153 results on '"Xingxu, Yan"'
Search Results
52. Exploring the Atomic Scale Structure and Properties of Grain Boundary in SrTiO3 by Electron Beam Imaging and Spectroscopy
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Xiaowang Wang, Chaitanya Gadre, Christopher Addiego, Huaixun Huyan, Mingjie Xu, Xingxu Yan, and Xiaoqing Pan
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Instrumentation - Published
- 2022
53. Facet-controlled Single Atom Catalysts for Efficient CO Oxidation
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Wenjie Zang, Xingxu Yan, Peter Tieu, and Xiaoqing Pan
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Instrumentation - Published
- 2022
54. High-density switchable skyrmion-like polar nanodomains integrated on silicon
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Lu Han, Christopher Addiego, Sergei Prokhorenko, Meiyu Wang, Hanyu Fu, Yousra Nahas, Xingxu Yan, Songhua Cai, Tianqi Wei, Yanhan Fang, Huazhan Liu, Dianxiang Ji, Wei Guo, Zhengbin Gu, Yurong Yang, Peng Wang, Laurent Bellaiche, Yanfeng Chen, Di Wu, Yuefeng Nie, and Xiaoqing Pan
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Multidisciplinary ,TK ,QC - Abstract
Topological domains in ferroelectrics have received much attention recently owing to their novel functionalities and potential applications in electronic devices. So far, however, such topological polar structures have been observed only in superlattices grown on oxide substrates, which limits their applications in silicon-based electronics. Here we report the realization of room-temperature skyrmion-like polar nanodomains in lead titanate/strontium titanate bilayers transferred onto silicon. Moreover, an external electric field can reversibly switch these nanodomains into the other type of polar texture, which substantially modifies their resistive behaviours. The polar-configuration-modulated resistance is ascribed to the distinct band bending and charge carrier distribution in the core of the two types of polar texture. The integration of high-density (more than 200 gigabits per square inch) switchable skyrmion-like polar nanodomains on silicon may enable non-volatile memory applications using topological polar structures in oxides.
- Published
- 2022
55. A serum lipidomics study for the identification of specific biomarkers for endometrial polyps to distinguish them from endometrial cancer or hyperplasia
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Xingxu Yan, Wen Zhao, Jinxia Wei, Yaqi Yao, Guijiang Sun, Lei Wang, Wenqing Zhang, Siyu Chen, Wenjie Zhou, Huan Zhao, Xiaomeng Li, Yu Xiao, and Yubo Li
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Uterine Diseases ,Cancer Research ,Hyperplasia ,Oncology ,Endometrial Hyperplasia ,Lipidomics ,Biomarkers, Tumor ,Humans ,Female ,Biomarkers ,Endometrial Neoplasms - Abstract
Endometrial diseases, including endometrial polyps (EP), endometrial cancer (EC) and endometrial hyperplasia (EH), are common gynecological diseases that affect women of childbearing and perimenopausal age. Clinically, biopsy or imaging methods are usually used to screen and diagnose these diseases; however, due to the invasiveness and heterogeneity of these tests, a noninvasive, convenient, objective and accurate biomarker is needed for the differential diagnosis of EP, EC or EH. In the present study, serum samples from 326 patients with endometrial diseases and 225 healthy volunteers were analyzed using nontargeted lipidomics. A combination of multivariate and univariate analyses was used to identify and qualify six, eight and seven potential biomarkers in the sera from patients with EP, EC and EH, respectively. Using a logistic regression algorithm and receiver operating characteristic (ROC) curve analysis, a biomarker panel including four specific EP biomarkers, 6-keto-PGF1α, PA(37:4), LysoPC(20:1) and PS(36:0), showed good classification and diagnostic ability in distinguishing EP from EC or EH. The biomarker panel for distinguishing EP from EC yielded an area under the curve (AUC) of 0.915, sensitivity of 100% and specificity of 72.41%, while that for distinguishing EP from EH yielded an AUC of 1.000, sensitivity of 100% and specificity of 100%. The two diagnostic models also showed good diagnostic abilities in the validation set. Therefore, this biomarker panel can be used as a rapid diagnostic method to assist in imaging examinations and provide a reference for clinicians in the identification and diagnosis of endometrial diseases.
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- 2022
56. Size‐Dependent Nickel‐Based Electrocatalysts for Selective CO 2 Reduction
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Zhida Li, Dong He, Xingxu Yan, Sheng Dai, Sabrina Younan, Zunjian Ke, Xiaoqing Pan, Xiangheng Xiao, Hongjun Wu, and Jing Gu
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General Medicine - Published
- 2020
57. General synthesis of two-dimensional van der Waals heterostructure arrays
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Yuan Liu, Xingxu Yan, Weiqi Dang, Huifang Ma, Zhengwei Zhang, Xiangfeng Duan, Bei Zhao, Yu Huang, Bo Li, Xiaoqing Pan, Zhaoyang Lin, Xiangdong Yang, Bolong Huang, Jia Li, Guangyu Zhang, Ruixia Wu, Jun Luo, Kai Wang, Zheng Wei, Yang Liu, Xidong Duan, and Mingzi Sun
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Multidisciplinary ,Materials science ,Superlattice ,Bilayer ,Transistor ,Nucleation ,Nanotechnology ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,symbols.namesake ,law ,Scanning transmission electron microscopy ,Monolayer ,symbols ,van der Waals force ,0210 nano-technology - Abstract
Two-dimensional van der Waals heterostructures (vdWHs) have attracted considerable interest1–4. However, most vdWHs reported so far are created by an arduous micromechanical exfoliation and manual restacking process5, which—although versatile for proof-of-concept demonstrations6–16 and fundamental studies17–30—is clearly not scalable for practical technologies. Here we report a general synthetic strategy for two-dimensional vdWH arrays between metallic transition-metal dichalcogenides (m-TMDs) and semiconducting TMDs (s-TMDs). By selectively patterning nucleation sites on monolayer or bilayer s-TMDs, we precisely control the nucleation and growth of diverse m-TMDs with designable periodic arrangements and tunable lateral dimensions at the predesignated spatial locations, producing a series of vdWH arrays, including VSe2/WSe2, NiTe2/WSe2, CoTe2/WSe2, NbTe2/WSe2, VS2/WSe2, VSe2/MoS2 and VSe2/WS2. Systematic scanning transmission electron microscopy studies reveal nearly ideal vdW interfaces with widely tunable moire superlattices. With the atomically clean vdW interface, we further show that the m-TMDs function as highly reliable synthetic vdW contacts for the underlying WSe2 with excellent device performance and yield, delivering a high ON-current density of up to 900 microamperes per micrometre in bilayer WSe2 transistors. This general synthesis of diverse two-dimensional vdWH arrays provides a versatile material platform for exploring exotic physics and promises a scalable pathway to high-performance devices. A general strategy for the synthesis of two-dimensional van der Waals heterostructure arrays is used to produce high-performance electronic devices, showing the potential of this scalable approach for practical technologies.
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- 2020
58. Improved Electrical Properties of Layer Structured La2Ti1.96V0.04O7 Ceramics
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Jianguo Zhu, Zhifeng Jiao, Wenwu Wang, Mingjie Xu, Xingxu Yan, Qiang Chen, Yueyi Li, Dayun Liang, Laiming Jiang, Thomas K. Lee, and Xiaoqing Pan
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010302 applied physics ,Materials science ,Piezoelectric coefficient ,Dopant ,Doping ,Direct current ,Analytical chemistry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Ion ,Dielectric spectroscopy ,Electrical resistivity and conductivity ,visual_art ,0103 physical sciences ,Materials Chemistry ,visual_art.visual_art_medium ,Ceramic ,Electrical and Electronic Engineering ,0210 nano-technology - Abstract
La2Ti1.96V0.04O7 (LTVO) ceramics with Ti4+ ions partially substituted by V5+ ions at B sites show excellent electrical properties. The dopant V5+ ions do not result in collapse of the cell layered structure, but they lead to the enhanced distortions of BO6 oxygen octahedrons. Impedance spectroscopy reveals that a certain number of defects are formed due to the substitution of Ti4+ ions by V5+ ions. Meanwhile, the concentration of oxygen vacancies is decreased compared to pure La2Ti2O7 (LTO) ceramics. The direct current resistivity of LTVO ceramics obtained from alternating current (AC) impedance fitting at 600°C is 1.3 × 106 Ω cm, which is more than five times of that of the pure LTO at the same temperature (2.2 × 105 Ω cm). The substitution of Ti4+ ions by V5+ ions greatly enhances the piezoelectric coefficient, d33 = 4.8 pC/N. Therefore, the doping of V5+ ions in the B sites of LTO ceramics should be a good choice for enhancing their piezoelectric properties and resistivity at high temperature regimes.
