Journal of Power and Energy Engineering, 2013, 1, 95-100
http://dx.doi.org/10.4236/jpee.2013.15016 Published Online October 2013 (http://www.scirp.org/journal/jpee)
Copyright © 2013 SciRes. JPEE
95
Performance Investi gation of Membrane Elec trode
Assemblies for High Tem perature Proton Exchange
Membrane Fu el C el l
Huaneng Su, Sivakumar Pasupathi, Bernard Bladergroen, Vladimir Linkov, Bruno G. Pollet
HySA Systems Competence Centre, South African Institute for Advanced Materials Chemistry, University of the Western Cape,
Private Bag X17, Bellville 7535, South Africa.
Email: suhuaneng@gmail.com
Received August 2013
ABSTRACT
Different types of ABPBI (poly(2,5-benzimidazole)) membranes and polymer binders were evaluated to investigate the
performance of MEAs for high temperature proton exchange membrane fuel cell (HT-PEMFC). The properties of the
prepared MEAs were evaluated and analyzed by polarization curve, electrochemistry impedance spectroscopy (EIS),
cyclic voltammetry (CV) and durability test. Th e results showed that MEA with modified ABPBI membrane (AM) has
satisfactory performance and durability for fuel cell application. Compare to conventional PBI or Nafion binders, poly-
tetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF) are more attractive as binders in the catalyst layer
(CL) of gas diffusion electrode (GDE) for HT-PEMFC.
Keywords: High Temperature Proton Exchange Membrane Fuel Cell; ABPBI (Poly(2,5-Benzimidazole)); Polymer
Binders; Gas Diffusion Electrode; Membrane Electrode Assembly
1. Introduction
Polybenzimidazole (PBI) based high temperature proton
exchange membrane fuel cells (HT-PEMFCs) have at-
tracted more and more attention in these years due to
their advantages over low temperature PEMFCs based on
perfluorosulphonic acid polymer electrolytes ( e.g. Nafion)
[1]. However, the sluggish kinetics of the oxygen reduc-
tion reaction (ORR) [2] and the transport limitations of
protons and reactants in cathode, especially in the pres-
ence of phosphoric acid (PA), limit the cell performance
of the high temperature PEMFC. Therefore, enhancing
the cell performance is one of the most important issues
for high temperature PEMFC being more widely consi-
dered as an alternative to the low temperature PEMFC
systems.
Membrane electrode assembly (MEA) is the most im-
portant component in high temperature PEMFC system
and it plays a major role in determining cell performance.
It consists of a proton exchange membrane sandwiched
between two gas diffusion electrodes (GDEs), which pos-
sess a porous structure that allows easy transport of reac-
tant gases and water to and from the catalytically active
zone. Therefore, the components of MEA, i.e. electrolyte
membrane and GDEs, have significant influence on the
performance of high temperature PEMFC.
Several types of electrolyte membrane, such as poly
[2,2’-(m-phenylene)-5,5’-bibenzimidazole (PBI or mPBI),
poly(2,5-benzimidazole) (ABPBI) and their derivatives
[3]; several types of polymer ionomers, such as PBI [4-6],
polytetrafluoroethylene (PTFE) [7,8], polyvinylidene dif-
luoride (PVDF) [9,10] and Nafion [11,12], can be used in
the MEA as proton exchange membranes and catalyst
layer (CL) binders for high temperature PEMFC. The phy-
sicochemical properties of these membranes and binders
are different from each other; consequently the resultant
MEAs have their own advantages and shortcomings. In
this work, the MEAs with four types of ABPBI mem-
branes and four types of binders were investigated to
evaluate their fuel cell performances. The properties of
these MEA were characterized by single cell polarization,
electrochemical analysis and dur ability test.
2. Experimental
2.1. Preparation of GDEs
Hispec 4000 Pt/C catalyst (40 wt% Pt, Johnson Matthey)
was used in this study. All GDEs were prepared by our
newly developed spraying method [13]. The catalyst powd-
ers were deposited onto the microporous layer of com-
mercially available GDL (Freudenberg, Germany). The
Performance Investigation of Membrane Electrode Assemblies for High Temperature Proton Exchange Membrane Fuel Cell
Copyright © 2013 SciRes. JPEE
96
catalyst loadings were calculated by weighing the GDEs
before applying the catalyst inks, and then after applica-
tion and oven drying for overnight. The platinum load-
ings of all GDEs (both anode and cathode) used for this
study are 0.5 mgcm2, unless otherwise stated.
