Ionomer Cross-Linking Immobilization of Catalyst Nanoparticles for High Performance Alkaline Membrane Fuel Cells

Article abstract of DOI:10.1021/acs.chemmater.9b00999

Polymer electrolyte membrane fuel cells can generate high power densities with low local emissions of pollutants. Optimal ionomer-Pt/C catalyst interactions in the electrodes enable the efficient generation and transport of ions and electrons required for high fuel cell performances. Critical durability issues involve agglomeration of the Pt/C nanoparticles (Pt/C NPs) and ionomer during discharging. Our novel approach involves ionomer cross-linking immobilization for the fabrication of durable catalyst layers for application in alkaline anion exchange membrane fuel cells (AEMFCs). Pt/C NP catalysts are employed alongside a poly(2,6-dimethyl-p-phenylene oxide)-(PPO)-based quaternary ammonium ionomer (containing terminal styrenic side-chain groups) to form porous catalyst layers. Following thermally initiated cross-linking of the terminal vinyl groups, an interconnected ionomer network forms conductive shells around the Pt/C aggregates. Ex situ catalytic activity and in situ durability tests demonstrate that this immobilization strategy inhibits Pt/C NP coalescence without sacrificing catalyst layer porosity. An initial demonstration of an H₂/O₂ AEMFC containing the new CBQPPO?Pt/C cathode shows that high peak power densities can be achieved (1.02 W cm^-2 at 70 °C, raising to 1.37 W cm^-2 with additional 0.1 MPa back-pressurization).

Full text of DOI:10.1021/acs.chemmater.9b00999

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Article
Ionomer Cross-linking Immobilization of Catalyst Nanoparticles
for High Performance Alkaline Membrane Fuel Cell
Xian Liang, Muhammad Aamir Shehzad, Yuan Zhu, Lianqin Wang, Xiaolin Ge,
Jianjun Zhang, Zhengjin Yang, Liang Wu, John Robert Varcoe, and Tongwen Xu
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b00999 • Publication Date (Web): 04 Sep 2019
Downloaded from pubs.acs.org on September 11, 2019
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Chemistry of Materials
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Ionomer Cross-linking Immobilization of Catalyst Nanoparticles for
High Performance Alkaline Membrane Fuel Cell
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†
,‡
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Xian Liang, Muhammad Aamir Shehzad, Yuan Zhu, Lianqin Wang, Xiaolin Ge, Jianjun Zhang,
†
,†
§
,†
Zhengjin Yang, Liang Wu,* John Robert Varcoe, and Tongwen Xu *
†
CAS Key Laboratory of Soft Matter Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials,
School of Chemistry and Material Science, University of Science and Technology of China, Hefei 230026, P. R. China
‡ School of Chemistry and Material Engineering, Huainan Normal University, Huainan 232001, P. R. China
§ Department of Chemistry, The University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom
ABSTRACT: Polymer electrolyte membrane fuel cells can generate high power densities with low local emissions of
pollutants. Optimal ionomer-Pt/C catalyst interactions in the electrodes enables the efficient generation and transport of
ions and electrons required for high fuel cell performances. Critical durability issues involve agglomeration of the Pt/C
nanoparticles (Pt/C NPs) and ionomer during discharging. Our novel approach involves ionomer cross-linking
immobilization for the fabrication of durable catalyst layers for application in alkaline anion exchange membrane fuel cells
(
AEMFCs). Pt/C NP catalysts are employed alongside a poly (2,6-dimethyl-p-phenylene oxide)-(PPO)-based quaternary
ammonium ionomer (containing terminal styrenic side-chain groups) to form porous catalyst layers. Following thermally
initiated crosslinking of the terminal vinyl groups, an inter-connected ionomer network forms conductive shells around the
Pt/C aggregates. Ex situ catalytic activity and in situ durability tests demonstrate that this immobilization strategy inhibits
Pt/C NP coalescence without sacrificing catalyst layer porosity. An initial demonstration of an H
2
2
/O
2
AEMFC containing the
-
new CBQPPO@Pt/C cathode shows that high peak power densities can be achieved (1.02 W cm at 70 °C, raising to 1.37 W
-2
cm with additional 0.1 MPa back-pressurization).
For acidic PEMFCs, perfluorosulfonic acid (PFSA)
ionomers are the state-of-the-art, which are supplied as
colloidal dispersions to enable fabrication of porous
INTRODUCTION
The development of efficient and clean energy conversion
devices is urgently needed due to the growing
sustainability and environmental concerns associated with
8
catalyst layers. The combination of these porous catalyst
layers with highly proton conductive perfluorosulfonic
acid membranes (namely Nafion®) have resulted in
PEMFCs making great progress in recent decades. Over the
past 5 years, the alkaline counterparts (AEMFCs) have
made remarkable strides in improving the performances of
1,2
the use of fossil fuels. Low temperature hydrogen fuel
cells, i.e. (alkaline) anion exchange membrane fuel cells
(AEMFCs) and proton exchange membrane fuel cells
(PEMFCs), produce electrical energy directly from
electrochemical reactions (oxygen reduction reaction
−
2
H
2
/O
2
AEMFC with power densities achieving > 1 W cm
(
ORR) and hydrogen oxidation reaction (HOR)) without
(summarized in Table S1 in the Supporting
Information).
3
9,10
the local generation of pollutants. Carbon black supported
platinum nanoparticles (Pt/C NPs) are the most widely
These studies clearly indicate that the
combination of highly conductive and stable anionomer
4
11,12
used electrocatalysts for such fuel cells. However, Pt/C NP
coalescence represents a critical durability limitation with
extended fuel cell operation. To improve in situ Pt
utilization and durability, ionomers are commonly
employed, in porous catalyst layers, to act as both binder
with optimized electrode design
is essential for high
power densities. Zhuang et al. enhanced the fuel cell
5
-
performance through improving the OH conductivity of
1
3-
electrolyte (AEMs) and the ORR performance of catalyst.
15
Varcoe et al. substantially improved the performance of
6,7
and ion conductor. Typically, the catalyst layer exhibits a
the AEMFCs by development of highly conducting AEMs
16-21
heterogeneous morphology with inter-connections
between the Pt/C NPs and ionomer. The Pt/C aggregates
enable electrical current to flow to/from the catalytic sites,
whilst providing the micro-/meso-porosity (interstitial
voids) required for gas/water permeation. The ionomer
aggregates are expected to uniformly coat and inter-
connect the catalyst aggregates to provide an ion
conductive pathway to the polymer electrolyte membrane
without inhibiting gas diffusivity.
and anionomer powders.
Mustain et al. improved the
fuel cell peak power density and operation durability of
the AEMFC through perfect water management and
optimization of electrodes – even without Pt in the
2
2-25
cathode.
