Co-reporter:Tongtao Li, Bin Xue, Biwei Wang, Guannan Guo, Dandan Han, Yancui Yan, and Angang Dong
Journal of the American Chemical Society September 6, 2017 Volume 139(Issue 35) pp:12133-12133
Publication Date(Web):August 24, 2017
DOI:10.1021/jacs.7b06587
Self-assembled nanocrystal (NC) superlattices are emerging as an important class of materials with rationally modulated properties. Engineering the nanoscale structure of constituent building blocks as well as the mesoscale morphology of NC superlattices is a crucial step in widening their range of applications. Here, we report a template-assisted epitaxial assembly strategy, enabling growth of freestanding, carbon-coated tubular monolayer superlattices (TMSLs). Specifically, we design and construct TMSLs of hollow Mn3O4 NCs (h-Mn3O4-TMSLs) by exploiting structural evolution of MnO NCs. The tubular superlattices obtained possess a number of unique and advantageous structural features unavailable in conventional NC superlattices, rendering them particularly attractive for energy conversion applications. We demonstrate this by employing h-Mn3O4-TMSLs as electrocatalysts for oxygen reduction, the catalytic performance of which is comparable to that of state-of-the-art Pt/C catalysts and superior to that of most manganese oxide-based catalysts reported.
Co-reporter:Jiahui Zheng, Guannan Guo, Hanwen Li, Lei Wang, Biwei Wang, Huijuan Yu, Yancui Yan, Dong Yang, and Angang Dong
ACS Energy Letters May 12, 2017 Volume 2(Issue 5) pp:1105-1105
Publication Date(Web):April 18, 2017
DOI:10.1021/acsenergylett.7b00230
Hybrid micro–mesoporous graphitic carbon spheres (M-MGCSs) featuring ordered mesoporous graphene-like cores and uniform microporous carbon shells are designed by transformation of self-assembled Fe3O4 nanoparticle supraparticles and are used as an efficient, dual spatially confined sulfur reservoir for lithium–sulfur (Li–S) batteries. Such rationally designed M-MGCSs synergistically combine the merits of micro- and mesoporous carbons when used as the sulfur host in Li–S batteries: the core having interconnected spherical mesopores of 9.0 nm provides sufficient space for loading S8 molecules, while the shell having micropores of 0.6 nm can entrap only small S2–4 molecules, which are converted into electrolyte-insoluble polysulfides during discharge, minimizing the outward diffusion of long-chain polysulfides from the core. These advantageous structural features, combined with the highly graphitic nature and mesoscale spherical morphology of M-MGCSs, enable Li–S cathodes with greatly improved performance even at high sulfur areal loadings.
Co-reporter:Biwei Wang, Xinxia Wang, Jinxiang Zou, Yancui Yan, Songhai Xie, Guangzhi Hu, Yanguang LiAngang Dong
Nano Letters March 8, 2017 Volume 17(Issue 3) pp:
Publication Date(Web):January 27, 2017
DOI:10.1021/acs.nanolett.7b00004
Iron and nitrogen codoped carbons (Fe–N–C) have attracted increasingly greater attention as electrocatalysts for oxygen reduction reaction (ORR). Although challenging, the synthesis of Fe–N–C catalysts with highly dispersed and fully exposed active sites is of critical importance for improving the ORR activity. Here, we report a new type of graphitic Fe–N–C catalysts featuring numerous Fe single atoms anchored on a three-dimensional simple-cubic carbon framework. The Fe–N–C catalyst, derived from self-assembled Fe3O4 nanocube superlattices, was prepared by in situ ligand carbonization followed by acid etching and ammonia activation. Benefiting from its homogeneously dispersed and fully accessible active sites, highly graphitic nature, and enhanced mass transport, our Fe–N–C catalyst outperformed Pt/C and many previously reported Fe–N–C catalysts for ORR. Furthermore, when used for constructing the cathode for zinc–air batteries, our Fe–N–C catalyst exhibited current and power densities comparable to those of the state-of-the-art Pt/C catalyst.Keywords: Fe−N−C catalyst; oxygen reduction reaction; Self-assembly; single atom; zinc−air battery;
Co-reporter:Xiudi Shen, Wenfeng Jiang, Huajun Sun, Yun Wang, Angang Dong, Jianhua Hu, Dong Yang
Journal of Alloys and Compounds 2017 Volume 691() pp:178-184
Publication Date(Web):15 January 2017
DOI:10.1016/j.jallcom.2016.08.265
