Co-reporter:Chuan Xu, Shuang Song, Zhibo Liu, Long Chen, Libin Wang, Dingxun Fan, Ning Kang, Xiuliang Ma, Hui-Ming Cheng, and Wencai Ren
ACS Nano June 27, 2017 Volume 11(Issue 6) pp:5906-5906
Publication Date(Web):June 7, 2017
DOI:10.1021/acsnano.7b01638
Vertical heterostructures of two-dimensional (2D) crystals have led to the observations of numerous exciting physical phenomena and presented the possibilities for technological applications, which strongly depend on the quality, interface, relative alignment, and interaction of the neighboring 2D crystals. The heterostructures or hybrids of graphene and superconductors offer a very interesting platform to study mesoscopic superconductivity and the interplay of the quantum Hall effect with superconductivity. However, so far the heterostructures of graphene and 2D superconductors are fabricated by stacking, and consequently suffer from random relative alignment, weak interfacial interaction, and unavoidable interface contaminants. Here we report the direct growth of high-quality graphene/2D superconductor (nonlayered ultrathin α-Mo2C crystal) vertical heterostructures with uniformly well-aligned lattice orientation and strong interface coupling by chemical vapor deposition. In the heterostructure, both graphene and 2D α-Mo2C crystal show no defect, and the graphene is strongly compressed. Different from the previously reported graphene/superconductor heterostructures or hybrids, the strong interface coupling leads to a phase diagram of superconducting transition with multiple voltage steps being observed in the transition regime. Furthermore, we demonstrate the realization of highly transparent Josephson junction devices based on these strongly coupled high-quality heterostructures, in which a clear magnetic-field-induced Fraunhofer pattern of the critical supercurrent is observed.Keywords: 2D transition metal carbides; graphene; heterostructure; high quality; superconductivity;
Co-reporter:Han Xiao, Zhong-Shuai Wu, Long Chen, Feng Zhou, Shuanghao Zheng, Wencai Ren, Hui-Ming Cheng, and Xinhe Bao
ACS Nano July 25, 2017 Volume 11(Issue 7) pp:7284-7284
Publication Date(Web):June 19, 2017
DOI:10.1021/acsnano.7b03288
Rational engineering and simplified fabrication of high-energy micro-supercapacitors (MSCs) using graphene and other 2D nanosheets are of great value for flexible and integrated electronics. Here we develop one-step mask-assisted simplified fabrication of high-energy MSCs (PG-MSCs) based on the interdigital hybrid electrode (PG) patterns of stacking high-quality phosphorene nanosheets and electrochemically exfoliated graphene in ionic liquid electrolyte. The hybrid PG films with interdigital patterns were directly manufactured by layer-by-layer deposition of phosphorene and graphene nanosheets with the assistance of a customized interdigital mask, and directly transferred onto a flexible substrate. The resultant patterned PG films present outstanding uniformity, flexibility, conductivity (319 S cm–1), and structural integration, which can directly serve as binder- and additive-free flexible electrodes for MSCs. Remarkably, PG-MSCs deliver remarkable energy density of 11.6 mWh cm–3, outperforming most nanocarbon-based MSCs. Moreover, our PG-MSCs show outstanding flexibility and stable performance with slight capacitance fluctuation even under highly folded states. In addition, our simplified mask-assisted strategy for PG-MSCs is highly flexible for simplified production of parallelly and serially interconnected modular power sources, without need of conventional metal-based interconnects and contacts, for designable integrated circuits with high output current and voltage.Keywords: energy storage; graphene; ionic liquid; micro-supercapacitors; phosphorene;
Co-reporter:Weili Zhang;Chuan Xu;Chaoqun Ma;Guoxian Li;Yuzuo Wang;Kaiyu Zhang;Feng Li;Chang Liu;Hui-Ming Cheng;Youwei Du;Nujiang Tang
Advanced Materials 2017 Volume 29(Issue 36) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/adma.201701677
An N-superdoped 3D graphene network structure with an N-doping level up to 15.8 at% for high-performance supercapacitor is designed and synthesized, in which the graphene foam with high conductivity acts as skeleton and nested with N-superdoped reduced graphene oxide arogels. This material shows a highly conductive interconnected 3D porous structure (3.33 S cm−1), large surface area (583 m2 g−1), low internal resistance (0.4 Ω), good wettability, and a great number of active sites. Because of the multiple synergistic effects of these features, the supercapacitors based on this material show a remarkably excellent electrochemical behavior with a high specific capacitance (of up to 380, 332, and 245 F g−1 in alkaline, acidic, and neutral electrolytes measured in three-electrode configuration, respectively, 297 F g−1 in alkaline electrolytes measured in two-electrode configuration), good rate capability, excellent cycling stability (93.5% retention after 4600 cycles), and low internal resistance (0.4 Ω), resulting in high power density with proper high energy density.