2 2
Most recently, Kohl et al. reported a H /O
AEMFC with an exceptionally high peak power density of
2
o
26
3.4 W cm at 80 C, which is the highest reported, to date.
These competitive fuel cell performances are closely
approaching to that of PEMFCs owing to the high
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Scheme 1. Schematic of the ionomer cross-linking immobilization strategy for fabricating durable CBQPPO@Pt/C catalyst
layers: (a) Menshutkin reaction between the bromomethyl groups of BPPO and the tertiary amine groups of VBN to obtain
quaternary ammonium-functionalized ionomer with terminal vinyl pendants (VBQPPO); (b) Thermally triggered
crosslinking of the vinyl groups to form CBQPPO; (c) Preparation of ionomer/catalyst ink by mixing Pt/C NPs with
VBQPPO in alcohol aqueous solution; (d) Conversion of the VBQPPO@Pt/C into the thermally crosslinked CBQPPO@Pt/C
catalyst layer; (e) An illustration highlighting the ionomer cross-linking immobilization effect on porosity of the catalyst
layer (to maximise catalytic efficiency).
performance of the membrane electrode assembly (MEA)
by the use of highly OH conductive AEMs and well control
focused on the aim of eliminating the use Pt-based
-
electrocatalysts, but for development of new anionomer
concepts, it is useful for initial studies to involve widely
available, commercial Pt/C electrocatalysts. Scheme 1
summarizes our anionomer strategy. Pt/C NPs are mixed
in alcohol aqueous solution with a poly(2,6-dimethyl-p-
phenylene oxide)-(PPO)-based quaternary ammonium
ionomer, containing pendant groups with terminal
styrenic functionality, to form a highly solvated particle
dispersion. This particle dispersion can be exploited to
control the porosity of a catalyst layer (Scheme 1c).
Thermally triggered crosslinking of the terminal, pendant
vinyl groups, converts the physically aggregated ionomer
phases into covalent network shells that envelope the Pt/C
aggregates, hence providing ionically conductive
interconnections and preventing Pt coalescence (Scheme
over the subsequently heterogeneous microstructure of
the catalyst layer. Particularly, the importance of the
optimization of catalytic electrode design in securing high
AEMFC performance requires an anionomer morphology
that can generate optimized porous catalyst layers,
essential for the promotion of efficient simultaneous ion
and fuel transport.
In addition, the durability of catalyst layers, particularly
at elevated temperatures and under high current density
1
0,27
operation, is another area concern.
During fuel cell
operation, the hydrophilic ionomer phases in the catalyst
layers adsorb and desorb large quantities of water, which
can lead to electrode flooding and impeded gas
2
8,29
transport.
Moreover, hydrated ionomers can
1
d). A vinyl-pendant-free quaternary ammonium PPO
excessively swell under such conditions, resulting in large
isolated agglomerates of ionomer and/or Pt/C NPs.
Isolated ionomer agglomerates would not form the desired
ionomer (QPPO) was prepared as a non-crosslinked
benchmark. The importance of the crosslink-immobilized
effect in stabilizing Pt/C NPs catalyst and securing high
AAEMFC performance is discussed.
-
OH conductive networks. Unsuppressed electrochemical
Ostwald ripening and Brownian-like Pt mobility will lead
3
0-32
to Pt NP growth and coalescence.
The development of
EXPERIMENTAL SECTION
high performance AEMFCs mandates the advancement of a
general synthetic strategy for stabilizing Pt/C NPs within
high performance porous catalyst layers.
Chemicals and Materials. Poly (2,6-dimethyl-1,4-
phenylene oxide) (PPO) was manufactured by Asahi Kasei
Chemicals Corporation (Japan) and kindly supplied by
Tianwei Membrane Company (Shandong, P.R. China). N-
bromosuccinimide (NBS), 2,2'-azobis-isobutyronitrile
(AIBN), and 4-vinylbenzyl chloride (VBC) were purchased
To address this challenge, this study reports an ionomer
cross-linking immobilization strategy aimed at stabilizing
Pt/C NPs for AEMFCs, while retaining high catalytic
efficiencies. We acknowledge that AEMFCs development is
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Chemistry of Materials
from Energy Chemical Co. Ltd. (Shanghai, P.R. China) and
used as received. N-methyl-2-pyrrolidolone (NMP, AR),
in the corresponding experimental sections below.
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dimethylamine solution, trimethylamine solution, ether,
chlorobenzene, ethanol, methanol and sodium hydroxide
(AR) were purchased from Sinopham Chemical Reagent
Co. Ltd. The Nafion DE-521 PFSA polymer dispersions was
manufactured by DuPont. The commercial Pt/C catalyst
and PtRu/C catalyst were manufactured by Johnson
Matthey. The commercial Pt/C catalyst is 60% wt. Pt
nanoparticles (ca. 3 nm diameter) on Vulcan XC-72 carbon
support. The commercial PtRu/C catalyst is 40% wt. Pt
nanoparticles and 20% wt. nanoparticles (both ca. 3 nm
diameter) on Vulcan XC-72 carbon support. Deionized
water was used throughout.
Instruments and characterizations.
Nuclear Magnetic Resonance (NMR) spectroscopy: 1H
NMR spectra were recorded on a Bruker 510 instrument
1
( H resonance at 400 MHz) at 298 K. Chemical shifts are
reported in ppm relative to the signals corresponding to
the residual non-deuterated protons in the NMR solvents
(CDCl δ = 7.26 ppm, DMSO-d6 δ = 2.53 ppm, CD OD δ =
3
3
3.31 ppm).
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Fourier Transform Infrared spectroscopy (FT-IR):
Variable temperature FT-IR spectra were collected using a
NICOLET iS10 (Thermo Fisher Scientific). All polymers
were measured in the membrane form. A sample of AEM,
Experimental.
-
which was naturally dried in the atmosphere in the OH
Synthesis of BPPO: BPPO was produced as our previous
work and described as follows: PPO (10 g, 83 mmol) was
dissolved in chlorobenzene (200 ml) and then NBS (10.5g,
anion form, was fixed between two CaF
samples were heated from 30 °C to 70 °C in four stages: 40
C, 50 °C, 60 °C, and 70 °C (10 °C temperature rise over 10
2
optical plates. The
°
5
8.3 mmol) and AIBN (0.1 g, 0.61 mmol) were added. The
minutes followed by a thermal hold at each temperature of
60 min). FT-IR absorbances were recorded with a
measurement every 1 min.
reaction solution was heated to 130 °C for 4 h with stirring.
After reaction, the mixture was poured into excess ethanol
(
2 L) to form a light-brown fibrous precipitate of BPPO.
X-ray and electron microscopy analyses: Powder X-ray
diffraction patterns of catalyst samples were conducted on
a Rigaku D/MAX2500VL/PC X-ray diffractometer with Cu
Kα radiation and X-ray photoelectron spectroscopy (XPS,
ESCALAB 250 System) using Al K_ excitation radiation
The precipitate was then washed with ethanol (6 ×) with a
final drying in a vacuum oven at 40 °C for 48 h. The H
NMR spectrum of BPPO (in CDCl ) is shown in Figure S1.
