This document provides information on a project to develop resilient oxidation catalysts for electrochemical hydrogen pumps. The project goals were to improve the activity and durability of electrocatalysts used in hydrogen pumps by designing composite support structures. Specifically, the project involved synthesizing platinum electrocatalysts supported on carbon nanotube-titania and carbon nanotube-titanium niobium oxide composites, and testing their performance in membrane electrode assemblies. Testing showed the composite supported catalysts had better tolerance to carbon monoxide poisoning and higher carbon corrosion resistance compared to platinum on carbon nanotubes alone.

1. Resilient Oxidation Catalysts for Electrochemical Hydrogen Pump
Final Presentation
May 21, 2013
William A. Rigdon
Diana Larrabee
Xinyu Huang, Ph.D.

2. Electrochemical Hydrogen Pump
Pump serves to separate and compress hydrogen. Process is performed by
applying power across the electrochemical cell. No moving parts in this design
and this method provides the most efficient way to compress hydrogen.
2

3. Project Goals
• Problem: Hydrogen oxidation electrocatalysts are used
in anode of hydrogen pump and fuel cell. They are subject
to poisoning from impurities like carbon monoxide [CO]
and durability concerns that arise from cleaning up CO.
• Challenge: Develop supports which can improve the
activity and durability of electrocatalysts for H2 pump.
• Approach: Design a composite support structure which
can aid in the improvement of both desired properties.
Demonstrate performance improvements through
working membrane electrode assemblies (MEA). Study
the material behavior and elucidate the benefits.
3

4. Electrocatalyst Degradation
The corrosion mechanisms are all related, but it can be understood by four
simple schematics of the contribution to the detachment, dissolution, diffusion,
and re-deposition of Pt catalysts resulting in particle growth and loss of activity
Y. Shao-Horn, W. C. Sheng, S. Chen, P. J. Ferreira, E. F. Holby, D. Morgan. Instability of Supported Platinum Nanoparticles in Low-Temperature Fuel
Cells. Topics in Catalysis. 46 (3-4), 285-305 (2007).
4

5. Project Approach
Prepare composite supports: CNT-Titania
Synthesize Pt electrocatalysts on supports
Characterize material structure/properties
Design and construct MEAs for testing
Test electrochemical performance
Observe carbon corrosion resistance
Report results and publish
5

6. Carbon Structure
Carbon chemistry and Pt support stability effects
-o- High surface
area amorphous
carbon black
supports have best
activity, but have
high defect density
and poor stability
-□- A carbon
nanotube (CNT)
demonstrates long
range order and
graphitic bonding
with fewer defect
sites on the surface
F. Hasché, M. Oezaslan, P. Strasser. Activity, stability and degradation of MWCNT supported Pt
fuel cell electrocatalysts. Physical Chemistry Chemical Physics. 12, 15251-15258, 2010.
6

7. Titanium Dioxide Support Durability
A titanium dioxide platinum support was used to
generate a performance similar to a commercial
carbon black electrode with excellent durability,
but required a very high platinum content.
S.-Y. Huang, P. Ganesan, S. Park, B. N. Popov. Development of a Titanium
Dioxide-Supported Platinum Catalyst with Ultrahigh Stability for Polymer
Electrolyte Membrane Fuel Cell Applications. Journal of the American Chemical
Society. 131, 13898-13899, 2009.
7

8. Metal and Oxide Stability
• Pourbaix Diagram
– Immunity
– Corrosion
– Passivation
Region of
electrode
operation
Passivation
Corrosion
E. Asselin , T. M. Ahmed , A. Alfantazi.
Corrosion of niobium in sulphuric and
hydrochloric acid solutions at 75 and 95 °C.
Corrosion Science. 49, 694-700, 2007.
Immunity
M. Pourbaix. Atlias of Electrochemical Equilibria in
Aqueous Solutions. 1974.
8

9. Mechanistic Effect on Activity of
CO Oxidation for Pt-TiOx
D. Jiang, S. H. Overbury, and S. Dai. Structures and Energetics of
Pt Clusters on TiO2: Interplay between Metal-Metal Bonds and
Metal-Oxygen Bonds. J. of Physical Chemistry. 116, 2188021885, 2012.
TiOx−OH + Pt−COad  CO2 + Pt + TiO2 + H+ + e-
S. Bonanni, K. Aït-Mansour, W. Harbich, H. Brune. Effect of the
TiO2 Reduction State on the Catalytic CO Oxidation on Deposited
Size-Selected Pt Clusters. J. of the American Chemical Society.
134, 3445-3450, 2012.
S. C. Ammal, A. Heyden. Nature of Ptn/TiO2(110)
Interface under Water-Gas Shift Reaction Conditions:
A Constrained ab Initio Thermodynamics Study. J. of
9
Physical of Chemistry. 115, 19246–19259, 2011.

