pyrolysed (PANI-melamine) as catalyst support

pyrolysed (PANI-melamine) as catalyst support

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Ultra low loading of anode catalyst for direct methanol fuel cells with ZrO2/ pyrolysed (PANI-melamine) as catalyst support Aristatil Ganesan a,b, Mani Narayanasamy b, Karthikeyan Shunmugavel c,*, Ingersoll Jayanthi Chinnappa b a

Research & Development Centre, Bharathiar University, Coimbatore 641 046, India Ingsman Energy and Fuel Cell Research Organization Private Limited, Chennai 600096, India c Madras Christian College, Department of Physics, Tambaram East, Chennai 600 059, India b

article info

abstract

Article history:

A new electrochemical methodology is developed for coating ultra-low PtRu catalyst by

Received 8 November 2015

depositing ZrO2/PANI/Melamine as a strong catalyst support for the electrode. Electrode-

Received in revised form

position of PtRu alloy on the surface of pyrolysed ZrO2/PANI/ Melamine enhances the

21 March 2016

catalyst utilization (Pt: 78.4 mg/cm2, Ru: 0.57 mg/cm2) in the methanol fuel cell. Pyrolysis of

Accepted 21 March 2016

PANI and melamine on ZrO2 forms high porous graphene like structure which is identified

Available online xxx

by XRD/SEM/TEM. The surface composition and chemical oxidation states of Pt, Ru, Zr, C, N, and O are examined by XPS spectra. The DMFC performance has reached a peak power

Keywords:

density of 68 mW/cm2 in 5 M methanol concentration at 100  C with ultra-low catalyst

Ultra-low loading

loading in the anode. Comparing with commercial catalyst, 98% of PtRu usage has been

DMFC

reduced in this method which is first of kind ever reported.

Electrodeposition

Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

PANI

reserved.

Melamine ZrO2

Introduction For several portable power pack applications particularly for defence applications, methanol fuel cells are preferred for its high energy density [1]. But methanol fuel cells are cost uncompetitive because of high loading of costly catalysts on the electrodes. Normally, about 4 mg cm2 of Pt, PtRu alloy are loaded in DMFC, which is almost 10 times higher than that of PEM fuel cells [2]. Generally in DMFC, the catalyst is highly loaded based on its poor catalyst utilisation at the triple-phase zones of the

electrodes. The enhanced catalyst utilization with Ultra low catalyst loading has been reported by Shan Zhu et al. [3]. The catalyst utilisation can be enhanced by increasing the surface area of both catalyst support and catalyst materials. In general, activated carbon acts as catalyst support for fuel cell electrodes. The surface area of catalyst support can be increased by adding Carbon nanotubes (CNT) [4], carbon nanofibers [5,6] and ordered mesoporous carbon (OMC) [7,8] with the catalyst. Also the increase in surface area of the catalyst support enhances the rate of MeOH oxidation [9]. The melamine impregnated with PANI/C and upon doping with Fe

* Corresponding author. Department of Physics, Madras Christian College, East Tambaram, Chennai, Tamil Nadu 600 059, India. Tel.: þ91 09095563850. E-mail address: [email protected] (K. Shunmugavel). http://dx.doi.org/10.1016/j.ijhydene.2016.03.135 0360-3199/Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Ganesan A, et al., Ultra low loading of anode catalyst for direct methanol fuel cells with ZrO2/ pyrolysed (PANI-melamine) as catalyst support, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/ j.ijhydene.2016.03.135

