saberi 2018 ELSEVIER

international journal of hydrogen energy xxx (2018) 1e17

Available online at www.sciencedirect.com

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Designing of some platinum or palladium-based

nanoalloys as effective electrocatalysts for

methanol oxidation reaction

S.Jafar Hoseini a,b,*,1 , Mehrangiz Bahrami a,b , Zahra Samadi Fard b ,

S. Fatemeh Hashemi Fard b , Mahmoud Roushani c , Behnaz Habib Agahi b ,

Roghayeh Hashemi Fath a,b , Sajad Saberi Sarmoor b

a Prof. Rashidi Laboratory of Organometallic Chemistry, Department of Chemistry, College of Sciences, Shiraz

University, Shiraz, 7194684795, Iran

b Department of Chemistry, Faculty of Sciences, Yasouj University, Yasouj, 7591874831, Iran

c Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, 69315516, Iran

article info

Article history:

Received 13 April 2018

Received in revised form

6 June 2018

Accepted 8 June 2018

Available online xxx

Keywords:

Liquid-liquid interface

Thin film

Supported catalyst

Methanol oxidation

abstract

Nano alloys contain noble metal nanostructures exhibit a wide theoretical and experimental

interest in the field of fuel cells. Hard endeavors have been enhanced to improve

the catalytic performance and minimize the usage of precious metals by alloying them

with non-precious ones. Formation of bimetallic and trimetallic noble metal alloys with

well-designed structures provide the opportunity to reach this goal. In this study, we first

discuss the synthesis of noble metal alloy nanostructured thin films such as PtCu, PdCu,

PtCu/reduced-graphene oxide (RGO), PdCu/RGO, PtCo, PtCo/RGO, PtPdCu and PtPdCu/RGO

via a simple reduction of organometallic precursors including [PtCl 2 (cod)] and [PdCl 2 (cod)],

(cod ¼ cis, cis-1,5-cyclooctadiene), in the presence of [Cu(acac) 2 ] and [Co(acac) 3 ]

(acac ¼ acetylacetonate) at oil/water interface and room temperature, including nanoparticles

and nanosheets. Then the effects of the well-defined nanostructures on the

improved electrochemical properties are outlined. Finally, we conclude that these nonprecious

bi and trimetallic alloy nanostructured thin films have better electrocatalytic

performance than Pt monometallic thin films and other Pt nanostructures due to the

geometric, electronic and stabilizer effect.

© 2018 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

Introduction

Increasing the energy usage in spite of depletion of fossil fuel

reserves and also rising environmental pollution, energy

conversion devices such as fuel cells exhibit great interest

[1e10]. Among various kinds of fuel cells, alcohol fuel cells are

attractive power sources for different electric vehicle and

mobile and immobile applications. Methanol fuel cells have a

lot of advantages such as having low cost, easy storage and

moving, being available and soluble in aqueous electrolytes

[11e17]. Platinum-based catalysts are important for fuel cells

* Corresponding author.

E-mail addresses: sj.hoseini@shirazu.ac.ir, sjhoseini54@yahoo.com (S.Jafar Hoseini).

1 Dedicated to the life-time achievements of Dr. Ahmadreza Esmaeilbeig in the field of inorganic chemistry.

https://doi.org/10.1016/j.ijhydene.2018.06.062

0360-3199/© 2018 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

Please cite this article in press as: Hoseini SJ, et al., Designing of some platinum or palladium-based nanoalloys as effective electrocatalysts

for methanol oxidation reaction, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/

j.ijhydene.2018.06.062

2


to enhance the redox reactions due to their high catalytic

activity and stability [18e23]. Extensive studies are simulated

to decrease the Pt dosage in these catalysts due to their high

cost and scarcity, and also increase and improve the catalytic

activity [24,25]. Recently, there are some reports about

decrease the loading amount of Pt in the catalysts with

enhanced performance by alloying Pt with transition metals

such as Co, Fe, Ni, Cu, Pb, etc [26e31]. Du et al. synthesized

PtAu nanodendrites with interesting electrochemical properties

than commercial Pt/C catalysts for methanol oxidation

due to the dendritic structure, synergistic and electronic effects

between Pt and Au [32]. Also, this group attempted for

the synthesis of PtCu nanocrystal catalysts under ultrasonic

condition that exhibit better electrocatalytic activity than

commercial Pt/C toward ethylene glycol electrooxidation [33].

Furthermore, they reported the synthesis of PdNi hollow

nanospheres with high active sites with the assistant of polyvinylpyrrolidone

for ethylene glycol electrooxidation [34].

The main important facts that influence the catalytic activity

are: (i) electronic and geometric effect (component, size and

morphology of the catalysts) [35] and (ii) stabilizer effect

(using carbon-based stabilizers such as graphene and carbon

black) [36,37]. Previously, graphene-Pt composites have been

attempted in the fuel cells for oxygen reduction reaction

[38,39] and the methanol oxidation reaction (MOR) purposes

[40,41]. Also, PdeRu alloy nanoparticles (NPs) dispersed on

CoWO 4 -doped graphene nanosheets was used for enhanced

methanol electro-oxidation and obtained from the

microwave-assisted polyol reduction method [42]. Pt NPs

supported on titanium iron nitride nanotubes was synthesized

at 120 C and applied as electrocatalysts for MOR [43].

Microwave synthesis of the Pt NPs supported on undoped

nanodiamond for MOR was also reported [44]. The role of Pb

and MnOx in PtPb/MnOx-CNTs catalyst for MOR was also

investigated [45]. Electrochemical deposition of hair shaped

PtRu as methanol oxidation catalyst was investigated by

Raoof et al. [46]. In all the reports, the synthesis of the electrocatalysts

was done in the microwave or high temperature

conditions. The “liquideliquid interfacial assembly” is an

interesting, simple, novel and low-cost bottom-up approach

to provide a thin film applied in nanodevice fabrication due to

their low cost [47e49]. Recently, there are some reports about

various types of Pt and Pt-based NPs thin films that can be

easily obtained at the liquideliquid (organiceaqueous) interface

by Hoseini et al. [50e57]. We have investigated the

application of monometallic Pt thin films with different precursors

in the MOR for the first time [51]. Also, we have reported

the formation of monometallic Pd [53] and bimetallic

PtPd [53], PtSn [52] and PtFe/Fe 2 O 3 [54] NPs thin films at

toluene-water interface and investigating their applications

in methanol oxidation. Furthermore, Pd [58], PdZn [59], PdSn

[59], PdCu [60] and PdCu/reduced-graphene oxide (RGO) [61]

thin films were synthesized at liquid-liquid interface and

applied as catalyst in the Suzuki-Miyaura CeC coupling reaction.

Girault et al. have investigated the activities of a series

of MoS 2 -based hydrogen evolution catalysts studied by

interfacial biphasic reactions. Carbon supported MoS 2 catalysts

(supported with multi-walled carbon nanotube and RGO)

performed best due to an abundance of catalytic edge sites

and strong electronic coupling of catalyst to support [62].

Dryfe and coworkers have investigated the assembly of

nanomaterials at liquid-liquid interface [47]. Toth and Dryfe

used liquid-liquid interface strategy for the deposition of Pd

and Au noble metal NPs on a free-standing chemical vapor

deposited graphene monolayer that opens an alternative and

useful way to prepare low dimensional carbon-based nanocomposites

and electrode materials [63]. The present work

reports the synthesis of several Pt-based and Pd-based

bimetallic and trimetallic electrocatalysts for methanol

electro-oxidation. Three interesting aspects of our study are

notable. First, in this study, for the first time, we demonstrated

a facile synthesis of PtCu, PtCu/RGO, PtCo, PtCo/RGO,

PtPdCu and PtPdCu/RGO alloy electrocatalysts by reduction of

organometallic precursors, [PtCl 2 (cod)] and [PdCl 2 (cod)],

(cod ¼ cis, cis-1,5-cyclooctadiene), in the presence of [Cu(acac)

2 ] and [Co(acac) 3 ] (acac ¼ acetylacetonate) at toluene/

water interface. PtCo thin films exhibit a nanosheet

morphology which is promising candidate for electrocatalytic

reactions. This potential is due to its large surface area to

volume ratio and high active sites, makes the nanosheets

highly useful for a number of applications including catalysis

and chemical sensing [64,65]. Second, organometallic precursors

show excellent potential for the production of nano

thin films. Third, the synthesized alloy nano films exhibit a

high catalytic activity and CO tolerance among most other

catalysts that were tested up to now toward methanol electrooxidation

[66e68]. Furthermore, using the bimetallic and

trimetallic alloys strategy can lead to a lower amount of Pt

catalysts and in turn, can decrease the price of the electrocatalysts

for MOR.

Experimental

Materials and methods

All of the chemical compounds were purchased from Merck

and Aldrich companies. The [PtCl 2 (cod)] [69] and [PdCl 2 (cod)]

[70] complexes were synthesized using reported procedures.

