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1.
Nanoscale ; 14(45): 17065-17071, 2022 Nov 24.
Artigo em Inglês | MEDLINE | ID: mdl-36367305

RESUMO

Strain engineering has been extensively applied as a promising strategy in the regulation of physical and chemical properties of two-dimensional (2D) materials, which remarkably broadens their application prospects in flexible electronics and chip manufacturing. However, the difficulty in fixing a flexible substrate under compression and the challenge in adjusting the focal distance have hindered the in-depth investigation of compressive strain. Here, we fabricated a home-made strain loading device and proposed a compressive strain measurement method, via which the strain-dependent optical absorption properties of MoS2 monolayers under compression has been studied. According to the measured optical absorption spectra, the first blueshift and then redshift trend under compression was obviously observed. The reliability of the experimentally observed trend in peak position shift was theoretically verified by density functional theory calculation. Our work offers a feasible way to characterize optical properties of 2D materials under compressive strain and expands the space for the development of next-generation micro/nano-scale optoelectronic devices.

2.
Chemistry ; 2022 Nov 09.
Artigo em Inglês | MEDLINE | ID: mdl-36349874

RESUMO

To explore highly active and robust self-supporting air electrode is the key for flexible Zn-air batteries (FZABs). Therefore, we report a novel 3D structural bimetal-based self-supporting electrode consisting of hybrid Cu, Co nanoparticles co-modified nitrogen-doped carbon nanosheets on carbon cloth (Cu, Co NPs@NCNSs/CC), which displays excellent electrochemical activity and durability of oxygen reduction/evolution reaction (ORR/OER). The Cu, Co NPs@NCNSs/CC exhibits a half-wave potential of 0.863 V toward ORR and an overpotential of 225 mV at 10 mA cm-2 toward OER, owing to its exposed bimetallic sites accelerating kinetic reaction. In addition, the density functional theory calculation proves that the synergistic effect of CuCo sites favors ORR and OER. Hence, the FZABs based on Cu, Co NPs@NCNSs/CC achieve a larger open-circuit potential (1.45 V), higher energy density (130.10 mW cm-2), and outstandingly cycling stability. All remarkable results demonstrate valuable enlightenment for seeking advanced energy materials of portable and wearable electronics.

3.
Small ; : e2204634, 2022 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-36310123

RESUMO

The precise facet modulation of transition metal nitrides (TMNs) has been regarded as an essential issue in boosting electrocatalytic H2 production. Compared to thermal nitridation, the plasma technique serves as a favorable alternative to directly achieve TMNs, but the apparent surface heating effect during plasma treatment inevitably causes the thermally stabilized nitride formation, resulting in the deterioration of the highly reactive facet. To optimize the hydrogen evolution reaction (HER) behavior, an auxiliary cooling assisted plasma system to selectively expose Ni3 N (2-10) with favorable activity by controlling surface heating during plasma nitridation is designed. The resultant nickel nitride (cp-Ni3 N) nano-framework delivers exceptional catalytic performance, evidenced by its low overpotential of 58 and 188 mV at the current density of 10 and 100 mA cm-2 for HER, in stark comparison with that of normal plasma and thermally fabricated Ni3 N. Operando plasma diagnostics along with numerical simulation further confirm the effect of surface heating on typical plasma parameters as well as the Ni3 N nanostructure, indicating the key factor responsible for the high-performance nitride electrocatalyst.

4.
Nanotechnology ; 34(4)2022 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-36301681

RESUMO

Graphene nanomesh (GNM), an emerging graphene nanostructure with a tunable bandgap, has gained tremendous interests owing to its great potentials in the fields of high-performance field-effect transistors, electrochemical sensors, new generation of spintronics and energy converters. In previous works, GNM has been successfully obtained on copper foil surface by employing hydrogen as an etching agent. A more facile, and low-cost strategy for the preparation of GNM is required. Here, we demonstrated a direct and feasible means for synthesizing large-area GNM with symmetrical fractal patterns via a hydrogen-free chemical vapor deposition method. The influences of the growth time and the gas source flow on the morphology of GNM patterns were systematically investigated. Then, we exhibited the key reaction details and proposed a growth mechanism of the GNM synthesis during the hydrogen-free chemical vapor deposition process. This work provides a valuable guidance for quality control in GNM mass production.

