research article synthesis and characterization of...

Research ArticleSynthesis and Characterization ofElectrodeposited C-PANI-Pd-Ni CompositeElectrocatalyst for Methanol Oxidation

S S Mahapatra1 S Shekhar2 B K Thakur3 and H Priyadarshi3

1 Department of Chemistry Birla Institute of Technology (Mesra) Ranchi Jharkhand 835215 India2Department of Chemistry Government Engineering College Ramgarh Jharkhand 829122 India3 Department of Chemical amp Polymer Engineering Birla Institute of Technology (Mesra) Ranchi Jharkhand 835215 India

Correspondence should be addressed to S S Mahapatra ssmahapatrabitmesraacin

Received 7 August 2014 Revised 30 September 2014 Accepted 30 September 2014 Published 16 October 2014

Academic Editor Hamilton Varela

Copyright copy 2014 S S Mahapatra et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Electropolymerization of aniline at the graphite electrodes was achieved by potentiodynamic method Electrodeposition of Pd(C-PANI-Pd) and Ni (C-PANI-Ni) and codeposition of Pd-Ni (C-PANI-Pd-Ni) microparticles into the polyaniline (PANI) filmcoated graphite (C-PANI) were carried out under galvanostatic control The morphology and composition of the compositeelectrodes were obtained using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) techniquesThe electrochemical behavior and electrocatalytic activity of the electrode were characterized using cyclic voltammetry (CV)electrochemical impedance spectroscopy (EIS) and chronoamperometric (CA) methods in acidic medium The C-PANI-Pd-Nielectrode showed an improved catalytic performance towards methanol oxidation in terms of lower onset potential higher anodicoxidation current greater stability lower activation energy and lower charge transfer resistance The enhanced electrocatalyticactivitymight be due to the greater permeability of C-PANI films formethanol molecules better dispersion of Pd-Nimicroparticlesinto the polymer matrixes and the synergistic effects between the dispersed metal particles and their matrixes

1 Introduction

Direct methanol fuel cell (DMFC) is regarded as a potentialcandidate as portable power sources [1] Platinum modifiedpolyaniline (PANI) electrocatalysts for methanol electroox-idation have been widely studied in recent years [2] Butslow methanol oxidation kinetics high cost and limitedresource do not allow use of Pt at commercial level In addi-tion Pt-based electrocatalysts generally undergo deactiva-tionpoisoning by the reaction intermediates particularly byCOmolecule in acidmediumTheuse of non-platinummetallike palladium in fuel cell catalysts is interesting becauseit is more widespread in the Earth crust than platinum(abundance of 15 times 10minus2 versus 5 times 10minus3 parts per million bymass resp) and it is less expensive than Pt [3] In additionit is very stable in the acidic fuel cell environment andalso exhibits interesting electrocatalytic properties for CO

electrooxidationThese properties have led to considering Pdas a possible catalyst for those reactions in which CO appearsas a poisoning intermediate such as in the methanol [4]The catalytic activity of Pd can be modified by alloying withother metals such as Ni the combination of Pd with Ni isexpected to further enhance the tolerance of Pd to poisoningas Ni is an oxophilic element [5]The study of alloy electrodesis motivated primarily from the anticipation of a synergisticelectrocatalytic benefit from the combined properties of thecomponent metals of alloys [6] The use of Ni enables areduction in cost of the catalyst [7 8] The electrocatalyticactivity of Pd-Ni alloy electrode can be further improvedby dispersion of catalyst particle on suitable catalyst sup-port [9] Carbons of different forms are generally used toload the metal catalysts but metal particles are physicallyisolated in the carbon matrix and the catalyst system doesnot provide a conductive environment for the migration

Hindawi Publishing CorporationInternational Journal of ElectrochemistryVolume 2014 Article ID 383892 8 pageshttpdxdoiorg1011552014383892

2 International Journal of Electrochemistry

of protons [10] In contrast conducting polymers (CPs)function as redox mediators for electron and proton betweenthe electrodes and the electroactive reactants shows permse-lectivity towards some species they permit the diffusion ofredox active species (eg methanol) to the active sites ofelectrode and enhance the electrooxidation current [11 12]The film of a conducting polymer on the electrode surfaceimproves the interfacial properties between the electrodeand electrolyte and the mediation of charge transfer betweenthe substrate and the dispersed metal particles is facile inthe matrix of a conducting polymer [13] CPs deposited oncarbon substrates are favorable and attractive hybrid supportsfor catalyst particles The hybrid materials possessing theproperties of each component or even with a synergisticeffect would present improved characteristics and electro-catalytic activity with respect to the individual componentsAmong conducting polymers polyaniline (PANI) is oneof the most frequently utilized matrixes for dispersing themetal particles because they can easily be prepared on theelectrode substrate as a homogeneous and strong adher-ent film with a desirable thickness high accessible surfacearea low resistance and good mechanical and chemicalstability in acidic media Introduction of PANI into theelectrode catalyst layer increases the catalyst utilization andhelps water absorption on the catalyst and formation of anactive oxycompound which will promote CO oxidation toCO2

