With the discovery of graphene in 2004, other two-dimensional (2D) layered materials, such as, boron nitride, black phosphorus, transition metal dichalcogenides (TMDCs), etc., have attracted ...worldwide research interests. In particular, TMDCs have attracted much attention in virtue of their tunable bandgaps and excellent properties. The construction of heterostructures based on graphene and TMDCs is an important strategy to tailor their electronic structures, which has opened up a new era for the next-generation electronic and optoelectronic devices. According to the combination of different 2D heterostructures, they can be divided into two categories: lateral heterostructures and vertical heterostructures. Considering 2D materials are usually grown on specific substrates (e.g. Cu foils), developing cost-effective and eco-friendly transfer methods without degrading their performance is very crucial. In this review article, we summarize the synthesis strategies of 2D heterostructures and discuss the key experimental parameters for their growth, including growth temperature, growth time, and the addition of halide and water. Then, we summarize the transfer methods with respect to different growth substrates. Also, the applications of 2D heterostructures in the field of electronic and optoelectronic devices are briefly introduced. Finally, the challenges ahead for research on 2D heterostructures are proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Pristine graphene behaves like a zero-band-gap semiconductor and in order to develop electronic applications, it is highly desirable to open the band gap of graphene. In this context, doping ...constitutes a powerful route to tailor the electronic properties of graphene. In this review, we summarize the state-of-the-art achievements regarding the doping of graphene sheets and nanoribbons. The characterization techniques and applications of doped graphene sheets and nanoribbons are reviewed. Based on recent achievements, the perspectives and future research related to doped graphenes are discussed.
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► Doping is a powerful way to modify the properties of graphene-like materials. ► Their electronic properties could be tailored by controlling doping parameters. ► Spectroscopy and microscopy have been used to characterize doped graphenes. ► Doped graphenes could be used in electronics, energy storage, and bio-devices. ► Further experimental and theoretical work on doped graphene need to be carried out.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Graphene is theoretically a robust two-dimensional (2D) sp2-hybridized carbon material with high electrical conductivity and optical transparency. However, due to the existence of grain boundaries ...and defects, experimentally synthesized large-area polycrystalline graphene sheets are easily broken and can exhibit high sheet resistances; thus, they are not suitable as flexible transparent conductors. As described in this issue of ACS Nano, Tour et al. circumvented this problem by proposing and synthesizing a novel hybrid structure that they have named “rebar graphene”, which is composed of covalently interconnected carbon nanotubes (CNTs) with graphene sheets. In this particular configuration, CNTs act as “reinforcing bars” that not only improve the mechanical strength of polycrystalline graphene sheets but also bridge different crystalline domains so as to enhance the electrical conductivity. This report seems to be only the tip of the iceberg since it is also possible to construct novel and unprecedented hybrid carbon architectures by establishing covalent interconnections between CNTs with graphene, thus yielding graphene–CNT hybrids, three-dimensional (3D) covalent CNT networks, 3D graphene networks, etc. In this Perspective, we review the progress of these carbon hybrid systems and describe the challenges that need to be overcome in the near future.
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IJS, KILJ, NUK, PNG, UL, UM
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•Nanopore regulation strategy can improve the sodium storage capacity of hard carbon.•The relationship between nanopore and sodium storage capability was investigated.•Micropores ...hardly accommodate Na+ ions and hinder Na+ ion diffusion.•Mesopores facilitate Na+ ion intercalation and shorten the ion diffusion pathway.
Hard carbon is regarded as one of the most promising anode material for sodium-ion batteries in virtue of the low cost and stable framework. However, the correlation between pore structures of hard carbon and sodium-ion storage is still ambiguous. In this work, based on precise control of pore-size distribution, the capacity, ion diffusion, and initial Coulombic efficiency were improved. Meanwhile, the relationship between pore structure and capacity was investigated. Our result indicates that the micropores hinder ion diffusion and hardly ever accommodate Na+ ions, while mesopores facilitate Na+ ion intercalation. Hard carbon with negligible micropores and abundant mesopores delivers a maximum capacity of 283.7 mAh g−1 at 20 mA g−1, which is 83% higher than that of micropore-rich one. Even after 320 cycles at 200 mA g−1, the capacity still remains 189.4 mAh g−1.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Exploring high-activity and earth-abundant electrocatalysts for electrochemical reactions, including the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR) and oxygen evolution ...reaction (OER), etc. are crucial for building future large-scale green energy conversion and storage systems. Recently, some low-cost and resourceful two-dimensional (2D) semiconductor materials such as transition metal dichalcogenides (TMDCs) and layered oxides, have attracted increasing attention in electrocatalysis applications in virtue of their comparable catalytic activity and long-term stability to conventional noble metal-based catalysts (e.g. Pt/C, RuO2, IrO2, etc.). However, the intrinsic activity of some 2D materials still cannot meet the increasing requirement for highly efficient and reliable eletrocatalysts for future energy conversion and storage systems. In this context, designing elctrocatalysts with sufficient amount of active sites accessible for electrolyte, high activity of each active sites, and excellent conductivity is of great significance. To this end, defect engineering is a powerful strategy for tailoring the physical and chemical properties of 2D materials for efficient electrocatalysis. In this article, an overview of recent progress on defect engineering in 2D eletrocatalysts for HER, ORR and OER is presented. The effects of defects on the structure and tuned properties of 2D materials in eletrocatalysts applications are also summarized. Additionally, the challenges and opportunities ahead in this emerging field are also proposed.
