Due to their excellent electrical conductivity, substantial theoretical surface area and superior chemical stability, carbon nanotubes (CNTs) are viewed as perfect electrochemical energy storage materials.
However, strong van der Waals pressure causes the CNTs to clump together, which decreases the electrochemically active surface area. Due to their high length-to-diameter ratio, single-walled carbon nanotubes (SWNTs) face an even worse variant of this problem.
SWNTs (about 1.4 nm in diameter) have recently been encapsulated with polyoxometalate guest molecules to enhance the electrochemical energy storage of CNTs, according to a recent study led by Dr. Xiao Wang from the Shenzhen Institute of Advanced Technology (SIAT) in Chinese Academy of SciencesDr. Sheng Zhu from Shanxi University, and Prof. Yan Li from Peking University.
On June 8th2023, this research was published in Cells Reporting Physics.
Polyoxometalate molecules create a one-dimensional chain-like structure in the CNT cavity as a result of the confinement effect of the CNT. Such precise (enamel protected) hybrids hold promise as a potential choice of supercapacitor electrode material.
The reduction in the surface charge density of the nanotubes caused by the transfer of electrons from the CNT to the polyoxometalate decreases the van der Waals forces and inhibits aggregation. Consequently, the polyoxometalate-filled SWNTs exhibit a larger electrochemical active area and a larger double-layer capacitance.
By activating apparent capacitance via a reversible redox process, polyoxometalate molecules can enhance hybrid capacitive (enamel protected) performance. A notable increase in the stability of the encapsulated polyoxometalate cycle is made possible by the CNT confinement effect.
As a result, this one-dimensional hybrid material displays enhanced electrochemical energy storage capabilities, with a larger specific capacitance than pure SWNT (172.2 farads per gram) and 328.6 farads per gram (10 millivolts per second). In addition, after 10,000 cycles, the assembled supercapacitor has a capacity retention rate of 91.3%.
Our study offers valuable insights into research on the confinement effect of CNTs, which have great potential for harnessing high-performance energy storage and conversion materials.
Dr Xiao Wang, Corresponding Author of the Study and Associate Professor, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences
Zhu, S., et al. (2023) One-dimensional heterostructure of polyoxometalate-encapsulated carbon nanotubes to enhance capacitive energy storage. Cells Reporting Physics. doi:10.1016/j.xcrp.2023.101446