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- 2020
59. Anomalous Linear Layer-Dependent Blue Shift of Ultraviolet-Range Interband Transition in Two-Dimensional MoS2
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Mian Zhang, Xingxu Yan, Jingying Zheng, Xiaoqing Pan, Peng Wang, Ruqian Wu, Zhe Wang, Yi Zhang, Liying Jiao, Feng Xue, Mingjie Xu, Lin Xie, and Chaitanya Gadre
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Range (particle radiation) ,Materials science ,Band gap ,business.industry ,Physics::Optics ,Electronic structure ,medicine.disease_cause ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Blueshift ,Condensed Matter::Materials Science ,General Energy ,medicine ,Optoelectronics ,Electronics ,Physical and Theoretical Chemistry ,Linear layer ,business ,Ultraviolet - Abstract
The unique electronic structure of two-dimensional materials paves the way for abundant cutting-edge applications, including electronic devices and optoelectronic devices. The bandgap excitations a...
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- 2019
60. Uniformity Is Key in Defining Structure–Function Relationships for Atomically Dispersed Metal Catalysts: The Case of Pt/CeO2
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Xiaoqing Pan, Joseph P. Chada, Sergei Hanukovich, Adam S. Hoffman, Sheng Dai, Jordan Finzel, Phillip Christopher, Joaquin Resasco, Leo DeRita, Simon R. Bare, Mingjie Xu, Xingxu Yan, and George W. Graham
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Chemistry ,Structure function ,Sintering ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Atomic units ,Catalysis ,0104 chemical sciences ,Characterization (materials science) ,Metal ,Colloid and Surface Chemistry ,Adsorption ,Chemical engineering ,visual_art ,visual_art.visual_art_medium ,Metal catalyst - Abstract
Catalysts consisting of atomically dispersed Pt (Ptiso) species on CeO2 supports have received recent interest due to their potential for efficient metal utilization in catalytic convertors. However, discrepancies exist between the behavior (reducibility, interaction strength with adsorbates) of high surface area Ptiso/CeO2 systems and of well-defined surface science and computational model systems, suggesting differences in Pt local coordination in the two classes of materials. Here, we reconcile these differences by demonstrating that high surface area Ptiso/CeO2 synthesized at low Pt loadings ( 0.1 weight % produce a distribution of sub-nanometer Pt structures, which are difficult to distinguish using common characterization techniques, and exhibit strong interactions with CO and weak resistance to sintering, even in 0.05 bar H2 at 50 °C-properties previously seen for high surface area materials. This work demonstrates that low metal loadings can be used to selectively populate the most thermodynamically stable adsorption sites on high surface area supports with atomically dispersed metals. Further, the site uniformity afforded by this synthetic approach is critical for the development of relationships between atomic scale local coordination and functional properties. Comparisons to recent studies of Ptiso/TiO2 suggest a general compromise between the stability of atomically dispersed metal catalysts and their ability to interact with and activate molecular species.
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- 2019
61. Real-space charge-density imaging with sub-ångström resolution by four-dimensional electron microscopy
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Dianxiang Ji, Xingxu Yan, Colin Heikes, Christopher Addiego, Huaixun Huyan, Xiaoqing Pan, Thomas Blum, Ruqian Wu, Linze Li, Yi Zhang, Hui Wang, Toshihiro Aoki, Yuefeng Nie, Wenpei Gao, Darrell G. Schlom, and Yusheng Hou
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Multidisciplinary ,Materials science ,Charge density ,Heterojunction ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Space charge ,Molecular physics ,Condensed Matter::Materials Science ,Electron diffraction ,0103 physical sciences ,Microscopy ,Scanning transmission electron microscopy ,Density functional theory ,010306 general physics ,0210 nano-technology - Abstract
The distribution of charge density in materials dictates their chemical bonding, electronic transport, and optical and mechanical properties. Indirectly measuring the charge density of bulk materials is possible through X-ray or electron diffraction techniques by fitting their structure factors1-3, but only if the sample is perfectly homogeneous within the area illuminated by the beam. Meanwhile, scanning tunnelling microscopy and atomic force microscopy enable us to see chemical bonds, but only on the surface4-6. It remains a challenge to resolve charge density in nanostructures and functional materials with imperfect crystalline structures-such as those with defects, interfaces or boundaries at which new physics emerges. Here we describe the development of a real-space imaging technique that can directly map the local charge density of crystalline materials with sub-angstrom resolution, using scanning transmission electron microscopy alongside an angle-resolved pixellated fast-electron detector. Using this technique, we image the interfacial charge distribution and ferroelectric polarization in a SrTiO3/BiFeO3 heterojunction in four dimensions, and discover charge accumulation at the interface that is induced by the penetration of the polarization field of BiFeO3. We validate this finding through side-by-side comparison with density functional theory calculations. Our charge-density imaging method advances electron microscopy from detecting atoms to imaging electron distributions, providing a new way of studying local bonding in crystalline solids.
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- 2019
62. Graphene-nanopocket-encaged PtCo nanocatalysts for highly durable fuel cell operation under demanding ultralow-Pt-loading conditions
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Zipeng Zhao, Zeyan Liu, Ao Zhang, Xingxu Yan, Wang Xue, Bosi Peng, Huolin L. Xin, Xiaoqing Pan, Xiangfeng Duan, and Yu Huang
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Biomedical Engineering ,General Materials Science ,Bioengineering ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics - Abstract
The proton exchange membrane fuel cell (PEMFC) as an attractive clean power source can promise a carbon-neutral future, but the widespread adoption of PEMFCs requires a substantial reduction in the usage of the costly platinum group metal (PGM) catalysts. Ultrafine nanocatalysts are essential to provide sufficient catalytic sites at a reduced PGM loading, but are fundamentally less stable and prone to substantial size growth in long-term operations. Here we report the design of a graphene-nanopocket-encaged platinum cobalt (PtCo@Gnp) nanocatalyst with good electrochemical accessibility and exceptional durability under a demanding ultralow PGM loading (0.070 mg
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- 2021
63. Experimental observation of localized interfacial phonon modes
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Mark S. Goorsky, Chaitanya Gadre, Nicholas J. Hines, Glenn G. Jernigan, Samuel Graham, Xingxu Yan, Ruiyang Li, Michael E. Liao, Eungkyu Lee, Zhe Cheng, Tengfei Luo, Xiaoqing Pan, Juan Carlos Idrobo, Jingjing Shi, and Karl D. Hobart
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Materials science ,Phonon ,Science ,FOS: Physical sciences ,General Physics and Astronomy ,Interatomic potential ,Electron ,Article ,General Biochemistry, Genetics and Molecular Biology ,Physics::Fluid Dynamics ,symbols.namesake ,Molecular dynamics ,Surfaces, interfaces and thin films ,Affordable and Clean Energy ,Condensed Matter::Superconductivity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Thermal ,Scanning transmission electron microscopy ,Condensed Matter - Materials Science ,Multidisciplinary ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Materials Science (cond-mat.mtrl-sci) ,Conductance ,General Chemistry ,Mechanical engineering ,Condensed Matter::Soft Condensed Matter ,symbols ,Raman spectroscopy - Abstract
Interfaces impede heat flow in micro/nanostructured systems. Conventional theories for interfacial thermal transport were derived based on bulk phonon properties of the materials making up the interface without explicitly considering the atomistic interfacial details, which are found critical to correctly describing thermal boundary conductance. Recent theoretical studies predicted the existence of localized phonon modes at the interface which can play an important role in understanding interfacial thermal transport. However, experimental validation is still lacking. Through a combination of Raman spectroscopy and high-energy-resolution electron energy-loss spectroscopy in a scanning transmission electron microscope, we report the experimental observation of localized interfacial phonon modes at ~12 THz at a high-quality epitaxial Si-Ge interface. These modes are further confirmed using molecular dynamics simulations with a high-fidelity neural network interatomic potential, which also yield thermal boundary conductance agreeing well with that measured in time-domain thermoreflectance experiments. Simulations find that the interfacial phonon modes have an obvious contribution to the total thermal boundary conductance. Our findings significantly contribute to the understanding of interfacial thermal transport physics and have impact on engineering thermal boundary conductance at interfaces in applications such as electronics thermal management and thermoelectric energy conversion., Conventional theories for interfacial thermal transport are derived from bulk phonon properties. Here, the authors report experimental observation of interfacial phonon modes localized at interfaces, changing how interfacial thermal transport should be understood.
