Synthesis and characterization of m doped tio2 (m=w, ir) materials as supports for platinum nanoparticles to improve catalytic activity and durability in fuel cells

VIETNAM NATIONAL UNIVERSITY - HO CHI MINH CITY
UNIVERSITY OF TECHNOLOGY

TAI THIEN HUYNH

SYNTHESIS AND CHARACTERIZATION OF M-DOPED TIO2
(M=W, Ir) MATERIALS AS SUPPORTS FOR PLATINUM
NANOPARTICLES TO IMPROVE CATALYTIC ACTIVITY
AND DURABILITY IN FUEL CELLS

DOCTORAL DISSERTATION

HO CHI MINH CITY, 2020


VIETNAM NATIONAL UNIVERSITY - HO CHI MINH CITY
UNIVERSITY OF TECHNOLOGY

TAI THIEN HUYNH

SYNTHESIS AND CHARACTERIZATION OF M-DOPED TIO2
(M=W, Ir) MATERIALS AS SUPPORTS FOR PLATINUM
NANOPARTICLES TO IMPROVE CATALYTIC ACTIVITY
AND DURABILITY IN FUEL CELLS

Major subject: Chemical Engineering
Major subject code: 62520301

Advisor: 1. ASSOC. PROF. VAN THI THANH HO
2. DR. SON TRUONG NGUYEN

i


PLEDGE
I pledge that this dissertation is my own research under the direction of the Assoc.
Prof. Van Thi Thanh Ho and Dr. Son Truong Nguyen. The research results and
conclusions in this dissertation are honest, and not copied from any one source and in any
form. The reference to the sources of documents (if any) has been cited and the reference
sources are recorded as prescribed.

Signature

Tai Thien Huynh

ii


ABSTRACT
Low-temperature fuel cell systems have been drastically gaining attention
because of their high energy production efficiency and near-zero emissions that can
solve the serious reliance on fossil fuel. In fuel cell technology, electrocatalysts play
an important role at anode electrode and cathode electrode which directly impact the
fuel cell performance. Nowadays, carbon-supported Platinum catalysts are widely
utilized in fuel cell technologies, however, they exhibit some restrictions; namely, poor
durability due to the corroded carbon leading to sintering/detachment and
agglomeration of Pt nanocatalysts, sluggish kinetics of fuel anodic oxidation and
oxygen reduction reaction (ORR), CO poisoning of active sites of platinum
nanocatalyst at even low CO concentration (< 5 ppm) causing significant performance
deterioration in the long-term operating condition of fuel cells.
Up to now, developing robust electrocatalysts is still a major challenge for

further commercialization of fuel cell technologies. One of the most effective
approaches to solve these problems is to use non-carbon materials, which have
emerged as promising alternative catalyst supports due to the superior corrosion
resistance in electrochemical media and strong interaction with Pt nanocatalysts and
therefore, the electrocatalytic activity and stability of Pt-based catalysts can be
significantly enhanced. Among carbon-free supports, titanium dioxide (TiO2) material
has gained considerable attention in fuel cell application owing to superior
electrochemical stability, non-toxicity and affordability. Furthermore, the strong
metal-support interaction (so-called ―SMSI‖) between TiO2 support and Pt
nanocatalyst is a synergistic effect resulting in the significant enhancement of both
electrocatalytic activity and durability of this electrocatalyst. The intrinsic low
electrical conductivity of TiO2, however, is a major hindrance to be solved for its
further application in fuel cell technologies. Recently, doping strategy of titania with
transition metals has come to be known as the best way to enhance both the electronic
conductivity of TiO2 and electrochemical activity and durability of Pt-based catalysts
for fuel cell application.

iii


To this end, I introduce the combination between Platinum nanocatalysts and
M-doped TiO2 (M=W, Ir) supports, which were successfully synthesized by means of
one-pot synthesis without surfactants/stabilizers or further heat treatment, to assemble
robust 20 wt. % Pt/Ti0.7M0.3O2 (M=W, Ir) catalysts for the methanol oxidation reaction
(MOR) and oxygen reduction reaction (ORR). Experimental results demonstrated that
20 wt. % Pt/M-doped TiO2 (M=W, Ir) electrocatalysts are promising anodic and
cathodic electrocatalysts for low-temperature fuel cells.
In this work, a novel Pt catalyst supported on mesoporous Ti0.7W0.3O2, which
exhibited high conductivity (2.2x10-2 S.cm-1) and large specific surface area (201.481
m2.g-1), was prepared successfully via rapid microwave-assisted polyol route. It is

