Yunxia Guo

Bio: Yunxia Guo is an academic researcher from Nanjing University of Aeronautics and Astronautics. The author has contributed to research in topics: Mesoporous material & Coating. The author has an hindex of 16, co-authored 26 publications receiving 1281 citations. Previous affiliations of Yunxia Guo include Jiangsu University.

Laminated magnetic graphene with enhanced electromagnetic wave absorption properties

Abstract: Graphene is highly desirable as an electromagnetic wave absorber because of its high dielectric loss and low density. Nevertheless, pure graphene is found to be non-magnetic and contributes to microwave energy absorption mostly because of its dielectric loss, and the electromagnetic parameters of pure graphene, which are out of balance, result in a bad impedance matching characteristic. In this paper, we report a facile solvothermal route to synthesize laminated magnetic graphene. The results show that there have been significant changes in the electromagnetic properties of magnetic graphene when compared with pure graphene. Especially the dielectric Cole–Cole semicircle suggests that there are Debye relaxation processes in the laminated magnetic graphene, which prove beneficial to enhance the dielectric loss. We also proposed an electromagnetic complementary theory to explain how laminated magnetic graphene, with the combined advantages of graphene and magnetic particles, helps to improve the standard of impedance matching for electromagnetic wave absorbing materials. Besides, microwave absorption properties indicate that the reflection loss of the as-prepared composite is below −10 dB (90% absorption) at 10.4–13.2 GHz with a coating layer thickness of 2.0 mm. This further confirms that the nanoscale surface modification of magnetic particles on graphene makes graphene-based composites have a certain research value in electromagnetic wave absorption.

Facile Synthesis for LiFePO4 Nanospheres in Tridimensional Porous Carbon Framework for Lithium Ion Batteries

Abstract: The excellent electronic conductivity and high surface area are two crucial factors for electrode materials to achieve high energy and power capabilities in lithium ion batteries. This article presents a feasible method to obtain nanospherical electrode materials in the versatile carbon framework. A facile synthesis has been developed to prepare LiFePO4 nanospheres with an average diameter of ∼300 nm lodged in the tridimensional (3D) porous carbon structure. This LiFePO4/C composite possesses the considerably enhanced electronic conductivity of ∼10−2 Scm−1 and amazing high surface area of 200.5 m2g−1, and the lithium ion diffusion coefficient of ∼10−15−10−14 cm2s−1 is calculated. The LiFePO4/C cathode material delivers discharge capacities of 155.0 mAhg−1 at 0.1 C and 69.5 mAhg−1 at 20 C. Furthermore, the pristine LiFePO4/C entity has exhibited discharge capacity of 127.8 mAhg−1 at 0.1 C without conductive carbon additives.

Synthesis and Electrochemical Characterization of N-Doped Partially Graphitized Ordered Mesoporous Carbon–Co Composite

Abstract: N-doped ordered mesoporous carbon–Co composites (Co-N-OMC) with 2D hexagonal structure, uniform pore size (4.4 nm), high surface area (550 m2 g–1), and medium pore volume (0.61 cm3 g–1) were successfully fabricated through facile one-step template method. We employed resol as the carbon precursor, triblock copolymer as the template agent, and cobaltous acetate and urea as additives. XPS analysis revealed that nitrogen was successfully doped in ordered mesoporous carbon and existed in the form of pyridine-like and quaternary-N nitrogen atoms. More importantly, metallic Co nanoparticles with uniform diameter around 15 nm highly dispersed in carbon matrix without adding any dispersion agent, which was probably due to the confinement effect of mesoporous structure. It was unambiguously demonstrated by HRTEM analysis that there were layered graphitic sheets present around Co particles, resulting from in situ catalytic graphitization of amorphrous carbon by Co species. Pt catalyst deposited on Co-N-OMC composit...

Metal-free catalysts for oxygen reduction reaction.

Abstract: Liming Dai,*,†,‡ Yuhua Xue,†,‡ Liangti Qu,* Hyun-Jung Choi, and Jong-Beom Baek* †Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Department of Chemistry, School of Science, Beijing Institute of Technology, Beijing 100081, People’s Republic of China School of Energy and Chemical Engineering/Center for Dimension-Controllable Covalent Organic Frameworks, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon, Ulsan, 689-798, South Korea

Thermal Conversion of Core–Shell Metal–Organic Frameworks: A New Method for Selectively Functionalized Nanoporous Hybrid Carbon

Abstract: Core–shell structured ZIF-8@ZIF-67 crystals are well-designed and prepared through a seed-mediated growth method. After thermal treatment of ZIF-8@ZIF-67 crystals, we obtain selectively functionalized nanoporous hybrid carbon materials consisting of nitrogen-doped carbon (NC) as the cores and highly graphitic carbon (GC) as the shells. This is the first example of the integration of NC and GC in one particle at the nanometer level. Electrochemical data strongly demonstrate that this nanoporous hybrid carbon material integrates the advantageous properties of the individual NC and GC, exhibiting a distinguished specific capacitance (270 F·g–1) calculated from the galvanostatic charge–discharge curves at a current density of 2 A·g–1. Our study not only bridges diverse carbon-based materials with infinite metal–organic frameworks but also opens a new avenue for artificially designed nanoarchitectures with target functionalities.

From Bimetallic Metal‐Organic Framework to Porous Carbon: High Surface Area and Multicomponent Active Dopants for Excellent Electrocatalysis

Abstract: Bimetallic metal-organic frameworks are rationally synthesized as templates and employed for porous carbons with retained morphology, high graphitization degree, hierarchical porosity, high surface area, CoNx moiety and uniform N/Co dopant by pyrolysis. The optimized carbon with additional phosphorus dopant exhibits excellent electrocatalytic performance for the oxygen reduction reaction, which is much better than the benchmark Pt/C in alkaline media.

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

Abstract: The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.

Laminated magnetic graphene with enhanced electromagnetic wave absorption properties

Abstract: Graphene is highly desirable as an electromagnetic wave absorber because of its high dielectric loss and low density. Nevertheless, pure graphene is found to be non-magnetic and contributes to microwave energy absorption mostly because of its dielectric loss, and the electromagnetic parameters of pure graphene, which are out of balance, result in a bad impedance matching characteristic. In this paper, we report a facile solvothermal route to synthesize laminated magnetic graphene. The results show that there have been significant changes in the electromagnetic properties of magnetic graphene when compared with pure graphene. Especially the dielectric Cole–Cole semicircle suggests that there are Debye relaxation processes in the laminated magnetic graphene, which prove beneficial to enhance the dielectric loss. We also proposed an electromagnetic complementary theory to explain how laminated magnetic graphene, with the combined advantages of graphene and magnetic particles, helps to improve the standard of impedance matching for electromagnetic wave absorbing materials. Besides, microwave absorption properties indicate that the reflection loss of the as-prepared composite is below −10 dB (90% absorption) at 10.4–13.2 GHz with a coating layer thickness of 2.0 mm. This further confirms that the nanoscale surface modification of magnetic particles on graphene makes graphene-based composites have a certain research value in electromagnetic wave absorption.