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1
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)
2
Schematic Diagram of a Fuel Cell
3
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)
13
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
14
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
16
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
17
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
18
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
21
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
22
Membrane Characterization
Scanning electron microscopy (SEM)
Crossectional view of the membrane
Ceramic Support
Membrane layer
23
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
26
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
27
++
+ + + + + + + + + + +++
++
+ + + + + + + + + + +++
++
+ + + + + + + + + + + ++
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
28
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
29
(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
30
(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
31
( 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
32
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
33
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
29
0
2
( 2)( 4)i
i
bk
i i
Space Charge Model
34
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
35
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
36