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shows thin and transparent graphene-like nanosheets structure with high surface area (up to ca. 702 m2 g1) which improves the formation of particular CeN bonds, in support materials [10]. The synthesis of ORR electrocatalysts for alkaline media through high temperature pyrolysis process is studied wherein; CNT has been used as a high surface area carbon source and PANI/melamine as dual nitrogen source [11]. ZrO2 can also exhibit a strong electro catalyst support for oxidation catalysts with longer cycling stability and excellent chemical stability. An internal porosity of pore diameter in the range of 2e20 nm and surface area of 100 m2 g1 is obtained for ZrO2 [12]. Recently, the enhancement of catalyst utilisation of electrodeposited PtRu alloy in direct methanol Fuel cell was studied by Coutanceau et al. [13] and reported an increased performance with the PtRu loading of 2 mg cm2. The enhancement of the catalyst activity by the electrochemical fabrication of core shell structured catalyst was also reported by Hsieh et al. [14]. In this work, we demonstrate a simple three step electro deposition method viz., Zirconium oxide, PANI/melamine and PtRu alloy on carbon cloth to fabricate anode for DMFC. The choice of ZrO2 as catalyst support is preferred for its enhanced performance, and, particularly, for its durability on methanol oxidation [15]. The excellent stability of Pt/ZrO2 is also been explained by the production of unstable carbonates on the ZrO2 surface and hence there is no Pt sintering occurs during the Water gas Shift reaction (WGS) [16]. Additionally, Croy et al. shows that the Pt/ZrO2 is most active for methanol conversion to hydrogen [17,53]. The use of Pyrolytic carbon derived from the pyrolysis of PANI-melamine as a catalyst support increases the fuel cell performance due to its high surface area [11]. These aspects interests the possibility of using ZrO2 with Pyrolytic carbon derived from the pyrolysis of PANI-melamine as catalyst support for DMFC. Moreover, the synthesis of PtRu alloy nanoparticle using electrochemical method can increase the catalyst utilisation with low loading in fuel cell [3]. Upon high temperature pyrolysing after each electrodeposition steps, the surface of each layer exhibits porous structure with carbon composite consists of graphene and CNT as catalyst support material for PtRu. Due to its high surface area, the loading of catalyst is reduced in anode with the same performance and cyclic stability [3]. A best performance with an ultra-low catalyst loading of ~79 mgcm2 is achieved by increasing the surface area of both catalyst support and catalyst.

Materials and methods Electrodeposition method Formation of ZrO2 on carbon cloth Cathodic electro deposition of ZrO2 is carried out in nonaqueous electrolyte bath containing 25 ± 4.6  105 g/L ZrCl4 (Merck), diluted in ethyl alcohol. The pH of the solution is 0.8 ± 0.1 at 10  C ± 0.1  C. The carbon cloth is treated in 1 ± 0.009 M H2SO4 and is employed as working electrode.

The cathode is placed at a distance of 27 ± 0.2 mm from anode. ZrO2 is coated on carbon cloth at a DC potential of 25.6 V ± 5 mV in the temperature range of 10  C ± 0.1  Ce0  C ± 0.1  C for one hour. The ZrO2 coated electrode is annealed at temperature of 550 ± 1  C in N2 atmosphere for one hour [18].

Formation of PANI-melamine Anodic Electrodeposition of PANI-melamine is performed on the ZrO2 coated carbon cloth in a two-electrode cell. Electrodeposition of PANI-melamine is performed using pulse power supply [Dynatronix model: PMC10-20-60-PR Pulse power supply, Make: USA] with ±5 mA and ±5 mV as instrument uncertainty values for current and voltage, respectively. An electrolyte consisting of lithium perchlorate LiClO4 (Alfa aesar): 0.5 ± 0.002 mol L1, aniline C6H5NH2(Merck): 0.25 ± 0.0001 mol L1 and melamine C3N3(NH2)3 (LOBA chemie): 0.025 ± 0.0001 mol L1 at room temperature [19] is employed. The pH of the solution is observed as 10.8 ± 0.1. The electrochemical synthesis of PANI þ melamine on ZrO2 coated carbon cloth as a working electrode is maintained at a DC potential of 3 V ± 5 mV. After plating, the electrode is dried in the oven at 40 ± 0.1  C for one hour and the electrode is pyrolysed at 900 ± 1  C in N2 atmosphere for one hour.

Formation of PteRu A plating bath is prepared by mixing 99.9 wt% RuCl3 (AG Merck), 97 wt% NaNO2 (AG Merck) in de-ionized water. The bath is heated to a temperature of 100 ± 1  C and kept at this temperature for one hour in which 99.9 wt% H2PtCl6. XH2O (Alfa aesar) is added. Then the solution is cooled to room temperature and H2SO4 of 97 wt% is added drop by drop. The concentrations of the components in the solution are: H2PtCl6 0.005 ± 2  105 M, RuCl3 0.005 ± 2  105 M, NaNO2 0.050 ± 2  104 M and H2SO4 0.250 ± 0.00380 M. The solution is aged for two weeks to get a homogenous solution. With this bath, the PtRu alloy is deposited on PANI-melamine coated electrode using pulse electro deposition technique. The pulse parameters used for PtRu electrodeposition are given below. Ton: 50 ms, Toff: 100 ms Ja: 50 mAcm2, Coulomb of 8 C cm2 After the successful deposition of PtRu, the electrodes are dried at 100 ± 1  C in N2 atmosphere for one hour [20].

