Supporting Information

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Supporting Information

Platinum-Copper Bimetallic Nanodendritic Electrocatalyst on TiO

₂

-based Support for Methanol Oxidation in Alkaline Fuel Cells

Hau Quoc Pham,

^1,2

and Tai Thien Huynh

^3,*

1

Future Materials & Devices Lab., Institute of Fundamental and Applied Sciences, Duy Tan

University, Ho Chi Minh City, 700000, Viet Nam

2

The Faculty of Environmental and Chemical Engineering, Duy Tan University, Da Nang,

550000, Viet Nam

3

Ho Chi Minh City University of Natural Resources and Environment (HCMUNRE), Ho Chi

Minh City, 700000, Viet Nam

*Corresponding author. E-mail: [email protected]

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EXPERIMENTAL DETAILS

Preparation for the mesoporous Ti

0.7

W

0.3

O

2

nanosupport

The mesoporous Ti

0.7

W

0.3

O

2

nanosupport was prepared via a calcination-free solvothermal

process

¹

. Firstly, 0.238 mg of tungsten (VI) chloride (WCl

6

, 99.9%, Sigma-Aldrich, USA) was

dissolved into 50 mL of ethanol absolute (C

2

H

5

OH, 99.9%, Merck, Belgium) for 30 min. Next,

0.155 mL titanium (IV) chloride (TiCl

4

, 99.5%, Aladdin, China) was added to the solution and

then was dropped into a Teflon-lined autoclave and then transferred to an oven in which the

reaction proceeded at 200

^o

C for 10 h. Next, the as-prepared suspension was washed with

acetone (CH

3

COCH

3

, 99.9%, Merck, Belgium) and purified water, and the resulting product

was dried at 80

^o

C for analysis.

Material characterization

The X-ray diffraction (XRD) pattern of the catalysts was collected on a D2 PHASER (Bruker,

Germany) equipped with a Cu K



radiation source in the 2 range of 20

^o

– 80

^o

. Transmission

electron microscopy (TEM) images were recorded on a JOEL-JEM 2100F instrument at 200 kV

to determine the morphology of the electrocatalysts. The composition and distribution of

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energy-dispersive X-ray spectroscopy (EDX) mapping on a JEOF-JSM 6500F device with an

acceleration voltage of 10 kV. The X-ray photoelectron spectroscopy (XPS) was obtained on a

Kratos AXIS Nova (Shimadzu, Japan) with an Al K



source.

Electrochemical properties

The electrochemical properties of the catalysts were tested on a CHI 660C Electrochemical

Workstation (CH Instruments Inc., USA) equipped with a three-electrode electrochemical cell,

including a glassy carbon electrode as a working electrode, a Pt wire, and Hg/HgO electrode

as a count and reference electrodes, respectively. For preparing the electrocatalyst ink, 1.7 mg

of catalysts was dispersed in a mixture of 20 µL of Nafion (5%, Sigma-Aldrich, USA) and 180

µL of absolute ethanol (99.9%, Merck, Belgium) and then ultrasonicated of 30 min to form a

homogeneous ink. Before coating catalyst ink, the surface of the working electrode was

polished with 0.5 µm Al

2

O

3

(BAS) and cleaned with absolute ethanol and purged water. To get

an active working electrode, 2.5 µL of the catalyst inks was drop-cast onto the surface of the

working electrode and dried naturally, then scanned in N

2

-saturated 1.0 M KOH at a scan rate

of 50 mV s

^-1

for 100 cycles. The electrochemically surface area (ECSA) of different catalysts

was calculated based on hydrogen adsorption/desorption region from CV (cyclic voltammetry)

(4)

curves in N

2

-purged 1 M KOH solution at a scan rate of 25 mV s

^-1

. The MOR performance of

the catalysts was determined by CV test in N

2

-saturated 1.0 M KOH + 1.0 M CH

3

OH solution

at a scan rate of 25 mV s

^-1

. Linear sweep voltammetry (LSV) was performed at a scan rate of

1 mV s

^-1

in N

2

-saturated 1.0 M KOH + 1.0 M CH

3

OH. Additionally, the accelerated durability

test (ADT) was performed in N

2

-purged 1.0 M KOH + 1.0 M CH

3

OH solution at a scan rate of

50 mV s

^-1

with 5000 cycling tests. Chronoamperometry (CA) tests were carried out at 0.5 V for

3600 s in N

2

-saturated 1.0 M KOH + 1.0 M CH

3

OH solutions. The commercial Pt NPs/C (E-

TEK) was used as a reference catalyst for comparison. All values of potentials were reported

vs. the reversible hydrogen electrode using the Nernst equation.

