Comparative study of aliphatic alcohols electrooxidation on zero-valent palladium complex for direct alcohol fuel cells

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Comparative study of aliphatic alcoholselectrooxidation on zero-valent palladium complexfor direct alcohol fuel cells

Mohammad Zhiani*, Somayeh Majidi, Hussein Rostami,Mohammad Mohammadi Taghiabadi

Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran

a r t i c l e i n f o

Article history:

Received 27 July 2014

Received in revised form

27 October 2014

Accepted 30 October 2014

Available online xxx

Keywords:

Pd (DBA)2Alcohol electrooxidation

Direct alcohol fuel cell

Alkaline media

* Corresponding author. Tel./fax: þ98 31 339E-mail address: [email protected] (M.

Please cite this article in press as: Zhianpalladium complex for direct alcohol fuj.ijhydene.2014.10.144

http://dx.doi.org/10.1016/j.ijhydene.2014.10.10360-3199/Copyright © 2014, Hydrogen Ener

a b s t r a c t

In this paper, bis (dibenzylidene acetone) palladium (0), Pd (DBA)2, was used as an effective

catalyst for the electrooxidation of different aliphatic alcohols such as ethylene glycol (EG),

ethanol (EtOH), glycerol (Gly), methanol (MeOH)) in the alkaline media. The activity and

stability of Pd (DBA)2 were assessed for the electrooxidation of the mentioned alcohols

using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chro-

noamperometry (CA). Pd (DBA)2 exhibited significantly high anodic current density and

lower onset potential in EtOH oxidation compared to EG, Gly and MeOH. CV and CA results

demonstrated that Pd (DBA)2 is still active even after 200 CV cycles. The tolerance of Pd

(DBA)2 against poisoning intermediate products in case EtOH was higher than other

mentioned alcohols. Finally, Pd (DBA)2 successfully employed as an anode catalyst in a

passive air breathing direct alcohol fuel cell (DAFC). The maximum power density (MPD) of

30, 31, 25 and 18 mW cm�2 were achieved for EG, EtOH, Gly and MeOH, respectively. These

results indicated that Pd (DBA)2 can be a promising anode catalyst for DAFCs.

Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

Introduction

Compared to H2-fueled fuel cells, direct alcohol fuel cells

(DAFCs) have attracted enormous attention due to the simple

production, storage of liquid fuels and fuel purification [1,2].

Liquid fuels such as; ethylene glycol (EG), ethanol (EtOH),

glycerol (Gly) and methanol (MeOH) not only are more easily

stored and transported but also, have a higher volumetric

energy density and more energy efficiency than gaseous fuels

[3]. The volumetric energy density of EG, EtOH, Gly and MeOH

at 20 MPa is 5.79, 6.31, 6.26 and 4.82 (kWh L�1), respectively.

They are much higher than hydrogen (0.53 kWh L�1).

13263.Zhiani).

i M, et al., Comparativeel cells, International J

44gy Publications, LLC. Publ

Nevertheless, DAFCs have suffered slow kinetics of the

alcohols electrooxidation reaction on the surface of synthe-

sized catalysts in spite of great efforts, which have beenmade

for development of catalyst materials.

Pt and Pt-based catalysts have been extensively investi-

gated and recognized as the traditional catalysts with suitable

catalytic efficiency for the alcohols electrooxidation reaction

[4e6]. However, the toxic intermediate species of the alcohols

electrooxidation reaction would reduce catalytic performance

of the mentioned catalysts. In addition, the high cost and

limited supply of Pt would restrict its application in DAFCs.

As compared to the electrooxidation of MeOH, the oxida-

tion of EG, EtOH and Gly not only depend on the ability of the

study of aliphatic alcohols electrooxidation on zero-valentournal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/

ished by Elsevier Ltd. All rights reserved.

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http://dx.doi.org/10.1016/j.ijhydene.2014.10.144



Fig. 1 e Structure of Pd (DBA)2 catalyst.

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 x x x ( 2 0 1 4 ) 1e92

catalyst in oxidative removal of poisoning intermediates, but

also depend on its activity in CeC and CeH bond breakage [7].

