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A passive anion-exchange membrane directethanol fuel cell stack and its applications
Y.S. Li a,*, T.S. Zhao b,**
a Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'anJiaotong University, Xi'an, Shaanxi 710049, Chinab Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear
Water Bay, Kowloon, Hong Kong Special Administrative Region
a r t i c l e i n f o
Article history:
Received 4 May 2016
Received in revised form
14 August 2016
Accepted 25 August 2016
Available online 18 September 2016
Keywords:
Fuel cell
Direct ethanol fuel cell
Anion-exchange membrane
Stack
Dual-cell stack
Performance
* Corresponding author.** Corresponding author.
E-mail addresses: [email protected] (http://dx.doi.org/10.1016/j.ijhydene.2016.08.10360-3199/© 2016 Hydrogen Energy Publicati
a b s t r a c t
We report a passive anion-exchange membrane direct ethanol fuel cell (AEM DEFC) stack
that consists of two back-to-back independent-tank single cells. This particular design
not only enables a reduction in the weight and volume of the stack, but also avoids the
cross reaction of the liquid alkali occurring between two single cells. Experimental re-
sults indicate that the passive dual-cell stack that uses a non-Pt anode catalyst and a
non-precious metal cathode catalyst yields a peak power density of as high as
38 mW cm�2 at room temperature, a figure which is about 22 times higher than that of
the conventional proton-exchange membrane DEFC stack. The improved performance is
ascribed to: i) the accelerated electrochemical kinetics for the both anode and cathode
reactions, and ii) the use of the ethanol-tolerant cathode catalyst that eliminates the
cathode mixed overpotential. Finally, a power pack consisting of two series-connected
stacks is applied to power a toy car, which is demonstrated to continuously run for
one hour at a high constant speed of 0.52 m s�1 with on each fueling of a fuel tank with a
volume of 4.5 mL.
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction
Direct liquid fuel cell (DLFC) that offers a broader range of
benefits including high specific energy, fast refueling and ease
transport has been regarded as one of the most promising
alternative energy sources to replace conventional primary
and secondary batteries for powering portable electronics
[1e7]. Among various liquid fuels, ethanol is a less toxic fuel
and can be efficiently produced by fermenting biomass.
Hence, considerable interests have been focused on the direct
Y.S. Li), [email protected] LLC. Published by Els
ethanol fuel cells (DEFCs) [8e13], especially the anion-
exchange membrane (AEM) DEFCs, because of the fact that
when changing the proton-exchange membrane (PEM) to
AEM, both anode and cathode electrode reactions can be
significantly improved [14e20].
Over the past decade, tremendous efforts have beenmade
on the active AEM DEFC, in which the fuel and oxygen were
fed by a liquid pump and a gas compressor, respectively
[21,22]. For example, Fujiwara et al. [21] reported the alkaline-
based DEFCs with an unsupported PtRu anode and a Pt
cathode, reached the peak power density of 58 mW cm�2 at
(T.S. Zhao).
evier Ltd. All rights reserved.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 2 0 3 3 6e2 0 3 4 2 20337
room temperature with the 100-sccm humidified oxygen and
4-mL min�1 ethanol aqueous solution. Zhao et al. [22]
designed an ultra-low Pd-loading cathode for AEM DEFC by
directly depositing Pd particles onto the surface of themicro-
porous layer. It was demonstrated that this new cathode,
albeit with a Pd loading as low as 0.035 mg cm�2, enables the
peak power density to be as high as 88 mW cm�2 at 60 �Cwhen supplying the fuel to anode by a peristaltic pump at a
flow rate of 1.0 mL min�1 and feeding oxygen without hu-
midification by a mass flow controller at ambient pressure
with a flow rate of 10 sccm. Although the active cell perfor-
mance is appealing, it is essential to ensure the fuel cell
system simple and compact for the portable applications.