10. Support Effect on Methanol
Electrocatalytic Oxidation
R. E. Fuentes, B. L. GarcÍa, and J. W. Weidner. Effect of Titanium Dioxide Supports on the Activity of Pt-Ru toward Electrochemical
Oxidation of Methanol. Journal of the Electrochemical Society. 158 (5), B461-B466, 2011.
10

11. Metal Oxides & Defect Chemistry
By metal oxide doping of Ti site with Nb,
𝑁𝑏2 𝑂5
2 𝑇𝑖𝑂2
1
2 𝑁𝑏·𝑇𝑖 + 4 𝑂 𝑂𝑋 + 2 𝑂2 + 2 𝑒 −
The equilibrium reaction for oxygen at low pressures is:
1
𝑂 𝑂𝑋 ⇌ 𝑉 ·· + 2 𝑒 − + 2 𝑂2
𝑂
The mass action law follows this expression for the equilibrium constant K
for electrons
𝑉 ·· ∗[𝑛]2
𝑂
[𝑂2 ]1/2
= 𝐾 𝑛 where [O2] = Partial pressure of O2 or P(O2)
At low P(O2), where e- compensates for the oxygen vacancies [n] ≈ 2 𝑉 ··
𝑂
1
2
𝑛 ∗ 𝑛
2
1
−2
= 𝐾 𝑛 ∗ 𝑃(𝑂2 )
1
3
𝑛 = (2𝐾 𝑛 ) ∗ 𝑃(𝑂2 )
therefore,
1
−6
11

12. TiOx-CNT Support Synthesis
N. G. Akalework , C.-J. Pan , W.-N. Su , J. Rick , M.-C. Tsai , J.-F. Lee , J.-M. Lin , L.-D. Tsai and B.-J. Hwang. Journal
Materials Chemistry. 22, p. 20977-20985, 2012.
12

13. MEA Manufacturing
• Novel in our approach for application of electrocatalysts for benefit to
CO oxidation in working electrochemical cells
• Prepared electrocatalyst powders and mixed into inks
• Ultrasonic spray deposition to prepare MEAs
• MEA is greater design challenge than half cell study
• Compared 3 symmetric 10 cm2 electrode designs with 0.3 mgPt/cm2
1. Pt-CNT
2. Pt-TiOx-CNT
3. Pt-TiNbOx-CNT (10 atomic % Nb substituted for Ti)
13

14. 1.0
Pt-CNT
0.8
32.1 m2/gPt
0.6
Current (A)
b)
0.683 V max
0.4
0.2
0.0
-0.2
0.0
0.2
0.4
0.8
38.7
0.6
Current (A)
0.6
0.8
1.0
1.2
Pt-TiNbOx-CNT
m2/g
Pt
0.631 V max
0.4
0.601 V peak 1
0.2
0.0
-0.4
0.646 V max
0.4
0.2
0.0
0.2
0.4
0.6
0.8
Potential (V)
-0.2
-0.4
Potential (V)
1.0
-0.2
36.5 m2/gPt
0.0
-0.4
c)
Pt-TiOx-CNT
0.8
0.6
Current (A)
a)
1.0
1.0
1.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Potential (V)
Figure 1. Electrodes are first
exposed to 100 ppm CO for 60
minutes and then purged with N2
gas. Cyclic voltammetry is
performed and 1st scan is
compared to 3rd. The onset for CO
oxidation is left-shifted more than
50 mV for 10% Nb doped titania
supported Pt electrocatalysts.
14

15. Electrochemical Impedance Spectroscopy
Shows CO Deactivation of Electrode
N. Wagner, E. Gülzow. Change of electrochemical impedance spectra (EIS) with time during CO-poisoning
of the Pt-anode in a membrane fuel cell. Journal of Power Sources. 127, 341-347, 2004.
15