The elemental composition of the treated samples was acquired

by means of energy dispersive analysis of X-ray (EDAX)

and elemental mapping. X-ray diffraction (XRD) patterns were

recorded using a Bruker AXS (D8, Advance) instrument

equipped with Cu Ka radiation. Transmission electron microscopy

(TEM) images were recorded using a Philips CM-10

TEM microscope operated at 100 kV. By comparing the scale

bar of the TEM images with the diameter of different obtained

particles, the near mean diameter of the particles can be

estimated. Scanning electron micrographs (SEM) were obtained

using a Cambridge S-360 instrument with an accelerating

voltage of 20 kV. These samples were sputter-coated

with gold for this analysis. Inductively coupled plasma (ICP)

was performed on Agilent 7500ce quadrupole ICP-AES. The

surface atomic concentration and chemical composition of

the samples were investigated by X-ray photoelectron spectroscopy

(XPS) equipped with an Al KaX-ray source at energy

of 1486.6 eV in an ultrahigh vacuum (UHV) system with a base

pressure lower than 2 10 9 Torr.




international journal of hydrogen energy xxx (2018) 1e17 3

Preparation of bimetallic PtCu, PdCu, PtCo and trimetallic

PtPdCu nanostructured thin films at the oil/water interface

Toluene solution of [PtCl 2 (cod)] and [Cu(acac) 2 ] (1:1) (25 mL,

1 mM) was added to deionized water (25 mL) in a 100 mL

beaker. After the stabilization of two layers, aqueous NaBH 4

solution (0.1 M, 5 mL) was injected into the aqueous layer

dropwisely. Finally, PtCu NPs thin film was synthesized at the

liquideliquid interface. This procedure was continued similar

for the synthesis of PdCu and PtCo nanostructured thin films

but [PdCl 2 (cod)]) and [Co(acac) 3 ] was used, respectively (See

Figs. S1eS2 in the supporting information file). A similar

method was applied for the synthesis of PtPdCu NPs thin film,

using [PtCl 2 (cod)], [PdCl 2 (cod)] and [Cu(acac) 2 ] (1:1:1) complexes

as precursors in toluene (25 mL) and NaBH 4 as the

reducing agent.

Preparation of PtCu/RGO, PdCu/RGO, PtCo/RGO and PtPdCu/

RGO nanostructured thin films at the oil/water interface

Graphene oxide (GO) was prepared from natural graphite

flakes by a modified Hummers method (See Fig. S3 in the

supporting information file) [53]. The preparation method for

the synthesis of these composite nanostructured thin films

was similar to the PtCu synthesis, but GO (10 mg) was first

exfoliated in double distilled water (25 mL) by sonication for

10 min. This aqueous phase (containing GO) is contacted with

toluene phase (containing metal precursors) and the reducing

agent is dropwisely added (0.1 M, 10 mL).

Electrochemical measurements

Autolab Potentiostat/Galvanostat PGSTAT12 (Eco Chemie,

Switzerland) was used for electrochemical measurements. All

characterizations were conducted in a standard three electrode

system using an Ag/AgCl (sat. KCl) reference electrode, a

bare or modified glassy carbon (GC) electrode with the area

diameter of 2 mm with prepared electrocatalysts as a working

electrode and a platinum wire as a counter electrode. Also, all

potentials were converted to values with reference to a

normal hydrogen electrode (NHE) and all cyclic voltammograms

(CVs) were recorded under the same conditions and at

room temperature.

Electrocatalysts transfer to the GC electrode

In order to transfer electrocatalysts to the surface of GC electrode,

first electrodes were polished with alumina, sonicated

with H 2 O: EtOH mixture, washed with distilled water and

dried. The organic phase of the as prepared thin film was

removed by a syringe, the thin film was put on a glass by

immerse the glass lamella under the thin film and bringing up

the glass. Then the electrode was put on the glass surface

contain thin film and impacted for 5 min. These thin films

were transferred to the surface of GC electrode by using no

nafion and they stuck excellent to the electrode surface even

better than using nafion. Fig. S4 shows the transferring

process.

Results and discussion

In this study, the synthesis of PtCu, PdCu, PtCo, PtCu/RGO,

PdCu/RGO, PtCo/RGO, PtPdCu and PtPdCu/RGO nanostructured

thin films, which involves the chemical reduction

of the [PtCl 2 (cod)], [PdCl 2 (cod)], [Cu(acac) 2 ] and [Co(acac) 3 ]

complexes at the oil/water interface with NaBH 4 , are

demonstrated. In the case of graphene-supported thin films,

after addition of NaBH 4 aqueous solution, the reduction of GO

sheets was started. GO sheet is contain hydroxyl, epoxide and

carboxyl functional groups that make it hydrophile. Reduction

of GO by using NaBH 4 , reduces these functional groups on GO

and decreases its hydrophilicity. This process is followed by

moving the sheets to the interface (decrease in the polar

functionality on the surface of the GO sheets). Therefore, RGO

layers in water can support the nanostructures forming at the

oil-water interface (Fig. 1).

Catalysts characterization

PtCu thin film electrocatalyst

Fig. 2a shows the XRD patterns of the bimetallic PtCu alloy

thin film. The main characteristic peaks of face centered cubic

(fcc) crystalline Pt appear in the XRD patterns with the reflection

planes [(111), (200), (220), (311), and (222)] [53]. Other weak

diffraction peaks are belong to Cu(0) and correspond to the

planes [(111), (200) and (220)] [60]. The diffraction peaks of this

bimetallic nanoalloy thin film are shifted to higher 2q values

compare to the same reflections for Pt (0) and approving that

the alloying is happened [60]. The chemical composition of

this alloy thin film was determined by EDAX analysis, confirming

the existence of Pt and Cu elements (Fig. 2b).

TEM was used to characterize the PtCu bimetallic alloy thin

film. The spherical nanostructures with the average diameter

of approximately 18 nm were seen (Figs. S5aec). Furthermore,

the SEM analysis was used to characterize the thin film. This

image confirms a continuous surface of the thin films

(Fig. S5d).

PdCu thin film electrocatalyst

Figure S6b shows the XRD patterns of the bimetallic PdCu

alloy thin film and confirms the fcc crystalline structure for

this alloy [53,60]. TEM was used to characterize this bimetallic

alloy thin film. The spherical NPs with the average diameter of

approximately 15 nm were seen (Figs. S6a and c). Also, the

surface of this thin film is shown by SEM analysis (Fig. S6d).

EDAX analysis shows the chemical composition of the PdCu

alloy thin film, confirming the existence of Pd and Cu elements

(Fig. S7a).

PtCo thin film electrocatalyst

Fig. 3a shows the XRD patterns of the bimetallic PtCo alloy

thin film. The main characteristic peaks of crystalline Pt (0)

and Co(0) appear in the XRD patterns [53,71]. Also, the

diffraction peaks of the PtCo thin film are shifted to higher 2q

values and approve alloy formation. TEM was used to characterize

this bimetallic alloy thin film. Nanosheet structure




4


Fig. 1 e Schematic illustration of the Pt (Pd)-based/ RGO bimetallic thin films formation at the toluene-water interface, (a)

stabilized mixture of metallic precursors in toluene (blue color) and GO in water (brown color), (b) dropwise addition of

NaBH 4 to the stabilized mixture, (c) the reduction of GO sheets and metallic precursors were started and they moved to the

interface, (d) thin films of bimetallic alloys/RGO nanostructures appeared at the toluene-water interface. (For interpretation

of the references to color in this figure legend, the reader is referred to the Web version of this article.)

with the thickness of approximately 5 nm was obtained

which can obviously confirm the PtCo alloy formation (Fig. 3b

and c). SEM analysis shows a continuous surface of the thin

film (Fig. 3d).

In this investigation, only PtCo thin film shows nanosheet

structure. Considering the lattice structures for platinum (fcc),

palladium (fcc), copper (fcc) and cobalt (simple hexagonal), it

can be concluded that both metallic atoms in all alloys such as

PtCu and PdCu have the same crystal lattice structure except

PtCo alloy. The difference between the crystal structure of two

metals leads to different assembly and growth of particles and

results in the formation of nanosheets. PtCo sheets probably

resulted from the oriented attachment of the PtCo NPs in twodimensional

fashion. The highly reactive facets were preferentially

consumed in the growth process that led to the sheetlike

PtCo crystal growth [72]. Fig. S8 shows the mechanism for

the formation of PtCo nanosheets. However, it is difficult to

understand the exact reaction mechanism of nanosheet assemblies.

The details of the proposed mechanism for the

synthesis of PtCo nanosheets thin film is as follows: [PtCl 2

(cod)] and [Co(acac) 3 ] were dissolved in toluene (a). The

reduction was initiated by dropwise addition of NaBH 4 and Pt

precursor reduced in the form of sphere (b). This reduction

was followed by the reduction of the second metal, (Co(III)) (c).

