direct methanol fuel cell study on anode and cathode catalysts 曹殿学
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Direct Methanol Fuel CellStudy on anode and cathode catalysts
曹殿学
• Direct methanol fuel cells
• Major problems facing DMFCs
Introduction
Study on the anode electrocatalyst(Pt-Ruad)
Study on the cathode electrocatalyst(Ru/Se)
Acknowledgements
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
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.
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.
What I have done on the study of anode(University of Alberta, Canada)
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
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
# 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.
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
Membrane Electrode Assembly (MEA)
Anode:Pt-Ruad
Cathode:Pt black
Nafion-117
Nanoparticle catalysts
Nafion
ionomer
[ (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
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
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
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
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
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)
What I have done on the study of cathode(University of Illinois, USA)
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-
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
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).