1. Electrochimica Acta 139 (2014) 217–224
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Effect of Polytetrafluoroethylene on Ultra-Low Platinum Loaded
Electrospun/Electrosprayed Electrodes in Proton Exchange Membrane
Fuel Cells
Xuhai Wang, Francis W. Richey, Kevin H. Wujcik, Roman Ventura,
Kyle Mattson, Yossef A. Elabd∗
Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States
a r t i c l e i n f o
Article history:
Received 2 May 2014
Received in revised form 19 June 2014
Accepted 20 June 2014
Available online 11 July 2014
Key words:
electrospinning
nanofiber
fuel cell
Nafion
platinum
a b s t r a c t
In this study, catalyst layers (CLs) were fabricated using a simultaneous electrospinning/electrospraying
(E/E) technique to produce unique nanofiber/nanoparticle membrane electrolyte assemblies (E/E MEAs)
evidenced by scanning electron microscopy. Specifically, the effect of polytetrafluoroethylene (PTFE) in
these E/E MEAs on polymer electrolyte membrane (PEM) fuel cell performance was evaluated. E/E MEAs
result in high fuel cell performance at ultra-low platinum (Pt) loadings with higher electrochemical
surface areas as evidenced by cyclic voltammetry experiments. Without PTFE, an E/E MEA operated
at 172 kPa (25 psi) back pressure results in a maximum power density of 1.090 W/cm2
(H2/O2) and
0.647 W/cm2
(H2/air) with only 0.112 mgPt/cm2
total Pt MEA loading. Introducing PTFE (at only 1 wt%)
to the electrospinning process results in an E/E MEA operated at the same back pressure (172 kPa (25
psi)) with an even higher maximum power density of 1.240 W/cm2
(H2/O2) and 0.725 W/cm2
(H2/air) at
a lower total Pt MEA loading of 0.094 mgPt/cm2
. This corresponds to a significant reduction in Pt loading
(16% of control) with only a modest reduction in power density (∼86-87% of control), where the control
MEA was produced using a conventional coating method and resulted in maximum power density of
1.420 W/cm2
(H2/O2) and 0.839 W/cm2
(H2/air) at a Pt MEA loading of 0.570 mgPt/cm2
(172 kPa (25 psi)).
An excellent total MEA platinum utilization of 0.076 gPt/kW (∼13.2 kW/gPt) was achieved with the E/E
MEA with PTFE at only a 0.094 mgPt/cm2
total Pt MEA loading. The improvement in E/E MEA with PTFE
was a result of increased hydrophobicity of the nanofibers evidenced by contact angle measurements
and improved PEM fuel cell performance at higher limiting current density in the mass transport region.
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Proton exchange membrane (PEM) fuel cells are an excellent
alternative energy source for both stationary and mobile applica-
tions. However, currently the requirement for a significant amount
of platinum (Pt), the most active catalyst for PEM fuel cells, lim-
its the mass commercialization of PEM fuel cells [1,2]. In previous
work in our laboratory [3], an alternative electrode design was
explored to reduce the amount of required Pt, while still producing
adequate PEM fuel cell power output. A simultaneous electrospin-
ning/electrospraying (E/E) technique was employed to produce
unique nanofiber/nanoparticle electrodes as evidenced by scan-
∗ Corresponding author.
E-mail address: elabd@drexel.edu (Y.A. Elabd).
ning electron microscopy (SEM). Specifically, Nafion nanofibers and
Pt/C nanoparticles were introduced separately and simultaneously
by two different needles using electrospinninig and electrospray-
ing, respectively, to produce nanofiber/nanoparticle electrodes and
subsequently membrane electrode assemblies (MEAs). In this pre-
vious study, only cathodes were produced via E/E process and
anodes were produced using a conventional coating technique.