3
1
33
Synthesis of VBN: 4-vinylbenzyl chloride (3.1 g, 20 mmol)
was added dropwise into 10 ml aqueous dimethylamine
solution (33 % wt.) with vigorously stirring at room
temperature. After 24 h reaction, the product was
extracted into chloroform (3 × 50 ml). The organic fraction
was collected and washed with deionized water (3 × 50
ml). The solvent was removed by evaporation and the
(
1486.6 eV). TEM and EDS micrographs of the catalyst
powders were recorded by a Hitachi-7700 working at 100
kV. The cross-section structure of the catalyst layers in the
MEAs were characterized using an environmental scanning
electron microscopy (ESEM, XL-30 ESEM).
1
Brunauer–Emmett–Teller
(BET)
test:
BET
gas
product (VBN) was obtained as bright yellow liquid. The H
NMR spectrum of VBN (DMSO-d ) is shown in Figure S2.
sorptometry measurements were performed on an
Autosorb iQ (Quantachrome, Autosorb iQ, USA) at 77K.
Before each isotherm, approximately 200-220 mg of
ionomer-based MEAs samples were activated by heating
for 5 hours under high vacuum at 140 °C. The samples
were then transferred to a pre-weighed sample tube and
de-gassed at 140 °C for approximately 7 h.
6
Synthesis of VBQPPO: BPPO (1.0 g, 4.77 mmol, 56 %
degree of bromination) was dissolved in 20 ml NMP at 25
°
C, after which VBN (1.0 g, 6.21 mmol) was added
dropwise followed by stirring for 24 at room
h
temperature. The mixture was then dropped into diethyl
ether, which formed a white precipitate that was
recovered by filtration. The precipitates were washed with
ether (6 ×). The VBQPPO ionomer powder obtained was
Water contact angle (WCA) test: The water contact angle
WCA) of the GDE surface was measured by a contact angle
(
1
meter (SL200B, Solon Tech Co., Ltd., CHN) using the sessile
drop technique at room temperature. Six parallel tests
were conducted to gauge the precision of the experimental
data.
further dried in a vacuum oven at 30 °C for 12 h. The H
NMR spectrum of VBQPPO (CD OD) is shown in Figure S3.
3
Synthesis of QPPO: BPPO (1.0 g, 4.77 mmol, 56 % degree
of bromination) was dissolved in 20 ml NMP at 25 °C. A
methanol solution of trimethylamine (1.0 ml, 33 % wt.)
was then added and the resulting mixture was stirred for
Electrochemical testing of the catalyst inks.
Electrochemical measurements were performed using a
CHI 760E electrochemical workstation with a three-
electrode system and aqueous KOH (0.1 M) electrolyte. A
glassy carbon (GC) rotating disk electrode (RDE, 5mm
diameter) was coated with a catalyst ink and served as the
working electrode; a Ag/AgCl and Pt wire were used as the
reference and counter electrodes, respectively. The
homogeneous Pt/C catalyst ink samples (20% wt. CBQPPO
content) were prepared by ultrasonically mixing 4 mg of
the catalyst powder with a mixture consisting of 480 μL
33
2
4 h. After reaction, the solution was dropped into
diethyl ether, which formed a white precipitate that was
recovered by filtration. The precipitates were washed with
ether (6 ×). The synthesized QPPO ionomer powders were
1
further dried in vacuum oven at 40 °C for 12 h. The H
3
NMR spectrum of QPPO (CD OD) is shown in Figure S4.
Formation of CBQPPO: CBQPPO was formed via the
thermally-initiated inter-crosslinking of VBQPPO during
the catalyst ink preparation step (when preparing the
catalyst inks for the ORR catalytic activity test and when
preparing the CBQPPO@Pt/C catalyst layer for the fuel cell
test). The conditions of formation of CBQPPO are reported
ethanol, 480 μL H
5% wt.) for 20 min, then heated at 70 C for 2 h to ensure
VBQPPO was converted to CBPPO. Other inks with 11%
2
O and 20 μL VBQPPO/ alcohol solution
o
(
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wt., 33 % wt., and 50 % wt. CBQPPO content were under full humidification and with no backpressure
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prepared by using formulations involving addition of 10
μL, 40 μL and 80 μL of VBQPPO/ alcohol solution (5 % wt.).
10 µL of the catalyst resulting inks were pipetted
applied to either gas feed. Power density of the ionomer-
based MEAs held at 0.5 V cell voltage were recorded one
point in each hour. A longer-term durability test was
conducted with gradually decreasing gases relative
humidity (RH) from 100% to 80% within 50 h. Constant
current density stability tests were performed at 0.6
2
separately onto a polished GC-RDE (0.196 cm ) and dried
under an infrared (IR) lamp for each ink tested to obtained
-2
Pt/C catalyst loadings of 0.204 mg cm .
2
A/cm , and the voltage was recorded as a function of time.
Before voltammetry was conducted, the aqueuos KOH
0.1 M) electrolyte was purged with O for 30 min. The
2
The operating voltages were recorded as a function of time
(
-2
at 70 °C with the cell held at 0.6 A cm current density.
linear sweep voltammetry (LSV) measurements at room
temperature were measured at the rotating speed of 1600
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Electrochemical AC impedance spectroscopy (EIS)
-1
rpm with a sweep rate of 10 mV s . The stability of the
catalyst was evaluated by chronoamperometry (i-t) at a
constant potential of -0.5 V vs. Ag/AgCl (0.498 V vs. RHE)
analysis. Electrochemical impedance spectroscopy (EIS)
analysis, involving alternating current (AC) stimuli, is
considered a well-established experimental technique
which can elucidate individual fuel cell polarization effects.
With complementary simulation of the EIS data, further
quantification of the capacitive-resistive contributions at
membrane-electrode interfaces in the single cell fuel cells
can be achieved (Table S1), that can include the
at a rotation rate of 1600 rpm (with O
KOH (0.1 M) electrolyte).
2
-purged aqueous
Membrane Electrode Assembly (MEA) fabrication
and fuel cell testing. The gas diffusion electrodes (GDEs)
method was adopted to prepare the membrane electrode
assemblies for fuel cell testing. 10 mg Pt/C (for cathode)
catalyst or PtRu/C (for anode) catalyst (both 60% wt.
metal content) were ultrasonically mixed with 100 mg
deionized water, 400 mg 1-propanol, and 50 mg ionomer
solution (5% wt. VBQPPO in alcohol aqueous) to prepare
the inks that will yield catalyst layers containing 20% wt.
ionomer and 80% wt. catalyst. To obtain GDEs, the catalyst
inks were inkjet printed onto the gas diffusion layer (GDL,
Toray TGP-H-060). The metal loading in both anode and
3
4
determination of changes in materials morphology.