It also accelerates the Langmuir absorption behaviorof methanol [14] Hence DMFCs using PANI-containingelectrodes are expected to give superior performance In thepresent work the film of PANI was deposited on graphitesubstrate by cyclic voltammetric methodThe metal particleswere homogeneously dispersed into a porous PANI film bya constant current electrodeposition technique and C-PANI-Pd C-PANI-Ni and C-PANI-Pd-Ni electrocatalysts wereprepared The electrocatalytic activity of the prepared cata-lysts towardsmethanol oxidation reactionwas investigated bydifferent electrochemical method such as cyclic voltammetry(CV) chronoamperometry and electrochemical impedancespectroscopy (EIS) Scanning electron microscopy (SEM)and energy-dispersive X-ray spectroscopy (EDX) was alsoemployed to morphological and elemental studies of themodified catalyst layer

2 Experimental

21 Materials and Equipment The graphite block (saw cutfinish grade) purchased from Graphite India Limited wasused as substrate for the electrode matrix PdCl

2

H2

SO4

aniline methanol and other chemicals were of analyticalgrades from Merck All the aqueous solutions were preparedwith distilled water All electrochemical experiments wereperformed using a CHI680B electrochemical analyzer (CHInstruments Inc Austin USA) controlled by CH instrumentelectrochemical software by using a double-compartmentglass cell with conventional three-electrode configurationThe substrate working electrode was polished graphite (geo-metric area 10 cm2) The counter electrode was a large areaPt-wire and the reference electrode was AgAgCl electrode

22 Electrode Preparation Electropolymerization of anilineat the graphite electrodes was achieved by potentiodynamicmethodThe electrode potential was swept between minus05 and05 V versus AgAgCl at a scan rate of 50mV sminus1 using anaqueous solution of 01MH

2

SO4

containing 03M aniline for40 cycles The thickness of the deposited films (PANI filmthickness 12 120583m) was calculated from the charge consumedduring the electrodeposition of PANI considering two elec-tron mechanism [15]

119889 =

119876119872

2119865120588

(1)

where 119876 is the area specific overall charge (Cmminus2) 119872is molecular weight of aniline 119865 is Faraday constant(asymp96500Cmolminus1) and 120588 is the density of PANI The Pdand Ni microparticles were incorporated in the PANI filmcoated graphite (C-PANI) by electrochemical depositionfrom an aqueous 01M sulphuric acid solution of 005MPdCl2

and 005M NiCl2

respectively For electrochemicalcodeposition of Pd and Ni microparticles an equimolarmixture of 005M PdCl

2

and 005M NiCl2

was used Foreach case electrodeposition was performed at room tem-perature under galvanostatic control by applying 3mA cmminus2current density The duration of electrochemical depositionfor different metals was varied between 5ndash10 minutes to keepthe metal loading fixed (2mg cmminus2) at the electrode surfaceAssuming 100 efficiency for the reduction of119872119899+ to119872 theamount of metal deposited was evaluated from the quantityof charge 119876dep that passed during the electrodeposition Inthis process the metal loading (119882 in mg cmminus2) is

119882 =

119876dep119872

119899119865

(2)

where 119872 is the atomic weight of metal 119899 is the number ofexchanged electrons and 119865 is the Faraday constant

23 Characterization of the Working Electrodes The compo-site electrodes were characterized by scanning electronmicroscopy (SEM) and their chemical composition wasanalyzed by energy dispersive X-ray analysis (EDX) TheSEM and EDX analysis were performed using electronmicroscope JSM-6390LV (JEOL Co Japan) equipped withenergy-dispersive full range X-ray microanalysis systemThemethanol electrooxidation reaction at surface of the electrodewas investigated in electrolyte solution containing 10Mmethanol and 05M H

2

SO4

by CV Chronoamperometricand EIS measurements In CV measurements the potentialwas scanned between minus08 and 10 V at a scan rate of50mV sminus1 In EIS measurements the AC frequency rangeextended from 100 kHz to 1Hz with an excitation signal of5mV The impedance spectra were fitted to an equivalentcircuit model using a nonlinear fitting program A constanttemperature water bath was used to keep the experimentsrunning at a preset temperature All current densities werecalculated according to geometric areas of electrodes andwere normalized to weight of the catalyst

International Journal of Electrochemistry 3

00 02 04 06

00000

00005

00010

00015

i (A

)

E (V) versus AgAgClminus06 minus04 minus02

minus00015

minus00010

minus00005

Figure 1 Cyclic voltammograms (40 cycles) during electropolymerization of aniline on graphite in 05M H2

SO4

solution containing 01Maniline at a scan rate of 50mV sminus1 at room temperature

3 Results and Discussion

31 Electrodeposition of PANI Thin Film Electropolymeriza-tion of PANI offers the possibility of controlling the thicknessand homogeneity of the conducting polymer film on theelectrode surface Figure 1 shows the cyclic voltammogramsduring electropolymerization of aniline on the graphiteelectrode in 01M H

2

SO4

solution containing 03M anilineAs can be seen the oxidative polymerization of aniline startsat 01 V in the first cycle rendering the first layer of PANISubsequent cycles indicate the subsequent growth of thepolymer films as evidenced by an increase in the redoxcurrent suggested that the film was conductive electroactiveand also uniform

