, the most prominent site is identified with the highest adsorption energy for all the NCGs. Considering the most stable configuration site of the NCGs, we have obtained relevant electronic properties by utilizing the band unfolding technique. The considerable adsorption energies are obtained for NO and NO2 compared to NH3. Although physisorption is observed for all the NCGs on the PC3 surface, NO2 is found to convert into NO and O at 5.05 ps (at 300 K) under molecular dynamics simulation. The maximum charge transfer (0.31e) and work function (5.17 eV) are observed for the NO2 gas molecule in the series. Along with the considerable adsorption energies for NO and NO2 gas molecules, their shorter recovery time (0.071 s and 0.037 s, respectively) from the PC3 surface also identifies 2D PC3 as a promising sensor material for those environmentally toxic gases. The experimental viability and actual implications for PC3 monolayer as NCGs sensor material are also confirmed by examining the humidity effect and transport properties with modeled sensor devices. The transport properties (I-V characteristics) reflect the significant sensitivity of PC3 monolayer toward NO and NO2 molecules. These results certainly confirm PC3 monolayer as a promising sensor material for NO and NO2 NCG molecules.

5.
Chempluschem ; 86(8): 1211-1224, 2021 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-34448548

RESUMO

Electrocatalytic reduction of dinitrogen has emerged as a new strategy for ammonia synthesis. Despite being environmentally benign and energy-saving, it suffers from low conversion efficiency and short yield of ammonia because of the challenges of activating the inert N≡N bond at room temperature and atmospheric pressure. As a result of this, researchers proposed to reduce the nitrogenous species, one category of air and water pollutants, into valuable ammonia. Although remaining largely underexplored, this alternative approach shows promising efficiency for ammonia synthesis, while achieving high catalytic activity and selectivity remains challenging. In this Minireview, we summarize recent electrocatalytic performances of denitrification with selective formation to ammonia in terms of proposed active sites and reaction mechanisms. Additionally, we discuss the common issues in the state-of-the-art experimental tests and highlight the breakthroughs via computational screening of electrode materials. The aim of this is to steer the future research directions in the field, which is aiming for an optimal catalytic system with higher activity and selectivity for electrocatalytic denitrification.

6.
Phys Chem Chem Phys ; 23(32): 17129-17133, 2021 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-34355230

RESUMO

Theoretical calculations are an effective strategy to complement and understand the experimental results in atomistic detail. Ehrenfest molecular dynamics simulations based on the real-time time-dependent density functional tight-binding (RT-TDDFTB) approach are performed to reveal for the first time the electron dynamics for the charge separation of pyrene-functionalized middle-sized Au70S20(PH3)16 and large-sized Au108S24(PR3)16 (R = H, CH3, C2H5, C6H5) clusters. The proposed mechanism uncovers an ultrafast and irreversible photoinduced charge transfer from the gold nanocluster (GNC) unit to the pyrene derivative in all cases. By a Fourier transform analysis of the dynamics, the effect of vibronic couplings is highlighted. The Au108S24(PPh3)15PPh2Pyr system exhibits the best performance for charge separation.

7.
J Phys Chem Lett ; 12(32): 7708-7716, 2021 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-34355897

RESUMO

NOx emission heavily affects our environment and human health. Photocatalytic denitrification (deNOx) attracted much attention because it is low-cost and nonpolluting, but undesired nitrite and nitrate were produced in reality, instead of harmless N2. Unveiling the active sites and the photocatalytic mechanism is very important to improve the process. Herein, we have employed a combinational scenario to investigate the reaction mechanism of NO2 and H2O on anatase TiO2(101). On the one hand, a polaron-corrected GGA functional (GGA + Lany-Zunger) was applied to improve the description of electronic states in photoassisted processes. On the other hand, a reaction phase diagram (RPD) was established to understand the (quasi) activity trend over both perfect and defective surfaces. It was found that a perfect surface is more active via the Eley-Rideal mechanism without NO2 adsorption, while the activity on defective surfaces is limited by the sluggish recombinative desorption. A photogenerated hole can weaken the OH* adsorption energies and circumvents the scaling relation of the dark reaction, eventually enhancing the deNOx activity significantly. The insights gained from our work indicate that tuning the reactivity by illumination-induced localized charge and diverse reaction pathways are two methods for improving adsorption, dissociation, and desorption processes to go beyond the conventional activity volcano plot limit of dark conditions.