Reduced Pt and Co was self-assembled and grew with each

other (d) to form a nanosheet structure (see, Fig. S8).

To better show the composition of the PtCo nanosheets

and distribution of elements, EDAX and elemental mapping is

applied (Fig. 4aed).

PtPdCu thin film electrocatalyst

Figure S9b shows the XRD patterns of the trimetallic PtPdCu

alloy thin film. The main characteristic peaks of fcc crystalline

Pt and Pd appear in the XRD patterns with the reflection

planes [(111), (200), (220), (311), and (222)] [53]. Other diffraction

peaks confirm the presence of Cu(0) [60]. Also, EDAX analysis,

confirms the existence of Pt, Pd and Cu elements (Fig. S7b).

TEM was used to characterize the as-synthesized trimetallic

alloy thin film. Nanosphere structure with the mean diameter

of 8 nm was obtained (Figs. S9a and c). Fig. S9d shows a SEM

image for this thin film.

To investigate the stabilizer effect on the morphology,

surface area, size and catalytic activity of NPs (geometry and

electronic effect that have influence on the catalytic activity),

Fig. 2 e (a) XRD pattern of the PtCu thin film deposited on a glass and (b) EDAX spectrum of the as-prepared thin film.





Fig. 3 e (a) XRD pattern, (b,c) TEM images and (d) SEM image of the PtCo nanosheets thin film.

we used GO and investigating the effect of the addition of this

stabilizer to the synthesized thin films.

PtCu/RGO thin film electrocatalyst

The main characteristic peaks of fcc crystalline Pt appear in

the XRD patterns (Fig. 5a) [53]. Also, other diffraction peaks

confirm the presence of Cu(0) [60]. Furthermore, the first peak

located at 2q ¼ 25 (002) is attributed to RGO [53]. The spherical

NPs with the average diameter of approximately 4 nm were

seen by TEM analysis for this bimetallic alloy thin film which

can obviously confirms the PtCu alloy formation on the RGO

support (Fig. 5b and c). Fig. 5d shows the SEM image of the assynthesized

thin film.

PdCu/RGO thin film electrocatalyst

Figure S10a shows the XRD patterns of the bimetallic PdCu/

RGO alloy thin film with the characteristic peaks of crystalline

Pd(0) and Cu(0) [53,60]. The first peak located at 2q ¼ 25 (002) is

attributable to RGO [53]. The morphology of this bimetallic

alloy thin film was characterized by TEM. The spherical NPs

with the average diameter of approximately 9 nm, was seen

which can obviously confirm the alloy formation on the RGO

support (Figs. S10b and c). Fig. S10d exhibits the SEM analysis

for this thin film in low magnification.

PtCo/RGO thin film electrocatalyst

Fig. 6b shows the XRD patterns of the bimetallic PtCo/RGO

alloy thin film. The main characteristic peaks of Pt (0) and

Co(0) appear in the XRD patterns [53,71]. Also, the first broad

peak located at 2q ¼ 25 (002) is attributable to RGO [53]. TEM

was used to characterize this thin film. Multipod structures

with the mean diameter of 5 nm were obtained (Fig. 6a,c).

Fig. 6d shows the SEM image of the PtCo/RGO thin film in low

magnification and exhibits the multipod structure of this thin

film.

One of the effective strategies for the synthesis of multipod

nanostructures is seed-mediated diffusion coupled with the

aggregation route with a core of one metal attached by the

branched arms of another metal which is similar for the

synthesis of nanodendrites [55]. The rate of nucleation and

growth is dependent to the reduction rate. Reduction of the

metallic precursors (Fig. 7a), [PtCl 2 (cod)] and [Co(acac) 3 ], occurs

according to the standard electrode potential values of

each metal which firstly happened for Pt (Fig. 7b) and spherical

Pt (0) is formed which applied as seeds for nucleation sites for

further growing followed by the reduction of Co(III) as a second

metal precursor (Fig. 7c). Keeping on the addition of

NaBH4 and reduction process led to aggregation (Fig. 7c). In

this growth mode, high surface energy particles are produced




6


Fig. 4 e (a) EDAX and (bed) elemental mapping analysis for PtCo thin film.

through the reduction of metal precursors, and minimize the

total surface energy by aggregation. Dendritic structures formation

is the result of continuing the addition of NaBH 4

(Fig. 7d). Reduction of the metals and GO occurs simultaneously

which leads to the increase of GO hydrophobicity and

move toward the interface. Multipod nanostructures are

formed on the RGO surface at the interface (Fig. 7eeg). In this

process, GO acts as a stabilizer and controls the NPs growth.

PtPdCu/RGO thin film electrocatalyst

Figure S11a shows a TEM image for PtPdCu/RGO thin film.

Spherical nanostructures with the mean diameter of approximately

3 nm have been achieved on the RGO surface

(Fig. S11c). Fig. S11b shows the SEM image of the assynthesized

thin film. Also, to better show the composition

of the thin film and distribution of Pt, Pd, Cu, C and O elements

in PtPdCu/RGO electrocatalyst, EDAX and elemental mapping

is applied (Fig. S12) which improve the presence of Pt, Pd, Cu, O

and C elements in the as-prepared thin film.

The exact loadings of Pt (Pd) in the samples are provided

using ICP. The results indicated that the Pt (Pd) loading of the

PtCu, PtCu/RGO, PdCu, PdCu/RGO, PtCo, PtCo/RGO, PtPdCu,

PtPdCu/RGO and Pt thin films was 3.25, 2.53, 5.3, 3.2, 2.64,

2.33, 1.86, 1.27 and 4.55 wt%, respectively. The chemical

states of Pt Pd Cu Co in the samples are confirmed by XPS

(Figs. S13eS14).

Investigating the electrocatalytic activity for methanol

oxidation

There are some reports about measuring the in situ catalytic

performance by liquid-liquid electrochemistry. Dissolution of

supporting electrolyte in either liquid phase allows liquidliquid

systems to be electrified. This special form of

biphasic interface is known as the interface between two

immiscible electrolyte solutions (ITIES). Applying the Galvani

potential difference across the ITIES is useful to drive reactions

between the two phases. These systems are similar to

the more commonly encountered solid electrode/ liquid

systems, with current generated by the passage of charge

across the ITIES [73,74]. We have investigated the MOR as a

model reaction in the external system which is important for

the realization of the efficiency of the electrocatalysts in fuel

cells. Cyclic voltammograms of the Pt (Pd)Cu, PtCo, Pt (Pd)Cu/

RGO, PtCo/RGO, PtPdCu and PtPdCu/RGO thin films in

0.5 M H 2 SO 4 at a scan rate of 50 mV s-1 are shown in Figs.

8e9a and S15-20a. The humps on the diagrams of these

nanostructures are associated with atomic hydrogen

desorption and adsorption (I and IV regions in Figs. 8e9a and

S15e20a). Also, metal oxide formation and their reduction

were observable (II and III regions in Figs. 8e9a and S15e20a).

Furthermore, the MOR for these electrodes contain different

electrocatalysts was measured by cyclic voltammetry in





Fig. 5 e (a) XRD pattern, (b) TEM image, (c) histogram of particles size distribution and (d) SEM image for PtCu/RGO

nanostructured thin film.

0.5 M CH 3 OH þ 0.5 M H 2 SO 4 solution between 2.0 and 0.5 V

(Figs. 8e9b and S15e20b).

Previous investigations about MOR have proposed the

following steps [75]:

CH 3 OH bulk þ Pt / Pt-C oad þ 4H þ þ 4e (1)

H 2 O þ Pt / Pt-OH ad þ H þ þ e (2)

Pt-CO ads þ Pt-OH ads / CO 2 þ 2Pt þ H þ þ e (3)

In the third step the CO adsorbed on Pt surface, which

cause poisoning of the catalyst, can be changed to CO2 and

oxidized by OH which is produced in step 2 as an oxygen

source via the Langmuir-Hinshelwood mechanism [75]. The

total oxidation equation is:

CH 3 OH þ H 2 O / CO 2 þ 6H þ þ 6e (4)

In this reaction, 6 electrons per mol of methanol are

delivered. Considering these equations, it can be concluded

that a catalyst for methanol oxidation should have these two

properties: (i) it should be able to dissociate the CeH bond and

(ii) facilitate the reaction of the resulting residue with some O-

containing species and change it to CO 2 . Pure Pt electrode

which is known as the best electrocatalyst can easily break the

CeH bond, but two processes for the complete oxidation is

occurred at different potential regions. In step (i), methanol

molecules are adsorbed which requires several neighboring

places at the catalyst surface. Effective adsorption can occur

at the potential that Pt sites are free from H due to the fact that

methanol is not able to displace adsorbed H atoms (~0.8 V vs.