Co-reporter:Yanfeng Dong, Zhong-Shuai Wu, Wencai Ren, Hui-Ming Cheng, Xinhe Bao
Science Bulletin 2017 Volume 62, Issue 10(Volume 62, Issue 10) pp:
Publication Date(Web):30 May 2017
DOI:10.1016/j.scib.2017.04.010
Graphene, with unique two-dimensional form and numerous appealing properties, promises to remarkably increase the energy density and power density of electrochemical energy storage devices (EESDs), ranging from the popular lithium ion batteries and supercapacitors to next-generation high-energy batteries. Here, we review the recent advances of the state-of-the-art graphene-based materials for EESDs, including lithium ion batteries, supercapacitors, micro-supercapacitors, high-energy lithium-air and lithium-sulfur batteries, and discuss the importance of the pore, doping, assembly, hybridization and functionalization of different nano-architectures in improving electrochemical performance. The major roles of graphene are highlighted as (1) a superior active material, (2) ultrathin 2D flexible support, and (3) an inactive yet electrically conductive additive. Furthermore, we address the enormous potential of graphene for constructing new-concept emerging graphene-enabled EESDs with multiple functionalities of lightweight, ultra-flexibility, thinness, and novel cell configurations. Finally, future perspectives and challenges of graphene-based EESDs are briefly discussed.
Co-reporter:Zhibo Liu;Zeyuan Fei;Chuan Xu;Yixiao Jiang;Xiu-Liang Ma;Hui-Ming Cheng
Nanoscale (2009-Present) 2017 vol. 9(Issue 22) pp:7501-7507
Publication Date(Web):2017/06/08
DOI:10.1039/C7NR01609C
Lateral heterostructures of 2D materials have several interesting properties and potential applications, and they are usually fabricated by chemical vapor deposition. However, it still remains a great challenge to fabricate 2D lateral heterostructures with well-controlled patterns and sharp interfaces. Herein, we found that the 2D α-Mo2C crystal, a recently emerging 2D superconductor, experiences a phase transition from the α phase to β phase on electron beam irradiation in a transmission electron microscope because of the migration of carbon atoms among the molybdenum octahedrons. Combined with first-principles calculations, the carbon atom migration paths and the corresponding energy barriers were discussed. Utilizing this unique phase transition property of 2D α-Mo2C crystal, we demonstrated the precise in situ construction of the lateral heterostructure of 2D superconducting α/β Mo2C with a well-controlled pattern and sharp interface using advanced aberration-corrected scanning transmission electron microscopy.
Co-reporter:Xing Xin;Zeyuan Fei;Teng Ma;Long Chen;Mao-Lin Chen;Chuan Xu;Xitang Qian;Dong-Ming Sun;Xiu-Liang Ma;Hui-Ming Cheng
Advanced Materials 2017 Volume 29(Issue 16) pp:
Publication Date(Web):2017/04/01
DOI:10.1002/adma.201605451
Monolayer circular graphene platelets with a grain structure gradient in the radial direction are synthesized by chemical vapor deposition on immiscible W–Cu substrates. Because of the different interactions and growth behaviors of graphene on Cu and tungsten carbide, such substrates cause the formation of grain size and orientation gradients through the competition between Cu and tungsten carbide in graphene growth.
Co-reporter:Yang Gao;Yi-Lun Hong;Li-Chang Yin;Zhangting Wu;Zhiqing Yang;Mao-Lin Chen;Zhibo Liu;Teng Ma;Dong-Ming Sun;Zhenhua Ni;Xiu-Liang Ma;Hui-Ming Cheng
Advanced Materials 2017 Volume 29(Issue 29) pp:
Publication Date(Web):2017/08/01
DOI:10.1002/adma.201700990
The ultrafast growth of high-quality uniform monolayer WSe2 is reported with a growth rate of ≈26 µm s−1 by chemical vapor deposition on reusable Au substrate, which is ≈2–3 orders of magnitude faster than those of most 2D transition metal dichalcogenides grown on nonmetal substrates. Such ultrafast growth allows for the fabrication of millimeter-size single-crystal WSe2 domains in ≈30 s and large-area continuous films in ≈60 s. Importantly, the ultrafast grown WSe2 shows excellent crystal quality and extraordinary electrical performance comparable to those of the mechanically exfoliated samples, with a high mobility up to ≈143 cm2 V−1 s−1 and ON/OFF ratio up to 9 × 106 at room temperature. Density functional theory calculations reveal that the ultrafast growth of WSe2 is due to the small energy barriers and exothermic characteristic for the diffusion and attachment of W and Se on the edges of WSe2 on Au substrate.
Co-reporter:Long Chen;Guangmin Zhou;Zhibo Liu;Xiaomeng Ma;Jing Chen;Zhiyong Zhang;Xiuliang Ma;Feng Li;Hui-Ming Cheng
Advanced Materials 2016 Volume 28( Issue 3) pp:510-517
Publication Date(Web):
DOI:10.1002/adma.201503678
Co-reporter:Guangjian Hu;Chuan Xu;Zhenhua Sun;Shaogang Wang;Hui-Ming Cheng;Feng Li
Advanced Materials 2016 Volume 28( Issue 8) pp:1603-1609
Publication Date(Web):
DOI:10.1002/adma.201504765
Co-reporter:Zhibo Liu, Chuan Xu, Ning Kang, Libin Wang, Yixiao Jiang, Jiao Du, Ying Liu, Xiu-Liang Ma, Hui-Ming Cheng, and Wencai Ren
Nano Letters 2016 Volume 16(Issue 7) pp:4243-4250
Publication Date(Web):June 21, 2016
DOI:10.1021/acs.nanolett.6b01265
The properties of two-dimensional (2D) materials such as graphene and monolayer transition metal dichalcogenides are strongly influenced by domain boundaries. Ultrathin transition metal carbides are a class of newly emerging 2D materials that are superconducting and have many potential applications such as in electrochemical energy storage, catalysis, and thermoelectric energy conversion. However, little is known about their domain structure and the influence of domain boundaries on their properties. Here we use atomic-resolution scanning transmission electron microscopy combined with large-scale diffraction-filtered imaging to study the microstructure of chemical vapor deposited high-quality 2D α-Mo2C superconducting crystals of different regular shapes including triangles, rectangles, hexagons, octagons, nonagons, and dodecagons. The Mo atom sublattice in all these crystals has a uniform hexagonal closely packed arrangement without any boundaries. However, except for rectangular and octagonal crystals, the C atom sublattices are composed of three or six domains with rotational-symmetry and well-defined line-shaped domain boundaries because of the presence of three equivalent off-center directions of interstitial carbon atoms in Mo octahedra. We found that there is very small lattice shear strain across the domain boundary. In contrast to the single sharp transition observed in single-domain crystals, transport studies across domain boundaries show a broad resistive superconducting transition with two distinct transition processes due to the formation of localized phase slip events within the boundaries, indicating a significant influence of the boundary on 2D superconductivity. These findings provide new understandings on not only the microstructure of 2D transition metal carbides but also the intrinsic influence of domain boundaries on 2D superconductivity.