This review article summarizes the recent progress on defect engineering of 2D materials for improved electrocatalytic activity towards hydrogen evolution reaction (HER), oxygen reduced reaction (ORR) and oxygen evolution reaction (OER). Display omitted
•2D materials are attractive to serve as noble-metal-free electrocatalysts for HER, ORR and OER.•Defect engineering can enhance catalytic activity of 2D elctrocatalysts.•Recent progress on defect engineering of two-dimensional 2D eletrocatalysts for HER, ORR and OER are summarized.•Challenges and opportunities of defect engineering for electrocatalysts are proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Doping modifies physico-chemical properties of graphene and dichalcogenides.•Non-metal elements such as N, B, Si, P, and S are the common dopants to graphene.•Semiconducting ...dichalcogenide dopants include W, Co, Fe, Mn, Nb, Se and S.•Doped 2D materials exhibit improved performance as sensors and optoelectronic devices.
In recent years, research on two-dimensional (2D) materials including graphene and transition metal dichalcogenides (TMDCs), especially molybdenum and tungsten disulfides (MoS2 and WS2), has rapidly developed. In order to meet the increasing demands of using these 2D materials in fields as diverse as optoelectronics and sensing, heteroatom doping has become an effective method to tune their electronic and physico-chemical properties. This review discusses versatile doping methods applied to graphene and TMDCs, the corresponding changes to their properties, and their potential applications. Future perspectives and new emerging areas are also presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Defects are usually seen as imperfections in materials that could significantly degrade their performance. However, at the nanoscale, defects could be extremely useful since they could be exploited ...to generate novel, innovative and useful materials and devices. Graphene and graphene nanoribbons are no exception. This review therefore tries to categorize defects, emphasize their importance, introduce the common routes to study and identify them and to propose new ways to construct novel devices based on 'defective' graphene-like materials. In particular, we will discuss defects in graphene-like systems including (a) structural (sp2-like) defects, (b) topological (sp2-like) defects, (c) doping or functionalization (sp2- and sp3-like) defects and (d) vacancies/edge type defects (non-sp2-like). It will be demonstrated that defects play a key role in graphene physicochemical properties and could even be critical to generate biocompatible materials. There are numerous challenges in this emerging field, and we intend to provide a stimulating account which could trigger new science and technological developments based on defective graphene-like materials that could be introduced into other atomic layered materials, such as BN, MoS2 and WS2, not discussed in this review.
Individual monolayers of metal dichalcogenides are atomically thin two-dimensional crystals with attractive physical properties different from those of their bulk counterparts. Here we describe the ...direct synthesis of WS2 monolayers with triangular morphologies and strong room-temperature photoluminescence (PL). The Raman response as well as the luminescence as a function of the number of S–W–S layers is also reported. The PL weakens with increasing number of layers due to a transition from direct band gap in a monolayer to indirect gap in multilayers. The edges of WS2 monolayers exhibit PL signals with extraordinary intensity, around 25 times stronger than that at the platelet’s center. The structure and chemical composition of the platelet edges appear to be critical for PL enhancement.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
Stabilizing active sites of non-iridium-based oxygen evolution reaction (OER) electrocatalysts is crucial, but remains a big challenge for hydrogen production by acidic water splitting. ...Here, we report that non-stoichiometric Ti oxides (TiO
x
) can safeguard the Ru sites through structural-confinement and charge-redistribution, thereby extending the catalyst lifetime in acid by 10 orders of magnitude longer compared to that of the stoichiometric one (Ru/TiO
2
). By exploiting the redox interaction-engaged strategy, the in situ growth of TiO
x
on Ti foam and the loading of Ru nanoparticles are realized in one step. The as-synthesized binder-free Ru/TiO
x
catalyst exhibits low OER overpotentials of 174 and 265 mV at 10 and 500 mA cm
−2
, respectively. Experimental characterizations and theoretical calculations confirm that TiO
x
stabilizes the Ru active center, enabling operation at 10 mA cm
−2
for over 37 days. This work opens an avenue of using non-stoichiometric compounds as stable and active materials for energy technologies.
Developing flexible photodetectors is crucial for both military and civil fields. Large-area MoS2 films from several to dozens of layers are controllably synthesized via a facile atmospheric-pressure ...sulfurization route of predeposited Mo films and transferred onto other substrates (e.g. SiO2/Si wafers, quartz slides, polymers). The flexible photodetectors were fabricated by transferring as-synthesized MoS2 films onto interdigital electrodes patterned on polyethylene terephthalate (PET) substrates. No additional complex lithography positioning techniques were needed during the device fabrication process due to the large area of as-grown atomic thin MoS2 films. As-obtained flexible photodetectors showed responsibilities of ~ 20 mA/W and response time of several seconds. This demonstrates the possibility of employing large-area two-dimensional semiconductors to meet the increasing demands for wearable and portable electronics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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