WATER PERMEABILITY OF MEA FUEL CELL FABRICATION USING X-Y ROBOTIC SPRAYER.
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
WAT
TER PERM
MEABILITY
Y OF MEA FUEL CEL
LL FABRICATION USING
U
X-Y
Y
ROBOT
TIC SPRAY
YER
R
Ramli
Sitangggang, Dana
ang Jaya
a. Fuel
F Cell Insttitute, Univeersiti Kebanggsaan Malayysia, 43600 U
UKM, Bangii, Selangor,
M
Malaysia
b.
b Teknik Kimia, FTI, UP
PN ”Veterann”. Jl. SWK 104 Condonngcatur, Yoggyakarta,
Indonnesia, 552833
A
Abstract
The fabriccation of ME
EA is conducted using an
a in-house robotic sprrayer machinne
capable of adjustting its X-Y
Y motions. T
The MEA produced waas analyzed for porosity
ty;
BET and SE
EM based oon the waterr permeabiliity
distribbutions poree and water flux using B
methodology. Thee results off the MEA shown that the pore geometry
g
off MEA has a
i greater thhan the MEA
A’s thicknesss while thee permeabiliity
tortuocity parameeter which is
meter of watter is 9.10-55 gcm-1men–11psia-1 or thhe tortuocityy of 2. Thesse
coefficcient param
resultss were then compared
c
too the ones avvailable from
m the commeercial MEA.
Keywo
ords: permeeability coeff
fficient, membbrane electrrode assemblly
I. INTR
RODUCTION
N
Membrrane Electrode Assemblies (M
MEA) is the ccore componennt of fuel celll. It consists of
o the electrolyyte
membraane, anode and
d cathode electrodes. The eleectrochemical reactions occuur when a fuell and oxidant are
a
applied
d to the anode and cathode sides
s
of the M
MEA. There aree several fabriication methodds of MEA weere
reportedd, such as rollling, screen-prrinting, castingg, and sprayin
ng. Each of these
t
types prroduces differeent
MEA’s structure. Onee of the recent researches in sprayer
s
as whaat we interestedd in our laborattory, used one or
multi nozzle (Chun, 2001).
2
The most important paarameter in ME
EA is the wateer flux, usuallyy named as watter
transport phenomenoon. The wateer flux itself depends on electro – osm
motic behaviorr, diffusion annd
permeaability coefficieent, and protoon movement (Eikerling, 19
998, Hu, 20044). Some of researchers
r
haave
approacched the waterr transport pheenomenon in one, two and three dimensional (Hu, 200
04, Chen, 20033).
Based oon the mechan
nism of hydroggen bridge witthin membranee (Bansal,19988), we observeed that the watter
flux is pressure depenndent. The baalancing of hum
midity has to be
b insured withh avoiding thee floods of watter
and dehhydration that will cause ann ohmic lost. The minimizzing of ohmic lost was sugggested by manny
researchher by achievinng various com
mposition of m
materials and recconstruction off pore size of diffusion
d
layer of
electrodde. In this reseearch, we obseerved the perm
meability coeffi
ficient of MEA
A by setting thhe slope of watter
flux in a certain valuee.
2.THEO
ORY
MEA consists
c
of thrree componennt Gas Diffusiion Layer (GD
DL), Gas Difffusion Electro
ode (GDE), annd
membraane. The fabrrication processs of GDL andd GDE was made
m
using in-hhouse robotic sprayer machiine
adopted
d the Chun’s method (20001). The peermeability coefficient of thhe fabricated electrodes was
w
characteerized. We are
a assuming the
t water mass transfer reprresents by thee simplest equation as follow
ws
(Midlem
man, 1997, Muuider, 1991, Baaker,200, Frankk,2004):
(1)
N = κ .∆Peff
Where K is the memb
brane permeabiility coefficientt that depends on the porosityy, pore radius, viscosity and
turtocityy factor, effecttive pressure difference
d
( ∆Peff ) and N perrmeate flux. Thhe System connfiguration in our
o
study iss an in-house robotic
r
sprayerr was in house fabricates. Datta of work piecce is computerr controlled. The
T
post pro
ocessor converts the spray coating
c
carbonn ink path-line to the robot ccontrol commaand to move the
t
sprayerr in X-Y direcction. Such sp
praying system
m will producee an even GD
DL. The GDE
E is produced by
b
sprayin
ng the GDL wiith a similar prrocess as menttioned above but
b with differrence formula of ink-platinum
m.
The prooduced MEA is
i subjected to hot pressing in
i a sandwich form of GDE with membranne inside in high
temperaature and high pressure (Chunn, 2001). Afteer that we activvate the MEA using
u
treatmentt method (Kwaak,
B.2-1
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
2000), and
a then boileed it to avoid water
w
and gasess inside the poore. MEA wass characterize the
t dimension of
pore off MEA, GDL and
a GDE usingg BET and SE
EM by analyzinng the permeaate and the slop
pe of water fluux.