found that uniform 3 nm spherical-like Pt of nano-form adhered homogeneously on the
surface of Ti0.7W0.3O2. Intriguingly, the electrochemical surface area of the 20 wt. %
Pt/Ti0.7W0.3O2 was found to be ~90 m2.g-1Pt, which is profoundly higher than that of
the commercial 20 wt. % Pt/C (E-TEK) catalyst. For MOR, the If/Ib ratio of the 20 wt.
% Pt/Ti0.7W0.3O2 catalyst was found to be approximately 2.33, which is 2.5-fold higher
than that of the commercial 20 wt. % Pt/C (E-TEK) catalyst. Similarly, the
chronoamperometry data also revealed that the 20 wt. % Pt/Ti0.7W0.3O2 catalyst
possessed higher durability than the 20 wt. % Pt/C (E-TEK) catalyst. These
aforementioned results indicated the much higher catalytic activity and better COpoisoning tolerance toward MOR of the 20 wt. % Pt/Ti0.7W0.3O2 electrocatalyst which
could be due to the strong interaction (SMSI) between Pt and M-doped TiO2 support
leading to the weak adsorption of carbonaceous species on the active sites of Pt and
thus increasing the catalyst’s activity and stability for the MOR in the direct methanol
fuel cell.
For the first time, novel Ti0.7Ir0.3O2 support was prepared by means of a one-pot
hydrothermal route as a catalyst support for Pt nanocatalysts to assemble robust
electrocatalyst for both anodic and cathodic catalysts in low-temperature fuel cells. For
starter, the electrochemical surface area (ECSA) of the 20 wt. % Pt/Ti0.7Ir0.3O2
nanoparticles (NPs) catalyst was found to be ~96.98 m2.g-1Pt, which is higher the 20
wt. % Pt/C (E-TEK) catalyst. For MOR, the superior catalytic activity and CO
tolerance of the 20 wt. % Pt/Ti0.7Ir0.3O2 electrocatalyst compared to the 20 wt. % Pt/C
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(E-TEK) catalyst was demonstrated through the negative shift of 0.3 V, ~1.5-fold
higher oxidation current density and ~1.87-fold higher If/Ib ratio of the 20 wt. % Pt/C
(E-TEK) catalyst. For ORR, the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs electrocatalyst exhibited
the good onset potential, which was positively shifted ~90 mV, and high
electrocatalytic stability after 5000 cycling test compared to that of the 20 wt. % Pt/C
(E-TEK) catalyst. Besides, ―electronic transfer mechanism‖, which does not appear in
the conventional Pt/C catalyst, was founded in 20 wt. % Pt/Ti0.7Ir0.3O2 NPs catalyst

that could interpret for these enhancements of the robust Pt/Ti0.7Ir0.3O2 NPs catalyst.
Interestingly, even with low iridium doping concentration, the Ti0.9Ir0.1O2
support possessed a high electronic conductivity of 1.6x10-2 S.cm-1, which was ~105
times as high as pure TiO2 (1.37x10-7 S.cm-1), suggesting the efficient doping of
iridium into TiO2 lattice. The modified chemical reduction route utilized to fabricate
the 20 wt. % Pt/Ti0.9Ir0.1O2 electrocatalyst exhibited the good anchoring and uniform
distribution of Pt nanoparticles (~3 nm) over Ti0.9Ir0.1O2 surface and thus eventually
resulting in the high electrochemical surface area (~85 m2.g-1Pt) compared to that of
the 20 wt. % Pt/C (E-TEK) catalyst (~70 m2.g-1Pt). The cyclic voltammetry results in
the methanol media revealed that the 20 wt. % Pt/Ti0.9Ir0.1O2 exhibited superior
electrocatalytic activity compared to the 20 wt. % Pt/C (E-TEK) catalyst. For instance,
the 20 wt. % Pt/Ti0.9Ir0.1O2 catalyst possessed a higher oxidation current density (~28.8
mA/cm2), a lower onset potential (~0.12 V) and a higher If/Ib ratio in comparison with
the commercial 20 wt. % Pt/C (E-TEK) catalyst. It is worth noting that the
chronoamperometry results also indicated that the 20 wt. % Pt/Ti0.9Ir0.1O2 exhibited
higher durability than the commercial 20 wt. % Pt/C (E-TEK) catalyst. This effective
approach contributes to designing other advanced catalysts to revise conventional
catalysts in low-temperature fuel cells.

v


ACKNOWLEDGEMENTS
First of all, I would like to express my deepest gratitude to my advisors, Assoc
Prof. Dr. Van Thi Thanh Ho and Dr. Son Truong Nguyen for suggesting the problem,
supervising the work and being a potential source of inspiration at each stage of this
dissertation research work. I would like to express my deepest gratitude to Prof. Nam
Thanh Son Phan supported me during this dissertation research work at the HCMUT.
I would like to give deep thanks to Mr. Hau Quoc Pham for the collaboration
during 3 years of working together. The enthusiasm and generous support of him is

highly appreciated.
I would like to express my gratitude towards my students, Mr. At Van Nguyen,
Ms. Vi Thi Thuy Phan and Ms. Anh Ngoc Tram Mai for their consistent support in this
research. Without them, the research process will not be as smooth and I also
appreciate their valuable supports as well as help in achieving the results presented in
this dissertation.
I would like to thank the Faculty of Chemical Engineering - HCMUT, the
MANAR Laboratory - Faculty of Chemical Engineering – HCMUT, the Physical
Chemistry Laboratory – HCMUNRE, the Applied Physical Chemistry Laboratory –
HCMUS and the Key Laboratory of Polymer and Composite Materials – HCMUT for
their support during the research period.
My special thanks to my parents, my wife and my children for their love,
understanding, encouragement and consistent support throughout my dissertation
journey. Without their enthusiastic support, I could not complete my research.
Finally, I acknowledge The Young Innovative Science and Technology
Incubation Program, managed by Youth Promotion Science and Technology Center,
Hochiminh Communist Youth Union, HCMC, Vietnam (Project No. 17/2017/HĐKHCN-VƯ and Project No. 10/2018/HĐ-KHCN-VƯ) for financial support.