Herein, EIS analyses of the MEAs were performed with
single cells assembled using a pair of gaskets and a pair of
2 2
graphite blocks. The anode and cathode gases (H and N
-1
respectively) were supplied at 1 L min . For EIS testing,
the temperatures for the cells and gases was all controlled
at 70 °C. All testing parameters were by the 890e fuel cell
tester.
The EIS analysis was performed by externally connected
-2
cathode was controlled to be 0.5 mgmetal cm , and the final
Autolab
workstation
(PGSTAT
302N,
Metrohm,
2
electrode areas were 12.25 cm . The prepared GDEs and
Netherlands) controlled by Nova 2.1.2 software. A small
sinusoidal potential perturbation (10 mV amplitude, f
range 0.01Hz - 100 kHz) was applied to the cathode and
anode plates and the AC current response was measured.
Impedance data is presented as Nyquist plots and
anion-exchange membrane (AEM, TMImPPO type with an
-1
2
-
IEC = 1.65 mmol g ) were then converted to OH form by
immersing in aqueous NaOH (1 M) solution for 12 h
followed by thorough washing with deionized water. The
resulting GDEs were correctly placed (PtRu/C at anode and
Pt/C at cathode) on each side of the AEM to make the
membrane electrode assembly (MEA). The MEA was hot-
pressed in situ (no hot press procedure was used prior to
fuel cell assembly).
®
simulated using ZSimpWin electrochemical analysis
software (PAR Inc. USA). The electrical equivalent circuit
(EEC) model was selected based on the possible physical
replica comprising membrane and GDE. The best fits for
each EEC parameter are presented in Table S1.
The single cell Anion-Exchange Membrane Fuel Cells
AEMFC) were tested using an 890e multi range fuel cell
RESULTS AND DISCUSSION
(
test station (Scribner Associates, USA) in a galvanostatic
mode between 30 and 70 C. To convert the
VBQPPO@Pt/C cathode and VBQPPO@PtRu/C anode
catalysts layers into crosslinked immobilized forms
Synthesis. The vinyl-group containing quaternary
ammonium ionomer (VBQPPO) and the ensuing
ionomer/catalyst ink were prepared as summarized in
Scheme 1. VBQPPO ionomer was synthesized using the
Menshutkin reaction between the bromomethyl groups of
bromomethylated PPO (BPPO) and the tertiary amine
o
(
CBQPPO@Pt/C and CBQPPO@PtRu/C), the cell
o
o
temperature was increased from 30 C to 70 C over 1 h
and held at 70 C for 2 h with H
o
2 2
and O gas feeds (100%)
groups of N,N-dimethylvinylbenzylamine (VBN) (Scheme
being supplied to anode and cathode electrodes,
1
1
a, H NMR spectra presented in Figures S1-S3 in the
-1
respectively (flow rates of 1 L min ). Then, the MEAs were
broken in under potentiostatic mode at 0.5 V cell voltage at
Supporting Information). The presence of vinyl proton
signals (δ = 5.25, 5.75 and 6.75 ppm) provides evidence of
H
7
0 °C and the corresponding relative humidity (100%) of
successful Menshutkin reaction with vinyl groups
remaining unreacted.
both the cathode and anode were adjusted until a steady
current density was achieved for at least 30 min. After
break-in procedure, the current density at each cell voltage
was recorded with either no backpressure or 0.1 MPa
backpressure (symmetrically applied to both sides) after
the power output had stabilized. A short-term durability
In situ FTIR analyses shows that the inter-crosslinking
reaction between vinyl groups (VBQPPO ionomer
conversion into crosslinked CBQPPO networks, Scheme
1b) occurs gradually as the temperature is increased from
3
0 °C to 70 °C (Figure S5): the intensity of the vinyl C–H
2 2
test of H /O AEMFCs containing the different ionomers
-1
-1
vibrations (1320 cm and 3090 cm ) and the C=C
vibration (1610 cm ) decrease on increasing temperature.
(
CBQPPO vs. QPPO benchmark) was conducted at 70 °C
-1
-1
2 2
with a flow rate of 1 L min (both H and O gas supplied)
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Figure 1. (a) Linear scan voltammograms in O
2
-saturated aqueous KOH (0.1 M) solution (room temperature with a sweep rate of
-1
1
0 mV S and a rotation rate of 1600 rpm) of the non-crosslinked benchmark cathode catalyst (QPPO@Pt/C) before (red) and
after (black) chronoamperometry (i-t) test (potential hold at -0.5 V vs. Ag/AgCl reference electrode (0.498 V vs. RHE) for 250 min).
TEM images of QPPO@Pt/C catalyst particles both before (b) and after (c) the i-t test. Parts (d), (e), and (f) present the analogous
data for the thermally crosslinked CBQPPO@Pt/C cathode catalyst.
photoelectron spectroscopy (XPS) data for VBQPPO@Pt/C
are consistent with a uniform distribution of Pt/C
aggregates in the ionomer phase (Figure S7 and Figure S8).
Typically, the N1s peak at 402.25 eV in XPS data is
-1
+
assigned to the C-N species in the quaternary ammounium
(QA) groups of CBQPPO, providing initial evidence of
CBQPPO loading on Pt/C NPs surface. TEM and relative
mapping images further certify the well distribution of
VBQPPO ionomer on Pt/C aggregates (Figure S9).
To investigate the ionomer crosslink-immobilized effect,
the optimized VBQPPO@Pt/C particle dispersing ink was
o
heated at 70 C for 2h, followed by being deposited onto a
rotating disk electrode to form an inter-crosslinked
CBQPPO@Pt/C catalyst layer. Additionally, two benchmark
catalyst layer prepared from a non-crosslinked (vinyl-free)
PPO-based ionomer of the same quaternary ammonium
chemistry (QPPO) and Nafion ionomer were prepared as
for comparison (synthesis and characterizations in Scheme
S1 and Figure S4). The ORR performances of three
catalysts, before and after 250 min of potential hold at -0.5
V vs. Ag/AgCl reference electrode (0.498 V vs. RHE) are
shown in Figure 1 and Figure S10 (typical i-t curves
presented in Figure S11). The activity of the benchmark
QPPO@Pt/C and Nafion@Pt/C catalysts decreased in
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-
1 33
2 2
Figure 2. (a) H /O AEMFC performance data at 70 °C for MEAs containing the same AEM (TMImPPO, IEC = 1.65 mmol g ) but
different ionomers in catalyst layers (non-crosslinked QPPO benchmark vs. thermally crosslinked CBQPPO). All catalyst layers
contained 20 wt % ionomer. PtRu/C anode and Pt/C cathode electrocatalysts were used where all electrodes contained a metal
loading of 0.5 mgmetal cm . All gases were supplied at 1 L min and RH = 80% or 100%. The inserts present illustrations
-2
-1
2
highlighting the differences in morphology between the two types of catalyst layer. (b) HFR data (stack area = 12.25 cm ) at 70 °C
-1
for MEAs containing the same AEM (TMImPPO, IEC = 1.65 mmol g ) but different ionomers in catalyst layers.
activity as seen when comparing the pre- and post-i-t test
Fuel cell performance (in-situ evaluation). Although
CBQPPO@Pt/C exhibits high catalytic activity and
durability in ex situ electrochemical tests, an initial in situ
half-wave potential (E1/2): 17 mV and 14 mV negative shift
in E1/2 were observed (Figure 1a and Figure S10). Such
activity loss is recognized to be due to the formation of
2 2
evaluation of its performance in a simple benchmark H /O
3
0, 31
large agglomerates of Pt/C NPs via coalescence.