5.
Nanoscale ; 14(38): 14038-14045, 2022 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-36111827

RESUMO

Semiconducting two-dimensional intrinsic silicon nanosheets are ideal materials for many applications in modern industry, since they are the only ones that can match well with previous silicon components. However, such materials are still lacking, especially those with moderate band gaps. In this work, by using first-principles theory, a series of two-dimensional intrinsic silicon nanosheets are assembled from zigzag silicene nanoribbons with different widths. The result shows that all the nanosheets behave as semiconductors, although some of them possess small band gaps of dozens of meV. Two of them, individually assembled from the two narrowest zigzag silicene nanoribbons, possess the largest indirect band gaps of 0.20 and 0.26 eV, respectively. Under low compressive strain, these two nanosheets would turn into quasi-direct or direct band gap semiconductors, and the gaps increase up to 0.62 or 0.54 eV, respectively. Due to the electron transfer from three-fold to four-fold coordinated Si atoms, the charge carriers prefer to transport along the zigzag direction, and electrons and holes transport in the respective Si chains. Interestingly, the investigation of Poisson's ratio reveals that the assembled silicon nanosheets have a negative Poisson's ratio in certain strain ranges if the width n of zigzag silicene nanoribbons is even. This work provides a new approach to design semiconducting silicon nanosheets and benefits to the applications of two-dimensional silicon nanosheets in many electronic and mechanical fields.

6.
Small ; 18(42): e2204143, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-36108133

RESUMO

Magnetic field enhanced electrocatalysis has recently emerged as a promising strategy for the development of a viable and sustainable hydrogen economy via water oxidation. Generally, the effects of magnetic field enhanced electrocatalysis are complex including magnetothermal, magnetohydrodynamic and spin selectivity effects. However, the exploration of magnetic field effect on the structure regulation of electrocatalyst is still unclear whereas is also essential for underpinning the mechanism of magnetic enhancement on the electrocatalytic oxygen evolution reaction (OER) process. Here, it is identified that in a mixed NiFe2 O4 (NFO), a large magnetic field can force the Ni2+ cations to migrate from the octahedral (Oh ) sites to tetrahedral (Td ) sites. As a result, the magnetized NFO electrocatalyst (NFO-M) shows a two-fold higher current density than that of the pristine NFO in alkaline electrolytes. The OER enhancement of NFO is also observed at 1 T (NFO@1T) under an operando magnetic field. Our first-principles calculations further confirm the mechanism of magnetic field driven structure regulation and resultant OER enhancement. These findings provide a strategy of manipulating tetrahedral units of spinel oxides by a magnetic field on boosting OER performance.

7.
Chemistry ; : e202201034, 2022 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-35674444

RESUMO

The CO2 reduction reaction (CRR) represents a promising route for the clean utilization of renewable resources. But mass-transfer limitations seriously hinder the forward step. Enhancing the surface hydrophobicity by using polymers has been proved to be one of the most efficient strategies. However, as macromolecular organics, polymers on the surface hinder the transfer of charge carriers from catalysts to reactants. Herein, we describe an in-situ surface fluorination strategy to enhance the surface hydrophobicity of TiO2 without a barrier layer of organics, thus facilitating the mass transfer of CO2 to catalysts and charge transfer. With less obstruction to charge transfer, a higher CO2, and lower H+ surface concentration, the photocatalytic CRR generation rate of methanol (CH3 OH) is greatly enhanced to up to 247.15 µmol g-1 h-1 . Furthermore, we investigated the overall defects; enhancing the surface hydrophobicity of catalysts provides a general and reliable method to improve the competitiveness of CRR.

8.
J Am Chem Soc ; 144(25): 11138-11147, 2022 Jun 29.
Artigo em Inglês | MEDLINE | ID: mdl-35674660

RESUMO

Developing efficient hydrogen oxidation reaction (HOR) electrocatalysts in alkaline media is of great significance for anion exchange membrane fuel cells. Herein, we report the synthesis of hollow colloidosomes composed of Ru nanocrystals based on a novel gas/liquid interface self-assembly strategy. Structural characterizations reveal that much defects are present in the building block (Ru nanocrystals) of Ru colloidosomes. Theoretical calculations suggest that the defects in the Ru structure can optimize the adsorption binding energy of reaction intermediates for the HOR. Benefiting from the assembled colloidosome and optimized electronic structure, the Ru colloidosomes exhibit remarkable HOR catalytic performance in alkaline media with a mass activity higher than that of benchmark Pt/C. Our work may shed new light on the rational design of advanced electrocatalysts with an assembled structure for energy-related applications.