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TABLE OF CONTENTS
PLEDGE ..........................................................................................................................ii
ABSTRACT .................................................................................................................. iii
ACKNOWLEDGEMENTS ........................................................................................... vi
TABLE OF CONTENTS ..............................................................................................vii
LIST OF TABLES ......................................................................................................... xi
LIST OF FIGURES .......................................................................................................xii
LIST OF SYMBOLS AND ABBREVIATIONS ......................................................... xix
THE MOTIVATION OF RESEARCH ........................................................................... 1

CHAPTER 1. INTRODUCTION AND LITERATURE REVIEW ................................ 3
1.1.

Fuel cell systems ...................................................................................................3

1.1.1. Overview of fuel cell technologies ....................................................................... 3
1.1.2. Proton Exchange Membrane Fuel Cell ................................................................. 8
1.1.3. Direct Methanol Fuel Cell .................................................................................. 12
1.1.4. Challenges and current issues of fuel cell systems ............................................. 15
1.2.

Non-carbon support materials .............................................................................17

1.2.1. Tungsten trioxide (WO3) material ...................................................................... 18
1.2.2. Iridium dioxide (IrO2) material........................................................................... 20
1.2.3. Titanium dioxide (TiO2) material ....................................................................... 20
1.2.4. Metal-doped TiO2 materials ............................................................................... 23
1.3.

W-doped TiO2 material .......................................................................................26

1.4.

Ir-doped TiO2 material ........................................................................................27

1.5.

Methods for synthesizing M-doped TiO2 materials ............................................28

vii

1.5.1. Sol-gel method .................................................................................................... 28
1.5.2. Hydrothermal method ......................................................................................... 28
1.5.3. Solvothermal method .......................................................................................... 29
1.5.4. Other methods ..................................................................................................... 30
1.6.

Methods for preparing Pt-based catalyst .............................................................30

1.6.1. Polyol method ..................................................................................................... 30
1.6.2. Chemical reduction method ................................................................................ 30
1.7.

Objectives of thesis research ...............................................................................31

CHAPTER 2. MATERIALS AND EXPERIMENT ..................................................... 34
2.1.

Materials ..............................................................................................................34

2.2.

Experimental procedure ......................................................................................34

2.2.1. Synthesis of W-doped TiO2 ................................................................................ 35
2.2.2. Synthesis of 20 wt. % Pt/Ti0.7W0.3O2 catalyst ................................................... 36
2.2.3. Synthesis of Ir-doped TiO2 ................................................................................. 38
2.2.4. Synthesis of Pt/Ti0.7Ir0.3O2 catalyst ..................................................................... 40
2.3.

Characterization techniques ................................................................................41

2.3.1. X-ray diffraction (XRD) ..................................................................................... 41
2.3.2. X-ray photoelectron spectroscopy (XPS) ........................................................... 41
2.3.3. Scanning electron microscopy with energy dispersive X-ray spectroscopy
(SEM-EDX) ................................................................................................................... 42
2.3.4. Transmission electron microscopy (TEM) and High-resolution transmission
electron microscopy (HR-TEM).................................................................................... 43
2.3.5. Brunauer Emmett Teller (BET) surface area analysis ........................................ 43
2.3.6. Electrical conductivity measurements ................................................................ 43
2.3.7. Electrode preparation and electrochemical measurements................................. 44

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2.3.8. Electrochemical characterization techniques...................................................... 47
CHAPTER 3. HIGH CONDUCTIVITY AND SURFACE AREA OF Ti0.7W0.3O2
NANOSTRUCTURE

SUPPORT

FOR

Pt

NANOPARTICLES

TOWARD

ENHANCED METHANOL OXIDATION IN DMFC................................................. 53
3.1.

Synthesis of Ti0.7W0.3O2 support .........................................................................53

3.1.1. Effect of reaction temperature on W-doped TiO2 .............................................. 53
3.1.2. Effect of reaction time on W-doped TiO2 .......................................................... 55
3.2.

Characterization of the novel Ti0.7W0.3O2 support (optimum condition at 200oC

for 10 hours) ..................................................................................................................60
3.2.1. The structure of Ti0.7W0.3O2 and un-doped TiO2 ................................................ 60
3.2.2. X-ray photoelectron spectroscopy (XPS) of Ti0.7W0.3O2 ................................... 60
3.2.3. The morphology of Ti0.7W0.3O2 and un-doped TiO2 .......................................... 61
3.2.4. Elemental composition of Ti0.7W0.3O2 ................................................................ 62
3.2.5. BET surface area of the Ti0.7W0.3O2 ................................................................... 63
3.2.6. The electronic conductivity of the Ti0.7W0.3O2 ................................................... 65
3.3.

Synthesis of the 20 wt. % Pt/Ti0.7W0.3O2 catalyst................................................66

3.4.

Electrochemical properties of the 20 wt. % Pt/Ti0.7W0.3O2 catalyst ....................69

3.5.

