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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: ysli@mail.xjtu.edu.cn (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), metzhao@ust.hk80ons 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.