Co-reporter:S. Jia, H. D. Sun, J. H. Du, Z. K. Zhang, D. D. Zhang, L. P. Ma, J. S. Chen, D. G. Ma, H. M. Cheng and W. C. Ren
Nanoscale 2016 vol. 8(Issue 20) pp:10714-10723
Publication Date(Web):21 Apr 2016
DOI:10.1039/C6NR01649A
The relatively high sheet resistance, low work function and poor compatibility with hole injection layers (HILs) seriously limit the applications of graphene as transparent conductive electrodes (TCEs) for organic light emitting diodes (OLEDs). Here, a graphene oxide/graphene (GO/G) vertical heterostructure is developed as TCEs for high-performance OLEDs, by directly oxidizing the top layer of three-layer graphene films with ozone treatment. Such GO/G heterostructure electrodes show greatly improved optical transmittance, a large work function, high stability, and good compatibility with HIL materials (MoO3 in this work). Moreover, the conductivity of the heterostructure is not sacrificed compared to the pristine three-layer graphene electrodes, but is significantly higher than that of pristine two-layer graphene films. In addition to high flexibility, OLEDs with different emission colors based on the GO/G heterostructure TCEs show much better performance than those based on indium tin oxide (ITO) anodes. Green OLEDs with GO/G heterostructure electrodes have the maximum current efficiency and power efficiency, as high as 82.0 cd A−1 and 98.2 lm W−1, respectively, which are 36.7% (14.8%) and 59.2% (15.0%) higher than those with pristine graphene (ITO) anodes. These findings open up the possibility of using graphene for next generation high-performance flexible and wearable optoelectronics with high stability.
Co-reporter:Libin Wang, Chuan Xu, Zhibo Liu, Long Chen, Xiuliang Ma, Hui-Ming Cheng, Wencai Ren, and Ning Kang
ACS Nano 2016 Volume 10(Issue 4) pp:4504
Publication Date(Web):April 11, 2016
DOI:10.1021/acsnano.6b00270
Ultrathin transition metal carbides are a class of developing two-dimensional (2D) materials with superconductivity and show great potentials for electrical energy storage and other applications. Here, we report low-temperature magnetotransport measurements on high-quality ultrathin 2D superconducting α-Mo2C crystals synthesized by a chemical vapor deposition method. The magnetoresistance curves exhibit reproducible oscillations at low magnetic fields for temperature far below the superconducting transition temperature of the crystals. We interpret the oscillatory magnetoresistance as a consequence of screening currents circling around the boundary of triangle-shaped terraces found on the surface of ultrathin Mo2C crystals. As the sample thickness decreases, the Mo2C crystals exhibit negative magnetoresistance deep in the superconducting transition regime, which reveals strong phase fluctuations of the superconducting order parameters associated with the superconductor–insulator transition. Our results demonstrate that the ultrathin superconducting Mo2C crystals provide an interesting system for studying rich transport phenomena in a 2D crystalline superconductor with enhanced quantum fluctuations.Keywords: magnetotransport properties; transition metal carbides; two-dimensional superconductivity
Co-reporter:Teng Ma, Wencai Ren, Zhibo Liu, Le Huang, Lai-Peng Ma, Xiuliang Ma, Zhiyong Zhang, Lian-Mao Peng, and Hui-Ming Cheng
ACS Nano 2014 Volume 8(Issue 12) pp:12806
Publication Date(Web):November 23, 2014
DOI:10.1021/nn506041t
Reducing nucleation density and healing structural defects are two challenges for fabricating large-area high-quality single-crystal graphene, which is essential for its electronic and optoelectronic applications. We have developed a method involving chemical vapor deposition (CVD) growth followed by repeated etching–regrowth, to solve both problems at once. Using this method, we can obtain single-crystal graphene domains with a size much larger than that allowed by the nucleation density in the initial growth and efficiently heal structural defects similar to graphitization but at a much lower temperature, both of which are impossible to realize by conventional CVD. Using this method with Pt as a growth substrate, we have grown ∼3 mm defect-free single-crystal graphene domains with a carrier mobility up to 13 000 cm2 V–1 s–1 under ambient conditions.Keywords: chemical vapor deposition; defect free; graphene; large size; single crystal;
Co-reporter:Zongping Chen;Chuan Xu;Chaoqun Ma;Hui-Ming Cheng
Advanced Materials 2013 Volume 25( Issue 9) pp:1296-1300
Publication Date(Web):
DOI:10.1002/adma.201204196
Co-reporter:Yang Gao, Wencai Ren, Teng Ma, Zhibo Liu, Yu Zhang, Wen-Bin Liu, Lai-Peng Ma, Xiuliang Ma, and Hui-Ming Cheng
ACS Nano 2013 Volume 7(Issue 6) pp:5199
Publication Date(Web):May 10, 2013
DOI:10.1021/nn4009356