Conclusion ...........................................................................................................74

CHAPTER 4. NEW Ir DOPED TiO2 NANOSTRUCTURE SUPPORT FOR
PLATINUM: ENHANCING CATALYTIC ACTIVITY AND DURABILITY FOR
FUEL CELLS ................................................................................................................ 75
4.1.

Synthesis of the Ti0.7Ir0.3O2 support ....................................................................75

4.1.1. Effect of reaction time on Ir-doped TiO2............................................................ 75
4.1.2. Effect of reaction temperature on Ir-doped TiO2 ............................................... 78
4.1.3. Effect of pH value on Ir-doped TiO2 .................................................................. 80

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4.2.

Novel Ti0.7Ir0.3O2 nanorod support prepared by a facile hydrothermal process: A

promising non-carbon support for Pt in PEMFC ..........................................................84
4.2.1. Characterization of novel Ti0.7Ir0.3O2 nanorod support ...................................... 84
4.2.2. Characterization of the 20 wt. % Pt/Ti0.7Ir0.3O2 NRs catalyst ............................ 88
4.2.3. Electrochemical properties of the 20 wt. % Pt/Ti0.7Ir0.3O2 NRs catalyst ............ 90
4.2.4. Conclusions ........................................................................................................ 95
4.3.

Advanced nanoelectrocatalyst of Pt nanoparticles supported on robust

Ti0.7Ir0.3O2 nanoparticles as a promising catalyst for fuel cells .....................................96
4.3.1. Characterization of Ti0.7Ir0.3O2 nanoparticles ..................................................... 96
4.3.2. Characterization of the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs catalyst ............................. 99

4.3.3. Electrochemical properties of the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs catalyst .......... 101
4.3.4.Conclusions ........................................................................................................ 110
4.4.

High conductivity of novel Ti0.9Ir0.1O2 support for Pt as a promising catalyst for

low-temperature fuel cell applications ........................................................................111
4.4.1. Characterization of the Ti0.9Ir0.1O2 support....................................................... 111
4.4.2. Characterization of the 20 wt. % Pt/Ti0.9Ir0.1O2 catalyst .................................. 115
4.4.3. Electrocatalytic properties of the 20 wt. % Pt/Ti0.9Ir0.1O2 catalyst ................... 116
4.4.4. Conclusions ...................................................................................................... 120
CONTRIBUTIONS OF THIS DISSERTATION ....................................................... 121
LIST OF PUBLICATIONS ......................................................................................... 124
LIST OF CONFERENCES ......................................................................................... 124
LIST OF RESEARCH PROJECTS............................................................................. 125
REFERENCES ............................................................................................................ 126

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LIST OF TABLES
Table 1. 1. Summary of main types of fuel cell systems 11 .............................................7
Table 1. 2. The particle size and the electrochemical surface area of Pt/TiO2 and Pt/C
electrocatalysts at potential 1.2 V for 0 hours and 80 hours 80 ......................................22
Table 2. 1. Materials for this research ...........................................................................34
Table 2. 2. The effect of reaction temperature on the synthesis of W-doped TiO2......36
Table 2. 3. The effect of reaction time on synthesis of W-doped TiO2.........................36
Table 2. 4. The effect of reaction time on the synthesis of Ir-doped TiO2 ....................39
Table 2. 5. The effect of reaction temperature on synthesis of Ir-doped TiO2..............39
Table 2. 6. The effect of pH value on synthesis of Ir-doped TiO2 ................................39

Table 3. 1. Electrochemical properties of the 20 wt. % Pt/Ti0.7W0.3O2 and others
electrocatalyst ................................................................................................................72
Table 4. 1. The methanol electro-oxidation characterization of our catalyst and other
electrocatalysts in the previous studies........................................................................105
Table 4. 2. The electrochemical properties of the 20 wt. % Pt/Ti0.9Ir0.1O2 and other
catalysts in the previous studies ..................................................................................118

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LIST OF FIGURES
Figure 1. 1. A series of experiments of William Grove ..................................................3
Figure 1. 2. The basic structure of a fuel cell system ......................................................4
Figure 1. 3. Applications of different fuel cells ..............................................................5
Figure 1. 4. Advantages of fuel cell systems compared to others generating power ......6
Figure 1. 5. Some commercialized cars using PEMFC ...................................................8
Figure 1. 6. Proton Exchange Membrane Fuel Cell (PEMFC) .......................................9
Figure 1. 7. Polymer Electrolyte Membrane (PEM) fuel cell stacks ............................11
Figure 1. 8. The direct methanol fuel cell (DMFC) system ..........................................12
Figure 1. 9. The activity performance of electrocatalysts decrease 20 ...........................15
Figure 1. 10. TEM of Pt/C catalyst before 0 cycle (a) and 3600 cycles (b) 23 ..............16
Figure 1. 11. The activity degradation of Pt/C catalyst 28 .............................................17
Figure 1. 12. Mechanism transition of nanotube H-titanate to single-phase TiO2 with
the different morphology and structure 84 .....................................................................21
Figure 1. 13. The strong interaction between Pt and TiO2 (SMSI) 87 ...........................23
Figure 1. 14. The ―electron transition‖ mechanism from Ti0.7Ru0.3O2 to Pt versus that
Pt foil and the commercial Pt/C 95 .................................................................................25
Figure 1. 15. The ―electron transition‖ mechanism of Pt/Ti0.7Mo0.3O2 catalyst 88 ........25
Figure 2. 1. Process for preparing W-doped TiO2 .........................................................35
Figure 2. 2. Schematic drawing for synthesis Pt/Ti0.7W0.3O2 catalyst via microwaveassisted polyol route ......................................................................................................37