In
single cell AEMFCs is useful in order to gauge its future
potential for the desired application. To achieve this aim,
the ionomer/catalyst dispersions (VBQPPO@Pt/C for
cathode and VBQPPO@PtRu/C for anode) were sprayed on
gas diffusion layers (GDL, Toray TDP-H-060) to fabricate
contrast, the ionomer crosslink-immobilized
CBQPPO@Pt/C catalysts maintained its ORR activity after
the i-t test (Figure 1d), supporting our hypothesis that
encapsulation of the Pt/C aggregates by the inter-
crosslinked ionomer networks leads to an increase in the
durability.
gas diffusion electrodes (GDEs). A benchmark AEM
-1 33
(
TMImPPO with an IEC value of 1.65 mmol g ) was
To further prove this point, transmission electron
microscopy (TEM) was employed to detect changes in
morphology of the Pt/C NPs distribution in both catalyst
layers during the i-t tests. As shown in Figure 1b and 1e,
both the pre-i-t test catalysts (QPPO@Pt/C and
CBQPPO@Pt/C) show a similar morphology with the Pt/C
NPs being uniformly covered by ionomer thin films (mean
size of Pt: 2.3nm(QPPO@Pt/C) vs 2.5nm(CBQPPO@Pt/C)).
However, the Pt/C NPs in QPPO@Pt/C agglomerate into
much bigger particles after the i-t test with accompanying
isolation from the ionomer aggregates (Figure 1c, mean
size of Pt: 4.8nm).
sandwiched between the anode and cathode GDEs to
fabricate a membrane electrode assembly (MEA). The MEA
was assembled between two graphite bipolar flow field
plates. To convert the VBQPPO@Pt/C cathode and
VBQPPO@PtRu/C anode catalysts layers into crosslink-
immobilized
forms
(CBQPPO@Pt/C
and
CBQPPO@PtRu/C), the cell temperature was increased
from 30 C to 70 C in 1 hour and held at 70 C for 2 h with
and O gas feeds being supplied to anode and cathode
electrodes, respectively (flow rates of 1 L min ). Then, the
MEAs were activated under a potentiostatic mode by
discharging the cell at a constant voltage of 0.5 V at 70 °C
until a steady current density was achieved for at least 30
o
o
o
H
2
2
-1
During the ORR, the weak physical contact between the
ionomer and Pt/C aggregates is not sufficient to prevent
such agglomeration and isolation (Ostwald ripening and
coalescence phenomenon can still occur). This leads to an
increased fraction of large NPs and thus a decreased ORR
activity (reflected in the data discussed in Figure 1a). In
contrast, no visible morphological changes to
CBQPPO@Pt/C catalyst layer were detected by TEM
min. Another benchmark single cell containing
a
QPPO@Pt/C cathode and a QPPO@PtRu/C anode was
fabricated using the same procedure for comparison.
Figure 2a presents the polarization curves for the two
cells. The CBQPPO-based cell (crosslinked ionomer
immobilized catalysts) achieved 1.02 W cm peak power
density (at a current density of 1.91 A cm ), which
increased to 1.37 W cm (at 3.0 A cm ) on addition of 0.1
MPa backpressures to the gas supplies, attributed to the
uniform distribution of CBQPPO in the MEA as shown in
Figure 4b. These AEMFC performance characteristics were
significantly higher to those achieved with the use of
3
2
-2
-2
-2
-2
(
Figure 1f, mean size of Pt: 2.7nm), which manifests itself
in the unchanged ORR LSV data (Figure 1d). This data
again supports our strategy where the ionomer cross-
linking immobilization stabilizes the Pt/C catalyst during
cell discharge.
-2
-2
QPPO-based ionomers (0.6 W cm at 1.05 A cm ). These
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tests highlight that our strategy does translate into higher
in situ performances.
correlates with changes in membrane (R
M
) and interfacial
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P
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Figure 3. (a) Power density of the ionomer-based MEAs at 70 °C with the AEMFCs held at 0.5 V cell voltage recording one point of
every hour (CBQPPO vs. QPPO benchmark). The insert SEM images show the CBQPPO@Pt/C and QPPO@Pt/C cathode catalysts
both before and after this in situ short-term durability test. (b) In situ electrochemical impedance spectroscopy (EIS) analysis of
2 2
/N
anode/cathode feeds, before and after the short-term durability test.35 The measured (msd) EIS-
the same MEAs with H
Nyquist data was simulated (sim) with a best-fit equivalent electrical circuit model (insert, error < 0.5 %), see details in Table S2.
Considering both cells contained the same AEM, the
large differences AEMFC performances must primarily
result from the differences between catalyst layers, e.g.
reduced ohmic and mass transport losses, which proved by
the high frequency resistance (HFR) data (Figure 2b). As
discussed above, the CBQPPO@Pt/C catalyst layers were
formed in-situ during initial fuel cell start-up and operation
fitting the experimental EIS data (Table S2 in SI) both
before and after the durability test using the equivalent
circuit shown in Figure 3b). The simulated EIS for the
QPPO based MEA indicates a small change in R (increased
M
by 32.7 mΩ) and a large change in Rct (640 ± 2.6 mΩ)
leading to the observed decline in power density. In
M
contrast, negligible increases in R (4.2 mΩ) and charge
transfer (52.9 mΩ) resistances were elucidated for the in
situ crosslinked CBQPPO-MEA.
with both H
2
/O
2
being continuously supplied. The thermal
crosslinking under high gas flow facilitates formations of a
stable porous geometry (schematically illustrated in the
top insert of Figure 2a), where the inter-crosslinked
ionomer covers the interconnecting Pt/C aggregates for
efficient fuel permeation and ion transport. However, the
physically aggregated ionomer in QPPO@Pt/C catalyst
layer has the tendency to form isolated ionomer phases
reducing its effectiveness as a binder and anion conductor
Changes in the morphology of the GDEs observed during
the SEM analysis (inserts in Figure 3a) can also be mapped
to the EIS simulation capacitive data (Table S2). Notably,
the index value (0 < Q
n
< 1) of the constant phase element
(
Q) is believed to be inversely related with the porosity (of
36-39
the GDE).
Thus, the large increases, after the durability
test, in Q
n
values (approaching to 1) for the QPPO-based
(
bottom insert of Figure 2a). Meanwhile, the MEA with
GDE confirms the shutting off of the pores and
agglomeration of components observed by SEM (bottom
insert in Figure 3a) and the loss in AEMFC power.