NHE). In the step (ii), the water should be dissociated to produce

oxygen. The effective interaction between H 2 O and Pt

catalyst is occurring at the potential (1.01e1.06 V vs. NHE).

From these facts, it can be concluded that on pure crystalline

Pt, complete methanol oxidation cannot begin below 1.06 V

[76].

Investigating the effect of alloy formation and using

stabilizer on the morphology of nanostructures

Table 1 shows the result of the addition of the second/third

metal in the presence or absence of GO.

According to Table 1, PtCu/RGO and PdCu/RGO (4 and 9 nm,

respectively) show a smaller size than PtCu and PdCu thin




8


Fig. 6 e (a) TEM image, (b) XRD pattern, (c) histogram of particles size distribution and (d) SEM image for the PtCo/RGO thin

film.

films (18.0 and 15.0 nm, respectively) according to the addition

of the GO as stabilizer. Stabilizer limits the growth regions of

the particles and reduces their size.

In the MOR process, there are some important facts that

can affect the catalytic activity.

(i) Current density: After careful comparing between the

peak current density of the PtCo/RGO thin film and pure

Pt NPs thin film [51] (approximately 661.95 and

31.3 mA.cm -2 , respectively) it can be concluded that the

catalytic activity of the PtCo/RGO thin film is at least 21

times higher than that of the Pt NPs film (Table 2).

Therefore, metal alloying exhibit excellent effect on the

catalytic activity of electrocatalysts in MOR due to the

synergistic effect. According to the reports on bimetallic

alloy catalysts, it is well concluded that when a nonnoble

metal was placed near to Pd or Pt, it will have an

important effect on the electronic structure of the Pd or

Pt due to the electron transfer effect which is the result

of their different electronegativity [77]. Furthermore,

addition of the GO as stabilizer increases the electric

conductivity and also increases the current density.

This fact is obviously observable for PtCu/RGO thin film

in comparison with PtCu thin film. In the case of

PtPdCu/RGO, the current density almost shows no

change due to the very low metal loading as established

by ICP analysis. Also, using GO as stabilizer provide

good dispersity and thus large effective surface area of

the supported catalyst particles.

(ii) (j f /j b ) ratio: It is clear that the tolerance of catalysts toward

the poisoning species such as adsorbed CO intermediates

produces in the MOR process, is dependent

to the ratio of the forward anodic peak current (jf) to the

backward peak current (jb), j f /j b . Therefore, more effective

removal of the poisoning species on the catalyst

surface is the result of the higher j f /j b ratio [53]. The j f /j b

ratio for the PtPdCu thin film is 6.50 that is larger than

those for the ETEK Pt (0.99), other type of commercial Pt/

C (0.605), and Pt NPs thin films [51] (1.28), respectively.

Therefore, thin film electrode can lead to more complete

methanol oxidation and less accumulation of CO

or CO-like species than other investigated catalysts,





Fig. 7 e Synthesis of multipod PtCo nanostructures on RGO (a) dissolving the [PtCl 2 (cod)] and [Co(acac) 3 ] in toluene and GO in

water, (b) reduction of the Pt precursor, (c) reduction of the Co precursor and aggregation, (d) dendritic structures formation,

(e, f, g) reduction of the metal precursors and GO occurs simultaneously and multipod nanostructures are formed on the RGO

surface at the interface.

commercial Pt and Pt NPs thin film due to its higher jf/jb

ratio and demonstrating that most of the intermediates

were oxidized to CO 2 in the forward scan. PtCu, PdCu

and PdCu/RGO thin films show no considerable j f and j b .

The j f /j b ratios are compared in Table 2. Higher j f /j b ratio

for the PtPdCu thin film is due to the higher synergic

effect. PtPdCu thin film shows a spherical structure with

a large surface area and all the atoms are on the surface

of this catalyst.

(iii) -Lower voltage for the onset of current attributed to

methanol oxidation: The onset of current attributed to

methanol oxidation is at approximately 0.48 V (vs. NHE)

for PtCu/RGO thin film and 0.51, 0.60, 0.56, 0.50 and

0.70 V for PtCu, PtCo, PtCo/RGO, PtPdCu and PtPdCu/

RGO, respectively, lower than that at a pure Pt NPs thin

film electrode [51] (ca. 0.73 V vs. NHE, except PdCu and

PdCu/RGO thin films) (Fig. S21). The shift to the lower

amounts is indicating that these synthesized alloy thin

films have a positive effect on promoting the oxidation

of methanol by lowering its over potential (Table 2). In

order to compare the activities of the as-synthesized

catalysts which contain Pt and/ or Pd as a noble metal,

the mass activity is calculated (Table 2). According to

Table 2, PtPdCu thin film has the highest mass activity.

According to Table 2, most of these alloy thin films are

better electrocatalysts for methanol oxidation than bulk materials

and also Pt monometallic thin film that is due to these

three facts: (i) high specific surface area that is due to the thin

films structures and also presence of GO, (ii) high active sites

Fig. 8 e Cyclic voltammograms of the PtCu thin film in (a) 0.5 M H 2 SO 4 electrolyte and (b) 0.5 M H 2 SO 4 electrolyte þ 0.5 M

CH 3 OH with a 50 mV/s scan rate.




10


Fig. 9 e Cyclic voltammograms of the PtCu/RGO thin film in (a) 0.5 M H 2 SO 4 electrolyte and (b) 0.5 M H 2 SO 4 electrolyte

containing 0.5 M CH 3 OH with a scan rate of 50 mV/s.

that is due to the thin films structures and presence of all

atoms on the surface of the structures and (iii) the synergistic

effect, with considering the molecular orbital and band theories,

is obviously show that the valance and conduction

bands of the metals are changed and electron donating from

noble metals such as Pt to some other metals was observed

[55].

Typically, cyclic voltammograms recorded for the PtCu/

RGO and also PtCu, PdCu, PtCo, PdCu/RGO, PtCo/RGO, PtPdCu

and PtPdCu/RGO thin films in 0.5 M H 2 SO 4 and 0.5 M CH 3 OH at

Fig. 10 e Linear parts of the anodic Tafel curves for (a) PtCu/RGO, (b) PtPdCu/RGO, (c) PdCu/RGO and (d) PtCo electrodes in

basic electrolyte solution containing 0.5 M CH 3 OH with a scan rate of 50 mV/s.





Fig. 11 e Diagram of current density-overpotential for (a) PtCu/RGO and (b) PtPdCu electrocatalyst thin films.

Fig. 12 e Arrhenius plot for methanol at PtCo, PtCo/RGO,

PtCu/RGO, PdCu/RGO, PtPdCu and PtPdCu/RGO electrodes.

different scan rates are shown in Figs. S22e29a. Increase in

the current density with the scan rate is observed and the

peak potentials almost show no change. Figs. S22e29b show

that peak current densities are linearly proportional to the

square root of the scan rates, suggesting that the electrocatalytic

oxidation of methanol on these alloys thin films are

diffusion-controlled process [83,84].

Multiple CV curves of the as-prepared film electrodes for

the first 1000 cycles at a scan rate of 50 mVs -1 in the voltage

range of 0.5e2.0 V was used to show the stability of the

synthesized catalysts toward poisoning with CO and deactivation.

Fig. S30 shows this voltammogram for PtCo/RGO thin

film.

At last, it is obvious that all the electronic, synergistic,

geometric and morphological, stabilizer, surface area and

size effects can influence the catalytic activity of the

Fig. 13 e Chronoamperometric curve of (a’) PdCu, (b’) PtCu/RGO, (c’) PtPdCu/RGO and (d’) PdCu/RGO thin film electrocatalysts

in 0.5 M H 2 SO 4 and 0.5 M CH 3 OH at room temperature for 1800 s, (b) dJ/dt obtained from the slope of the linear portion of the

current decay for PtPdCu/RGO.




12


Table 1 e Investigating the effect of alloy formation and stabilizer on the morphology of nanostructures.

Entry Thin Film Morphology Size (nm) Ref.

1 Pt Spherical NPs 2.2 [51]

2 Pd Spherical NPs 6.6 [53]

3 PtPd Snowman like-shaped nanostructures 37.9 [53]

4 PtCu Spherical NPs 18.0 This work

5 PdCu Spherical NPs 15.0 This work

6 PtCo Nanosheets e This work

7 PtPdCu Spherical NPs 8.0 This work

8 PtCu/RGO Spherical NPs 4 This work

9 PdCu/RGO Spherical NPs 9 This work

10 PtCo/RGO Multipod structure 5.0 This work

11 PtPdCu/RGO Spherical NPs 3.0 This work

electrocatalysts. A closer look shows that some facts control

the electrocatalysts activity:

(i) Particle size is the important fact.