Figure 2. 3. Procedure for preparing Ir-doped TiO2 ......................................................39
Figure 2. 4. Schematic drawing for synthesizing Pt/Ti0.7Ir0.3O2 catalyst ......................40
Figure 2. 5. The basic principle of XPS ........................................................................42
Figure 2. 6. Three-electrode electrochemical cell for measuring polarization curve ....46
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Figure 2. 7. CV of Pt supported on carbon black in 0.5 M H2SO4 solution ..................48
Figure 2. 8. ORR polarization curves Pt supported on carbon black in oxygen saturated
0.5 M H2SO4 electrolyte solution ..................................................................................49
Figure 2. 9. The cyclic voltammogram of Pt/C catalyst for methanol oxidation 164 .....52
Figure 3. 1. XRD profile of WTO_180_4; WTO_200_4; WTO_220_4 samples .........53
Figure 3. 2. TEM images of WTO_180_4 at different scale bar (a) 100 nm;

(b)

nm

54

50

Figure 3. 3. TEM images of WTO_200_4 at scale bar (a) 50 nm; (b) 20 nm ...............54
Figure 3. 4. TEM images of WTO_220_4 at scale bar (a) 50 nm; (b) 20 nm ............55
Figure 3. 5. XRD profile of WTO_220_2, WTO_220_4, WTO_220_6 .......................56
Figure 3. 6. TEM images of (a) WTO_220_2, (b) WTO_220_4 and
WTO_220_6

(c)
57

Figure 3. 7. XRD profile of WTO_200_4, WTO_200_6, WTO_200_8 and
WTO_200_10 samples ..................................................................................................58
Figure 3. 8. TEM images of WTO_200_6 with scale bar (a) 50nm, (b) 20nm .............58
Figure 3. 9. TEM images of WTO_200_8 with scale bar (a) 50nm, (b) 20nm .............59
Figure 3. 10. TEM images of WTO_200_10 with scale bar (a) 50nm, (b) 20nm .........59
Figure 3. 11. XRD profile of WTO_200_10 and TO_200_10 in the 2range of (a) 20o80o and (b) 20o-30o ........................................................................................................60
Figure 3. 12. X-ray photoelectron spectroscopy (XPS) of (a) Ti 2p and (b) W 4f .......61
Figure 3. 13. TEM images of (a) TiO2 and (b) Ti0.7W0.3O2 at 200oC for 10 hours .......61
Figure 3. 14. (a) SEM image, (b) EDX spectroscopy, (c) XRF spectroscopy and (d-f)
elemental mapping of the Ti0.7W0.3O2 ...........................................................................62
Figure 3. 15. N2 adsorption/desorption isotherms of (a) un-doped TiO2; (b)
Ti0.7W0.3O2; inset: the pore size distribution of catalyst supports .................................63

xiii


Figure 3. 16. Comparison of the surface area of Ti0.7W0.3O2 with other supports in the
previous studies .............................................................................................................64
Figure 3. 17. Comparison of the electronic conductivity of Ti0.7W0.3O2 with other
supports in the previous studies .....................................................................................65
Figure 3. 18. XRD profile of the 20 wt. % Pt/Ti0.7W0.3O2 catalyst ...............................66
Figure 3. 19. (a) SEM image; (b) EDX spectroscopy and (c-e) the elemental mapping
of 20 wt. % Pt/Ti0.7W0.3O2 catalysts. .............................................................................67
Figure 3. 20. (a, b) TEM, (c) HR-TEM of the20 wt. % Pt/Ti0.7W0.3O2 catalyst ...........68
Figure 3. 21. X-ray photoelectron spectroscopy of (a) 20 wt. % Pt/Ti0.7W0.3O2; (b) Pt
4f and (c) Ti 2p of the as-synthesized 20 wt. % Pt/Ti0.7W0.3O2 catalyst .......................69
Figure 3. 22. Cyclic voltammogram of the electrocatalysts in N2-purged 0.5 M H2SO4
at a scan rate of 50 mV.s-1, inset: HR-TEM of Pt/Ti0.7W0.3O2 catalyst .........................70
Figure 3. 23. Cyclic voltammogram of methanol oxidation; inset: the onset oxidation

potential of the Pt/Ti0.7W0.3O2 and Pt/C (E-TEK) catalysts in N2-purged 10 v/v %
CH3OH/0.5 M H2SO4 solution at a scan rate of 50 mV.s-1 ...........................................71
Figure 3. 24. Cyclic voltammograms of (a) the 20 wt. % Pt/Ti0.7W0.3O2 catalyst and (b)
the 20 wt. % Pt/C (E-TEK) catalyst for 2000 cycles in N2-purged 10 v/v % CH3OH/0.5
M H2SO4 solution with scan rate of 50 mV.s-1 ..............................................................73
Figure 3. 25. Chronoamperometry curves of the electrocatalysts in N 2-purged 10 v/v %
CH3OH in 0.5 M H2SO4 solution at the oxidation potential 0.7 for 60 min .................73
Figure 4. 1. The XRD profile of the as-synthesized Ti0.7Ir0.3O2 at 210oC, pH=0 for the
different reaction times ..................................................................................................75
Figure 4. 2. TEM images of the as-synthesized Ti0.7Ir0.3O2 at 210oC, pH=0 with
reaction time (a) 12 hours; (b) 10 hours; (c) 8 hours and (d) 6 hours ...........................76
Figure 4. 3. SEM image and EDX spectroscopy of Ti0.7Ir0.3O2 at 210oC for 8 hours ...77
Figure 4. 4. The influence of reaction time to the electrical conductivity of materials 78