RESULTS AND DISCUSSION

As shown in Figure S1 (a), the Ti

0.7

W

0.3

O

2

nanosupport exhibited the anatase-TiO

2

structures

(JCPDS 84-1286) with the typical diffraction peaks at 25.3

^o

; 38.1

^o

; 47.5

^o

; 54.4

^o

and 62.8

^o

corresponding to (101); (004); (200); (105) and (204) crystal facets. No typical diffraction peaks

of tungsten oxide (JCPDS 020-1324) or the segregation of W and TiO

2

were detected in the

XRD profile. The diffraction peak of the (101) crystal facet was negatively shifted compared to

the undoped TiO

2

and the standard XRD pattern of anatase-TiO

2

structure (JCPDS 84-1286),

(5)

suggesting incorporation of W into the anatase-TiO

2

structure. In addition, the XRF result

indicated that the proportion of Ti and W was 70.67 and 29.33, respectively, which is close to

the theoretical ratio (Ti: W = 70: 30) (Figure S1(c)). The elemental mapping images of the

Ti

0.7

W

0.3

O

2

nanosupport are shown in Fig. S3d-e and indicate the uniform distribution of the

elements in the as-obtained catalyst support.

(6)

Figure S1. (a) XRD profile in the 2 range of 20

^o

– 80

^o

at a step size of 0.02

^o

; (b) TEM image,

(c) XRF spectrum, and (d-f) elemental mapping of the mesoporous Ti

0.7

W

0.3

O

2

nanosupport.

Figure S2 shows the N

2

adsorption/desorption isotherms and pore size distribution of the as-

obtained Ti

0.7

W

0.3

O

2

nanosupport. As a result, the Ti

0.7

W

0.3

O

2

catalyst support demonstrated

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the hysteresis loops of the type IV isotherm, suggesting that the as-synthesized nanosupport

are the mesoporous materials with a pore size of around 3 nm. The surface area of the

mesoporous Ti

0.7

W

0.3

O

2

supports was 201.48 m

²

g

^-1

, which is comparable to the surface area

of the carbon black (~230 m

²

g

^-1

). Additionally, the electrical conductivity of the Ti

0.7

W

0.3

O

2

nanosupport was around 2.20x10

^-2

S cm

^-1

that was measured by a four-point probe technique.

Figure S2. N

2

adsorption-desorption isotherm of the mesoporous Ti

0.7

W

0.3

O

2

nanosupport.

Figure S3 shows the X-ray photoelectron spectroscopy (XPS) results of the mesoporous

Ti

0.7

W

0.3

O

2

nanosupport. As shown in Figure S3(a), the Ti 2p spectrum of the Ti

0.7

W

0.3

O

2

nanosupport was deconvoluted to doublets peaks at 464.5 for Ti 2p

1/2

and 458.75 eV for Ti

2p

3/2

of Ti(4) states. These peaks were shifted to slightly higher binding energies than those of

the undoped TiO

2

(464.0 for Ti 2p

1/2

and 458.4 eV for Ti 2p

3/2

)

²

. In addition, the W 4f spectrum

(8)

of the Ti

0.7

W

0.3

O

2

nanosupport was deconvoluted into components of W(6) and W(4) states

(Figure S3(b)), suggesting the co-existence of W(6) and W(4) in the mesoporous Ti

0.7

W

0.3

O

2

nanosupport. Furthermore, the W 4f

5/2

and W 4f

7/2

peaks of the anatase Ti

0.7

W

0.3

O

2

nanosupport were observed at 37.25 and 35.15 eV, respectively, and were lower than that of

pure WO

3

(37.4 eV for W 4f

5/2

and 35.3 eV for W 4f

7/2

)

^3,4

. These results indicate the successful

incorporation of tungsten into the anatase-TiO

2

structures.

Figure S3. High-resolution of (a) Ti 2p and (b) W 4f spectrums of the Ti

0.7

W

0.3

O

2

nanosupport.

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Figure S4. XRD pattern of the commercial 20 wt% Pt/C electrocatalysts at a step size of 0.02

^o

.

Figure S5. EDX spectroscopy of the as-obtained PtCu NDs/Ti

0.7

W

0.3

O

2

electrocatalysts.

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Figure S6. (a-d) 2000-cycle ADT of investigated electrocatalysts in N

2

-saturated 1.0 M KOH

aqueous solution at a scan rate of 25 mV s

^-1

.

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(12)

Figure S7. (a, c, e, g) CV curves at different scan rate (5, 10, 25, 50, 75, 100 mV s

^-1

) and (b, d,

f, h) The plots of anodic peak current density vs. the square root of a scan rate of the different

electrocatalysts in N

2

-saturated 1.0 M KOH + 1.0 M CH

3

OH solution.