Fabrication of membrane electrode assembly (MEA) Nafion 5 wt % solution (Aldrich) is coated on the surface of anode catalyst to achieve a dry nafion loading of 0.8 ± 4.6  105 mg cm2. From FuelcellEtc, USA a purchased catalyst of 40 wt % Pt/C with 4 mgcm2 loading and a dry nafion loading of 1 mgcm2 is used as cathode. Nafion 117 membrane is used as the ion exchange membrane. The cathode, Nafion 117 and the anode are bonded to form the MEA by hot pressing at 130 ± 1  C for 3 min under a pressure of 30 ± 1 bar. The prepared MEA is then tested in a single cell DMFC assembly using an electronic load (Amrel, USA) with ±4.5 mA and ±0.19 mV as instrument uncertainty values for current and voltage, respectively under standard experimental conditions.

Please cite this article in press as: Ganesan A, et al., Ultra low loading of anode catalyst for direct methanol fuel cells with ZrO2/ pyrolysed (PANI-melamine) as catalyst support, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/ j.ijhydene.2016.03.135

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Results and discussion Scanning electron microscopy (SEM) Fig. 1 (aef) shows the SEM images of the catalyst which appears as irregular shape and the size of each agglomerate is more than 50 nm, which consists of numerous nano particles of Pt and Ru. A distinct and uniform separation is clearly

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observed in all agglomerates. The honeycomb structure [Fig. 1c] with relatively smaller pores favours low catalyst loading due to its high surface area. The pyrolysis of PANI-melamine coated on Zirconium oxide layer gives porous carbon network with high surface area which supports the PtRu nanoparticle as shown in the Fig. 1c. Electrodeposition of PtRu alloy forms dense particles and agglomerates in the range of approximately 10e50 nm [Fig. 1(def)]. Fig. 1b illustrates the formation of PtRu alloy on

Fig. 1 e (aef). Scanning Electron Microscopic images of electrodeposited catalyst in different magnifications, (g). SEM-EDX spectrum of catalyst, (hei). Back Scattered Electron images of cross section of MEA. Please cite this article in press as: Ganesan A, et al., Ultra low loading of anode catalyst for direct methanol fuel cells with ZrO2/ pyrolysed (PANI-melamine) as catalyst support, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/ j.ijhydene.2016.03.135

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Fig. 1 e (continued).

Pyrolytic carbon derived from the pyrolysis of PANI-melamine on the carbon fibre cloth with an average size of 45 nm. Fig. 1g shows EDX spectrum of the PtRu catalyst coated electrodes. The EDX confirms the presence of all expected elements in the surface with their reasonable percentage. The atomic percentage of Pt: 34% and Ru: 26.89% are shown in the spectrum.

Back scattered electron microscopy (BSE) The cross section of MEA shown in Fig. 1(h and i) confirms the presence of anode (Electrodeposited PtRu), electrolyte and the cathode (Pt/C) as separate regions. The thickness and physical profile variations are observed at both anode and cathode sides. Anode catalyst is well bonded to the membrane than the cathode catalyst in the MEA which enhances the formation of triple phase zone as seen in the Fig. 1 (h and i).