2.2. Preparation of MEAs
The membranes used in this study are ABPBI (denoted
as AM, AM 55, AMcl and APcl), which were supplied
by FuMA-Tech. The properties (thickness, composition,
process method etc.) of these membranes vary from each
other. For doping with PA, the membranes were im-
mersed in 85% acid solution for certain time at 100˚C
until their acid doping level of about 3.7 molecules of
H3PO4 per polymer repeating unit (PRU) were obtained.
Before being used, the membrane was taken from the PA
bath, and the superficial acid onto the membrane was
thoroughly wiped off with lab tissue. To ge the r w ith gaskets
made of fluorinated polymer, the MEA was assembled
by sandwiching the doped membrane between two GDEs
impregnated with PA in a single cell fixture (BalticFuel-
Cells GmbH, Germany) without a preceding hot-pressing
step. The active areas of all MEAs are 5 cm2, unless oth-
erwise stated.
2.3. Single Cell Test and Electrochemical
Characteriz ation
The cells were operated at 150˚C (unless otherwise stated)
and 2 Nmm2 piston pressure in a FuelCon Evaluator C
test station (FuelCon, Germany). Pure hydrogen was fed
to the anode and air to the cathode respectively, with
flow rates (unless otherwise stated) of 100 mlmin1 (hy-
drogen) and 250 mlmin1 (air), at ambient pressure. Both
hydrogen and air were used as dry gases, directly from
the compressed bottles without external humidification.
Electrochemical impedance spectroscopy (EIS) and cyc-
lic voltammetry (CV) were performed using an Autolab
PGSTAT 30 Potentiostat/Galvanostat (Metrohm). EIS
measurements were carried out at a cell voltage of 0.6 V
with amplitude of 5 mV, and in the frequency range of
100 mHz to 20 kHz. The impedance data were obtained
by calculation and simulation with Autolab Nova soft-
ware. Voltammetric measurements, undertaken to study
the electrochemical active surface area (EASA), were con-
ducted using dry N2 at the cathode (working electrode)
and dry H2 at the anode (counter electrode and reference
electrode) at cell working temperature. Cyclic voltam-
mograms were recorded from 1.2 V to 0.05 V at a scan
rate of 0.05 Vs1.
3. Results and Discussion
3.1. Effect of Electrolyte Membrane
Figure 1 shows the FT-IR spectra of the four ABPBI
membranes. The characteristic peaks of PBI are shown in
all membranes; hydrogen-bonded N-H stretching at 3184
cm1, the free non-hydrogen-bonded N-H stretching at
3415 cm1, and C=C and C=N stretching bands for ben-
zimidazole group at 1612, 1590, and 1443 cm1 can be
observed from all the membrane samples [14], indicating
that no significant structural changes took place in the
bulk polymer of the above ABPBI membranes. However,
it should be noted that sharp new peaks in the zone
ranged between 800 and 1300 cm1 are observed for the
three modified ABPBI membranes (AM, AM 55 and
AMcl), which are indicatives of interactions between the
additives and ABPBI groups [11]. Interactions between
the additives and ABPBI groups should increase the sta-
bility of the modified ABPBI membranes, as demon-
strated in the durability test later in current study (see
Section 3.3).
The single cell performance comparison of the MEA
with AM, AM 55, AMcl and APcl are shown in Figure 2.
It should be noted that the polymer binders used in these
MEAs are PVDF (the binder content in CL has been pre-
optimized for this comparison), which is the preferred
4000 3000 2000 10000
Intensity / a.u.
W avenum b er / cm
1
AM
AM5 5
AMc l
APcl
Figure 1. FT-IR spectra of various ABPBI membranes.
0.0 0.4 0.8 1.2 1.6
0.2
0.4
0.6
0.8
1.0
AM
AM 55
AMcl
APcl
Current density
/ A cm
2
Cell voltage / V
0.0
0.1
0.2
0.3
0.4
P
ower density / W cm
2
Figure 2. Polarization curves and power density curves of
HTPEMFC with MEAs using different ABPBI membranes,
operated at atmosphere pressure and 150˚C.
Performance Investigation of Membrane Electrode Assemblies for High Temperature Proton Exchange Membrane Fuel Cell
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97
binder pre-optimized in Section 3.2. It is clear that the
MEA prepared by AM membrane yields much better per-
formance than the MEA prepared with other membranes.