•Preparation of core-shell Si@N-doped carbon nanoparticles using ionic liquid as the C and N precursors.•N-doped carbon shell was prepared by one facile step reaction.•The capacity of Si@N-doped carbon was twice higher than that of Si@C.Silicon is a potential next generation anode material for lithium-ion battery, however, its commercial application was hindered by its poor electronic conductivity and huge volume change upon lithiation. Herein, Si@N-doped carbon nanoparticles with commercial Si nanoparticle as the core and N-doped carbon as the shell were prepared by a facial, low-cost and scalable one-step method using ionic liquid (3-cyanopyridine/H2SO4) as both of the N and C sources. While using as anode material for lithium-ion batteries, Si@N-doped carbon exhibited a high reversible capacity of 725 mAh/g after 100 discharge/charge cycles at a current density of 420 mA/g, about twice higher than that of Si@C, a control sample prepared by a similar process using sucrose as the carbon precursor, which showed a capacity of 360 mAh/g after 100 cycles at 420 mA/g. The improved electrochemical performance could be ascribed to the stable core-shell structure of the nanocomposite and more importantly the doping of N element into the carbon shell. Furthermore, this work also provides a versatile strategy for preparation of core-shell N-doped carbon coated nanoparticles.
Co-reporter:Huijuan Yu;Hanwen Li;Shouyi Yuan;Yuchi Yang;Jiahui Zheng;Jianhua Hu
Nano Research 2017 Volume 10( Issue 7) pp:2495-2507
Publication Date(Web):04 April 2017
DOI:10.1007/s12274-017-1454-1
Mesoporous carbons have been widely utilized as the sulfur host for lithium-sulfur (Li-S) batteries. The ability to engineer the porosity, wall thickness, and graphitization degree of the carbon host is essential for addressing issues that hamper commercialization of Li-S batteries, such as fast capacity decay and poor high-rate performance. In this work, highly ordered, ultrathin mesoporous graphitic-carbon frameworks (MGFs) having unique cage-like mesoporosity, derived from self-assembled Fe3O4 nanoparticle superlattices, are demonstrated to be an excellent host for encapsulating sulfur. The resulting S@MGFs exhibit high specific capacity (1,446 mAh·g–1 at 0.15 C), good rate capability (430 mAh·g–1 at 6 C), and exceptional cycling stability (~0.049% capacity decay per cycle at 1 C) when used as Li-S cathodes. The superior electrochemical performance of the S@MGFs is attributed to the many unique and advantageous structural features of MGFs. In addition to the interconnected, ultrathin graphitic-carbon framework that ensures rapid electron and lithium-ion transport, the microporous openings between adjacent mesopores efficiently suppress the diffusion of polysulfides, leading to improved capacity retention even at high current densities.
Co-reporter:Yibing Xu;Qiang Zhang;Longfei Lv;Wenqian Han;Guanhong Wu;Dong Yang
Nanoscale (2009-Present) 2017 vol. 9(Issue 44) pp:17248-17253
Publication Date(Web):2017/11/16
DOI:10.1039/C7NR06959F
Discretely sized semiconductor clusters have attracted considerable attention due to their intriguing optical properties and self-assembly behaviors. While lead halide perovskite nanostructures have been recently intensively explored, few studies have addressed perovskite clusters and their self-assembled superstructures. Here, we report the room-temperature synthesis of sub-2 nm CsPbBr3 clusters and present strong evidence that these ultrasmall perovskite species, obtained under a wide range of reaction conditions, possess a specific size, with optical properties and self-assembly characteristics resembling those of well-known II–VI semiconductor magic-sized clusters. Unlike conventional CsPbBr3 nanocrystals, the as-synthesized CsPbBr3 nanoclusters spontaneously self-assemble into a hexagonally packed columnar mesophase in solution, which can be further converted to single-crystalline CsPbBr3 quantum nanoribbons with bright deep-blue emission at room temperature. Such a conversion of CsPbBr3 nanoclusters to nanoribbons is found to be driven by a ligand-destabilization-induced crystallization and mesophase transition process. Our study will facilitate the investigation of perovskite nanoclusters and offer new possibilities in the low-temperature synthesis of anisotropic perovskite nanostructures.