Tunnelling electron microscopy (TEM) TEM images in Fig. 2 (aed) shows the PtRu bimetallic and nano particle formation. The PtRu alloy is having spherical and polycrystalline structures which are already observed

through SEM analysis. Nanoparticles with a size of 2e5 nm are formed in the agglomerated spherical structure. The similar particle formation was observed by Tao Huang et al. [21]. Even though, the catalyst is having a lot of microspores, it also has several nanopores. The surface area of catalyst is increased due to the presence of numerous nanopores. A TEM image of Pt and Ru bimetallic formation as black and white contrast variations are shown in the Fig. 2 (eeh). The other intensity variations may be attributed to the formation of other elemental structures, say carbon or graphene like carbon structures. The exact crystallite structures are well defined by the formation of fringes with the fringe width of about 0.12 nm. The CNT formation in the catalyst is confirmed by the lattice separation of 0.12 nm [22,23] which enhances the fuel cell performance even with the ultra-low loading of catalyst. The compositions of PtRu are analysed by EDX spectra (Fig. 2i). The EDX spectra depict dispersive peaks of Carbon, Platinum, Ruthenium and Zirconium. The atomic ratios of Pt:Ru:Zr, as 7.27:4.88:1.22 are formed on the surface of the electrode. The loading of Pt is higher than Ru in the alloy for which the reason is explained in the following Section ICP-MS.

Please cite this article in press as: Ganesan A, et al., Ultra low loading of anode catalyst for direct methanol fuel cells with ZrO2/ pyrolysed (PANI-melamine) as catalyst support, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/ j.ijhydene.2016.03.135

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Fig. 2 e (aed). TEM images in high resolution of catalyst system:ZrO2/PANI-mela/PtRu developed by electro deposition and subsequent pyrolysis method, (eeh). TEM images in high resolution displaying bimetallic formation and crystallite structures, (i). TEM-EDX spectrum of various elements present in catalyst.

X-ray diffraction The crystallinity of Carbon, ZrO2 and PtRu on the electrodes is investigated by XRD. As shown in Fig. 3, the diffraction peaks at 25.7 is the signals from graphene like structures. XRD patterns of the PtRu deposit shows the formation of Pt with face centred cube structure from the peaks of (111), (2 0 0) planes. 2q values of the corresponding peaks of (111) and (200) are obtained as 40.8 and 46.7 . A slight shift in the diffraction peaks of higher 2q values are observed for PtRu alloy when compared with pure Pt. Further, there is an increase in peak broadening with the decrease of Pt atom % of the deposits is also seen in the pattern. The presence of a small amount of PtRu alloy in the deposits may be the reason for these appearances [24,25]. The catalyst particle size

measurement from XRD using debye-sherrer formula is found to be 1.62 nm which is close agreement as observed in TEM image.

ZrO2 The presence of the ZrO2 phase in the catalyst is identified by the sharp peaks at (111), (111), (020), (200), (211) and (220) planes. The broadening of peaks for (221), (132) and (240) planes shows the amorphous nature of ZrO2 [26]. The coexistence of amorphous and crystalline phases reveals the crystallization of ZrO2 taking place from amorphous structure. The broadening of diffraction peaks indicates that the formation of fine Zirconia particles. Using Scherer equation the average crystallite size of the ZrO2 is 8.73 nm which is calculated from the angular width of planes (111), (11) and (220).

Please cite this article in press as: Ganesan A, et al., Ultra low loading of anode catalyst for direct methanol fuel cells with ZrO2/ pyrolysed (PANI-melamine) as catalyst support, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/ j.ijhydene.2016.03.135

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Fig. 2 e (continued).

Please cite this article in press as: Ganesan A, et al., Ultra low loading of anode catalyst for direct methanol fuel cells with ZrO2/ pyrolysed (PANI-melamine) as catalyst support, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/ j.ijhydene.2016.03.135

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N1s

X-ray photo electron spectroscopy (XPS)

Significant XPS N1s core-level spectra for the catalyst system is shown in Fig. 4d. These spectra show many peaks, implying the presence of several nitrogen structures. The XPS peaks of N1s are wisely composed of four GaussianeLorentzian peaks with the binding energy of 397.27, 397.80, 398.70, 399.61, 399.80 and 401.63 eV. The peak at 397.27 eV is associated to the presence of zirconium nitride (ZreN) [37,38]. Based on literature, the peak is observed for our catalyst at 397.80 eV and 399.6 eV that are recognised as pyridinic and pyrollic, respectively which are active species for ORR. The peak at 401.6 eV is assigned to Oxidized N species and also recognised as cationic nitrogen atoms on the polymer backbone [39,40]. The XP N1s spectra can be deconvoluted into many peaks with the nitrogen state located at 398.7 eV and 401.6 eV is assigned to pyridinic N and graphitic/quaternary N [41,42]. The peak presents at 398.7 eV correspond to SP2 hybridized nitrogen (Na) [30]. The weakly deconvoluted signal at 401.6 is also observed and attributed to the eNH2 or ]NH groups, which corresponds to discontinued with uncondensed amino groups [30]. The intrinsic structures and distribution of benzenoid amine (eNHe) of PANI favours for the electrochemical stability and strong catalytic support, which is displayed in XPS after pyrolysing catalyst at 900  C ± 1  C in the peak 399.80 eV [10,40,43].