CBQPPO@Pt/C exhibits higher total pore volume and BET
surface area than that with QPPO@Pt/C. This result
provides further evidence of the ionomer-crosslinking
induced formation of the porous geometry, thus facilitating
efficient gas and ions transport (Table S3). Additionally,
contact angle data (Figure S12) shows that the QPPO-
based electrode is much more hydrophilic than the
CBQPPO-based electrode. This could lead to a propensity
for the QPPO@PtRu/C anode to flood, which will impede
gas transport and lower the AEMFC performance.
n
However, less significant increases in Q values were
observed for the CBQPPO-based GDE, again explaining the
retention in power with the use of this ionomer cross-
linking immobilization concept. This high stability stems
from the inter-crosslinking of the CBQPPO, which
immobilized the Pt-based NPs and keeps the pores
structure intact (for fast and easy transfer of fuel and high
AEMFC performance). Furthermore, BET test was
conducted to analyse the change of porosity in catalyst
To highlight the ionomer crosslink-immobilized effect
on in situ Pt/C stabilization, initial short-term durability
tests with each MEA were conducted by discharging each
AEMFC at a cell voltage of 0.5 V at 70 °C with no gas
backpressures (Figure 3a). In contrast to the AEMFC
containing the new in situ crosslinked CBPPO ionomer, a
layer before and after fuel cell durability test. N
2
adsorption isotherms of QPPO@Pt/C-based MEA (Figure
S13 and Table S3) show a significant decline in total pore
volume and BET surface area after the durability test.
However, CBQPPO@Pt/C-based MEA maintains its
porosity, suggesting that the inter-crosslinking of the
CBQPPO enable to produce durable electrode catalyst
layers with high porosity. The BET experiment result is
-2
sharp decline in peak power density from 0.6 W cm to <
-2
0
.2 W cm was observed for the AEMFC containing the
benchmark QPPO ionomer. The fuel cell power loss
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consistent to the SEM analysis and the EIS simulation delamination between the anode catalyst layer and the
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capacitive data in Figure 3.
AEM is responsible for the performance decline (Figure
0
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Figure 4. (a) The durability evaluation of H
2
/O
2
AEMFCs containing the different ionomers (CBQPPO vs. QPPO benchmark) with
gradually decreasing relative humidity (RH). The AEMFCs used the same MEAs as described in Figure 2. The operating voltages
were recorded as a function of time at 70 °C with the cell held at 0.6 A cm-2 current density. (b), (d) Cross-sectional SEM and EDX
2 2
analysis of CBQPPO-based MEA before and after the durability test. (c) In situ recorded HFR data of the H /O AEMFCs during the
durability test.
It is well recognized that anode flooding and cathode
drying out present critical durability limitations with the
AEMFCs operation. To further investigate the benefits of
ionomer cross-linking immobilization concept, we
conducted evaluation of the durability of H /O AEMFCs
2 2
containing the different ionomers (CBQPPO vs. QPPO
benchmark) with gradually decreasing relative humidity
R4b, d). The corresponding HFR data of each MEA in
Figure 4c provide further evidence of the increased MEA
resistance, possibly resulted from the interfacial
delamination. However, we would like to emphasize that
this is an initial catalyst layer development study where
we focused on evaluating our hypothesis that the use of
ionomer cross-linking immobilization concept to prevent
Pt/C NP coalescence inside the electrode catalyst layers.
We will of course take this concept forward in future
studies by enhancing the membrane-electrode interfacial
adhesion via chemical bound or electrostatic interactions.
(
7
RH). Cell voltages were recorded as a function of time at
0 C with the cell held at 0.6 A cm current density. As
o
-2
shown in Figure 4a, the CBQPPO@Pt/C-based MEA
maintains its stability in the initial 25h with both anode
and cathode gases 100% hydrated. The voltage tends to
decrease slightly within the next 25h at 90 % RH, then, to
decline speedily at a lower humidity (80%). In contrast to
the CBQPPO@Pt/C-based MEA, a sharp decline in voltage
from 0.7 V to < 0.2 V has been observed within 20h for the
AEMFC containing the benchmark QPPO ionomer. Cross-
sectional SEM images of the CBQPPO@Pt/C-based MEA
before and after durability test suggest that interfacial
CONCLUSIONS
In conclusion, this study describes an ionomer-assisted
immobilization strategy for the production of durable
electrode catalyst layers for use in alkaline anion-exchange
membrane fuel cells (AEMFC). TEM microscopy show that
on thermally triggered crosslinking, the developed
ionomer forms a conductive, interconnected network that
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covers the Pt/C nanoparticles (NP), thus significantly
(3) Jacobson, M. Z.; Colella, W. G.; Golden, D. M. Cleaning the Air
and Improving Health with Hydrogen Fuel-Cell Vehicles. Science
005, 308, 1901-1905.
4) Shao, M. H.; Chang, Q. W.; Dodelet, J. P.; Chenitz, R. Recent
Advances in Electrocatalysts for Oxygen Reduction Reaction.
Chem. Rev. 2016, 116, 3594-3657.
(5) Debe, M. K. Electrocatalyst Approaches and Challenges for
Automotive Fuel Cells. Nature 2012, 486, 43-51.
(6) Holdcroft, S. Fuel Cell Catalyst Layers: A Polymer Science
Perspective. Chem. Mater. 2014, 26, 381-393.
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preventing NP coalescence when catalyzing the oxygen
reduction reaction. In situ fuel cell durability tests
determine that this thermal initiated cross-linking
ionomer-assisted immobilization strategy prevents
significant Pt/C NPs coalescence without sacrificing the
porosity of the catalyst layer. The resulting AEMFC can
2
(
-
2
produce competitive peak power densities of 1.02 W cm
-2
and 1.37 W cm at 70 °C with unpressured gases and with
.1 MPa backpressures, respectively.
(
7) Peron, J.; Shi, Z. Q.; Holdcroft, S. Hydrocarbon Proton
0
Conducting Polymers for Fuel Cell Catalyst Layers. Energy
Environ. Sci. 2011, 4, 1575-1591.
0
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2
3
4
5
6
7
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ASSOCIATED CONTENT
Supporting Information.
(8) Lopez-Haro, M.; Guetaz, L.; Printemps, T.; Morin, A.; Escribano,
S.; Jouneau, P. H.; Bayle-Guillemaud, P.; Chandezon, F.; Gebel, G.
Three-Dimensional Analysis of Nafion Layers in Fuel Cell
Electrodes. Nat. Commun. 2014, 5, 1-6.
The Supporting Information is available free of charge on
the ACS Publications website at DOI: .
(
9) Dekel, D. R. Review of Cell Performance in Anion Exchange
Membrane Fuel Cells. J. Power Sources 2018, 375, 158-169.