The anaalyzed permeatte was done ussing continuouus membrane syystem method and the analyzzing of the slope
water flux
fl by linear fitting
fi
curve aggainst pressure difference as presented
p
in Eq.(1). Permeaability coefficieent
and ME
EA performancce was investiggated using FCT
TS.
The robbot used in the system employys a specific atttitude expressiion of the x-y configuration
c
s
shown
in Fig 1.
S
W
Z
Subsstra
Y
W2
Fig 1. Thee x-y configuraation
The sprray variable is expressed by frequency ( ω ), nozzle heigght (W1), distriibution distancce (W2), division
numberr of spray coatiing line on subbstrate (n) and nozzle velocitty (S). The sprray direction cooating process is
designeed perpendicular to substratee. If thick sizee ( t e ), pore diiameter (dp,), pporosity ( ε ), typical
t
activatted
specificc surface (as). The
T variable off ink drop distrribution of the nozzle will afffect the layer size
s are µ , v annd
p.
t e , dp, ε , as = f(K, µ , v, σ , p) ………3
…
Assumee p is constantt, surface tensiion ( σ ) consttant, thus theooretically the correlation
c
of t e , dp,
ε ,and as
toward all variables and the robotic movement as well as thee drop variablle are given by
b dimensionleess
equation 4
t e , dp, ε , as.= f(Nsprayy,,Re,W)……………….………44
The visscosity effect and surface tension
t
are coonstant and neeglecting the ssolidifying efffect on substraate
surface. Based on equ
uation 3, the t e , dp, ε , as aree given by the dimensionless
d
equation 4 to 5,
5 as follows :
t e , dp, ε , as.= f(Nsprayy) ………………
…………..….. 5
Equatioons 4 to 5, the t e , dp, ε and as of an electrrode can be dettermined by thee robotic charaacteristic numbber
(Nspray). Assumed the layers results from
f
robotic spprayer is set too be the MEA, therefore the relationship
r
off N
with thee current densiity of PEM fuel cell can be formulated usiing Grujicic (22004) . The sprraying techniqque
model for
f MEA fabriccation is as folllows:
Currentt density (i):
i = K 4CO 2 (1 − ( K 5 exp( − K 6 (φ s ))1 / 2 )
x cothh( K 5 exp( − K 6 (ϕ s )))1 / 2
12t e (1 − ε ) FD
F O2
=f(Nsprayy)…………..…7
)
7
K4 =
0 .5 d p
K5 =
i0, c as1 (0.5d p ) 2
4 FCoref2 DO 2
………………………
…………………
…………………..6
= f(Nspray)…
………………88
and Voltage (V):
B.2-2
V =
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
RT
R
ln{ f1 (dp, ε )CO 2 (1 − ( f1 (dp, ε )
0.5 F
i0,c
RT
(φs ))1 / 2 ) x
exxp(−
ref
0.5F
Co 2
E−
coth( f1 (dp, ε )
i0,c
C
ref
o2
e −
exp(
…
………………………………
…………………
……..9
RT
(ϕ s )))1/ 2 ) / io ,c
0.5F
Based on
o equations, the
t value of cooeffisient modeel of current density
d
depend on Nspray. The Nspray becom
mes
the maiin control for manufacturing
m
layer
l
size of MEA
M
design forrm
d
form coonfiguration em
mployed by ressearches as shoown in Fig.3a is
i the G-GDL-EGenerallly, the MEA design
M-E-GD
DL-G. In this paper
p
the catallyst layer emplloyed the confi
figuration as shhown in Fig.3bb to obtain highhly
activateed specific surrface area. In Fig.3c the cattalyst utilised a support to composite
c
the catalyst into the
t
membraane (novel).
3.EXPE
ERIMENT
Active carbo
on with 400 meshes
m
was lam
minated on carrbon cloth. Poolytetrafluoroeethylene (PTFE
E),
Nafion liquid was ussed also. Modderately polar of mix solvennt from water and isopropan
nol was used as
medium
m for carbon mobilition,
m
annd the membraane used in th
his observatioon is nafion 117 produced by
b
DuPontt. The fabricattion process of
o MEA consiists of three steps;
s
the layinng of GDL, GDE,
G
membraane
activation and assembbly of membraane electrodes (MEA). In thee GDL fabricaation layer mixxture of activatted
d PTPE are stirred for 10 minutes. The sluurry produce has
h viscosity for
f
carbon, alcohol, wateer, Nafion and
about 1.17
1
cp and ussually called as
a carbon ink. The carbon in
nk is sprayed on carbon clo
oth with flow of
sprayin
ng as 0.5 ccs, 6 bar air presssure through spraying nozzzle, with patteern of 4 cm, and
a the standinng
positionn of nozzle is perpendicular
p
w the objectt, with 10 timees moving periiod. The fabriicated GDL muust
with
be dried
d using vacuum
m dryer in room
m temperature for about 2 hoours, and then w
will be subjected to BET, SE
EM
and perrmeate test charracterization. The
T profile andd permeability coefficient of tthe material waas test also.