Carbon (C1s)

Zr3d

The XPS spectrum (Fig. 4a) in wide scan shows the existence of all elements in catalyst. The C1s (Fig. 4b) spectrum of the catalyst can be separated by the peaks with binding energy values observed at 280.30 eV, 284.52 eV and 284.85 eV. The XPS C1s spectra reveal that the C1s strongest peak at approximately 284.6 eV and are slightly asymmetric, confirming the formation of N-doped carbon materials [11,28]. From the literature, the C1s strongest peak at binding energy nearly 284.6 eV, confirms the formation of nitrogenated carbon materials [11] and the shift observed in our peak at 284.52 eV may be due to pyrolysing PANI-mela at 900  C. The peak with less intensity at 284.85 eV is a significant C1s spectrum for the presence of Graphene oxide or graphitic carbon [29,30]. The peak at 280.30 eV reveals the presence of Ru in the form of 3d5/2 in C1s spectrum [31].

Fig. 4e shows the peaks of Zr3d at 181.39, 182.29, 183 and 184.41 eV in scan of our catalyst and found that the peaks are characteristic nature of ZrO2. The prominent peaks of Zr3d5/2 and Zr 3d3/2 of metal Zr are observed at 178.7 and 181.1 ± 0.1 eV, respectively [44]. The shift in binding energy of metal Zr3d5/2 is observed as 4.3 eV which is identified as ZrO2 [45] and there is only 0.3 eV shift from literature value of 4.6 eV [44,45]. This shift is observed for our catalyst synthesized via electrochemical method. The peak position observed at 181.39 eV corresponding to monocrystalline structure of Zr 3d5/2 [46]. The shift of Zr 3d3/2 (184.41 eV) from metal Zr [44] is observed as 3.31 eV which is designated as sub oxide II and has expected compositions of Zr2O3 [44] or low oxygen content in ZrO2 [45]. These sub oxides may be formed due to the impurity effects at the surface of oxide layer [44]. The peak of Zr 3d5/2 at 183.0 eV is agreed with value of bulk ZrO2 peaks with maxima at 182.9 eV [47] and around 183 is the characteristic of bulk ZrO2 [45]. This characteristic peak matches with range observed from 182.9 to 183.7 eV in the literature [35,10e14]. The Zr3d peaks observed in our catalyst are very close to the value of BE of ZrO2 in Zr/Ni/NiO substrates which are in range of 181.9 eV, 182.4 eV and 183.2 eV [48]. From the existence of various structures and form of ZrO2 as displayed in XPS, is certainly be an active catalyst support for noble metals and favours for active methanol oxidation with longer life cycles.

Fig. 3 e XRD results of catalyst, showing diffraction angles at PtRu (111), (200) peaks and different phases of ZrO2.

ZrO2 phase shows a mixed nanocrystalline/amorphous structure [27].

O1s O1s peak in the catalyst has symmetric peaks with BE in the region of 529.36, 530.35, 531.09 and 532.43 eV (Fig. 4c). The observed peak at 530.4 eV assigned to the oxide of Zirconium presence in the catalyst [32]. The peaks at 531.13 eV, indicates the existence of oxygen in ZrO2 and the small quantity of adsorbed OH groups. Furthermore the presence of OeN and OeC are revealing in the catalyst by the existence of value 532.43 eV in the spectrum [18,33,34]. There is 0.33 eV shift of these peaks from the reference [35] and this shift is due to the pyrolysing of catalyst at high temperature. The peaks presents at 529.35 eV for the O1s line confirm the prevalent existence of RuO2 in the surface region of the catalyst [36]. This may be the reason for the enhancement in catalyst utilisation with low catalyst loading.

