Chapter 4.Results and Discussion
4.1 Morphology of carbon nanotube on carbon cloth
In this study, the purpose is that the longer MWNTs are fabricated vertically by MPECVD. The use of a support, well-aligned MWNTs, for catalyst has many advantages including more the anchoring sites of available catalyst, producing a lot of functional groups to attract catalyst at the caps and the sidewalls of MWNTs easily by modified the surface structure, using inner specific surface area of tube by opening end of MWNTs.
Fig 4.1 shows that a piece of carbon cloth without any treatment. It is composed of textured carbon fibers which have a smooth surface. Fig 4.2 shows that the images of long MWNTs fabricated on carbon cloth densely and vertically. Then, MWNTs are analyzed in the higher magnification. The length of MWNTs is about 20 μm and its diameter is about 20 nm in Fig 4.3. As shown in Fig. 4.4, the TEM images show that MWNTs display hollow tubes with amorphous and crystalline layers. On the other hand, the growth model of MWNTs could be found including tip growth model and base growth model.
The density of the vertical MWNTs may not be controlled dispersedly so the spraying of Pt particle may just stop on the top surface. Therefore, even the high specific surface area of MWNTs still can not be utilized totally until Pt is deposited uniformly by using polyol process. However, the raw surface of MWNTs is relatively inert and difficult to support particles homogeneously, which often results in the agglomeration of nanoparticles. Thus, it is important to improve the adhesion through the following surface chemical modification techniques.
Fig. 4.1 SEM images of pristine carbon cloth with different magnification
Fig 4.2 SEM images of MWNTs on carbon cloth with different magnification
Fig 4.3 The length of MWNTs is about 20 μm and its diameter is about 20 nm.
Base growth model Tip growth model
20 μm 20 nm
20 nm
20 nm
4.2. Multi-wall carbon nanotubes are modified by HNO
3, H
2SO
4, and KOH
Surface chemical modification is a common method and is essential for the deposition of catalysts and other species onto carbon nanotube surfaces for nanocatalytic applications [34]. Oxidation, with popular oxidants including HNO3, KMnO4, HNO3 / H2SO4, is an often attempted approach to activate the surface of CNTs [35, 36]. However, there is little analysis about functional groups after surface chemical modification of CNTs. In this study, MWNTs are modified by HNO3, H2SO4, and KOH at 800C in Table 4.1 and may produce different functional groups to attract more Pt ions nucleating uniformly and densely. Thus, after the following experiments, it would be found that which chemical solution is better for surface chemical modification of MWNTs.
Table 4.1 MWNTs are modified by HNO3, H2SO4, and KOH
Solution HNO3 H2SO4 KOH
Concentration 16M 18M 6M
Temperature 800C 800C 800C
Time 6 hr 6 hr 6 hr
Hypothetical functional groups
-COOH -OH
-SO3H -OH
4.2.1 Analysis of functional groups
The information on the surface chemistry of the modified nanotubes has been provided by the FTIR. Table 4.2 indicates the absorption spectra ranges of several functional groups. Fig 4.5 shows the absorption spectra of MWNTs modified by HNO3, H2SO4, and KOH at 800C for 6 hr. In fact, one broad intensive band observing at 1375 cm-1 is assigned to the alcoholic hydroxyl groups (-OH) or the carboxylic acids (-COOH) and the other observing at 1574 cm-1 is assigned to the carboxylic acids (-COOH).
However, the functional group, sulfonic acid (-SO3H), can not be observed. Therefore, the reaction pathways for forming the functional group most probably involve the following reaction. Hydration of the olefinic C=C moieties is released from the conjugation network by decarbonization of the nanotube sidewalls due to HNO3, H2SO4, and KOH oxidation so the alcoholic hydroxyl groups (-OH) and carboxylic acids (-COOH) could be formed [32].