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- 2021
64. Chiral molecular intercalation superlattices
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Qi Qian, Huaying Ren, Jingyuan Zhou, Zhong Wan, Jingxuan Zhou, Xingxu Yan, Jin Cai, Peiqi Wang, Bailing Li, Zdenek Sofer, Bo Li, Xidong Duan, Xiaoqing Pan, Yu Huang, and Xiangfeng Duan
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Multidisciplinary - Abstract
The discovery of chiral-induced spin selectivity (CISS) opens up the possibility to manipulate spin orientation without external magnetic fields and enables new spintronic device designs
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- 2021
65. Bifunctional hydroformylation on heterogeneous Rh-WO
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Insoo, Ro, Ji, Qi, Seungyeon, Lee, Mingjie, Xu, Xingxu, Yan, Zhenhua, Xie, Gregory, Zakem, Austin, Morales, Jingguang G, Chen, Xiaoqing, Pan, Dionisios G, Vlachos, Stavros, Caratzoulas, and Phillip, Christopher
- Abstract
Metal-catalysed reactions are often hypothesized to proceed on bifunctional active sites, whereby colocalized reactive species facilitate distinct elementary steps in a catalytic cycle
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- 2021
66. Application of lipidomics strategy to explore aging-related biomarkers and potential anti-aging mechanisms of ginseng
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Xiaokai Li, Yuechen Liu, Yaqian Dong, Xingxu Yan, Hui Liu, Haihua Su, Guijiang Sun, Shenshen Yang, Guoxiang Jia, and Yubo Li
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Virtual screening ,Aging ,Adolescent ,Atomic force microscopy ,business.industry ,Panax ,Middle Aged ,Bioinformatics ,Sphingolipid ,Molecular Docking Simulation ,Metabolic pathway ,Ginseng ,Potential biomarkers ,Lipidomics ,Sphingolipid metabolism ,Medicine ,Humans ,Geriatrics and Gerontology ,business ,Gerontology ,Biomarkers ,Aged - Abstract
Aging often leads to an increase risk of age-related diseases, and the development of anti-aging drugs have become the trend and focus of the current scientific research. In this experiment, serum samples from healthy people of different ages were analyzed based on clinical lipidomics, and a total of 10 potential biomarkers in middle-aged and youth group, 20 biomarkers in the youth and the elderly group were obtained. Furthermore, dhSph and dhCer involved above may affect the aging process through sphingolipid metabolic pathway. As the first and rate-limiting step of catalyzing de novo sphingolipid pathway, SPT may play a key role in human anti-aging, which is revealed by lipidomics liposome tracer analysis. The potential active components in ginseng on SPT was further verified by molecular docking virtual screening and atomic force microscope. Four ingredients of ginseng may reduce the levels of metabolites dhSph and dhCer by inhibiting the activity of SPT, and play an anti-aging effect by affecting the sphingolipid metabolism pathway.A clinical trials registration number: ChiCTR1900026836.
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- 2021
67. Nanoscale Imaging of Phonon Dynamics by Electron Microscopy
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Toshihiro Aoki, Ruqian Wu, Xiaoqing Pan, Chaitanya Gadre, Qichen Song, Sheng-Wei Lee, Gang Chen, Jie Li, Lei Gu, and Xingxu Yan
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Condensed Matter::Materials Science ,Materials science ,Condensed matter physics ,Phonon ,law ,Dynamics (mechanics) ,Electron microscope ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Nanoscopic scale ,law.invention - Abstract
Spatially resolved vibrational mapping of nanostructures is indispensable to the development and understanding of thermal nanodevices1, modulation of thermal transport2, and novel nanostructured thermoelectric materials3–5. Through the engineering of complex structures such as alloys, nanostructures, and superlattice interfaces, one can significantly alter the propagation of phonons and suppress material thermal conductivity while maintaining electrical conductivity2. Probing local vibrations and phonon dispersions in nanostructured semiconductors informs structure-property correlations and offers insights into the design and optimization of novel thermoelectric materials. There have been no correlative experiments that spatially track the modulation of phonon properties in and around nanostructures due to spatial resolution limitations of conventional optical phonon detection techniques. Here we demonstrate two-dimensional spatial mapping of phonons in a single silicon-germanium (SiGe) quantum dot (QD) using monochromated electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM). Tracking the variation of the Si optical mode in and around the QD, we observe the nanoscale modification of the composition induced redshift. We observe nonequilibrium phonons that only exist near the interface and furthermore, develop a novel technique to differentially map phonon momenta providing direct evidence that the interplay between diffusive and specular reflection largely depends on the detailed atomistic structure --a major advancement in the field. Our work unveils the nonequilibrium phonon dynamics at nanoscale interfaces and can be used to study actual nanodevices and aid in the understanding of heat dissipation near nanoscale hotspots, which is crucial for future high-performance nanoelectronics. Our work demonstrates high spatial resolution vibrational characterization of nanostructures and interfaces that can be extended to other nanostructures and superlattice systems, in terms of composition, composition gradient, and structure driven phonon dynamics.
- Published
- 2021
68. Activating a Two-Dimensional PtSe
- Author
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Xiaofan, Ping, Dan, Liang, Yueyang, Wu, Xingxu, Yan, Shengxue, Zhou, Dake, Hu, Xiaoqing, Pan, Pengfei, Lu, and Liying, Jiao
- Abstract
Two-dimensional (2D) PtSe
- Published
- 2021
69. In Situ Observations of Post-Synthesis Modification of a Metal-Organic Framework Using Atomic Resolution S/TEM and EELS
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Xiaoqing Pan, Xingxu Yan, Djawhar Ferrah, Peter Tieu, Wenpei Gao, Zhengtao Xu, Chaitanya Gadre, and Muqing Li
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In situ ,Materials science ,Atomic resolution ,Analytical chemistry ,Post synthesis ,Instrumentation - Published
- 2020
70. Unexpected Strong Thermally Induced Phonon Energy Shift for Mapping Local Temperature
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Chengyan Liu, Kehang Yu, Sheng Dai, Lei Gu, Xiaoqing Pan, Xingxu Yan, Toshihiro Aoki, Chaitanya Gadre, and Ruqian Wu
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Materials science ,Condensed matter physics ,business.industry ,Phonon ,Mechanical Engineering ,Anharmonicity ,Bioengineering ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Temperature measurement ,Thermal expansion ,Temperature gradient ,Semiconductor ,General Materials Science ,Surface plasmon resonance ,0210 nano-technology ,business ,Plasmon - Abstract
Measuring temperature in nanoscale is crucial for the research and development of microelectronic devices. Plasmon resonance has been utilized to map local temperature gradient in metallic materials (Al) due to their large coefficients of thermal expansion. However, most semiconductors (including Si and SiC) possess much smaller coefficients of thermal expansion due to their strong covalent bonding in crystal structure, for which the plasmon-based temperature measurement becomes unreliable. Here, we report an unexpected strong, thermally induced phonon energy shift in SiC by spatially resolved vibrational spectroscopy in transmission electron microscopy with in situ heating, demonstrating that this shift can be applied as a useful tool for measuring nanoscale temperature. When a bulk phonon spectrum is used, the spatial resolution of vibrational spectroscopy can be as high as one nanometer. Molecular dynamics simulations reveal that lattice expansion only contributes a small fraction of phonon energy shift and that vibrant motions away from the bonds are predominate factors. This study gains deeper insight into the understanding of dynamic behaviors of the phonon and provides a new avenue to measure local temperature in nanodevices.
- Published
- 2019
71. Effective Electrochemical Modulation of SERS Intensity Assisted by Core-Shell Nanoparticles
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Govinda Ghimire, Mingjie Xu, Xiaoqing Pan, Xingxu Yan, Jin He, and Jing Guo
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Chemistry ,010401 analytical chemistry ,Nanoparticle ,Nanotechnology ,010402 general chemistry ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Analytical Chemistry ,symbols.namesake ,Electrode ,Monolayer ,symbols ,Molecule ,Raman scattering ,Plasmon ,Electrode potential - Abstract
An effective and reversible tuning of the intensity of surface-enhanced Raman scattering (SERS) of nonelectroactive molecules at nonresonance conditions by electrochemical means has been developed on plasmonic molecular nanojunctions formed between Au@Ag core-shell nanoparticles (NPs) and a gold nanoelectrode (AuNE) modified with a self-assembled monolayer. The Au@Ag nanoparticle on nanoelectrode (NPoNE) structures are formed in situ by the electrochemical deposition of Ag on AuNPs adsorbed on the AuNE and can be monitored by both the electrochemical current and SERS signals. Instead of introducing molecular changes by the applied electrode potential, the highly effective SERS intensity tuning was achieved by the chemical composition transformation of the ultrathin Ag shell from metallic Ag to insulating AgCl. The electrode potential-induced electromagnetic enhancement (EME) tuning in the Au@Ag NPoNE structure has been confirmed by finite-difference time-domain simulations. Moreover, the specific Raman band associated with Ag-molecule interaction can also be tuned by the electrode potential. Therefore, we demonstrated that the electrode potential could effectively and reversibly modulate both EME and chemical enhancement in Au@Ag NPoNE structures.