(10) Gottesfeld, S.; Dekel, D. R.; Page, M.; Bae, C.; Yan, Y. S.;
Zelenay, P.; Kim, Y. S. Anion Exchange Membrane Fuel Cells:
Current Status and Remaining Challenges. J. Power Sources 2018,
Additional data of the performance of recently reported
2 2
AEIs or AEMs for H /O alkaline membrane fuel cell,
1
additional experimental procedures and H NMR spectra of
BPPO, VBN, VBQPPO, QPPO and CBQPPO, additional
variable temperature in situ FTIR spectroscopy of
VBQPPO, additional electrochemical test for binder
loading, additional XRD, XPS and TEM data for the
characterization of Pt/C catalyst encapsulated by VBQPPO,
additional i–t chronoamperometric analysis, static water
contact angle test, BET test of ionomer-based MEA, and
additional simulation electrical equivalent circuit (EEC) fits
for the impedance spectra.
3
75, 170-184.
(
11) Wang, Y.; Wang, G.; Li, G.; Huang, B.; Pan, J.; Liu, Q.; Han, J.;
Xiao, L.; Lu, J.; Zhuang, L. Pt–Ru Catalyzed Hydrogen Oxidation in
Alkaline Media: Oxophilic Effect or Electronic Effect? Energy
Environ. Sci. 2015, 8, 177-181.
(
12) Kaspar, R. B.; Letterio, M. P.; Wittkopf, J. A.; Gong, K.; Gu, S.;
Yan, Y. Manipulating Water in High-Performance Hydroxide
Exchange Membrane Fuel Cells Through Asymmetric
Humidification and Wetproofing. J. Electrochem. Soc. 2015, 162,
F483-F488.
(
13) Peng, H.; Li, Q.; Hu, M.; Xiao, L.; Lu, J.; Zhuang, L. Alkaline
AUTHOR INFORMATION
Polymer Electrolyte Fuel Cells Stably Working at 80ꢀ°C. J. Power
Sources 2018, 390, 165-167.
Corresponding Author
* E-mail: twxu@ustc.edu.cn (T.X.)
(
14) Wang, Y.; Yang, Y.; Jia, S.; Wang, X.; Lyu, K.; Peng, Y.; Zheng,
H.; Wei, X.; Ren, H.; Xiao, L.; Wang, J.; Muller, D. A.; Abruna, H. D.;
Hwang, B. J.; Lu, J.; Zhuang, L. Synergistic Mn-Co Catalyst
Outperforms Pt on High-Rate Oxygen Reduction for Alkaline
Polymer Electrolyte Fuel Cells. Nat. Commun. 2019, 10, 1506.
*
E-mail: liangwu8@ustc.edu.cn (L.W.)
Author Contributions
(
15) Li, Q.; Peng, H.; Wang, Y.; Xiao, L.; Lu, J.; Zhuang, L. The
The manuscript was written through contributions of all
the authors. All the authors have given approval to the
final version of the manuscript.
Comparability of Pt to Pt-Ru in Catalyzing the Hydrogen Oxidation
Reaction for Alkaline Polymer Electrolyte Fuel Cells Operated at
80 C. Angew. Chem. Int. Ed. Engl. 2019, 58, 1442-1446.
o
(
16) Wang, L.; Bellini, M.; Miller, H. A.; Varcoe, J. R. A High
Notes
Conductivity Ultrathin Anion-Exchange Membrane with 500+ h
Alkali Stability for Use in Alkaline Membrane Fuel Cells that can
Achieve 2 W cm at 80 °C. J. Mater. Chem. A 2018, 6, 15404-
The authors declare no competing financial interest.
−2
15412.
ACKNOWLEDGMENT
This research was supported by the National Natural
Science Foundation of China (Nos. 21720102003,
(
17) Wang, L.; Brink, J. J.; Liu, Y.; Herring, A. M.; Ponce-González, J.;
Whelligan, D. K.; Varcoe, J. R. Non-fluorinated Pre-Irradiation-
Grafted (Peroxidated) LDPE-Based Anion-Exchange Membranes
with High Performance and Stability. Energy Environ. Sci. 2017,
10, 2154-2167.
2
1875233, 51934203), National Key R&D Program of
China (No. 2018YFB1502301) and Key Technologies R & D
Program of Anhui Province (No. 18030901079). Lianqin
Wang’s and John Varcoe’s time was funded by EPSRC grant
EP/M014371/1. We also acknowledge Dr. Xiuxia Wang
and Jinlan Peng from the center for Micro- and Nanoscale
Research and Fabrication at University of Science and
Technology of China for collecting the SEM images.
(18) Wang, L.; Magliocca, E.; Cunningham, E. L.; Mustain, W. E.;
Poynton, S. D.; Escudero-Cid, R.; Nasef, M. M.; Ponce-Gonzalez, J.;
Bance-Souahli, R.; Slade, R. C. T.; Whelligan, D. K.; and Varcoe, J. R.
An Optimised Synthesis of High Performance Radiation-Grafted
Anion-Exchange Membranes. Green Chem. 2017, 19, 831-843.
(19) Wang, L.; Peng, X.; Mustain, W. E.; Varcoe, J. R. Radiation-
Grafted Anion-Exchange Membranes: The Switch from Low- to
High-Density Polyethylene Leads to Remarkably Enhanced Fuel
Cell Performance. Energy Environ. Sci. 2019, 12, 1575-1579.
REFERENCES
(
20) Gonçalves Biancolli, A. L.; Herranz, D.; Wang, L.; Stehlíková,
(1) Chu, S.; Cui, Y.; Liu, N. The Path Towards Sustainable Energy.
Nat. Mater. 2017, 16, 16-22.
G.; Bance-Soualhi, R.; Ponce-González, J.; Ocón, P.; Ticianelli, E. A.;
Whelligan, D. K.; Varcoe, J. R.; Santiago, E. I. ETFE-Based Anion-
Exchange Membrane Ionomer Powders for Alkaline Membrane
Fuel Cells: A First Performance Comparison of Head-Group
Chemistry. J. Mater. Chem. A 2018, 6, 24330-24341.
(
2) Kerr, R. A. Do We Have the Energy for the Next Transition.
Science 2010, 329, 780-781.
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 11
(
21) Ponce-González, J.; Ouachan, I.; Varcoe, J. R.; Whelligan, D. K.
(36) Abouzari, M. R. S.; Berkemeier, F.; Schmitz, G.; Wilmer, D. On
the Physical Interpretation of Constant Phase Elements. Solid
State Ionics 2009, 180, 922-927.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Radiation-Induced Grafting of a Butyl-Spacer Styrenic Monomer
onto ETFE: The Synthesis of the Most Alkali Stable Radiation-
Grafted Anion-Exchange Membrane to Date. J. Mater. Chem. A
(37) Cordoba-Torres, P.; Mesquita, T. J.; Devos, O.; Tribollet, B.;
Roche, V.; Nogueira, R. P. On the Intrinsic Coupling between
Constant-Phase Element Parameters α and Q in Electrochemical
Impedance Spectroscopy. Electrochim. Acta 2012, 72, 172-178.