In case of the fabricattion of GDE, the
t GDL must be sprayed wiith another mixxed material thhat consists of CPt, wateer, and alcoholl. Nafion, PTPE
E. The materiaals must be mixxed for 5 minuutes, and the reesult is namely as
carbon ink C-Pt and has
h 1.16 cp viiscosity. The pprocedures of spraying afterr mixing proceess are similar as
above.
The thiird material thaat we used is membrane
m
Naafion 117. Mem
mbrane were ccleaned to remove any trace of
impuritties and stored in deionized water
w
further use.
u The MEA, GDE and mem
mbrane will saandwich togethher
using hot
h press. The produces electtrode will be rrinsed with 0.55 M H2SO4 annd have to be dried in vacuuum
dryer inn room temperrature for 2 hoours. The resuult then has to be characterizzed using perm
meability test annd
FCTS.
ULT AND DIS
SCUSSION
4.RESU
Characcterization. Th
he fabrication process of G
GDE was repeaated seven tim
mes in insure reproductabilitty.
Surfacee scanning wass done using SEM
S
have produced to charaacterized the ccrack and the roughness
r
of the
t
GDE suurface. From the
t SEM charaacterization of experimental 1 to 6 (see Fig.. 2a), the resultts still has cracck,
and in experimental (see Fig. 2b) the result is free
f
of crack. Experimentaal (b) also hass similar surfaace
roughneess with com
mmercial GDE
E (see Fig. 2c).
2
Matrix morphology
m
w
was investigateed for particlles
characteerization BET studies was peerformed and reveal
(a)
B.2-3
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
(b
b)
(c)
Fig. 2 Surface microscope
m
scaanning of (a). F
First trial (b). After
A
modified, (c). Referencee electrode
Table 11. BET analyssis
Propperty
GDE
(a)
GDE
(b)
ME
A
(a)
MEA
(b)
ME
A
(c
Diameeter
pore (A
A o)
Surfacce
area (m
m2/g)
Volum
me
pore (ccc/g)
34.3
1
472
41.15
34.4
1
410
39.41
68.2
450
220
0.09
7
0.157
0.06
0
0.102
0.08
1
451
For the next observatiion, we will focus on experim
mental (b) that has activated ccarbon as 1.05 g cm-2 and 0.53
g cm-2 PTFE, 0.51 g cm-2 C-Pt and
d the scale chaaracteristic as mentioned
m
in T
Table 1. Usingg pore dimension
point of
o view withinn micropore sccale, experimeental (a) and (b)
( have mesoopore characterristics (Ruthveen,
1997). Another advanntage of experrimental (b) is that it has greeater adsorption capacity andd pore capabiliity
mental in our observation.
o
Affter assembly the
t membrane with electrodee of experimenttal
than thee other experim
(b), the pore dimensioon of MEA rem
mains similar w
with GDE expeerimental (b) sttand alone. Wee could concluude
that thee experimental (b) is appropriiate as a materiial for fabricatiing fuel cell.
Permea
ability Coefficcient. Within MEA
M
fuel cell, the GDL has a function to diistribute humid
dity water and
evacuatte water from electrode
e
part, meanwhile thee electrode is used
u
to distributte humidity waater and will usse
for trigggering the reacction between Pt
P and CO. Thhe membrane allso has task to bond water forr bridging
hydrogeen and sweepin
ng out the electron (Mikko, 2003).
2
If we flo
ow water throuugh the layers within
w
MEA,
then thee water flux insside each layerr will depend oon the channel structure.
B.2-4
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
GDL (3a)
Electrode (3b)
Mem
mbrane (3c)
Fig 3. Surface
S
of GD
DE
For GD
DL, the water flux
fl will be affe
fected by channnel that has beeen built withinn the carbon clo
oth (see Fig. 3aa),
meanwhhile the waterr flux inside the electrode will be affectted by channeel that has beeen built by the
t
mesopoore.
Figure 3c
3 illustrates good
g
profile off pore within m
membrane to make possible w
water flux flow through it. Suuch
kinds of
o pore profile are usually callled as porosityy and tortuositty. To build beetter understandd about what we
w
mention
ned above, we will explain more
m
detail abouut the capabilitty of MEA to flow
f
water fluxx as follow
N = 3.100 −4 ∆Peff
N = 10 −44 ∆Peff
(2)
(3)
N = 2.100 −4 ∆Peff
(4)
-4
-1
Eq. (2) is developed from
f
eq. (1) wiith κ for abouut 3.10 gcm men–1psia-1 thaat has been fouund using Figuure
o water flux. Using tortuossity table we got
g 1.1 for 3.100-4
4, and ∆Peff indicatees the pressuree differences of
Water flux (gmol/cm2 men)
f flowing watter within GDL
L is greater thhan
permeaability coefficieent. It means that the lengthh of channel for
the thicckness of GDL itself. Furtherrmore, for calcculating the cap
pability of elecctrode to flow water
w
follows eq.