- Published
- 2021
72. Capturing 3D atomic defects and phonon localization at the 2D heterostructure interface
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Lain-Jong Li, Georgios Varnavides, Yakun Yuan, Xiaoqing Pan, Christopher J. Ciccarino, Prineha Narang, Dennis S. Kim, Jianwei Miao, Xingxu Yan, Xuezeng Tian, Ming-Yang Li, and Polina Anikeeva
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Engineering ,Condensed Matter - Materials Science ,Quantum Physics ,Multidisciplinary ,business.industry ,Science and engineering ,Library science ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Materials Science ,0103 physical sciences ,ComputingMilieux_COMPUTERSANDEDUCATION ,010306 general physics ,0210 nano-technology ,business ,Quantum Physics (quant-ph) ,ComputingMilieux_MISCELLANEOUS - Abstract
The 3D local atomic structures and crystal defects at the interfaces of heterostructures control their electronic, magnetic, optical, catalytic and topological quantum properties, but have thus far eluded any direct experimental determination. Here we determine the 3D local atomic positions at the interface of a MoS2-WSe2 heterojunction with picometer precision and correlate 3D atomic defects with localized vibrational properties at the epitaxial interface. We observe point defects, bond distortion, atomic-scale ripples and measure the full 3D strain tensor at the heterointerface. By using the experimental 3D atomic coordinates as direct input to first principles calculations, we reveal new phonon modes localized at the interface, which are corroborated by spatially resolved electron energy-loss spectroscopy. We expect that this work will open the door to correlate structure-property relationships of a wide range of heterostructure interfaces at the single-atom level.
- Published
- 2021
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73. Fe-N-C Electrocatalysts' Durability: Effects of Single Atoms' Mobility and Clustering
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Michel Mermoux, Frédéric Maillard, Kavita Kumar, Plamen Atanassov, Xiaoyan Li, Yechuan Chen, Xingxu Yan, Xiaoqing Pan, Yuanchao Liu, Laetitia Dubau, Tristan Asset, Electrochimie Interfaciale et Procédés (EIP), Laboratoire d'Electrochimie et de Physico-chimie des Matériaux et des Interfaces (LEPMI), Institut de Chimie du CNRS (INC)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Institut de Chimie du CNRS (INC)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), University of California [Irvine] (UCI), University of California, Laboratoire de Physique des Solides (LPS), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Matériaux Interfaces ELectrochimie (MIEL), and ANR-19-CE05-0039,ANIMA,Aérogels de carbone poreux dopés à l'azote et avec des métaux abondants pour des assemblages membrane-électrodes efficaces et durables(2019)
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Materials science ,010405 organic chemistry ,chemistry.chemical_element ,General Chemistry ,[CHIM.CATA]Chemical Sciences/Catalysis ,[CHIM.MATE]Chemical Sciences/Material chemistry ,Platinum group ,010402 general chemistry ,7. Clean energy ,01 natural sciences ,Durability ,Catalysis ,3. Good health ,0104 chemical sciences ,chemistry ,Chemical engineering ,Cathode material ,Atom ,Metal nanoparticles ,Carbon ,ComputingMilieux_MISCELLANEOUS - Abstract
Atomically dispersed (or single atom) iron–nitrogen–carbon (Fe–N–C) catalysts are promising alternatives to platinum group metal nanoparticles supported on dispersed carbon as a cathode material in...
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- 2020
74. High-order superlattices by rolling up van der Waals heterostructures
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Yuan Liu, Xingxu Yan, Yi Qiao, Fei Wei, Xiaoqing Pan, Huifang Ma, Xidong Duan, Yue Zhang, Bo Li, Zucheng Zhang, Xiangfeng Duan, Yuan Ping, Jia Li, Bei Zhao, Chunhao Guo, Zhaoyang Lin, Xiangdong Yang, Bailing Li, Junqing Xu, Zeyad Almutairi, Dingyi Shen, Yu Huang, Ruixia Wu, Xiao Chen, Imran Shakir, Qi Qian, Zhengwei Zhang, and Zhong Wan
- Subjects
Multidisciplinary ,Materials science ,Magnetoresistance ,Condensed matter physics ,Superlattice ,Nanowire ,Heterojunction ,02 engineering and technology ,Substrate (electronics) ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,0103 physical sciences ,symbols ,van der Waals force ,010306 general physics ,0210 nano-technology ,Electronic band structure ,Topology (chemistry) - Abstract
Two-dimensional (2D) materials1,2 and the associated van der Waals (vdW) heterostructures3-7 have provided great flexibility for integrating distinct atomic layers beyond the traditional limits of lattice-matching requirements, through layer-by-layer mechanical restacking or sequential synthesis. However, the 2D vdW heterostructures explored so far have been usually limited to relatively simple heterostructures with a small number of blocks8-18. The preparation of high-order vdW superlattices with larger number of alternating units is exponentially more difficult, owing to the limited yield and material damage associated with each sequential restacking or synthesis step8-29. Here we report a straightforward approach to realizing high-order vdW superlattices by rolling up vdW heterostructures. We show that a capillary-force-driven rolling-up process can be used to delaminate synthetic SnS2/WSe2 vdW heterostructures from the growth substrate and produce SnS2/WSe2 roll-ups with alternating monolayers of WSe2 and SnS2, thus forming high-order SnS2/WSe2 vdW superlattices. The formation of these superlattices modulates the electronic band structure and the dimensionality, resulting in a transition of the transport characteristics from semiconducting to metallic, from 2D to one-dimensional (1D), with an angle-dependent linear magnetoresistance. This strategy can be extended to create diverse 2D/2D vdW superlattices, more complex 2D/2D/2D vdW superlattices, and beyond-2D materials, including three-dimensional (3D) thin-film materials and 1D nanowires, to generate mixed-dimensional vdW superlattices, such as 3D/2D, 3D/2D/2D, 1D/2D and 1D/3D/2D vdW superlattices. This study demonstrates a general approach to producing high-order vdW superlattices with widely variable material compositions, dimensions, chirality and topology, and defines a rich material platform for both fundamental studies and technological applications.
- Published
- 2020
75. Promotion of Ternary Pt–Sn–Ag Catalysts toward Ethanol Oxidation Reaction: Revealing Electronic and Structural Effects of Additive Metals
- Author
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Xingxu Yan, Tzu Hsi Huang, Sheng Dai, Xiaoqing Pan, Tsan-Yao Chen, Chao Yu Yang, Kuan Wen Wang, and Jeng Han Wang
- Subjects
Ethanol ,Renewable Energy, Sustainability and the Environment ,Chemistry ,Acetaldehyde ,Energy Engineering and Power Technology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,Acetic acid ,Fuel Technology ,Chemical engineering ,Chemistry (miscellaneous) ,Oxidizing agent ,Materials Chemistry ,Nanorod ,Ethanol fuel ,0210 nano-technology ,Ternary operation - Abstract
The use of a computation-guided method and the discovered structure–property relationship would establish a rational strategy to aid the development of ethanol oxidation reaction (EOR) catalysts for possible commercialization of direct ethanol fuel cells. Here, we investigate the promotion roles of additive metals in ternary Pt–Sn–Ag catalysts toward EOR via a combination of density functional theory calculation and experimental evidence. By calculating the EOR energetics, the promotion roles of Sn and Ag were revealed from the viewpoints of electronic and structural effects, respectively: (1) The addition of Sn and Ag on Pt essentially reduce the reaction energy and activation barrier of the second two-electron transfer process of EOR, facilitating the oxidation of acetaldehyde to acetic acid; (2) a homogeneous Pt–Sn–Ag surface configuration strengthens the adsorption energy of ethanol, thus improving the activity for ethanol oxidizing to acetaldehyde. Experimentally, various Pt–Sn–Ag nanorod catalysts ...
