ORCID Profile
0000-0002-0252-7530
Current Organisation
Korea Astronomy and Space Science Institute
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Publisher: Elsevier BV
Date: 12-2015
Publisher: Wiley
Date: 08-2018
Publisher: American Astronomical Society
Date: 04-2020
Abstract: We present the results from the 43 GHz Very Long Baseline Array (VLBA) observations of 124 compact radio-loud active galactic nuclei (AGNs) that were conducted between 2014 November and 2016 May. The typical dimensions of the restoring beam in each image are about 0.5 mas × 0.2 mas. The highest resolution of 0.2 mas corresponds to a physical size of 0.02 pc for the lowest redshift source in the s le. The 43 GHz very long baseline interferometry (VLBI) images of 97 AGNs are presented for the first time. We study the source compactness on milliarcsecond and submilliarcsecond scales, and suggest that 95 sources in our s le are suitable for future space VLBI observations. By analyzing our data supplemented with other VLBA AGN surveys from the literature, we find that the core brightness temperature increases with increasing frequency below a break frequency ∼7 GHz, and decreases between ∼7 and 240 GHz but increases again above 240 GHz in the rest frame of the sources. This indicates that the synchrotron opacity changes from optically thick to thin. We also find a strong statistical correlation between radio and γ -ray flux densities. Our correlation is tighter than those in the literature derived from lower-frequency VLBI data, suggesting that the γ -ray emission is produced more cospatially with the 43 GHz VLBA core emission. This correlation can also be extrapolated to the unbeamed AGN population, implying that a universal γ -ray production mechanism might be at work for all types of AGNs.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5TA04424C
Abstract: Hollow spherical particles illustrate low specific surface area (0.4648 m 2 g −1 ) and short diffusion path (about 1.5 μm) at the same time, which enhanced their performance during the electrode process.
Publisher: Elsevier BV
Date: 08-2017
Publisher: Elsevier BV
Date: 02-2020
Publisher: Springer Science and Business Media LLC
Date: 27-02-2019
DOI: 10.1007/S40820-019-0249-1
Abstract: Extensive efforts have been devoted to the design of micro-, nano-, and/or molecular structures of sulfur hosts to address the challenges of lithium–sulfur (Li–S) batteries, yet comparatively little research has been carried out on the binders in Li–S batteries. Herein, we systematically review the polymer composite frameworks that confine the sulfur within the sulfur electrode, taking the roles of sulfur hosts and functions of binders into consideration. In particular, we investigate the binding mechanism between the binder and sulfur host (such as mechanical interlocking and interfacial interactions), the chemical interactions between the polymer binder and sulfur (such as covalent bonding, electrostatic bonding, etc.), as well as the beneficial functions that polymer binders can impart on Li–S cathodes, such as conductive binders, electrolyte intake, adhesion strength etc. This work could provide a more comprehensive strategy in designing sulfur electrodes for long-life, large-capacity and high-rate Li–S battery.
Publisher: American Chemical Society (ACS)
Date: 22-08-2018
DOI: 10.1021/ACS.CHEMREV.8B00241
Abstract: Tremendous efforts have been devoted to the development of electrode materials, electrolytes, and separators of energy-storage devices to address the fundamental needs of emerging technologies such as electric vehicles, artificial intelligence, and virtual reality. However, binders, as an important component of energy-storage devices, are yet to receive similar attention. Polyvinylidene fluoride (PVDF) has been the dominant binder in the battery industry for decades despite several well-recognized drawbacks, i.e., limited binding strength due to the lack of chemical bonds with electroactive materials, insufficient mechanical properties, and low electronic and lithium-ion conductivities. The limited binding function cannot meet inherent demands of emerging electrode materials with high capacities such as silicon anodes and sulfur cathodes. To address these concerns, in this review we ide the binding between active materials and binders into two major mechanisms: mechanical interlocking and interfacial binding forces. We review existing and emerging binders, binding technology used in energy-storage devices (including lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and supercapacitors), and state-of-the-art mechanical characterization and computational methods for binder research. Finally, we propose prospective next-generation binders for energy-storage devices from the molecular level to the macro level. Functional binders will play crucial roles in future high-performance energy-storage devices.
