The product of the PAN/DMF electrospinning was a relatively dense mat of white nanofibers. Technically speaking, this was the intended product; however, in order to unlock the conductive properties of the nanofiber so that it could be used in a capacitor, calcination was required. Calcination is the specific process of heating PAN/DMF nanofibers up to the immensely hot temperature of 580°C in order to stabilize their molecular structure. This stabilization is a result of the cyclic voltammetry that PAN undergoes at this temperature; it becomes both very brittle and very resistant to chemical or physical change.
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| Before Calcination |
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| After Calcination |
The two samples were also put under a Scanning Electron Microscope. The following images are ordered from highest zoom to lowest zoom.
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| After Calcination |
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| Before Calcination |
As you can see, the post-calcination nanofibers are much more condensed than that of its pre-calcination counterpart. Also, the post-calcination nanofibers are much more brittle, and have clearly defined angles in the curves of an individual strand. This ultimately allows for the nanofibers to be used as a conductive substance because it allows for a high energy density in the nanofiber electrode.
After the successful calcination of the PAN/DMF nanofibers, the resulting black sheet of nanofibers was divided into several disk-shaped electrodes. These electrodes, when combined with an electrolytic solution of sulfuric acid and an insulating separator, would make a capacitor. Ensuring that all components were thoroughly covered in the sulfuric acid, two of the disk-shaped electrodes were separated by an insulating separator, and then attached to two separate pieces of graphite that would serve as connectors for the two halves of the capacitor. The resulting capacitor was then covered by two small slabs of acrylic so that it would remain isolated from its surroundings.
- The created capacitor was then attached to a data collector, which proceeded to run various tests on it. The first test, called Charge Discharge, measured the total energy that could be stored in the capacitor. The second, PotentiostaticEIS, measured the internal resistance of the capacitor. The third and final test, titled Cyclic Voltammetry, measured the stability of the sample over a wide range of currents.
Cyclic Voltammetry
Charge Discharge
PotentiostaticEIS
- Based upon the performance tests and analysis, the capacitor exhibited a capacitance of 240.7 milliFarads. This translates to 100 Farads per gram, the standard units used in capacitance. For a relatively small capacitor (the size of a human thumb) this capacitance is extremely efficient compared to the typical capacitance of a capacitor, 185 microFarads [10].
