direct methanol fuel cell study on anode and cathode catalysts
DESCRIPTION
Direct Methanol Fuel Cell Study on anode and cathode catalysts. 曹殿学. Introduction. Direct methanol fuel cells Major problems facing DMFCs. Study on the anode electrocatalyst(Pt-Ru ad ). Study on the cathode electrocatalyst(Ru/Se). Acknowledgements. Direct Methanol Fuel Cell. e -. Load. - PowerPoint PPT PresentationTRANSCRIPT
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Direct Methanol Fuel CellStudy on anode and cathode catalysts
曹殿学
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• Direct methanol fuel cells
• Major problems facing DMFCs
Introduction
Study on the anode electrocatalyst(Pt-Ruad)
Study on the cathode electrocatalyst(Ru/Se)
Acknowledgements
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Direct Methanol Fuel Cell
e-
H+
e-
e- CH3OH + H2OO2
(air)
O2
H2O
Anode
PEM
Cathode
Load+ -
CO2
H2O +CH3OH
Membrane Electrode Assembly (MEA)
eHCOOHOHCH 66223OHeHO 22 3662
3
OHCOOOHCH 2223 22
3
E= -0.02VE= 1.23V
E= 1.21V
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Power vehicles
• More efficient than ICE (97% vs. 40%).
• Lower emission(no NOx).
• Quite.
Power portable electronic devices
• Last longer than batteries.
• Easy to refill.
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Key Issues Hindering the
Development of Practical DMFCs:
• Sluggish anode kinetics a
• Methanol crossover c
Current Density (mA/cm2)
Cel
l Vo
ltag
e (V
)
Eocell
fuelcell
(b) Region of Ohmic Polarization(Resistance Loss)
(c) Region of Concentration Polarization
(Mass Transport Loss)
Equilibrium Voltage
(a) Region of Activation Polarization(Kinetics Loss)
-- 过电势
Ecel l= Ecell
- ( a + c )
Ecell / Ecell
<< 100%
• Develop active methanol electrooxidation catalysts.
• Overcome methanol crossover issue.
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What I have done on the study of anode(University of Alberta, Canada)
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What is the optimum surface composition? Best Pt:Ru ratio?
Hard to measure surf. comp. of nanoparticle PtRu.
10~50% Ru was reported.
Best catalyst for CH3OH electrooxidation:
PtRu nanoparticles
PtRu
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ClHRuPtaqRuClHPt adsurfOHAratmTR
adssurf 33)()()(3 3,.,.
32
Pt
H H H
Ru3+
Pt
H+
Pt
K2S2O8 in 4.0 M KOH
Inductively Coupled Plasma-
Atomic Emission Spectrometry (ICP-AES)
# of Ru atom
# of surf. Pt atom was measured
by cyclic voltammetry(CV)
Pt/Ru comp. =# of Ru atom
# of surf. Pt atom
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# of Deposition (n) 1 2 3 5 7
Surf. Equiv. Ruad 0.18 0.38 0.57 0.85 1.31
(Surf. Equiv. Ruad)/n 0.18 0.19 0.19 0.17 0.19
Ru Surf. Coverage 0.18 0.33 0.45 0.63 0.75
1) Ruad form a submonolayer on the substrate at each deposition.
2) Ruad were deposited onto Ptsurf and Ruad at similar probabilities.
Cao, D. X.; Bergens, S. H. Electrochimica Acta, 2003, 48, 4021-4031.
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Time / min.
0 5 10 15 20 25 30
Cur
rent
Den
sity
/ (
A c
m-2
)
0
10
20
30
40
50
60
Time / min.