Indeed, we try to assay sulfonic acid (-SO3H) groups with FTIR. However, the detection is too difficult because of their weak response in the IR mode. For the reason, we used XPS to directly detect the sulfur atom [37]. No S spectra of various MWNTs, given in Fig. 4.6, show that there is no sulfonic acid (-SO3H). On the other hand, the carboxyl groups would be detected in Fig. 4.7(a) (b) (c). The C 1s spectrum appears to be composed of C=C (~284.6 eV), C-C (~285.85 eV), CO (287.46 eV), COO-(289.24 eV), OCOO- (~291.5 eV) functional groups [38]. The observed chemical shift following the chemical treatment is about 1 eV. Therefore, the result from the FTIR and XPS analysis indicates that MWNTs merely forms the alcoholic hydroxyl groups (-OH) and the carboxylic acids (-COOH) with chemical modification of HNO3, H2SO4, and KOH at 800C for 6 hr.
Table 4.2 The absorption spectra ranges of several functional groups
Fig 4.5 The absorption spectra of MWNTs modified by HNO3, H2SO4, and KOH Functional group
Wave number (cm-1) -OH alcoholic hydroxyl groups 1410-1260
-SO3H sulfonic acid 1150-1250
-COOH carboxylic acids 1610-1550 1420-1300 -C=O carboxyl groups 1690-1760
4000 3000 2000 1000
-COOH -OH -COOH
800C 16M HNO
3 06hr 800C 18M H
2SO
4 06hr 800C 6M KOH 06hr w/o
absorptions (a.u.)
wave number (cm -1 )
Fig. 4.6 XPS survey spectra of MWNTs modified by HNO3, H2SO4, and KOH
Fig.4.7 (a) The C 1s spectrum of HNO3-MWNTs
1200 1000 800 600 400 200 0
O (1s)
C (1s)
Binding Energy (eV)
Intesity (a.u.)
HNO3 C (1s) (285.2 eV) O (1s) (532 eV) H2SO4 C (1s) (285.1 eV) O (1s) (533 eV) KOH C (1s) (285 eV) O (1s) (531 eV)
294 292 290 288 286 284 282 280
OCOO- COO- C-O C-C
C=C
Binding Energy (eV)
Intesity (a.u.)
C (1s)
sp2 C=C (284.6) sp3 C-C (285.85) C-O (287.46) COO- (289.24) OCOO- (291.5)
Fig.4.7 (b) The C 1s spectrum of H2SO4-MWNTs
Fig.4.7 (c) The C 1s spectrum of KOH-MWNTs
292 290 288 286 284 282 280
OCOO- COO
300 295 290 285 280
Intesity (a.u.)
4.2.2 Qualitative analysis of Pt on MWNTs
Pt particles are deposited on MWNTs by using polyol process after samples are modified chemically. Then, we take EDX and XPS of qualitative analysis for samples in order to be sure that polyol process is successful. Fig. 4.8 shows the mapping of EDX for HNO3-MWNTs. It indicates that the dispersive nanoparticles on MWNTs are Pt. On the other hand, Fig. 4.9 also shows the XPS survey spectrum of HNO3-MWNTs after the Pt reduction. Notably, a very strong Pt4f peak indicates that there are Pt nanoparticles on MWNTs because XPS is a surface-sensitive tool.
The formation process of PVP-protected Pt nanoparticles synthesized in ethylene glycol is presented that the H2PtCl6 may be completely reduced according to the eq (1) and the eq (2).
Pt4+(aq) + 6Cl-(aq) + 2H+(aq) ⇌ H2PtCl6 (aq) (1)
H2PtCl6(aq)+ CH2OHCH2OH(aq) ⇌ Pt0 + 6HCl(aq)+ 2HCHO(aq) (2)
As mentioned above, the Pt precursors are reduced to Pt0 atoms at 1600C for 3hr [39]. Fig. 4.10 shows that the dispersive Pt nanoparticles on MWNTs are Pt0 because there is no significant chemical shift of binding energy in Pt4f7/2 and Pt4f5/2 with Ar+ etching [40]. Table 4.3 shows that the binding energy of Pt4f7/2 and Pt4f5/2 are developed by Ar+ etching (25mA and 3kV) with time. Finally, the Pt0 nanoparticles are stabilized on MWNTs by using ethylene glycol.
Fig. 4.8 The mapping of EDX for HNO3-MWNTs
Fig. 4.9 The XPS survey spectrum of HNO3-MWNTs after reduction of Pt
1200 1000 800 600 400 200 0
Intesity (a.u.)