e
(3) as shown
s
in Figuure 4b. With 10-4 gcm-1menn–1psia-1 of peermeability coeefficient it is similar with 1.7
1
tortuosiity. It also meeans that the channel
c
for floowing water within
w
electrodee greater than the thickness of
electrodde itself. From
m the calculation of water fluux as mention
ned above, we could emphasize that the floow
resistan
nce of water within
w
electrodee is greater thaan within GDL
L. It means thaat GDL is capaable to distribuute
and evaacuate water eaasier and electrrode could flow
w in or out wateer faste
0,0035
Membrane
0,003
MEA
GDL
0,0025
GDE
0,002
0,0015
0,001
0,0005
0
0
2
4
6
8
10
12
Pressure difference (p
psi)
Fig
g 4. Characterristic Permeab
bility Water
For calcculating the water
w
flux withiin membrane N
Nafion 177, wee use eq. (4) w
with permeabiliity coefficient of
2.10-4 gcm
g -1men–1psiaa-1 or 1.4 tortuuosity, it meanss that the chan
nnel length wiithin membranne is also greatter
than itss thickness. From
F
these thrree layers disccussed above, we could connclude that waater resistance as
followss
GDL < membrane < electrode
(5)
After assembly of meembrane and electrodes
e
on 335 kgfcm-2 preessure and 130 °C temperatuure, we get watter
flux as in eq. (6).
N = 9.10 −5 ∆Peff
B.2-5
(6)
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
The cappability of ME
EA to distribuute water is prooportional withh the pressuree difference thhat is attached to
MEA. With 2.8 psiaa pressure diffferences, MEA
A could flow water
w
around 3.3 10-5 gmol cm-2 min-1 annd
mrestore around 3.6 10-4 gmol cm-2. The permeabiility coefficientt of water withhin MEA is aroound 9.10-5 gcm
1
–1
-1
men psia
p
or with to
ortuosity greateer than 2. Theerefore we cou
uld modify eq. ((5)
GDL < membrane < electrode
e
< ME
EA
(7)
Electrodde has greatestt water resistannce, it means thhat to fabricatee MEA, we havve to modify electrode
e
layer to
control the water disttribution and evacuation
e
prooperties. Inclu
uding the comm
mercial MEA (with 2.10-6gcm
m1
–1
-1
men psia
p
permeabiility coefficien
nt), eq. (7) will have to modify
fy to
(8)
GDL < membrane < electrode
e
< ME
EA < MEA Com
m
4.3. Perrmeability expeeriment relatedd to performancce of MEA fueel Cell
In obseerving the MEA
A fuel cell wiith single stackk, pressure at anode is set up
u greater thann the pressure of
oxygen
n. With pressurre difference of
o 2.8 psi and fl
flow rate of H2
2 as 0.3 slpm, oxygen
o
0.4 slpm
m and a floodinng
water iss happened witthin membranee, then the perfformance of MEA
M
fuel cell ccould be illustrated as in Figuure
5.
1200
1200
Curr.MEA exp.
Curr.MEA com.
1000
Volt.MEA exp.
Volt MEA com.
800
800
600
600
400
400
200
200
0
Voltage (mV)
Current (mA/cm2)
1000
0
0
20
Time (men.))
40
Fig 5. Characteristiic Performancce MEA fuel C
Cell
As can be seen in Figure 5, the MEA fuel cell w
with greater peermeability coeefficient will have
h
less curreent
density voltage. In thhis operation, the
t anode MEA
A fuel cell will be dehydrateed and osmoticc electron will be
happeneed through thee membrane. This
T
osmotic eelectron or usuually called ass electron diffu
fusion will cauuse
ohmic losses
l
inside th
he MEA fuel cell. In such coondition, the chhanging of currrent within ME
EA tends to drop
rapidly than the comm
mercial MEA for
f 30 minutes operation timees. This differrence is due to the permeabiliity
coefficiient of our ME
EA greater thann the commerciial MEA. If H2 and O2 suddeenly drop out to
t zero, the ME
EA
current will be dischaarged very rappidly than the commercial MEA.
M
It meanns that MEA with
w very rapiddly
nt current (risee time and fall time) is good enough to con
ntrol dehydratiion in low tem
mperature withoout
transien
any dryying process (Savadogo, 20033)
5.CON
NCLUSION
a
the wateer flux within the
t geometricaal structure of M
MEA is influennced strongly by
b
From thhe discussion above,
porosity
y and tortuosityy. The tortuoccity of the layeer could be deffined as GDL < membrane < electrode or we
w
got thee permeability coefficient of DGL as 3.110-4 gcm-1men
n–1psia-1, Electrrode as 10-4 gcm
g -1men–1psia-1
-4
-5
-1
–1
-1
membraane as 2. 10 , MEA as 9.100 gcm men psia
p
or tortuoosity greater thaan 2 for MEA. The MEA will
w
occur ohmic
o
losses ussing greater perrmeability coeffficient.