The redox peaks at around 01 V are attributed to thetransformation of PANI from the reduced leucoemaraldine(LE) state to the partly oxidized emeraldine (EM) state andthe redox peaks at around 04V correspond to transition ofthe PANI from LE to pernigraniline (PE) state [15 16] Thefilm thickness was controlled by controlling the number ofpotentials cycles and calculated by the height of the first peakAfter electropolymerization a green film was formed on theworking electrode

32 Physical Characterization of the Electrodes The surfacemorphology of the catalyst was revealed through scanningelectron microscopy The SEM of C-PANI film in Figure 2(a)shows a polymeric three-dimensional matrix with randomlygrown fibrilar branched and porous structure characteristicof electrochemically deposited PANI and highly suitable fordispersion of the metal particlesThe SEM image of C-PANI-Ni electrode in Figure 2(b) shows compact layer structure

The SEM images of C-PANI-Pd and C-PANI-Pd-Nielectrodes in Figures 2(c) and 2(d) show a wide spread ofcoarse grained closely packed clusters of Pd and Pd-Ni metalparticles distributed over the whole polymeric film The Pd-Ni particles show better dispersion on the C-PANI As Pd

and Ni were coelectrodeposited on the C-PANI surfaceboth the metals were grown together on the same spheremaking an assembly of ad-atoms in the form of agglomer-ated particlesThe elemental compositions of electrocatalystswere investigated using EDX spectroscopy as shown inFigures 3(a)ndash3(c)

The depositions of metal particles are evident from EDXspectraThe atomic percent ratio of PdNi in the C-PANI-Pd-Ni catalyst is 27 01The relative low content of Ni element intheC-PANI-Pd-Ni catalyst is ascribed to the higher reductionpotential of Pd2+Pd compared to Ni2+Ni

33 Electrochemical Characterization of the Synthesized Elec-trode Electrocatalytic properties of the synthesized elec-trodes towardmethanol oxidation were investigated by cyclicvoltammetry in a solution of 05MH

2

SO4

and 10MCH3

OHat a scan rate of 50mV sminus1 at room temperature as shown inFigure 4

The current density was normalized by the geometric areaof the working electrode to indicate the catalyst mass activityThe C-PANI electrode shows small methanol oxidation peakat minus005V which is in agreement with the reported results[17] whereas C-PANI-Ni electrode shows small methanoloxidation peak at higher potential For C-PANI-Pd and C-PANI-Pd-Ni electrodes twowell-defined current peaks in theforward scans were observed The first peak corresponds tothe oxidation of freshly chemisorbed methanolic species andthe second peak corresponds to oxide formation at higherpotentialThe oxide reduction peak was observed for Pd con-taining electrodes only Increasing current was not observedin the reverse scan therefore methanol was not oxidizedin reverse Values of CV parameters such as onset potential(119864op) peak current density (119894

119901

) and peak potential (119864119901

) forMOR on different electrodes are shown in Table 1 The onsetpotential of C-PANI-Pd-Ni for methanol oxidation occurs atminus032V which is more negative than that of the other three


(a) (b)

(c) (d)

Figure 2 SEM images of (a) C-PANI (b) C-PANI-Ni (c) C-PANI-Pd and (d) C-PANI-Pd-Ni electrodes

Table 1 Comparison of different electrochemical parameters for methanol oxidation on different electrodes

Electrochemical parameters ElectrodesC-PANI C-PANI-Pd C-PANI-Ni C-PANI-Pd-Ni

119864op (V) minus0297 minus0303 minus0203 minus0320119864119901

(V) minus0054 0190 0473 0350119894119901

(A cmminus2 mgminus1) 00058 0031 00045 0186120575 ( per s) times 10minus5 1362 824 1330 370119864app (kJmolminus1) 1084 452 753 306119877ct (ohm) mdash 40 250 20

catalystsThe peak current density of the methanol oxidationon C-PANI-Pd-Ni is 0186A cmminus2mgminus1 which is muchhigher than C-PANI (00058A cmminus2mgminus1) C-PANI-Ni(00045A cmminus2mgminus1) and C-PANI-Pd (0031 A cmminus2mgminus1)It is clear that the current densities are higher at correspond-ing potentials on C-PANI-Pd-Ni electrode than that on otherelectrodes The current density of methanol oxidation on C-PANI-Pd-Ni electrode begins to rise more sharply at muchmore negative potential compared to the other electrodesThus the C-PANI-Pd-Ni catalyst is capable of oxidizingmethanol at lower potential than that of other electrode

The enhancement in catalytic activity with codeposited cata-lyst may be attributed to the increase in surface area synergiceffect by the interaction between Ni and Pd and the fact thatthe occluded hydrogen can accelerate dehydrogenation and atthe same time prevent adsorption of intermediate species onthe electrode surface so that more active sites are available foradsorption of methanolThe increase in surface area is due tothe better dispersion ofmetal particles in polymermatrixTheenhancement in activity on Ni or Pd based alloy catalysts iscorrelated to the geometric and electronic change of themetal[18] FromTable 1 it is evident that C-PANI-Pd-Ni is themost


0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

S

NiNi

NiO

Cou

nts

(keV)

C

(a)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

O

C

PdS

Cou

nts

(keV)