Atomically thin hexagonal boron nitride (h-BN), as a graphene analogue, has attracted increasing interest because of many fascinating properties and a wide range of potential applications. However, it still remains a great challenge to synthesize high-quality h-BN with predetermined number of layers at a low cost. Here we reported the controlled growth of h-BN on polycrystalline Pt foils by low-cost ambient pressure chemical vapor deposition with ammonia borane as the precursor. Monolayer, bilayer and few-layer h-BN domains and large-area films were selectively obtained on Pt by simply changing the concentration of ammonia borane. Moreover, using a bubbling method, we have achieved the nondestructive transfer of h-BN from Pt to arbitrary substrates and the repeated use of the Pt for h-BN growth, which not only reduces environmental pollution but also decreases the production cost of h-BN. The monolayer and bilayer h-BN obtained are very uniform with high quality and smooth surfaces. In addition, we found that the optical band gap of h-BN increases with decreasing number of layers. The repeated growth of large-area, high-quality monolayer and bilayer h-BN films, together with the successful growth of graphene, opens up the possibility for creating various functional heterostructures for large-scale fabrication and integration of novel electronics.Keywords: bilayer; bubbling transfer; chemical vapor deposition; hexagonal boron nitride; monolayer
Co-reporter:Zhibo Liu;Xiuyun Zhang;Teng Ma;Feng Ding;Li-Chang Yin;Yang Gao;Xiu-Liang Ma;Hui-Ming Cheng
PNAS 2013 Volume 110 (Issue 51 ) pp:20386-20391
Publication Date(Web):2013-12-17
DOI:10.1073/pnas.1312802110
The controlled growth of large-area, high-quality, single-crystal graphene is highly desired for applications in electronics
and optoelectronics; however, the production of this material remains challenging because the atomistic mechanism that governs
graphene growth is not well understood. The edges of graphene, which are the sites at which carbon accumulates in the two-dimensional
honeycomb lattice, influence many properties, including the electronic properties and chemical reactivity of graphene, and
they are expected to significantly influence its growth. We demonstrate the growth of single-crystal graphene domains with
controlled edges that range from zigzag to armchair orientations via growth–etching–regrowth in a chemical vapor deposition
process. We have observed that both the growth and the etching rates of a single-crystal graphene domain increase linearly
with the slanted angle of its edges from 0° to ∼19° and that the rates for an armchair edge are faster than those for a zigzag
edge. Such edge-structure–dependent growth/etching kinetics of graphene can be well explained at the atomic level based on
the concentrations of the kinks on various edges and allow the evolution and control of the edge and morphology in single-crystal
graphene following the classical kinetic Wulff construction theory. Using these findings, we propose several strategies for
the fabrication of wafer-sized, high-quality, single-crystal graphene.
Co-reporter:Zhong-Shuai Wu;Lili Xue;Feng Li;Lei Wen ;Hui-Ming Cheng
Advanced Functional Materials 2012 Volume 22( Issue 15) pp:3290-3297
Publication Date(Web):
DOI:10.1002/adfm.201200534
Abstract
Surface modification of carbon materials plays an important role in tailoring carbon surface chemistry to specify their electrochemical performance. Here, a surface modification strategy for graphene is proposed to produce LiF-nanoparticle-modified graphene as a high-rate, large-capacity pre-lithiated electrode for high-power and high-energy lithium ion batteries. The LiF nanoparticles covering the active sites of the graphene surface provide an extra Li source and act as an effective solid electrolyte interphase (SEI) inhibiter to suppress LiFP6 electrolyte decomposition reactions, affect SEI components, and reduce their thickness. Consequently, the Li-ion diffusion is greatly sped up and the thermodynamic stability of the electrode is significantly improved. This modified graphene electrode shows excellent rate capability and improved first-cycle coulombic efficiency, cycling stability, and ultrahigh power and energy densities accessible during fast charge/discharge processes.
Co-reporter:Jinping Zhao, Wencai Ren and Hui-Ming Cheng
Journal of Materials Chemistry A 2012 vol. 22(Issue 38) pp:20197-20202
Publication Date(Web):13 Aug 2012
DOI:10.1039/C2JM34128J
Seeking highly-efficient, low-cost and robust methods to disinfect and decontaminate water from source to point-of-use is very much in demand. Here, we developed a new material, graphene sponge (GS), for water treatment, which was assembled with graphene oxide sheets by hydrothermal treatment with the assistance of thiourea. These GSs show a tunable pore structure and surface properties, and are mechanically strong. They show high adsorption ability for various water contaminations such as dyes, oils and many other organic solvents. The adsorption capacity of methylene blue and diesel oil in GSs can reach 184 mg g−1 and 129 g g−1, respectively. Moreover, the GSs can be repeatedly used by simple treatment without obvious structure and performance degradation. Additionally, we studied the relationship between the structure and contamination adsorption performance of GSs. It was found that the dye adsorption performance of GSs strongly depends on their surface charge concentration and specific surface area, but the oil adsorption capacity is mainly related to their specific surface area, indicating the different adsorption mechanism. These findings open up many possibilities for the use of graphene in water cleaning, including disinfection, decontamination, re-use, reclamation and desalination.