- Published
- 2018
76. Uniformity Is Key in Defining Structure-Function Relationships for Atomically Dispersed Metal Catalysts: The Case of Pt/CeO
- Author
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Joaquin, Resasco, Leo, DeRita, Sheng, Dai, Joseph P, Chada, Mingjie, Xu, Xingxu, Yan, Jordan, Finzel, Sergei, Hanukovich, Adam S, Hoffman, George W, Graham, Simon R, Bare, Xiaoqing, Pan, and Phillip, Christopher
- Abstract
Catalysts consisting of atomically dispersed Pt (Pt
- Published
- 2019
77. End-On Bound Iridium Dinuclear Heterogeneous Catalysts on WO3 for Solar Water Oxidation
- Author
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Gary W. Brudvig, Qi Dong, Dunwei Wang, Xiaoqing Pan, James E. Thorne, Maria Flytzani-Stephanopoulos, Sufeng Cao, Ke R. Yang, Shasha Zhu, Kelly L. Materna, Victor S. Batista, Yanyan Zhao, and Xingxu Yan
- Subjects
inorganic chemicals ,Materials science ,General Chemical Engineering ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,Chemical reaction ,Catalysis ,Solar water ,Metal ,Atom ,Iridium ,QD1-999 ,Substrate (chemistry) ,General Chemistry ,021001 nanoscience & nanotechnology ,Combinatorial chemistry ,0104 chemical sciences ,Chemistry ,chemistry ,Homogeneous ,visual_art ,visual_art.visual_art_medium ,0210 nano-technology - Abstract
Heterogeneous catalysts with atomically defined active centers hold great promise for high-performance applications. Among them, catalysts featuring active moieties with more than one metal atom are important for chemical reactions that require synergistic effects but are rarer than single atom catalysts (SACs). The difficulty in synthesizing such catalysts has been a key challenge. Recent progress in preparing dinuclear heterogeneous catalysts (DHCs) from homogeneous molecular precursors has provided an effective route to address this challenge. Nevertheless, only side-on bound DHCs, where both metal atoms are affixed to the supporting substrate, have been reported. The competing end-on binding mode, where only one metal atom is attached to the substrate and the other metal atom is dangling, has been missing. Here, we report the first observation that end-on binding is indeed possible for Ir DHCs supported on WO3. Unambiguous evidence supporting the binding mode was obtained by in situ diffuse reflectanc...
- Published
- 2018
78. Stacking-mode confined growth of 2H-MoTe2/MoS2 bilayer heterostructures for UV–vis–IR photodetectors
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Jie Pan, Zhiyong Fan, Qicheng Zhang, Aashir Waleed, Xingxu Yan, Tianyou Zhai, Peng Wang, Zhengtang Luo, Xuewu Ou, Ruizhe Wu, Lin Gan, Nan Zhou, Minghao Zhuang, Yao Ding, Xiaoqing Pan, and Irfan Haider Abidi
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Materials science ,Renewable Energy, Sustainability and the Environment ,business.industry ,chemistry.chemical_element ,Heterojunction ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Dark field microscopy ,0104 chemical sciences ,symbols.namesake ,chemistry ,Scanning transmission electron microscopy ,symbols ,Optoelectronics ,General Materials Science ,Quantum efficiency ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Tellurium ,Spectroscopy ,Raman spectroscopy - Abstract
The atomic thin, vertically-stacked 2H-MoTe2/MoS2 heterostructures are successfully synthesized using the single step chemical vapor deposition (CVD) method and a magnet-assisted secondary precursor delivery tool. The second material (MoTe2) was grown in a well-controlled, unique and epitaxial 2H-stacking mode atop the first material (MoS2), starting from the edges. This led to the construction of a vertical p-n junction with a broadband photoresponse from the ultraviolet (UV, 200 nm) to the near-infrared (IR, 1100 nm) regions. The high crystallinity of MoTe2/MoS2 heterostructures with a modulation of sulfur and tellurium distribution is corroborated by multiple characterization methods, including Raman spectroscopy, photoluminescence (PL) spectroscopy and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Furthermore, the photoelectrical measurements exhibit a tremendous photoresponsivity with an external quantum efficiency (EQE) as high as 4.71 A/W and 532% at 1100 nm, while as 4.67 A/W and 1935% at 300 nm, one to two orders of magnitude higher than other exfoliated MoTe2 heterostructure devices have been reported so far. This synthetic method is a controllable stacking mode confined synthesis approach for 2D heterostructures, and paves the way for the fabrication of high-performance functional telluride-based broadband photodetectors.
- Published
- 2018
79. Layer-Dependent Chemically Induced Phase Transition of Two-Dimensional MoS2
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Xingxu Yan, Lina Liu, Zhixing Lu, Liying Jiao, Peng Wang, Jingying Zheng, Hongde Yu, Zhiguo Wang, Shang-Peng Gao, Lifei Sun, Xiaoqing Pan, and Dong Wang
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Phase transition ,Materials science ,Mechanical Engineering ,Bioengineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Transition metal ,Electron injection ,Chemical physics ,Scaling effect ,Monolayer ,Density of states ,General Materials Science ,0210 nano-technology ,Molybdenum disulfide ,Layer (electronics) - Abstract
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with layered structures provide a unique platform for exploring the effect of number of layers on their fundamental properties. However, the thickness scaling effect on the chemical properties of these materials remains unexplored. Here, we explored the chemically induced phase transition of 2D molybdenum disulfide (MoS2) from both experimental and theoretical aspects and observed that the critical electron injection concentration and the duration required for the phase transition of 2D MoS2 increased with decreasing number of layers. We further revealed that the observed dependence originated from the layer-dependent density of states of 2H-MoS2, which results in decreasing phase stability for 2H-MoS2 with increasing number of layers upon electron doping. Also, the much larger energy barrier for the phase transition of monolayer MoS2 induces the longer reaction time required for monolayer MoS2 as compared to multilayer MoS2. The layer-dependen...
- Published
- 2018
80. PdCo bimetallic nano-electrocatalyst as effective air-cathode for aqueous metal-air batteries
- Author
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Wenbo Du, Changwei Ji, Xingxu Yan, Chenchen Zhao, Yuhong Jin, Ling Sun, Du Xian, and Guoqing Wang
- Subjects
Battery (electricity) ,Materials science ,Renewable Energy, Sustainability and the Environment ,Oxygen evolution ,Energy Engineering and Power Technology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Borohydride ,Electrocatalyst ,01 natural sciences ,Cathode ,Nanomaterial-based catalyst ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Fuel Technology ,chemistry ,Chemical engineering ,law ,0210 nano-technology ,Bimetallic strip ,Power density - Abstract
For wide application of metal-air batteries, the key factor is the development of catalysts for air cathodes. In the present study, PdCo/C bimetallic nanocatalysts are prepared by a facile borohydride reduction method. To improve the activity and stability, the catalysts are heat-treated at 200 °C in H2/Ar atmosphere from 4 h to 24 h. The optimal heat-treatment time is found to be 8 h, at which the highest activity for both oxygen reduction reaction and oxygen evolution reaction is obtained. With the 8 h heat-treated PdCo/C catalyst, the rechargeable zinc-air battery exhibits a high power density of 180 mW cm−2 and retains stability for more than 50 h at a discharge-charge current density of 10 mA cm−2, while the magnesium-air battery obtains a power density of more than 200 mW cm−2 and remains stable within 8 h at a discharge current density of 65 mA cm−2.