The E/E MEAs in this previous study resulted in ultra-low Pt
cathode loadings of 0.052 and 0.022 mgPt/cm2, where maximum
power densities (at 172 kPa (25 psi) back pressure) of 1.090 and
0.936 W/cm2 (H2/O2) and 0.656 and 0.625 W/cm2 (H2/air) were
achieved at these two Pt loadings, respectively. This was compared
to a conventional control MEA at a 0.42 mgPt/cm2 cathode cata-
lyst loading with maximum power densities (at 172 kPa (25 psi)
back pressure) of 1.420 and 0.839 W/cm2 for H2/O2 and H2/air,
respectively. These results correspond to a significant reduction in
http://dx.doi.org/10.1016/j.electacta.2014.06.139
0013-4686/© 2014 Elsevier Ltd. All rights reserved.

2. 218 X. Wang et al. / Electrochimica Acta 139 (2014) 217–224
Pt cathode loading (5-12% of control) at only a modest reduction
in power density (∼66-78% of control) for the E/E MEAs. Excellent
platinum utilization in the cathode of 0.024 gPt/kW (∼42 kW/gPt)
was achieved for the E/E MEAs at 0.022 mgPt/cm2 cathode loading.
These lower Pt loadings were achieved by increasing the triple
phase boundaries (TPBs), which are the junction points where
catalytic and electron conduction sites, reactant gases (pores),
and proton conducting Nafion ionomer meet. Cyclic voltammetry
results confirm these findings, where increased electrochemical
surface areas were observed for the E/E MEAs compared to the
control, i.e., more accessible Pt in the cathode. This E/E technique
differs from electrospinning [4,5] or electrospraying [6–9] alone,
where a mixture of Nafion and Pt/C are expelled from the same
needle. Contrastingly, the E/E technique allows for a higher level of
control over fiber size and Pt loading compared to other electrode
fabrication techniques.
In this study, we explore the impact of having both cathode
and anode catalyst layers (CLs) prepared via the E/E tech-
nique and the effect of polytetrafluoroethylene (PTFE) in these
nanofiber/nanoparticle CLs. Previously, the effect of PTFE in gas dif-
fusion layers (GDLs), micro-porous layers (MPLs), and conventional
CLs on fuel cell performance has been investigated [10–19]. Pre-
vious work [10,11] has shown that GDLs loaded with 5-30 wt%
PTFE results in improved fuel performance due to an increase
in hydrophobicity, which improves mass transport of the reac-
tants from the gas flow channels to the CLs. However, excessive
PTFE loading in GDLs results in poor fuel cell performance due
to reduced electrical conductivity and gas permeability [12]. For
some MEAs, a hydrophobic MPL is supported on the GDL sub-
strate. Previous results have shown that ∼10-30 wt% of PTFE in
the MPL results in optimal fuel cell performance [13–15] due to
increased pressure on cathode side, which improves water man-
agement in the fuel cell [11,13,16,17]. The effect of PTFE in CL
on the performance of the fuel cell has been previously investi-
gated for conventionally painted electrodes [18,19]. Uchida et al.
[18] showed that the PTFE had an effect at high current densi-
ties, where flooding can limit fuel cell performance. Friedmann
and Nguyen [19] optimized their MEAs by varying the ratios of
Nafion, Pt/C, and PTFE in a two-step method to prepare the elec-
trodes, where their results showed that a PTFE content of 10-24
wt% produced the best fuel cell performances. This previous work
[10–19] demonstrates that a relatively high PTFE content (>10 wt%)
in the GDL, MPL, and CL is required to improve fuel cell perfor-
mance. Subsequently, the fuel cell performance decreases when
excessive PTFE is added due reductions in pore size and electrical
conductivity.
In this study, the effect of including PTFE in the E/E process
and subsequently on the fuel cell performance/Pt loading ratio was
explored. Both anodes and cathodes in the MEAs were produced via
E/E process. This is the first study to investigate the effect of PTFE
on nanofiber/nanoparticle CLs.