(ii) Using GO as a stabilizer, not only controls the particle

size, but also can increase the current density due to its

high electronic conductivity.

(iii) Nanostructures with a high surface to volume ratio

such as very small particles or nanosheets with high

surface area can be a good candidate in the field of

electrocatalysis for MOR.

(iv) Using non-noble metal near the Pd or Pt can disturb the

electronic structure of the Pt and Pd and change the

highest occupied and lowest unoccupied molecular orbitals

of these metals due to the electron transfer effect.

The difference between the electronegativity of two

atoms is the fact that causes different electron density

between atoms and leads to electron transfer [85].

Kinetic investigation

Exchange current density

The exchange current density, j 0 , is an important parameter

used in the Tafel and Butler-Volmer equations. It corresponds

to the current where the forward and reverse reactions are at

equilibrium state. The representation of the log j against E is

suitable for the analysis of kinetic parameters such as the

slope of the anodic Tafel plot, ba and the exchange current

density, j 0 (Figs. 10 and S31). The Tafel slopes for the asprepared

electrocatalysts were determined, and the extrapolation

of the obtained Tafel lines to 0.043 V (which is the

reversible potential for methanol oxidation, [86]) led to obtain

the exchange current density. J0 is widely applied to measure

the electrocatalytic activity of any electrode material for a

special reaction process. The values of Tafel slopes and exchange

current densities are given in Table 3 for the thin film

electrocatalysts obtain in a 0.5 M H 2 SO 4 solution, where

Table 2 e Comparing different electrocatalysts.

Electrode j f /j b Ratio Current density

(mA.cm -2 )

E (V, NHE) Mass activity (mA mg -1 ) a Reference

Commercial-Pt/C 0.57 e e 100 [78,79]

Pt/C 0.605 e e e [80]

PtRuCo/C 0.868 e e e [80]

PtRu/XC-72 1.05 e 0.64 370.11 [81]

Pt/C 1.18 e e e [80]

PtPd thin film 1.19 e 0.54 558.82 [53]

Pt thin film 1.28 31.3 0.73 47.92 [51]

PtFe3O4/CeO2 1.32 e e e [53]

PtRu/C (E-TEK) 1.88 e 0.37 797.18 [53]

Pd/Fe 2 O 3 1.98 e e e [81]

PtRu/CMK-8-II 2.25 e 0.41 383.14 [81]

PtRu/CMK-8-I 3.3 e 0.37 505.65 [81]

PPy-MOH-Pd b 2.43 350 e e [82]

Pd/C 0.67 15 e e [82]

PtCu thin film e 284.87 0.51 502.51 This work

PdCu thin film e 247.87 1.2 e This work

PtCo thin film 2.60 217.60 0.60 105.71 This work

PtCu/RGO thin film 3.31 540.74 0.48 924.36 This work

PdCu/RGO thin film e 249.53 0.80 125 This work

PtCo/RGO thin film 2.61 661.95 0.56 1209.67 This work

PtPdCu thin film 6.50 559.59 0.50 1796.40 This work

PtPdCu/RGO thin film 2.38 573.06 0.70 296.26 This work

a

b

Activity per milligram Pt.

ppy: polypyrrole, MOH: Manganese oxyhydroxide.





Table 3 e Comparison of j 0 for MOR in 0.5 M H 2 SO 4 .

Electrode material j 0 /mA cm -2 b a /mV ƞ a Ea (kJ/mol) A Reference

PtCu/RGO 0.1135 b 0.37692 3.20 15.22 0.11 This work

PtPdCu 0.7218 c 0.47036 0.96 4.32 0.72 This work

PtPdCu/RGO 4.2719 b 0.14142 0.004 2.16 e This work

PtCo/RGO 0.5243 c 0.44896 0.756 7.23 0.52 This work

PdCu/RGO 0.8329 b 1.31130 0.186 10.81 0.83 This work

PdCu 4.1434 c 0.13553 0.0011 e e This work

PtCo 3.3038 b 0.16435 0.0052 14.30 e This work

PtCu 0.07615 c 0.35713 4.044 32.51 e This work

Pt53Ru47/CNT d e e e 41.90 e [87]

Pt69Ru31/CNT d e e e 46.00 e [87]

Pt77Ru23/CNT d e e e 43.80 e [87]

Pt e e e 17.7 e [88]

PtSn e e e 10.6 e [88]

a

b

c

d

Obtain from Butler-Volmer equation.

See Fig. 10 for more details.

See Fig. S31 for more details.

Carbon nanotube.

PtPdCu/RGO thin film shows the lowest (j 0 ) and have a potential

to be the better alloy for MOR. Also, the diagram of

current density-overpotential is shown for PtCu/RGO and

PtPdCu thin films (Fig. 11 a,b).

Calculating the overpotential value

The overpotential value is calculated by using Butler-Volmer

Eq. (5) which is an activation controlled reaction and describes

how the current on a given electrochemical cell depends

on the electrode potential. By using approximation, this

equation can be given as:

nF

j ¼ j 0

RT n (5)

where n is the number of transferred electrons, F is the

Faraday constant (coulombs per mole), R is the ideal gas

constant (joules per kelvin per mole), T is the temperature

(kelvin) and ƞ is the overpotential (Table 3).

Calculating the activation energy

In order to calculate the apparent activation energy, the

Arrhenius equation is used (equation (6)),

log j 0 ¼ log A e Ea / (2.3RT) (6)

where (A) is the Arrhenius pre-exponential factor, (T) is the

temperature and (Ea) is the activation energy. Fig. 12 represents

the Arrhenius plot of logarithm of exchange current

density (Logj 0 ) versus the reciprocal of temperature (Te1) that

applied to obtain the apparent activation energy from the

slope of linear fitted diagram [87]. The apparent activation

energy of all as-synthesized electrocatalysts is shown in Table

3. The lower Ea is due to the PtPdCu/RGO electrocatalyst. In

the case of PtCu, PdCu, PtCo, PtPdCu, PtCu/RGO, PdCu/RGO,

PtCo/RGO and PtPdCu/RGO thin film electrocatalysts, the

apparent activation energy was lower than those found for

other Pd and Pt electrodes (Table 3). This result indicated that

Cu and Co sites improved the electro-oxidation of methanol in

MOR process. Some of the values reported in the literature are

compared with our data in Table 3.

Calculating the turnover number (TON)

To obtain the number of turnovers, cyclic voltammograms

were applied for all as-synthesized catalysts and also Pt thin

film for various numbers of potential cycles (Table 4). The

catalysts show good stability (90% of the initial value) in long

time duration of the catalytic cycles.

Steady state performance (long-term poisoning rate and power

calculation)

The chronoamperometry curves (current vs. time for 1800s)

are shown in Fig. 13 a, for (a’) PdCu, (b’) PtCu/RGO, (c’) PtPdCu/

RGO and (d’) PdCu/RGO thin film electrocatalysts in

0.5 M H2SO4 and 0.5 M CH3OH at room temperature. For all the

catalysts, the potentiostatic current is rapidly decreased due

to the formation of CO and some similar species during the

methanol oxidation process. The current density decay more

gradually with time and a pseudo-steady state was achieved.

This decay maybe due to the adsorption of (SO 4 2- ) on the

electrocatalyst surfaces which leads to the restriction of MOR.

From the following equation, the long-term poisoning rate (d)

is calculated for all the as-synthesized electrocatalysts from

the linear decay of the current measurement for a period of

more than 500s [89,90]:

d ¼ 100 dJ

J 0 dt

Table 4 e The number of turnovers for the as-synthesized

thin film catalysts for methanol electro-oxidation at 25 C.

Entry Catalyst TON at 25 C (cycle)

1 PtCu/RGO 2500

2 PtPdCu 4000

3 PtPdCu/RGO 4000

4 PtCo/RGO 3000

5 PdCu/RGO 2500

6 PdCu 2500

7 PtCo 2500

8 PtCu 2000

9 Pt 1900

(7)




14


Table 5 e Comparision of the maximum power output, long-term poisoning rate and EASA for various electrocatalyst.

Electrocatalyst Maximum power (mW cm -2 ) long-term poisoning rate (d, %s -1 ) EASA (m 2 g -1 ) Reference

PtCu/RGO 25.9 0.062 106.3 This work

PtPdCu 23.0 0.006 246.0 This work

PtPdCu/RGO 82.0 0.120 197.9 This work

PtCo/RGO 163.8 0.075 201.0 This work

PdCu/RGO 67.0 0.014 123.7 This work

PdCu 209.9 0.004 74.2 This work

PtCo 23.2 0.018 208.7 This work

PtCu 13.0 0.087 22.4 This work

Pt e e 40.0 [51]

MEA a /PtRu 18.1 e e [91]

MEA b /PtRu 12.3 e e [91]

MEA c /PtRu 6.8 e e [91]

PtRu 16.2 e e [93]

PtRuIr/C d e 0.100 e [94]

PtRuIr/C e e 0.130 e [94]

Pt/C E-TEK f e 0.004 e [95]

Fe2O3/Pt e 0.010 e [95]

Pd/TiO2eC e 0.017 e [96]

Pd/AC g e 0.022 e [96]

a

Membrane electrode assemblies (methanol concentration 2 M).

b Methanol concentration 4 M.

c Methanol concentration 3 M.

d Crystalline form

e Amorphous form

f

Commercial platinum-supported carbon catalyst (40 wt% Pt/C catalyst)

g Activated carbon.