- Published
- 2018
81. Gate-Induced Interfacial Superconductivity in 1T-SnSe2
- Author
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Hongtao Yuan, Yu Wang, Yi Cui, Zhuoyu Chen, Harold Y. Hwang, Junwen Zeng, Songhua Cai, Chenyu Wang, Shi-Jun Liang, Xiaowei Liu, Chen Pan, Peng Wang, Feng Miao, Xingxu Yan, Miao Wang, Yajun Fu, Erfu Liu, Kang Xu, and Yaojia Wang
- Subjects
Materials science ,Chalcogenide ,FOS: Physical sciences ,Bioengineering ,02 engineering and technology ,Nitride ,01 natural sciences ,law.invention ,Superconductivity (cond-mat.supr-con) ,Metal ,chemistry.chemical_compound ,Transition metal ,law ,Condensed Matter::Superconductivity ,0103 physical sciences ,General Materials Science ,010306 general physics ,Superconductivity ,Condensed matter physics ,Condensed Matter - Superconductivity ,Mechanical Engineering ,Transistor ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,chemistry ,Pairing ,visual_art ,visual_art.visual_art_medium ,Ising model ,0210 nano-technology - Abstract
Layered metal chalcogenide materials provide a versatile platform to investigate emergent phenomena and two-dimensional (2D) superconductivity at/near the atomically thin limit. In particular, gate-induced interfacial superconductivity realized by the use of an electric-double-layer transistor (EDLT) has greatly extended the capability to electrically induce superconductivity in oxides, nitrides and transition metal chalcogenides and enable one to explore new physics, such as the Ising pairing mechanism. Exploiting gate-induced superconductivity in various materials can provide us with additional platforms to understand emergent interfacial superconductivity. Here, we report the discovery of gate-induced 2D superconductivity in layered 1T-SnSe2, a typical member of the main-group metal dichalcogenide (MDC) family, using an EDLT gating geometry. A superconducting transition temperature Tc around 3.9 K was demonstrated at the EDL interface. The 2D nature of the superconductivity therein was further confirmed based on 1) a 2D Tinkham description of the angle-dependent upper critical field, 2) the existence of a quantum creep state as well as a large ratio of the coherence length to the thickness of superconductivity. Interestingly, the in-plane approaching zero temperature was found to be 2-3 times higher than the Pauli limit, which might be related to an electric field-modulated spin-orbit interaction. Such results provide a new perspective to expand the material matrix available for gate-induced 2D superconductivity and the fundamental understanding of interfacial superconductivity., Comment: 18 pages, 4 figures, accepted by Nano Letters
- Published
- 2018
82. Intercorrelated In-Plane and Out-of-Plane Ferroelectricity in Ultrathin Two-Dimensional Layered Semiconductor In2Se3
- Author
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Husam N. Alshareef, Xingxu Yan, Xixiang Zhang, Tom Wu, Linze Li, Wenpei Gao, Wenguang Zhu, Peng Li, Weijin Hu, Yingchun Cheng, Xiaoqing Pan, Zhe Wang, Lain-Jong Li, Chaojie Cui, Yao Wang, and Christopher Addiego
- Subjects
Materials science ,business.industry ,Band gap ,Mechanical Engineering ,Bioengineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Polarization (waves) ,01 natural sciences ,Ferroelectricity ,0104 chemical sciences ,Non-volatile memory ,symbols.namesake ,Semiconductor ,Electric field ,symbols ,Optoelectronics ,General Materials Science ,van der Waals force ,0210 nano-technology ,business ,Diode - Abstract
Enriching the functionality of ferroelectric materials with visible-light sensitivity and multiaxial switching capability would open up new opportunities for their applications in advanced information storage with diverse signal manipulation functions. We report experimental observations of robust intralayer ferroelectricity in two-dimensional (2D) van der Waals layered α-In2Se3 ultrathin flakes at room temperature. Distinct from other 2D and conventional ferroelectrics, In2Se3 exhibits intrinsically intercorrelated out-of-plane and in-plane polarization, where the reversal of the out-of-plane polarization by a vertical electric field also induces the rotation of the in-plane polarization. On the basis of the in-plane switchable diode effect and the narrow bandgap (∼1.3 eV) of ferroelectric In2Se3, a prototypical nonvolatile memory device, which can be manipulated both by electric field and visible light illumination, is demonstrated for advancing data storage technologies.
- Published
- 2018
83. Discovery of a magnetic conductive interface in PbZr0.2Ti0.8O3 /SrTiO3 heterostructures
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Alexander Stern, Xingxu Yan, Jeongwoo Kim, Qiyin Lin, Xiaoqing Pan, Hui Wang, Yichun Zhou, Gejian Zhao, Lin Xie, Tingyong Chen, Chaitanya Gadre, Ruqian Wu, Henry Liu, Ctirad Uher, Linze Li, Kui Zhang, Jing Xia, Yi Zhang, Ying-Hao Chu, and Hang Chi
- Subjects
Materials science ,Science ,General Physics and Astronomy ,Insulator (electricity) ,02 engineering and technology ,7. Clean energy ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Condensed Matter::Materials Science ,0103 physical sciences ,Multiferroics ,010306 general physics ,lcsh:Science ,Multidisciplinary ,Spintronics ,business.industry ,Heterojunction ,General Chemistry ,021001 nanoscience & nanotechnology ,Polarization (waves) ,Ferroelectricity ,3. Good health ,Band bending ,Optoelectronics ,lcsh:Q ,0210 nano-technology ,business ,Fermi gas - Abstract
Emergent physical properties often arise at interfaces of complex oxide heterostructures due to the interplay between various degrees of freedom, especially those with polar discontinuities. It is desirable to explore if these structures may generate pure and controllable spin currents, which are needed to attain unmatched performance and energy efficiency in the next-generation spintronic devices. Here we report the emergence of a spin-polarized two-dimensional electron gas (SP-2DEG) at the interface of two insulators, SrTiO3 and PbZr0.2Ti0.8O3. This SP-2DEG is strongly localized at the interfacial Ti atoms, due to the interplay between Coulomb interaction and band bending, and can be tuned by the ferroelectric polarization. Our findings open a door for engineering ferroelectric/insulator interfaces to create tunable ferroic orders for magnetoelectric device applications and provide opportunities for designing multiferroic materials in heterostructures.
- Published
- 2018
84. Stone-Wales defect-rich carbon-supported dual-metal single atom sites for Zn-air batteries
- Author
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Cheng-Jun Sun, Khalil Amine, Bilu Liu, Sang-Hoon Bae, Tangchao Liu, Yun Wang, Xiaoqing Pan, Jessica Jein White, Xingxu Yan, Jeehwan Kim, Hui-Ming Cheng, Qiangmin Yu, Kishwar Khan, Zhengtang Luo, and Junxian Liu
- Subjects
Tafel equation ,Materials science ,Renewable Energy, Sustainability and the Environment ,Graphene ,Stone–Wales defect ,Oxygen evolution ,chemistry.chemical_element ,Overpotential ,Catalysis ,law.invention ,Metal ,Crystallography ,chemistry ,law ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,Electrical and Electronic Engineering ,Carbon - Abstract
This work aims to obtain a fundamental understanding of active sites near stone-wales (SW) defects rich nitrogen-doped graphene (DG) with specific coordination of carbon atom rings. It reveals that the SW rich defects (e.g., pentagon (5), pentagon—octagon—pentagon (i.e. 585), or pentagon-heptagon-heptagon-pentagon (5775) rings, appears correspondingly with carbon rings that brought active sites during catalytic reactions. Moreover, we anchored dual isolated metallic atoms (Ni/Fe) on DG support via linkers (O/N) called NiFe-DG. X-ray absorption spectroscopy indicates Ni/Fe metal single atoms are embedded via Fe-N4 and Ni-N4 coordination on DG surfaces. It exhibits high catalytic activity for oxygen reduction reaction (ORR) with an onset potential of 0.97 V, a half-wave potential of 0.86 V, and diffusion current density of 5.7 mA cm− 2, which is at par with commercial Pt/C. The catalyst shows superior stability, retained 82% of the initial current density even after 12 h under an applied potential of 0.86 V. Similarly, the oxygen evolution reaction (OER) overpotential of 358 mV was achieved at 10 mA cm− 2 with a lower Tafel slope value (76 mV/dec) than commercial Pt/C. It maintains 85% stability for 12 h at a constant potential of 1.588 V, shows better stability than commercial Pt/C.
- Published
- 2021
85. Laser‐Irradiated Holey Graphene‐Supported Single‐Atom Catalyst towards Hydrogen Evolution and Oxygen Reduction
- Author
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Zhengtang Luo, Xiaoqing Pan, Delowar Hossain, Jing Yang, Jeehwan Kim, Tangchao Liu, Muhammad Arif, Kishwar Khan, Sheng Zhou, Xingxu Yan, Khalil Amine, Sang-Hoon Bae, Faisal Rehman, and Cheng-Jun Sun
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,Graphene ,Dangling bond ,Atom (order theory) ,Photochemistry ,Laser ,Oxygen reduction ,Catalysis ,law.invention ,law ,General Materials Science ,Hydrogen evolution ,Irradiation - Published
- 2021
86. Revealing Surface Elemental Composition and Dynamic Processes Involved in Facet-Dependent Oxidation of Pt3Co Nanoparticles via in Situ Transmission Electron Microscopy
- Author
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Yusheng Hou, Ruqian Wu, Shu-yi Zhang, Masatoshi Onoue, Wenpei Gao, Xiaoqing Pan, Sheng Dai, Xingxu Yan, and George W. Graham
- Subjects
In situ ,Surface (mathematics) ,Elemental composition ,Materials science ,Mechanical Engineering ,Analytical chemistry ,Nanoparticle ,Bioengineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Atomic units ,0104 chemical sciences ,Catalysis ,In situ transmission electron microscopy ,Chemical engineering ,General Materials Science ,Facet ,0210 nano-technology - Abstract
Since catalytic performance of platinum-metal (Pt-M) nanoparticles is primarily determined by the chemical and structural configurations of the outermost atomic layers, detailed knowledge of the distribution of Pt and M surface atoms is crucial for the design of Pt-M electrocatalysts with optimum activity. Further, an understanding of how the surface composition and structure of electrocatalysts may be controlled by external means is useful for their efficient production. Here, we report our study of surface composition and the dynamics involved in facet-dependent oxidation of equilibrium-shaped Pt3Co nanoparticles in an initially disordered state via in situ transmission electron microscopy and density functional calculations. In brief, using our advanced in situ gas cell technique, evolution of the surface of the Pt3Co nanoparticles was monitored at the atomic scale during their exposure to an oxygen atmosphere at elevated temperature, and it was found that Co segregation and oxidation take place on {111} surfaces but not on {100} surfaces.