Co-reporter:Bilu Liu, Wencai Ren, Shisheng Li, Chang Liu and Hui-Ming Cheng
Chemical Communications 2012 vol. 48(Issue 18) pp:2409-2411
Publication Date(Web):03 Jan 2012
DOI:10.1039/C2CC16491D
Chirality-controlled synthesis of single-walled carbon nanotubes (SWCNTs) is a prerequisite for their practical applications in electronic and optoelectronic devices. We report here a novel bimetallic CoPt catalyst for the selective growth of high quality SWCNTs with a narrow chirality distribution at relatively high temperatures of 800 °C and 850 °C using atmospheric pressure alcohol chemical vapor deposition. The addition of Pt into a Co catalyst forms a CoPt alloy and significantly reduces the diameters of the as-grown SWCNTs and narrows their chirality distributions.
Co-reporter:LaiPeng Ma;ZaiLi Dong;LianQing Liu;HuiMing Cheng
Science Bulletin 2012 Volume 57( Issue 23) pp:2995-2999
Publication Date(Web):2012 August
DOI:10.1007/s11434-012-5335-4
Recently, chemical vapor deposition (CVD) on copper has been becoming a main method for preparing large-area and high- quality monolayer graphene. In this paper, we first briefly introduce the preliminary understanding of the microstructure and growth behavior of graphene on copper, and then focus on the recent progress on the quality improvement, number of layers control and transfer-free growth of graphene. In the end, we attempt to analyze the possible development of CVD growth of graphene in future, including the controlled growth of large-size single-crystal graphene and bilayer graphene with different stacking orders.
Co-reporter:Zhong-Shuai Wu, Wencai Ren, Li Xu, Feng Li, and Hui-Ming Cheng
ACS Nano 2011 Volume 5(Issue 7) pp:5463
Publication Date(Web):June 22, 2011
DOI:10.1021/nn2006249
One great challenge in the development of lithium ion batteries is to simultaneously achieve high power and large energy capacity at fast charge and discharge rates for several minutes to seconds. Here we show that nitrogen- or boron-doped graphene can be used as a promising anode for high-power and high-energy lithium ion batteries under high-rate charge and discharge conditions. The doped graphene shows a high reversible capacity of >1040 mAh g–1 at a low rate of 50 mA g–1. More importantly, it can be quickly charged and discharged in a very short time of 1 h to several tens of seconds together with high-rate capability and excellent long-term cyclability. For example, a very high capacity of ∼199 and 235 mAh g–1 was obtained for the N-doped graphene and B-doped graphene at 25 A g–1 (about 30 s to full charge). We believe that the unique two-dimensional structure, disordered surface morphology, heteroatomic defects, better electrode/electrolyte wettability, increased intersheet distance, improved electrical conductivity, and thermal stability of the doped graphene are beneficial to rapid surface Li+ absorption and ultrafast Li+ diffusion and electron transport, and thus make the doped materials superior to those of pristine chemically derived graphene and other carbonaceous materials.Keywords: anode; boron; doped graphene; high rate; lithium ion batteries; nitrogen
Co-reporter:Bilu Liu ; Dai-Ming Tang ; Chenghua Sun ; Chang Liu ; Wencai Ren ; Feng Li ; Wan-Jing Yu ; Li-Chang Yin ; Lili Zhang ; Chuanbin Jiang ;Hui-Ming Cheng
Journal of the American Chemical Society 2010 Volume 133(Issue 2) pp:197-199
Publication Date(Web):December 14, 2010
DOI:10.1021/ja107855q
To understand in-depth the nature of the catalyst and the growth mechanism of single-walled carbon nanotubes (SWCNTs) on a newly developed silica catalyst, we performed this combined experimental and theoretical study. In situ transmission electron microscopy (TEM) observations revealed that the active catalyst for the SWCNT growth is solid and amorphous SiOx nanoparticles (NPs), suggesting a vapor−solid−solid growth mechanism. From in situ TEM and chemical vapor deposition growth experiments, we found that oxygen plays a crucial role in SWCNT growth in addition to the well-known catalyst size effect. Density functional theory calculations showed that oxygen atoms can enhance the capture of −CHx and consequently facilitate the growth of SWCNTs on oxygen-containing SiOx NPs.
Co-reporter:Zhong-Shuai Wu;Da-Wei Wang;Jinping Zhao;Guangmin Zhou;Feng Li;Hui-Ming Cheng
Advanced Functional Materials 2010 Volume 20( Issue 20) pp:3595-3602
Publication Date(Web):
DOI:10.1002/adfm.201001054
Abstract
Hydrous ruthenium oxide (RuO2)/graphene sheet composites (ROGSCs) with different loadings of Ru are prepared by combining sol–gel and low-temperature annealing processes. The graphene sheets (GSs) are well-separated by fine RuO2 particles (5–20 nm) and, simultaneously, the RuO2 particles are anchored by the richly oxygen-containing functional groups of reduced, chemically exfoliated GSs onto their surface. Benefits from the combined advantages of GSs and RuO2 in such a unique structure are that the ROGSC-based supercapacitors exhibit high specific capacitance (∼570 F g−1 for 38.3 wt% Ru loading), enhanced rate capability, excellent electrochemical stability (∼97.9% retention after 1000 cycles), and high energy density (20.1 Wh kg−1) at low operation rate (100 mA g−1) or high power density (10000 W kg−1) at a reasonable energy density (4.3 Wh kg−1). Interestingly, the total specific capacitance of ROGSCs is higher than the sum of specific capacitances of pure GSs and pure RuO2 in their relative ratios, which is indicative of a positive synergistic effect of GSs and RuO2 on the improvement of electrochemical performance. These findings demonstrate the importance and great potential of graphene-based composites in the development of high-performance energy-storage systems.
