Pore size analysis by nitrogen adsorption and thermal desorption

An improvement was proposed for the pore-size analysis of active carbons based on low-temperature (77 K) nitrogen adsorption isotherms measured over a wide range of relative pressures (5 × 10−7–0.995). It was shown that the applicability of the Barrett, Joyner and Halenda (BJH) computational method based on the Kelvin equation could be extended significantly towards small mesopores and large micropores when a proper t-curve was used to represent the film thickness of nitrogen adsorbed on the carbon surface. It was proposed that the aforementioned t-curve be obtained from the nitrogen adsorption isotherm at 77 K on a macroporous carbon black by fitting its multilayer part to the calibrated t-curve for nitrogen adsorbed at 77 K on a macroporous silica. To date, the Harkins–Jura or Halsey t-curves have been used to describe the pressure-dependence of the film thickness. This appears to be inaccurate, especially in the range of low relative pressures. It was shown that this inaccuracy makes the pore-size analysis questionable. However, the t-curve proposed in this work gave the pore-size distribution functions for the carbons studied thereby reproducing the total pore volume and showing realistic behaviour in the range at the borderline between micropores and mesopores.

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The Synthesis and Electrochemical Performance of Si Composite with Hollow Carbon Microtubes by the Carbonization of Milkweed from Nature as Anode Template for Lithium Ion Batteries

Energies ◽

10.3390/en13195124 ◽

2020 ◽

Vol 13 (19) ◽

pp. 5124

Author(s):

Eun Hyuk Chung ◽

Jong Pil Kim ◽

Hyun Gyu Kim ◽

Jae-Min Chung ◽

Sei-Jin Lee ◽

...

Keyword(s):

Electron Microscopy ◽

Electrical Conductivity ◽

Electrochemical Performance ◽

Pore Size ◽

Lithium Ion Batteries ◽

Polyvinylidene Fluoride ◽

Lithium Ion ◽

Size Analysis ◽

Pore Size Analysis ◽

Hollow Carbon

It has been reported that improving electrical conductivity and maintaining stable structure during discharge/charge process are challenge for Si to be used as an anode for lithium ion batteries (LIB). To address this problem, milkweed (MW) was carbonized to prepare hollow carbon microtubes (HCMT) derived from biomass as an anode template for LIB. In order to improve electrical conductivity, various materials such as chitosan (CTS), agarose, and polyvinylidene fluoride (PVDF) are used as carbon source (C1, C2, and C3) by carbonization. Carbon coated HCMT@Si composits, HCMT@Si@C1, HCMT@Si@C1@C2, and HCMT@Si@C1@C3, have been successfully synthesized. Changes in structure and crystallinity of HCMT@Si composites were characterized by using X-ray diffraction (XRD). Specific surface area for samples was calculated by using BET (Brunauer–Emmett–Teller). Also, pore size and particle size were obtained by particle and pore size analysis system. The surface morphology was evaluated using high resolution scanning electron microscopy (HR-SEM), Field Emission transmission electron microscopy (TEM). The thermal properties of HCMT@Si composites were analyzed by thermogravimetric analysis (TGA). Our research was performed to study the synthesis and electrochemical performance of Si composite with HCMT by the carbonization of natural micro hollow milkweed to form an inner space. After carbonization at 900 °C for 2 h in N2 flow, inner diameter of HCMT obtained was about 10 μm. The electrochemical tests indicate that HCMT@Si@C1@C3 exhibits discharge capacity of 932.18 mAh/g at 0.5 A/g after 100 cycles.

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