- Published
- 2017
87. Two‐Dimensional Semiconductors Grown by Chemical Vapor Transport
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Dake Hu, Guanchen Xu, Lei Xing, Xingxu Yan, Jingyi Wang, Jingying Zheng, Zhixing Lu, Peng Wang, Xiaoqing Pan, and Liying Jiao
- Subjects
02 engineering and technology ,General Medicine ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,0104 chemical sciences - Published
- 2017
88. Anomalous Linear Layer-dependent Blue Shift of Interband Transition in Two-Dimensional Materials
- Author
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Ruqian Wu, Xingxu Yan, Xiaoqing Pan, Feng Xue, Chaitanya Gadre, Peng Wang, and Zhe Wang
- Subjects
Materials science ,Condensed matter physics ,Linear layer ,Instrumentation ,Blueshift - Published
- 2020
89. Directly Probing Local Coordination, Charge State and Stability of Single Atom Catalysts
- Author
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Mingjie Xu, Xingxu Yan, George W. Graham, Sheng Dai, and Xiaoqing Pan
- Subjects
Materials science ,Chemical physics ,Atom (order theory) ,Charge (physics) ,State (functional analysis) ,Instrumentation ,Catalysis - Published
- 2020
90. Probing Local Vibration Modes at Single Planar Defects by Vibrational Spectroscopy
- Author
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Chaitanya Gadre, Niklas Dellby, Toshihiro Aoki, Chengyan Liu, Ondrej L. Krivanek, Lei Gu, Tracy C. Lovejoy, Xingxu Yan, Ruqian Wu, and Xiaoqing Pan
- Subjects
Materials science ,Planar ,Normal mode ,Infrared spectroscopy ,Instrumentation ,Molecular physics - Published
- 2020
91. Nanoscale Phonon Mapping of Single SiGe Quantum Dots by Vibrational EELS
- Author
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Toshihiro Aoki, Lei Gu, Xingxu Yan, Gang Chen, Xiaoqing Pan, Ruqian Wu, Qichen Song, Jie Li, Chaitanya Gadre, and Sheng-Wei Lee
- Subjects
Materials science ,Condensed matter physics ,Quantum dot ,Phonon ,Instrumentation ,Nanoscopic scale - Published
- 2020
92. Controlled Synthesis of Lead-Free and Stable Perovskite Derivative Cs2SnI6 Nanocrystals via a Facile Hot-Injection Process
- Author
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Mian Zhang, Xiaoqing Pan, Wei Shen, Peng Wang, Aifei Wang, Zhengtao Deng, Xingxu Yan, Shibin Sun, and Ming Yang
- Subjects
Materials science ,General Chemical Engineering ,Nanowire ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Flexible electronics ,0104 chemical sciences ,chemistry ,Nanocrystal ,Quantum dot ,Scanning transmission electron microscopy ,Materials Chemistry ,Nanorod ,0210 nano-technology ,Tin ,Perovskite (structure) - Abstract
Colloidal nanocrystals of lead halide perovskites have recently received great attention due to their remarkable performance in optoelectronic applications (e.g., light-emitting devices, flexible electronics, and photodetectors). However, the use of lead remains of great concern due to its toxicity and bioaccumulation in the ecosystem; herein we report a strategy to address this issue by using tetravalent tin (Sn4+) instead of divalent lead (Pb2+) to synthesize stable Cs2SnI6 perovskite nanocrystals. The shapes of as-synthesized Cs2SnI6 nanocrystals are tuned from spherical quantum dots, nanorods, nanowires, and nanobelts to nanoplatelets via a facile hot-injection process using inexpensive and nontoxic commercial precursors. Spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) and simulation studies revealed a well-defined face-centered-cubic (fcc) perovskite derivative structure of Cs2SnI6 nanocrystals. The solution-processed Cs2SnI6 nanocrystal-based field effect...
- Published
- 2016
93. Observation of Strong Polarization Enhancement in Ferroelectric Tunnel Junctions
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Lin Xie, Darrell G. Schlom, Long Qing Chen, Zijian Hong, Linze Li, Carolina Adamo, Toshihiro Aoki, Xiaoxing Cheng, Chaitanya Gadre, Colin Heikes, Mingjie Xu, Xingxu Yan, Thomas Blum, Xiaoqing Pan, Huaixun Huyan, and Yi Zhang
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Oxide ,Bioengineering ,Heterojunction ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Polarization (waves) ,Ferroelectricity ,law.invention ,chemistry.chemical_compound ,chemistry ,Transmission electron microscopy ,law ,Miniaturization ,Optoelectronics ,General Materials Science ,Electron microscope ,0210 nano-technology ,business ,Nanoscopic scale - Abstract
Ferroelectric heterostructures, with capability of storing data at ultrahigh densities, could act as the platform for next-generation memories. The development of new device paradigms has been hampered by the long-standing notion of inevitable ferroelectricity suppression under reduced dimensions. Despite recent experimental observation of stable polarized states in ferroelectric ultrathin films, the out-of-plane polarization components in these films are strongly attenuated compared to thicker films, implying a degradation of device performance in electronic miniaturization processes. Here, in a model system of BiFeO3/La0.7Sr0.3MnO3, we report observation of a dramatic out-of-plane polarization enhancement that occurs with decreasing film thickness. Our electron microscopy analysis coupled with phase-field simulations reveals a polarization-enhancement mechanism that is dominated by the accumulation of oxygen vacancies at interfacial layers. The results shed light on the interplay between polarization and defects in nanoscale ferroelectrics and suggest a route to enhance functionality in oxide devices.
- Published
- 2019
94. Intrinsic Conductance of Domain Walls in BiFeO
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Yi, Zhang, Haidong, Lu, Xingxu, Yan, Xiaoxing, Cheng, Lin, Xie, Toshihiro, Aoki, Linze, Li, Colin, Heikes, Shu Ping, Lau, Darrell G, Schlom, Longqing, Chen, Alexei, Gruverman, and Xiaoqing, Pan
- Abstract
Ferroelectric domain walls exhibit a number of new functionalities that are not present in their host material. One of these functional characteristics is electrical conductivity that may lead to future device applications. Although progress has been made, the intrinsic conductivity of BiFeO
- Published
- 2019
95. Real-space charge-density imaging with sub-ångström resolution by four-dimensional electron microscopy
- Author
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Wenpei, Gao, Christopher, Addiego, Hui, Wang, Xingxu, Yan, Yusheng, Hou, Dianxiang, Ji, Colin, Heikes, Yi, Zhang, Linze, Li, Huaixun, Huyan, Thomas, Blum, Toshihiro, Aoki, Yuefeng, Nie, Darrell G, Schlom, Ruqian, Wu, and Xiaoqing, Pan
- Abstract
The distribution of charge density in materials dictates their chemical bonding, electronic transport, and optical and mechanical properties. Indirectly measuring the charge density of bulk materials is possible through X-ray or electron diffraction techniques by fitting their structure factors
- Published
- 2018
96. Directly Probing the Local Coordination, Charge State, and Stability of Single Atom Catalysts by Advanced Electron Microscopy: A Review
- Author
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Xiaoqing Pan, Xingxu Yan, Peter Tieu, Phillip Christopher, and Mingjie Xu
- Subjects
Materials science ,Electron energy loss spectroscopy ,Resolution (electron density) ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic units ,0104 chemical sciences ,Characterization (materials science) ,Biomaterials ,Transmission electron microscopy ,Molecular vibration ,Atom ,General Materials Science ,0210 nano-technology ,Spectroscopy ,Biotechnology - Abstract
The drive for atom efficient catalysts with carefully controlled properties has motivated the development of single atom catalysts (SACs), aided by a variety of synthetic methods, characterization techniques, and computational modeling. The distinct capabilities of SACs for oxidation, hydrogenation, and electrocatalytic reactions have led to the optimization of activity and selectivity through composition variation. However, characterization methods such as infrared and X-ray spectroscopy are incapable of direct observations at atomic scale. Advances in transmission electron microscopy (TEM) including aberration correction, monochromators, environmental TEM, and micro-electro-mechanical system based in situ holders have improved catalysis study, allowing researchers to peer into regimes previously unavailable, observing critical structural and chemical information at atomic scale. This review presents recent development and applications of TEM techniques to garner information about the location, bonding characteristics, homogeneity, and stability of SACs. Aberration corrected TEM imaging routinely achieves sub-Ångstrom resolution to reveal the atomic structure of materials. TEM spectroscopy provides complementary information about local composition, chemical bonding, electronic properties, and atomic/molecular vibration with superior spatial resolution. In situ/operando TEM directly observe the evolution of SACs under reaction conditions. This review concludes with remarks on the challenges and opportunities for further development of TEM to study SACs.