(38) Dlugolecki, P.; Ogonowski, P.; Metz, S. J.; Saakes, M.;
Nijmeijer, K.; Wessling, M. On the Resistances of Membrane,
Diffusion Boundary Layer and Double Layer in Ion Exchange
Membrane Transport. J. Membr. Sci. 2010, 349, 369-379.
(39) Park, J. S.; Choi, J. H.; Woo, J. J.; Moon, S. H. An Electrical
Impedance Spectroscopic (EIS) Study on Transport
Characteristics of Ion-Exchange Membrane Systems. J. Colloid
Interf. Sci. 2006, 300, 655-662.
2
018, 6, 823-827.
22) Peng, X.; Kashyap, V.; Ng, B.; Kurungot, S.; Wang, L.; Varcoe, J.
(
R.; Mustain, W. E. High-Performing PGM-Free AEMFC Cathodes
from Carbon-Supported Cobalt Ferrite Nanoparticles. Catalysts
2
019, 9, 264.
(
23) Omasta, T. J.; Wang, L.; Peng, X.; Lewis, C. A.; Varcoe, J. R.;
Mustain, W. E. Importance of Balancing Membrane and Electrode
Water in Anion Exchange Membrane Fuel Cells. J. Power Sources
2018, 375, 205-213.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(24) Omasta, T. J.; Peng, X.; Miller H. A.; Vizza, F.; Wang, L.; Varcoe,
-2
J. R.; Dekel, D. R.; Mustain, W. E. Beyond 1.0 W cm Performance
without Platinum: The Beginning of a New Era in Anion Exchange
Membrane Fuel Cells. J. electrochem. Soc. 2018, 165, J3039-J3044.
(
25) Omasta, T. J.; Park, A. M.; LaManna, J. M.; Zhang, Y.; Peng, X.;
Wang, L.; Jacobson, D. L.; Varcoe, J. R.; Hussey, D. S.; Pivovar, B. S.;
Mustain, W. E. Beyond Catalysis and Membranes: Visualizing and
Solving the Challenge of Electrode Water Accumulation and
Flooding in AEMFCs. Energy Environ. Sci. 2018, 11, 551-558.
(
26) Huang, G.; Mandal, M.; Peng, X.; Yang-Neyerlin, A. C.; Pivovar,
B. S.; Mustain, W. E.; Kohl, P. A. Composite Poly(norbornene)
Anion Conducting Membranes for Achieving Durability, Water
2
Management and High Power (3.4 W/cm ) in Hydrogen/Oxygen
Alkaline Fuel Cells. J. Electrochem. Soc. 2019, 166, F637-F644.
(
27) Borup, R.; Meyers, J.; Pivovar, B.; Kim, Y. S.; Mukundan, R.;
Garland, N.; Myers, D.; Wilson, M.; Garzon, F.; Wood, D.; Zelenay,
P.; More, K.; Stroh, K.; Zawodzinski, T.; Boncella, J.; McGrath, J. E.;
Inaba, M.; Miyatake, K.; Hori, M.; Ota, K.; Ogumi, Z.; Miyata, S.;
Nishikata, A.; Siroma, Z.; Uchimoto, Y.; Yasuda, K.; Kimijima, K. i.;
Iwashita, N. Scientific Aspects of Polymer Electrolyte Fuel Cell
Durability and Degradation. Chem. Rev. 2017, 107, 3904-3951.
(
28) Hwang, G. S.; Kim, H.; Lujan, R.; Mukundan, R.; Spernjak, D.;
Borup, R. L.; Kaviany, M.; Kim, M. H.; Weber, A. Z. Phase-Change-
Related Degradation of Catalyst Layers in Proton-Exchange-
Membrane Fuel Cells. Electrochim. Acta 2013, 95, 29-37.
(
29) Steinbach, A. J.; Allen, J. S.; Borup, R. L.; Hussey, D. S.;
Jacobson, D. L.; Komlev, A.; Kwong, A.; MacDonald, J.; Mukundan,
R.; Pejsa, M. J.; Roos, M.; Santamaria, A. D.; Sieracki, J. M.; Spernjak,
D.; Zenyuk, I. V.; Weber, A. Z. Anode-Design Strategies for
Improved Performance of Polymer-Electrolyte Fuel Cells with
Ultra-Thin Electrodes. Joule 2018, 2, 1297-1312.
(
30) Sneed, B. T.; Cullen, D. A.; Reeves, K. S.; Dyck, O. E.; Langlois,
D. A.; Mukundan, R.; Borup, R. L.; More, K. L. 3D Analysis of Fuel
Cell Electrocatalyst Degradation on Alternate Carbon Supports.
ACS Appl. Mater. Inter. 2017, 9, 29839-29848.
(31) Yu, K.; Groom, D. J.; Wang, X.; Yang, Z.; Gummalla, M.; Ball, S.
C.; Myers, D. J.; Ferreira, P. J. Degradation Mechanisms of Platinum
Nanoparticle Catalysts in Proton Exchange Membrane Fuel Cells:
the Role of Particle Size. Chem. Mater. 2014, 26, 5540-5548.
(
32) Jones, J.; Xiong, H. F.; Delariva, A. T.; Peterson, E. J.; Pham, H.;
Challa, S. R.; Qi, G. S.; Oh, S.; Wiebenga, M. H.; Hernandez, X. I. P.;
Wang, Y.; Datye, A. K. Thermally Stable Single-Atom Platinum-on-
Ceria Catalysts via Atom Trapping. Science 2016, 353, 150-154.
(
33) Zhu, Y.; He, Y.; Ge, X.; Liang, X.; Shehzad, M.A.; Hu, M.; Liu, Y.;
Wu, L.; Xu, T. A Benzyltetramethylimidazolium-Based Membrane
with Exceptional Alkaline Stability in Fuel Cells: Role of its
Structure in Alkaline Stability. J. Mater. Chem. A 2018, 6, 527-534.
(34) Yuk, S.; Choo, M. J.; Lee, D.; Guim, H.; Kim, T. H.; Lee, D. G.;
Choi, S.; Lee, D. H.; Doo, G.; Hong, Y. T.; Kim, H. T.
Three-Dimensional
Interlocking
Interface:
Mechanical
Nanofastener for High Interfacial Robustness of Polymer
Electrolyte Membrane Fuel Cells. Adv. Mater. 2017, 29, 1-7.
(35) Sun, C. N.; Delnick, F. M.; Aaron, D. S.; Papandrew, A. B.;
Mench, M. M.; Zawodzinski, T. A. Probing Electrode Losses in All-
Vanadium Redox Flow Batteries with Impedance Spectroscopy.
ECS Electrochem. Lett. 2013, 2, A43-A45.
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Membrane Fuel Cell
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