Co-reporter:Zongping Chen, Wencai Ren, Bilu Liu, Libo Gao, Songfeng Pei, Zhong-Shuai Wu, Jinping Zhao, Hui-Ming Cheng
Carbon 2010 Volume 48(Issue 12) pp:3543-3550
Publication Date(Web):October 2010
DOI:10.1016/j.carbon.2010.05.052
A method for the bulk growth of mono- to few-layer graphene on nickel particles by chemical vapor deposition from methane at atmospheric pressure is described. A graphene yield of about 2.5% of the weight of nickel particles used was achieved in a growth time of 5 min. Scanning and transmission electron microscopy, Raman spectroscopy, thermogravimetry, and electrical conductivity measurements reveal the high quality of the graphene obtained. Suspended graphene can be prepared during this process, bridging the gaps between nearby nickel grains. After the growth of graphene the nickel particles can be effectively removed by a modest FeCl3/HCl etching treatment without degradation of the quality of the graphene sheets.
Co-reporter:Zhong-Shuai Wu, Wencai Ren, Da-Wei Wang, Feng Li, Bilu Liu, and Hui-Ming Cheng
ACS Nano 2010 Volume 4(Issue 10) pp:5835
Publication Date(Web):September 21, 2010
DOI:10.1021/nn101754k
In order to achieve high energy and power densities, we developed a high-voltage asymmetric electrochemical capacitor (EC) based on graphene as negative electrode and a MnO2 nanowire/graphene composite (MGC) as positive electrode in a neutral aqueous Na2SO4 solution as electrolyte. MGC was prepared by solution-phase assembly of graphene sheets and α-MnO2 nanowires. Such aqueous electrolyte-based asymmetric ECs can be cycled reversibly in the high-voltage region of 0−2.0 V and exhibit a superior energy density of 30.4 Wh kg−1, which is much higher than those of symmetric ECs based on graphene//graphene (2.8 Wh kg−1) and MGC//MGC (5.2 Wh kg−1). Moreover, they present a high power density (5000 W kg−1 at 7.0 Wh kg−1) and acceptable cycling performance of ∼79% retention after 1000 cycles. These findings open up the possibility of graphene-based composites for applications in safe aqueous electrolyte-based high-voltage asymmetric ECs with high energy and power densities.Keywords: asymmetric; composite; electrochemical capacitor; graphene; manganese oxide
Co-reporter:Zhong-Shuai Wu;Libo Gao;Bilu Liu;Jinping Zhao
Nano Research 2010 Volume 3( Issue 1) pp:16-22
Publication Date(Web):2010 January
DOI:10.1007/s12274-010-1003-7
Co-reporter:Jinping Zhao, Songfeng Pei, Wencai Ren, Libo Gao, and Hui-Ming Cheng
ACS Nano 2010 Volume 4(Issue 9) pp:5245
Publication Date(Web):September 3, 2010
DOI:10.1021/nn1015506
Large-area sheets are highly desirable for fundamental research and technological applications of graphene. Here we introduce a modified chemical exfoliation technique to prepare large-area graphene oxide (GO) sheets. The maximum area of the GO sheets obtained can reach ∼40000 μm2. We found that the GO area is strongly correlated with the C−O content of the graphite oxide, which enables the area of the synthesized GO sheets to be controlled. By simply changing oxidation conditions, GO sheets with an average area of ca. 100−300, ca. 1000−3000, and ∼7000 μm2 were selectively synthesized. For transparent conductive film applications, thin GO films were fabricated by self-assembly on a liquid/air interface and reduced by HI acid. We found that the sheet resistance of the reduced GO (rGO) films decreases with increasing sheet area at the same transmittance because of the decrease in the number of intersheet tunneling barriers. The rGO film made from GO sheets with an average area of ∼7000 μm2 shows a sheet resistance of 840 Ω/sq at 78% transmittance, which is much lower than that (19.1 kΩ/sq at 79% transmittance) of a rGO film made from small-area GO sheets of ca. 100−300 μm2, and comparable to that of graphene films grown on Ni by chemical vapor deposition.Keywords: graphene; large area; reduction; size control; transparent conductive film
Co-reporter:Zhong-Shuai Wu, Wencai Ren, Lei Wen, Libo Gao, Jinping Zhao, Zongping Chen, Guangmin Zhou, Feng Li and Hui-Ming Cheng
ACS Nano 2010 Volume 4(Issue 6) pp:3187-3194
Publication Date(Web):May 10, 2010
DOI:10.1021/nn100740x
We report a facile strategy to synthesize the nanocomposite of Co3O4 nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co3O4 nanoparticles obtained are 10−30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co3O4/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co3O4 nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.Keywords: anode; cobalt oxide; cyclic performance; graphene; lithium-ion batteries; nanomaterial;
Co-reporter:Zhong-Shuai Wu;Songfeng Pei;Daiming Tang;Libo Gao;Bilu Liu;Feng Li;Chang Liu ;Hui-Ming Cheng
Advanced Materials 2009 Volume 21( Issue 17) pp:1756-1760
Publication Date(Web):
DOI:10.1002/adma.200802560
Co-reporter:Libo Gao ; Wencai Ren ; Bilu Liu ; Zhong-Shuai Wu ; Chuanbin Jiang ;Hui-Ming Cheng
Journal of the American Chemical Society 2009 Volume 131(Issue 39) pp:13934-13936
Publication Date(Web):September 10, 2009
DOI:10.1021/ja906610e
In this communication, we demonstrate nonmetal SiOx nanoparticles (NPs) can tailor few-layer graphenes (FLGs) into graphene nanoribbons (GNRs) and regular pieces with smooth edges. The tailoring of graphene is realized by the movements of SiOx NPs along the graphene lattice in the atmosphere of H2, and the tailored trenches exhibit high selectivity of the crystallographic orientation compared to the reported metal NPs. The low tailoring rate and the long lifetime provide great potential for accurate control of the trench length or the length of the tailored GNRs. As a result, smooth GNRs with a length of several micrometers and a width narrower than 10 nm are obtained. A catalytic hydrogenation mechanism is proposed for the tailoring of graphene by SiOx NPs. These findings open up the possibility for atomically precise graphene device fabrication without metal contamination and indicate the potential catalytic activity of nonmetal NPs for the hydrogenation of carbon materials.
