Amplified Electrochemical energy storage via carbon nanotube confinement on polyoxometalates

(Nanowerk News) As outstanding electrochemical energy storage materials, carbon nanotubes (CNTs) owe their reputation to their superior electrical conductivity, expansive theoretical surface area, and exceptional chemical stability.
However, this prestige is shadowed by a significant drawback. Due to the influence of robust van der Waals forces, CNTs display a tendency to aggregate, which in turn diminishes their electrochemically active area. This issue is particularly amplified for single-walled carbon nanotubes (SWNTs), attributable to their heightened length-to-diameter ratio.
Seeking a solution, a coordinated research effort, led by Dr. WANG Xiao from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences, Dr. ZHU Sheng from Shanxi University, and Prof. LI Yan from Peking University, encapsulated polyoxometalate guest molecules within SWNTs (averaging a diameter of approximately 1.4 nm) to bolster the electrochemical energy storage capability of CNTs.
Schematic illustration and electron microscopy characterization of one-dimensional heterostructures of SWNT-confined polyoxometalate clusters
Schematic illustration and electron microscopy characterization of one-dimensional heterostructures of SWNT-confined polyoxometalate clusters. (Image: WANG Xiao)
The results of this study were published in Cell Reports Physical Science ("One-dimensional heterostructures of polyoxometalate-encapsulated carbon nanotubes for enhanced capacitive energy storage").
As a result of the confinement effect demonstrated by CNTs, polyoxometalate molecules construct one-dimensional, chain-like structures within the CNT cavity. These meticulously structured polyoxometalate@SWNT hybrids present promising potential as electrode material candidates for supercapacitors.
Electron transfer from CNTs to polyoxometalates lessens the surface charge density of the nanotubes, consequently attenuating the van der Waals forces and inhibiting aggregation. Thus, SWNTs infused with polyoxometalates demonstrate a more expansive electrochemically active area and heightened double-layer capacitance.
Polyoxometalate molecules contribute pseudocapacitance via reversible redox reactions, thereby enhancing the capacitive performance of the polyoxometalate@SWNT hybrids. Notably, the confinement effect of CNTs significantly augments the cycling stability of encapsulated polyoxometalates.
Ultimately, this one-dimensional hybrid material showcases amplified electrochemical energy storage properties, achieving a specific capacitance of 328.6 farads per gram (@ 10 millivolts per second), a feat surpassing that of pure SWNTs (172.2 farads per gram). Moreover, the assembled supercapacitor retains a capacity retention rate of 91.3% after 10,000 cycles.
Dr. WANG Xiao, a corresponding author of the study, comments, "Our study provides valuable insights into the research on the confinement effect of CNTs, which promises substantial potential for the development of high-performance energy storage and conversion materials."
Source: Chinese Academy of Sciences (Note: Content may be edited for style and length)
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