Therefore, the passive AEM DEFC that eliminates the moving
devices associated with the parasitic energy losses needed to
be developed. Moreover, in practical applications, to meet
the voltage requirement of the electronics, rather than
directly operating a single cell, particular scheme is paid on
the series-connected collection of single cells, referred to as
the “stack”. Presently, the AEMDEFC-based passive stack has
not yet been reported in the open literature. Being motivated
by this need, in this work, we design, fabricate and test a
passive dual-cell AEM DEFC stack that consists of two back-
to-back independent-tank single cells and successfully
apply it to powering a toy car.
Fig. 1 e Schematic illustration (a) and prototype (b) of the
passive dual-cell AEM DEFC stack.
Experimental
Dual-cell stack design
The dual-cell stack was designed by assembling two fuel
tanks, two end plates, and two single cells that are composed
of one membrane electrode assembly (MEA), two gaskets, and
two current collectors, as illustrated in Fig. 1a. Two back-to-
back independent fuel tanks, each having a volume of
4.5 mL, were designed based on the polymethyl methacrylate
(PMMA). The MEA, comprising subsequently the anode elec-
trode, membrane, and cathode electrode, was sandwiched
between a pair of current collectors that were made of the
material of 316L stainless steel plate with the thickness of
1.0 mm. To provide the passages of fuel and air, 54 circle holes
with a diameter of 2.0 mm were machined in the current
collector. The Polytetrafluoroethylene (PTFE)-fabricated
gasket was applied between the MEA and current collector to
prevent leakage. Two single cells were clamped between a
pair of printed-circuit-board-fabricated end pleats, in which a
2.2 cm� 3.2 cm� 1.5mmwindowwas carved to transport air.
Finally, eight stainless steel nut-and-bolt pairs were employed
to hold all the components together to form the dual-cell
stack, as shown in Fig. 1b.
Preparation of membrane electrode assembly
The in-house fabricated MEA with an active area of
2.0 cm � 3.0 cm was comprised of an anode, a commercial
anion exchange membrane with a thickness of 28 mm (A201),
and a cathode. The home-made PdNi/C and the commercial
FeeCueN4/C (Acta 4020) were employed as anode and cathode
catalysts, respectively. Before fabricating the electrode, the
catalyst inks, made of catalysts and 5 wt.% PTFE (Sigma-
eAldrich), were prepared by stirring in an ethanol as the sol-
vent. The nickel foam (RECEMAT BV, Netherlands) and the
micro-porous layer-based carbon paper (ETEK) were used as
the anode and cathode gas diffusion layers, respectively. The
prepared catalyst ink was directly brushed onto the surface of
the gas diffusion layerwith the catalyst loading of 2.0mg cm�2
to form the electrode.
Measurement instrumentation and test conditions
The voltageecurrent curves were controlled and measured by
an electrochemical workstation (Arbin BT-G, Arbin Instru-
ment Inc.) that was linked to a computer interface to adjust
the discharge conditions. All the experiments of the passive
AEM DEFC stack were performed at room temperature and a
relative humidity of around 63%. The aqueous fuel solutions
were injected into anode tanks. Simultaneously, the cathode
was directly exposed to the surroundings.
0 20 40 60 80 100 120 140 160 1800.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Vol
tage
(V)
Current density (mA cm )
0
5
10
15
20
25
30
35
40
45Anode: 5.0 M KOH + 3.0 M EtOHCathode: Air breathingRoom temp.: 21 C
Pow
er d
ensi
ty (m
W c
m)
Fig. 2 e Performance of the passive dual-cell AEMDEFC stack.