Co-reporter:Zhong-Shuai Wu, Wencai Ren, Libo Gao, Bilu Liu, Chuanbin Jiang, Hui-Ming Cheng
Carbon 2009 Volume 47(Issue 2) pp:493-499
Publication Date(Web):February 2009
DOI:10.1016/j.carbon.2008.10.031
A simple and effective strategy is proposed to tune the number of graphene layers by selecting suitable starting graphite, using a chemical exfoliation method. It is found that both the lateral size and the crystallinity of the starting graphite play important roles in the number of graphene layers obtained. Using artificial graphite, flake graphite powder, Kish graphite, and natural flake graphite as starting materials, ∼80% of the final products are single-layer, single- and double-layer, double- and triple-layer, and few-layer (4–10 layers) graphene, respectively, while a mixture of few-layer (4–10 layers) and thick graphene (>10 layers) is obtained when highly-oriented pyrolytic graphite is used. The smaller the lateral size and the lower the crystallinity of the starting graphite, the fewer the number of graphene layers obtained. Moreover, the graphenes obtained are of high-quality with an electrical conductivity of ∼1 × 103 S/cm. These findings open up the possibility for controlled production of high-quality graphene with a selected number of layers in a large quantity.
Co-reporter:Bilu Liu, Wencai Ren, Chang Liu, Cheng-Hua Sun, Libo Gao, Shisheng Li, Chuanbin Jiang and Hui-Ming Cheng
ACS Nano 2009 Volume 3(Issue 11) pp:3421
Publication Date(Web):October 26, 2009
DOI:10.1021/nn900799v
We report on the observation of a very low growth velocity of single-walled carbon nanotubes (SWNTs) and consequently the direct length-sorted growth and patterned growth of SWNTs by using a metal-catalyst-free chemical vapor deposition (CVD) process proposed recently by our group, in which SiO2 serves as catalyst. We found that the growth velocity of the SWNTs from SiO2 catalyst is only 8.3 nm/s, which is about 300 times slower than that of the commonly used iron group catalysts (Co as a counterpart catalyst in this study). Such a slow growth velocity renders direct length-sorted growth of SWNTs, especially for short SWNTs with hundreds of nanometers in length. By simply adjusting the growth duration, SWNTs with average lengths of 149, 342, and 483 nm were selectively obtained and SWNTs as short as ∼20 nm in length can be grown directly. Moreover, comparative studies indicate that the SiO2 catalyst possesses a much longer catalytic active time, showing sharp contrast with the commonly used Co catalyst which quickly loses its catalytic activity. Taking advantage of the very slow growth velocity of the SiO2 catalyst, patterned growth of SWNT networks confined in a narrow region of <5 μm was also achieved. The short SWNTs may show intriguing physics owing to their finite length effect and are attractive for various practical applications.Keywords: carbon nanotubes; catalyst activity; growth velocity; length; metal-catalyst-free; patterned growth
Co-reporter:Libo Gao, Wencai Ren, Bilu Liu, Riichiro Saito, Zhong-Shuai Wu, Shisheng Li, Chuanbin Jiang, Feng Li and Hui-Ming Cheng
ACS Nano 2009 Volume 3(Issue 4) pp:933
Publication Date(Web):March 24, 2009
DOI:10.1021/nn8008799
We propose a novel surface and interference coenhanced Raman scattering technique to dramatically enhance the Raman signal intensity of graphene by using a specifically designed substrate of Si capped with surface-active metal and oxide double layers (SMO). The total enhancement ratio can reach the order of 103 compared with the original Si substrate. Combining the visibility of graphene on the SMO substrate, we demonstrate that the tiny structure change and surface structure of graphene can be easily detected. This technique makes Raman spectroscopy a more powerful tool in the field of ultrasensitive characterization of graphene, isolated carbon nanotubes, and other film-like materials.Keywords: enhancement; graphene; interference; Raman scattering; surface
Co-reporter:Zhong-Shuai Wu, Wencai Ren, Libo Gao, Jinping Zhao, Zongping Chen, Bilu Liu, Daiming Tang, Bing Yu, Chuanbin Jiang and Hui-Ming Cheng
ACS Nano 2009 Volume 3(Issue 2) pp:411
Publication Date(Web):February 3, 2009
DOI:10.1021/nn900020u
We developed a hydrogen arc discharge exfoliation method for the synthesis of graphene sheets (GSs) with excellent electrical conductivity and good thermal stability from graphite oxide (GO), in combination with solution-phase dispersion and centrifugation techniques. It was found that efficient exfoliation and considerable deoxygenation of GO, and defect elimination and healing of exfoliated graphite can be simultaneously achieved during the hydrogen arc discharge exfoliation process. The GSs obtained by hydrogen arc discharge exfoliation exhibit a high electrical conductivity of ∼2 × 103 S/cm and high thermal stability with oxidization resistance temperature of 601 °C, which are much better than those prepared by argon arc discharge exfoliation (∼2 × 102 S/cm, 525 °C) and by conventional thermal exfoliation (∼80 S/cm, 507 °C) with the same starting GO. These results demonstrate that this hydrogen arc discharge exfoliation method is a good approach for the preparation of GSs with a good quality.Keywords: arc discharge; electrical conductivity; exfoliation; graphene; synthesis; thermal stability
