Core – Shell anodic catalysts
for
Direct Methanol
and
Direct Ethylene Glycol Fuel Cells
Dima Kaplan
26.1.11
OUTLINE




DMFC and DEGFC
DMFC and DEGFC problems
Why Core-Shell catalysts?
Home made Core-Shell catalysts and their
performance
 Summary
2
What is DMFC?
MeOH
in
CO2 out
Anode reaction
Cathode reaction
Overall reaction
CH3OH  H 2O  CO2  6H   6e
1.5O2  6 H   6e  3H 2O
E˚a = 0.04 Volt vs. SHE
E˚c = 1.23 Volt vs. SHE
CH 3OH  1.5O2  CO2  2 H 2O E˚cell = E˚c – E˚a = 1.19 Volt
3
What is DEGFC?
EG in
CO2 out
Anode reaction CH 2OH   2H 2O  2CO2  10H   10e E˚a = 0.01 Volt vs. SHE
2
Cathode reaction
2.5O2  10 H   10e  5H 2O
E˚c = 1.23 Volt vs. SHE
Overall reaction CH 2OH 2  2.5O2  2CO2  3H 2O E˚cell = E˚c – E˚a = 1.22 Volt
4
DMFC: current and possible applications
Civilian applications
SFC EFOY – works like a mobile charger for the car’s battery.
Toshiba Dynario – Allows charging of Mobile Electronic Devices via a USB cable.
Military applications
SFC Emily – recharges batteries that power the electrical devices on board the
vehicle (radios, GPS, onboard computers) while the engine isn’t running.
SFC JENNY 600S – man portable FC, can power a number of electrical devices
such as digital communications and navigation systems, computer and laser
tracking devices, remote sensors, cameras and metering devices
5
Catalysts for DAFC
• Currently, PtRu alloys are the most
apropriate catalysts for DMFC.
• For operational temperature of 60°C –
80°C an alloy with atomic ratio of 1:1 was
found to be most suitable for DMFC.
• Pt is responsible for MeOH and EG
dehydrogenation, while Ru is responsible
for H2O breakup, thus enabling the
formation of CO2 at an acceptable
potentials
6
Problems preventing wide spread
usage of DMFC
• Platinum is used as catalyst on both electrodes. Currently, fuel
cells use high Pt loadings, which leads to high catalyst cost.
• Nafion is used as the PEM. However, nafion is also expensive.
• Methanol crossover trough the PEM leads to reduction of
efficiency
• Long term durability is questionable due to:
– Anode catalyst poisoning by oxidation intermediates and loss of
structure integrity
– Cathode catalyst poisoning by methanol crossover, surface oxide
formation and loss of hydrophobic properties
7
EG as potential fuel for DAFC
Pros:
• Higher boiling point (1980C vs. 64.70C )
• Lower toxicity than methanol
• Greater volumetric capacity (4.8Ah/ml vs. 4.0Ah/ml)
• Larger molecule, fuel crossover to the cathode can be much
lower
Cons
• Lower gravimetric capacity (4.32Ah/g vs. 5Ah/gr)
• Complicated oxidation mechanism, high number of
intermediates
• Current anode catalysts are optimized for methanol oxidation
8
So what about the
catalyst’s cost…..?