2. Experimental
2.1. Materials
Isopropanol (99.5%, Sigma-Aldrich), ethanol (99.5%, Decon
Labs, Inc.), Nafion solution (1000 EW, 5 wt% in a 3/1 v/v
of isopropanol/water, Ion Power), poly(acrylic acid) (PAA;
MV = 450,000 g/mol, Aldrich), 20 wt% Pt on carbon catalyst (Pt/C;
Vulcan XC-72, Premetek Co.), gas diffusion layer (GDL; SGL-25BC,
Fuel Cells Etc.), and Nafion NR-212 membrane (1100 EW, ∼50 ␮m
(0.002 in) dry thickness, Ion Power) were used as received. 60 wt%
polytetrafluoroethylene (PTFE) dispersion in water (Aldrich) was
diluted to 5 wt% with 3/1 v/v of isopropanol/water before use.
Ultrapure deionized (DI) water with resistivity ∼16 M cm was
used as appropriate. Ultra high purity grade N2, H2, O2 and ultra
zero grade air were all purchased from Airgas and used for all fuel
cell experiments.
2.2. Two-needle electrospinning/electrospraying (E/E) system
A custom-designed E/E apparatus was used and consists of
two high-voltage power supplies (Model PS/EL50R00.8, Glassman
High Voltage, Inc. and Model ES40P-10 W/DAM, Gama High Volt-
age Research), two syringe pumps (Model NE-1000, New Era Pump
Systems), two syringe needles (i.d. = 0.024 in., Hamilton), tubing (Pt.
No. 30600-65, Cole-Parmer), and a grounded collector (aluminum
foil coated cylindrical drum, o.d. = 4.85 cm). The collector drum is
connected to a motor (Model 4IK25GN-SW2, Oriental Motor) to
allow for rotation during the E/E process. The rotational speed of
the collector drum was set to 100 rpm. A gas diffusion layer (GDL)
was adhered to the collector drum, where nanofibers/nanoparticles
could be directly collected via the E/E process and catalyst ink
is electrosprayed and polymer solution is electrospun simulta-
neously. The needle tip to collector distances, applied voltages, and
solution flow rates were 15 and 9 cm, 10.5 and 12.5 kV, and 0.3
and 3 ml/h for the electrospinning and electrospraying processes,
respectively. 0.25-0.7 ml and 2.5-7 ml of solutions were electrospun
and electrosprayed, respectively, resulting in catalyst layers of sev-
eral micormeters in thickness on average. More details regarding
the two-needle E/E apparatus are described in Wang et al. [3].
2.3. Membrane electrode assembly (MEA)
Catalyst ink used in the electrospraying portion of the E/E elec-
trodes consisted of 20 mg Pt/C catalyst, 0.248 ml DI water, 0.043 ml
Nafion solution, 0.171 ml isopropanol/water (3/1 v/v), and 1.970 ml
ethanol. This mixture was sonicated for 3 min (Model CL-18, Qson-
ica Sonicator) prior to electrospraying. The polymer solution used
in the electrospinning portion of the E/E electrodes consisted of
79.2/19.8/1 wt/wt/wt Nafion/PAA/PTFE. A 5 wt% polymer (Nafion,
PAA and PTFE) solution was prepared by combining 131.1 mg PAA,
10494 mg of Nafion solution (5 wt%), 131.2 mg of PTFE solution (5
wt%), and 2491.7 mg isopropanol/water (3/1 v/v). This solution was
stirred at ∼70–80 ◦C for ∼12 h to ensure complete dissolution. The
solution was cooled down to ambient temperature before electro-
spinning. The catalyst ink and the polymer solution were used to
make E/E electrodes as described in the previous section. After the
E/E process, the E/E electrodes were annealed at 135 ◦C for 5 min.
