Chapter 4.Results and Discussion
4.4 Analysis of 14M HNO 3 -MWNTs
4.4.2 Analysis of MWNTs morphology
Fig. 4.44 (a) shows that raw MWNTs display hollow tubes with amorphous and crystalline layers. It is known that 14M HNO3-MWNTs not only opens the closed tips of the tubes, but creates functional groups, -COOH, on the surface to attract metal ions to nucleate. Fig. 4.44 (b) shows that the amorphous surface layers and the cap of MWNTs are removed first with 14M HNO3 due to its non-crystalline structure. The open cap of MWNTs may allow Pt to get into the inner surface of tubes by the other method in Fig. 4.45. Then, even crystalline layer may be broken for a longer time. In other words, the functional groups on the surface layer of 14M HNO3-MWNTs may be removed for a longer time. However, the total number of functional groups may keep a balance on 14M HNO3-MWNTs after a certain time. In this work, we take a hypothetical model for stable state in Fig. 4.46 to explain it with TEM image. Although functional groups on the surface layer of 14M HNO3-MWNTs may be removed, new functional groups would be formed on the new surface layer which is inner the removed surface layer. Therefore, the total number of functional groups may keep a balance after some time.
4.4.3 Summary
1. The amount of functional groups is in the equilibrium during the stable state.
2. COO-H+ attract more Pt precursors to nucleate Pt particle so it produce the larger particle against its efficiency.
Fig. 4.41 XRD patterns of Pt on raw-MWNTs and 14M HNO3-MWNTs
Table 4.8 The average size of Pt/raw-MWNTs and Pt/14M HNO3-MWNTs
time K λ Kα1 B2θ θB size (Ǻ)
0 29.74 1.54 1.08 39.8 53.226
6 29.74 1.54 0.88 39.8 67.74
12 29.74 1.54 0.884 39.7 67.34
18 29.74 1.54 0.8832 39.93 67.6
24 29.74 1.54 0.882 39.7 67.5
20 30 40 50 60
2 theta degree
Intesit y (a.u.)
C(101)C(002)
Pt(200) Pt(111)
no treatment
900C 14M HNO3 06hr 900C 14M HNO3 12hr 900C 14M HNO3 18hr 900C 14M HNO3 24hr
Fig. 4.42 The average diameters for Pt/raw-MWNTs is 5.8802 nm
Fig. 4.43 The average diameters for Pt/14M HNO3-MWNTs is 7.29 nm
Fig. 4.44 (a) raw MWNTs (b) 14M HNO3-MWNTs
Fig. 4.45 (a) raw MWNTs with Pt (b) 14M HNO3-MWNTs with Pt
Fig. 4.46 Hypothetical model for stable state of 14M HNO3-MWNTs
8.09 nm
(a) (b)
Chapter 5 Conclusions
1. Various solvents, eg. HNO3, H2SO4, and KOH (800C, 6 hr), modified MWNTs can form the same functional group -COOH and –OH.
2. Well-dispersed functional groups on MWNTs could improve the efficiency of half-cell test.
3. The functional groups on MWNTs increase anchoring sites of Pt precursors to increase the efficiency of half-cell test.
4. The amount of functional groups in order to attract Pt on HNO3-MWNTs is more than on H2SO4-MWNTs and on KOH-MWNTs due to a strong oxidizing agent HNO3.
5. Temperature is one of the main factors if MWNTs modified by HNO3 form functional groups -COOH and –OH.
6. 2M and 14M HNO3-MWNTs at 800C are unfavorable to form functional groups.
7. The modified MWNTs at 1000C could oxidize and destroy the surface of MWNTs very much.
8. 900C is the optimum temperature for 2M and 14M HNO3-MWNTs to form functional groups.
9. 2M HNO3-MWNTs form a lot of functional groups (stable state) from 12hr to 24hr.
10. 14M HNO3-MWNTs form a lot of functional groups (stable state) from 6hr to 24hr.
11. Higher concentration of HNO3 allows the surface of MWNTs to form functional groups quickly.
12. The amount of functional groups is in the equilibrium during the stable state.
13. COO-H+ attract more Pt precursorsto nucleate Pt particle so it produce the larger particle against its efficiency.
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個人簡歷
姓名：莊方慈 性別：男
出生日期：民國 71 年 2 月 16 日 籍貫：台北市
住址：台北市北投區知行路 91 巷 5 號 3 樓
學歷：國立清華大學材料科學與工程學系學士 （89.9-93.6）
國立交通大學材料科學與工程學系碩士 （93.9-95.6）
碩士論文題目：
奈米碳管化學表面改質應用於直接甲醇燃料電池陰極電極之研究
Study of Chemical Surface Modifications of CNTs as cathode electrode for DMFC