Assuntos
Dióxido de Nitrogênio/química , Titânio/química , Adsorção , Catálise/efeitos da radiação , Cinética , Modelos Químicos , Termodinâmica , Titânio/efeitos da radiação , Raios Ultravioleta , Água/química
8.
Adv Sci (Weinh) ; 8(18): e2101624, 2021 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-34291609

RESUMO

While graphene grain boundaries (GBs) are well characterized experimentally, their influence on transport properties is less understood. As revealed here, phononic thermal transport is vulnerable to GBs even when they are ultra-narrow and aligned along the temperature gradient direction. Non-equilibrium molecular dynamics simulations uncover large reductions in the phononic thermal conductivity (κp ) along linear GBs comprising periodically repeating pentagon-heptagon dislocations. Green's function calculations and spectral energy density analysis indicate that the origin of the κp reduction is hidden in the periodic GB strain field, which behaves as a reflective diffraction grating with either diffuse or specular phonon reflections, and represents a source of anharmonic phonon-phonon scattering. The non-monotonic dependence with dislocation density of κp uncovered here is unaccounted for by the classical Klemens theory. It can help identify GB structures that can best preserve the integrity of the phononic transport.

9.
J Chem Theory Comput ; 17(8): 5239-5247, 2021 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-34231365

RESUMO

Band alignment effects of anatase and rutile nanocrystals in TiO2 powders lead to electron-hole separation, increasing the photocatalytic efficiency of these powders. While size effects and types of possible alignments have been extensively studied, the effect of interface geometries of bonded nanocrystal structures on the alignment is poorly understood. To allow conclusive studies of a vast variety of bonded systems in different orientations, we have developed a new density functional tight-binding parameter set to properly describe quantum confinement in nanocrystals. By applying this set, we found a quantitative influence of the interface structure on the band alignment.

10.
ACS Appl Mater Interfaces ; 13(30): 36098-36105, 2021 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-34308645

RESUMO

The spin transport across a zero-dimensional (0D) single-molecule sandwiched by two-dimensional (2D) van der Waals (vdW) ferromagnetic electrodes may open vast opportunities to create novel mixed-dimensional spintronics devices. However, this remains unexplored yet. Inspired by the recent discovery of 2D intrinsic ferromagnets Fe3GeTe2, using first-principles spin transport calculations, we show that single-molecule junctions based on Fe3GeTe2 can yield perfect spin filtering and a significant magnetoresistance (MR) of up to ∼6075%. This remarkable MR is more than 2 orders of magnitude higher than the MR obtained for the corresponding junctions with conventional ferromagnetic metals (e.g., Ni, Fe, and Co). We demonstrate the results of two representative examples that are feasible in the experiments: (i) A benzene or (ii) bezenedithiol (BDT) connected either through a scanning tunneling microscope or break-junction setups. We find that the conductance of BDT junctions is more than 10 times larger than that of the benzene junction due to a much stronger hybridization effect at the molecule-metal interfaces. The key mechanism of the perfect spin filtering and large MR in single-molecule junctions is mainly determined by the intrinsic properties of Fe3GeTe2 electrodes, while the actual conductance is determined by the hybridization strength of the majority spin channel at the molecule-metal interfaces. It is also predicted that the perfect spin filtering and the remarkably huge MR are highly insensitive to structural variations, interface defects, and stacking orders of the electrodes. Our results provide important insights for expanding molecular spintronics platforms from conventional ferromagnetic metals to new 2D vdw magnets.

11.
Sci Adv ; 7(25)2021 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-34144986

RESUMO

Using an innovative quantum mechanical method for an open quantum system, we observe in real time and space the generation, migration, and dissociation of electron-hole pairs, transport of electrons and holes, and current emergence in an organic photovoltaic cell. Ehrenfest dynamics is used to study photoexcitation of thiophene:fullerene stacks coupled with a time-dependent density functional tight-binding method. Our results display the generation of an electron-hole pair in the donor and its subsequent migration to the donor-acceptor interface. At the interface, electrons transfer from the lowest unoccupied molecular orbitals (LUMOs) of thiophenes to the second LUMOs of fullerene. Further migration of electrons and holes leads to the emergence of current. These findings support previous experimental evidence of coherent couplings between electronic and vibrational degrees of freedom and are expected to stimulate further work toward exploring the interplay between electron-hole pair (exciton) binding and vibronic coupling for charge separation and transport.

12.
Nano Lett ; 21(10): 4351-4356, 2021 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-33979160

RESUMO

Monolayer molybdenum trioxide (MoO3) is an emerging two-dimensional (2D) material with high electrical conductivity but unexplored thermal conductivity. Using first-principles calculations and a Boltzmann transport theoretical framework, we predict a record low room-temperature phonon thermal conductivity (κp) of 1.57 and 1.26 W/mK along the principal in-plane directions of the MoO3 monolayer. The behavior is attributed to the combination of soft flexural and in-plane acoustic modes, which are coupled through the finite layer thickness, and to the strong bonding anharmonicity, which gives rise to significant 3- and 4-phonon scattering. These insights suggest new indicators for guiding the search of 2D materials with low κp and motivates κp measurements in MoO3 and its applications as a thermoelectric and thermally protective material.