Where (dJ/dt) is the slope of the linear portion of the current

decay and J 0 is the initial current and extrapolated from the

linear current decay (Fig. 13b). The obtained (d) values show

acceptable tolerance against poisoning of the active sites

during methanol oxidation process which is 0.004 and 0.006%.

in the case of PdCu and PtPdCu thin films, respectively and are

comparable with the reported data in literature (Table 5). The

lower (d) amount can leads to the lower poisoning rate.

Despite the higher ratio of j f /j b for PtPdCu electrocatalyst, PdCu

thin film exhibits the lowest (d) amount. This can probably be

the result of the faster and higher process of methanol

oxidation on the surface of PtPdCu electrocatalyst that leads

to the formation of a larger amount of poisoning species and

results in producing the larger d value.

J-V curve is also obtained to calculate the power for the assynthesized

thin films which is important for micro direct

methanol fuel cell (DMFC) and application in portable devices

(Figs. S32e33). The as-synthesized films exhibit considerable

power amount in comparison with the reported data for

anode catalysts in literature (Table 5) [91]. PdCu (209.9 mW cm -

2 ) and PtCo/RGO (163.8 mW cm-2) show the highest power for

MOR reaction.

The electrochemically active surface area (EASA) values

are calculated [92] for all the as-synthesized thin films and

compared with Pt thin film [51] (Table 5) using the curves

related to hydrogen desorption and adsorption at a scan rate

of 50 mV s -1 (Figs. 8, and 9, S15-20). The obtained values are

much larger than that of commercial Pt/C (41.4 m 2 g -1 ) and Pt/

multiwalled carbon nanotubes (27.3 m 2 g -1 ) [92]. The highest

EASA of the as-synthesized thin films is due to the presence of

well-dispersed, small-sized particles as displayed in the TEM

images. Also, alloy formation with many active sites plays an

important role in this area.

Cyclic voltammetry measurements at elevated temperatures

Furthermore, the cyclic voltammetry of the as-prepared thin

films were performed at different temperatures ranging from

25 to 60 C. The obtained polarization curves are shown in

Figs. S34e35. It is observable that the MOR process is occurred

at all temperatures with increase in the oxidation current.

Conclusion

In the present study, self-assembly strategy between two

immiscible liquid interfaces was used for producing the Ptbased

nanoalloy thin films by reduction of the organometallic

complexes at room temperature. Comparing the synthesized

alloys with Pt monometallic thin film show that all of

these alloys exhibit better catalytic activity in order to their

high specific surface area, high active sites, synergistic effect

and presence of stabilizer. According to these facts, PtPdCu

trimetallic nanoalloy thin film show a good CO tolerance than

Pt thin film and also PtCu and PdCu thin films due to the good

synergistic effect. PtCu/RGO and PtCo/RGO thin films showed

highly improved electrocatalytic activity toward methanol

oxidation compared with PtCu and PtCo NPs thin films due to

the high electronic conductivity and fast electron transfer of

RGO. These findings clearly demonstrate that RGO effectively

enhance electrocatalytic activity of PtCu and PtCo alloys for

the oxidation of methanol into CO 2 . Also, PtPdCu ternary

electrocatalyst has shown enhanced electrocatalytic activity

toward methanol oxidation compared with their binary

counterparts such as PtCu, PtCu/RGO, PtPd and PtPd/RGO.

The present method is promising for the synthesis of high

performance catalysts for fuel cells and sensors. Through

the construction of these noble metal alloy thin films, the





electrocatalytic performance has been greatly improved and

the usage of precious metals has been effectively minimized.

Acknowledgements

We thank Shiraz University and Yasouj University Research

Council, and the Iranian Nanotechnology Initiative Council for

their support.

Appendix A. Supplementary data

Supplementary data related to this article can be found at

https://doi.org/10.1016/j.ijhydene.2018.06.062.

references

[1] Zeng J, Lee JY. Ruthenium-free, carbon-supported cobalt and

tungsten containing binary & ternary Pt catalysts for the

anodes of direct methanol fuel cells. Int J Hydrogen Energy

2007;32:4389e96.

[2] Mench MM, Kumbur EC, Veziroglu TN, editors. Polymer

electrolyte fuel cell degradation. Academic Press; 2011.

[3] Cottrell CA, Grasman SE, Thomas M, Martin KB, Sheffield JW.

Strategies for stationary and portable fuel cell markets. Int J

Hydrogen Energy 2011;36:7969e75.

[4] Zhu B, Basile A, Tseng CJ. Materials as a player in hydrogen

and fuel cell technologies: preface to the special issue

section. Int J Hydrogen Energy 2017;42. 22090e22090.

[5] Jiang Z, Xia C, Chen F. Nano-structured composite cathodes

for intermediate-temperature solid oxide fuel cells via an

infiltration/impregnation technique. Electrochim Acta

2010;55:3595e605.

[6] Shih ZY, Wang CW, Xu G, Chang HT. Porous palladium

copper nanoparticles for the electrocatalytic oxidation of

methanol in direct methanol fuel cells. J Mater Chem A

2013;1:4773e8.

[7] Mert SO, Ozcelik Z, Dincer I. Comparative assessment and

optimization of fuel cells. Int J Hydrogen Energy

2015;40:7835e45.

[8] Thimmappa R, Devendrachari MC, Kottaichamy AR,

Tiwari O, Gaikwad P, Paswan B, et al. Stereochemistrydependent

proton conduction in proton exchange

membrane fuel cells. Langmuir 2016;32:359e65.

[9] Huang W, Wang H, Zhou J, Wang J, Duchesne PN, Muir D,

et al. Highly active and durable methanol oxidation

electrocatalyst based on the synergy of platinumenickel

hydroxideegraphene. Nat Commun 2015;6:1e8.

[10] Reinholdt MX, Kaliaguine S. Proton exchange membranes for

application in fuel cells: grafted silica/SPEEK nanocomposite

elaboration and characterization. Langmuir

2010;26:11184e95.

[11] Sebastian D, Serov A, Artyushkova K, Gordon J, Atanassov P,

Arico AS, et al. High performance and cost-effective direct

methanol fuel cells: Fe-N-C methanol-tolerant oxygen

reduction reaction catalysts. Chem Sus Chem.

2016;9:1986e95.

[12] Sundarrajan S, Allakhverdiev SI, Ramakrishna S. Progress

and perspectives in micro direct methanol fuel cell. Int J


[13] Zhou C, Wang H, Peng F, Liang J, Yu H, Yang J. MnO2/CNT

supported Pt and PtRu nanocatalysts for direct methanol fuel

cells. Langmuir 2009;25:7711e7.

[14] Tong X, Dong L, Jin G, Wang Y, Guo XY. Electrocatalytic

performance of Pd nanoparticles supported on SiC

nanowires for methanol oxidation in alkaline media. Fuel

Cell 2011;11:907e10.

[15] Jeon TY, Lee KS, Yoo SJ, Cho YH, Kang SH, Sung YE. Effect of

surface segregation on the methanol oxidation reaction in

carbon-supported Pt Ru alloy nanoparticles. Langmuir

2010;26:9123e9.

[16] Lanova B, Wang H, Baltruschat H. Methanol oxidation on

carbon supported Pt and Ru - modified Pt nanoparticles: a

comparison with single crystal and polycrystalline

electrodes. Fuel Cell 2006;6:214e24.

[17] Lin Y, Cui X. PtRu/carbon nanotube nanocomposite

synthesized in supercritical fluid: a novel electrocatalyst for

direct methanol fuel cells. Langmuir 2005;21:11474e9.

[18] Fujigaya T, Okamoto M, Matsumoto K, Kaneko K,

Nakashima N. Interfacial engineering of platinum catalysts

for fuel cells: methanol oxidation is dramatically improved

by polymer coating on a platinum catalyst. Chem Cat Chem

2013;5:1701e4.

[19] Morozan A, Jousselme B, Palacin S. Low-platinum and

platinum-free catalysts for the oxygen reduction reaction at

fuel cell cathodes. Energy Environ Sci 2011;4:1238e54.

[20] Nie Y, Li L, Wei Z. Recent advancements in Pt and Pt-free

catalysts for oxygen reduction reaction. Chem Soc Rev

2015;44:2168e201.