Obviously, it is necessary to find high active and stable cata-

lysts for electrooxidation of alcohols in DAFCs.

Notableworks have been done for replacing of the Pt-based

catalysts with Pd-based catalysts toward alcohols oxidation in

DAFCs because, it is more abundant and less expensive than

Pt. Also, Pd-based catalysts have been used successfully for

the alcohols electrooxidation reaction in the alkaline envi-

ronment. For example, many researchers have devoted to

investigating of large variety of conductive materials for the

support of the Pd nanoparticles in alcohols oxidation,

including Vulcan XC-72R carbon black [8], tungsten carbides/

carbon nanotubes [9], ultrahigh-surface hollow carbon

spheres [10], carbonized TiO2 nanotube [11] and carbon mi-

crospheres [12]. Pd nanoparticles supported on multi-walled

carbon nanotubes were scrutinized for the oxidation of

EtOH, Gly or MeOH in the 2 M KOH solution in half cells [13].

The catalyst was very active for the electrooxidation of all

alcohols, with Gly providing the best performance in terms of

the specific current density and EtOH showing the lowest

onset potential.

Compositing or alloying Pd with other elements such as Sn

[14,15], Au [14,16], Ag [17], Ni [18,19], Pt [20e22] and Bi [23]

could potentially enhanced the catalysts activity, lower

degradation of the active surface and overcome the poisoning

effects by reducing surface coverage by adsorbed CO. Chen

et al. [24] found that the catalytic activity of PdeRu is

considerably higher than that of Pd toward the electro-

oxidation of EG, EtOH, and MeOH. The activity sequence of

PdeRu toward the alcohol electrooxidation was

EtOH > EG >MeOH, and PdeRu with 1:1 atomic ratio exhibited

the highest activity. They also compared the activities of

PdeRu and PteRu catalysts for alcohol electrooxidations in

alkaline media. For the electrooxidation of MeOH and EG, the

activity of PdeRu was lower than that of PteRu. For the EtOH

electrooxidation reaction, instead, the activity of PdeRu was

higher than that of PteRu.

To diminishing the CO poisoning effect on the catalyst

surface, metal oxides (CeO2, NiO, Co3O4 and Mn3O4) were

added into Pd-based catalysts in electrooxidation of alcohols

[25e27]. The results indicated that addition of the metal oxide

remarkably improves the activity and CO tolerance of the Pd-

based catalysts in alcohols electrooxidation. All investigations

suggested that Pd-based catalysts could make up for the

deficiency of Pt-based catalysts in DAFCs.

All zero-valent complexes with dl0 electronic configura-

tions have considerable catalytic interest toward alcohols

oxidation. Specially, zero-valent Pd complexes are efficient

catalysts in the field of organic synthesis and in all reactions

involving aryl, vinyl and allelic derivatives because of their

good nucleophilic properties [28]. Among factors influencing

the reactivity, electronic effects are very important, namely

oxidizing of the metal center and tuning the donor/acceptor

properties of the p-coordinated unsaturated hydrocarbon li-

gands and other co-ligands to vary the distribution of the

electron density in the complexes [29].

In our previous work [30], we have successfully employed

on first time zero-valent Pd complex, Pd (DBA)2, as an catalyst

toward the Gly electrooxidation reaction. Results showed that

Please cite this article in press as: Zhiani M, et al., Comparativepalladium complex for direct alcohol fuel cells, International Jj.ijhydene.2014.10.144

Pd (DBA)2 exhibits a superior catalytic performance with high

long-term stability for the direct Gly fuel cell in alkalinemedia.

Pd (DBA)2 was synthesized in 1970 [31]. Different substitu-

tion and addition reactions have been reported along with an

investigation of the potential utility of the Pd (DBA)2 as a

catalyst [32,33]. The complex structure of Pd (DBA)2 is shown

in Fig. 1.