At a working voltage of 0.6 V, the current density of the
MEA with AM membrane reaches 0.208 Acm2, the
maximum power density of the MEA with GDE-1 can
reach 0.363 Wcm2 at 0.313 V.
To understand the performance difference of the MEAs
prepared with these membranes, overall analysis on the
polarization curves and electrochemical measurements
on both GDEs are performed. Generally, the po larization
curve of a PEMFC could be divided into three segments
(corresponding to different electrochemical processes) ac-
cording to its different voltage drop rates. The initial
drop of the curve at a very low current density is due to
the sluggish kinetics of oxygen reduction at the cathode,
determined by the nature of the electrodes. It can be seen
in Figure 2 that all MEAs show similar voltage drop in
this region (0 - 0.1 A cm–2), which is reasonable consi-
dering the GDEs used in all MEAs were the same. To
prove this point, CV measurements are performed to
study the EASAs of the all MEAs, as shown in Figure 3
(only H2 desorption peaks were showed for clarity).
The corresponding EASAs were calculated from the
H2 desorption peak of each voltammogram and the re-
sults are summarized in Table 1. It can be seen that the
EASA values of all MEAs are between 17.4 and 22.3
m2g1, only small differences were detected among these
MEAs. The EASA results are certainly consistent with
their performances (activation polarization zone) pre-
sented in Figure 2.
Figure 3. Cyclic voltammograms of the MEAs with differ-
ent ABPBI membranes.
Table 1. Electrochemical characteristics of the MEAs with
different ABPBI membranes.
MEA type RΩ (Ω) Rct (Ω) EASA (m2g1)
AM 0.05 0.07 22.3
AM 55 0.12 0.13 17.4
AMcl 0.13 0.11 18.7
APcl 0.12 0.13 19.1
The subsequent drop in the polarization curve is as-
cribed to ohmic loss, which originates from ionic flow
through the electrolyte membrane, and from electron
flow through the electrode layers, current collectors and
flow field plates. As shown in Figure 2, the four MEAs
present much different decreasing slopes in the linear
region, implying that they had different ohmic resis-
tances. To verify the resistances of the single cells with
these MEAs, in situ impedance measurements are per-
formed at the cell voltage of 0.6 V, as shown in Figure 4.
Only one semicircular loop can be observed in the Ny-
quist plot as the electrode process is dominated by ORR
[15]. Through simulation with a simple RC equivalent
circuit, their corresponding cell resistances (RΩ) and charge
transfer resistances (Rct) can be calculated, which are also
presented in Table 1. It can be seen that there is no sig-
nificant difference in cell ohmic resistance for the MEAs
with the last three membranes (i.e. AM 55, AMcl and
APcl), which is consistent with the similar decreasing
slopes in the linear regions of their polarization curves
presented in Figure 2. However the ohmic resistance of
the MEA with AM membrane is only 0.05 Ω, less than
half of the other membranes. It suggests that AM mem-
brane has higher proton conductivity than other mem-
branes because all other parts in the test fixture during
testing were identical. Moreover, the charge transfer re-
sistance of the AM MEA is much smaller than those of
the other three, which suggests that AM MEA yielded a
more efficient electrochemical active layer, which means
that the interactions between the GDE and the AM mem-
brane are more efficient.
The last voltage drop at high current density is due to
mass transport limitations o ccurring in the electrodes and
the membrane. However, from Figure 2 it can be seen
that, for all MEAs, the vo ltage drop rates in low cell vo l-
tage region (<0.4 V) of their polarization curves are al-
most the same with that in their linear regions, which
means that no obvious mass transfer limitations in these
Figure 4. In situ impedance curves of the MEAs with dif-
ferent membranes, at a cell voltage of 0.6 V.
0.05 0.10 0.15 0.20 0.25
-0.02
0.00
0.02
0.04
0.06
AM
AM 55
AMcl
APcl
Z' ' /
Z' /
Performance Investigation of Membrane Electrode Assemblies for High Temperature Proton Exchange Membrane Fuel Cell
Copyright © 2013 SciRes. JPEE
98
MEAs even at the high current densities. It is unders-
tandable when considering the high operating tempera-
ture (150˚C, only water vapor existed in the GDEs) and
the high stoichiometries reactants (ca. 7/7.5 for H2/A ir at
0.4 Acm–2) due to the small active area (~5 cm2) even at
low gases flow rates [16].
