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1,067 results on '"Chi, Miaofang"'

202. In situ Electric Field Manipulation of Ferroelectric Vortices

Author

Nelson, Christopher T., primary, Hong, Zijian, additional, Zhang, Cheng, additional, Yadav, Ajay K., additional, Das, Sujit, additional, Hsu, Shang-Lin, additional, Chi, Miaofang, additional, Rack, Philip D, additional, Chen, Long-Qing, additional, Martin, Lane W., additional, and Ramesh, Ramamoorthy, additional

Published
2019
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214. Understanding the Low-Voltage Hysteresis of Anionic Redox in Na2Mn3O7

Author

Song, Bohang, primary, Tang, Mingxue, additional, Hu, Enyuan, additional, Borkiewicz, Olaf J., additional, Wiaderek, Kamila M., additional, Zhang, Yiman, additional, Phillip, Nathan D., additional, Liu, Xiaoming, additional, Shadike, Zulipiya, additional, Li, Cheng, additional, Song, Likai, additional, Hu, Yan-Yan, additional, Chi, Miaofang, additional, Veith, Gabriel M., additional, Yang, Xiao-Qing, additional, Liu, Jue, additional, Nanda, Jagjit, additional, Page, Katharine, additional, and Huq, Ashfia, additional

Published
2019
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228. Elucidating the mobility of H+and Li+ions in (Li6.25−xHxAl0.25)La3Zr2O12viacorrelative neutron and electron spectroscopy

Author

Liu, Xiaoming, primary, Chen, Yan, additional, Hood, Zachary D., additional, Ma, Cheng, additional, Yu, Seungho, additional, Sharafi, Asma, additional, Wang, Hui, additional, An, Ke, additional, Sakamoto, Jeff, additional, Siegel, Donald J., additional, Cheng, Yongqiang, additional, Jalarvo, Niina H., additional, and Chi, Miaofang, additional

Published
2019
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229. Hard-Magnet L10-CoPt Nanoparticles Advance Fuel Cell Catalysis

Author

Li, Junrui, primary, Sharma, Shubham, additional, Liu, Xiaoming, additional, Pan, Yung-Tin, additional, Spendelow, Jacob S., additional, Chi, Miaofang, additional, Jia, Yukai, additional, Zhang, Peng, additional, Cullen, David A., additional, Xi, Zheng, additional, Lin, Honghong, additional, Yin, Zhouyang, additional, Shen, Bo, additional, Muzzio, Michelle, additional, Yu, Chao, additional, Kim, Yu Seung, additional, Peterson, Andrew A., additional, More, Karren L., additional, Zhu, Huiyuan, additional, and Sun, Shouheng, additional

Published
2019
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230. In situ TEM observation of the electrochemical lithiation of N-doped anatase TiO2 nanotubes as anodes for lithium-ion batteries

Author

Zhang, Minghao, Yin, Kuibo, Hood, Zachary D, Bi, Zhonghe, Bridges, Craig A, Dai, Sheng, Meng, Ying Shirley, Paranthaman, Mariappan Parans, and Chi, Miaofang

Subjects
technology, industry, and agriculture, human activities, Macromolecular and Materials Chemistry
Abstract

The effects of N-doping and the lithiation mechanism of TiO2 nanotubes were elucidated by integrated in situ microscopy and electrochemical measurements.

Published
2017

235. A Simple Route to the Synthesis of Pt Nanobars and the Mechanistic Understanding of Symmetry Reduction.

Author

Chen, Ruhui, Nguyen, Quynh N., Zhao, Ming, Chen, Zitao, Chi, Miaofang, and Xia, Younan

Subjects
SYMMETRY, PYRROLIDINONES, NANOCRYSTALS, ETCHING, SYMMETRY breaking
Abstract

Noble‐metal nanocrystals with anisotropic shapes have received increasing interest owing to their unique properties. Here, a facile route to the preparation of Pt nanobars with aspect ratios tunable up to 2.1 was reported by simply reducing a PtIV precursor in N,N‐dimethylformamide (DMF) at 160 °C in the presence of poly(vinyl pyrrolidone) (PVP). In addition to its commonly observed roles as a solvent and a reductant, DMF could also decompose to generate CO, a capping agent capable of selectively passivating Pt{100} facets to promote the formation of nanobars. The size and aspect ratio of the nanobars could be tuned by varying the amount of PtIV precursor involved in the synthesis, as well as the concentration of PVP because of its dual roles as a stabilizer and a co‐reductant. Our mechanistic study indicated that the anisotropic growth resulted from both particle coalescence and localized oxidative etching followed by preferential growth. [ABSTRACT FROM AUTHOR]

Published
2021
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236. Essential effect of the electrolyte on the mechanical and chemical degradation of LiNi0.8Co0.15Al0.05O2 cathodes upon long-term cycling.