In the present work, the performance of Pd (DBA)2 in

electrooxidation of different aliphatic alcohols (EG, EtOH, Gly

and MeOH) have been investigated in the half cell by cyclic

voltammetry (CV), electrochemical impedance spectroscopy

(EIS) and chronoamperometry (CA) techniques in the alkaline

medium. To determine the performance of Pd (DBA)2 in real

alkaline DAFCs, membrane electrode assembly (MEA) was

fabricated by using the Pd (DBA)2 catalyst in the anode elec-

trode. All the obtained results from the half and whole cell

indicate that Pd (DBA)2 represents an acceptable activity and

performance for DAFCs in the alkaline medium.

Experimental

Half-cell electrochemical investigation

Deposition of Pd (DBA)2 on the glassy carbonA thin film of the catalyst layer on the glassy carbon (GC)

electrode was prepared as follows: a mixture containing

2.0 mg of Pd (DBA)2 (Aldrich, molecular weight of 575 g mol�1,

melting point of 150 �C), 1 mL of 2-propanol, 1 mL of the ultra

pure water (MilliQ, Millipore) and 0.01 mL of 5 wt.% Nafion

solution (Aldrich) were sonicated for 5 min. The well-

dispersed catalyst ink was then quantitatively transferred

onto the surface of the GC electrode by using a micropipette,

and finally was dried in the oven at 60 �C for 15 min. The

catalyst loading on the electrode surface was 0.033 mg cm�2.

All chemical materials (Merck) were analytical grade.

CV, EIS and CA measurementsThe electrochemical activity and stability of Pd (DBA)2 in

alcohol electrooxidation reaction were investigated by CV, EIS

and CA techniques. Electrochemical measurements were

carried out with a conventional three-electrodic cell and an




Fig. 2 e Cyclic voltammograms of Pd (DBA)2 in 10 wt.% KOH

in the absence (a) and present (b) of 5 wt.% alcohol at scan

rate of 50 mV s¡1 and 25 �C.

i n t e rn a t i o n a l j o u rn a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e9 3

Auto-lab PGSTAT30 potentiostat/galvanostat at 25 �C. The GC

coated with the catalyst layer was used as a working elec-

trode. A commercial Ag/AgCl electrode and a Pt wire were also

chosen as reference and counter electrodes, respectively. All

electrochemical measurements were carried out in an alka-

line solution containing 10 wt.% KOH. The concentration of

alcohols in the solution was 5 wt.%. The alcohols examined in

the present study were EG, EtOH, Gly and MeOH.

The CV technique was carried out by scanning of the po-

tential between�0.7 and 0.4 V with the scan rate of 50mV s�1.

EIS results were obtained by scanning of the frequencies be-

tween 100 kHz and 0.005 Hz at zero volt potential. The

amplitude of the sinusoidal potential signal was 10 mV. CA

measurements were also carried out at potential of zero volt.

All potentials in this article have been reported versus

normal hydrogen electrode (NHE).

Table 1 e Comparison of electrochemical performance ofalcohol electrooxidation on Pd (DBA)2 in 10 wt.% KOH and5 wt.% alcohols with a scan rate of 50 mV s¡1 at 25 �C.

Alcohol Eonset (V) Ep (V) Jp (mA cm�2)

EG �0.32 0.14 28.4

EtOH �0.5 0.07 20.7

Gly �0.35 0.08 15.8

MeOH �0.26 0.06 5.2

DAFC preparation and evaluation

A mixture of 95 wt.% Pd (DBA)2 and 5 wt.% PTFE (Aldrich) was

ultrasonically dispersed in isopropyl alcohol and double dis-

tillated water for 20 min, to obtain the anode catalyst ink. The

ink was precisely coated on the nickel foam. The cathode

electrode was made as follows: the cathode catalyst ink was

prepared by mixing Hypermec™ K14 (Acta SpA) with 10 wt.%


PTFE (on dry weight basis) and water, and coated on the car-

bon cloth (E-TEK) as a diffusion medium. The both anode and

cathode electrodes were dried at 60 �C for 30 min in the oven.

The anode and cathode catalyst loading were 5 and

3.5 mg cm�2, respectively. An anion-exchange membrane

(Tokuyama) was placed between two electrodes to obtain an

MEA. The MEA was then assembled into an air-breathing

DAFC for performance measurements according to V. Bam-

bagioni et al. [4].