- Published
- 2021
97. Capturing 3D atomic defects and phonon localization at the 2D heterostructure interface.
- Author
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Xuezeng Tian, Xingxu Yan, Varnavides, Georgios, Yakun Yuan, Kim, Dennis S., Ciccarino, Christopher J., Anikeeva, Polina, Ming-Yang Li, Lain-Jong Li, Narang, Prineha, Xiaoqing Pan, and Jianwei Miao
- Abstract
The article provides information about the utilization of atomic electron tomography to determine the three-dimensional (3D) atomic structures and crystal defects at the interface of a MoS2-WSe2 heterojunction with high precision. This research reveals the existence of point defects, bond distortion, and atomic-scale ripples at the heterointerface and quantifies the 3D strain tensor.
- Published
- 2021
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98. Pyridinic-Nitrogen-Dominated Graphene Aerogels with Fe-N-C Coordination for Highly Efficient Oxygen Reduction Reaction
- Author
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Xingxu Yan, Pulickel M. Ajayan, Zhengjun Zhang, Xiaoyang Cui, Jiugou Leng, Shubin Yang, and Shuang Shuang
- Subjects
Graphene ,Inorganic chemistry ,Doping ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,Thermal treatment ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Nitrogen ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Catalysis ,law.invention ,Biomaterials ,chemistry.chemical_compound ,chemistry ,law ,Electrochemistry ,Methanol ,0210 nano-technology ,Selectivity - Abstract
Here, pyridinic nitrogen dominated graphene aerogels with/without iron incorporation (Fe-NG and NG) are prepared via a facile and effective process including freeze-drying of chemically reduced graphene oxide with/without iron precursor and thermal treatment in NH3. A high doping level of nitrogen has been achieved (up to 12.2 at% for NG and 11.3 at% for Fe-NG) with striking enrichment of pyridinic nitrogen (up to 90.4% of the total nitrogen content for NG, and 82.4% for Fe-NG). It is found that the Fe-NG catalysts display a more positive onset potential, higher current density, and better four-electron selectivity for ORR than their counterpart without iron incorporation. The most active Fe-NG exhibits outstanding ORR catalytic activity, high durability, and methanol tolerance ability that are comparable to or even superior to those of the commercial Pt/C catalyst at the same catalyst loading in alkaline environment. The excellent ORR performance can be ascribed to the synergistic effect of pyridinic N and Fe-N x sites (where iron probably coordinates with pyridinic N) that serve as active centers for ORR. Our Fe-NG can be developed into cost-effective and durable catalysts as viable replacements of the expensive Pt-based catalysts in practical fuel cell applications.
- Published
- 2016
99. Electrocatalysis enhancement of iron-based catalysts induced by synergy of methanol and oxygen-containing groups
- Author
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Li-Min Liu, Shanfu Lu, Jun Luo, Jianguo Liu, Xin Xu, Xingxu Yan, Fang Fang, Dongsheng Song, Zhen-Kun Tang, and Jing Zhu
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,Inorganic chemistry ,chemistry.chemical_element ,Environmental pollution ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,Oxygen ,0104 chemical sciences ,Catalysis ,Direct methanol fuel cell ,chemistry.chemical_compound ,Membrane ,Chemical engineering ,chemistry ,General Materials Science ,Methanol ,Electrical and Electronic Engineering ,0210 nano-technology ,Methanol fuel - Abstract
Direct methanol fuel cells (DMFCs) have been recognized as a promising type of power sources to solve the energy shortage and environmental pollution from fossil energy consumption. However, their commercialization is still hindered by two major problems, the high cost of Pt-based catalysts and the crossover of methanol from anodes to cathodes. In the second problem, the methanol molecules can poison the Pt-based catalysts and lower the cell voltages by reacting with oxygen. Fe-based catalysts containing Fe–N–C active sites are well known as low-cost candidates that are promising to replace the Pt-based. But they cannot prevent the methanol molecules from reacting with oxygen. For the first time, we discovers a new enhancement of the electrocatalysis of Fe–N–C nanofiber catalysts induced by a synergy of methanol and oxygen-containing groups in the catalysts. Its mechanism is revealed by first-principles calculations of density functional theory and then proven experimentally. More significantly, the synergy-induced enhancement (SIE) is further improved experimentally by 40.8 times and reaches 21.60±0.05%. This indicates that the SIE has an enormous upside potential. Moreover, the methanol molecules in the SIE react with not oxygen but epoxy, reducing the harm of the reaction of methanol and oxygen in DMFCs. Further, the SIE has been employed in fuel cells and realized enhancement of current density by 3.0±0.5% in anion-exchange membrane DMFC and by 5.95±0.07% in H2–O2 anion exchange membrane fuel cell (AEMFC). Therefore, the new SIE can simultaneously solve both of the two problems and thus facilitate the DMFC commercialization for easing the crises of energy and pollution.
- Published
- 2016
100. Atomically engineering activation sites onto metallic 1T-MoS
- Author
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Yongge Wei, Xin He, Jun Hu, Yuanhui Sun, Sabrina Younan, Jier Huang, Xueli Zheng, Jingxuan Ge, Xingxu Yan, Brian Pattengale, Toshihiro Aoki, Xiaoqing Pan, Lijun Zhang, Jing Gu, Yi-Chao Huang, Ning Pu, Nicholas Williams, and Wei Bian
- Subjects
0301 basic medicine ,inorganic chemicals ,Materials science ,Catalyst synthesis ,Science ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,Overpotential ,Electrochemistry ,Electrocatalyst ,Two-dimensional materials ,7. Clean energy ,General Biochemistry, Genetics and Molecular Biology ,Article ,Catalysis ,03 medical and health sciences ,lcsh:Science ,Hydrogen production ,Multidisciplinary ,General Chemistry ,021001 nanoscience & nanotechnology ,Publisher Correction ,Nickel ,Hydrogen fuel ,030104 developmental biology ,chemistry ,Chemical engineering ,Polyoxometalate ,lcsh:Q ,0210 nano-technology ,Platinum ,Electrocatalysis - Abstract
Engineering catalytic sites at the atomic level provides an opportunity to understand the catalyst’s active sites, which is vital to the development of improved catalysts. Here we show a reliable and tunable polyoxometalate template-based synthetic strategy to atomically engineer metal doping sites onto metallic 1T-MoS2, using Anderson-type polyoxometalates as precursors. Benefiting from engineering nickel and oxygen atoms, the optimized electrocatalyst shows great enhancement in the hydrogen evolution reaction with a positive onset potential of ~ 0 V and a low overpotential of −46 mV in alkaline electrolyte, comparable to platinum-based catalysts. First-principles calculations reveal co-doping nickel and oxygen into 1T-MoS2 assists the process of water dissociation and hydrogen generation from their intermediate states. This research will expand on the ability to improve the activities of various catalysts by precisely engineering atomic activation sites to achieve significant electronic modulations and improve atomic utilization efficiencies., While heterogeneous catalysts can act as tangible, efficient materials for energy conversion, understanding the active catalytic sites is challenging. Here, authors engineer specific catalytic sites into molybdenum sulfide to improve and elucidate hydrogen evolution electrocatalysis.
- Published
- 2018
Catalog
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