Pd

(b)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

Ni

Pd

PdS

Ni

C

Ni

Cou

nts

(keV)

O

(c)

Figure 3 EDX spectra of (a) C-PANI-Ni (b) C-PANI-Pd and (c) C-PANI-Pd-Ni catalysts

00 02 04 06 08 10 12

000

005

010

015

020

C-PANIC-PANI-Pd

C-PANI-NiC-PANI-Pd-Ni

minus10 minus08 minus06 minus04 minus02

minus020

minus015

minus010

minus005

E (V) versus AgAgCl

i(A

cmminus2

mgminus

1)

Figure 4 Cyclic voltammograms for methanol oxidation on differ-ent electrodes in 05M H

2

SO4

solution containing 10M methanolat a scan rate of 50mV sminus1 at room temperature

effective electrode in terms of onset potential and anodic peakcurrent density

The stability and electrocatalytic activity of different cata-lysts were evaluated by chronoamperometry Figure 5 showsthe chronoamperograms of the C-PANI C-PANI-Pd C-PANI-Ni and C-PANI-Pd-Ni electrodes in a solution of05M H

2

SO4

containing 10M CH3

OH at a fixed potentialof 02 V It can be is observed from Figure 5 that the C-PANI-Pd-Ni catalyst exhibits higher current density and slower rateof decay in comparison to other catalysts during the time ofexperiment

The current density decreases as a function of time at agiven potential for all electrodesThis current decrease can beattributed to adsorption of poisonous intermediates anionadsorption in the case of the H

2

SO4

system and the decreasein production of CO

2

as the surface oxide was consumedleading to the formation of other soluble intermediates [19]The final current densities at 1000 s are 024 times 10minus3 064 times10minus3 056 times 10minus3 and 177 times 10minus3 A cmminus2mgminus1 for C-PANIC-PANI-Pd C-PANI-Ni and C-PANI-Pd-Ni catalysts


0 200 400 600 800 1000 12000000

0001

0002

0003

0004

0005

Time (s)

C-PANIC-PANI-Pd


i(A

cmminus2

mgminus

1)

Figure 5 Chronoamperograms formethanol oxidation on differentelectrodes in 05M H

2

SO4

solution containing 10M methanol at02 V

respectively Long-term poisoning rates (120575) were evaluatedfrom the record of current decay (Figure 5) at times greaterthan 500 s using the following equation [20]

120575 =

100

1198940

times (

119889119894

119889119905

)

119905gt500 s( per s) (3)

where (119889119894119889119905)119905gt500 s is the slope of the linear portion of the

current decay and 1198940

is the current at the start of polarizationback extrapolated from the linear current decay It is evidentfromTable 1 that the long-term poisoning effect formethanoloxidation can be significantly controlled on C-PANI-Pd-Niwhereas other electrode suffers from extensive poisoning

The results are consistent with those of CV measure-ments The improved antipoisoning ability of the electrodemay be attributed to the reaction between strongly boundCO species and OHads on neighboring of C-PANI-Pd-Nisites [21]TheC-PANI-Pd-Ni electrode shows goodmethanoloxidation kinetics and stability over a longer period of time

The apparent activation energy (119864app) value determinedusing electrochemical techniques gives information regard-ing the chemical rate determining step Figure 6 shows theArrhenius plots for methanol oxidation on the C-PANI C-PANI-Pd C-PANI-Ni and C-PANI-Pd-Ni electrodes at afixed potential of 02 V and different temperatures

The activation energies were obtained from the slopes ofthe log 119894 versus 1119879 plots constructed from chronoampero-metric experiments by fitting the Arrhenius equation [22]The activation energies from these plots are summarized inTable 1 The order of activity in terms of activation energywas C-PANI-Pd-Ni gt C-PANI-Pd gt C-PANI-Ni gt C-PANIin agreement with the order of onset potential and oxidationcurrent at a constant temperature This drastic decrease inactivation energy for C-PANI-Pd-Ni electrode leads to theincrease in methanol oxidation current

28 29 30 31 32 33 34 35

10

12

14

16

18

20

22

C-PANIC-PANI-Pd


103Tminus1 (Kminus1)

log i

(A cm

minus2

mgminus

1)

Figure 6 Arrhenius plots for methanol oxidation on differentelectrodes in 05M H

2

SO4


0 50 100 150 200 250 300 350

0

50

100

150

200

5 10 15 20 25 30 35 40

05

1015202530

C-PANIC-PANI-Pd


Z998400 (Ohm)

minusZ998400998400

(Ohm

)

Figure 7 Electrochemical impedance spectra (Nyquist) for metha-nol oxidation on different electrodes in 05M H

2

SO4

solution con-taining 10M methanol at 02 V

Electrochemical impedance spectroscopy was used toinvestigate reaction process and kinetics of methanol oxida-tion on the different electrodes at a fixed potential of 02 VThe Nyquist plots for methanol oxidation in a solutioncontaining 05M H