The DAFC was tested using alkaline fuels containing al-

cohols (5 wt.% EG, 5 wt.% EtOH, 5 wt.% Gly and 5 wt.% MeOH)

and 5 wt.% KOH. All tests were performed by the fuel cell test

station (Scribner model 850e) at room temperature and

ambient pressure. The DAFC was activated according to the

procedure mentioned in Ref. [34]. Prior to recording the po-

larization curves for each fuel, the DAFC was conditioned at

the open circuit voltage (OCV) for 30 min for the stabilization.

Polarization curves were obtained by scanning the cell voltage

from the OCV to 250 mV with the scan rate of 5 mV s�1 after

reaching the steady state.

Results and discussion

Electrocatalytic activity and stability of Pd (DBA)2

The electrocatalytic activity of the Pd (DBA)2 was examined by

the CV technique in the electrooxidation of aliphatic alcohols;

EG, EtOH, Gly and MeOH. Firstly, the Pd (DBA)2 leaching test

was carried out by CV in the KOH solution. Fig. 2a shows 5th

and 80th cycles of the Pd (DBA)2 in 1 M KOH. As it can be seen,

the position and magnitude of the forward and backward

peaks did not change during 80 cycles. Therefore, it could be

concluded that Pd (DBA)2 did not leach to the KOH solution.

Fig. 2 represents CV of Pd (DBA)2 in the solution containing

10wt.% KOH in the absence (Fig. 2a) and present (Fig. 2b) of the

mentioned alcohols.

By comparing the CVs of Pd (DBA)2 in the absence and

present of the alcohols (Fig. 2a and b), a number of anodic

peaks were observed which could be clearly assigned to the

alcohols electrooxidation peaks on Pd (DBA)2. Generally, the

oxidation peak in the forward scan is corresponding to the

oxidation of freshly chemisorbed species coming from the

alcohol adsorption. In the reverse scan, the anodic peak is

correlated with the removal of carbonaceous species not

completely oxidized in the forward scan [35]. These results

demonstrate that Pd (DBA)2 is an active catalyst for electro-

oxidation of all mentioned alcohols which could be used in

alkalineDAFCs. For better comparison the activity of Pd (DBA)2




Fig. 3 e Cyclic voltammograms (1st, 30th, 70th, 100th, 130th, 170th and 200th cycle) of Pd (DBA)2 in the solution containing

10 wt.% KOH and 5 wt.% a) EtOH, b) EG, c) Gly and d) MeOH at room temperature with the scan rate of 50 mV s¡1.

Fig. 4 e IR spectra of Pd (DBA)2 before and after 50 CV cycles of Gly oxidation.


Please cite this article in press as: Zhiani M, et al., Comparative study of aliphatic alcohols electrooxidation on zero-valentpalladium complex for direct alcohol fuel cells, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/j.ijhydene.2014.10.144




in electrooxidation of the mentioned alcohols, all CVs were

analyzed and their results were listed in Table 1. As it can be

seen in Table 1, Pd (DBA)2 exhibits higher activity for EtOH

electrooxidation compared to other alcohols. Although the

anodic peak current density of EtOH electrooxidation on Pd

(DBA)2 is less than EG but, it occurred at more negative onset

potential compared to EG. The worst result was obtained by

the MeOH electrooxidation reaction in terms of the peak

current density and onset potential. Based on the anodic

oxidation peak current density and onset oxidation potential,

the activity sequence of Pd (DBA)2 in alcohols electrooxidation

is as follow; EtOH > EG > Gly > MeOH.

Electrocatalytic activity of the Pd (DBA)2 was also investi-

gated by CV during 200 cycles. Fig. 3aed shows consecutive

CVs for electrooxidation of EG, EtOH, Gly and MeOH,

respectively.

In all cases, the anodic peak current densities increased by

increasing of the CV cycle number. However, this trend in the

growth of the peak currents declines with further increasing

Fig. 5 e Products obtained by electro-oxidation of (a) M


of the CV cycle number. The enhancement of the peak current

density is related to increasing the activity of Pd (DBA)2 during

potential cycling [36], and the subsequent decline in the peak

current density is attributed to two factors; (i) consumption of

the alcohol during the long time scanning, and (ii) poisoning

the catalyst by the intermediates produced during the alcohol

oxidation reaction [37]. Fig. 3 also indicates that Pd (DBA)2 still

exhibits well defined forward and reverse peaks for the alco-

hols oxidation reaction after 200 cycles.