9.
Nano Lett ; 22(13): 5191-5197, 2022 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-35639726

RESUMO

Electrical control of magnetic order in van der Waals (vdW) two-dimensional (2D) systems is appealing for high-efficiency and low-dissipation nanospintronic devices. For realistic applications, a vdW 2D material with ferromagnetic (FM) and ferroelectric (FE) orders coexisting and strongly coupling at room temperature is urgently needed. Here we present a potential candidate for nonvolatile electric-field control of magnetic orders at room temperature. Using first-principles calculations, we predict the coexistence of room-temperature FM and FE orders in a 2D transition metal carbide, where the spatial distribution of magnetic moments strongly couples with the orientation of out-of-plane electric polarization. Furthermore, an electric-field switching between interfacial FM and ferrimagnetic orders is realizable through constructing a multiferroic vdW heterostructure based on this material. These findings make a significant step toward realizing room-temperature multiferroicity and strong magnetoelectric coupling in 2D materials.

10.
Small ; 18(19): e2200073, 2022 05.
Artigo em Inglês | MEDLINE | ID: mdl-35257478

RESUMO

Atomically dispersed metal catalysts often exhibit high catalytic performances, but the metal loading density must be kept low to avoid the formation of metal nanoparticles, making it difficult to improve the overall activity. Diverse strategies based on creating more anchoring sites (ASs) have been adopted to elevate the loading density. One problem of such traditional methods is that the single atoms always gather together before the saturation of all ASs. Here, a chemical scissors strategy is developed by selectively removing unwanted metallic materials after excessive loading. Different from traditional ways, the chemical scissors strategy places more emphasis on the accurate matching between the strength of etching agent and the bond energies of metal-metal/metal-substrate, thus enabling a higher loading up to 2.02 wt% even on bare substrate without any pre-treatment (the bare substrate without any pre-treatment generally only has a few ASs for single atom loading). It can be inferred that by combining with other traditional methods which can create more ASs, the loading could be further increased by saturating ASs. When used for CH3 OH generation via photocatalytic CO2 reduction, the as-made single-atom catalyst exhibits impressive catalytic activity of 597.8 ± 144.6 µmol h-1 g-1 and selectivity of 81.3 ± 3.8%.


Assuntos
Nanopartículas Metálicas , Metais , Catálise , Metais/química , Fenômenos Físicos
11.
Phys Rev Lett ; 128(6): 067601, 2022 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-35213175

RESUMO

van der Waals materials possess an innate layer degree of freedom and thus are excellent candidates for exploring emergent two-dimensional ferroelectricity induced by interlayer translation. However, despite being theoretically predicted, experimental realization of this type of ferroelectricity is scarce at the current stage. Here, we demonstrate robust sliding ferroelectricity in semiconducting 1T^{'}-ReS_{2} multilayers via a combined study of theory and experiment. Room-temperature vertical ferroelectricity is observed in two-dimensional 1T^{'}-ReS_{2} with layer number N≥2. The electric polarization stems from the uncompensated charge transfer between layers and can be switched by interlayer sliding. For bilayer 1T^{'}-ReS_{2}, the ferroelectric transition temperature is estimated to be ∼405 K from the second harmonic generation measurements. Our results highlight the importance of interlayer engineering in the realization of atomic-scale ferroelectricity.

12.
Phys Chem Chem Phys ; 23(34): 18863-18868, 2021 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-34612424

RESUMO

Low-dimensional ferroelectricity has attracted enormous attention due to its applications in miniaturized devices and understanding the dimension effect on ferroelectricity is of significant importance. Based on first-principles calculations, we have investigated the dimension effect on the ferroelectricity of group-IV monochalcogenide MX nanoribbons. Our results reveal that H-terminated armchair GeSNRs exhibit large in-plane polarization along the ribbon direction which converges to the value of 2D GeS as the width increases, while out-of-plane polarization only arises in those with n = odd number. Interestingly, for bare A-GeSNRs, the structure with small n transforms into a paraelectric phase and the critical width for the PE/FE transition is calculated to be n = 10. On the side of zigzag GeSNRs, H-terminated ribbons possess polarization along both the out-of-plane and width directions, while bare Z-GeSNRs are expected to be polar ferromagnetic metals.