13.
Nano Lett ; 21(10): 4403-4409, 2021 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-34000186

RESUMO

Van der Waals heterostructures composed of two-dimensional materials offer an unprecedented control over their properties and have attracted tremendous research interest in various optoelectronic applications. Here, we study the photoinduced charge transfer in graphene/WS2 heterostructure by time-dependent density functional theory molecular dynamics. Our results show that holes transfer from graphene to WS2 two times faster than electrons, and the occurrence of interlayer charge transfer is found correlated with vibrational modes of graphene and WS2. It is further demonstrated that the carrier dynamics can be efficiently modulated by external electric fields. Detailed analysis confirms that the carrier transfer rate at heterointerface is governed by the coupling between donor and acceptor states, which is the result of the competition between interlayer and intralayer relaxation processes. Our study provides insights into the understanding of ultrafast interlayer charge transfer processes in heterostructures and broadens their future applications in photovoltaic devices.

14.
J Am Chem Soc ; 143(17): 6649-6656, 2021 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-33896175

RESUMO

Carbon nanotubes (CNTs) are appealing candidates for solar and optoelectronic applications. Traditionally used as electron sinks, CNTs can also perform as electron donors, as exemplified by coupling with perylenediimide (PDI). To achieve high efficiencies, electron transfer (ET) should be fast, while subsequent charge recombination should be slow. Typically, defects are considered detrimental to material performance because they accelerate charge and energy losses. We demonstrate that, surprisingly, common CNT defects improve rather than deteriorate the performance. CNTs and other low dimensional materials accommodate moderate defects without creating deep traps. At the same time, charge redistribution caused by CNT defects creates an additional electrostatic potential that increases the CNT work function and lowers CNT energy levels relative to those of the acceptor species. Hence, the energy gap for the ET is decreased, while the gap for the charge recombination is increased. The effect is particularly important because charge acceptors tend to bind near defects due to enhanced chemical interactions. The time-domain simulation of the excited-state dynamics provides an atomistic picture of the observed phenomenon and characterizes in detail the electronic states, vibrational motions, inelastic and elastic electron-phonon interactions, and time scales of the charge separation and recombination processes. The findings should apply generally to low-dimensional materials, because they dissipate defect strain better than bulk semiconductors. Our calculations reveal that CNT performance is robust to common defects and that moderate defects are essential rather than detrimental for CNT application in energy, electronics, and related fields.

15.
Phys Chem Chem Phys ; 23(11): 6536-6543, 2021 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-33690742

RESUMO

Here, we used collinear and noncollinear density functional theory (DFT) methods to explore the interfacial properties of two heterojunctions between a fullerene (C60 and C70) and the MAPbI3(110) surface. Methodologically, consideration of the spin-orbit interaction has been proven to be required to obtain accurate energy-level alignment and interfacial carrier dynamics between fullerenes and perovskites in hybrid perovskite solar cells including heavy atoms (such as Pb atoms). Both heterojunctions are predicted to be the same type-II heterojunction, but the interfacial electron transfer process from MAPbI3 to C60 is completely distinct from that to C70. In the former, the interfacial electron transfer is slow because of the associated large energy gap, and the excited electrons are thus trapped in MAPbI3 for a while. In contrast, in the latter, the smaller energy gap induces ultrafast electron transfer from MAPbI3 to C70. These points are further supported by DFT-based nonadiabatic dynamics simulations including the spin-orbit coupling (SOC) effects. These gained insights could help rationally design superior fullerene-perovskite interfaces to achieve high power conversion efficiencies of fullerene-perovskite solar cells.