MEAs were fabricated by sandwiching the Nafion NR-212 mem-
brane between two catalyst-coated GDLs (anode and cathode
catalyst layers) and hot pressing (heat press, Carver) for 5 min at
135 ◦C and 1.5 MPa (213 psi). All anode and cathode catalyst lay-
ers in this study were E/E electrodes, unless otherwise specified.
Fuel cell performance of E/E anode/cathode MEAs were compared
to MEAs where only cathodes were fabricated using E/E and where
both anode and cathodes were prepared using a standard hand-
painting GDL procedure (control). Details regarding the preparation
of these MEAs can be found elsewhere [3].
2.4. Electrode characterization
Morphological characterizations of the E/E electrodes were
investigated with scanning electron microscopy (SEM, Model
FEI/Philips XL-30, 10 kV). SEM images of the E/E electrodes
were collected after electrospinning/electrospraying of the
nanofibers/nanoparticles on GDLs, but before MEA fabrication. All
samples were sputter coated (Denton Desk II Sputtering System)
with platinum at 40 mA for 30 s before SEM analysis. The nanofiber
and nanoparticle diameters were measured using ImageJ software

3. X. Wang et al. / Electrochimica Acta 139 (2014) 217–224 219
by counting 30 randomly selected fibers and particles for each
SEM image.
The Pt loading was measured with thermal gravimetric analysis
(TGA; TGA 7, Perkin Elmer). A small portion of the E/E electrode
(∼5–7 mg) was heated in the TGA from ambient temperature to
900 ◦C at 5 ◦C/min in air at 20 ml/min. Since all components in E/E
electrode degrade above 900 ◦C with the exception of Pt, the Pt load-
ing was determined by comparing the weight of the E/E electrode
before and after exposure to 900 ◦C in the TGA.
Contact angle measurements of electrodes were measured at
ambient temperature. A microsyringe was used to apply a droplet
(12 l) of DI water onto the electrodes. A digital camera (Nikon
Coolpix 7900) was used to capture the droplet image after the
droplet was applied to and stable on the E/E electrode surface.
The contact angle was the angle measured at the gas-liquid-solid
triple point between the liquid-gas interface and the solid surface
as shown on the images [20].
2.5. Fuel cell tests and cyclic voltammetry (CV)
Each MEA (1.21 cm2 area) was placed between two serpentine
flow field graphite plates (1 cm2 flow area) separated by two
0.160 mm thick Teflon coated gaskets (Pt No. 381-6, Saint Gobian).
The entire fuel cell assembly consisted of an MEA, two gaskets,
and two flow plates placed between two copper current collectors
followed by endplates all held together by tie rods (bolts) with 11.3
N-m (100 lb-in) of torque. The fuel cell performance (polarization
curves: voltage vs. current density) of each MEA was evaluated
with a Fuel Cell Test Station (850 C, Scribner Associates, Inc.). Fuel
cell tests were conducted at both ambient and 172 kPa (25 psi) of
back pressure with saturated (RH = 100%) anode and cathode flow
rates of 0.42 L/min hydrogen and 1.0 L/min air, respectively. The
cathode, anode, and cell were all maintained at 80 ◦C. Polarization
curves were collected from open circuit voltage (OCV) to 0.2 V at
increments of 0.05 V/min. The fuel cell performance was recorded
after a new MEA was fully activated. The activation process
included operating an MEA at 0.7 V for ∼1-2 hours followed by
voltage scanning from OCV to 0.2 V several times. This activation
process was repeated until the MEA reached steady state and no
further increase in current was observed when the fuel cell was
held at constant voltage. The activation process typically occurs
over 4-6 h before the MEA reached a steady state.
Cyclic voltammetry (CV) was performed on a two-electrode
MEA with a potentiostat (Solartron SI 1287, Corrware Software)
at 20 mV/s from 0 to 0.9 V. In this configuration, the anode serves
as both the counter and reference electrodes. The fuel cell anode
and cathode were supplied with 0.040 L/min H2 and 0.018 L/min
N2, respectively. Temperatures of the cathode, anode and cell were
maintained at 30 ◦C. The Pt catalyst was assumed to have an average
site density of 210 ␮C/cm2 [21]. The electrochemical surface area
(ECSA) was determined from the hydrogen adsorption area from
0.1 to 0.4 V of the CV data.