13.
Nanoscale ; 13(30): 13048-13056, 2021 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-34477788

RESUMO

Two-dimensional (2D) multiferroic materials with the coexistence of electric and spin polarization offer a tantalizing potential for high-density multistate data storage. However, intrinsic 2D multiferroic semiconductors with high thermal stability are still rare to date. Here, we propose a new mechanism of single-phase multiferroicity. Based on first-principles calculations, we predicted that in a CrO3 monolayer, the unconventional distortion of the square antiprismatic crystal field on Cr-d orbitals will induce an in-plane electric polarization, making this material a single-phase multiferroic semiconductor. Importantly, the magnetic Curie temperature is estimated to be ∼220 K, which is quite high as compared to those of the recently reported 2D ferromagnetic and multiferroic semiconductors. Moreover, both ferroelectric and antiferroelectric phases are observed, providing opportunities for electrical control of magnetism and energy storage and conversion applications. These findings provide a comprehensive understanding of the magnetic and electric behavior in 2D multiferroics and will motivate further research on the application of related 2D electromagnetics and spintronics.

14.
Sci Adv ; 7(30)2021 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-34301602

RESUMO

Nanoscale magnetic structures are fundamental to the design and fabrication of spintronic devices and have exhibited tremendous potential superior to the conventional semiconductor devices. However, most of the magnetic moments in nanostructures are unstable due to size effect, and the possible solution based on exchange coupling between nanomagnetism is still not clear. Here, graphene-mediated exchange coupling between nanomagnets is demonstrated by depositing discrete superparamagnetic Ni nano-islands on single-crystal graphene. The heterostructure exhibits ideal two-dimensional (2D) ferromagnetism with clear hysteresis loops and Curie temperature up to 80 K. The intrinsic ferromagnetism in graphene and antiferromagnetic exchange coupling between graphene and Ni nano-islands are revealed by x-ray magnetic circular dichroism and density functional theory calculations. The artificial 2D ferromagnets constitute a platform to study the coupling mechanism between complex correlated electronic systems and magnetism on the nanoscale, and the results and concept provide insights into the realization of spin manipulation in quantum computing.

15.
Small ; 17(20): e2008036, 2021 05.
Artigo em Inglês | MEDLINE | ID: mdl-33797192

RESUMO

Advanced fabrication of surface metal-organic complexes with specific coordination configuration and metal centers will facilitate to exploit novel nanomaterials with attractive electronic/magnetic properties. The precise on-surface synthesis provides an appealing strategy for in situ construction of complex organic ligands from simple precursors autonomously. In this paper, distinct organic ligands with stereo-specific conformation are separately synthesized through the well-known dehalogenative coupling. More interestingly, the exo-bent ligands promote the mono-iron chelated complexes with the Fe center significantly decoupled from the surface and of high spin, while the endo-bent ligands lead to bi-iron chelated ones instead with ferromagnetic properties.


Assuntos
Complexos de Coordenação , Ferro , Ligantes , Modelos Moleculares , Conformação Molecular
16.
Nanoscale ; 13(6): 3627-3632, 2021 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-33537694

RESUMO

Finding photocatalysts that fully utilize the visible solar light to split water into hydrogen and oxygen has been a challenging problem for a long time. In this regard, compared to traditional three-dimensional materials, graphene-like two-dimensional materials offer many advantages such as ultra-high surface area for photochemical reactions and minimal migration distance for carriers. Herein, using density functional theory (DFT), we examine the potential of a new series of two-dimensional boron chalcogenides, B2X3 (X = S, Se, Te) as candidates for such photocatalysts. We show that B2Se3 and B2Te3 possess the ideal energy levels for photon excitation for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Furthermore, a bilayer van der Waals heterostructure consisting of B2Te3/B2Se3 is found to have the greatest potential for two-step photo-excitation for water splitting reaction. Our results can stimulate the synthesis of new two dimensional materials for photocatalysis.