Platinum (Pt4f) The Pt4f spectrum of PteRu/ZrO2 catalyst (Fig. 4f) shows a doublet containing a low-energy band (Pt 4f7/2) and a highenergy band (Pt4f 7/2) at 71.5 and 74.87 eV, respectively. The

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Fig. 4 e (aeg): XPS spectra of ZrO2/PANI-mela/PtRu: (a) the survey spectrum; (b) C1s (c) O1s; (d) N1s; (e) Zr3d; (f) Pt4f; and (g) Ru3d.

lower binding energy value is in good agreement and close to the literature on peak of Pt at 71.0 eV [49] and they are designated as zero-valent platinum [50]. The major amount of platinum (>70%) nanoparticles in catalyst have a zero

oxidation state whereas small quantity (<30%) of Platinum have a 4 þ oxidation state with peaks at BE values in range of 71.2e72.2 (Pt 4f7/2) and 74.3e75.5 eV (Pt 4f7/2), respectively [51,52].

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Fig. 4 e (continued).

The peak Pt0 4f7/2 is shifted 0.5 eV from 71.0 eV as reported for fresh Pt [53]. This positive shift is suggested as final state effects due to the interaction with catalyst metal support ZrO2. Similar work is reported for AueTiO2 interaction [54]. The XPS studies show that our catalyst favours greater possibility for the formation of interfacial PteZr compounds. The formation of alloy PteRueZr in the catalyst may be present and a similar observation of Pt10.25 Zr0.25/C alloy formed as reported in the literature [55]. The binding energy shift for the formation of alloys PteZr is very well agreed with our BE shift observed for Pt04f7/2 peak as 0.5 eV which falls in the range of reported values in literatures [56,57]. The formation of alloy PteRueZr will encompass the greater catalytic activity and chemical stability. The BE difference of Pt04f7/2 (71.50 eV) from PtO2 (75.42 eV) is 3.92 eV which is almost close to the one observed in literature [53] for supported Pt metal systems.

ICP-MS The amounts of Pt and Ru deposited on the electrodes are determined using ICP-MS analysis. ICP-MS is a suitable method of choice for elemental analysis as it can go for low detection limits and analyse multi element capability. The analysis is taken using the Perkin Elmer optima 5300 dv ICPMS instrument (PerkinElmer, Inc. Shelton, CT, USA) which shows similar loading of catalyst for all samples. In our catalyst Pt and Ru loading is observed as 78 mg cm2 and 0.57 mgcm2 respectively, which shows Pt loading in the alloy is greater than the Ru. During pulse plating, the excess Pt atoms on the PteRu alloy is formed which is due to the displacement reaction between Ru atoms and Pt in the electrolyte during Toff period. And so the Pt loading in the alloy is greater than Ru [20].

Fuel cell performances Ruthenium (Ru3d) The spectrum of Ru3d (Fig. 4g) is usually occurs with coexistence of C1s at 284.55 eV and it is in good agreement with literatures [58]. The Ru scan of the synthesized catalyst shows a distinct peaks of Ru3d5/2 and Ru3d3/2 at 280.4 eV and 284.55 eV, respectively which are referred as significant peaks of metallic Ruthenium and confirms the presence of Ru element with good agreement of literature references [59]. PtRu XPS peaks show the presence of Ru0 states at 280.4 eV [53,58]. The catalyst system so formed as PtRu/ZrO2 is supporting for the higher state of oxidation for Ru and increases the chances of reduction of Pt [53]. The Ru3d5/ 2 peak appears to be shifted by about 0.3 eV towards higher BE with respect to the corresponding characteristic binding energy (BE) of Ru3d5/2 peak for Ru metal at 280.1 eV [60], and this shift is probably due to the overlapping C1s peak tail. The BE shift of major Ru3d5/2 peaks of the catalysts relative to the Ru metal reference standards are attributed as interaction of electronic effects due to the presence of metallic Pt in these materials [60]. The intensity of peak above 282 eV is attributed to RueO speciation.