9
Proposed solution
Core – Shell catalysts: Pt only in the shell
Because the catalysis occurs only on the surface of the electrode it’s logical to
use Pt only in the shell of the nano-particals
Since exposed Ru sites are needed to break down H2O molecules, a partial
monolayer of Pt on top of Ru core should be used
PtRu shell
Ru core
It’s likely, that the best surface PtRu composition for methanol
oxidation will be atomic ~1-3:1 depending on the electro-oxidation mechanism
EG oxidation might require a different surface composition
10
MA1 catalyst
Pt on Ru on XC72
MA1 catalyst was prepared in a two stage synthesis:
1. Electroless deposition of Ru on XC72, using EG as reducing agent
2. Electroless deposition of Pt on Ru/XC72, using NaBH4 as reducing agent
MA1a catalyst - composition
Metal
XPS results
Surface atomic ratio
EDS results
Weight ratio
Ru
1
55
Pt
4.28
45
XRD particle size
5.4 nm for Ru
2.7 nm for Pt
Comparison to JM HiSPEC 7000:
Pt:Ru (1:1) alloy catalyst with carbon support, 45% TM
11
MA1 catalyst – MeOH oxidation activity
Catalytic activity - MeOH oxidation
ECSA
Metal
MeOH oxidation
0.5 H2SO4 + 0.1M MeOH
1200
800
-1
Ma [amp*gr Pt]
1000
MA1 catalyst
I0.45V
[m2/gr PtRu]
[A/gr Pt]
[A/gr PtRu]
[A/m2
PtRu]
MA1
29
471
214
7.37
JM
HiSPEC
7000
27
346
230
8.52
JM HiSPEC 7000
600
400
200
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
V Vs SHE [volt]
0.9
1.0
1.1
1.2
12
MA1 catalyst – EG oxidation activity
Catalytic activity - EG oxidation
ECSA
Metal
2500
2250
-1
Ma [amp*gr Pt]
2000
EG oxidation
MA1 catalyst
JM
JMHiSPEC
HiSPEC7000
7000
0.5M H2SO4 + 0.4M EG
I0.45V
[m2/gr PtRu]
[A/gr Pt]
[A/gr PtRu]
[A/m2
PtRu]
MA1
29
241
109
3.75
JM
HiSPEC
7000
27
263
175
6.50
1750
1500
1250
1000
750
500
250
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
V Vs SHE [volt]
0.9
1.0
1.1
1.2
13
DK6a catalyst
Pt on Ru on XC72
DK6a catalyst was prepared in a two stage successive deposition synthesis:
1. Electroless deposition of Ru on XC72, using NaBH4 as reducing agent
2. Electroless deposition of Pt on Ru/XC72, using NaBH4 as reducing agent
DK6a catalyst - composition
Metal
XPS results
Surface atomic ratio
EDS results
Weight ratio
Ru
1
80
Pt
0.47
20
XRD particle size
1.3 nm
14
DK4a catalyst
PtRu on IrNi on XC72
DK4a catalyst was prepared in a two stage successive deposition synthesis:
1. Electroless deposition of IrNi on XC72, using NaBH4 as reducing agent
2. Electroless deposition of PtRu on IrNi/XC72, using NaBH4 as reducing agent
DK4a catalyst - composition
Metal
XPS results
Surface atomic ratio
EDS results
Weight ratio
Ru
1
11
Pt
0.33
19
Ir
0.28
69
XRD particle size
2 nm
15
MeOH oxidation activity
summary
Catalyst
Surface
composition
(XPS)
MA1
20%Pt/24%Ru/XC72
Ma
Ma
ECSA
Sa
]amp/gr Pt]
]amp/gr
TM]
Ru:Pt
1:4.28
471
214
29
7.37
DK6a
15%Pt/59%Ru/XC72
Ru:Pt
1:0.47
204
41
29
1.40
DK4a
22%PtRu/54%IrNi/XC72
Ru:Pt:Ir
1:0.33:028
920
101
25
4.04
JM HiSPEC 7000
45%PtRu/carbon
Ru:Pt
1:1.67
346
230
27
8.52
JM HiSPEC 12100
75%PtRu/carbon
Ru:Pt
1:1.9
620
416
50
8.32
2
]m /gr
TM[
]amp/m2
TM[
JM HiSPEC 12100: PtRu (1:1) alloy catalyst with carbon support, 75% TM
16
EG oxidation activity
summary
Catalyst
surface
composition
(XPS)
MA1
20%Pt/24%Ru/XC72
Ma
Ma
ECSA
Sa
[amp/gr Pt]
]amp/gr
TM]
Ru:Pt
1:4.28
241
109
29
3.75
DK6a
15%Pt/59%Ru/XC72
Ru:Pt
1:0.47
526
105
29
3.62
DK4a
22%PtRu/54%IrNi/XC72
Ru:Pt:Ir
1:0.33:028
341
37
25
1.48
JM HiSPEC 7000
45%PtRu/carbon
Ru:Pt
1:1.67
263
175
27
6.50
JM HiSPEC 12100
75%PtRu/carbon
Ru:Pt
1:1.9
316
212
50
4.24
2
]m /gr
TM]
]amp/m2
TM]
17
Summary
 Several core – shell catalysts were synthesized. One of
them (DK4a) showed a superior performance in
methanol oxidation over commercial HiSPEC 12100
catalyst. The other catalyst (DK6a) showed a superior
performance in EG oxidation over commercial HiSPEC
12100 catalyst.
 Core shell catalysts have a potential to drastically reduce
the Pt loadings currently needed in DMFC and DEGFC.
Efforts to find a durable and cheaper (than Ru) core
metal should be made.
 The results show that EG and methanol might require
different surface compositions of Pt:Ru.
18
Acknowledgments
•
•
•
•
•
Prof. Emanuel Peled
Dr. Larisa Burstein
Dr. Yuri Rosenberg
Dr. Jack Penciner
All the electrochemistry group of TAU
19