3. Results and Discussion
Fig. 1 shows SEM images of E/E electrodes prior to MEA fabrica-
tion along with nanofiber diameter and nanoparticle diameter size
distributions. Specifically, Fig. 1 (a) shows an SEM image of an E/E
electrode with 1 wt% PTFE and 0.047 mg/cm2 Pt loading and Fig. 1
(b) shows a magnified view of Fig. 1 (a). Fig. 1 (a) shows that the
E/E electrode is highly porous, which should improve gas trans-
port throughout the electrode from the gas flow channel to the
catalyst layer. The continuously connected network of nanofibers
and nanoparticles should increase the triple phase boundary, which
requires intimate junction points for combined ORR, proton and
Fig. 1. (a) SEM image of E/E electrode with 1 wt% PTFE and 0.047 mg/cm2
Pt loading,
(b) higher magnification of (a), nanofiber diameter (c) and nanoparticle diameter (d)
size distributions, respectively, (e) SEM image of E/E electrode with 1 wt% PTFE and
0.013 mg/cm2
Pt loading, (f) higher magnification of (e), nanofiber diameter (g) and
nanoparticle diameter (h) size distributions, respectively, (i) SEM image of E/E elec-
trode with 1 wt% PTFE and 0.003 mg/cm2
Pt loading, (j) higher magnification of (i),
nanofiber diameter (k) and nanoparticle diameter (l) size distributions, respectively.

4. 220 X. Wang et al. / Electrochimica Acta 139 (2014) 217–224
Fig. 2. Fuel cell performances of the E/E #1 (no PTFE), E/E #3 (no PTFE) and E/E #4 (1 wt% PTFE) with operating conditions of (a) H2/O2 with 172 kPa (25 psi) back pressure,
(b) H2/O2 at ambient pressure, (c) H2/air with 172 kPa (25 psi) back pressure, (d) H2/air at ambient pressure.
electron transport. Several large catalyst agglomerates (1-2 ␮m)
were observed in Fig. 1 (b), however, the majority were in the
100-300 nm size range as evidenced in Fig. 1 (d). Fig. 1 (c) shows
a broad nanofiber diameter size distribution with the majority of
fibers (87%) at 100-200 nm in diameter. The nanoparticle diame-
ter size distribution is broader than the nanofiber size distribution
with ∼30% of the nanoparticles with diameters over 800 nm.
Fig. 1 (e) shows an SEM image of an E/E electrode with a lower Pt
cathode loading (0.013 mg/cm2 and 1wt% PTFE) and Fig. 1 (f) shows
a magnified view of Fig. 1 (e). Compared to Fig. 1 (c), Fig. 1 (g) shows
a broader diameter size distribution with 87% of the nanofibers in
the range of 100-300 nm. 23% of the nanoparticles in Fig. 1 (h) have
the diameters greater than 500 nm, which was attributed to the
lack of large agglomerates in the E/E electrodes. Figs. 1 (i) to (l)
show SEM images and nanofiber/nanoparticle size distributions of
an E/E electrode with a Pt loading of 0.003 mg/cm2 and 1 wt% PTFE.
Figs. 1 (i) and 1 (j) show more porous and randomly oriented fibers
in the E/E electrode compared to Figs. 1 (a) and 1 (b). After MEA
fabrication, SEM images reveal more particle-particle contacts [3],
which should result in effective electron transfer throughout the
E/E electrode.