The DMFC performances are studied for MeOH concentrations from 1 M to 5 M ± 0.01 M at temperatures from 70 ± 0.1  C to 100 ± 0.1  C and compared with commercial (PtRu)/C coated anodes. So electrochemically prepared PtRu anodes are tested with active area of 8.41 cm2 DMFC and the resulting polarization curves are compared with commercial (Fuelcelletc) anode. Anode (Fuelcelletc) with a catalyst loading of 4 mg cm2 is used for comparison. Commercial electrodes (Fuelcelletc) with Pt/C loadings of 4 mg cm2 and 2 mg cm2 are used as standard cathode. The current density of 59, 178, 357, and 535 mAcm2 are obtained at 0.4, 0.3, 0.2 and 0.1 V, respectively. The peak power of 68 mWcm2 at 0.2 V and with a peak current density of 535 mAcm2 is achieved using 5 M MeOH concentration at 100 ± 0.1  C. The oxygen flow rate of Oxygen is maintained as 600 ± 6 ml min1 using a mass flow controller (MKS 1179A controller) and the MeOH flow at 2 ± 0.2 ml min1 is controlled by a peristaltic pump (Rabbit). A peak power density of 44.5 mWcm2 with a peak current density 300 mAcm2 is obtained for commercial catalyst (fuelcelletc) at 0.25 V under same experimental conditions.

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Fig. 5 e (aee): DMFC performances of prepared anode with fuelcelletc cathode, at different concentrations of MeOH at temperatures from 70 to 100  C. a)1 M MeOH b) 2 M MeOH c) 3 M MeOH d) 4 M MeOH e) 5 M MeOH.

Hence it is observed that enhanced peak power density is achieved with ultra-low Pt and Ru loading of 78 mgcm2 and 0.57 mgcm2 respectively using the electrodeposition method on pyrolysed ZrO2/PANI-melamine surface. To our knowledge this is the best fuel cell performance with ultra-low loading of Pt and Ru using electrodeposition method for DMFC. Coutanceau et al. has reported that the electrodeposited PtRu alloy shows a peak power density of 90 mWcm2 at 100  C with catalyst loading of 2 mg cm2 which is 25 times higher than our work [13]. Most of the

works reported on the electrodeposited catalysts for DMFC anodes are studied only for the electrochemical activity of the catalyst. The enhanced performance of porous PtRu/C for methanol fuel cell can be ascribed by the formation of core shell structure on the high surface area pyrolysed ZrO2/ PANI-melamine during the pulse electrodeposition [20]. The formation of Pt shell with Ru core on the graphene/CNT like structure with nano size may be the reason for enhancing the fuel cell performance [Fig. 2(aed)] [20,21]. On ZrO2 coated electrode, melamine is co-deposited with PANI/C and upon

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Fig. 6 e (aee): DMFC performances of etc make anode and cathode (for comparison), at different concentrations of MeOH at temperatures from 70 to 100  C. a)1 M MeOH b) 2 M MeOH c) 3 M MeOH d) 4 M MeOH e) 5 M MeOH.

pyrolysing at high temperatures, this exhibits different structure of carbon as graphene-like and the CNT morphology [22,23] demonstrates porous structure and gives space for low loading of anode catalyst as Pt:78 mgcm2 Ru: 0.57 mgcm2 with an increase in fuel cell performance. The activity of PtRu catalyst towards methanol oxidation is improved by the presence of pyrolysed/PANI-melamine structure on ZrO2 coated on carbon cloth [15]. It is proposed that the presence of ZrO2 in the catalyst promotes the activity of methanol oxidation by PtRu which is explained by the following reaction [15].

Pt þ H2 O /Pt  OH þ Hþ þ e ZrO2 þ H2 O/ZrO2  OH þ Hþ þ e Pt  CO þ Pt  OH/2Pt þ CO2 Hþ þ e Pt  CO þ ZrO2  OH/Pt þ ZrO2 þ CO2 þ Hþ þ e The breaking of CeH and OeH bonds is essential for methanol oxidation and CO2 is formed by the reaction of CO

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Fig. 7 e (aec): a) Power density comparison with different MeOH concentrations of prepared anode; b) Power density comparison with different MeOH concentrations of etc make anode and cathode; c) Power density comparison with prepared anode (low loading) and etc make anode (4 mg cm¡2).