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 2 0 3 3 6e2 0 3 4 220338
Results and discussion
Working principle
As demonstrated in Fig. 1a, at the anode of the cell 01, a fuel
solution stored in the fuel tank is transported through the
anode gas diffusion layer to the anode active sites, where
ethanol reacts with hydroxyl ions to generate electrons, water
and carbon dioxide according to the equation,
CH3CH2OHþ 12OH�/2CO2 þ 9H2Oþ 12e� E0anode ¼ �0:74
(1)
The electrons are conducted by the electric wire to the
cathode electrode of cell 02. At the cathode of the cell 02, the
oxygen provided by the air, diffuses from the cathode current
collector through the gas diffusion layer to the cathode active
sites, where oxygen reacts with water and electrons to pro-
duce hydroxide ions, i.e.,
3O2 þ 6H2Oþ 12e�/12OH� E0cathode ¼ 0:4 (2)
The hydroxide ions are transferred through the anion ex-
change membrane from cell 02 cathode to cell 02 anode to
induce another ethanol oxidation reaction (EOR), as expressed in
Eq. (1). And then the generated electrons travel through the
external circuit to the cell 01 cathode electrode, thus leading to
another oxygen reduction reaction (ORR), as described by Eq. (2).
Subsequently, the produced hydroxide ions penetrate the anion
exchange membrane from cell 01 cathode to cell 01 anode.
The ideal overall reactions in both cells can be expressed as:
CH3CH2OHþ 3O2/2CO2 þ 3H2O E0overall ¼ 1:14 (3)
However, it should be noticed that even with the state-of-
the-art anode catalysts, the dominant reaction pathway of
the EOR is a 4-electron transfer process, i.e.,
CH3CH2OH þ 4OH� / CH3COOH þ 3H2O þ 4e� (4)
On the other hand, to achieve both high electro-kinetics of
EOR and high ionic conductivity, the externally-supplied hy-
droxyl ions that typically come from an alkali added to the
ethanol solution are needed. On this occasion, the acetic ion is
generated as follows,
CH3COOH þ OH� / CH3COO� þ H2O (5)
Accordingly, the present actual overall reaction in both cell
01 and 02 is,
CH3CH2OH þ O2 þ OH� / CH3COO� þ 2H2O (6)
In summary, the theoretical voltage of the series-
connected dual-cell AEM DEFC stack is as high as 2.28 V,
thus promising a potential high performance. In addition, it is
noted that the dual-cell stack has an independent fuel tank for
each single cell (see Fig. 1b) to avoid the cross reactions of the
liquid alkali occurring between two single cells.
General behavior
Fig. 2 shows both the polarization and power density curves of
the passive dual-cell AEM DEFC stack at room temperature
when an aqueous solution of 3.0 M ethanol mixed with 5.0 M
KOHwas injected into fuel tanks. It can be seen that the passive
dual-cell stack yields a peak power density as high as
38mW cm�2, 22 times higher than that of the passive two-cell-
based PEMDEFC [23]. It should be also appreciated that the AEM
DEFC stack employs a non-Pt anode catalyst (PdNi/C) and a
non-precious metal cathode catalyst (FeeCueN4/C). On the
contrast, the PEM DEFC stack used PtRu/C and Pt as anode and
cathode catalysts, respectively [23]. The excellent performance
of the dual-cell AEM DEFC stack is mainly ascribed to two
reasons. On one hand, unlike the acid environment in PEM
stack, the alkaline AEM stack can boost higher kinetics for both
the EOR and ORR [22]. On the other hand, the use of ethanol-
tolerant catalyst in the cathode eliminates the mixed over-
potential, thereby lowering the activation loss and resulting in a
higher stack performance.
The elimination of the cathode mixed overpotential in the
passive dual-cell AEM DEFC stack can be confirmed from its
transient OCV behavior as shown in Fig. 3. Before testing the
OCV, the dual-cell stack was first discharged at a large current
density of 170 mA cm�2 for a short time, and then rested for
10 min. It can be observed from Fig. 3 that at the first two
minutes, the OCV of the dual-cell stack rapidly increases.
Subsequently, unlike a PEMDEFC inwhich the OCV goes down
to a stable value [24], it goes straightly towards a plateau of
around 1.76 V. This is because of the fact that the ethanol
crossed from the anode to cathode cannot react with the ox-
ygen when using the ethanol-tolerant cathode catalyst,
thereby avoiding the overshoot behavior of the OCV, and
eliminating the cathode mixed overpotential.
