1 Development of Direct Methanol Fuel Cell and Special Proton Exchange Membranes Impervious to...

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Development of Direct Methanol Fuel Cell and Special Proton Exchange Membranes

Impervious to Methanol

by

Professor Anil KumarDepartment of Chemical Engineering

Indian Institute of Technology Kanpur, Kanpur – 208016 (India)

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Schematic Diagram of a Fuel Cell

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Fuel Cell Stack

4

• Electrosorption (forming Pt-CH2OH, Pt2-CHOH

species) of methanol onto Platinum layer deposited on MEA

• Addition of oxygen to adsorbed carbon containing intermediates generating CO2

Mechanism for Methanol Oxidation

5

Operation of Fuel Cell

Types of Fuel Cells

Fuel Cell Operating Conditions

Alkaline FC (AFC) Operates at room temp. to 80 0C

Apollo fuel cell

Proton Exchange

Membrane FC (PEMFC)

Operates best at 60-90 0C

Hydrogen fuel

Originally developed by GE for space

Phosphoric Acid FC (PAFC) Operates best at ~200 0C

Hydrogen fuel

Stationary energy storage device

Molten Carbonate FC (MCFC) Operates best at 550 0C

Nickel catalysts, ceramic separator membrane

Hydrocarbon fuels reformed in situ

Solid Oxide FC (SOFC) Operates at 900 0C

Conducting ceramic oxide electrodes

Hydrocarbon fuels reformed in situ

Direct Methanol Fuel Cell

(DMFC)

Operates best at 60-90 0C

Methanol Fuel

For portable electronic devices

Summary of Reactions and Processes in Various Fuel Cells

Block Diagram of the Component Parts of a Fuel Cell

Depiction of Components of Complete Fuel Cell System

Polyelectrolyte Membrane Fuel Cell (PEMFC)

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Technology Limitations with DMFC

Poor Electrode Kinetics

Large activation work potential

200-300 mV Cell Voltage Loss

Catalyst Development

Mass Transport

CO2 Rejection Low MeOH concentration

Electrode Structure

25-150mVCell Voltage Loss

Electrode Material Development

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Technology Limitations with DMFC Cathode

Electrode Material Development

Poor Electrode Kinetics

Methanol Crossover

Mass Transport

Large Activation Overpotential

Mixed Cathode Potential

Reduced GasPermeability

200-300mVCell Voltage Loss

25-100mV Loss

Above 100mV Loss

Catalyst Development

• Electrode Material: Special conducting carbon Vulcan XE-72 available with Cabot Corporation, USA.

•Anodic Catalyst: Platinum-Ruthenium adsorbed on conducting carbon. Procedure of making it is well documented.

•Cathodic Catalyst: Platinum adsorbed on conducting carbon. Procedure of making it is well documented.

•Membrane: Nafion Membrane available with DuPont USA. They create lot of problems before supplying.

Three components of the Fuel Cells

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Polystyrene (PS) Membranes

• Dense membranes used for gas separation and pervaporation

• Sulfonated PS membrane used in methanol based fuel cells

• Sulfonated PS blended with Nafion® membrane

• High impact PS blended with polyaniline

• Anion exchange membranes prepared by chloromethylation of

polystyrene

Ion Exchange Membranes

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Experimental Section

Preparation of clay support

Casting of prepolymersyrup on wet clay support

Gas phase nitration of the membrane at 1100 C

Amination of the membrane using hydrazine hydrate

Quaternizationby dichloroethaneand triethylamine

Styrene, AIBN, BPO, DMA, Bulk polymerization at 700 C

700 C, 12 h

Membrane Preparation

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Clay raw material

Composition(wt. %)

Kaolin 10.15

Ball clay 12.90

Feldspar 4.08

Quartz 18.85

Calcium carbonate

22.52

Pyrophyllite 11.50

Water 20.00

Composition

I CastingClay mixture casted on a gypsum surface

II DryingAmbient Temp : 24 h100 0C : 12 h250 0C : 12 h

III Sintering900 0C : 6 - 8 h

IV Dip CoatingDip coated in polymerized TEOS (tetraethyl orthosilicate)Drying, 100 0C : 24 hSintering, 1000 0C : 5 h

