AM: Effect of carbonization temperature on the properties of polyacrylonitrile based carbon nanofibers

Tech 2023-05-14 05:33:45 Source: Network

Welcome to follow WeChat official account [Polymer Energy]Accurately understanding the conductivity of individual fibers and their networks is crucial for adjusting the overall macroscopic performance of polyacrylonitrile (PAN) based carbon nanofibers (CNFs). Therefore, conductive atomic force microscope (C-afm) was used to study the micro electrical properties of CNF networks and the nano electrical properties of a single CNF carbonized at 600 to 1000

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Accurately understanding the conductivity of individual fibers and their networks is crucial for adjusting the overall macroscopic performance of polyacrylonitrile (PAN) based carbon nanofibers (CNFs). Therefore, conductive atomic force microscope (C-afm) was used to study the micro electrical properties of CNF networks and the nano electrical properties of a single CNF carbonized at 600 to 1000 . At the micro scale, CNF networks exhibit good electrical interconnection, resulting in uniform current distribution. The strong correlation between the macroscopic conductivity determined by the four point method and the microscopic results emphasizes the homogeneity of the network. The micro and macro electrical properties depend entirely on the carbonization temperature and the obtained fiber structure. Remarkably, the nanoscale high-resolution current map of a single CNF shows a large proportion of high resistance surfaces, which represents a significant limitation. The high resistance surface domain can be attributed to the disordered high resistance carbon structure on the surface, as well as the lack of electron permeation paths in the volume. As the carbonization temperature increases, the size of conductive surface domains increases and the conductivity increases. This work extends the existing microstructure model of CNFs through electrical properties, especially electron permeation pathways.

Introduction to images and text

SEM images of CNF pads carbonized at temperatures of 600 C (a), 800 C (b), and 1000 C (C) are displayed. CNFs are mostly straight, without a preferred direction, and exhibit similar diameters. The histogram (d-f) shows the relative diameter frequencies determined by the diameter j algorithm, and analyzes the SEM images of each sample from another point, as shown in Figure S1a-c, resulting in a similar diameter distribution (red bar). The dashed line represents the average diameter.

twenty m20 The terrain map (a-e) shows the carbonization of the CNF pad in the temperature range of 600 to 1000 . All samples exhibit fibrous morphology with randomly oriented CNFs. The contact current map (f-j) obtained simultaneously indicates that the current has a wide spatial distribution and is detected along all CNFs. CNFs carbonized between 700 C and 1000 C (g-j) are measured at a bias voltage of 20mV, while CNFs carbonized at 600 C (f) are measured at a bias voltage of 100mV to overcome the current detection limit

The contact current maps of two different CNFs with high resolution of 200nm 200nm within the fiber optic network of each sample carbonized in the range of 600 C to 1000 C. Obtain the topographic map simultaneously at a deviation voltage of 20mV, as shown in Figure 3e. As the carbonization temperature increases, the conductive area fraction and maximum observed current significantly increase

(The bias voltage is 20 mV) and the contact current diagram of 600 C carbonized CNFs shown in Figure S3e-f (the bias voltage is 100 mV to overcome the detection limit). Conductivity is calculated by dividing the contact current by the bias voltage. As shown in Figure S6, changing the applied bias voltage has no significant effect on the average conductivity. The histogram is plotted as the average of two current maps for each sample, and the histogram of a single CNF is shown in Figures S4.1 to 4.3. The dashed line represents the average conductivity of each sample. In addition, the average conductivity of each sample is correlated with the macroscopic conductivity measured by the four point method (b). Micro data and macro data have a strong correlation, both of which depend on the carbonization temperature. Note the logarithmic scale and the different units of conductivity and conductance.

The TEM micrograph shows the structure obtained from the fractured portion of CNFs carbonized at 600 (a) and 1000 (b). Both exhibit ordered and disordered structural domains, and the degree of order increases with the increase of carbonization temperature. The model (C-e) shows a schematic cross-section of the near surface structure of CNFs carbonized at 600 C (C), 800 C (d), and 1000 C (e). The lines represent highly ordered, potentially conductive carbon structures (black and yellow) and less ordered, high resistance carbon (gray). However, current can only flow in highly ordered structures to form an electron permeation path from the surface to the body (yellow). As the carbonization temperature increases, the order of the carbon structure increases, leading to the growth of conductive surfaces and bulk structures, thereby improving electron permeation.

Paper Information

Original link:
https://onlinelibrary.wiley.com/doi/10.1002/adma.202300936

Corresponding author: Florian Hausen, Aachen University of Technology

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