0 5 10 15 20 25 30
Cur
rent
Den
sity
/ (
A c
m-2
)
0
2
4
6
8
10
12T=22 oC, E=0.45 V[MeOH]=[H2SO4]=1.0 M
T=60 oC, E=0.40 V
Ru
0.33 0.45 0.18 0.63 0.75Pt
Ru
0.33 0.45 0.63 0.75 0.18Pt
RE WE CE
Ar in Ar out
Pt:Ru ~ 67:33
1 M CH3OH1 M H2SO4
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Membrane Electrode Assembly (MEA)
Anode:Pt-Ruad
Cathode:Pt black
Nafion-117
Nanoparticle catalysts
Nafion
ionomer
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[ (CF2 - CF2)x-CF - CF2 ]
O
CF2CF - CF3
O
SO3-
H+
CF2
m
y
CF2
x = 5- 13.5y = 1000m = 1, 2, 3
CH3OH
H+
H2OSO3
-
H+
H+ H2O
H2O H2O H2O
[CF2]2
[CF2]2
H+
H+
H2O
H2O
[CF2]2
[CF2]2
SO3-SO3
-
SO3-
CH3OHCH3OH H2O
H+
Nafion-117 Membrane
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Catalyst / Water / Nafion
Steel plate
Nafion-117membrane
Teflon decal
Painting
Paint brush
Teflon tape
Catalyst layer
Hot-Pressing(125oC, 1500psig)
Ink Preparation(sonication)
Fuel Cell Hardware
Membrane Electrode Assembly
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Current Density / (mA.cm-2)
0 100 200 300 400
Cel
l Vol
tage
/ V
0.1
0.2
0.3
0.4
0.5
0.6
0.7 Pt-Ruad-0.18
Pt-Ruad-0.33
Pt-Ruad-0.45
Pt-Ruad-0.63
Pt-Ruad-0.75
Pt
Current Density / (mA.cm-2)
0 50 100 150 200
Cel
l Vol
tage
/ V
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7 Pt-Ruad-0.18
Pt-Ruad-0.33
Pt-Ruad-0.45
Pt-Ruad-0.63
Pt-Ruad-0.75
Pt
(b) T=90oC
(a) T=60oC
T = 60oC, Pt:Ru ~ 65:35
T = 90oC, Pt:Ru ~ 50:50
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Cur
rent
/ (
A.c
m-2
)
-15
-10
-5
0
5
10
15(a) Pt black
(e) Pt-Ruad-0.81(0.63)
Cur
rent
/ (
A.c
m-2
)
-15
-10
-5
0
5
10
15(b) Pt-Ruad-0.18 (0.18)
E / V
0.0 0.2 0.4 0.6
(f) Pt-Ruad-1.31(0.75)
E / V
0.0 0.2 0.4 0.6
Cur
rent
/ (
A.c
m-2
)
-15
-10
-5
0
5
10
15(c) Pt-Ruad-0.38 (0.33)
(d) Pt-Ruad-0.57 (0.45)
CVs for fresh Pt-Ruad
RE WE CE
Ar in Ar out
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Cu
rre
nt /
(m
A.m
g-1
)
-2
-1
0
1
2
Cu
rre
nt /
(m
A.m
g-1
)
-2
-1
0
1
2
E / V
0.0 0.2 0.4 0.6
Cu
rre
nt /
(m
A.m
g-1
)
-2
-1
0
1
2
Pt
Pt-Ruad-0.18
Pt-Ruad-0.33
E / V
0.0 0.2 0.4 0.6
Pt-Ruad-0.63
Pt-Ruad-0.75
Pt-Ruad-0.45 CVs measured in fuel cells
H2O(Ar)
H2
(H2O)
AnodePt-Ruad
CathodePt
WE
CE RE
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Time / day
0 5 10 15 20
Cur
ren
t Den
sity
/ (m
A c
m-2
)
0
50
100
150
200
E=0.40 VE=0.35 VE=0.30 V
Time / day
0 5 10 15 20
Cur
ren
t Den
sity
/ (m
A c
m-2
)
0
100
200
300
400 E=0.50 VE=0.40 VE=0.30 V
(a) T=60oC
(b) T=90oC
Fuel CellStability Test
Is Pt-Ruad stable?(Ruad might come off)
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What I have done on the study of cathode(University of Illinois, USA)
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Problems:
Methanol crossover causes a mixed potential at cathode,increases the cathode overpotential, decreases fuel cellvoltage, thereby efficiency.
Solutions:
1. Methanol impermeable membrane. 2. Methanol tolerant ORR electrocatalysts.
Nafionmembrane
CH3OH
Anode Cathode
O2 + e-
H2O
CH3OH
CO2 + e-
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E / V (vs RHE)
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
j / (
mA
cm
-2)
-8
-7
-6
-5
-4
-3
-2
-1
0
1
Pt(without CH3OH)
Pt(with CH3OH)
Ru/Se
Activity Comparison
Methanol Tolerance
E / V (vs RHE)
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
j / (
mA
cm
-2)
-7
-6
-5
-4
-3
-2
-1
0
Ru
Ru/Se
RuxSey
Rotating Disc Electrode1600 rpm 20 mV/s
O2-saturated
0.1 M H2SO4
旋转电极
Oxygen Reduction Reaction
Ru/Se
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Acknowledgements
Dr. Steve BergensDr. Andrzej Wieckowski
• People:
• Funding:Natural Sciences and Engineering Research Council of Canada.
US Army Research Office (MURI grant DAAD19-03-1-0169).