Application and characteristics of carbon nanorod synthesized by radio frequency magnetron sputtering
| Autor: | Hsin-Yueh Chang, 張心悅 |
|---|---|
| Rok vydání: | 2015 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 103 We present a method for growing carbon nano rods (CNR), an allotrope of 1-D carbon, using radio frequency magnetron sputtering at low temperature. We first investigate how the growth temperature (from room temperature to 380℃) and sputtering gas (Ar and N2) influence the CNR morphology and structure. The resulting CNRs were observed to be aligned vertically onto the substrate with uniform length exhibiting an amorphous structure with semiconducting properties. The CNR morphology did not change obviously but the crystallinity was enhanced with an increase in the growth temperature. Moreover, different CNR morphologies were observed when synthesized using various Ar/N2 sputtering gas ratios. Film-like CNRs were formed when pure N2 (or Ar) was used as the sputtering gas. Rod-like CNRs were formed when mixed Ar and N2 sputtering gas was applied. These inconsistent results indicate that sputtered carbon particles of different sizes and energy can be ascribed to the CNR formation. CNRs doped with different nitrogen content was used as the cathode catalysts for the proton exchange membrane fuel cell (PEMFC). The catalytic activity toward the oxygen reduction reaction (ORR) was studied. The nitrogen content was controlled directly by adjusting the Ar/N2 ratio during CNR growth. The nitrogen content and C–N bonding configuration of the samples were characterized using X-ray photoelectron spectroscopy, which demonstrated that the nitrogen content can reach up to 31.87% and the pyridinic-type nitrogen content increased with the increase in nitrogen content. The nitrogen-doped CNR with the largest amount of pyridinic-type nitrogen configuration exhibits superior ORR activity, which leads to a four-electron transfer in alkaline solution. The reduction current density can reach up to -7.8 mA/cm2, which opens the possibility for metal-free PEMFC catalysts applications. On the other hand, a hybrid 3-D structure, CNRs/graphene, was fabricated by combining highly conductive graphene (2-D) with vertically aligned CNRs (1-D). We used CNRs as the electrode and graphene as the current collector for electric double layer capacitor (EDLC) applications. The CNR and graphene combination has the following advantages: (1) The C–C bonding of the interface can effectively lower the impedance; (2) The structure can enhance the electron transmission speed in the device. The synthesized CNRs on graphene presented high number density, high direct aspect and large surface area, which can increase the reactive surface area between the electrode and electrolyte. The capacitor performance was characterized using cyclic voltammetry and galvanostatic charge-discharge testing in 1 M KOH electrolyte at 30℃, 40℃, 50℃, and 60℃. The CNR specific capacitance was observed to increase with increasing measurement temperature and could reach up to 830 F/g at 60℃. Even after extensive measurements, the CNR electrode maintained good adhesion to the graphene current collector, thereby suggesting electrode material stability. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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