xiv


Figure 4. 5. XRD profile of Ir-doped TiO2 at pH=0 for 10 hours with different reaction
temperature ....................................................................................................................79
Figure 4. 6. TEM images of Ir-doped TiO2 for 10 hours at (a) 190oC and (b) 170oC...79
Figure 4. 7. SEM - EDX spectroscopy of Ti0.7Ir0.3O2 at 190oC for 10 hours ................80
Figure 4. 8. XRD profile of the as-synthesized Ti0.7Ir0.3O2 at 210oC for 8 hours with the
different pH value ..........................................................................................................81
Figure 4. 9. TEM images of Ti0.7Ir0.3O2 were prepared at 210oC for 8 hours with (a, b)
pH value of 0; (c, d) pH value of 1 and (e, f) pH value of 2 .........................................82
Figure 4. 10. (a) XRD profile and TEM image (inset) of Ti0.7Ir0.3O2 NR; (b) XRD
profile of Ti0.7Ir0.3O2 NR in the range from 25o to 30o; (c-e) XPS of Ti0.7Ir0.3O2 NRs..85
Figure 4. 11. The TEM image of Ti0.7Ir0.3O2 NRs with different scale bar for overview
(a,b) and local (high resolution) observation (c,d) .......................................................86
Figure 4. 12. SEM-EDX of the Ti0.7Ir0.3O2 support.......................................................87

Figure 4. 13. The comparison of electrical conductivity between Ti0.7Ir0.3O2 NRs and
other non-carbon materials in the previous research .....................................................88
Figure 4. 14. X-ray diffraction pattern of 20 wt. % Pt/Ti0.7Ir0.3O2 NRs ........................88
Figure 4. 15. TEM images of Pt nanoparticles deposited on Ti0.7Ir0.3O2 NRs with
different scale bar for overview (a, b) and local observation (c, d) ..............................89
Figure 4. 16. Cyclic voltammograms of Pt/Ti0.7Ir0.3O2 NRs catalysts and commercial
Pt/C (E-TEK) and in 0.5 M H2SO4 at a scan rate of 50 mV.s-1 .....................................90
Figure 4. 17. The cyclic voltammograms after 2000 cycles of the 20 wt. %
Pt/Ti0.7Ir0.3O2 NRs catalyst and 20 wt. % Pt/C (E-TEK) catalyst in 0.5 M H2SO4
electrolyte solution at 25 oC at a scan rate of 50 mV.s-1................................................91
Figure 4. 18. The TEM images (a, b) of the 20 wt. % Pt/Ti0.7Ir0.3O2 NRs catalyst and
(c, d) the 20 wt. % Pt/C (E-TEK) catalyst before and after the stability test ................92

xv


Figure 4. 19. Polarization curves showed ORR current of the 20 wt. % Pt/Ti0.7Ir0.3O2
NRs catalyst and the 20 wt. % Pt/C (E-TEK) catalyst with the scan rate of 1 mV.s-1;
(inset) the onset potential evaluation .............................................................................93
Figure 4. 20. ORR polarization curves after 2000 cyclic voltammetry cycles of (a) 20
wt. % Pt/Ti0.7Ir0.3O2 NRs catalyst and (b) 20 wt. % Pt/C (E-TEK) catalyst, (c) the mass
activity before and after stabilizing test of the electrocatalysts.....................................94
Figure 4. 21. (a) XRD profile and (b, c) TEM images of Ti0.7Ir0.3O2 NPs ....................96
Figure 4. 22. (a) XPS spectroscopy of Ti0.7Ir0.3O2 NPs; (b) XPS spectroscopy of Ti 2p
and (c) XPS spectroscopy of Ir 4f in Ti0.7Ir0.3O2 nanoparticles .....................................97
Figure 4. 23. (a) XRF spectroscopy; (b) EDX spectroscopy and (c-e) elemental
mapping of Ti, Ir, O of Ti0.7Ir0.3O2 nanoparticles ..........................................................98
Figure 4. 24. Comparison surface area the Ti0.7Ir0.3O2 and other non-carbon materials99
Figure 4. 25. (a, b) TEM images, (c) HR-TEM image, (d) SEM image, (e) EDX
spectroscopy and (f-h) elemental mapping of the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs ..........100