After 200th CV cycles, the oxidation current densities of EG,

EtOH, Gly and MeOH declined approximately 19%, 14%, 52%

and 33%, respectively (Fig. 3). Higher reduction in the peak

current density of the Gly electrooxidation reaction could be

related to higher Gly oxidation intermediates. Fig. 4 indicates

FTIR spectra of Pd (DBA)2 before and after 50 CV cycles of Gly

oxidation. It shows that the catalyst structure does not change

during Gly electrooxidation. Thus, the subsequent decline in

the peak current density of Gly electrooxidation is attributed

to the catalyst poisoning.

eOH; (b) EtOH; (c) EG and (d) Gly in alkaline media.




Fig. 7 e Equivalent circuit of Nyquist plots analysis in

DAFCs made by Pd (DBA)2 anode catalyst with fuel

containing 5 wt.% KOH and aliphatic alcohols.


Fig. 5aed shows products obtained for electrooxidation of

MeOH, EtOH, EG, and Gly, in alkaline media, respectively. The

electrooxidation of alcohols, especially polyalcohols, can be

mechanistically complicated by the occurrence of parallel

steps. In Fig. 5, it can be seen the oxidation of Gly is more

complex than other alcohols [4,35]. As it described in Fig. 3 and

Fig. 5, most of the Gly oxidation intermediates can be adsor-

bed on the catalyst active sites and therefore reduces the

catalyst active surface area. It causes a reduction in the peak

current of Gly oxidation during CV cycling. These results show

that Pd (DBA)2 catalyst has highest stability in electro-

oxidation of EtOH and lowest stability toward Gly

electrooxidation.

EIS spectra of alcohols electrooxidation on Pd (DBA)2

The EIS technique was employed to compare the impedance

characteristics of EG, EtOH, Gly and MeOH electrooxidation

reaction on Pd (DBA)2. Fig. 6 indicates the Nyquist plots of the

alcohols electrooxidation reaction on Pd (DBA)2 in the solution

containing 10 wt.% KOH and 5 wt.%mentioned alcohols at the

constant potential of zero volt, after 1st (Fig. 6a) and 200th

cycle (Fig. 6).

Fig. 6 e Nyquist plots of Pd (DBA)2 catalyst after the cyclic

voltammograms 1st (a) and 200th cycle (b) in the solution

containing 10 wt.% KOH and 5 wt.% the alcohol at potential

of 0 V.


Although, general shapes of all Nyquist plots shown in

Fig. 6 are similar, however, the arcs diameter of the Nyquist

plots are different depend on the alcohols electrooxidation

kinetic and their structures. The Nyquist diagram comprises a

depressed semicircle at high frequencies, which is related to

the combination of the charge transfer resistance (Rct) of al-

cohols electrooxidation and the constant phase element (CPE),

followed by a straight line with a slope of nearly 45�. The latter

is due to the mass transport as modeled by the infinite War-

burg impedance [38]. The intersection of the imaginary

impedance with the real impedance reflects the solution

resistance (Rs). Based on the impedance spectra, Rct and Rs can

be extracted using the equivalent circuit set up in Fig. 7 [38].

The Nyquist plots were fitted by Zview software. The extrac-

ted resistances after 1st and 200th cycles for all alcohols were

summarized in Table 2. As it can be seen in Table 2, EtOH

electrooxidation on Pd (DBA)2 has the lowest Rct value and

MeOH has the highest value after 1st cycle. The small charge

transfer resistance of EtOH electrooxidation has a good cor-

relation with the obtained CVs results in

section Electrocatalytic activity and stability of Pd (DBA)2.