ACKNOWLEDGEM
MENTS
The autthors would likke to express their
t
gratitude to the UKM University
U
andd Environmentt of Malaysia for
f
the finaancial support through
t
IRPA grant: IRPA 022-02-02-0003-PR0023 11-088
B.2-6
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
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B.2-7
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
WAT
TER PERM
MEABILITY
Y OF MEA FUEL CEL
LL FABRICATION USING
U
X-Y
Y
ROBOT
TIC SPRAY
YER
R
Ramli
Sitangggang, Dana
ang Jaya
a. Fuel
F Cell Insttitute, Univeersiti Kebanggsaan Malayysia, 43600 U
UKM, Bangii, Selangor,
M
Malaysia
b.
b Teknik Kimia, FTI, UP
PN ”Veterann”. Jl. SWK 104 Condonngcatur, Yoggyakarta,
Indonnesia, 552833
A
Abstract
The fabriccation of ME
EA is conducted using an
a in-house robotic sprrayer machinne
capable of adjustting its X-Y
Y motions. T
The MEA produced waas analyzed for porosity
ty;
BET and SE
EM based oon the waterr permeabiliity
distribbutions poree and water flux using B
methodology. Thee results off the MEA shown that the pore geometry
g
off MEA has a
i greater thhan the MEA
A’s thicknesss while thee permeabiliity
tortuocity parameeter which is
meter of watter is 9.10-55 gcm-1men–11psia-1 or thhe tortuocityy of 2. Thesse
coefficcient param
resultss were then compared
c
too the ones avvailable from
m the commeercial MEA.
Keywo
ords: permeeability coeff
fficient, membbrane electrrode assemblly
I. INTR
RODUCTION
N
Membrrane Electrode Assemblies (M
MEA) is the ccore componennt of fuel celll. It consists of
o the electrolyyte
membraane, anode and
d cathode electrodes. The eleectrochemical reactions occuur when a fuell and oxidant are
a
applied
d to the anode and cathode sides
s
of the M
MEA. There aree several fabriication methodds of MEA weere
reportedd, such as rollling, screen-prrinting, castingg, and sprayin
ng. Each of these
t
types prroduces differeent
MEA’s structure. Onee of the recent researches in sprayer
s
as whaat we interestedd in our laborattory, used one or
multi nozzle (Chun, 2001).
2
The most important paarameter in ME
EA is the wateer flux, usuallyy named as watter
transport phenomenoon. The wateer flux itself depends on electro – osm
motic behaviorr, diffusion annd
permeaability coefficieent, and protoon movement (Eikerling, 19
998, Hu, 20044). Some of researchers
r
haave
approacched the waterr transport pheenomenon in one, two and three dimensional (Hu, 200
04, Chen, 20033).
Based oon the mechan
nism of hydroggen bridge witthin membranee (Bansal,19988), we observeed that the watter
flux is pressure depenndent. The baalancing of hum
midity has to be
b insured withh avoiding thee floods of watter
and dehhydration that will cause ann ohmic lost. The minimizzing of ohmic lost was sugggested by manny
researchher by achievinng various com
mposition of m
materials and recconstruction off pore size of diffusion
d
layer of
electrodde. In this reseearch, we obseerved the perm
meability coeffi
ficient of MEA
A by setting thhe slope of watter
flux in a certain valuee.
2.THEO
ORY
MEA consists
c
of thrree componennt Gas Diffusiion Layer (GD
DL), Gas Difffusion Electro
ode (GDE), annd
membraane. The fabrrication processs of GDL andd GDE was made
m
using in-hhouse robotic sprayer machiine
adopted
d the Chun’s method (20001). The peermeability coefficient of thhe fabricated electrodes was
w
characteerized. We are
a assuming the
t water mass transfer reprresents by thee simplest equation as follow
ws
(Midlem
man, 1997, Muuider, 1991, Baaker,200, Frankk,2004):
(1)
N = κ .∆Peff
Where K is the memb
brane permeabiility coefficientt that depends on the porosityy, pore radius, viscosity and
turtocityy factor, effecttive pressure difference
d
( ∆Peff ) and N perrmeate flux. Thhe System connfiguration in our
o
study iss an in-house robotic
r
sprayerr was in house fabricates. Datta of work piecce is computerr controlled. The
T
post pro
ocessor converts the spray coating
c
carbonn ink path-line to the robot ccontrol commaand to move the
t
sprayerr in X-Y direcction. Such sp
praying system
m will producee an even GD
DL. The GDE
E is produced by
b
sprayin
ng the GDL wiith a similar prrocess as menttioned above but
b with differrence formula of ink-platinum
m.
The prooduced MEA is
i subjected to hot pressing in
i a sandwich form of GDE with membranne inside in high
temperaature and high pressure (Chunn, 2001). Afteer that we activvate the MEA using
u
treatmentt method (Kwaak,
B.2-1
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
2000), and
a then boileed it to avoid water
w
and gasess inside the poore. MEA wass characterize the
t dimension of
pore off MEA, GDL and
a GDE usingg BET and SE
EM by analyzinng the permeaate and the slop
pe of water fluux.
The anaalyzed permeatte was done ussing continuouus membrane syystem method and the analyzzing of the slope
water flux
fl by linear fitting
fi
curve aggainst pressure difference as presented
p
in Eq.(1). Permeaability coefficieent
and ME
EA performancce was investiggated using FCT
TS.