16. Pt- TiOx-CNT
0.070
0.070
0.042
0.028
0.014
0.056
-Z imaginary (ohms)
0.056
0.042
0.028
0.014
0.000
0.000
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.00
0.070
0.042
0.028
0.014
-Z imaginary (ohms)
0.056
0.000
als
)
E2
int
e
m
inu
te
C14
D2
0.06
0.08
Z real (ohms)
0.10
0.12
0.14
0.16
Ti
m
D6
e
(5
C10
rv
C18
0.04
0.02
0.04
0.06
0.08
0.10
0.12
0.14
inu
te
m
0.16
Z real (ohms)
Pt- TiNbOx-CNT
0.02
e
Ti
m
C2
Z real (ohms)
0.00
Ti
m
e
(5
C10
C6
C2
0.00
int
int
m
inu
te
C14
(5
C10
C6
er
C18
er
C18
va
va
ls)
C22
ls)
C22
C14
-Z imaginary (ohms)
Pt- CNT
Figure 2. Anodes under open
circuit condition after exposure to
100 ppm CO in H2 gas stream at 50
mL/min at 70 °C measured every 5
minutes up to 1 hour show the
magnitude of catalyst deactivation
(CO poisoning). The Pt-TiNbOxCNT shows best tolerance to CO at
these conditions (least deactivation).
16

17. Electrochemical Output from Pump
Pt-CNT
15.0
0
5
15
10.0
7.5
5.0
10.0
7.5
5.0
2.5
2.5
0.0
0.0
0.00
15.0
12.5
Current (A)
0
5
10
15
12.5
10
Current (A)
Current (A)
12.5
Pt-TiOx-CNT
15.0
10.0
0.05
0.10
Potential (V)
0.15
0.20
Pt-TiNbOx-CNT
0
5
10
15
7.5
5.0
2.5
0.0
0.00
0.05
0.10
Potential (V)
0.15
0.20
0.00
0.05
0.10
Potential (V)
0.15
0.20
Figure 3. Hydrogen pump
polarization at 5 minute intervals
under 100 ppm CO in H2 at 50
mL/min, 70 °C, 95% RH. The PtTiNbOx-CNT electrocatalyst show
the greatest tolerance. An earlier
onset for oxidation can be seen at
15 minute scan above 150 mV.
17

18. XRD Spectra of Composite Support
and effect of [C:Ti] atomic ratio
Effect of Titanium Isopropoxide
added to fixed 0.1 g mass of CNT
Titanium Moles Added
Power (Ti moles)
6.E-04
[10:1]
60000
Ti moles
7.E-04
5.E-04
4.E-04
3.E-04
50000
40000
30000
20000
[80:1]
2.E-04
[80:1]
70000
[10:1]
8.E-04
80000
Intensity (counts)
9.E-04
XRD Spectra of TiOx-CNT Catalyst Supports
10000
1.E-04
0.E+00
0
100
200
[Ti:C] Atomic Ratio
300
400
0
10
30
50
70
90
2Ѳ
XRD scans show the presence of small anatase crystallites on the carbon nanotube
support. A higher titanium loading of 10:1 had a greater resistance and also
lacked sufficient electronic contact to function as electrocatalyst as evidenced by
the minimal ECSA and lack of i-V performance. A lowered ration of C:Ti [80:1] (5%
18
mass ratio of Ti) was used successfully.

19. Raman Spectra of Composite Support
Raman Spectra of CNT:Titania
18000
Titania-CNT
Oxidized-CNT
16000
25000
12000
20000
10000
8000
6000
4000
2000
0
0
500
1000
1500
2000
Intensity (a.u.)
Intensity (a. u.)
14000
[80:1]
15000
[10:1]
10000
TiNbOx
5000
-1
Raman Shift (cm )
0
0
500
1000
1500
2000
Raman Shift (cm-1)
Raman data from red laser also shows the confirmation
of dual phase support with presence of anatase. The
concentration of titania on the surface may have an effect
on the material’s band gap, Eg. Later, dopant Nb atoms
wer added to effectively reduce the titanium oxidation
state and increase its electronic conductivity.
W. F. Zhang, Y. L. He, M. S. Zhang, Z Yin, Q. Chen. Raman scattering study on anatase TiO2 nanocrystals. J. Phys. D: Appl. Phys. 33, 912–916 (2000).
19

20. 3000
O-CNT
Emergence of peak
at 160 cm-1 in 10%
Nb doped composite
titania supports
2500
TiNbOx-CNT
Intensity (a.u.)
2000
1500
1000
500
0
0
500
1000
Raman Shift (cm-1)
1500
2000
20