Preparation of Clay Support

Steps of Preparation

Solid Oxide Electrolyte Ceramics

Overpotential ηOP= ηAOP – ηCOP – IRinternal

Perovskite Oxides: La1-aAaM1-bBbO3-x

A=Sr2+, Ln3+, Ce4+

M=Fe, Co, Ga a=0.1 to 1molB=Co, Fe, Mg b=0.1 to 0.5 mol

High Temperature Superconductors YBa2Cu3O7-x

Piezoelectric material BaTiO3

Semiconductor sensors SrTiO3

Oxygen Ion Conductors LaGaO3-x

Proton Conductor doped BaCeO3-x

Cathode Material La0.8Sr0.2CoO3-x

Working Temperature range: 100-20000C

Modification of the SupportNOxSup Sup NO2

Catalyst + NH2NH2

Sup NH2

Imidazole

FeCl3

Sup N

CH2CH2

Cl-

NN

CH2CH2

Cl-

NN

Sup N

CH2CH2

FeCl4-

NN

CH2CH2

FeCl4-

NN

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Experimental Section

P CH2CHC6H5

NOxP CH2CHC6H4NO2

P CH2CHC6H4NO2hydrazine

P CH2CHC6H4NH2

P CH2CHC6H4NH2

ClCH2CH2ClP CH2CHC6H4N(CH2CH2Cl)2

P CH2CHC6H4N(CH2CH2Cl)2TEA

P CH2CHC6H4N(CH2CH2N+(C2H5)3Cl-)2

Nitration:2NaNO2+H2SO4 NO + NO2 +H2O+Na2 SO4

Amination:

Quaternization:

Modification Reactions

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Membrane Characterization

Scanning electron microscopy (SEM)

Crossectional view of the membrane

Ceramic Support

Membrane layer

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Experimental Setup for Electrodialysis

HCl Solution NaCl solution

Pump Pump

O2 H2

DC Power Supply

Catholyte Anolyte

anode cathode

v

100/

CX

I t F

1000AvgV I t

EN

KWh/mol of NaOH produced

• Current efficiency

• Energy consumption

• Operating parameters

Salt concentrations, flow rate, current density

Performance of the Membrane

Overall performance of Anion Exchange Membrane

Flow rate (ml/min)

Current Density (A/m2)

NaCl(N)

Cell Voltage

(V)

Current Efficiency

(%)

Energy ConsumptionkWh/mol

33 254.6 4.2 4.52 92.56 0.130

66 254.6 4.2 4.30 91.62 0.133

100 254.6 4.2 4.52 88.63 0.138

66 254.6 2.5 4.54 85.07 0.146

66 254.6 5.2 4.50 96.5 0.1216

66 127.3 4.2 4.54 92.5 0.125

66 254.6 4.2 4.56 92.56 0.133

66 509.2 4.2 4.62 89.52 0.139

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Results and Discussion

Effect of number of runs

number of runs

0 2 4 6 8 10

Eff

icie

ncy(

%)

88

90

92

94

96

98

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++

+ + + + + + + + + + +++

++

+ + + + + + + + + + +++

++

+ + + + + + + + + + + ++

Physical pore

Region I

r

Cb

C1

x = lx = 0

x

Region II

Domain of EDL

Effective pore diameter (a)

C11

- - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - -

Domain of EDLEffective pore

Schematic Diagram of a Flat Membrane

Schematic Diagram of a Single Pore

Space Charge Model

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Space Charge Model

Assumptions

1. ( ) ( , )x x r

Re<10-6 as a ~ 10-9

3. Pores are long and narrow (l >>a)

• radial and axial variation of ur neglected

• neglected

• Axial variation of potential neglected

4. All external forces (for example, gravity etc.) assumed to be negligible.

2

2xu

x

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(a) Nernst Planck equation:

(b) Navier Stokes equation:

2

2

2

2

10 + (a)

10 + (b)

x xi i

i

r ri i

i

u uPFz c r

x x r r r x

u uPFz c r

r r r r r x

(2)