Co-reporter:Yancui Yan, Guannan Guo, Tongtao Li, Dandan Han, Jiahui Zheng, Jianhua Hu, Dong Yang, Angang Dong
Electrochimica Acta 2017 Volume 246(Volume 246) pp:
Publication Date(Web):20 August 2017
DOI:10.1016/j.electacta.2017.06.020
In this work, carbon-coated MnFe2O4 nanoparticle (NP) hollow microspheres are fabricated by a facile emulsion-based assembly method followed by in situ ligand carbonization. Specifically, MnFe2O4 NPs stabilized by oleic acid (OA) are the primary building blocks to assemble hollow microspheres, while the subsequent carbonization of OA ligands leads to the formation of uniform carbon coatings without degrading the ordering of NPs. As anode materials for lithium-ion batteries, such MnFe2O4 NP hollow composite microspheres exhibit significantly improved electrochemical performance in comparison with their solid counterparts and most MnFe2O4-based anodes reported to date, retaining a high reversible capacity of 730 mAh g−1 after 300 cycles at a current density of 2 A g−1. Furthermore, even when tested at an ultrahigh rate of 10 A g−1, MnFe2O4 NP hollow microspheres can still deliver a high specific capacity of 433 mAh g−1. The superior performance of MnFe2O4 NP hollow microspheres is attributable to their hollow superstructure, close-packed configuration of the constituent NPs, and uniform carbon coatings, which facilitate lithium-ion and electron transport while simultaneously alleviating the drastic volumetric change during cycling. Our work establishes that the optimized MnFe2O4 anode material offers great promise for high-performance lithium-ion batteries.Download high-res image (112KB)Download full-size image
Co-reporter:Fudong Wang, Angang Dong, and William E. Buhro
Chemical Reviews 2016 Volume 116(Issue 18) pp:10888-10933
Publication Date(Web):March 14, 2016
DOI:10.1021/acs.chemrev.5b00701
The solution–liquid–solid (SLS) and related solution-based methods for the synthesis of semiconductor nanowires and nanorods are reviewed. Since its discovery in 1995, the SLS mechanism and its close variants have provided a nearly general strategy for the growth of pseudo-one-dimensional nanocrystals. The various metallic-catalyst nanoparticles employed are summarized, as are the syntheses of III–V, II–VI, IV–VI, group IV, ternary, and other nanorods and nanowires. The formation of axial heterojunctions, core/shell nanowires, and doping are also described. The related supercritical-fluid–liquid–solid (SFLS), electrically controlled SLS, flow-based SLS, and solution–solid–solid (SSS) methods are discussed, and the crystallographic characteristics of the wires and rods grown by these methods are summarized. The presentation of optical and electronic properties emphasizes electronic structures, absorption cross sections, polarization anisotropies, and charge-carrier dynamics, including photoluminescence intermittency (blinking) and photoluminescence modulation by charges and electric fields. Finally, developing applications for the pseudo-one-dimensional nanostructures in field-effect transistors, lithium-ion batteries, photocathodes, photovoltaics, and photodetection are discussed.
Co-reporter:Xianfeng Zhang; Longfei Lv; Li Ji; Guannan Guo; Limin Liu; Dandan Han; Biwei Wang; Yaqi Tu; Jianhua Hu; Dong Yang
Journal of the American Chemical Society 2016 Volume 138(Issue 10) pp:3290-3293
Publication Date(Web):March 3, 2016
DOI:10.1021/jacs.6b00055
Self-assembly of nanocrystal (NC) building blocks into mesoscopic superstructures with well-defined symmetry and geometry is essential for creating new materials with rationally designed properties. Despite the tremendous progress in colloidal assembly, it remains a fundamental challenge to assemble isotropic spherical NCs into one-dimensional (1D) ordered superstructures. Here, we report a new and general methodology that utilizes molecular clusters to induce the anisotropic assembly of NCs in solution, yielding polymer-like, single-NC-wide linear chains comprising as many as ∼1000 close-packed NCs. This cluster-assisted assembly process is applicable to various metallic, semiconductor, and magnetic NCs of different sizes and shapes. Mechanistic investigation reveals that the solvent-induced association of clusters plays a key role in driving the anisotropic assembly of NCs. Our work opens a solution-based route for linearly assembling NCs and represents an important step toward the bottom-up construction of 1D ordered NC superstructures.