with OH on the surface of Pt. During this reaction CO is strongly adsorbed by Pt and does not take place in further reaction. The surface oxygen of reducible oxide (ZrO2) helps oxidizing the adsorbed CO on Pt surface. And hence the interface between pyrolysed/PANI-melamine structure on ZrO2 and Pt enhanced the methanol oxidation reaction [15]. The transformed porous carbon and different phases of nitrogen formed after high temperature pyrolysis results strong support materials for electrocatalytic activity of PtRu with ultra-low loading of precious catalysts. Also the catalyst synthesized via electrodeposition technique, greatly enhances the contact of the catalyst material on the threephase-zone. Fig. 5 (aee): demonstrates the DMFC performances of the MEA prepared using ZrO2/PANI-melamine/PtRu and commercial cathode (Fuelcelletc) with Pt/C loadings of 4 mg cm2. Different power density, current density values are obtained at different concentrations of MeOH (1 Me5 M) at 70  C e 100  C which are shown in Fig. 5 (aee). From the performances, it is observed that a peak power density of

68 mWcm2 is achieved at 5 M and 100  C. But the power density variations are observed only in the range of 60e68 mWcm2 for 1 Me5 M MeOH concentrations. At the same experimental conditions the performances of commercial anode (Fuelcelletc) with PtRu/C loadings of 4 mg cm2 is analysed. It is observed from Fig. 6 (aee) that the peak power density of 44.5 mWcm2 is achieved for 2 M MeOH at 100  C which is comparable with 41 mWcm2 for 1 M MeOH at 100  C. Fig. 7 (aec) depicts power density comparison between the prepared and commercial anodes at different concentrations of MeOH at 100  C. Fig. 7c justifies the peak power density values observed for our anode with commercial anode (Fuelcelletc). The catalyst prepared at our lab has a peak power density of 68 mWcm2 at higher methanol (5 M) concentration than the commercial catalyst which also reveals the lower methanol crossover due to the excellent catalytic activity of the fuel cell at higher concentrations. Longer life operation and higher methanol concentration (5 M) is preferred for successful cost effective commercialization of fuel cell.

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Conclusion In this interesting work, the anode catalyst and catalyst support materials (ZrO2/PANI-melamine) in the MEA preparation for DMFC are characterized. At the outset, the development of the carbon based support materials is concentrated for increasing the catalytic stability under laboratory DMFC conditions. PtRu alloy plated on the surface of Porous zirconium oxide and carbon derived from pyrolysed PANI-melamine enhances the catalyst utilisation at the triple phase interface thereby increasing DMFC performance. This catalyst support would definitely form highly ordered materials like CNT or grapheme-like structures for efficient catalytic activity and provides a favourable effect on the mass transport properties at the catalyst layer. This electrochemical synthesis of catalyst and electrode fabrication, can strongly replace other expensive methods which uses large amount of precious catalysts. Cost and size of DMFC stack can also be reduced significantly using this catalyst. This type of ultra-low loading of PtRu catalyst has viable potential in commercialising DMFC. The present catalyst enhances the catalyst utilisation up to 98% when compared with commercial catalyst loading.

Acknowledgements Authors gratefully acknowledge Mr. Kathiravan Subramanian Vice president, Ingsman Energy Fuel cell research organisation Pvt Ltd, for the finance support of this work. We acknowledge, Indian Institute of Technology Madras (IITM) for providing SEM, TEM facilities. We thank Dr S. Angappanne, Scientist Centre for nano and soft matter sciences, Bangalore for providing SEM/XRD facilities. Further, we thank Centre for nano science and Engineering, IISc, Bangalore for providing XPS facility. We thank SGS India Pvt ltd for providing the facility of ICP-MS. We acknowledge Mr. Sathya Sankaran (Ingsman) for his support on the fuel cell characterization studies. Also we thank Mr. Dhileepan from Ingsman for his assistance during this work. Authors specially thank Mr. M. Chellapandian, IITMadras, Mr. F. Devendran Palanivel, Madras University and Dr. M. Muruganandham, Anna University for their valuable support during this work. Last but not the least we sincerely thank Prof. Balasubramanian (Rtd) for his valuable grammar correction in manuscript.

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