Table 2 also indicates that after 200th cycle, the values of Rs

and Rct increased for all alcohols, especially for Gly which is

related to the acceleration rate of the catalyst poisoning by

many intermediate products of Gly electrooxidation during

200 cycles [39,40]. However, Rs of the MeOH solution did not

change too much compared to other alcohols during 200 cy-

cles, because its intermediate products is lower than others

(Fig. 5), and also Pd (DBA)2 activity for MeOH electrooxidation

is lower than other alcohols, as it demonstrated in section 3.1.

Chronoamperograms of alcohols electrooxidation on Pd(DBA)2

The chronoamperometry of Pd (DBA)2 was performed in the

solution containing 10 wt.% KOH and 5 wt.% alcohols at zero

volt of potential. Fig. 8aeb shows chronoamperograms of Pd

Table 2 e The obtained resistances values from Nyquistplots of the alcohols electrooxidation reaction on Pd(DBA)2 catalyst after 1st and 200th cycles.

Alcohol After 1 cycle After 200 cycle

Rct (U cm2) Rs (U cm2) Rct (U cm2) Rs (U cm2)

EG 117 0.25 433 4.8

EtOH 95 0.05 294 1.2

Gly 937 1.1 7121 7.8

MeOH 974 5.9 4383 6.6




Fig. 8 e Chronoamperograms of alcohols electrooxidation

on the Pd (DBA)2 catalyst after the CV cycles (a) 1st and (b)

200th in the solution containing 10 wt.% KOH and 5 wt.%

alcohol at potential of 0 V.

Fig. 9 e IeV and power density curves of alkaline passive

air-breathing DAFC made by Pd (DBA)2 anode catalyst with

fuel containing 5 wt.% KOH and aliphatic alcohols at room

temperature.


(DBA)2 in the alcohols oxidation reaction after 1st and 200th

cycles, respectively.

CA curves of all alcohols display the decay of the current

density along the time, which is related to the remaining the

adsorbed produced intermediates on the catalyst surface [36].

As it is shown in Fig. 8, current density of Pd (DBA)2 after 200th

cycle behaved with a more gently decreasing trend, because

Pd(DBA)2 is poisoned by Gly electrooxidation byproducts and

intermediates as it described before.

According to the obtained CA results, Pd (DBA)2 has higher

activity and better poisoning tolerance toward EtOH electro-

oxidation. The long-term stability results of Pd (DBA)2 in the

alcohols electrooxidation reaction are consistent with ob-

tained CV and EIS results.

Performance study of Pd (DBA)2 in a passive alkaline DAFC

A MEA based on the Pd (DBA)2 anode catalyst, commercial

FeeCo Hypermec™ cathode catalyst and Tokuyama A-006

anion-exchange membrane was used in a passive air breath-

ing DAFC.

The polarization and power density curves were obtained

in an air breathing alkaline DAFCwith different static alkaline

fuels; 5 wt.% EG, 5 wt.% EtOH, 5 wt.% Gly and 5 wt.% MeOH

(Fig. 9).


Among all mentioned fuels, EtOH showed the highest OCV

as well as the highest maximum power density (MPD)

(31 mW cm�2). The sequence of the produced power in the

DAFC was EtOH > EG > Gly > MeOH which is similar to that

obtained results in the half-cell. In the alkaline passive air

breathing DAFC fed by the aqueous solution of EG, EtOH, Gly

and MeOH, the value for OCV is 0.68, 0.71, 0.66 and 0.51 V,

respectively.

Table 3 indicates MPD of different DAFCs based on Pd

(DBA)2 anode catalyst compared to the MPD produced by

DAFCs reported earlier in the literature [4,35,41e48]. As it can

be seen in Table 3, MPD value of Pd (DBA)2 is comparable to

what observed by typical studies on Pt, Pd and Pd compound

in the alcohols oxidation reaction roughly under the same

conditions. Although, in DAFCs based on Pd (DBA)2 were used

air instead of O2 as an oxidant gas.

From Table 3 one can distinguish that Pd (DBA)2 exhibits

higher activity for EtOH electrooxidation in comparison with

other alcohols. These results are in line with ones reported

previously for the alcohols oxidation reaction in DAFCs.

Based on these results, Pd (DBA)2 could be a good candidate

for alkaline DAFCs specially for the alkaline direct EtOH fuel

cell.