Governing Equations

, (a) (1)i ii x x i i i i

c Dj u c D z c F

x T x

Convection Diffusion Migration

, (b)i ii r r i i i i

c Dj u c D z c F

r T r

(c) Poisson equation

2

2

1 - i

Fr c

r r r x

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(d) Poisson-Boltzmann equation (PBE)

2

1 1 sinh (5)

0

1

0 ( ) (6)

( ) w

da

d

b

Boundary conditions:

Space Charge Model

,

0

2 a

xQ UA u rdr

, ,

0

2 ( ) a

x xI F j j rdr

, ,

0

2 2 ( ) a

s x xJ A j j rdr

Volumetric flow rate

Electrical Current

Solute Fluxr

a ,

F k

RT a

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( 1) * ** 1 3

1 2 * *2 4( 0)

( 1) * ** 1 3

3 4 * *2 4( 0)

( / )[ ( )] (10)

( / )

( / )[ ( )] (11)

( / )

II

I

II

I

c

s

sc

c

ss

sc

L L I JI L L dc

L L I J

L L I JJ L L dc

L L I J

1 3 4

22 5 6

3 5 7

24 8 4

2( )

2( )

L k k

L k k

L k k

L k k

Space Charge Model

*1 2

*3 4

= (7)

(8 )s

dc dI L L c

d d

dc dJ L L c

d d

* *, Iss

II II

J l IlJ

D c D AFc

where

2

2

( ) , , ,

4 ( ) ,

2 ( )

II

x c x Fc

l c RT

a RTc x RTk

D F c x

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2 22sinh( ) ( 2) i

ii a 2

32 20

10

( 1)( 3)

cosh( ) (

3)

ii

iii

ii

i

i i ab

i a

Series Solution of PBE

Space Charge Model

0

ii

i

a

0

0 d

d

Calculate a1=0

2 1

2 02

0 0

( )2

2 1 !

ii

i ii

i

ai a

1 w

2 i wa

Step I

Step II

Step III

Step IV

Step V

Assume

Calculate ai

Calculate a0

Calculate k0 – k9

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Integral expressions Analytical expressions

1

0 0 wk d 00 2( 2)

i

i

iak

i

11 1

1 2 2 10 01

1coshk d d d

21

0 2( 2)( 4)i

i

bk

i i

1 2

2 01 sinhk d 2

20

2( 2)

4i

i

i ak

i

11 1

3 2 2 10 01

1sinh coshk d d d

2

22 23 22 2

0 0 0 0

( 2 )( 2)

( 2) ( 4)( 2)

ii j ji

ii i i j

i j a bbk i a

i i j

1

4 0k de e d 2 2

4 20 0

( 1) ( 2) ( 1) )( 2)

ii

i i

bk d i a d

i

1

5 0k de e d

1

6 0sinhwk d

11 1

7 2 2 10 01

1cosh coshk d d d

1

8 0coshwk d

1 29 0

1 coshk d

2 25 2

0 0

( 1) ( 2) ( 1) )( 2)

ii

i i

bk d i a d

i

22

6 20 0 0 0

( 2)( 2)

2

ij i j

i ii j i i

i j a ak a i a

i

27 2 2

0 0 0 0( 1) ( 1) ( 2) 2

ij i j i i

i j i i

b b b bk

i i i i

2 28

0 0 0 02 2

ij i j i

ii j i i

a b bk a

i i

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0

2

( 2)( 4)i

i

bk

i i

Space Charge Model

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StartInput Js*, I*, cII

Assume wall potential

Assume cI

Solve PBE equation 5, Calculate Js_cal eqn 11

Cal I*_cal using eqn 10

Is (Js_cal - Js*) < tol

Is (I* – I*

cal)2 is min

Stop

No

Yes

Yes

Solution SchemeSpace Charge Model

No

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Pore Diameter (nm)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

S p

ara

met

er

0

2e-7

4e-7

6e-7

8e-7

1e-6

30 min

60 min

90min

120 min

150 min

S parameter Vs pore diameter at different time interval

Results and Discussion

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