2

SO4

and 10M methanol are shown inFigure 7 The absence of semicircular behavior for the C-PANI electrode is indicative of very little methanol oxidationand a diffusion controlled process at this electrode whereassemicircular behavior is evident for other three electrodesThe C-PANI-Ni electrode shows characteristic semicircularbehavior in the high frequency region associatedwith charge-transfer process tending towards linear behavior in thelow frequency region associated with diffusion controlled


process whereas C-PANI-Pd and C-PANI-Pd-Ni electrodesshow single semicircle indicating charge-transfer processonly Although the shape of the impedance spectroscopy forC-PANI-Pd andC-PANI-Pd-Ni electrode is similar but differin the diameters of the two semicircles The diameter of thesemicircle with C-PANI-Pd is larger than that of C-PANI-Pd-NiThe charge transfer resistance (119877ct) was obtained fromthe Nyquist plot by taking the diameter of the semicircle andsummarized in Table 1

The lower value of 119877ct for the C-PANI-Pd-Ni electrodeindicates faster rate of electrochemical charge transfer Thusit is possible to attribute the increased electrocatalytic activityof the PANI-Pd-Ni composites with incorporated conductingpolymers can promote the formation of a three-dimensionallayer enhancingmethanol oxidation through increases in thesurface area and the number of active sites [23]

4 Conclusion

The C-PANI-Pd-Ni electrode exhibited an excellent electro-catalytic activity for methanol oxidation and stability com-pared to C-PANI C-PANI-Ni and C-PANI-Pd catalystsThemetal microparticles were well distributed into the polyani-line matrix Introduction of PANI as a conductive polymerwithin catalyst layer (i) improves electron transfer betweencatalyst particles and PANI matrix and also act as accessiblemesoporous network for catalytic particles (ii) it hindersthe formation of strong adsorbed poisons and catalyzes theoxidation of strongly and weakly adsorbed poisons so it pre-vents catalyst frommore poisoning by intermediate productsof methanol oxidation such as CO and (iii) improves themechanical properties of the catalyst layer by providing goodand flexible connections between metal particles Moreoverthe amount of noblemetal platinum at the prepared electrodewas remarkably reduced the cost of the processed catalystwas greatly decreased and the procedure was very simpleIn fact PANI acts also as a binder in catalyst layer withoutserious restriction in methanol diffusion to the active siteThe performance of the electrode is enhanced after partialchemical displacement of dispersed Ni with Pd Polyanilinematrix with higher electrochemical surface area and lowerresistance of charge transfer to electrode manifest themselvesto be highly suitable candidate for use in DMFC applications

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] X Li and A Faghri ldquoReview and advances of direct methanolfuel cells (DMFCs) part I design fabrication and testingwith high concentration methanol solutionsrdquo Journal of PowerSources vol 226 pp 223ndash240 2013

[2] A Kitani T Akashi K Sugimoto and S Ito ldquoElectrocatalyticoxidation of methanol on platinum modified polyaniline elec-trodesrdquo Synthetic Metals vol 121 no 1ndash3 pp 1301ndash1302 2001

[3] F Alcaide G Alvarez P L Cabot H-J Grande O Miguel andA Querejeta ldquoTesting of carbon supported Pd-Pt electrocata-lysts for methanol electrooxidation in direct methanol fuelcellsrdquo International Journal of Hydrogen Energy vol 36 no 7pp 4432ndash4439 2011

[4] F Miao B Tao L Sun et al ldquoPreparation and characteriza-tion of novel nickel-palladium electrodes supported by siliconmicrochannel plates for direct methanol fuel cellsrdquo Journal ofPower Sources vol 195 no 1 pp 146ndash150 2010

[5] Z Qi H Geng X Wang et al ldquoNovel nanocrystalline PdNialloy catalyst for methanol and ethanol electro-oxidation inalkaline mediardquo Journal of Power Sources vol 196 no 14 pp5823ndash5828 2011

[6] I Danaee M Jafarian F Forouzandeh F Gobal and M GMahjani ldquoElectrocatalytic oxidation of methanol on Ni andNiCu alloy modified glassy carbon electroderdquo InternationalJournal of Hydrogen Energy vol 33 no 16 pp 4367ndash4376 2008

[7] K S Kumar P Haridoss and S K Seshadri ldquoSynthesis andcharacterization of electrodeposited Ni-Pd alloy electrodes formethanol oxidationrdquo Surface and Coatings Technology vol 202no 9 pp 1764ndash1770 2008

[8] Y Zhao X Yang J Tian FWang and L Zhan ldquoMethanol elec-tro-oxidation on NiPd core-shell nanoparticles supported onmulti-walled carbon nanotubes in alkaline mediardquo Interna-tional Journal of Hydrogen Energy vol 35 no 8 pp 3249ndash32572010

[9] S Sharma and B G Pollet ldquoSupport materials for PEMFC andDMFCelectrocatalystsmdasha reviewrdquo Journal of Power Sources vol208 pp 96ndash119 2012

[10] G Wu L Li J-H Li and B-Q Xu ldquoPolyaniline-carbon com-posite films as supports of Pt and PtRu particles for methanolelectrooxidationrdquo Carbon vol 43 no 12 pp 2579ndash2587 2005

[11] H Gao J-B He Y Wang and N Deng ldquoAdvantageous com-bination of solid carbon paste and a conducting polymer filmas a support of platinum electrocatalyst for methanol fuel cellrdquoJournal of Power Sources vol 205 pp 164ndash172 2012