The effectiveness of the ethanol-tolerant cathode catalyst
can be proven by the transient temperature behavior of the
passive dual-cell AEM DEFC stack as demonstrated in Fig. 4. A
fuel solution of 3.0 M ethanol mixed with 5.0 M KOH was
injected into the fuel tanks. Subsequently, the stack was first
discharged at the current density of 80 mA cm�2 for 140 min,
and then rested for 460 min. As seen from the figure, at the
beginning, the stack temperature grows from room tempera-
ture, 21 �C, to a stable value around 24 �C along with the
0 2 4 6 8 100.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
Anode: 5.0 M KOH + 3.0 M EtOHCathode: Air breathingRoom temp.: 21 oCO
CV
(V)
Time (min)
Fig. 3 e Transient OCV behavior of the passive dual-cell
AEM DEFC stack.
0 20 40 60 80 100 120 140 160 1800.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0
5
10
15
20
25
30
35
40
45Anode: 5.0 M KOH + EtOHCathode: Air breathingRoom temp.: 21 oC
Pow
er d
ensi
ty (m
W c
m-2)
Volta
ge (V
)
Current density (mA cm-2)
EtOH: 1.0 M EtOH: 3.0 M EtOH: 5.0 M EtOH: 7.0 M
Fig. 5 e Effect of ethanol concentration on the performance
of the passive dual-cell AEM DEFC stack.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 2 0 3 3 6e2 0 3 4 2 20339
discharging time (0e140min).When the stackwas shut down,
the stack temperature gradually reduces back to the 21 �C(140e460min). This phenomenon can be explained as follows.
The increase in the stack temperature is caused by the
exothermic reactions of both the EOR and ORR rather than the
reaction from the ethanol crossover. Otherwise, when shut-
ting the stack down after 140 min, the amount of ethanol
crossover will significantly increase, thus resulting in
increasing the stack temperature from 140 to 460 min. In
conclusion, the cathode catalyst is ethanol-tolerant.
In summary, both the alkaline environment and the
ethanol-tolerant catalyst enable the passive dual-cell AEM
DEFC stack to possess a high peak power density.
Effect of ethanol concentration on the stack performance
Fig. 5 shows the effect of ethanol concentration on the perfor-
mance of the dual-cell stack at a fixed KOH concentration of
5.0 M and changing ethanol concentration from 1.0 to 7.0 M. It
can be observed that the stack voltage first increases and then
decreases over the whole current density region, including the
Fig. 4 e Transient stack temperature behavior with and
without discharge.
activation, ohmic and concentration-controlled regions. The
peak power density of the dual-cell stack is 34 mW cm�2 at the
ethanol concentration of 1.0 M. Whereas, it rises to
38 mW cm�2 when increasing the ethanol concentration to
3.0 M, which, however, goes back to 30 and 22 mW cm�2 as
further increasing the ethanol concentration to 5.0 and 7.0 M,
respectively. The maximum current density rises from 152 to
172 mA cm�2 when increasing ethanol concentration from 1.0
to 3.0 M, however, it reduces to 109 mA cm�2 as the ethanol
concentration increases to 7.0 M. The variation in the stack
performance with varying the ethanol concentration can be
explained as follows. Firstly, increasing the ethanol concen-
tration from 1.0 to 3.0 M leads to the local fuel concentration of
anode catalyst layer changing from shortage to sufficiency,
thereby improving the stack voltage, which can be confirmed
by the increased open-circuit voltage (OCV) indicated in Fig. 6.
However, too much high ethanol concentration, for example
5.0 and 7.0 M, will break down the tradeoff of the competitive
adsorption between ethanol and hydroxyl ions at anode active
sites, thus lowering the electrochemical kinetics of EOR, as
evidenced from the decrease in the OCV in Fig. 6. Too much
high ethanol concentration will also block the transport of
hydroxyl ions, thus leading to an increase in internal resistance
0 1 2 3 4 5 6 7 81.73
1.74
1.75
1.76
1.77
0.20
0.25
0.30
0.35
0.40
0.45
0.50
Inte
rnal
resi
stan
ce (O
hm)
OC
V (V
)
Ethanol concentration (M)
Fig. 6 e Effect of ethanol concentration on open-circuit
voltage and internal resistance of the passive dual-cell
AEM DEFC stack.