Pt C
Binding Energy (eV)
C (285.13eV) Pt (70.5eV)
Fig. 4.10 Chemical shift of binding energy in Pt4f7/2 and Pt4f5/2 with Ar+ etching
Table 4.3 The development of the binding energy of Pt4f7/2 and Pt4f5/2 with time
Ar+ (25mA, 3kV) 4f5/2 4f7/2
0 min 75.04 eV 71.77 eV
3 min 74.99 eV 71.76 eV
6 min 75.03 eV 71.77 eV
9 min 75.07 eV 71.80 eV
88 86 84 82 80 78 76 74 72 70 68
Intesity (a.u.)
4f7/2 4f5/2
Binding Energy (eV)
00 min sputter 03 min sputter 06 min sputter 09 min sputter
4.2.3 Analysis of dispersive Pt on MWNTs
Pt nanoparticles are actually deposited onto the surface of MWNTs from the last section. Then, by comparing Pt on the raw and modified MWNTs, we would like to understand the influence of the functional groups on Pt dispersion on MWCTNs. Fig.
4.11 illustrates many Pt nanoparticles are agglomerated on some areas like a larger nanoparticle. Fig. 4.12 illustrates many Pt nanoparticles disperse uniformly on HNO3-MWNTs due to presence of the carboxylic acids (-COOH). If Pt nanoparticles were agglomerated, the total effective activating catalyst area would decrease due to the clustered shelter of Pt nanoparticles. Therefore, MWNTs have to be modified chemically in order to disperse Pt nanoparticles on MWNTs uniformly.
4.2.4 EDX analysis of Pt on MWNTs
Pt loading on carbon nanotube would be increased because more functional groups, the carboxylic acids (-COOH), act nucleation sites and make active catalyst areas large.
The energy dispersive analysis in Fig. 4.13, Fig. 4.14, Fig. 4.15, and Fig. 4.16 show that the amount of Pt loaded on MWNTs with reference to carbon can be evaluated qualitatively as 16.88 wt%, 21.23 wt%, 22.84 wt%, and 26.08 wt% after the different chemical modification. The most Pt loading on MWNTs modified by HNO3 (strong oxidizing agent) in Fig. 4.17 may be suggested that the most functional groups would be formed on the surface of MWNTs at the same time with different chemical solutions.
Fig. 4.11 Pt nanoparticles are agglomerated like a larger nanoparticle
Fig. 4.12 Pt nanoparticles disperse uniformly on HNO3-MWNTs
100.00
Fig. 4.13 The amount of Pt loading on raw MWNTs is 16.88 wt%.
Fig. 4.14 The amount of Pt loading on KOH -MWNTs is 21.23 wt%.
Fig. 4.15 The amount of Pt loading on H2SO4 -MWNTs is 22.84 wt%.
Fig. 4.16 The amount of Pt loading on HNO3-MWNTs is 26.08 wt%.
Fig. 4.17 Pt loading on MWNTs with different chemical modification 100.00
Totals
2.13 26.08
Pt
97.87 73.92
C
Atomic%
Weight%
Element
WO KOH H2SO4 HNO3
0 10 20 30
40
Pt EDXPt weight %
4.2.5 Half-cell test
The activity of catalyst is practically important in the study on fuel cell, which is usually evaluated by the current peaks with the dispersion and the amount of catalyst.
The electrocatalytic activity of Pt nanoparticles is obtained from the CV measurements performed in 1M methanol and 1M sulfuric acid electrolyte. Fig. 4.18 shows that the electrocatalytic activity of Pt nanoparticles is evaluated by the current peaks of methanol oxidation in eq. (3) and eq. (4)
Pt-CO+Pt-OH 2Pt+CO2+H++e-
(3)
Pt-(CH3OH)ads Pt-(CO)ads+4H++4e-
(4)
As well known, it can be observed that the electrocatalytic activity of Pt nanoparticles on HNO3-MWNTs is higher than the others due to more amounts of dispersive Pt nanoparticles.
4.2.6 Summary
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 precursor 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.
W/O KOH H2SO4 HNO3
-Fig. 4.18 Electrocatalytic activity is evaluated by the current peaks
W/O KOH H2SO4 HNO3
(1) Pt-CO+Pt-OH -> 2Pt+ CO
2+H++e
4.3. Multi-wall carbon nanotubes are modified by HNO
3with Temperature (T), time (t), and concentration (conc.).