(13)

(14)

Figure S8. (a, c, e, g) CV curves at a scan rate of 25 mV s

^-1

with different methanol

concentrations (0.1; 0.3; 0.5; 0.7 and 1.0 M) and (b, d, f, h) The logarithm of the anodic peak

current density vs. the logarithm of methanol concentration of different catalysts.

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Table S1. Electrocatalytic performance of various MOR catalysts in alkaline electrolytes.

Electrocatalysts Electrolyte

ECSA

^(a)

(m

²

g

^-1

)

Current density

^(b)

(mA cm

^-2

)

Refs.

Pt

3

Cu NDs/Ti

0.7

W

0.3

O

2

1.0 M KOH + 1.0 M CH

3

OH 45.81 36.49 This work Pt NDs/Ti

0.7

W

0.3

O

2

1.0 M KOH + 1.0 M CH

3

OH 43.58 28.92 This work

Pt

3

Cu NDs/TiO

2

1.0 M KOH + 1.0 M CH

3

OH 32.41 19.41 This work

Pt NPs/C 1.0 M KOH + 1.0 M CH

3

OH 54.23 25.18 This work

RGOs/Pt-Pd HNSs

1.0 M NaOH + 1.0 M CH

3

OH

18.5 28.20

⁵

Au-GQDs@AgPt Yolk- shell

1.0 M NaOH + 0.5 M CH

3

OH

241.32 33.20

⁶

Au-GQDs@Pt

1.0 M NaOH + 0.5 M

CH

3

OH

103.22 15.68

⁶

Pd-Co porous array (PA) 0.5 M KOH + 1.0 M CH

3

OH – 16.90

⁷

Pt/WO

3

-NaTaO

3

W:Ta = 5:1

0.5 M KOH + 1.0 M CH

3

OH 13.70 28.00

⁸

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Pt/NaTaO

3

0.5 M KOH + 1.0 M CH

3

OH 14.20 30.00

⁸

NiFe-LDH/Pt 0.5 M KOH + 1.0 M CH

3

OH – 18.00

⁹

MgAl-LDH/Pt 0.5 M KOH + 1.0 M CH

3

OH – 12.00

⁹

Au@N-CQDs@Pd 20 1.0 M KOH + 1.0 M CH

3

OH 90.54 25.08

¹⁰

Pd

67

Au

33

0.5 M KOH + 2.0 M CH

3

OH – 5.34

¹¹

Commerical Pt/C 1.0 M KOH + 1.0 M CH

3

OH 35.10 15.28

¹²

Au@Pd/rGO 0.5 M KOH + 1.0 M CH

3

OH 39.01 28.48

¹³

PtCo bowl-like array (BA) 1.0 M KOH + 0.5 M CH

3

OH – 20.00

¹⁴

(a)

Calculation from CV curves in N

2

-saturated 1.0 M KOH aqueous solution at a scan rate of 25 mV s

^-1

(b)

Calculation from CV curves in N

2

-saturated 1.0 M KOH + 1.0 M CH

3

OH at a scan rate of 25

mV s

^-1

.

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Table S2. A summary of the electrocatalytic activity of catalysts before and after CO purging in

1.0 M KOH + 1.0 M CH

3

OH aqueous solution at a scan rate of 25 mV s

^-1

.

Methanol electro-oxidation

Before CO

^(a)

After CO

^(b)

Catalysts

Onset

potential V vs.

RHE

Current

density mA cm

^-2

I

f

/I

b

Onset

potential V vs.

RHE

Current

density mA cm

^-2

I

f

/I

b

Degradatio

n %

Pt

3

Cu NDs/Ti

0.7

W

0.3

O

2

0.28 36.49 6.05 0.29 34.12 5.98 6.49 Pt NDs/Ti

0.7

W

0.3

O

2

0.30 28.92 2.86 0.32 26.19 2.76 9.44

Pt

3

Cu NDs/TiO

2

0.35 19.41 3.35 0.37 17.92 3.27 7.68

Pt NPs/C 0.43 25.18 1.66 0.50 17.22 1.09 31.61

(a)

Calculation form CV curves before CO purging in 1.0 M KOH + 1.0 M CH

3

OH aqueous solution at a scan rate of 25 mV s

^-1

(b)

Calculation from CV curves after CO purging in 1.0 M KOH + 1.0 M CH

3

OH aqueous solution

at a scan rate of 25 mV s

^-1

.