Figure 4. 26. The cyclic voltammograms of the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs and 20 wt.
% Pt/C (E-TEK) catalysts in N2-purged 0.5 M H2SO4 solution at a sweep rate of 25
mV.s-1; inset: the estimated ECSA value of electrochemical catalysts .......................101
Figure 4. 27. Cyclic voltammograms of (a) the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs catalyst
and (b) the 20 wt. % Pt/C (E-TEK) catalyst in N2-purged 0.5 M H2SO4 at a scan rate of
25 mV.s-1 after potential cycling over 2000 cycles .....................................................102
Figure 4. 28. TEM images of (a, b) the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs and (c, d) the 20
wt. % Pt/C (E-TEK) catalyst before and after 2000 cyclic voltammetry (CV) cycles103
Figure 4. 29. Cyclic voltammograms of the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs catalyst and 20
wt. % Pt/C (E-TEK) catalyst in N2-purged 10 v/v % CH3OH/0.5 M H2SO4 solution at a
scan rate of 25 mV.s-1; inset: the onset potential of electrocatalysts ...........................104
Figure 4. 30. Cyclic voltammograms of (a) the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs catalyst
and (b) the commercial 20 wt. % Pt/C (E-TEK) catalyst in N2-purged 10 v/v%

xvi


CH3OH/0.5 M H2SO4 solution at a scan rate of 25 mV.s-1 after 2000 cyclic
voltammetry (CV) cycles ............................................................................................106
Figure 4. 31. Chronoamperometry curves of the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs catalyst
and the 20 wt. % Pt/C (E-TEK) catalysts in N2-purged 10 v/v% CH3OH/0.5 M H2SO4
solution at the oxidation potential of 0.7 V for 60 min ...............................................107
Figure 4. 32. (a) Polarization curves of the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs and 20 wt. %
Pt/C (E-TEK) catalyst; ORR curves after 5000 cycling test of (b) the 20 wt. %
Pt/Ti0.7Ir0.3O2 NPs catalyst and (c) the 20 wt. % Pt/C (E-TEK) catalyst .....................108
Figure 4. 33. XPS spectroscopy of (a) the 20 wt. % Pt/Ti0.7Ir0.3O2 NPs catalyst;
Pt

4f

and

(c)

Ti

(b)
2p
10

9
Figure 4. 34. (a) X-ray diffraction pattern of Ti0.9Ir0.1O2 support and the 20 wt. %
Pt/Ti0.9Ir0.1O2 catalyst; (b) XRD pattern of Ti0.9Ir0.1O2 in the range from 24o to 30o ..111
Figure 4. 35. The XPS spectroscopy of O 1s core level of Ti0.9Ir0.1O2 .......................112
Figure 4. 36. TEM images of (a) Ti0.9Ir0.1O2 NPs, (b) un-doped TiO2 NPs, (c)
Pt/Ti0.9Ir0.1O2 and (d) HR-TEM image of Pt/Ti0.9Ir0.1O2 catalyst ................................113
Figure 4. 37. (a, b) SEM/ EDX and (c – e) elemental mapping of Ti0.9Ir0.1O2............114
Figure 4. 38. (a, b) SEM/ EDX and (c – e) elemental mapping of Pt/Ti0.9Ir0.1O2 .......116
Figure 4. 39. The CV curves of the 20 wt. % Pt/Ti0.9Ir0.1O2 and 20 wt. % Pt/C (E-TEK)
in N2-saturated 0.5 M H2SO4 solution at a scan rate of 50 mV.s-1 ..............................117
Figure 4. 40. The CV curves; inset: the onset potential of the 20 wt. % Pt/Ti0.9Ir0.1O2
and 20 wt. % Pt/C (E-TEK) in N2-saturated 10 v/v% CH3OH/0.5 M H2SO4 solution at
a scan rate of 50 mV.s-1 ...............................................................................................117
Figure 4. 41. The cyclic voltammetry curves after 2000 cycles of (a) the 20 wt. %
Pt/Ti0.9Ir0.1O2 and (b) the 20 wt. % Pt/C (E-TEK) in N2-saturated 10 v/v% CH3OH/0.5
M H2SO4 solution at a scan rate of 50 mV.s-1 .............................................................119

xvii

Figure 4. 42. The CA curves of the 20 wt. % Pt/Ti0.9Ir0.1O2 and 20 wt. % Pt/C (E-TEK)
in N2-saturated 10 v/v % CH3OH/0.5 M H2SO4 solution at the oxidation potential 0.7
V for 60 min ................................................................................................................120

xviii


LIST OF SYMBOLS AND ABBREVIATIONS
C

Carbon

CE

Counter electrode

CV

Cyclic voltammetry

DMFC

Direct methanol fuel cell

ECSA

Electrochemical surface area

Ir

Iridium

MOR

Methanol oxidation reaction

NRs

Nanorods

NPs

Nanoparticles

NHE

Normal hydrogen electrode

ORR

Oxygen reduction reaction

PEMFC

Proton exchange membrane fuel cell

Pt

Platinum

RDE

Rotating disc electrode

RE

Reference electrode

TIO

Ir-doped TiO2

W

Tungsten

WTO

W-doped TiO2

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THE MOTIVATION OF RESEARCH
Nowadays, countries all over the world are developing toward industrialization,
leading to demand for energy to get higher and higher. Besides that, climate change
and pollution issues resulting from utilizing fossil fuel become more and more serious.
These problems require us to discover renewable resources that are environmentally
friendly, possibly replacing fossil fuels. Among them, fuel cells are sources of
electricity that are consistent with current energy trends and promising in the energy