[12] G Ciric-Marjanovic ldquoRecent advances in polyaniline compos-ites with metals metalloids and nonmetalsrdquo Synthetic Metalsvol 170 no 1 pp 31ndash56 2013

[13] F-J Liu L-M Huang T-C Wen and A Gopalan ldquoLarge-areanetwork of polyaniline nanowires supported platinum nano-catalysts for methanol oxidationrdquo Synthetic Metals vol 157 no16-17 pp 651ndash658 2007

[14] M Zhiani B Rezaei and J Jalili ldquoMethanol electro-oxidationon PtC modified by polyaniline nanofibers for DMFC applica-tionsrdquo International Journal of Hydrogen Energy vol 35 no 17pp 9298ndash9305 2010

[15] B Habibi and M H Pournaghi-Azar ldquoMethanol oxidation onthe polymer coated and polymer-stabilized Pt nano-particlesa comparative study of permeability and catalyst particle dis-tribution ability of the PANI and its derivativesrdquo InternationalJournal of Hydrogen Energy vol 35 no 17 pp 9318ndash9328 2010

[16] A Baba S Tian F Stefani et al ldquoElectropolymerization anddopingdedoping properties of polyaniline thin films as studiedby electrochemical-surface plasmon spectroscopy and by thequartz crystal microbalancerdquo Journal of Electroanalytical Chem-istry vol 562 no 1 pp 95ndash103 2004

[17] K R Prasad and N Munichandraiah ldquoElectrooxidation ofmethanol on polyaniline without dispersed catalyst particlesrdquoJournal of Power Sources vol 103 no 2 pp 300ndash304 2002


[18] ZWang Z-Z Zhu J Shi and H-L Li ldquoElectrocatalytic oxida-tion of formaldehyde on platinum well-dispersed into single-wall carbon nanotubepolyaniline composite filmrdquo AppliedSurface Science vol 253 no 22 pp 8811ndash8817 2007

[19] J L Cohen D J Volpe and H D Abruna ldquoElectrochemicaldetermination of activation energies for methanol oxidationon polycrystalline platinum in acidic and alkaline electrolytesrdquoPhysical Chemistry Chemical Physics vol 9 no 1 pp 49ndash772007

[20] S S Mahapatra A Dutta and J Datta ldquoTemperature effect onthe electrode kinetics of ethanol oxidation on Pd modified Ptelectrodes and the estimation of intermediates formed in alkalimediumrdquo Electrochimica Acta vol 55 no 28 pp 9097ndash91042010

[21] W He J Liu Y Qiao et al ldquoSimple preparation of Pd-Ptnanoalloy catalysts for methanol-tolerant oxygen reductionrdquoJournal of Power Sources vol 195 no 4 pp 1046ndash1050 2010

[22] S S Mahapatra A Dutta and J Datta ldquoTemperature depen-dence on methanol oxidation and product formation on Pt andPd modified Pt electrodes in alkaline mediumrdquo InternationalJournal of Hydrogen Energy vol 36 no 22 pp 14873ndash148832011

[23] Z Wang G Gao H Zhu Z Sun H Liu and X Zhao ldquoElec-trodeposition of platinum microparticle interface on conduct-ing polymer film modified nichrome for electrocatalytic oxida-tion ofmethanolrdquo International Journal of Hydrogen Energy vol34 no 23 pp 9334ndash9340 2009

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of protons [10] In contrast conducting polymers (CPs)function as redox mediators for electron and proton betweenthe electrodes and the electroactive reactants shows permse-lectivity towards some species they permit the diffusion ofredox active species (eg methanol) to the active sites ofelectrode and enhance the electrooxidation current [11 12]The film of a conducting polymer on the electrode surfaceimproves the interfacial properties between the electrodeand electrolyte and the mediation of charge transfer betweenthe substrate and the dispersed metal particles is facile inthe matrix of a conducting polymer [13] CPs deposited oncarbon substrates are favorable and attractive hybrid supportsfor catalyst particles The hybrid materials possessing theproperties of each component or even with a synergisticeffect would present improved characteristics and electro-catalytic activity with respect to the individual componentsAmong conducting polymers polyaniline (PANI) is oneof the most frequently utilized matrixes for dispersing themetal particles because they can easily be prepared on theelectrode substrate as a homogeneous and strong adher-ent film with a desirable thickness high accessible surfacearea low resistance and good mechanical and chemicalstability in acidic media Introduction of PANI into theelectrode catalyst layer increases the catalyst utilization andhelps water absorption on the catalyst and formation of anactive oxycompound which will promote CO oxidation toCO2

It also accelerates the Langmuir absorption behaviorof methanol [14] Hence DMFCs using PANI-containingelectrodes are expected to give superior performance In thepresent work the film of PANI was deposited on graphitesubstrate by cyclic voltammetric methodThe metal particleswere homogeneously dispersed into a porous PANI film bya constant current electrodeposition technique and C-PANI-Pd C-PANI-Ni and C-PANI-Pd-Ni electrocatalysts wereprepared The electrocatalytic activity of the prepared cata-lysts towardsmethanol oxidation reactionwas investigated bydifferent electrochemical method such as cyclic voltammetry(CV) chronoamperometry and electrochemical impedancespectroscopy (EIS) Scanning electron microscopy (SEM)and energy-dispersive X-ray spectroscopy (EDX) was alsoemployed to morphological and elemental studies of themodified catalyst layer