The robbot used in the system employys a specific atttitude expressiion of the x-y configuration
c
s
shown
in Fig 1.
S
W
Z
Subsstra
Y
W2
Fig 1. Thee x-y configuraation
The sprray variable is expressed by frequency ( ω ), nozzle heigght (W1), distriibution distancce (W2), division
numberr of spray coatiing line on subbstrate (n) and nozzle velocitty (S). The sprray direction cooating process is
designeed perpendicular to substratee. If thick sizee ( t e ), pore diiameter (dp,), pporosity ( ε ), typical
t
activatted
specificc surface (as). The
T variable off ink drop distrribution of the nozzle will afffect the layer size
s are µ , v annd
p.
t e , dp, ε , as = f(K, µ , v, σ , p) ………3
…
Assumee p is constantt, surface tensiion ( σ ) consttant, thus theooretically the correlation
c
of t e , dp,
ε ,and as
toward all variables and the robotic movement as well as thee drop variablle are given by
b dimensionleess
equation 4
t e , dp, ε , as.= f(Nsprayy,,Re,W)……………….………44
The visscosity effect and surface tension
t
are coonstant and neeglecting the ssolidifying efffect on substraate
surface. Based on equ
uation 3, the t e , dp, ε , as aree given by the dimensionless
d
equation 4 to 5,
5 as follows :
t e , dp, ε , as.= f(Nsprayy) ………………
…………..….. 5
Equatioons 4 to 5, the t e , dp, ε and as of an electrrode can be dettermined by thee robotic charaacteristic numbber
(Nspray). Assumed the layers results from
f
robotic spprayer is set too be the MEA, therefore the relationship
r
off N
with thee current densiity of PEM fuel cell can be formulated usiing Grujicic (22004) . The sprraying techniqque
model for
f MEA fabriccation is as folllows:
Currentt density (i):
i = K 4CO 2 (1 − ( K 5 exp( − K 6 (φ s ))1 / 2 )
x cothh( K 5 exp( − K 6 (ϕ s )))1 / 2
12t e (1 − ε ) FD
F O2
=f(Nsprayy)…………..…7
)
7
K4 =
0 .5 d p
K5 =
i0, c as1 (0.5d p ) 2
4 FCoref2 DO 2
………………………
…………………
…………………..6
= f(Nspray)…
………………88
and Voltage (V):
B.2-2
V =
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
RT
R
ln{ f1 (dp, ε )CO 2 (1 − ( f1 (dp, ε )
0.5 F
i0,c
RT
(φs ))1 / 2 ) x
exxp(−
ref
0.5F
Co 2
E−
coth( f1 (dp, ε )
i0,c
C
ref
o2
e −
exp(
…
………………………………
…………………
……..9
RT
(ϕ s )))1/ 2 ) / io ,c
0.5F
Based on
o equations, the
t value of cooeffisient modeel of current density
d
depend on Nspray. The Nspray becom
mes
the maiin control for manufacturing
m
layer
l
size of MEA
M
design forrm
d
form coonfiguration em
mployed by ressearches as shoown in Fig.3a is
i the G-GDL-EGenerallly, the MEA design
M-E-GD
DL-G. In this paper
p
the catallyst layer emplloyed the confi
figuration as shhown in Fig.3bb to obtain highhly
activateed specific surrface area. In Fig.3c the cattalyst utilised a support to composite
c
the catalyst into the
t
membraane (novel).
3.EXPE
ERIMENT
Active carbo
on with 400 meshes
m
was lam
minated on carrbon cloth. Poolytetrafluoroeethylene (PTFE
E),
Nafion liquid was ussed also. Modderately polar of mix solvennt from water and isopropan
nol was used as
medium
m for carbon mobilition,
m
annd the membraane used in th
his observatioon is nafion 117 produced by
b
DuPontt. The fabricattion process of
o MEA consiists of three steps;
s
the layinng of GDL, GDE,
G
membraane
activation and assembbly of membraane electrodes (MEA). In thee GDL fabricaation layer mixxture of activatted
d PTPE are stirred for 10 minutes. The sluurry produce has
h viscosity for
f
carbon, alcohol, wateer, Nafion and
about 1.17
1
cp and ussually called as
a carbon ink. The carbon in
nk is sprayed on carbon clo
oth with flow of
sprayin
ng as 0.5 ccs, 6 bar air presssure through spraying nozzzle, with patteern of 4 cm, and
a the standinng
positionn of nozzle is perpendicular
p
w the objectt, with 10 timees moving periiod. The fabriicated GDL muust
with
be dried
d using vacuum
m dryer in room
m temperature for about 2 hoours, and then w
will be subjected to BET, SE
EM
and perrmeate test charracterization. The
T profile andd permeability coefficient of tthe material waas test also.
In case of the fabricattion of GDE, the
t GDL must be sprayed wiith another mixxed material thhat consists of CPt, wateer, and alcoholl. Nafion, PTPE
E. The materiaals must be mixxed for 5 minuutes, and the reesult is namely as
carbon ink C-Pt and has
h 1.16 cp viiscosity. The pprocedures of spraying afterr mixing proceess are similar as
above.