Co-reporter:Li Ji, Guannan Guo, Hongyuan Sheng, Shanli Qin, Biwei Wang, Dandan Han, Tongtao Li, Dong Yang, and Angang Dong
Chemistry of Materials 2016 Volume 28(Issue 11) pp:3823
Publication Date(Web):May 12, 2016
DOI:10.1021/acs.chemmater.6b00870
Three-dimensional (3D) porous graphene frameworks, which combine the advantages of both porous materials and graphene, have recently attracted enormous attention for electrochemical energy storage. Despite the tremendous progress, it remains a grand challenge to synthesize graphene frameworks with ordered porosity and well-defined macroscopic morphologies. Herein, we report the design and synthesis of centimeter-scale, free-standing thin films of ordered mesoporous graphene frameworks (MGFs) from 2D nanocrystal superlattices self-assembled at the solid– or liquid–air interface. The resultant MGF films possess uniform thicknesses tunable in the range from a few hundred nanometers to several tens of micrometers, highly ordered and interconnected mesoporosity, ultrathin pore walls comprising few-layer graphene, and high surface areas. To demonstrate their potential applications in energy storage, MGF films are used as electrode materials to build supercapacitors, which exhibit high specific capacitances with excellent cycling stabilities in both aqueous and organic electrolytes, with the capacitive performance comparable to or higher than that of most graphene-based materials developed previously.
Co-reporter:Hanwen Li, Huijuan Yu, Xianfeng Zhang, Guannan Guo, Jianhua Hu, Angang Dong, and Dong Yang
Chemistry of Materials 2016 Volume 28(Issue 4) pp:1179
Publication Date(Web):January 22, 2016
DOI:10.1021/acs.chemmater.5b04750
Searching for new electrode materials with high capacities and excellent rate performance is crucial for the development of next-generation lithium-ion batteries (LIBs). Silicon carbide (SiC), which is traditionally considered to be electrochemically inert toward lithiation, has recently been demonstrated to be a potential high-performance anode material upon activation by surface graphitization. Despite the great potential, it remains a grand challenge to synthesize SiC nanostructures with precisely controlled morphologies and surface properties, due to the rather high reaction temperatures (>1200 °C) typically required for SiC crystallization. Herein, we designed and synthesized a novel type of SiC nanostructures in which bowl-like, ultrathin SiC nanoshells were encapsulated in hollow graphitic carbon spheres (designated as SiC@HGSs), which exhibited unexpectedly high electrochemical performance when used as LIB anodes. SiC@HGSs retained a stable capacity of 1345 mAh g–1 at a current density of 0.6 A g–1 after 600 cycles and 742 mAh g–1 at 3 A g–1 after 1000 cycles. Even at a high current density of 6 A g–1, SiC@HGSs could still deliver a capacity of ∼400 mAh g–1. The superior high-rate performance is attributable to the unique architecture and exceptional structural durability of SiC@HGSs.
Co-reporter:Longfei Lv, Yibing Xu, Hehai Fang, Wenjin Luo, Fangjie Xu, Limin Liu, Biwei Wang, Xianfeng Zhang, Dong Yang, Weida Hu and Angang Dong
Nanoscale 2016 vol. 8(Issue 28) pp:13589-13596
Publication Date(Web):21 Jun 2016
DOI:10.1039/C6NR03428D
All-inorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, and I) nanocrystals (NCs) are emerging as an important class of semiconductor materials with superior photophysical properties and wide potential applications in optoelectronic devices. So far, only a few studies have been conducted to control the shape and geometry of CsPbX3 NCs. Here we report a general approach to directly synthesize two-dimensional (2D) CsPbX3 perovskite and mixed perovskite nanosheets with uniform and ultrathin thicknesses down to a few monolayers. The key to the high-yield synthesis of perovskite nanosheets is the development of a new Cs-oleate precursor. The as-synthesized CsPbX3 nanosheets exhibit bright photoluminescence with broad wavelength tunability by composition modulation. The excellent optoelectronic properties of CsPbX3 nanosheets combined with their unique 2D geometry and large lateral dimensions make them ideal building blocks for building functional devices. To demonstrate their potential applications in optoelectronics, photodetectors based on CsPbBr3 nanosheets are fabricated, which exhibit high on/off ratios with a fast response time.