MWNTs are modified by HNO3, H2SO4, and KOH at high temperature in Section 4.2 and may produce the same functional groups, the alcoholic hydroxyl groups (-OH) and carboxylic acids (-COOH), to attract more Pt ions nucleating uniformly and densely.
Moreover, 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. However, there are the other parameters, temperature, time, and concentration, in the function of chemical modification for MWNTs. In this work, we would find the best temperature (T) for HNO3-MWNTs may produce a lot of functional groups to increase Pt anchoring sites in Table. 4.4. Furthermore, for 2M HNO3, the highest temperature would be lower 1000C to maintain the concentration.
Table 4.4 HNO3-MWNTs with different T
Temperature (T) 800C 900C 1000C 2M HNO3
(b.p. ~1050C)
24 hr 24 hr 24 hr
14M HNO3
(b.p. ~1220C)
24 hr 24 hr 24 hr
4.3.1.1 Analysis of MWNTs morphology with T
Fig. 4.19 and Fig. 4.20 show that there is little damage for 14 M HNO3-MWNTs at 800C and 900C for 24 hr. On the contrary, Fig. 4.21 shows that there is a serious damage for 14 M HNO3-MWNTs at 1000C for 24 hr. The total loading amount of Pt would decrease if the amount of MWCNT as support were broken. Therefore, the temperature of chemical modification would be lower than 1000C.
4.3.1.2 Analysis of functional groups with T
We try to assay the functional groups with FTIR after MWNTs are modified by 2 M or by 14 M HNO3 with temperature. Fig. 4.22(a) (b) show that oxidization with HNO3 at 900C and 1000C successfully introducedcarboxylic acids (-COOH), carboxyl groups (-C=O), and alcoholic hydroxyl groups (-OH) on MWNTs surfaces. However, the functional groups of 2M and 14M HNO3-MWNTs at 800C would be difficult to be detected because of their weak response in the IR mode. It is suggested that temperature is a main factor if the oxidization of chemical reaction could proceed. Finally, 900C is the optimum temperature for 2M and 14M HNO3-MWNTs to form a lot of functional groups.
Fig. 4.19 Little damage for 14M HNO3-MWNTs at 800C
Fig. 4.20 Little damage for 14M HNO3-MWNTs at 900C
Fig. 4.21 A serious damage for 14M HNO3-MWNTs at 1000C
Fig. 4.22 (a) FTIR of 2M HNO3-MWNTs with different T
Fig. 4.22 (b) FTIR of 14M HNO3-MWNTs with different T
4000 3000 2000 1000
From Section 4.3.1, the modified MWNTs at 900C form a lot of functional groups for 2 M HNO3 and14 M HNO3. In the followed Section 4.3.2 and Section 4.3.3, we would find the other best parameters time (t) with high (14M) and low (2M) concentration (conc.) for HNO3-MWNTs may produce the most functional groups to increase Pt anchoring sites in Table. 4.5
Table 4.5 MWNTs are modified by HNO3 at 900C for 2M and 14M with t
900C Time (hr)
2M HNO3 00 06 12 18 24 48
14M HNO3 00 06 12 18 24 48
4.3.2.1 FTIR of 2M HNO
3-MWNTs with t
The number of carboxylic acids (-COOH) would be expected by its intensity in the FTIR spectrum as MWNTs (0.01g) are diluted with a potassium bromide (KBr) dispersedly [32]. Fig. 4.23 shows that the number of carboxylic acids (-COOH) would increase with time gradually so more Pt could be anchored on MWNTs by more carboxylic acids (-COOH).
4.3.2.2 EDX analysis of Pt/2M HNO
3-MWNTs
Pt loading on carbon nanotube would be increased because more functional groups, the carboxylic acids (-COOH), act nucleation sites and make active catalyst areas large.
The energy dispersive analysis in Fig. 4.24, Fig. 4.25, Fig. 4.26, Fig. 4.27 and Fig. 4.28 show that the amount of Pt loaded on MWNTs with reference to carbon can be evaluated qualitatively as 14.37 wt%, 16.72 wt%, 24.38 wt%, 28.21 wt%, and 26.99 wt% after the chemical modification of 2M HNO3 with time. As mentioned above, 2M HNO3-MWNTs from 12 hr to 24 hr may anchor the most amount of Pt in Fig. 4.29.