1.77
1.78 0.40
)
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 2 0 3 3 6e2 0 3 4 220340
as shown in Fig. 6. In summary, when fixing the hydroxyl ion
concentration, an optimal ethanol concentration will yields the
best stack performance.
0 1 2 3 4 5 6 7 81.72
1.73
1.74
1.75
1.76
0.20
0.25
0.30
0.35
Inte
rnal
resi
stan
ce (O
hm
OC
V (V
)
KOH concentration (M)
Fig. 8 e Effect of hydroxyl ion concentration on open-circuit
voltage and internal resistance of the passive dual-cell
AEM DEFC stack.
Effect of hydroxyl ion concentration on stack performance
When giving a fixed ethanol concentration of 3.0M, the effect of
the hydroxyl ion concentration varying from 1.0 to 7.0 M on the
stack performance can be investigated as presented in Fig. 7. As
observed, when the current density is lower than 20 mA cm�2,
the stack voltage monotonically raises as the hydroxyl ion
concentration increases from 1.0 to 7.0 M, mainly owing to the
fact that the electrochemical kinetics of EOR can be accelerated
with increasing the pH value, which can be confirmed by the
increased OCV as shown in Fig. 8. However, when the current
density is larger than 20 mA cm�2, an optimal hydroxyl ion
concentration of 5.0M can be achieved. This is because too high
hydroxyl ion concentration not only reduces the ethanol
coverage at anode active sites, but also increases the internal
resistance as shown in Fig. 8. In summary, at a given ethanol
concentration, in the current density region higher than
20 mA cm�2, there exists an optimal hydroxyl ion concentra-
tion for yielding the best stack performance.
Application of the passive dual-cell AEM DEFC stack to atoy car
After finishing the dual-cell stack performance test, this kind
of stack was applied to a toy car to demonstrate their feasi-
bility as portable power sources. Fig. 9a shows the picture of
the as-developed passive AEM DEFC powered toy car that is
equipped with an electric motor with a rating power of about
500 mW. To meet the power need of the electric motor, a
series-connected four-cell stack (two units of the above-
mentioned dual-cell stack) with a total active area of
24 cm�2 was designed and fabricated. An important feature of
the AEMDEFC powered toy car is that the steering angle of the
front wheels can be pre-set so that the car can continuously
run along a circle track, as shown in Fig. 9b. The present circle
running track has a radius of 25 cm. An aqueous fuel solution
containing 3.0 M ethanol and 5.0 M potassium hydroxide was
0 20 40 60 80 100 120 140 160 1800.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0
5
10
15
20
25
30
35
40
45
Pow
er d
ensi
ty (m
W c
m-2)
Volta
ge (V
)
Current density (mA cm-2)
KOH: 1.0 M KOH: 3.0 M KOH: 5.0 M KOH: 7.0 M
Anode: 3.0 M EtOH + KOHCathode: Air breathingRoom temp.: 21 oC
Fig. 7 e Effect of hydroxyl ion concentration on the
performance of the passive dual-cell AEM DEFC stack.
injected into anode fuel tanks. Simultaneously, the cathode
was directly exposed to the surroundings.
Fig. 10 shows the variation in the car speeds with the
running time. The entire test course is divided into two pe-
riods as a result of two-times fueling. It can be seen that
during the first period after the first fueling (0e120 min), the
car run at an initial speed of about 0.52 m s�1. It remains
moving with this constant speed, even increasing the running
time to 60 min. As the running time increases to 90 min, it can
Fig. 9 e (a) Toy car powered by passive AEM DEFC stacks,
and (b) circle running track with a radius of 25 cm.