Conclusions

In this work, Pd (DBA)2, was used as an effective catalyst for

the electrooxidation of the different aliphatic alcohols such as

EG, EtOH, Gly and MeOH in alkaline media. Electrocatalytic

activity, stability and impedance of Pd (DBA)2 towards

mentioned alcohols oxidation were evaluated by CV, CA and

EIS techniques in alkaline media. Pd (DBA)2 exhibited signifi-

cantly high anodic current density and lower onset potential

in EtOH electrooxidation compared to EG, Gly and MeOH. The

activity sequence of the alcohols oxidation on Pd (DBA)2 was

EtOH> EG >Gly >MeOH. CV and CA results demonstrated that




Table 3 e MPD of different alkaline DAFCs.

Fuel Oxidant Anode Loading(mg cm�2)

Cathode Membrane Solution(KOH/alcohol)

MPD(mW/cm2)

T(oC) Ref.

EG O2 Pd/MWCNT 1 Hypermec K-14 Tokuyama A-006 2M, 5 wt% 5 25 4

EG O2 Pt 2 Pt/C loading 2 ADP 1M/2M 4 20 41

EG O2 PdNi 2 Hypermec K-14 Tokuyama A-006 1M/1M 35 60 42

EG air Pd(DBA)2 5 Hypermec K-14 Tokuyama A-006 10, 5% wt 25 Current study

EtOH O2 Pt/Ru 3 Pt/C AHA 1M/1M 58 25 43

EtOH O2 Hypermec K14 2 Hypermec K-14 Tokuyama A-006 1M/1M 12 30 44

EtOH O2 Pd/MWCNT 1 Hypermec K-14 Tokuyama A-006 2M, 10 wt% 18 25 4

EtOH O2 Pde(NieZn)/C 1 Hypermec K-14 Tokuyama A-006 2M, 10 wt% 65 25 45

EtOH/ air Pd(DBA)2 5 Hypermec K-14 Tokuyama A-006 2M, 5% wt 15.7 25 Current study

Gly O2 Pd/MWCNT 1 Hypermec K-14 Tokuyama A-006 2M, 5 wt% 6 20 4

Gly O2 Pt/C or Pd/C _ Pt/C ADP 4M/2M 4.2 or 2.4 25 46

Gly O2 Pde(NieZn)/C 1 Hypermec K-14 Tokuyama A-006 2M, 10 wt% 15 25 35

Gly air Pd(DBA)2 5 Hypermec K-14 Tokuyama A-006 2M, 5 wt% 7.2 25 Current study

MeOH O2 Pd/MWCNT 1 Hypermec K-14 Tokuyama A-006 2M, 10 wt% 7 25 4

MeOH Air Pt/C 2 Pt/C Nafion 1M/2M 4.5 60 47

MeOH Air PtRu/C 4 Pt/C Tokuyama A-006 1M/7M 12.8 25 48

MeOH O2 Pde(NieZn)/C 1 Hypermec K-14 Tokuyama A-006 2M, 10 wt% 22 25 35

MeOH Air Pd(DBA)2 5 Hypermec K-14 Tokuyama A-006 2M, 5% wt 7 25 Current study


Pd (DBA)2 is still active even after 200 cycles. The tolerance of

Pd (DBA)2 against poisoning intermediate products in case

EtOH was higher than other mentioned alcohols.

The performance of the MEA made by Pd (DBA)2 in the

anode side was evaluated in an alkaline passive air breathing

DAFC fed by the aqueous solution of the mentioned alcohols.

By considering the obtained peak power density, 31mWcm�2,

by the static fuel solution (EtOH) and air breathing condition at

room temperature, one can safely conclude that Pd (DBA)2exhibits acceptable activity in the anode side of the alkaline

direct EtOH fuel cell.

Acknowledgments

This work was carried out in electrochemical laboratory of

Isfahan University of Technology (IUT). The authors would

like to thanks the research council of IUT and special thanks

to Dr B. Rezaei and Dr K. Karami for their supporting. The

authors gratefully acknowledge the financial support of Iran

National Science Foundation through the project No. 93012722

and the support of fuel cell steering committee and Iranian

nano technology initiative council.

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