The thiird material thaat we used is membrane
m
Naafion 117. Mem
mbrane were ccleaned to remove any trace of
impuritties and stored in deionized water
w
further use.
u The MEA, GDE and mem
mbrane will saandwich togethher
using hot
h press. The produces electtrode will be rrinsed with 0.55 M H2SO4 annd have to be dried in vacuuum
dryer inn room temperrature for 2 hoours. The resuult then has to be characterizzed using perm
meability test annd
FCTS.
ULT AND DIS
SCUSSION
4.RESU
Characcterization. Th
he fabrication process of G
GDE was repeaated seven tim
mes in insure reproductabilitty.
Surfacee scanning wass done using SEM
S
have produced to charaacterized the ccrack and the roughness
r
of the
t
GDE suurface. From the
t SEM charaacterization of experimental 1 to 6 (see Fig.. 2a), the resultts still has cracck,
and in experimental (see Fig. 2b) the result is free
f
of crack. Experimentaal (b) also hass similar surfaace
roughneess with com
mmercial GDE
E (see Fig. 2c).
2
Matrix morphology
m
w
was investigateed for particlles
characteerization BET studies was peerformed and reveal
(a)
B.2-3
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
(b
b)
(c)
Fig. 2 Surface microscope
m
scaanning of (a). F
First trial (b). After
A
modified, (c). Referencee electrode
Table 11. BET analyssis
Propperty
GDE
(a)
GDE
(b)
ME
A
(a)
MEA
(b)
ME
A
(c
Diameeter
pore (A
A o)
Surfacce
area (m
m2/g)
Volum
me
pore (ccc/g)
34.3
1
472
41.15
34.4
1
410
39.41
68.2
450
220
0.09
7
0.157
0.06
0
0.102
0.08
1
451
For the next observatiion, we will focus on experim
mental (b) that has activated ccarbon as 1.05 g cm-2 and 0.53
g cm-2 PTFE, 0.51 g cm-2 C-Pt and
d the scale chaaracteristic as mentioned
m
in T
Table 1. Usingg pore dimension
point of
o view withinn micropore sccale, experimeental (a) and (b)
( have mesoopore characterristics (Ruthveen,
1997). Another advanntage of experrimental (b) is that it has greeater adsorption capacity andd pore capabiliity
mental in our observation.
o
Affter assembly the
t membrane with electrodee of experimenttal
than thee other experim
(b), the pore dimensioon of MEA rem
mains similar w
with GDE expeerimental (b) sttand alone. Wee could concluude
that thee experimental (b) is appropriiate as a materiial for fabricatiing fuel cell.
Permea
ability Coefficcient. Within MEA
M
fuel cell, the GDL has a function to diistribute humid
dity water and
evacuatte water from electrode
e
part, meanwhile thee electrode is used
u
to distributte humidity waater and will usse
for trigggering the reacction between Pt
P and CO. Thhe membrane allso has task to bond water forr bridging
hydrogeen and sweepin
ng out the electron (Mikko, 2003).
2
If we flo
ow water throuugh the layers within
w
MEA,
then thee water flux insside each layerr will depend oon the channel structure.
B.2-4
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
GDL (3a)
Electrode (3b)
Mem
mbrane (3c)
Fig 3. Surface
S
of GD
DE
For GD
DL, the water flux
fl will be affe
fected by channnel that has beeen built withinn the carbon clo
oth (see Fig. 3aa),
meanwhhile the waterr flux inside the electrode will be affectted by channeel that has beeen built by the
t
mesopoore.
Figure 3c
3 illustrates good
g
profile off pore within m
membrane to make possible w
water flux flow through it. Suuch
kinds of
o pore profile are usually callled as porosityy and tortuositty. To build beetter understandd about what we
w
mention
ned above, we will explain more
m
detail abouut the capabilitty of MEA to flow
f
water fluxx as follow
N = 3.100 −4 ∆Peff
N = 10 −44 ∆Peff
(2)
(3)
N = 2.100 −4 ∆Peff
(4)
-4
-1
Eq. (2) is developed from
f
eq. (1) wiith κ for abouut 3.10 gcm men–1psia-1 thaat has been fouund using Figuure
o water flux. Using tortuossity table we got
g 1.1 for 3.100-4
4, and ∆Peff indicatees the pressuree differences of
Water flux (gmol/cm2 men)
f flowing watter within GDL
L is greater thhan
permeaability coefficieent. It means that the lengthh of channel for
the thicckness of GDL itself. Furtherrmore, for calcculating the cap
pability of elecctrode to flow water
w
follows eq.