0 30 60 90 120 150 180 210 2400.1
0.2
0.3
0.4
0.5
0.6
0.7
Activation and Ohmic losses
2st fueling1st fueling
Car
spe
ed (m
s-1)
Running time (min)
Concentration loss
Fig. 10 e Variation in the demo car speedswith running time.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 2 0 3 3 6e2 0 3 4 2 20341
be seen, the car was reduced to a speed of 0.44 m s�1. When
further running the car for another half hour (90e120min), the
car moved relatively slowly with a speed of only 0.26 m s�1. At
the beginning of the second period (120e240 min), the second
fueling made the car speed boosted to 0.48 m s�1. After
continuously running for one hour, the speed almost remains
unchanged. When further running the car, the car speed kept
fallingwith the running time until the speed goes to 0.24m s�1
at 240 min. The fact of the speed recovery as the second
fueling suggests that the speed reduction before 75 min after
the first fueling is mainly attributed to the activation loss and
ohmic loss, including the catalyst loss, catalyst poisoning, the
coverage of the active area, and the decomposition of the
quaternary ammonium group [22]. However, after 75 min, the
car speed reduction is due to the decrease in the fuel solution
concentration in the fuel tanks.
In summary, the series-connected four-cell AEM DEFC
powered toy car can continuously run for one hour at a high
constant speed on each fueling of a fuel tank with a volume of
4.5 mL. This result suggests that the alkaline AEM DEFC is
indeed a promising power source, practically for portable
electronic devices.
Conclusions
In this work, a passive anion-exchange membrane direct
ethanol fuel cell stack that consists of two back-to-back in-
dependent-tank single cells was designed, fabricated and
tested. This particular design not only lessens the weight and
volume of the stack but also avoids the cross reaction of the
liquid alkali occurring between two single cells. The experi-
mental result indicated that this passive dual-cell stack yiel-
ded a peak power density as high as 38 mW cm�2 at room
temperature, even using the non-Pt anode catalyst and the
non-preciousmetal cathode catalyst, which is 22 times higher
than did the conventional PEM DEFC stack. The excellent
performance was mainly attributed to the accelerated elec-
trochemical kinetics for both anode and cathode electrode
reactions as well as the use of ethanol-tolerant cathode
catalyst eliminating the cathode mixed overpotential. It was
found that when injecting a fuel solution containing 3.0 M
ethanol mixed with 5.0 M KOH into anode fuel tanks, the best
stack performance can be achieved. Moreover, to demonstrate
that the AEM DEFC could be used as a portable power source,
practically for the electronic devices, this passive dual-cell
stack was applied to power a toy car. It has been indicated
that a series-connected two dual-cell stacks powered toy car
can continuously run for one hour at a high constant speed of
0.52 m s�1 on each fueling of a fuel tank with a volume of
4.5 mL, suggesting the alkaline AEM DEFC be a promising
power source for driving portable electronic devices.
Acknowledgements
This work was supported by the Research Project of Chinese
Ministry of Education (113055A) and the 111 Project (B16038).
r e f e r e n c e s
[1] An L, Chen R. Direct formate fuel cells: a review. J PowerSources 2016;320:127e39.
[2] Hong P, Liao S, Zeng J, Zhong Y, Liang Z. A miniature passivedirect formic acid fuel cell based twin-cell stack with highlystable and reproducible long-term discharge performance. JPower Sources 2011;196:1107e11.
[3] Li YS, He YL, Yang WW. A high-performance direct formate-peroxide fuel cell with palladium-gold alloy coated foamelectrodes. J Power Sources 2015;278:569e73.
[4] Verjulio RW, Santander J, Sabate N, Esquivel JP, Torres-Herrero N, Habrioux A, et al. Fabrication and evaluation of apassive alkaline membrane micro direct methanol fuel cell.Int J Hydrogen Energy 2014;39:5406e13.
[5] Li YS. A liquid-electrolyte-free anion-exchange membranedirect formate-peroxide fuel cell. Int J Hydrogen Energy2016;41:3600e4.
[6] Guo H, Chen Y, Xue Y, Ye F, Ma C. Three-dimensionaltransient modeling and analysis of two-phase mass transferin air-breathing cathode of a fuel cell. Int J Hydrogen Energy2013;38:11028e37.