Author

Liu, Xiaoming, Zhan, Xiaowen, Hood, Zachary D., Li, Wangda, Leonard, Donovan N., Manthiram, Arumugam, and Chi, Miaofang

Abstract

Capacity fading during long-term cycling (>1500×) is still a critical challenge for Li-ion batteries that use Ni-rich layered oxides, e.g. LiNi0.8Co0.15Al0.05O2 (NCA), as the cathode. Microcracks have been previously recognized as one of the primary reasons for the observed capacity fade. Although there exists a generally developed mechanical understanding of microcracks, the role of the electrolyte has not been clearly understood, especially after extended cycling and at the atomic scale. Here, we unveil the microstructural evolution of spherical NCA secondary particles after long-term cycling using scanning transmission electron microscopy accompanied with electron energy loss spectroscopy. We found that the microcracks initiated and grew through grain boundaries, which then serve as the pathway for electrolyte penetration into secondary NCA particles. Additionally, the rock-salt phase reconstruction is prone to occur at the (003) surfaces of the primary particles or the crack surfaces, largely due to electrolyte (LiPF6 EC/EMC) corrosion. Crack propagation within the NCA grains is primarily a joint consequence from electrolyte corrosion and mechanical strain during lithiation/delithiation. During extended cycling, due to the distinctive surface facets, the primary grains located in the center of the secondary particles experience more intensive electrolyte corrosion, leading to a reduced contact with nearby particles, impairing the overall capacity. These results establish the initiation and growth mechanism of microcracks and voids in NCA-based cathodes during cycling and point out the role of the electrolyte in affecting the degradation of NCA-based cathodes. [ABSTRACT FROM AUTHOR]

Published
2021
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237. Controlling the Surface Oxidation of Cu Nanowires Improves Their Catalytic Selectivity and Stability toward C2+ Products in CO2 Reduction.

Author

Lyu, Zhiheng, Zhu, Shangqian, Xie, Minghao, Zhang, Yu, Chen, Zitao, Chen, Ruhui, Tian, Mengkun, Chi, Miaofang, Shao, Minhua, and Xia, Younan

Subjects
ELECTROLYTIC reduction, NANOWIRES, OXIDATION, CATALYST selectivity, SURFACE roughness, CARBON dioxide
Abstract

Copper nanostructures are promising catalysts for the electrochemical reduction of CO2 because of their unique ability to produce a large proportion of multi‐carbon products. Despite great progress, the selectivity and stability of such catalysts still need to be substantially improved. Here, we demonstrate that controlling the surface oxidation of Cu nanowires (CuNWs) can greatly improve their C2+ selectivity and stability. Specifically, we achieve a faradaic efficiency as high as 57.7 and 52.0 % for ethylene when the CuNWs are oxidized by the O2 from air and aqueous H2O2, respectively, and both of them show hydrogen selectivity below 12 %. The high yields of C2+ products can be mainly attributed to the increase in surface roughness and the generation of defects and cavities during the electrochemical reduction of the oxide layer. Our results also indicate that the formation of a relatively thick, smooth oxide sheath can improve the catalytic stability by mitigating the fragmentation issue. [ABSTRACT FROM AUTHOR]

Published
2021
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240. Visualizing magnetic fields at the atomic scale

Author

Venkatraman, Kartik, Hachtel, Jordan A., and Chi, Miaofang

Abstract

In the recent work of Kohno et al., magnetic spin orientation changes were measured at the atomic scale for the first time via the differential phase contrast technique in scanning transmission electron microscopy using a novel magnetic-field-free objective lens system.

Published
2022
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242. Facile Synthesis of Ag@PdnL Icosahedral Nanocrystals as a Class of Cost‐Effective Electrocatalysts toward Formic Acid Oxidation.