Fig. 2 shows the effect of PTFE in MEAs fabricated with E/E elec-
trodes (i.e., E/E MEAs) on fuel cell performances. Fig. 2 compares
the fuel cell performance of E/E MEAs with 1 wt% PTFE (E/E #4)
and 0 wt% PTFE (E/E #3 and E/E #1). The difference between E/E
#3 and E/E #1 is that the E/E process was used for both anode and
cathode for E/E #3, while the E/E process was only used on the
cathode for E/E #1. The anode for E/E #1 was prepared by conven-
tional hand-painting technique described previously [3]. Details
regarding all MEAs in this study are listed in Table 1. The fuel cell
performance for these three MEAs are compared at four differ-
ent operating conditions: H2/O2 at 172 kPa back pressure (273 kPa
absolute pressure) on anode and cathode sides, H2/O2 at ambient
pressure, H2/air at 172 kPa back pressure (273 kPa absolute pres-
sure) on anode and cathode sides, and H2/air at ambient pressure
(Figs. 2(a) to (d), respectively). For all four fuel cell operation con-
ditions, E/E #4 (with 1 wt% PTFE) results in a higher peak power
and higher limiting current density in the mass transport region.
Note that the E/E MEAs with no PTFE (E/E #3 and E/E #1) have
similar fuel cell performances, however, the total MEA Pt loading
in E/E #3 is approximately half compared to E/E #1. The cathode
Pt loadings are similar between these two MEAs, where both were
fabricated via the E/E process. However, the anode Pt loading in
E/E #1 (0.150 mg/cm2) is higher than the anode Pt loading in E/E
#3 (0.056 mg/cm2), where a conventional hand-painting technique
was used for E/E #1 and the E/E process was used for E/E #3. This
suggests that Pt loading on the anode side is not a limiting factor and
the total MEA Pt loading can be reduced by using the E/E process
on both anode and cathode sides of the MEA.
It is well documented that the addition of PTFE to the cata-
lyst layer improves fuel cell performance due to improved liquid
water removal resulting in a faster transport path of reactants in
the catalyst layer, which can also be evidenced by higher oxy-
gen consumption in the cathode half cell reaction. When flooding
is more prevalent, oxygen consumption is reduced, which is also
referred to as oxygen gain. In this study, when the fuel cells were
operated with 172 kPa back pressure (273 kPa absolute pressure),
the oxygen gains at 1.5 A/cm2 for E/E #1, #3, and #4 were 0.16,
0.18, and 0.14 V, respectively (Fig. 2 (a) and (c)). The lower oxy-
gen gain or higher oxygen consumption of E/E #4 shows that the
catalyst layer with PTFE provides a more effective water removal
rate from the catalyst layer and consequently a faster transport
path of reactants to the catalyst layer is achieved. When the back
pressure was removed, the effect of PTFE on the oxygen gain was

5. X. Wang et al. / Electrochimica Acta 139 (2014) 217–224 221
Fig. 3. (left) Hand-painted electrode without PTFE, (middle) E/E electrode without PTFE, (right) E/E electrode with 1 wt% PTFE.
not as apparent as the case with back pressure (Fig. 2 (b) and (d)).
This is because at lower limiting current densities water flooding
is not as dominant, which mitigates the PTFE effect on the fuel cell
performance.
Table 2 summarizes the differences in fuel cell performance
among the different MEAs at the first fuel cell operating con-
dition of Fig. 2 (H2/O2 fuel cell performance at 172 kPa back
pressure (273 kPa absolute pressure) on anode and cathode sides,
respectively). Maximum power densities of 1.240, 1.090, and
1.090 W/cm2 were measured at total MEA Pt loadings of 0.094 (E/E
#4), 0.112 (E/E #3), and 0.202 (E/E #1) mg/cm2, respectively. In
other words, higher performance at lower loadings can be achieved
by using the E/E process on both anode and cathode catalyst layers
and including 1 wt% PTFE to the electrospinning polymer. In rela-
tion to the control MEA with no E/E process, the maximum power
density of 1.420 W/cm2 was measured at a total MEA Pt loading of
0.570 mg/cm2. This corresponds to a 87% maximum power output
at only 16% total MEA Pt loading for E/E #4 compared to the control,
i.e., a platinum utilization of 0.076 gPt/kW for E/E #4 compared to
0.401 gPt/kW for the control.