Therefore, it is called stable state for the most loading of Pt.
4.3.2.3 Half-cell test
The activity of catalyst is practically important in the study on fuel cell, which is usually evaluated by the current peaks with the dispersion and the amount of catalyst.
The electrocatalytic activity of Pt nanoparticles is obtained from the CV measurements performed in 1M methanol and 1M sulfuric acid electrolyte. Fig. 4.30 shows that the electrocatalytic activity of Pt nanoparticles is evaluated gradually by the current peaks of methanol oxidation. As a whole, it can be observed that the highest electrocatalytic activity of Pt nanoparticles for 2M HNO3-MWNTs range from 12 hr to 24 hr (stable state) due to the most amounts of dispersive Pt nanoparticles. However, the electrocatalytic activity of Pt nanoparticles for 2M HNO3-MWNTs decreases much significantly from 24 hr to 48 hr because MWNTs may be destroyed very much at 48 hr.
4.3.2.4 Effective activating area
The electrochemically active surface areas of the Pt nanoparticles are obtained from the CV measurements performed in 1M sulfuric acid electrolyte. A typical
reference platinum electrode. The hydrogen absorption and desorption peaks are clearly seen in the voltammogram at potentials between -0.1 and 0.2 V, which is consistent with those observed for platinized Pt. In detail, a redox peak at 0.5-0.7 V in all voltammograms can be attributed to the quinine and hydroquinone groups. Furthermore, there is a couple of redox peak at about 0.4 V, which may be associated with the C-O and C=O groups [41].
The electrochemically active surface area, Sact, in units of cm2/mg Pt, is calculated from the CV curves for Pt [42] by eq. (5)
Sact 210QH
= (5)
In which QH, in units of (mA/mg Pt) V, is the integrated area of the hydrogen adsorption region in the voltammogram and the charge for monolayer hydrogen adsorption on Pt equal to 210 μC/ cm2. To obtain the integrated area for the hydrogen adsorption peaks in Fig. 4.31, a horizontal line is drawn to correct the double-layer charging, and a vertical line is drawn to separate the molecular hydrogen region [42].
Thus, in Table 4.6, the electrochemically active surface areas of the Pt nanoparticles are evaluated gradually with the time of 2M HNO3-MWNTs due to the trend of the electrocatalytic activity of Pt nanoparticles.
Fig. 4.23 The number of -COOH would increase with t gradually
Fig. 4.24 The amount of Pt loading on raw MWNTs is 14.37 wt%
4000 3000 2000 1000
Fig. 4.25 The amount of Pt loading on 2M HNO3-MWNTs at 6 hr is 16.72 wt%
Fig. 4.28 The amount of Pt loading on 2M HNO3-MWNTs at 24 hr is 26.99 wt%
Fig. 4.29 2M HNO3-MWNTs from 12 hr to 24 hr may anchor the most Pt 100.00
Totals
2.23 26.99
Pt
97.77 73.01
C
Atomic%
Weight%
Element
0 5 10 15 20 25 0
10 20 30
40 Pt EDX
Pt weight %
Time (hr)
Stable state
Fig. 4.30 The currents peaks represent the activity of Pt with t
Fig. 4.31 Electrochemically active surface areas of Pt with t
Table 4.6 The value of electrochemically active surface areas of the Pt with the t Time of 2M HNO3 QH (mC) S pt (cm2)
00hr 0.28363 1.35064
06hr 0.43399 2.0666
12hr 0.44241 2.10672
18hr 0.52727 2.51081
24hr 0.6042 2.877
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -0.01
0.00 0.01
Current density (A/cm 2 )
Potential (V)
no treatment 2M HNO
3 06hr 2M HNO
3 12hr 2M HNO
3 18hr 2M HNO
3 24hr
4.3.3.1 FTIR of 14M HNO
3-MWNTs with t
The number of carboxylic acids (-COOH) would be expected by its intensity in the FTIR spectrum as MWNTs (0.01g) are diluted with a potassium bromide (KBr) dispersedly [32]. Fig. 4.32 shows that the number of carboxylic acids (-COOH) for 14M HNO3-MWNTs would increase with time more fast than for 2M HNO3-MWNTs so more Pt nanoparticles could be anchored on MWNTs in the short time.