2 Experimental

21 Materials and Equipment The graphite block (saw cutfinish grade) purchased from Graphite India Limited wasused as substrate for the electrode matrix PdCl

2

H2

SO4

aniline methanol and other chemicals were of analyticalgrades from Merck All the aqueous solutions were preparedwith distilled water All electrochemical experiments wereperformed using a CHI680B electrochemical analyzer (CHInstruments Inc Austin USA) controlled by CH instrumentelectrochemical software by using a double-compartmentglass cell with conventional three-electrode configurationThe substrate working electrode was polished graphite (geo-metric area 10 cm2) The counter electrode was a large areaPt-wire and the reference electrode was AgAgCl electrode

22 Electrode Preparation Electropolymerization of anilineat the graphite electrodes was achieved by potentiodynamicmethodThe electrode potential was swept between minus05 and05 V versus AgAgCl at a scan rate of 50mV sminus1 using anaqueous solution of 01MH

2

SO4

containing 03M aniline for40 cycles The thickness of the deposited films (PANI filmthickness 12 120583m) was calculated from the charge consumedduring the electrodeposition of PANI considering two elec-tron mechanism [15]

119889 =

119876119872

2119865120588

(1)

where 119876 is the area specific overall charge (Cmminus2) 119872is molecular weight of aniline 119865 is Faraday constant(asymp96500Cmolminus1) and 120588 is the density of PANI The Pdand Ni microparticles were incorporated in the PANI filmcoated graphite (C-PANI) by electrochemical depositionfrom an aqueous 01M sulphuric acid solution of 005MPdCl2

and 005M NiCl2

respectively For electrochemicalcodeposition of Pd and Ni microparticles an equimolarmixture of 005M PdCl

2

and 005M NiCl2

was used Foreach case electrodeposition was performed at room tem-perature under galvanostatic control by applying 3mA cmminus2current density The duration of electrochemical depositionfor different metals was varied between 5ndash10 minutes to keepthe metal loading fixed (2mg cmminus2) at the electrode surfaceAssuming 100 efficiency for the reduction of119872119899+ to119872 theamount of metal deposited was evaluated from the quantityof charge 119876dep that passed during the electrodeposition Inthis process the metal loading (119882 in mg cmminus2) is

119882 =

119876dep119872

119899119865

(2)

where 119872 is the atomic weight of metal 119899 is the number ofexchanged electrons and 119865 is the Faraday constant

23 Characterization of the Working Electrodes The compo-site electrodes were characterized by scanning electronmicroscopy (SEM) and their chemical composition wasanalyzed by energy dispersive X-ray analysis (EDX) TheSEM and EDX analysis were performed using electronmicroscope JSM-6390LV (JEOL Co Japan) equipped withenergy-dispersive full range X-ray microanalysis systemThemethanol electrooxidation reaction at surface of the electrodewas investigated in electrolyte solution containing 10Mmethanol and 05M H

2

SO4

by CV Chronoamperometricand EIS measurements In CV measurements the potentialwas scanned between minus08 and 10 V at a scan rate of50mV sminus1 In EIS measurements the AC frequency rangeextended from 100 kHz to 1Hz with an excitation signal of5mV The impedance spectra were fitted to an equivalentcircuit model using a nonlinear fitting program A constanttemperature water bath was used to keep the experimentsrunning at a preset temperature All current densities werecalculated according to geometric areas of electrodes andwere normalized to weight of the catalyst


00 02 04 06

00000

00005

00010

00015

i (A

)


minus00015

minus00010

minus00005


SO4




2

SO4








2

SO4

and 10MCH3



119901




(a) (b)

(c) (d)





(V) minus0054 0190 0473 0350119894119901





0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

S

NiNi

NiO

Cou

nts

(keV)

C

(a)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

O

C

PdS

Cou

nts

(keV)

Pd

(b)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

Ni

Pd

PdS

Ni

C

Ni

Cou

nts

(keV)

O

(c)


00 02 04 06 08 10 12

000

005

010

015

020

C-PANIC-PANI-Pd



minus020

minus015

minus010

minus005

E (V) versus AgAgCl

i(A

cmminus2

mgminus

1)


2

SO4




2

SO4

containing 10M CH3



2

SO4


2



0 200 400 600 800 1000 12000000

0001

0002

0003

0004

0005

Time (s)

C-PANIC-PANI-Pd


i(A

cmminus2

mgminus

1)


2

SO4



120575 =

100

1198940

times (

119889119894

119889119905

)

119905gt500 s( per s) (3)







28 29 30 31 32 33 34 35

10

12

14

16

18

20

22

C-PANIC-PANI-Pd



log i

(A cm

minus2

mgminus

1)


2

SO4


0 50 100 150 200 250 300 350

0

50

100

150

200

5 10 15 20 25 30 35 40

05

1015202530

C-PANIC-PANI-Pd


Z998400 (Ohm)

minusZ998400998400

(Ohm

)