Co-reporter:Bin Xue, Fangjie Xu, Biwei Wang and Angang Dong
CrystEngComm 2016 vol. 18(Issue 2) pp:250-256
Publication Date(Web):23 Nov 2015
DOI:10.1039/C5CE01955A
The ability to control the shape and morphology of inorganic nanocrystals (NCs) is essential to the development of various NC-based functional devices. Here we report the shape-controlled synthesis of β-In2S3 NCs and elucidate how the NC shape and morphology affect their lithium storage properties when used as anode materials in lithium-ion batteries. Three representative types of β-In2S3 NCs with precisely-controlled morphologies, including one-dimensional (1D) nanotubes, 2D nanosheets, and 3D nanoflowers, are synthesized by a ligand-assisted route under similar reaction conditions. Mild thermal treatment converts the organic ligands attached to the NC surface into a conformal carbon-coating layer while preserving the NC shape, resulting in In2S3/C nanocomposites having similar carbon contents irrespective of their shape. This, combined with identical electrode formulation and test procedures, allows us to probe the influence of shape on the electrochemical performance of In2S3 NCs. Compared with 1D nanotubes and 3D nanoflowers, 2D In2S3 nanosheets exhibit significantly higher capacities and rate capabilities, which is primarily attributed to their unique 2D layered structures.
Co-reporter:Huijuan Yu;Guannan Guo;Li Ji;Hanwen Li;Dong Yang;Jianhua Hu
Nano Research 2016 Volume 9( Issue 12) pp:3757-3771
Publication Date(Web):2016 December
DOI:10.1007/s12274-016-1246-z
Three-dimensional (3D) graphene has recently attracted enormous attention for electrochemical energy storage applications. However, current methods suffer from an inability to simultaneously control and engineer the porosity and morphology of the graphene frameworks. Here, we report the designed synthesis of ordered mesoporous graphene spheres (OMGSs) by transformation of self-assembled Fe3O4 nanocrystal superlattices. The resultant OMGSs have an ultrathin framework comprising few-layered graphene, with highly ordered and interconnected mesoporosity and a high surface area. These advantageous structural and textural features, in combination with the excellent electrical conductivity of the graphitic frameworks, render the OMGSs an ideal and general platform for creating hybrid materials that are well suited for use as composite electrodes in lithium-ion batteries (LIBs). As a proof-of-concept demonstration, SnO2 and GeO2 nanoparticles are incorporated into the OMGSs to afford SnO2@OMGSs and GeO2@OMGSs, respectively, both of which exhibit outstanding lithium storage properties when used as LIB anodes.
Co-reporter:Fangjie Xu, Bin Xue, Fudong Wang, and Angang Dong
Chemistry of Materials 2015 Volume 27(Issue 3) pp:1140
Publication Date(Web):January 13, 2015
DOI:10.1021/acs.chemmater.5b00070
Ternary alloyed semiconductor nanostructures have attracted increasingly greater attention due to their unique physiochemical properties that may not be available in the parent binary systems. In this work, we report the solution–liquid–solid (SLS) growth of colloidal, uniform ZnSexTe1–x nanowires (NWs), the composition of which can be tuned over a wide range by manipulating the growth rate of multicomponent constituents. Two sets of ZnSexTe1–x NWs with high compositional homogeneities are synthesized by using zinc stearate (Zn(St)2) and diethyl zinc (Zn(Et)2) as the Zn precursor, respectively. The resultant NWs are systematically characterized with respect to the structure, composition, and optical band gap, and on the basis of these, the composition dependence of band gaps is extracted. Both sets of colloidal ZnSexTe1–x NWs are found to exhibit strong band bowing with the band gap minimum occurring at x = 0.30, which is consistent with the previously reported results based on ZnSexTe1–x bulk materials and thin films.