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References

(1) Pham, H. Q.; Huynh, T. T.; Bach, L. G.; Ho, V. T. T. Synthesis and Characterization the Multifunctional Nanostructures Ti

x

W

1-x

O

2

(x = 0.5; 0.6; 0.7; 0.8) Supports as Robust Non- Carbon Support for Pt Nanoparticles for Direct Ethanol Fuel Cells. Int. J. Hydrog. Energy 2020, DOI: 10.1016/j.ijhydene.2020.03.066, In Press, Corrected Proof.

(2) Belver, C.; Han, C.; Rodriguez, J. J.; Dionysiou, D. D. Innovative W-Doped Titanium Dioxide Anchored on Clay for Photocatalytic Removal of Atrazine. Catal. Today 2017, 280 , 21-28.

(3) Liu, S.; Guo, E.; Yin, L., Tailored Visible-Light Driven Anatase TiO

2

Photocatalysts Based on Controllable Metal Ion Doping and Odered Mesoporous Structure. J. Mater. Chem. 2012, 22 , 5031-5041.

(4) Gao, B.; Ma, Y.; Cao, Y.; Yang, W.; Yao, J. Great Enhancement of Photocatalytic Activity of Nitrogen-Doped Titania by Coupling with Tungsten Oxide. J. Phys. Chem. B 2006, 110 , 14391-14397.

(5) Li, S.-S.; Yu, J.; Hu, Y.-Y.; Wang, A.-J.; Chen, J.-R.; Feng, J.-J. Simple Synthesis of Hollow Pt-Pd Nanospheres Supported on Reduced Graphene Oxide for Enhanced Methanol Electrooxidation. J. Power Sources 2014, 254 , 119-125.

(6) Yang, J.; Shao, T.; Luo, C.; Li, J.; He, S.; Meng, B.; Zhang, Q.; Zhang, D.; Xue, Z.;

Zhou, X. Simple Synthesis of the Au-GQDs@AgPt Yolk-Shell Nanostructures Electrocatalyst for Enhancing the Methanol Oxidation. J. Alloys Compd. 2020, 834 , 155056.

(7) Zhao, J.; Zhou, Y.; Qin, L.; Zhao, M. Synthesis of Pt-Co Micro/Nanoporous Array with High

Activity for Methanol Electrooxidation. Mater. Lett. 2018, 216 , 166-169.

(19)

(8) Bi, X.; Bai, P.; Lv, J.; Yang, T.; Chai, Z.; Wang, X.; Wang, C. Regulating Effect of Heterojunctions on Electrocatalytic Oxidation of Methanol for Pt/WO

3

-NaTaO

3

Catalysts. Dalton Trans. 2019, 48 , 3061.

(9) Li, L.; Yang, Y.; Wang, Y.; Liang, M.; Huang, Y. Electrochemical Activity of Layered Double Hydroxides Supported Nano Pt Clusters toward Methanol Oxidation Reaction in Alkaline Solutions. J. Mater. Res. Technol. 2020, 9 , 5463-5473.

(10) Luo, C.; Yang, J.; Li, J.; He, S.; Meng, B.; Shao, T.; Zhang, Q.; Zhang, D.; Zhou, X., Green Synthesis of Au@N-CQDs@Pd Core-Shell Nanoparticles for Enhanced Methanol Electrooxidation. J. Electroanal. Chem. 2020, 873 , 114423.

(11) Dobrovetska, O.; Saldan, I.; Orovčik, L.; Karlsson, D.; Sahlberg, M. H.; Semenyuk, Y.;

Pereviznyk, O.; Reshetnyak, O.; Kuntyi, O.; Mertsalo, I.; Serkiz, R.; Stelmakhovych, B.

Electrocatalytic Activity of Pd-Au Nanoalloys During Methanol Oxidation Reaction. Int. J.

Hydrog. Energy 2020, 45 , 4444-4456.

(12) Wu, F.; Eid, K.; Abdullah, A. M.; Niu, W.; Wang, C.; Lan, Y.; Elzatahry, A. A.; Xu, G.

Unveiling One-Pot Template-Free Fabrication of Exquisite Multidimensional PtNi Multicube Nanoarchitectonics for the Efficient Electrochemical Oxidation of Ethanol and Methanol with a Great Tolerance for CO. ACS Appl. Mater. Interfaces 2020, 12 , 31309-31318.

(13) He, L.-L.; Song, P.; Feng, J.-J.; Fang, R.; Yu, D.-X.; Chen, J.-R.; Wang, A.-J. Porous

Dandelion-Like Gold@Palladium Core-Shell Nanocrystals In-Situ Growth on Reduced

Graphene Oxide with Improved Electrocatalytic Properties. Electrochim. Acta 2016, 200 , 204-

213.

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