21. Carbon Corrosion Resistance
L. M. Roen, C. H. Paik, and T. D. Jarvi. Electrocatalytic Corrosion of Carbon Support in PEMFC Cathodes.
Electrochemical and Solid-State Letters. 7 (1), A-19-A22, 2004.
A method to quickly screen electrocatalyst durability achieved by scanning cell
potential and monitoring the evolution of carbon dioxide [CO2+] ion current by mass
spectrometer from sample capillary attached to the exhaust line. Real time
concentrations can be correlated with potential dynamic.
21

22. Comparison of Carbon Dioxide Evolution from Support
4.5E-11
Cell T = 80 C
Humidifier T = 70 C
Relative Humidity = 66%
Pt-TiOx-CNT
Pt-TiNbOx-CNT
Helium flow on cathode
@ 50 mL/min
Potential
1.3
Cyclic Voltammetry from
0.5 to 1.5 V at 10 mV/sec
3.5E-11
1.0
2.5E-11
Potential (Volts)
44 AMU Ion Current (Amps)
1.5
Pt-CNT
0.8
1.5E-11
0.5
0
50
100
150
200
Time (Seconds)
22

23. Electron Microscopy
Distribution of Pt Crystallites
0.40
Frequency
0.35
0.30
0.25
0.20
Atomic ratio near 1:1 between Ti:Pt
in this image from STEM and EDX
0.15
0.10
0.05
0.00
2-2.5 2.5-3 3-3.5 3.5-4 4-4.5 4.5-5 5-5.5
[Ti]
Pt Crtystallite Diameter (nm)
HRTEM of Pt particle distribution on support (above)
TEM at USC shows area for improvement and also a
single CNT/Pt electrocatalys (below; left and right)
[O]
Credit: Haijun Qian and JoAn Hudson at Clemson EMF for HRTEM and STEM images & EDX data
[Pt]
23

24. Industry Collaboration:
Sustainable Innovations, LLC
Template design for MEA construction
Before
Worked closely with industry partner to prepare a resilient
hydrogen oxidation catalyst and delivered MEA for testing.
Electrochemical hydrogen pump results will be presented at
the 2013 Fuel Cell Seminar & Energy Exposition.
After
24

25. Conclusions
Advantageous modification of both activity and
durability of electrocatalyst through design of a
composite support structure for platinum
Experimental results measured in working cells
show benefits to hydrogen oxidation reaction
Resilient effects in CO tolerance and carbon
corrosion resistance can prolong the life of the cell
which is critical to reducing material costs
 Reduced upper potential required for CO removal
 Decreased number of cycles required for cleaning
25

26. 26

27. Backup Slides
27

28. Background and Introduction
•
•
•
•
•
Application for H2 Pumps
Cost of Materials, Platinum
Cost of Fuel, Pure H2
High Pressure Delivery, Mechanical v. EC
Sources of CO and Impurities
– Natural Gas, water-gas shift
– Biofuels
• Carbon Monoxide Effect on Pt Catalysis
• CO clean up leads to corrosion!
28

29. 50 mV hold test + CO 100 ppm
5
Pt-C (TKK)
Pt-TiNbOx-CNT
4
Pt-TiOx-CNT
Current (A)
Pt-CNT
3
2
1
0
0
100
200
300
400
500
Time (seconds)
600
700
800
900
29

30. Polar
Pt-CNT
15.0
0
5
12.5
15
Current (A)
Current (A)
7.5
5.0
10.0
7.5
5.0
2.5
2.5
0.0
0.0
0.00
0.05
0.10
Potential (V)
0.15
0.20
Pt-TiNbOx-CNT
15.0
5
10
15
10.0
0.00
0.05
0.10
Potential (V)
0.15
0.20
Figure 3. Hydrogen pump
polarization at 5 minute intervals
show the greater tolerance to 100
ppm CO in the fuel stream
Hydrogen Pump Polarization under
CO 100 ppm in H2 at 50 mL/min, 70
°C, 95% RH
0
12.5
Current (A)
0
5
10
15
12.5
10
10.0
Pt-TiOx-CNT
15.0
7.5
5.0
2.5
0.0
0.00
0.05
0.10
Potential (V)
0.15
0.20
30

31. What’s Remaining?
Durability measurements by CO2 evolution
X-ray photoelectron spectroscopy
Electron Microscopy (TEM, STEM, FESEM)
Prepare MEA materials for stack tests by S. I.
Experimental data quantification + present
Submit abstracts to relevant conferences
o Electrochemical Society
o Fuel Cell Seminar & Exposition
o American Chemical Society
31

