Carbon materials are one of the most abundant materials in nature and have an important position in the research of electrochemical energy storage. As the electrode material of supercapacitors, carbon materials have an electric double-layer energy storage mechanism. However, its low specific capacitance limits a wide range of applications. Although the construction of multi-level pore structures to increase the specific surface area is currently the most common method to extend the specific capacitance of carbon materials, there is not always a positive correlation between the specific surface area and the specific capacitance. For example, activated carbon with a specific surface area of up to 3190 m2 g–1 exhibits a low specific capacitance of only 7 μF cm-2. In addition to the specific surface area, factors such as pore size, pore distribution, surface functional groups, structural disorder, and carrier properties also have important effects on the specific capacitance of carbon electrodes.
Compared with macroscopic systems, nanopores have a very narrow space and high specific surface area, exhibiting the characteristics of nanoconfinement (three-dimensional confinement). The nanoconfined space can induce enhanced adsorption between the adsorbate and the surface of these confined spaces. Therefore, the inconspicuous surface properties in the macroscopic system become the decisive factor affecting ion transport and adsorption in nanopores. Especially when the pore size is smaller than the Debye length, the electric double layer region overlaps, and the ion transport characteristics are determined by the surface charge, which leads to the enrichment of anisotropic ions, the dissipation and even emptying of homosexual ions, and exhibits ion selectivity. Therefore, in the nanopores, the potential synergistic enhancement mechanism of various key parameters determines the final specific capacitance of the carbon material.
Figure 1. The transport process of ions in multi-level pores.
The research team of Prof. Zheng Weitao, Prof. Zhang Wei and Prof. Zhu Xuanbo of Jilin University designed carbon fiber electrodes with different ultra-microporous structures, and optimized the electrode by adjusting the surface charge at the entrance of the ultra-microporous to improve the utilization rate of ultra-micropores. At a current density of 2 mA cm-2, the specific capacitance of the carbon fiber electrode increases from 3 mF cm-2 to 1430 mF cm-2. It has been found that when the inlet surface of the ultramicroporous is too small, the external charge of the pore will be reduced during charging, which in turn will reduce the selectivity of anisosexual ions. Numerical simulations based on the Poisson-Nernst-Planck equation also show that when the inlet surface of the ultramicroporous is reduced, it is difficult for ions to transport into the ultramicropores. This study combines the surface properties and pore structure of nanopores to more accurately describe the ion transport and adsorption phenomena in multi-level pores, providing a new perspective for understanding the relationship between specific surface area and specific capacitance of carbon-based porous materials.
Figure 2. Effect of pore structure and surface properties of ACC on capacitive properties and ion transport behavior.
In addition, the researchers constructed a dual-carbon hybrid supercapacitor that uses graphite as the positive electrode and carbon fiber cloth as the negative electrode, and adopts an electrolyte-liquid decoupling design that fuses an acidic electrolyte and an alkaline electrolyte. Compared to conventional carbon-based symmetric supercapacitors, the potential window of the dual-carbon hybrid supercapacitor is increased from about 1-2 V to 3 V, and an energy density of 602 μWh cm-2 is achieved at a power density of 3 mW cm-2.
Figure 3. Electrochemical performance of CC//GP dual-carbon hybrid supercapacitors.
这一成果近期发表在Journal of the American Chemical Society上，文章的第一作者是吉林大学博士研究生郑莹。
Significantly Increased Specific Discharge Capacitance at Carbon Fibers Created via Architected Ultramicropores
Ying Zheng, Wei Zhang*, Xuanbo Zhu*, Fuxi Liu, Chunming Yang, and Weitao Zheng*
J. Am. Chem. Soc., 2024, DOI: 10.1021/jacs.4c05647
【About the Corresponding Author】
Prof. Wei Zhang's profile: Wei Zhang, Director of the Microscopy Center of Jilin University, Tang Aoqing Scholar and Leading Professor of Jilin University. Clarivate Analytics "Global Highly Cited Researchers List" (2023, interdisciplinary), the eighth batch of experts with outstanding contributions in Changchun (2022). In 2004, he received his Ph.D. degree from the Institute of Metal Research, Chinese Academy of Sciences. He received his Ph.D. from the Institute of Metal Research, Chinese Academy of Sciences in 2004, and then engaged in independent or cooperative research at NIMS in Japan, Samsung in Korea, Fritz-Haber Institute of Max Planck Institute in Germany, Technical University of Denmark and CIC Energigune in Spain, with the main research interests in surface/interface chemistry of catalytic and energy materials, and electron microscopic analysis of advanced materials.
Prof. Zheng Weitao's profile: Zheng Weitao is a distinguished professor of the "Major Talent Project of the Ministry of Education" of Jilin University, a national outstanding young man, and a "Global Highly Cited Scientist List" (2023/2022, interdisciplinary) of Clarivate Analytics. He received his Ph.D. degree from Jilin University in 1990. He then worked at Linköping University, Chiba Institute of Technology, and Nanyang Technological University. His main research interests are the design of energy materials, functional films, and catalysts.
Zhu Xuanbo, associate professor of the School of Chemistry of Jilin University, outstanding young scientific and technological talent of Jilin Province, "Tang Aoqing" young scholar, vice chairman of the Young Chemist Committee of Jilin Chemical Society, and the fifth batch of "Boxin Plan". He is mainly engaged in the design and synthesis of high-performance polymer materials, functionalization modification and application research and development, and is good at organically combining scientific experiments, theoretical simulation and demonstration applications, and has carried out research on bionic ion channel separators and high-performance resin-based medical materials. Published Sci. Adv., J. Am. Chem. Soc., CCS Chemistry, ACS Nano, Adv. Funct. Mater., Adv. Energy Mater., Macromolecules, et al. He won the "Liwang" Outstanding Postdoctoral Award and the Tang Aoqing Young Talent Award.