Publisher: Wiley
Date: 15-04-2020
Publisher: Elsevier BV
Date: 10-2017
Publisher: American Astronomical Society
Date: 19-01-2018
Publisher: American Chemical Society (ACS)
Date: 22-07-2022
DOI: 10.1021/ACS.ACCOUNTS.2C00259
Abstract: ConspectusSilicon-based anode materials have become a research hot spot as the most promising candidates for next-generation high-capacity lithium-ion batteries. However, the irreversible degradation of the conductive network in the anode and the resultant dramatic capacity loss have become two ultimate challenges that stem from inherent characteristics of the Si-based materials, including poor conductivity and massive volume changes (up to 300%) during cycling. Apart from optimization of the active materials, one effective way to stabilize high-capacity Si-based anodes is by designing polymeric binders to reinforce the conductive networks during repeated charge and discharge processes. As an inactive component in the electrode, the binder not only holds other components (e.g., active materials, conductive agents, and current collectors) together to maintain the mechanical integrity of the electrode but also serves as a thickener to facilitate the homogeneous distribution of particles. Therefore, binders play a key role in Si-based anodes by maintaining the integrity of conductive networks in the electrode.In this Account, on the basis of the extensive binder-related work on Si-based anodes since the 2000s, efforts made on maintaining the conductive network can be categorized into two main strategies: (1) stabilization of the primary conductive network (which generally refers to conductive agents) by enhancing the binding strength and resilience of the binding between electrode components (i.e., Si particles, conducting agents, and current collectors) via various interactions (e.g., dipolar interactions and covalent bonds) and (2) construction of the secondary conductive network by employing conductive binders, which serve as a molecular-level conductive layer on active materials. In this sense, functional groups in binders can be ided into two categories: mechanical structural units and conductive structural units. On the one hand, functional groups with strong polarities (e.g., -OH, -COOH, -NH
Publisher: Elsevier BV
Date: 12-2015
Publisher: American Chemical Society (ACS)
Date: 20-03-2020
Publisher: Wiley
Date: 14-05-2023
Abstract: Lithium–sulfur batteries (LSBs) currently suffer from severe polysulfide shuttling, slow redox kinetics at the sulfur cathode, and irreversible dendrite growth at the lithium anode. To address these issues, a dual interfacial engineering strategy on both the cathode and anode is proposed. For the cathode, iminated polyaniline (iPANI) is used to achieve energetic engineering to induce mid‐energy level to the adsorption of polysulfides, and catalyze the redox conversion of sulfur species, and realize morphological engineering via self‐assembly of iPANI onto a scaffold integrated by reduced graphene oxide (rGO) and carbon nanotubes (CNTs), namely iPANI@rGO‐CNTs. For the anode, the highly conductive and lithiophilic nature and porous nanostructure of the iPANI@rGO‐CNTs composite facilitates the uniform deposition of lithium‐ions, significantly preventing the growth of lithium dendrites. Density functional theory calculations suggest that the iminated functional group at the excited state in iPANI can significantly suppress the shuttling effect, catalyze the conversion of sulfur species, and enhance the conversion of the sulfur species on the sulfur cathode. With the synergic effects of the iPANI@rGO‐CNTs nanoreactors, the as‐prepared LSBs deliver an excellent rate capability and outstanding cycling life. This large‐scale production and application of the iPANI@rGO‐CNTs nanocomposite may lead to the eventual commercialization of LSBs.
Publisher: Wiley
Date: 31-01-2023
DOI: 10.1002/CEY2.295
Abstract: One of the most unique properties of two‐dimensional carbides and nitrides of transition metals (MXenes) is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial‐scale application is limited by their costly chemical synthesis methods. In this work, the niche feature of MXenes was capitalized in the packed‐bed electrochemical reactor to produce MXenes at an unprecedented reaction rate and yield with minimal chemical waste. A simple NH 4 F solution was employed as the green electrolyte, which could be used repeatedly without any loss in its efficacy. Surprisingly, both fluoride and ammonium were found to play critical roles in the electrochemical etching, functionalization, and expansion of the layered parent materials (MAXs) through which the liberation of ammonia gas was observed. The electrochemically produced MXenes with excellent conductivity, applied as supercapacitor electrodes, could deliver an ultrahigh volumetric capacity (1408 F cm −3 ) and a volumetric energy density (75.8 Wh L −1 ). This revolutionary green, energy‐efficient, and scalable electrochemical route will not only pave the way for industrial‐scale production of MXenes but also open up a myriad of versatile electrochemical modifications for improved functional MXenes.
Publisher: Elsevier BV
Date: 03-2021
Publisher: Wiley
Date: 10-2023
DOI: 10.1002/CEY2.476
Publisher: Elsevier BV
Date: 2016
Publisher: American Chemical Society (ACS)
Date: 30-03-2022
Publisher: American Chemical Society (ACS)
Date: 23-02-2023
Publisher: Wiley
Date: 14-05-2023
Abstract: Lithium‐sulfur (Li‐S) batteries have been regarded as promising next‐generation energy storage systems due to their high energy density and low cost, but their practical application is hindered by inferior long‐cycle stability caused by the severe shuttle effect of lithium polysulfides (LiPSs) and sluggish reaction kinetics. This study reports a La 2 O 3 ‐MXene heterostructure embedded in carbon nanofiber (CNF) (denoted as La 2 O 3 ‐MXene@CNF) as a sulfur (S) host to address the above issues. The unique features of this heterostructure endow the sulfur host with synergistic catalysis during the charging and discharging processes. The strong adsorption ability provided by the La 2 O 3 domain can capture sufficient LiPSs for the subsequent catalytic conversion, and the insoluble thiosulfate intermediate produced by hydroxyl terminal groups on the surface of MXene greatly promotes the rapid conversion of LiPSs to Li 2 S via a “Wackenroder reaction.” Therefore, the S cathode with La 2 O 3 ‐MXene@CNF (La 2 O 3 ‐MXene@CNF/S) exhibits excellent cycling stability with a low capacity fading rate of 0.031% over 1000 cycles and a high capacity of 857.9 mAh g −1 under extremely high sulfur loadings. Furthermore, a 5 Ah‐level pouch cell is successfully assembled for stable cycling, which delivers a high specific energy of 341.6 Wh kg −1 with a low electrolyte/sulfur ratio (E/S ratio).
Location: Korea, Republic of
No related grants have been discovered for Hao Chen.