e
(3) as shown
s
in Figuure 4b. With 10-4 gcm-1menn–1psia-1 of peermeability coeefficient it is similar with 1.7
1
tortuosiity. It also meeans that the channel
c
for floowing water within
w
electrodee greater than the thickness of
electrodde itself. From
m the calculation of water fluux as mention
ned above, we could emphasize that the floow
resistan
nce of water within
w
electrodee is greater thaan within GDL
L. It means thaat GDL is capaable to distribuute
and evaacuate water eaasier and electrrode could flow
w in or out wateer faste
0,0035
Membrane
0,003
MEA
GDL
0,0025
GDE
0,002
0,0015
0,001
0,0005
0
0
2
4
6
8
10
12
Pressure difference (p
psi)
Fig
g 4. Characterristic Permeab
bility Water
For calcculating the water
w
flux withiin membrane N
Nafion 177, wee use eq. (4) w
with permeabiliity coefficient of
2.10-4 gcm
g -1men–1psiaa-1 or 1.4 tortuuosity, it meanss that the chan
nnel length wiithin membranne is also greatter
than itss thickness. From
F
these thrree layers disccussed above, we could connclude that waater resistance as
followss
GDL < membrane < electrode
(5)
After assembly of meembrane and electrodes
e
on 335 kgfcm-2 preessure and 130 °C temperatuure, we get watter
flux as in eq. (6).
N = 9.10 −5 ∆Peff
B.2-5
(6)
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
The cappability of ME
EA to distribuute water is prooportional withh the pressuree difference thhat is attached to
MEA. With 2.8 psiaa pressure diffferences, MEA
A could flow water
w
around 3.3 10-5 gmol cm-2 min-1 annd
mrestore around 3.6 10-4 gmol cm-2. The permeabiility coefficientt of water withhin MEA is aroound 9.10-5 gcm
1
–1
-1
men psia
p
or with to
ortuosity greateer than 2. Theerefore we cou
uld modify eq. ((5)
GDL < membrane < electrode
e
< ME
EA
(7)
Electrodde has greatestt water resistannce, it means thhat to fabricatee MEA, we havve to modify electrode
e
layer to
control the water disttribution and evacuation
e
prooperties. Inclu
uding the comm
mercial MEA (with 2.10-6gcm
m1
–1
-1
men psia
p
permeabiility coefficien
nt), eq. (7) will have to modify
fy to
(8)
GDL < membrane < electrode
e
< ME
EA < MEA Com
m
4.3. Perrmeability expeeriment relatedd to performancce of MEA fueel Cell
In obseerving the MEA
A fuel cell wiith single stackk, pressure at anode is set up
u greater thann the pressure of
oxygen
n. With pressurre difference of
o 2.8 psi and fl
flow rate of H2
2 as 0.3 slpm, oxygen
o
0.4 slpm
m and a floodinng
water iss happened witthin membranee, then the perfformance of MEA
M
fuel cell ccould be illustrated as in Figuure
5.
1200
1200
Curr.MEA exp.
Curr.MEA com.
1000
Volt.MEA exp.
Volt MEA com.
800
800
600
600
400
400
200
200
0
Voltage (mV)
Current (mA/cm2)
1000
0
0
20
Time (men.))
40
Fig 5. Characteristiic Performancce MEA fuel C
Cell
As can be seen in Figure 5, the MEA fuel cell w
with greater peermeability coeefficient will have
h
less curreent
density voltage. In thhis operation, the
t anode MEA
A fuel cell will be dehydrateed and osmoticc electron will be
happeneed through thee membrane. This
T
osmotic eelectron or usuually called ass electron diffu
fusion will cauuse
ohmic losses
l
inside th
he MEA fuel cell. In such coondition, the chhanging of currrent within ME
EA tends to drop
rapidly than the comm
mercial MEA for
f 30 minutes operation timees. This differrence is due to the permeabiliity
coefficiient of our ME
EA greater thann the commerciial MEA. If H2 and O2 suddeenly drop out to
t zero, the ME
EA
current will be dischaarged very rappidly than the commercial MEA.
M
It meanns that MEA with
w very rapiddly
nt current (risee time and fall time) is good enough to con
ntrol dehydratiion in low tem
mperature withoout
transien
any dryying process (Savadogo, 20033)
5.CON
NCLUSION
a
the wateer flux within the
t geometricaal structure of M
MEA is influennced strongly by
b
From thhe discussion above,
porosity
y and tortuosityy. The tortuoccity of the layeer could be deffined as GDL < membrane < electrode or we
w
got thee permeability coefficient of DGL as 3.110-4 gcm-1men
n–1psia-1, Electrrode as 10-4 gcm
g -1men–1psia-1
-4
-5
-1
–1
-1
membraane as 2. 10 , MEA as 9.100 gcm men psia
p
or tortuoosity greater thaan 2 for MEA. The MEA will
w
occur ohmic
o
losses ussing greater perrmeability coeffficient.
ACKNOWLEDGEM
MENTS
The autthors would likke to express their
t
gratitude to the UKM University
U
andd Environmentt of Malaysia for
f
the finaancial support through
t
IRPA grant: IRPA 022-02-02-0003-PR0023 11-088
B.2-6
SEMINAR NASIONAL
L TEKNIK KIIMIA SOEBA
ARDJO BROTOHARDJO
ONO IX
Program Stu
udi Teknik Kimia UPN “V
Veteran” Jawaa Timur
Surabayya, 21 Juni 20012
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B.2-7