5-1. Conclusions
The dependence of proton conductivities upon the pore sizes and surface properties of sulfated ZrO2 powders are compared and discussed. The proton conductivity increases with increasing surface areas. In contrast, it increases as pore sizes decrease. Reduction in the pore size enhances the conductivity till 2.8 nm. Post sulfation of the mesoporous ZrO2 samples with a 0.9 M H2SO4 solution increases their bulk content of sulfated species by 9 times and effectively promotes the conductivity from 2.0 to 9.5 ×10-2 S/cm. This value is twice higher than that of the commercial Nafion (5.2×10-2 S/cm). Polysulfated species, which is produced after calcination of the S-doped ZrO2 samples, introduces strong surface acid sites and contributes to the high proton conductivity. Both high surface acidity and microporous structure improve the capability of the samples for keeping water molecules at high temperatures. However, the highest proton conductivity was not given by these samples with the highest surface acidity or microporous texture. Appropriate surface acidity and pore size which exhibit adequate adsorption energy for water is required for efficient proton transport. In summary, an optimal combination of both the pore size (0.6-2.8 nm) and surface acidity can contribute to high proton conductivity.
71
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Appendix A. XPS patterns of S-ZrO
2180 178 176 174 172 170 168
C16S-ZrO2-sputter
C16S-ZrO2
ZrO2 TiO2-S
ZrO2-S
Binding Energy (eV)
Appendix A-1 XPS patterns of pure ZrO2
78
178 176 174 172 170 168 166
S
0.6M
1.2M 0.9M 0.3M C16S-ZrO
2
Binding Energy (eV)
Intensity (A.U.)
Appendix A-2 The S (2p) XPS spectra of the C16S-ZrO2 impregnated with sulfuric acid at different concentrations.
79
540 538 536 534 532 530 528 526 524
O-H
O-S O-Zr
1.2 M 0.9 M 0.6 M 0.3 M
C16S-ZrO
2
Binding Energy (eV)
Intensity (A.U.)
Appendix A-3 The O (1s) XPS spectra of the C16S-ZrO2 impregnated with sulfuric acid at different concentrations.
80
Appendix B. N
2adsorption and desorption isotherm and BJH pore size distribution of S-ZrO
2.
0.0 0.2 0.4 0.6 0.8 1.0
0 50 100 150 200 250
(a)
0 5 10 15 20 25 30
0.000 0.001 0.002 0.003
dV/dR (cm3 g-1 nm-1 )
Pore diamater (nm)
Volume N 2 adsorbed (cm3 g-1 )
P/P0
S-ZrO2
Appendix B-1 N2 adsorption and desorption isotherm and BJH pore size distribution of S-ZrO2.
81
0.0 0.2 0.4 0.6 0.8 1.0
(a)
Volume N 2 adsorbed (A.U.)
P/P0
0.3M 0.6M 0.9M 1.2M
1 2 3 4 5 6 7
(b)
dV/dR (A.U.)
Pore diameter (nm)
0.3M 0.6M 0.9M 1.2M
Appendix B-2 (a) Nitrogen adsorption-desorption isotherms and (b) the corresponding pore size distributions of the C16S-ZrO2 sample impregnated with sulfuric acid at different concentrations.
82
Appendix C. SEM images of sulfatd ZrO
2(a) (b)
(c) (d)
Appendix C-1 SEM images for the C16S-ZrO2 synthesized with different CTAB/Zr molar ratios. (a) 0.25 (b) 0.38 (c) 0.50 (d) 0.63
83
(a) (b)
(c) (d)
Appendix C-2 SEM images for (a) C16SS-ZrO2 (b) S-ZrO2 (c) C8S-ZrO2 (EtOH) (d) C8S-ZrO2 (IEE).
84
(a) (b)
(c) (d)
Appendix C-3 SEM images for the C16S-ZrO2 impregnated with sulfuric acid at different
concentrations. (a) C16S-ZrO2 - 0.3M (b) C16S-ZrO2 - 0.6M (c) C16S-ZrO2 - 0.9M (d) C16S-ZrO2 - 1.2M.
85
Appendix D. Water content of C
16S-ZrO
2series samples
Appendix D-1. The water content, proton conductivity and pore size of the C16S-ZrO2 series samples
CTAB/Zr molar ratio
WCtotal
(RT-400°C)
WC100-400
(100-400°C)
WC100-400/WCtotal
(×10-2)
Proton Conductivity
(mS/cm)
Pore diameter
(nm)
0.25 21.5% a 3.3% 15.3 12 8.2
0.38 23.8% 4.2% 17.6 16 2.4
0.50 27.4% 5.1% 18.6 20 2.8
0.63 18.9% 3.2% 16.9 17 3.0
a- weight loss%
86
Appendix E. NH
3TPD samples weight and patterns
Appendix E-1. The weight of the sulfated ZrO2 sample
100 200 300 400 500 600
0.3M 0.6M
0.9M 1.2M C16S-ZrO
2
TCD Intensity (A.U.)
Temperature (
oC)
Appendix E-2. The NH3 TPD patterns for the C16S-ZrO2 series samples
Sample Weight (g)
S-ZrO2 0.1260
C16S-ZrO2 0.1235
C16SS-ZrO2 0.1224
C16S-ZrO2-0.3M 0.1256
C16S-ZrO2-0.6M 0.1256
C16S-ZrO2-0.9M 0.1263
C16S-ZrO2-1.2M 0.1248
C8S-ZrO2(IEE) 0.1230
C8S-ZrO2(EtOH) 0.1225
(a)
(c)
Append concent 1.2M.
dix F-2 TEM trations. (a)
M images fo C16S-ZrO2
or the C16 S-- 0.3M (b)
88
(d)
ZrO2 impre C16S-ZrO2
egnated with - 0.6M (c)
h sulfuric ac C16S-ZrO2
cid at differ - 0.9M (d) C
ent
C16S-ZrO2 --