From all these analyses and electrochemical results, it
can be concluded that the good performance of the MEA
with AM membrane is primarily attributable to the high-
er proton conductivity and good interactivity of the elec-
trolyte membrane and the GDEs, which makes a more
efficient electrochemical active layer, accordingly the
minor ohmic resistance and charge transfer resistance.
For these reasons, the AM membrane, which performed
best at usual working voltage of 0.6 V and maximum
power density, is chose for all subsequent studies.
3.2. Effect of Polymer Binders
Figure 5 shows the performance comparison of the MEA
with the four different polymer binders. It is clear that the
PTFE and PVDF GDEs yield much better performance
than the GDEs prepared with PBI and Nafion binders in
all regions of the polarization curve. At a working vol-
tage of 0.6 V, the current density of the MEA with PVDF
GDEs reaches 0.53 Acm2, 121% higher than that (0.24
Acm2) of the MEA with PBI GDEs. The maximum
power density of the MEA with PTFE GDEs can reach
0.61 Wcm2 at 0.35 V. These values are almost the best
results yet reported for similar PA-doped PBI fuel cell
and operated using air, which are comparable to the per-
formances of the commercial MEAs with high Pt load-
ings [17]. This is mainly attribut able to the properties of
PTFE and PVDF binders that they exist in the CLs as a
fiber phase, which makes catalyst particles less likely to
be encapsulated in the binder, then making more Pt sur-
face available in the CLs. On the contrary, PBI and Na-
fion polymer ionomers are easily covered on the surface
of the catalyst particles, which could impose mass trans-
port limitation in CLs due to the low gas permeability of
these films formed on the catalyst sites [15].
3.3. Durability
From above physical characterizations and electrochem-
ical analysis results, it can be concluded that good MEA
performance (at usual working voltage of 0.6 V) can be
delivered by using PVDF as CL binder and AM mem-
brane as electrolyte membrane. However, the stability or
durability of this MEA is also a major concern for the
real application and commercialization of HT-PEMFC.
The remarkable long term stability of PA-doped PBI
MEA is achieved in some research groups’ works [9,
10,18,19]. To verify the stabilities of the MEA with AM
membrane and PVDF binder, a short term durability test
was performed, as shown in Figure 6.
0.0 0.5 1.0 1.5 2.0 2.5
0. 2
0. 4
0. 6
0. 8
1. 0
PVDF
PTFE
PBI
Nafion
Cell voltage / V
Current density / A cm
2
Figure 5. Polarization curves of PA-doped ABPBI (AM
membrane) fuel cell using GDEs prepared with different
polymer binders, operated with flow rates of 200 mlmin1
(hydrogen) and 1000 mlmin1 (air), at ambient pressure
and 160˚C.
Figure 6. The durability test of the MEA with AM mem-
brane and PVDF binder.
It can be seen that the cell voltage of the MEA remains
at ~0.56 V without obvious drop after almost 1000 h op-
eration. The degradation rate calculated by linear fitting
of cell voltage data points after the MEA activation is
about 56.8 μVh–1, which are acceptable for most appli-
cations [12,18-20].
4. Conclusion
Four types of ABPBI membranes and four types of po-
lymer binders were evaluated to investigate the perfor-
mance of MEAs for high temperature proton exchange
membrane fuel cell (HT-PEMFC). The results showed
that MEA with modified ABPBI membrane (AM) as
electrolyte and PVDF as CL binder has satisfactory per-
formance and durability for fu e l cell ap plication. At usual
working voltage of 0.6 V and cell temperature of 150˚C,
the peak power density reached 0.363 Wcm2, and the
current density at usual working voltage 0.6 V was up to
Performance Investigation of Membrane Electrode Assemblies for High Temperature Proton Exchange Membrane Fuel Cell
Copyright © 2013 SciRes. JPEE
99
0.208 Acm2, which are comparable to the results yet
reported for similar MEAs with Pt loading of ~0.5
mgcm2. The MEA showed good durability in a short
term operation: the cell voltage remained at ~0.56 V
without obvious drop after almost 1000 h operation.
5. Acknowledgements
This work is supported by Hydrogen and Fuel Cell
Technologies RDI Programme (HySA), funded by the
Dep artment of Science and Technology in South Africa
(project KP 1-S01).
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