Author

Wang, Wenxia, Chen, Zitao, Shi, Yifeng, Lyu, Zhiheng, Cao, Zhenming, Cheng, Haoyan, Chi, Miaofang, Xiao, Kaijun, and Xia, Younan

Subjects
FORMIC acid, OXIDATION of formic acid, NANOCRYSTALS, ELECTROCATALYSTS, BASE catalysts, CATALYSTS
Abstract

We report a facile synthesis of Ag@Pd core−shell icosahedral nanocrystals for the development of cost‐effective electrocatalysts toward formic acid oxidation. With 12.4 nm Ag icosahedra serving as seeds, Pd shells of controlled thicknesses in the range of 3.6–5.8 atomic layers are grown by adjusting the experimental parameters. When examined as catalysts toward formic acid oxidation, all the Ag@Pd nanocrystals exhibit enhanced mass activities relative to a commercial Pd/C catalyst, with the Ag@Pd4.2L nanocrystals showing enhanced mass activity that is almost twice that of a commercial Pd/C. The chronoamperometry measurements indicate that all the Ag@Pd/C catalysts are more robust than the Pd/C, with the catalyst based on Ag@Pd4.2L nanocrystals showing a mass activity greater than that of the pristine Pd/C after holding in a mixture of HCOOH and HClO4 at 0.75 V for 1,000 s. We believe that the strategy demonstrated here can also be extended to the development of other types of advanced electrocatalysts. [ABSTRACT FROM AUTHOR]

Published
2020
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243. Self-Assembled Framework Formed During Lithiation of SnS2 Nanoplates Revealed by in Situ Electron Microscopy

Author

Yin, Kuibo, Zhang, Minghao, Hood, Zachary D, Pan, Jie, Meng, Ying Shirley, and Chi, Miaofang

Subjects
Chemical Sciences, General Chemistry
Abstract

Lithium-ion batteries (LIBs) commercially dominate portable energy storage and have been extended to hybrid/electric vehicles by utilizing electrode materials with enhanced energy density. However, the energy density and cycling life of LIBs must extend beyond the current reach of commercial electrodes to meet the performance requirements for transportation applications. Carbon-based anodes, serving as the main negative electrodes in LIBs, have an intrinsic capacity limitation due to the intercalation mechanism. Some nanostructured carbon materials offer very interesting reversible capacities and can be considered as future anode materials. However, their fabrication processes are often complicated and expensive. Theoretically, using a lithium metal anode is the best way of delivering high energy density due to its largest theoretical capacity of more than 3800 mAh g-1; however, lithium metal is highly reactive with liquid electrolytes. Alternative anodes are being explored, including other lithium-reactive metals, such as Si, Ge, Zn, V, and so forth. These metals react reversibly with a large amount of Li per formula unit to form lithium-metal alloys, rendering these materials promising candidates for next-generation LIBs with high energy density. Though, most of these pure metallic anodes experience large volume changes during lithiation and delithiation processes that often results in cracking of the anode material and a loss electrical contact between the particles. Nanosized metal sulfides were recently found to possess better cycling stability and larger reversible capacities over pure metals. Further improvements and developments of metal sulfide-based anodes rely on a fundamental understanding of their electrochemical cycling mechanisms. Not only must the specific electrochemical reactions be correctly identified, but also the microstructural evolution upon electrochemical cycling, which often dictates the cyclability and stability of nanomaterials in batteries, must be clearly understood. Probing these dynamic evolution processes, i.e. the lithiation reactions and morphology evolutions, are often challenging. It requires both high-resolution chemical analysis and microstructural identification. In situ transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) has recently been raised as one of the most powerful techniques for monitoring electrochemical processes in anode materials for LIBs. In this work, we focus on elucidating the origin of the structural stability of SnS2 during electrochemical cycling by revealing the microstructural evolution of SnS2 upon lithiation using in situ TEM. Crystalline SnS2 was observed to undergo a two-step reaction after the initial lithium intercalation: (1) irreversible formation of metallic tin and amorphous lithium sulfide and (2) reversible transformation of metallic tin to Li-Sn alloys, which is determined to be the rate-determining step. More interestingly, it was discovered that a self-assembled composite framework formed during the irreversible conversion reaction, which has not been previously reported. Crystalline Sn nanoparticles are well arranged within an amorphous Li2S "matrix" in this self-assembled framework. This nanoscale framework confines the locations of individual Sn nanoparticles and prevents particle agglomeration during the subsequent cycling processes, therefore providing desired structural tolerance and warranting a sufficientelectron pathway. Our results not only explain the outstanding cycling stability of SnS2 over metallic tin anodes, but also provide important mechanistic insights into the design of high-performance electrodes for next-generation LIBs through the integration of a unique nanoframework.

Published
2017

244. In situ TEM observation of the electrochemical lithiation of N-doped anatase TiO 2 nanotubes as anodes for lithium-ion batteries

Author

Zhang, Minghao, Yin, Kuibo, Hood, Zachary D, Bi, Zhonghe, Bridges, Craig A, Dai, Sheng, Meng, Ying Shirley, Paranthaman, Mariappan Parans, and Chi, Miaofang

Subjects
Affordable and Clean Energy, Materials Engineering, Interdisciplinary Engineering, Macromolecular and Materials Chemistry
Abstract

The effects of N-doping and the lithiation mechanism of TiO2 nanotubes were elucidated by integrated in situ microscopy and electrochemical measurements.