16.
ACS Appl Mater Interfaces ; 13(12): 14283-14290, 2021 Mar 31.
Artigo em Inglês | MEDLINE | ID: mdl-33729753

RESUMO

MXenes, an emerging family of two-dimensional (2D) metal carbides and nitrides, have been demonstrated to be effective nitrogen reduction reaction (NRR) catalysts. So far, most of the theoretical studies toward NRR are based on bare MXenes; however, the structural stabilities are questionable. In this work, we studied the NRR process on several synthesized MXenes (Ti2C, V2C, Cr2C, Zr2C, Nb2C, Mo2C, Hf2C, and Ta2C) with hydroxyl (OH) termination since the structures are preferred under NRR operating conditions as per Pourbaix stability diagrams. It is found that OH plays an essential role in tuning the NRR chemistry, as a new surface-hydroxylation mechanism. Different from the widely accepted NRR mechanism where only protons are involved in the reaction, hydrogen (H) atoms from surface hydroxyl could be captured by the intermediate and participate into the NRR, while the remaining H vacancy can subsequently be self-repaired by the protons under the applied potential. The cooperative effect of surface hydroxylation can effectively boost the NRR, while Mo2C(OH)2 stands out with the most favorable limiting potential of -0.62 V and highest selectivity. Moreover, new scaling relationships based on the H vacancy energy are established, elucidating the possibility for structure-activity tuning. This study not only elaborates the essential role of surface OH functionalization in evaluating NRR performance but also affords new insights into advance sustainable NH3 production.

17.
Nano Lett ; 21(7): 3237-3244, 2021 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-33749285

RESUMO

Although light is the fastest means to manipulate the interfacial spin injection and magnetic proximity related quantum properties of two-dimensional (2D) magnetic van der Waals (vdW) heterostructures, its potential remains mostly untapped. Here, inspired by the recent discovery of 2D ferromagnets Fe3GeTe2 (FGT), we applied the real-time density functional theory (rt-TDDFT) to study photoinduced interlayer spin transfer dynamics in 2D nonmagnetic-ferromagnetic (NM-FM) vdW heterostructures, including graphene-FGT, silicene-FGT, germanene-FGT, antimonene-FGT and h-BN-FGT interfaces. We observed that laser pulses induce significant large spin injection from FGT to nonmagnetic (NM) layers within a few femtoseconds. In addition, we identified an interfacial atom-mediated spin transfer pathway in heterostructures in which the photoexcited spin of Fe first transfers to intralayered Te atoms and then hops to interlayered NM layers. Interlayer hopping is approximately two times slower than intralayer spin transfer. Our results provide the microscopic understanding for optically control interlayer spin dynamics in 2D magnetic heterostructures.

18.
Nanoscale ; 13(14): 6786-6797, 2021 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-33690747

RESUMO

The electron flow between a metallic aggregate and an organic molecule after excitation with light is a crucial step on which hybrid photovoltaic nanomaterials are based. So far, designing such devices with the help of theoretical approaches has been heavily limited by the computational cost of quantum dynamics models able to track the evolution of the excited states over time. In this article, we present the first application of the time-dependent density functional tight-binding (TD-DFTB) method for an experimental nanometer-sized gold-organic system consisting of a hexyl-protected Au25 cluster labelled with a pyrene fluorophore, in which the fluorescence quenching of the pyrene is attributed to the electron transfer from the metallic cluster to the dye. The full quantum rationalization of the electron transfer is attained through quantum dynamics simulations, highlighting the crucial role of the protecting ligand shell in electron transfer, as well as the coupling with nuclear movement. This work paves the way towards the fast and accurate theoretical design of optoelectronic nanodevices.

19.
Phys Rev Lett ; 126(7): 076401, 2021 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-33666477

RESUMO

Supercell models are often used to calculate the electronic structure of local deviations from the ideal periodicity in the bulk or on the surface of a crystal or in wires. When the defect or adsorbent is charged, a jellium counter charge is applied to maintain overall neutrality, but the interaction of the artificially repeated charges has to be corrected, both in the total energy and in the one-electron eigenvalues and eigenstates. This becomes paramount in slab or wire calculations, where the jellium counter charge may induce spurious states in the vacuum. We present here a self-consistent potential correction scheme and provide successful tests of it for bulk and slab calculations.

20.
Nano Lett ; 21(4): 1871-1878, 2021 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-33587621

RESUMO

Great enthusiasm in single-atom catalysts (SACs) for the nitrogen reduction reaction (NRR) has been aroused by the discovery of metal-Nx as a promising catalytic center. However, the poor activity and low selectivity of available SACs are far away from the industrial requirement. Through the first-principles high-throughput screening, we find that Fe-Fe distributed on graphite carbon nitride (Fe2/g-CN) can manipulate the binding strength of the target reaction species (compromises the ability to adsorb N2H and NH2), therefore achieving the best NRR performance among 23 transition metal (TM) centers. Our results show that Fe2/g-CN achieves a high theoretical Faradaic efficiency of 100% and, impressively, the lowest limiting potential of -0.13 V. Particularly, multiple-level descriptors shed light on the origin of NRR activity, achieving a fast prescreening among various candidates. Our predictions not only accelerate discovery of catalysts for ammonia synthesis but also contribute to further elucidate the structure-performance correlations.

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