32. Raman Spectra of Carbon:Titanium Catalyst Supports
Raman Spectroscopy
25000
20000
[80:1]
Intensity (a.u.)
15000
[10:1]
TiNbOx
10000
5000
0
0
200
400
600
800
1000
Raman Shift
1200
1400
1600
1800
2000
(cm-1)
32

33. XRD of Pt Composite Electrocatalysts
80000
70000
Intensity (a.u.)
60000
Pt-CNT
Pt-TiOx
50000
Pt-TiNbOx
40000
30000
20000
10000
0
30
35
40
45
50
2Ѳ
55
60
65
70
33

34. Carbon
Cyclic Voltammetry
Carbon chemistry and Pt
support stability effects
Polarization Air
Pt-TiOx-CNT
1.0
0.015
0.9
0.010
Cell Potential (V)
2
Current Density (mA/cm )
0.020
0.005
0.000
-0.005
-0.010
-0.020
0.0
0.8
0.7
0.6
0.5
0.4
Initial
12300
32000
-0.015
0.2
0.4
0.6
0.8
1.0
Initial
12300
32000
0.3
0
1.2
200
400
600
800
1000
1200
2
Cell Potential (V)
Current Density (mA/cm )
Pt-CNT
0.020
1.0
0.015
0.9
0.010
Cell Potential (V)
2
Current Density (mA/cm )
F. Hasché, M. Oezaslan, P. Strasser. Activity,
stability and degradation of MWCNT supported Pt
fuel cell electrocatalysts. Physical Chemistry
Chemical Physics. 12, 15251-15258, 2010.
0.005
0.000
-0.005
-0.010
Initial
10000
30000
-0.015
-0.020
0.0
0.2
0.4
0.6
0.8
Cell Potential (V)
1.0
1.2
Initial
10000
30000
0.8
0.7
0.6
0.5
0.4
0.3
0
200
400
600
800
34
1000 1200
2
Current Density (mA/cm )

35. 0.2
CV Composite Graph 100 mV/sec
0.1
0.0
Current (A)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-0.1
Pt-TiOx-CNT
-0.2
-0.3
Support
m2/g Pt (UPD)
Pt-TiOx-CNT
15.84045873
Pt-TiNbOx
13.17344286
Pt-CNT
18.99396032
Pt-C(TKK)
47.47620635
Potential (V)
Pt-TiNbOx-CNT
Pt-CNT
35

36. CO Stripping Voltammetry
J. Ma, A. Habrioux, N. Guignard, and N. Alonso-Vante. Functionalizing Effect of Increasingly Graphitic Carbon Supports on CarbonSupported and TiO2−Carbon Composite-Supported Pt Nanoparticles. Journal of Physical Chemistry C. 116, 21788−21794, 2012.
36

37. X-ray Photoelectro Spectroscoopy
L. R. Baker, A. Hervier, H. Seo, G. Kennedy, K. Komvopoulos, and
G. A. Somorjai. Highly n-Type Titanium Oxide as an Electronically
Active Support for Platinum in the Catalytic Oxidation of Carbon
Monoxide. J. Physical Chemistry C. 115, 16006-16011, 2011.
B. Y. Xia, B. Wang, H. B. Wu, Z. Liu, X. Wang, X. Wen Lou.
Sandwich-structured TiO2–Pt–graphene ternary hybrid
electrocatalysts with high efficiency and stability.
Journal of Materials Chemistry. 22, 16499-16505. 2012
37

38. CVs during Accelerated Testing coupled with Mass Spec
Pt-CNT
0.07
Pt-TiOx-CNT
0.05
Pt-TiNbOx-CNT
Current (A)
0.03
0.01
0.40
0.60
0.80
1.00
1.20
1.40
1.60
-0.01
-0.03
-0.05
Potential (V)
38

39. Pt-CNT Before & After ADT
Pt-TiOx-CNT Before & After
0.2
0.1
0.1
0.0
0.0
0.5
1.0
-0.1
-0.2
After
Current (A)
0.3
0.2
Current (A)
0.3
0.0
0.5
1.0
-0.1
-0.2
After
-0.3
-0.3
Before
-0.4
Before
-0.4
Potential (V)
Pt-TiNbOx-CNT Before & After
Potential (V)
Pt-C (TKK) Before & After ADT
0.3
0.2
0.2
0.1
0.1
0.0
0.0
0.5
1.0
-0.1
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-0.1
-0.2
After
Potential (V)
-0.2
Before
-0.3
-0.4
Current (A)
0.3
Current (A)
0.0
-0.3
-0.4
After
Before
Potential (V)
39

40. Industry Collaboration:
Sustainable Innovations
40