The improved fuel cell performance of E/E #4 with the inclusion
of 1 wt% PTFE compared to E/E #3 and E/E #1 (both with no PTFE),
where all three MEAs have similar cathode Pt loadings (0.047, 0.056,
and 0.052 mg/cm2, for E/E #4, E/E #3, and E/E #1, respectively),
suggests that an increase in hydrophobicity of the nanofibers in E/E
#4 enhances mass transfer and subsequently fuel cell performance.
The improvement is associated to the more hydrophobic surface of
the pores in catalyst layer. This hydrophobic surface is of critical
importance to achieve improved water management, particularly,
in the cathode side of the fuel cell by effectively removing liquid
water to provide a faster transport path for reactants to the reactive
sites.
Fig. 4. Fuel cell performances of the E/E MEAs (all with 1 wt% PTFE) at various total MEA Pt loadings (0.094, 0.026, 0.006 mg/cm2
for E/E #4, E/E #5, E/E #6, respectively)with
operating conditions of (a) H2/O2 with 172 kPa (25 psi) back pressure, (b) H2/O2 at ambient pressure, (c) H2/air with 172 kPa (25 psi) back pressure, (d) H2/air at ambient
pressure.

6. 222X.Wangetal./ElectrochimicaActa139(2014)217–224
Table 1
E/E MEAs.
MEA Type Cathode method Anode method PTFE content in both
anode and cathode
Cathode Pt loading
(mg Pt/cm2
)
Anode Pt loading
(mg Pt/cm2
)
Total MEA Pt loading
(mg Pt/cm2
)
Controla
Painted Painted 0% 0.420 0.150 0.570
E/E #1a
E/E Painted 0% 0.052 0.150 0.202
E/E #2a
E/E Painted 0% 0.022 0.150 0.172
E/E #3 E/E E/E 0% 0.056 0.056 0.112
E/E #4 E/E E/E 1% 0.047 0.047 0.094
E/E #5 E/E E/E 1% 0.013 0.013 0.026
E/E #6 E/E E/E 1% 0.003 0.003 0.006
a
MEAs prepared previously [3].
Table 2
Fuel cell performance of E/E MEAs.a
.
MEA Type ECSA (m2
/gPt) Total MEA Pt loading
(mg Pt/cm2
)
Pt loading/Control Peak power
(W/cm2
)
Peak power/Control Pt utilization at max.
power (gPt/kW)b
Control 53.2 0.570 100% 1.420 100% 0.401
E/E #1 86.8 0.202 36% 1.090 77% 0.185
E/E #2 93.9 0.172 30% 0.936 66% 0.184
E/E #3 84.6 0.112 20% 1.090 77% 0.103
E/E #4 81.0 0.094 16% 1.240 87% 0.076
E/E #5 87.7 0.026 4% 0.594 42% 0.040
E/E #6 81.1 0.006 1% 0.412 30% 0.015
a
Fuel cell operating conditions: H2/O2/bp; bp = back pressure of 172 kPa (25 psi); cathode/anode/cell: 80/80/80 ◦
C; 100% RH; PEM = Nafion 212. b
2015 DOE Target = 0.125 g/kW [22].

7. X. Wang et al. / Electrochimica Acta 139 (2014) 217–224 223
Fig. 5. Maximum fuel cell power output versus (a) total MEA Pt loading and (b) Pt utilization for all E/E MEAs and control MEA. Fuel cell operating conditions: H2/O2 with
172 kPa (25 psi) back pressure on both anode and cathode sides.