4.3.3.2 EDX analysis of Pt/14M HNO
3-MWNTs
Pt loading on carbon nanotube would be increased because more functional groups, the carboxylic acids (-COOH), act nucleation sites and make active catalyst areas large.
The energy dispersive analysis in Fig. 4.33, Fig. 4.34, Fig. 4.35, Fig. 4.36 and Fig. 4.37 show that the amount of Pt loaded on MWNTs with reference to carbon can be evaluated qualitatively as 15.38 wt%, 26.52 wt%, 27.94 wt%, 25.79 wt%, and 25.95 wt% after the chemical modification of 14M HNO3 with time. As mentioned above, 14M HNO3-MWNTs from 6 hr to 24 hr may anchor the most amount of Pt in Fig. 4.38.
Thus, it is called stable state for the most loading of Pt.
4.3.3.3 Half-cell test
The activity of catalyst is practically important in the study on fuel cell, which is usually evaluated by the current peaks with the dispersion and the amount of catalyst.
The electrocatalytic activity of Pt nanoparticles is obtained from the CV measurements performed in 1M methanol and 1M sulfuric acid electrolyte. Fig. 4.39 shows that the
of methanol oxidation. As a whole, it can be observed that the highest electrocatalytic activity of Pt nanoparticles for 14M HNO3-MWNTs range from 6 hr to 24 hr (stable state) due to the most amounts of dispersive Pt nanoparticles. However, like the decay of the electrocatalytic activity for 2M HNO3-MWNTs, the electrocatalytic activity of Pt nanoparticles for 14M HNO3-MWNTs decreases much significantly from 24 hr to 48 hr because MWNTs may be destroyed very much at 48 hr.
4.3.3.4 Effective activating area
The electrochemically active surface areas of the Pt nanoparticles are obtained from the CV measurements performed in 1M sulfuric acid electrolyte. A typical voltammogram is shown in Fig. 4.40, in which the potential is expressed versus that of a reference platinum electrode. It is the same as 2M HNO3-MWNTs to obtain the integrated area for the hydrogen adsorption peaks in Fig. 4.40. Thus, a horizontal line is drawn to correct the double-layer charging, and a vertical line is drawn to separate the molecular hydrogen region [42]. Moreover, in Table 4.7, the electrochemically active surface areas of the Pt nanoparticles for 14M HNO3-MWNTs from 6 hr to 24 hr are in the stable state due to the trend of the electrocatalytic activity of Pt nanoparticles.
4.3.4 Summary
1. Temperature is one of the main factors if MWNTs modified by HNO3 form functional groups -COOH and –OH.
2. 2M and 14M HNO3-MWNTs at 800C are unfavorable to form functional groups.
3. The modified MWNTs at 1000C could oxidize and destroy the surface of MWNTs very much.
4. 900C is the optimum temperature for 2M and 14M HNO3-MWNTs to form functional groups.
5. 2M HNO3-MWNTs form a lot of functional groups (stable state) from 12hr to 24hr.
6. 14M HNO3-MWNTs form a lot of functional groups (stable state) from 6hr to 24hr.
2. Higher concentration of HNO3 allows the surface of MWNTs to form functional groups quickly.
Fig. 4.32 The number of -COOH would increase with t gradually
Fig. 4.33 The amount of Pt loading on raw MWNTs is 15.38 wt%
4000 3000 2000 1000
Fig. 4.34 The amount of Pt loading on 14M HNO3-MWNTs at 6 hr is 26.52 wt%
Fig. 4.37 The amount of Pt loading on 14M HNO3-MWNTs at 24 hr is 25.95 wt%
Fig. 4.38 14M HNO3-MWNTs from 6 hr to 24 hr may anchor the most Pt 100.00
Totals
2.11 25.95
Pt
97.89 74.05
C
Atomic%
Weight%
Element
0 5 10 15 20 25
0 10 20 30
40 Pt EDX
Time (hr)
Pt weight %
Stable state
Fig. 4.39 The currents peaks represent the activity of Pt with t