[21] Elezovic NR, Radmilovic VR, Krstajic NV. Platinum

nanocatalysts on metal oxide based supports for low

temperature fuel cell applications. RSC Adv 2016;6:6788e801.

[22] Antolini E. Palladium in fuel cell catalysis. Energy Environ Sci

2009;2:915e31.

[23] Sun X, Zhang N, Huang X. Polyaniline-coated platinum

nanocube assemblies as enhanced methanol oxidation

electrocatalysts. Chem Cat Chem 2016;8:3436e40.

[24] Hoster H, Iwasita T, Baumgartner H, Vielstich W. PteRu

model catalysts for anodic methanol oxidation: influence of

structure and composition on the reactivity. Phys Chem

Chem Phys 2001;3:337e46.

[25] Rolison DR, Hagans PL, Swider KE, Long JW. Role of hydrous

ruthenium oxide in Pt Ru direct methanol fuel cell anode

electrocatalysts: the importance of mixed electron/proton

conductivity. Langmuir 1999;15:774e9.

[26] Luo B, Yan X, Xu S, Xue Q. Synthesis of worm-like PtCo

nanotubes for methanol oxidation. Electrochem Commun

2013;30:71e4.

[27] LvQ,XiaoY,YinM,GeJ,XingW,LiuC.ReconstructedPtFe

alloy nanoparticles with bulk-surface differential

structure for methanol oxidation. Electrochim Acta

2014;139:61e8.

[28] Zhu JH, Geng SJ, Ballard DA. Evaluation of several low

thermal expansion FeeCoeNi alloys as interconnect for

reduced-temperature solid oxide fuel cell. Int J Hydrogen

Energy 2007;32:3682e8.

[29] Tu K, Lardner MJ, Morhart TA, Rosendahl SM, Creighton S,

Burgess IJ. Spatial mapping of methanol oxidation activity on

a monolithic variable-composition PtNi alloy using

synchrotron infrared microspectroscopy. J Phys Chem C

2016;120:23640e7.

[30] Liao Y, Yu G, Zhang Y, Guo T, Chang F, Zhong CJ.

Composition-tunable PtCu alloy nanowires and

electrocatalytic synergy for methanol oxidation reaction. J

Phys Chem C 2016;120:10476e84.

[31] Huang Y, Zheng S, Lin X, Su L, Guo Y. Microwave synthesis

and electrochemical performance of a PtPb alloy catalyst for

methanol and formic acid oxidation. Electrochim Acta

2012;63:346e53.

[32] Xu H, Song P, Wang J, Gao F, Zhang Y, Guo J, et al. Visiblelight-improved

catalytic performance for methanol




16


oxidation based on plasmonic PtAu dendrites.

ChemElectroChem 2018;5:1191e6.

[33] Xu H, Yan B, Yang J, Li S, Wang J, Du Y, et al. Exceptional

ethylene glycol electrooxidation activity enabled by sub-16

nm dendritic Pt-Cu nanocrystals catalysts. Int J Hydrogen

Energy 2018;43:1489e96.

[34] Zhang K, Xu H, Yan B, Wang J, Du Y, Liu Q. Superior ethylene

glycol oxidation electrocatalysis enabled by hollow PdNi

nanospheres. Electrochim Acta 2018;268:383e91.

[35] Martinez de la Hoz JM, Balbuena PB. Geometric and

electronic confinement effects on catalysis. J Phys Chem C

2011;115:21324e33.

[36] Oh HS, Nong HN, Reier T, Bergmann A, Gliech M, de

Araujo JF, et al. Electrochemical catalyst-support effects and

their stabilizing role for IrOx nanoparticle catalysts during

the oxygen evolution reaction. J Am Chem Soc

2016;138:12552e63.

[37] Najafpour MM, Salimi S, Safdari R. Nanosized manganese

oxide supported on carbon black: a new, cheap and green

composite for water oxidation. Int J Hydrogen Energy

2017;42:255e64.

[38] Sato J, Higurashi K, Fukuda K, Sugimoto W. Oxygen reduction

reaction activity of Pt/graphene composites with various

graphene size. Electrochem 2011;79:337e9.

[39] Suh WK, Ganesan P, Son B, Kim H, Shanmugam S. Graphene

supported PteNi nanoparticles for oxygen reduction reaction

in acidic electrolyte. Int J Hydrogen Energy 2016;41:12983e94.

[40] Patil SH, Anothumakkool B, Sathaye SD, Patil KR.

Architecturally designed PteMoS 2 and Ptegraphene

composites for electrocatalytic methanol oxidation. Phys

Chem Chem Phys 2015;17:26101e10.

[41] Jo EH, Chang H, Kyung Kim S, Choi JH, Park SR, Lee CM, et al.

One-step synthesis of Pt/graphene composites from Pt acid

dissolved ethanol via microwave plasma spray pyrolysis.

Nature 2016;6:1e8.

[42] Kumar A, Kumari N, Srirapu VKVP, Singh RN. Palladiumruthenium

alloy nanoparticles dispersed on CoWO 4 -doped

graphene for enhanced methanol electro-oxidation. Int J


[43] Li W, Pan Z, Huang Z, Zhou Q, Xu Y, Wu S, et al. Pt

nanoparticles supported on titanium iron nitride nanotubes

prepared as a superior electrocatalysts for methanol

electrooxidation. Int J Hydrogen Energy 2018;43:9777e86.

[44] Bian LY, Wang YH, Zang JB, Meng FW, Zhao YL. Microwave

synthesis and characterization of Pt nanoparticles supported

on undoped nanodiamond for methanol electrooxidation. Int

J Hydrogen Energy 2012;37:1220e5.

[45] Huang Y, Cai J, Guo Y. Roles of Pb and MnOx in PtPb/MnOx-

CNTs catalyst for methanol electro-oxidation. Int J Hydrogen

Energy 2012;37:1263e71.

[46] Raoof JB, Rashid-Nadimi S, Ojani R. Parametric study on

electrochemical deposition of hair shaped PtRu as methanol

oxidation catalyst. Int J Hydrogen Energy 2013;38:16062e70.

[47] Booth SG, Dryfe RAW. Assembly of nanoscale objects at the

liquid/liquid interface. J Phys Chem C 2015;119:23295e309.

[48] Kalyanikutty KP, Gautam UK, Rao CNR. Ultra-thin crystalline

films of CdSe and CuSe formed at the organic-aqueous

interface. J Nanosci Nanotechnol 2007;7:1916e22.

[49] Gründer Y, Fabian MD, Booth SG, Plana D, Fermin DJ, Hill PI,

et al. Solids at the liquideliquid interface: electrocatalysis

with pre-formed nanoparticles. Electrochim Acta

2013;110:809e15.

[50] Hoseini SJ, Rashidi M, Bahrami M. Platinum nanostructures

at the liquideliquid interface: catalytic reduction of p-

nitrophenol to p-aminophenol. J Mater Chem

2011;21:16170e6.

[51] Hoseini SJ, Mousavi N, Roushani M, Mosaddeghi L,

Bahrami M, Rashidi M. Thin film formation of platinum

nanoparticles at oilewater interface, using

organoplatinum(II) complexes, suitable for electro-oxidation

of methanol. Dalton Trans 2013;42:12364e9.

[52] Hoseini SJ, Barzegar Z, Bahrami M, Roushani M, Rashidi M.

Organometallic precursor route for the fabrication of PtSn

bimetallic nanotubes and Pt3Sn/reduced-graphene oxide

nanohybrid thin films at oilewater interface and study of

their electrocatalytic activity in methanol oxidation. J

Organomet Chem 2014;769:1e6.

[53] Hoseini SJ, Bahrami M, Dehghani M. Formation of snowmanlike

Pt/Pd thin film and Pt/Pd/reduced-graphene oxide thin

film at liquideliquid interface by use of organometallic

complexes, suitable for methanol fuel cells. RSC Adv

2014;4:13796e804.

[54] Hoseini SJ, Bahrami M, Roushani M. High CO tolerance of Pt/

Fe/Fe 2 O 3 nanohybrid thin film suitable for methanol

oxidation in alkaline medium. RSC Adv 2014;4:46992e9.

[55] Hoseini SJ, Bahrami M, Zanganeh M, Roushani M, Rashidi M.

Effect of metal alloying on morphology and catalytic activity

of platinum-based nanostructured thin films in methanol

oxidation reaction. RSC Adv 2016;6:45753e67.

[56] Rao CNR, Kalyanikutty KP. The liquid-liquid interface as a

medium to generate nanocrystalline films of inorganic

material. Acc Chem Res 2008;41:489e99.

[57] Rao CNR, Kulkarni GU, Agrawal VV, Gautam UK, Ghosh M,

Tumkurkar U. Use of the liquid-liquid interface for

generating ultrathin nanocrystalline films of metals,

chalcogenides, and oxides. J Colloid Interface Sci

2005;289:305e18.