Published
2017

245. Reciprocal Salt Flux Growth of LiFePO4Single Crystals with Controlled Defect Concentrations

Author

Janssen, Yuri, Santhanagopalan, Dhamodaran, Qian, Danna, Chi, Miaofang, Wang, Xiaoping, Hoffmann, Christina, Meng, Ying Shirley, and Khalifah, Peter G.

Abstract

Improved methods for the flux growth of single crystals of the important battery material LiFePO4have been developed, allowing the facile preparation of single crystals up to 1 cm across with well-developed facets at relatively low temperatures. The structural characterization of these samples by both powder X-ray diffraction and single crystal diffraction (X-ray and neutron) indicates that the samples are typically stoichiometric with a very low concentration of Fe defects on the Li site, though crystals with larger concentrations of defects can be specifically grown using Fe-rich fluxes. These defects occur through the formation of a Fe-rich (Li1–2xFex)FePO4partial solid solution, in contrast to the antisite defects more commonly discussed in the literature which would preserve the ideal LiFePO4stoichiometry. The LiFePO4defects are shown to be sarcopside-like (2 Li+→ Fe2++ vacancy) based on compositions refined from single crystal diffraction data, the observed dependence of unit cell parameters on defect concentration, and their observed phase behavior (defects only appear in growths from fluxes which are Fe-rich relative to stoichiometric LiFePO4). The distribution of defects has been studied by aberration corrected scanning transmission electron microscopy and was found to be highly inhomogenous, suggesting that defect-containing crystals may consist of endotaxial intergrowths of olivine LiFePO4and sarcopside Fe3(PO4)2in a manner that minimizes the detrimental influence of FeLidefects on the rate of Li-ion transport within crystallites.

Published
2024
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246. Tailoring Local Chemical Ordering via Elemental Tuning in High-Entropy Alloys

Author

Huang, Zhennan, Li, Tangyuan, Li, Boyang, Dong, Qi, Smith, Jacob, Li, Shuke, Xu, Lin, Wang, Guofeng, Chi, Miaofang, and Hu, Liangbing

Abstract

Due to the large multi-elemental space desired for property screening and optimization, high-entropy alloys (HEAs) hold greater potential over conventional alloys for a range of applications, such as structural materials, energy conversion, and catalysis. However, the relationship between the HEA composition and its local structural/elemental configuration is not well understood, particularly in noble-metal-based HEA nanomaterials, hindering the design and development of nano-HEAs in energy conversion and catalysis applications. Herein, we determined precise atomic-level structural and elemental arrangements in model HEAs composed of RhPtPdFeCo and RuPtPdFeCo to unveil their local characteristics. Notably, by changing just one constituent element in the HEA (Rh to Ru), we found dramatic changes in the elemental arrangement from complete random mixing to a local single elemental ordering feature. Additionally, we demonstrate that the local ordering in RuPtPdFeCo can be further controlled by varying the Ru concentration, allowing us to toggle between local Ru clustering and distinct heterostructures in multicomponent systems. Overall, our study presents a practical approach for manipulating local atomic structures and elemental arrangements in noble-metal-based HEA systems, which could provide in-depth knowledge to mechanistically understand the functionality of noble-metal-based HEA nanomaterials in practical applications.

Published
2024
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248. Emerging Electron Microscopy Techniques for Probing Functional Interfaces in Energy Materials.

Author

Zachman, Michael J., Hachtel, Jordan A., Idrobo, Juan Carlos, and Chi, Miaofang

Subjects
ELECTRON microscope techniques, ELECTRON energy loss spectroscopy, SCANNING transmission electron microscopy, ELECTRON microscopy, ELECTRON spectroscopy
Abstract

Interfaces play a fundamental role in many areas of chemistry. However, their localized nature requires characterization techniques with high spatial resolution in order to fully understand their structure and properties. State‐of‐the‐art atomic resolution or in situ scanning transmission electron microscopy and electron energy‐loss spectroscopy are indispensable tools for characterizing the local structure and chemistry of materials with single‐atom resolution, but they are not able to measure many properties that dictate function, such as vibrational modes or charge transfer, and are limited to room‐temperature samples containing no liquids. Here, we outline emerging electron microscopy techniques that are allowing these limitations to be overcome and highlight several recent studies that were enabled by these techniques. We then provide a vision for how these techniques can be paired with each other and with in situ methods to deliver new insights into the static and dynamic behavior of functional interfaces. [ABSTRACT FROM AUTHOR]

Published
2020
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