In order to test this hypothesis, the contact angles for three
different electrodes (hand-painted control electrode, E/E electrode
without PTFE, and E/E electrode with 1 wt% PTFE) were measured
and are shown in Fig. 3. When 1 wt% PTFE is added to the electrode,
the measured contact angle, Fig. 3 (c), is much higher than the elec-
trodes without PTFE. These results suggest that the addition of a
small amount of PTFE can effectively change the wettability of the
electrode fabricated via the E/E process. The increased hydropho-
bicity in the pores of catalyst layer is advantageous in removing liq-
uid water and improving gas transport evidenced by the improve-
ment in the mass transfer region of the polarization curve (Fig. 2).
Fig. 4 shows the effect of Pt loading on fuel cell performance for
three different E/E MEAs (all with 1 wt% PTFE) at four different fuel
cell operating conditions. The total MEA Pt loadings of E/E #4, E/E
#5, and E/E #6 are 0.094, 0.026, 0.006 mg/cm2, respectively. In all
cases, the fuel cell performance increased with increasing Pt load-
ing. Fuel cell results for the first operating condition for all MEAs are
summarized in Table 2. In comparison to the control MEA (no E/E),
a 87%, 42%, and 30% maximum power output at only 16%, 4%, and
1% total MEA Pt loading for E/E #4, E/E #5, and E/E #6, respectively,
were observed at the first fuel cell operating condition. The signifi-
cant reduction in Pt loading from E/E #4 to E/E #6 does correspond
to a decrease in Pt utilization of 0.076, 0.040, and 0.015 gPt/kW.
Therefore, Fig. 4 does not necessarily suggest that higher Pt load-
ing is always desired for all cases, where the trade-off between
peak power and Pt utilization will vary based on application/cost
ratio.
The correlation between peak power and total MEA Pt loading
and Pt utilization is shown in Fig. 5. For both graphs, an MEA that
lies in the upper-left hand corner is the desired trade-off. It is clear
that E/E #4 is the most attractive MEA in terms of balancing power
output and Pt loading or Pt utilization. A higher power output can
still be achieved with the control MEA, but much lower Pt loadings
can be achieved without a significant reduction in power output
using both the E/E process with 1 wt% PTFE. Higher contents of PTFE
were also explored with the E/E process, however, reproducible
nanofibers were not attainable at PTFE contents above 1 wt% due
to electrospinning instability.
Table 2 also lists the measured electrochemical surface area
(ECSA) for each MEA in this study. The ECSAs of all E/E MEAs are
all over 80 m2/gPt, which are higher than the control MEA (53.2
m2/gPt). This provides a rationale for the improved Pt utilization
observed in E/E MEAs compared to the control MEA. Overall, the
E/E MEAs show that only 1-36% of the Pt can deliver 30-77% the
peak power compared to the control MEA.
4. Conclusions
The effect of PTFE in nanofiber/nanoparticle electrodes fabri-
cated using a simultaneous electrospinning/electrospraying (E/E)
technique on PEM fuel cell performance was explored in this study.
An improved fuel cell performance was observed for the E/E MEA
with PTFE compared to the E/E MEA without PTFE when the Pt
loading was similar in both MEAs. Specifically, an improvement
in the higher limiting current density of the fuel cell polarization
curve (mass transfer region) was observed in E/E MEA with PTFE
due to an increased hydrophobicity of the nanofibers evidenced
by contact angle measurements. As mentioned previously, results
with conventional electrodes requires higher PTFE contents (>10
wt%) to achieve improved fuel cell performance, whereas the
nanofiber/nanoparticle electrodes in this study only require 1 wt%
PTFE. Understanding the power/loading relationships in E/E fuel
cell electrodes not only as function of morphology (nanofiber size
and distribution, nanoparticle size and distribution, porosity, con-
nectivity), but also as a function of materials chemistry (PTFE, purity
of Nafion, differences in carbon supports and chemistries, other
Pt-based catalysts) will be of interest for future exploration.
Acknowledgements
This work is supported in part by the Energy Commercialization
Institute under grant no. DUETRF-5.
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