Co-reporter:Bilu Liu, Wencai Ren, Libo Gao, Shisheng Li, Qingfeng Liu, Chuanbin Jiang and Hui-Ming Cheng
The Journal of Physical Chemistry C 2008 Volume 112(Issue 49) pp:19231-19235
Publication Date(Web):November 12, 2008
DOI:10.1021/jp8060587
We demonstrate that manganese (Mn) can catalyze the growth of single-walled carbon nanotubes (SWNTs) with high efficiency via a chemical vapor deposition process. Dense and uniform SWNT films with high quality were obtained by using a Mn catalyst, as characterized by scanning electron microscopy, Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. Moreover, we found that the surface property of the substrate plays a critical role in the growth efficiency of SWNTs. By deposition of a thin oxide layer (SiO2 or Al2O3) on the top of a SiO2/Si substrate, the growth efficiency of SWNTs was dramatically improved. The successful growth of SWNTs by Mn catalyst provides new experimental information for understanding the growth mechanism of SWNTs, which may be helpful for their controllable synthesis.
Co-reporter:Libo Gao, Wencai Ren, Feng Li and Hui-Ming Cheng
ACS Nano 2008 Volume 2(Issue 8) pp:1625
Publication Date(Web):July 25, 2008
DOI:10.1021/nn800307s
For rapid and accurate identification of graphenes by optical images, a total color difference (TCD) method is proposed and demonstrated based on a combination of reflection spectrum and International Commission on Illumination color space. The preferential thickness of different dielectric films covered on a Si substrate is well elucidated, and a 72 nm thick Al2O3 film is found to be much better than the commonly used SiO2 or Si3N4 films. The TCD both between monolayer graphene and substrate and between graphene of different layers can be further improved by appropriately narrowing the wavelength range of the light source. Moreover, the influences of the objective lens in a real-world optical system on the TCD are also discussed. These findings provide useful information for rapid evaluation of the layer range of graphenes simply by different color bands and for accurate and reliable layer identification due to large TCD values, which opens up the possibility for the nondestructive identification and physical property measurements of graphene with an optical microscope.Keywords: graphene; light source; number of layers; objective lens; optical method; substrate; total color difference
Co-reporter:Jinping Zhao, Wencai Ren and Hui-Ming Cheng
Journal of Materials Chemistry A 2012 - vol. 22(Issue 38) pp:NaN20202-20202
Publication Date(Web):2012/08/13
DOI:10.1039/C2JM34128J
Seeking highly-efficient, low-cost and robust methods to disinfect and decontaminate water from source to point-of-use is very much in demand. Here, we developed a new material, graphene sponge (GS), for water treatment, which was assembled with graphene oxide sheets by hydrothermal treatment with the assistance of thiourea. These GSs show a tunable pore structure and surface properties, and are mechanically strong. They show high adsorption ability for various water contaminations such as dyes, oils and many other organic solvents. The adsorption capacity of methylene blue and diesel oil in GSs can reach 184 mg g−1 and 129 g g−1, respectively. Moreover, the GSs can be repeatedly used by simple treatment without obvious structure and performance degradation. Additionally, we studied the relationship between the structure and contamination adsorption performance of GSs. It was found that the dye adsorption performance of GSs strongly depends on their surface charge concentration and specific surface area, but the oil adsorption capacity is mainly related to their specific surface area, indicating the different adsorption mechanism. These findings open up many possibilities for the use of graphene in water cleaning, including disinfection, decontamination, re-use, reclamation and desalination.
Co-reporter:Bilu Liu, Wencai Ren, Shisheng Li, Chang Liu and Hui-Ming Cheng
Chemical Communications 2012 - vol. 48(Issue 18) pp:NaN2411-2411
Publication Date(Web):2012/01/03
DOI:10.1039/C2CC16491D
Chirality-controlled synthesis of single-walled carbon nanotubes (SWCNTs) is a prerequisite for their practical applications in electronic and optoelectronic devices. We report here a novel bimetallic CoPt catalyst for the selective growth of high quality SWCNTs with a narrow chirality distribution at relatively high temperatures of 800 °C and 850 °C using atmospheric pressure alcohol chemical vapor deposition. The addition of Pt into a Co catalyst forms a CoPt alloy and significantly reduces the diameters of the as-grown SWCNTs and narrows their chirality distributions.