[58] Hoseini SJ, Dehghani M, Nasrabadi H. Thin film formation of

Pd/reduced-graphene oxide and Pd nanoparticles at

oilewater interface, suitable as effective catalyst for

SuzukieMiyaura reaction in water. Catal Sci Technol

2014;4:1078e83.

[59] Hoseini SJ, Zarei A, Rafatbakhsh Iran H. Ligandless C-C

bond formation via SuzukieMiyaura reaction in micelles or

watereethanol solution using PdPtZn and PdZn

nanoparticle thin films. Appl Organomet Chem 2015;29:

489e94.

[60] Hoseini SJ, Habib Agahi B, Samadi Fard Z, Hashemi Fath R,

Bahrami M. Modification of palladiumecopper thin film by

reduced graphene oxide or platinum as catalyst for

SuzukieMiyaura reactions. Appl Organomet Chem

2017;31:e3607e14.

[61] Hoseini SJ, Aramesh N, Bahrami M. Effect of addition of iron

on morphology and catalytic activity of PdCu nanoalloy thin

film as catalyst in Sonogashira coupling reaction. Appl

Organomet Chem 2017;31:e3675e83.

[62] Ge P, Scanlon MD, Peljo P, Bian X, Vubrel H, O'Neill A, et al.

Hydrogen evolution across nano-Schottky junctions at

carbon supported MoS2 catalysts in biphasic liquid systems.

Chem Commun 2012;48:6484e6.

[63] Toth PS, Ramasse QM, Velicky M, Dryfe RAW.

Functionalization of graphene at the organic/water interface.

Chem Sci 2015;6:1316e23.

[64] Shi S, Gao D, Xia B, Liu P, Xue D. Enhanced hydrogen

evolution catalysis in MoS 2 nanosheets by incorporation of a

metal phase. J Mater Chem A 2015;3:24414e21.

[65] Das G, Biswal BP, Kandambeth S, Venkatesh V, Kaur G,

Addicoat M, et al. Chemical sensing in two dimensional

porous covalent organic nanosheets. Chem Sci

2015;6:3931e9.

[66] Sun H, You J, Yang M, Qu F. Synthesis of Pt/Fe 3 O 4 eCeO 2

catalyst with improved electrocatalytic activity for methanol

oxidation. J Power Sources 2012;205:231e4.

[67] Ge X, Wang R, Liu P, Ding Y. Platinum-decorated nanoporous

gold leaf for methanol electrooxidation. Chem Mater

2007;19:5827e9.





[68] Fu G, Yan X, Cui Z, Sun D, Xu L, Tang Y, et al. Catalytic

activities for methanol oxidation on ultrathin CuPt 3 wavy

nanowires with/without smart polymer. Chem Sci

2016;7:5414e20.

[69] Puddephatt RJ, Thomson MA. Binuclear alkynylplatinum(II)

complexes. J Organomet Chem 1982;238:231e4.

[70] Inorganic Syntheses New Jersey: Inorganic syntheses. Inc.

Ginsberg AP; 1990.

[71] Zhang L, Hu P, Zhao X, Tian R, Zou R, Xia D. Controllable

synthesis of core-shell Co@CoO nanocomposites with a

superior performance as an anode material for lithium-ion

batteries. J Mater Chem 2011;21:18279e83.

[72] Schliehe C, Juarez BH, Pelletier M, Jander S, Greshnykh D,

Nagel M, et al. Ultrathin PbS sheets by two-dimensional

oriented attachment. Science 2010;329:550e3.

[73] Toth PS, Rodgers ANJ, Rabiu AK, Ibanez D, Yang JX, Colina A,

et al. Interfacial doping of carbon nanotubes at the

polarisable organic/water interface: a liquid/liquid pseudocapacitor.

J Mater Chem A 2016;4:7365e71.

[74] Reymond F, Fermin D, Lee HJ, Girault HH. Interfacial doping

of carbon nanotubes at the polarisable organic/water

interface: a liquid/liquid pseudo-capacitor. Electrochim Acta

2000;45:2647e62.

[75] Young Chung D, Lee KJ, Sung YE. Methanol electro-oxidation

on Pt surface: revisiting the cyclic voltammetry

interpretation. J Phys Chem C 2016;120:9028e35.

[76] Iwasita T, Xia XH, Liess HD, Vielstich W. Electrocatalysis of

organic oxidations: influence of water adsorption on the rate

of reaction. J Phys Chem B 1997;101:7542e7.

[77] Liao F, Benedict Lo TW, Tsang SCE. Recent developments in

palladium-based bimetallic catalysts. Chem Cat Chem

2015;7:1998e2014.

[78] Kwak DH, Lee YW, Lee KH, Park AR, Moon JS, Park KW. Onestep

synthesis of hexapod Pt nanoparticles deposited on

carbon black for improved methanol electrooxidation. Int J

Electrochem Sci 2013;8:5102e7.

[79] Park JY. Current trends of surface science and catalysis. New

York Heidelberg, London: Springer; 2014.

[80] Lupan O, Chow L, Chai G, Heinrich H. Fabrication and

characterization of ZneZnO coreeshell microspheres from

nanorods. Chem Phys Lett 2008;465:249e53.

[81] Maiyalagan T, Alaje TO, Scott K. Highly stable PteRu

nanoparticles supported on three-dimensional cubic ordered

mesoporous carbon (PteRu/CMK-8) as promising

electrocatalysts for methanol oxidation. J Phys Chem C

2012;116:2630e8.

[82] Kannan R, Kim AR. Enhanced electrooxidation of methanol,

ethylene glycol, glycerol, and xylitol over a polypyrrole/

manganese oxyhydroxide/palladium nanocomposite

electrode. J Appl Electrochem 2014;44:893e902.

[83] WangHJ,YuH,PengF,LvP.Methanolelectrocatalytic

oxidation on highly dispersed Pt/sulfonated-carbon

nanotubes catalysts. Electrochem Commun 2006;8:

499e504.

[84] Che GL, Lakshmi BB, Martin CR, Fisher ER. Metalnanocluster-filled

carbon nanotubes: catalytic properties

and possible applications in electrochemical energy storage

and production. Langmuir 1999;15:750e8.

[85] Ghanbari N, Hoseini SJ, Bahrami M. Ultrasonic assisted

synthesis of palladium-nickel/iron oxide core-shell

nanoalloys as effective catalyst for Suzuki-Miyaura and p-

nitrophenol reduction reaction. Ultrason Sonochem

2017;39:467e77.

[86] Arico AS, Antonucci V, Giordano N. Methanol oxidation on

carbon- supported platinum- tin electrodes in sulfuric acid. J

Power Sources 1994;50:295e309.

[87] Li L, Xing Y. Methanol electro-oxidation on Pt-Ru alloy

nanoparticles supported on carbon nanotubes. Energies

2009;2:789e804.

[88] Villar TE, Rabockai T. Electrochemical oxidation of methanol

on platinum electrodes modified by tin atoms deposited at

underpotentials. J Braz Chem Soc 1991:86e8.

[89] Jiang J, Kucernak A. Electrooxidation of small organic

molecules on mesoporous precious metal catalysts. II: CO

and methanol on platinumeruthenium alloy. J Electroanal

Chem 2003;543:187e99.

[90] Jiang J, Kucernak A. Electrooxidation of small organic

molecules on mesoporous precious metal catalysts I: CO

and methanol on platinum. J Electroanal Chem 2002;533:

153e65.

[91] Falcao DS, Silva RA, Rangel CM, Pinto AMFR. Performance of

an active micro direct methanol fuel cell using reduced

catalyst loading MEAs. Energies 2017;10:1683e91.

[92] Huang H, Hu X, Zhang J, Su N, Cheng JX. Facile fabrication of

platinum cobalt alloy nanoparticles with enhanced

electrocatalytic activity for a methanol oxidation reaction.

Nat Sci Rep 2017;7:1e9.

[93] Lu Y, Reddy RG. Effect of flow fields on the performance of

micro-direct methanol fuel cells. Int J Hydrogen Energy

2011;36:822e9.

[94] Ma Y, Wang R, Wang H, Liao S, Key J, Linkov V, et al. The

effect of PtRuIr nanoparticle crystallinity in electrocatalytic

methanol oxidation. Materials 2013;6:1621e31.

[95] Liu YT, Yuan QB, Duan DH, Zhang ZL, Hao XG, Wei GQ, et al.

Electrochemical activity and stability of core-shell Fe 2 O 3 /Pt

nanoparticles for methanol oxidation. J Power Sources

2013;243:622e9.

[96] Liang R, Hu A, Persic J, Zhou YN. Palladium nanoparticles

loaded on carbon modified TiO2 nanobelts for enhanced

methanol electrooxidation. Nano-Micro Lett 2013;5:202e12.




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