17.
RSC Adv ; 11(7): 4035-4041, 2021 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-35424366

RESUMO

Magneto-optical effects, which originate from the interactions between light and magnetism, have provided an important way to characterize magnetic materials and hosted abundant applications, such as light modulators, magnetic field sensors, and high-density data storage. However, such effects are too weak to be detected in non-magnetic materials due to the absence of spin degree of freedom. Here, we demonstrated that applying a perpendicular magnetic field can produce a colossal Raman scattering rotation in non-magnetic MoS2, for A-mode representing the out-of-plane breathing vibration. Our experimental results show that linearly polarized scattering light is rotated by ∓125°, more apparent than the valley Zeeman splitting effect (∓1.2 meV) under the same experimental conditions (±5 T), near room temperature. A detailed and systematic analysis on the polarization-resolved magnetic field-dependent micro-zone Raman intensity offers a feasible way to manipulate the inelastically scattered light via a magnetic technique. This explored phenomenology and physical mechanism arouse a new ramification of probing burgeoning magneto-optical effects in the field of two-dimensional laminar materials.

18.
Nanoscale ; 12(29): 15670-15676, 2020 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-32677637

RESUMO

Two-dimensional (2D) ferromagnetic (FM) semiconductors with a direct electronic band gap have recently drawn much attention due to their promising potential for spintronic and magneto-optical applications. However, the Curie temperature (TC) of recently synthesized 2D FM semiconductors is too low (∼45 K) and a room-temperature 2D direct band gap FM semiconductor has never been reported, which hinders the development for practical magneto-optical applications. Here, we show that through isovalent alloying, one can increase the TC of a 2D FM semiconductor up to room temperature and simultaneously turn it from an indirect to a direct band gap semiconductor. Using the first-principles calculations, we predict that the alloyed CrMoS2Br2 monolayer is a direct band gap semiconductor with a TC of ∼360 K, whereas the pristine CrSBr monolayer is an indirect band gap semiconductor with a TC of ∼180 K. These findings provide a promising pathway to realize 2D direct band gap FM semiconductors with TC above room temperature, which will greatly stimulate theoretical and experimental interest in future spintronic and magneto-optical applications.

19.
Phys Rev Lett ; 124(6): 067602, 2020 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-32109087

RESUMO

Controlling magnetism of two-dimensional multiferroics by an external electric field provides special opportunities for both fundamental research and future development of low-cost electronic nanodevices. Here, we report a general scheme for realizing a magnetic phase transition in 2D type-I multiferroic systems through the reversal of ferroelectric polarization. Based on first-principles calculations, we demonstrate that a single-phase 2D multiferroic, namely, ReWCl_{6} monolayer, exhibits two different low-symmetric (C_{2}) phases with opposite in-plane electric polarization and different magnetic order. As a result, an antiferromagnetic-to-ferromagnetic phase transition can be realized by reversing the in-plane electric polarization through the application of an external electric field. These findings not only enrich the 2D multiferroic family, but also uncover a unique and general mechanism to control magnetism by electric field, thus stimulating experimental interest.

20.
Nat Commun ; 11(1): 845, 2020 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-32051407

RESUMO

Encapsulation strategies are widely used for alleviating dissolution and diffusion of polysulfides, but they experience nonrecoverable structural failure arising from the repetitive severe volume change during lithium-sulfur battery cycling. Here we report a methodology to construct an electrochemically recoverable protective layer of polysulfides using an electrolyte additive. The additive nitrogen-doped carbon dots maintain their "dissolved" status in the electrolyte at the full charge state, and some of them function as active sites for lithium sulfide growth at the full discharge state. When polysulfides are present amid the transition between sulfur and lithium sulfide, nitrogen-doped carbon dots become highly reactive with polysulfides to form a solid and recoverable polysulfide-encapsulating layer. This design skilfully avoids structural failure and efficiently suppresses polysulfide shuttling. The sulfur cathode delivers a high reversible capacity of 891 mAh g-1 at 0.5 C with 99.5% coulombic efficiency and cycling stability up to 1000 cycles at 2 C.

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