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).