industry because they possess several dominant merits such as high efficiency, low
noise along with near-zero pollution and high adaptability to different energy levels for
various devices [1, 2].
The structure of fuel cell consists of three basic compartments: an anode
electrode, a cathode electrode, and an electrolyte. Anode and cathode electrodes are
made of carbon and covered with a catalyst layer to enhance fuel cell performance.
The electrolyte between the cathode electrode and the anode electrode is used to
transfer ions between two electrodes. The conventional catalysts are Pt nanoparticles
or Pt-M alloys. However, there exist several obstacles preventing fuel cells from
commercialization, namely the poor stability of the carbon electrode and high cost of
the Pt catalyst [3-5]. More importantly, severe corrosion of carbon electrode leads to
loss and agglomeration of Pt NPs on the support, thus declining fuel cells of
performance. Moreover, the weak interaction between the carbon support and the Pt
nanocatalyst also contributes to the dissolution of Pt nanoparticles bringing about the
significant decrease of electrochemical surface area (ECSA) of the catalyst, hence the
declined performance of fuel cells under long-term operation [6]. One effective
approach to these aforementioned problems is to use carbon-free support due to the
high structural and electrochemical durability in an acidic and oxidative environment
and the strong interaction between them and Pt nanocatalyst [3].
For these reasons, we propose to conduct the research on ―Synthesis and
characterization of M-doped TiO2 (M=W, Ir) materials as supports for platinum
nanoparticles to improve catalytic activity and durability in fuel cells‖. New stable
and effective supports were fabricated for Pt nanocatalyst to enhance its catalytic

1


activity and stability, resulting in improving the performance of fuel cells. This
research orientation contributes to not only economically due to a decrease in the
composition of noble Pt metal in catalysts but also environmentally owing to the green

energy source potential of fuel cells.

2


CHAPTER 1. INTRODUCTION AND LITERATURE REVIEW
1.1.

Fuel cell systems

1.1.1. Overview of fuel cell technologies
The concepts related to fuel cells were demonstrated in the early nineteenth century
by Humphry Davy. This was followed by pioneering work on what were to become
fuel cell systems by the scientist Christian Friedrich Schönbein. In 1839, the basic
operating principle of fuel cells was discovered by William Grove through a series of
experiments (Figure 1.1) which he termed a gas voltaic battery, ultimately proving
that electricity could be created from an electrochemical reaction between hydrogen
and oxygen over a Platinum catalyst. This principle, which he discovered remains
unchanged today.

Figure 1. 1. A series of experiments of William Grove
( />A fuel cell is an electrochemical ―device‖ in which chemical energy is directly
converted into electrical energy through electrochemical reactions of fuels (H2,
CH3OH, CH4…) and oxidants (O2, air…) to form electricity and byproducts such as
heat, water (a little amount of CO2 in the case of direct methanol fuel cells) [7]. Fuel
cells do not contain energy inside, but can rather directly convert fuels into electricity,
so as to produce electricity continuously as long as resources are supplied. Unlike

3

engines or conventional batteries, a fuel cell does not need recharging and produce
only power and drinking water. Thus, fuel cells have been regarded as clean and
potential sources of electrical power for the future [8, 9].

Figure 1. 2. The basic structure of a fuel cell system
( />A fuel cell system consists of an electrolyte in contact with an anode electrode
(negative electrode) and a cathode electrode (positive electrode) (Figure 1.2). The
electrolytes used in fuel cells include acid, base and molten salt. Nafion membrane is
widely used in fuel cells with the aim of allowing penetration of appropriate ions but
not electrons. In addition, the catalyst layer can be placed between the electrolyte and
the electrode or directly utilized as an electrode or deposited on the surface of
electrodes. Pure Pt or alloy of Pt and metals such as Ni, Ru, Co, etc. or carbon
supported catalysts in the forms of Pt/C or Pt-M/C are commonly used as catalysts.
The fuel cell system can generate different energy levels when joining fuel cells
with each other. Thus, fuel cell systems can supply energy source in the range of 1
Watt to 10 Megawatt, meeting several applications in their lifetime (Figure 1.3). At
low energy levels below 50 W, fuel cells can be used for mobile phones, laptops or
any other type of personal electronic equipment. In the 1 kW – 100 kW range a fuel

4


cell can be used to power vehicles both domestic and military. Public transportation is
also a target for fuel cells, along with any APU application. In the 1 MW – 10 MW
range fuel cells can be used to convert energy for distributed power uses (grid-quality
AC) [8-10].

Figure 1. 3. Applications of different fuel cells
( />Compare to other power devices, fuel cells possess several advantages (Figure 1. 4):

 A high power conversion efficiency: the efficiency increasing with lower
load is considered an important characteristic for transportation applications
where load operation is the key and an internal combustion engine (ICE) run
at reduced efficiency in low load conditions.
 Very low gas emission: The actual emission of fuel cell systems depends on
the fuel fed. For instance, the fuel as pure hydrogen results in true zeroemission performance since the only reaction product is water. Even if
natural gas or petrol is employed as a fuel through a reforming route, CO2
emission will be much lower than an internal combustion engine (ICE). In
addition, no toxic nitrogen oxides (NOx), sulfur oxides (SOx) are created.

5