[7] Li YS, Wu H, He YL, Liu Y, Jin L. Performance of directformate-peroxide fuel cells. J Power Sources 2015;287:75e80.
[8] Moraes LPR, Matos BR, Radtke C, Santiago EI, Fonseca FC,Amico SC, et al. Synthesis and performance of palladium-based electrocatalysts in alkaline direct ethanol fuel cell. Int JHydrogen Energy 2016;41:6457e68.
[9] Antolini E. Palladium in fuel cell catalysis. Energy Environ Sci2009;2:915e31.
[10] Li Y, He Y. An all-in-one electrode for high-performanceliquid-feed micro polymer electrolyte membrane fuel cells. JElectrochem Soc 2016;163:F663e7.
[11] Liu L, Chen LX, Wang AJ, Yuan JH, Shen LG, Feng JJ. Hydrogenbubbles template-directed synthesis of self-supported AuPtnanowire networks for improved ethanol oxidation andoxygen reduction reactions. Int J Hydrogen Energy2016;41:8871e80.
[12] Bianchini C, Shen PK. Palladium-based electrocatalysts foralcohol oxidation in half cells and in direct alcohol fuel cells.Chem Rev 2009;109:4183e206.
[13] Li Y, Lv J, He Y. A monolithic carbon foam-supported Pd-based catalyst towards ethanol electro-oxidation in alkalinemedia. J Electrochem Soc 2016;163:F424e7.
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 2 0 3 3 6e2 0 3 4 220342
[14] Huang C, Lin J, Pan W, Shih C, Liu Y, Lue S. Alkaline directethanol fuel cell performance using alkali-impregnatedpolyvinyl alcohol/functionalized carbon nano-tube solidelectrolytes. J Power Sources 2016;303:267e77.
[15] Ogumi Z, Matsuoka K, Chiba S, Matsuoka M, Iriyama Y,Abe T, et al. Preliminary study on direct alcohol fuel cellsemploying anion exchange membrane. Electrochemistry2002;70:980e3.
[16] Li SS, Lv JJ, Teng LN, Wang AJ, Chen JR, Feng JJ. Facilesynthesis of PdPt@Pt nanorings supported on reducedgraphene oxide with enhanced electrocatalytic properties.ACS Appl Mater Interfaces 2014;6:10549e55.
[17] Li Y, He Y. Layer reduction method for fabricating Pd-coatedNi foams as high-performance ethanol electrode for anion-exchange membrane fuel cells. RSC Adv 2014;32:16879e84.
[18] Jiao K, Huo S, Zu M, Jiao D, Chen J, Du Q. An analytical modelfor hydrogen alkaline anion exchange membrane fuel cell.Int J Hydrogen Energy 2015;40:3300e12.
[19] Yu EH, Scott K. Direct methanol alkaline fuel cell withcatalyzed metal mesh anodes. Electrochem Commun2004;6:361e5.
[20] Yanagi H, Fukuta K. Anion exchange membrane andionomer for alkaline membrane fuel cells (AMFCs). ECSTrans 2008;16:257e62.
[21] Fujiwara N, Siroma Z, Yamazaki S, Ioroi T, Senoh H,Yasuda K. Direct ethanol fuel cells using an anion exchangemembrane. J Power Sources 2008;185:621e6.
[22] Li YS, Zhao TS. Ultra-low catalyst loading cathode electrodefor anion-exchange membrane fuel cells. Int J HydrogenEnergy 2012;37:15334e8.
[23] A. V�elez-Denhez, M. C�ordoba-Moreno, W.H. Lizcano-Valbuena, Investigation of passive DEFC mini-stacks atambient temperature, ECS Meet Abstr. MA2014-02 1178.
[24] Pethaiah SS, Arunkumar J, Ramos M, Al-Jumaily A,Manivannan N. The impact of anode design on fuel crossoverof direct ethanol fuel cell. Bull Mater Sci 2016;13:1e6.