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42. Highly porous carbon nanofiber electrodes for vanadium redox flow batteries

Author

Zhao, Yunhe, Li, Yang, Ihsan Ul Haq, Muhammad, Mubarak, Nauman, Xu, Mengyang, Qin, Xianying, Zhao, Tianshou, Kim, Jang Kyo, Zhao, Yunhe, Li, Yang, Ihsan Ul Haq, Muhammad, Mubarak, Nauman, Xu, Mengyang, Qin, Xianying, Zhao, Tianshou, and Kim, Jang Kyo

Abstract

The electrochemical performance of carbon nanofiber (CNF) electrodes in vanadium redox flow batteries (VRFBs) is enhanced by optimizing the morphological and physical properties of low-cost electrospun CNFs. The surface area, porosity and electrical conductivity of CNFs are tailored by modifying the precursor composition, especially the sacrificing agent, Fe(acac)3, in the polymer precursor and carbonization temperature. A highly porous structure with a large surface area is generated by the catalytic growth of graphitic carbon spheres surrounding the iron nanoparticles which are removed by an acid etching process. The graphitic carbon layers formed at a high carbonization temperature improve the electrical conductivity of CNFs. The large surface area of 349 m2 g−1 together with the abundant mesopore-dominant structure leads to high wettability and high activity for redox reactions of the electrode, giving rise to enhanced electrochemical performance in VRFBs. It delivers an energy efficiency (EE) of 91.4% at a current density of 20 mA cm−2 and 79.3% at 100 mA cm−2, and maintains an average EE of 72.5% after 500 charge/discharge cycles at 100 mA cm−2 © 2022 The Royal Society of Chemistry

Published
2022

45. TiO2/Cu2O heterostructure enabling selective and uniform lithium deposition towards stable lithium metal anodes.

Author

Ruan, Lingyan, Qin, Xianying, Lin, Kui, Yang, Zijin, Cai, Qiuchan, Li, Tong, Wu, Fangting, Kang, Feiyu, and Li, Baohua

Abstract

Lithium (Li) metal is the ultimate anode choice for next generation high energy density batteries. However, the high nucleation energy barrier and nonuniform electric field distribution, as well as huge volume expansion, lead to the uncontrollable growth of Li dendrites and poor utilization of Li metal, which hinders its practical application. Herein, titanium dioxide/cuprous oxide (TiO2/Cu2O) heterostructure is constructed on the rimous skeleton of Cu mesh, and the heterostructure decorated rimous Cu mesh (H-CM) can act as both current collector and host for dendrite-free Li metal anode. The TiO2/Cu2O heterostructure realizes selective Li nucleation by nano TiO2 and then induces fast and uniform Li conduction with the aid of heterostructure interface and nano Cu2O contributing to dendrite-free Li deposition. While the internal and external space of rimous skeletons in H-CM is used to accommodate the deposited Li and buffer its volume change. Therefore, the cycling reversibility of the derived Li metal anode in H-CM is improved to a high Coulombic efficiency of 98.8% for more than 350 cycles at a current density of 1 mA·cm−2, and 1,000 h (equals to 500 cycles) stable repeated Li plating/stripping can be operated in a symmetric cell. Furthermore, full cells with limited Li anode and high loading LiFePO4 cathode present excellent cycling and rate performances. [ABSTRACT FROM AUTHOR]

Published
2023
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49. Effect of heating and stretching polyacrylonitrile precursor fibers in steam on the properties of stabilized fibers and carbon fibers

Author

Qin, Xianying, Lu, Yonggen, Xiao, Hao, and Zhao, Weizhe

Subjects
Polyacrylonitrile -- Mechanical properties -- Thermal properties, Heating -- Research, Thermal stresses -- Research, Textile fibers, Synthetic -- Mechanical properties -- Thermal properties, Steam -- Properties, Engineering and manufacturing industries, Science and technology
Abstract

Polyacrylonitrile (PAN) fibers were heated and stretched in a steam bath mixed with nitrogen in the early stage of stabilization. During this process, the flexible linear chain of PAN molecule was converted to a rigid ladder structure by intramolecular cyclization. The shrinkage tension along the fiber axis decreased during this heat treatment, because water molecules here acted as a plasticizer for stretching. Consequently, the preferred orientation of ladder molecules in the stabilized fibers was enhanced. As a result, the preferred orientation, crystallite dimensions, and mechanical properties of the resultant carbon fibers (CFs) and graphite fibers (GFs) were improved, comparing with the corresponding CFs and GFs without pretreatment in the steam bath. POLYM. ENG. SCI., 53:827-832, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION The preferred orientation of crystallites along the fiber axis is one of the most important structure parameters for carbon fibers (CFs). Higher preferred orientation usually gives rise to higher [...]

Published
2013
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