Co-reporter:Limin Liu, Xianfeng Zhang, Li Ji, Hanwen Li, Huijuan Yu, Fangjie Xu, Jianhua Hu, Dong Yang and Angang Dong
RSC Advances 2015 vol. 5(Issue 110) pp:90570-90577
Publication Date(Web):15 Oct 2015
DOI:10.1039/C5RA18192E
In the surface treatment of colloidal nanocrystals (NCs), S2− ions have been widely employed as metal-free atomic ligands to efficiently replace the original long hydrocarbon ligands. Prior studies exclusively show that S2− ions considerably quench the photoluminescence (PL) of semiconductor NCs (e.g., CdSe and PbS) during ligand exchange. Here we report that the influence of S2− treatment on the luminescent properties of CdSe NCs is highly dependent on the NC size. We observe an unexpected PL brightening phenomenon when small CdSe NCs (<4 nm) are subject to S2− treatment followed by incubation in the presence of air and light irradiation, whereas PL enhancement is not observed in large CdSe NCs (>4 nm) treated under the same conditions. Systematic characterization establishes the evolution of CdSe/CdS core–shell structures in small CdSe NCs arising from anion exchange between Se2− and S2−, which in conjunction with the subsequent incubation process accounts for the PL enhancement. Notably, 2.1 nm CdSe NCs treated with (NH4)2S exhibit a PL quantum yield (QY) as high as ∼40% after 2 days of incubation, which is comparable to that of conventional hydrophobic CdSe/CdS core–shell NCs synthesized at high temperatures. Our studies demonstrate that S2− ions can substantially substitute Se2− in small CdSe NCs in addition to replacing the surface-coating ligands, enabling highly luminescent, hydrophilic CdSe/CdS core–shell NCs at room temperature.
Co-reporter:Yucong Jiao;Dan Han;Limin Liu;Li Ji;Guannan Guo; Jianhua Hu; Dong Yang; Angang Dong
Angewandte Chemie International Edition 2015 Volume 54( Issue 19) pp:5727-5731
Publication Date(Web):
DOI:10.1002/anie.201501398
Abstract
While great progress has been achieved in the synthesis of ordered mesoporous carbons in the past decade, it still remains a challenge to prepare highly graphitic frameworks with ordered mesoporosity and high surface area. Reported herein is a simple synthetic methodology, based on the conversion of self-assembled superlattices of Fe3O4 nanocrystals, to fabricate highly ordered mesoporous graphene frameworks (MGFs) with ultrathin pore walls consisting of three to six stacking graphene layers. The MGFs possess face-centered-cubic symmetry with interconnected mesoporosity, tunable pore width, and high surface area. Because of their unique architectures and superior structural durability, the MGFs exhibit excellent cycling stability and rate performance when used as anode materials for lithium-ion batteries, thus retaining a specific capacity of 520 mAh g−1 at a current density of 300 mA g−1 after 400 cycles.
Co-reporter:Yucong Jiao;Dan Han;Limin Liu;Li Ji;Guannan Guo; Jianhua Hu; Dong Yang; Angang Dong
Angewandte Chemie International Edition 2015 Volume 54( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/anie.201502712
Co-reporter:Yucong Jiao;Dan Han;Limin Liu;Li Ji;Guannan Guo; Jianhua Hu; Dong Yang; Angang Dong
Angewandte Chemie 2015 Volume 127( Issue 19) pp:5819-5823
Publication Date(Web):
DOI:10.1002/ange.201501398
Abstract
While great progress has been achieved in the synthesis of ordered mesoporous carbons in the past decade, it still remains a challenge to prepare highly graphitic frameworks with ordered mesoporosity and high surface area. Reported herein is a simple synthetic methodology, based on the conversion of self-assembled superlattices of Fe3O4 nanocrystals, to fabricate highly ordered mesoporous graphene frameworks (MGFs) with ultrathin pore walls consisting of three to six stacking graphene layers. The MGFs possess face-centered-cubic symmetry with interconnected mesoporosity, tunable pore width, and high surface area. Because of their unique architectures and superior structural durability, the MGFs exhibit excellent cycling stability and rate performance when used as anode materials for lithium-ion batteries, thus retaining a specific capacity of 520 mAh g−1 at a current density of 300 mA g−1 after 400 cycles.
