Abstract
Electrochemical reduction of CO
2
to multi-carbon fuels and chemical feedstocks is an appealing approach to mitigate excessive CO
2
emissions. However, the reported catalysts always show ...either a low Faradaic efficiency of the C
2+
product or poor long-term stability. Herein, we report a facile and scalable anodic corrosion method to synthesize oxygen-rich ultrathin CuO nanoplate arrays, which form Cu/Cu
2
O heterogeneous interfaces through self-evolution during electrocatalysis. The catalyst exhibits a high C
2
H
4
Faradaic efficiency of 84.5%, stable electrolysis for ~55 h in a flow cell using a neutral KCl electrolyte, and a full-cell ethylene energy efficiency of 27.6% at 200 mA cm
−2
in a membrane electrode assembly electrolyzer. Mechanism analyses reveal that the stable nanostructures, stable Cu/Cu
2
O interfaces, and enhanced adsorption of the *OCCOH intermediate preserve selective and prolonged C
2
H
4
production. The robust and scalable produced catalyst coupled with mild electrolytic conditions facilitates the practical application of electrochemical CO
2
reduction.
Abstract
The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices. However, ...controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging. Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe
2
ultrathin crystals with controlled thickness. Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition. With reducing the thickness of 1T-CrTe
2
from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane. Monotonic increase of Curie temperature with the thickness decreasing from ~130.0 to ~7.6 nm is observed. Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties.
Graphitic carbon nitride nanosheets are extracted, produced via simple liquid‐phase exfoliation of a layered bulk material, g‐C3N4. The resulting nanosheets, having ≈2 nm thickness and N/C atomic ...ratio of 1.31, show an optical bandgap of 2.65 eV. The carbon nitride nanosheets are demonstrated to exhibit excellent photocatalytic activity for hydrogen evolution under visible light.
MoS2 is a promising and low-cost material for electrochemical hydrogen production due to its high activity and stability during the reaction. However, the efficiency of hydrogen production is limited ...by the amount of active sites, for example, edges, in MoS2. Here, we demonstrate that oxygen plasma exposure and hydrogen treatment on pristine monolayer MoS2 could introduce more active sites via the formation of defects within the monolayer, leading to a high density of exposed edges and a significant improvement of the hydrogen evolution activity. These as-fabricated defects are characterized at the scale from macroscopic continuum to discrete atoms. Our work represents a facile method to increase the hydrogen production in electrochemical reaction of MoS2 via defect engineering, and helps to understand the catalytic properties of MoS2.
Phosphorene, a elemental 2D material, which is the monolayer of black phosphorus, has been mechanically exfoliated recently. In its bulk form, black phosphorus shows high carrier mobility (∼10 000 ...cm2/V·s) and a ∼0.3 eV direct band gap. Well-behaved p-type field-effect transistors with mobilities of up to 1000 cm2/V·s, as well as phototransistors, have been demonstrated on few-layer black phosphorus, showing its promise for electronics and optoelectronics applications due to its high hole mobility and thickness-dependent direct band gap. However, p–n junctions, the basic building blocks of modern electronic and optoelectronic devices, have not yet been realized based on black phosphorus. In this paper, we demonstrate a gate-tunable p–n diode based on a p-type black phosphorus/n-type monolayer MoS2 van der Waals p–n heterojunction. Upon illumination, these ultrathin p–n diodes show a maximum photodetection responsivity of 418 mA/W at the wavelength of 633 nm and photovoltaic energy conversion with an external quantum efficiency of 0.3%. These p–n diodes show promise for broad-band photodetection and solar energy harvesting.
The development of magnetic two-dimensional (2D) materials in its infancy has generated an enormous amount of attention as it offers an ideal platform for the exploration of magnetic properties down ...to the 2D limit, paving the way for spintronic devices. Due to the nonnegligible advantages including time efficiency and simplified process, the facile bottom-up chemical vapor deposition (CVD) is regarded as a robust method to fabricate ultrathin magnetic nanosheets. Recently, some ultrathin magnets possessing fascinating properties have been successfully synthesized via CVD. Here, the recent researches toward magnetic 2D materials grown by CVD are systematically summarized with special emphasis on the fabrication methods. Then, heteroatoms doping and phase transition induced in CVD growth to bring or tune the magnetic properties in 2D materials are discussed. Characterizations and applications of these magnetic materials are also discussed and reviewed. Finally, some perspectives in need of urgent attention regarding the development of CVD-grown magnetic 2D materials are proposed.
Two dimensional (2D) materials have attracted great attention due to their unique properties and atomic thickness. Although various 2D materials have been successfully synthesized with different ...optical and electrical properties, a strategy for fabricating 2D heterostructures must be developed in order to construct more complicated devices for practical applications. Here we demonstrate for the first time a two-step chemical vapor deposition (CVD) method for growing transition-metal dichalcogenide (TMD) heterostructures, where MoSe2 was synthesized first and followed by an epitaxial growth of WSe2 on the edge and on the top surface of MoSe2. Compared to previously reported one-step growth methods, this two-step growth has the capability of spatial and size control of each 2D component, leading to much larger (up to 169 μm) heterostructure size, and cross-contamination can be effectively minimized. Furthermore, this two-step growth produces well-defined 2H and 3R stacking in the WSe2/MoSe2 bilayer regions and much sharper in-plane interfaces than the previously reported MoSe2/WSe2 heterojunctions obtained from one-step growth methods. The resultant heterostructures with WSe2/MoSe2 bilayer and the exposed MoSe2 monolayer display rectification characteristics of a p–n junction, as revealed by optoelectronic tests, and an internal quantum efficiency of 91% when functioning as a photodetector. A photovoltaic effect without any external gates was observed, showing incident photon to converted electron (IPCE) efficiencies of approximately 0.12%, providing application potential in electronics and energy harvesting.
Modern lithium ion batteries are often desired to operate at a wide electrochemical window to maximize energy densities. While pushing the limit of cutoff potentials allows batteries to provide ...greater energy densities with enhanced specific capacities and higher voltage outputs, it raises key challenges with thermodynamic and kinetic stability in the battery. This is especially true for layered lithium transition-metal oxides, where capacities can improve but stabilities are compromised as wider electrochemical windows are applied. To overcome the above-mentioned challenges, we used atomic layer deposition to develop a LiAlF4 solid thin film with robust stability and satisfactory ion conductivity, which is superior to commonly used LiF and AlF3. With a predicted stable electrochemical window of approximately 2.0 ± 0.9 to 5.7 ± 0.7 V vs Li+/Li for LiAlF4, excellent stability was achieved for high Ni content LiNi0.8Mn0.1Co0.1O2 electrodes with LiAlF4 interfacial layer at a wide electrochemical window of 2.75–4.50 V vs Li+/Li.
Recently, two-dimensional layers of transition metal dichalcogenides, such as MoS2, WS2, MoSe2, and WSe2, have attracted much attention for their potential applications in electronic and ...optoelectronic devices. The selenide analogues of MoS2 and WS2 have smaller band gaps and higher electron mobilities, making them more appropriate for practical devices. However, reports on scalable growth of high quality transition metal diselenide layers and studies of their properties have been limited. Here, we demonstrate the chemical vapor deposition (CVD) growth of uniform MoSe2 monolayers under ambient pressure, resulting in large single crystalline islands. The photoluminescence intensity and peak position indicates a direct band gap of 1.5 eV for the MoSe2 monolayers. A back-gated field effect transistor based on MoSe2 monolayer shows n-type channel behavior with average mobility of 50 cm2 V–1 s–1, a value much higher than the 4–20 cm2 V–1 s–1 reported for vapor phase grown MoS2.
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