2

SO4



2

SO4





4 Conclusion




References


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


00 02 04 06

00000

00005

00010

00015

i (A

)


minus00015

minus00010

minus00005


SO4




2

SO4








2

SO4

and 10MCH3



119901




(a) (b)

(c) (d)





(V) minus0054 0190 0473 0350119894119901





0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

S

NiNi

NiO

Cou

nts

(keV)

C

(a)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

O

C

PdS

Cou

nts

(keV)

Pd

(b)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

Ni

Pd

PdS

Ni

C

Ni

Cou

nts

(keV)

O

(c)


00 02 04 06 08 10 12

000

005

010

015

020

C-PANIC-PANI-Pd



minus020

minus015

minus010

minus005

E (V) versus AgAgCl

i(A

cmminus2

mgminus

1)


2

SO4




2

SO4

containing 10M CH3



2

SO4


2



0 200 400 600 800 1000 12000000

0001

0002

0003

0004

0005

Time (s)

C-PANIC-PANI-Pd


i(A

cmminus2

mgminus

1)


2

SO4



120575 =

100

1198940

times (

119889119894

119889119905

)

119905gt500 s( per s) (3)







28 29 30 31 32 33 34 35

10

12

14

16

18

20

22

C-PANIC-PANI-Pd



log i

(A cm

minus2

mgminus

1)


2

SO4


0 50 100 150 200 250 300 350

0

50

100

150

200

5 10 15 20 25 30 35 40

05

1015202530

C-PANIC-PANI-Pd


Z998400 (Ohm)

minusZ998400998400

(Ohm

)


2

SO4



2

SO4





4 Conclusion




References


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(a) (b)

(c) (d)





(V) minus0054 0190 0473 0350119894119901





0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

S

NiNi

NiO

Cou

nts

(keV)

C

(a)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

O

C

PdS

Cou

nts

(keV)

Pd

(b)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

Ni

Pd

PdS

Ni

C

Ni

Cou

nts

(keV)

O

(c)


00 02 04 06 08 10 12

000

005

010

015

020

C-PANIC-PANI-Pd



minus020

minus015

minus010

minus005

E (V) versus AgAgCl

i(A

cmminus2

mgminus

1)


2

SO4




2

SO4

containing 10M CH3



2

SO4


2



0 200 400 600 800 1000 12000000

0001

0002

0003

0004

0005

Time (s)

C-PANIC-PANI-Pd


i(A

cmminus2

mgminus

1)


2

SO4



120575 =

100

1198940

times (

119889119894

119889119905

)

119905gt500 s( per s) (3)







28 29 30 31 32 33 34 35

10

12

14

16

18

20

22

C-PANIC-PANI-Pd



log i

(A cm

minus2

mgminus

1)


2

SO4


0 50 100 150 200 250 300 350

0

50

100

150

200

5 10 15 20 25 30 35 40

05

1015202530

C-PANIC-PANI-Pd


Z998400 (Ohm)

minusZ998400998400

(Ohm

)


2

SO4



2

SO4





4 Conclusion




References


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

S

NiNi

NiO

Cou

nts

(keV)

C

(a)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

O

C

PdS

Cou

nts

(keV)

Pd

(b)

0 2 4 6 8 10 12 14 16 18 20 220

1000

2000

Ni

Pd

PdS

Ni

C

Ni

Cou

nts

(keV)

O

(c)


00 02 04 06 08 10 12

000

005

010

015

020

C-PANIC-PANI-Pd



minus020

minus015

minus010

minus005

E (V) versus AgAgCl

i(A

cmminus2

mgminus

1)


2

SO4




2

SO4

containing 10M CH3



2

SO4


2



0 200 400 600 800 1000 12000000

0001

0002

0003

0004

0005

Time (s)

C-PANIC-PANI-Pd


i(A

cmminus2

mgminus

1)


2

SO4



120575 =

100

1198940

times (

119889119894

119889119905

)

119905gt500 s( per s) (3)







28 29 30 31 32 33 34 35

10

12

14

16

18

20

22

C-PANIC-PANI-Pd



log i

(A cm

minus2

mgminus

1)


2

SO4


0 50 100 150 200 250 300 350

0

50

100

150

200

5 10 15 20 25 30 35 40

05

1015202530

C-PANIC-PANI-Pd


Z998400 (Ohm)

minusZ998400998400

(Ohm

)


2

SO4



2

SO4





4 Conclusion




References


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 200 400 600 800 1000 12000000

0001

0002

0003

0004

0005

Time (s)

C-PANIC-PANI-Pd


i(A

cmminus2

mgminus

1)


2

SO4



120575 =

100

1198940

times (

119889119894

119889119905

)

119905gt500 s( per s) (3)







28 29 30 31 32 33 34 35

10

12

14

16

18

20

22

C-PANIC-PANI-Pd



log i

(A cm

minus2

mgminus

1)


2

SO4


0 50 100 150 200 250 300 350

0

50

100

150

200

5 10 15 20 25 30 35 40

05

1015202530

C-PANIC-PANI-Pd


Z998400 (Ohm)

minusZ998400998400

(Ohm

)


2

SO4



2

SO4





4 Conclusion




References


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




4 Conclusion




References


































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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