Co-reporter:Yucong Jiao;Dan Han;Limin Liu;Li Ji;Guannan Guo; Jianhua Hu; Dong Yang; Angang Dong
Angewandte Chemie 2015 Volume 127( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/ange.201502712
Co-reporter:Angang Dong
Science Bulletin 2015 Volume 60( Issue 22) pp:1964-1965
Publication Date(Web):2015 November
DOI:10.1007/s11434-015-0927-4
Co-reporter:Liu Yang, Jianhua Hu, Angang Dong, Dong Yang
Electrochimica Acta 2014 Volume 144() pp:235-242
Publication Date(Web):20 October 2014
DOI:10.1016/j.electacta.2014.08.099
As the promising anode material for Li-ion batteries (LIBs), transition metal oxides possess much higher theoretical lithium storage capacities than the commercially used graphite. However, the large volume variation during the lithium insertion/desertion processes and the relatively low electrical conductivity of transition metal oxides usually lead to poor battery performance, impeding their extensive use for LIBs. Here, we report the synthesis of a new type of nanocomposite consisting of Fe3O4 nanocrystals (NCs) and multiwalled carbon nanotubes (CNTs), which can be used as high-performance LIB anode materials. The nanocomposite is formed by hydrolysis of iron precursors in the presence of poly(acrylic acid)-functionalized CNTs (PAA-CNTs), resulting into Fe3O4 NCs which are firmly and uniformly attached to the CNT surface. When the as-formed nanocomposite is coated with a carbon layer by pyrolysis of the low-cost petroleum pitch, the nanocomposite electrodes exhibit significantly enhanced lithium storage capacities and cyclability. In particular, a reversible lithium storage capacity of 850 mAh g−1 is retained after 100 charge/discharge cycles at a current rate of 0.1 C. In comparison, considerably poor battery performance is observed when the CNT- or carbon-free counterpart is used as the LIB anode.
Co-reporter:Angang Dong, Yucong Jiao, and Delia J. Milliron
ACS Nano 2013 Volume 7(Issue 12) pp:10978
Publication Date(Web):November 19, 2013
DOI:10.1021/nn404566b
The ability to remove long, insulating ligands from nanocrystal (NC) surfaces without deteriorating the structural integrity of NC films is critical to realizing their electronic and optoelectronic applications. Here we report a nondestructive ligand-exchange approach based on in situ chemical treatment of NCs floating at the liquid–air interface, enabling strongly coupled NC superlattice films that can be directly transferred to arbitrary substrates for device applications. Ligand-exchange-induced structural defects such as cracks and degraded NC ordering that are commonly observed using previous methods are largely prevented by performing ligand exchange at the liquid–air interface. The significantly reduced interparticle spacing arising from ligand replacement leads to highly conductive NC superlattice films, the electrical conductivities and carrier mobilities of which are 1 order of magnitude higher than those of the same NC films subject to substrate-supported exchange using previously reported procedures. The in situ, free-floating exchange approach presented here opens the door for electronically coupled NC superlattices that hold great promise for high-performance, flexible electronic and optoelectronic devices.Keywords: electronic coupling; in situ treatment; ligand exchange; liquid−air interface; nanocrystal devices; nanocrystal superlattices
Co-reporter:Guannan Guo, Li Ji, Xiudi Shen, Biwei Wang, Hanwen Li, Jianhua Hu, Dong Yang and Angang Dong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 41) pp:NaN16135-16135
Publication Date(Web):2016/09/22
DOI:10.1039/C6TA07184H
Self-assembled nanoparticle (NP) superlattices consisting of close-packed NPs represent a new type of solid-state materials that have been widely used in thin-film electronic and optoelectronic devices. The ability to engineer the architecture of NP superlattices is critical to expand their applications beyond electronics and optoelectronics. Transition metal oxides (TMOs) such as Fe3O4 are earth-abundant and environmentally benign materials with rich electrochemical properties. Herein, we report the emulsion-based assembly of TMO NP supraparticles with or without hollow interiors by manipulating the oil/water interfacial tension, which can be realized by controlling the concentration of the surfactant. Using Fe3O4 NPs as a model system we show that the original organic ligands attached to the NP surface can be transformed into a three-dimensional interconnected carbon network by in situ heat treatment, resulting in carbon-coated NP supraparticles that are particularly suited for energy storage applications. When evaluated as an anode material for lithium-ion batteries, the carbon-coated, hollow Fe3O4 NP supraparticles exhibit significantly enhanced lithium storage properties when compared with their solid counterparts as well as most Fe3O4-based anodes reported previously. The superior electrochemical performance of hollow NP supraparticles benefits from their hollow interiors, conformal carbon coating, and close-packed configuration of NPs.
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