Dimensionality Control of Carbon Support

Effect on Oxygen Reduction Activity of Non-

Precious Catalysts Meng-Hsiu Tu (杜孟修) and Ru-Shi Liu* (劉如熹)

Department of Chemistry, National Taiwan University, Taipei 106, Taiwan

Abstract

In recent decades, most scientific activity in the search for outstanding catalysts has been driven primarily by the demands of fuel cells. Non-precious metal nitrides

are possible candidates due to their low cost and acceptable catalytic activity, comparable to that of Pt in the oxygen reduction reaction (ORR). Herein, two iron nitride

(FeCN)-based catalysts using the zero-dimensional Black pearl 2000 and two-dimensional graphene as supporting materials were prepared by impregnation to explore the

dimensionality control of carbon support effect on ORR. It was found that lower hydrogen peroxide yield and approximately 4-electron transportation were observed for

both catalysts. It was anticipated that the as-prepared FeCN/C are potential catalyst for fuel cells under acidic condition. However, the ORR activity of the Black pearl

2000-supported FeCN catalyst recorded at 0.6 V was around eight times higher than that of graphene-supported FeCN catalyst. It was ascribed to the different dimension of

the carbon was selected as the supporting material. The possible mechanism for the dimensionality of carbon support effect on the ORR of FeCN-based catalysts was

further proposed in the present study.

Acknowledgments

Financial supports from National Science Council of Taiwan

(NSC 97-2113-M-002-012-MY3) and Industrial Technology

Research Institute are gratefully acknowledged.

C. W. Tsai, M. H. Tu, C. J. Chen, T. F. Hung, R. S. Liu,* W. R. Liu, M. Y. Lo, Y. M. Peng, L. Zhang, J. J. Zhang,

D. S. Shy and X. K. Xing, RSC Adv., 1, 1349-1357 (2011). Conclusions

In summary, a series of FeCN/C electrocatalysts were synthesized by varying the pyrolysis temperature and dimension of carbon support from 500℃ to 1000℃ under NH3 atmosphere. It was

found that their crystal structure and particle size of the FeCN nanoparticles were varied with the pyrolysis temperature and dimension of carbon support. The particle size of FeCN from 10 to

30 nm and less than 10 nm using 2D NG and 0D NBP carbon support with temperature between 500 and 900℃, respectively. Both two series heat treatment at 700℃ exhibited higher catalytic

activity than 800℃, even 800℃ had more percentages of graphitic nitrogen. Moreover, high activity of ORR and tolerance of methanol with particle size less than 10 nm of FeCN using 0D BP

carbon support with temperature at 700℃ are obtained .Consequently, it was concluded that the dimension of carbon support effect particle size of FeCN nano-particles was a predominant

factor for ORR catalysis.

Synthesis Strategy

X-ray Powder Diffraction Mechanism

Nitrogen Analysis

Electrochemical Properties

X-ray Absorption Spectroscopy

Transmission Electron Microscopy Images

H2O2 Yield %

Graphene Oxide (2D) Black pearl 2000 (0D)

Tem

per

atu

re

Tem

per

atu

re

Decreasing of particle size

10 nm

30 nm 10 nm

< 10 nm

NG NBP

Heat treatment

Low NH3 activity High

Fe(Phen)32+ Fe2N FeN0.056

Publication

N-doped graphene; NG (2D) N-doped BP; NBP (0D)

10 20 30 40 50 60

1000oC

900oC

800oC

700oC

600oC

N

orm

aliz

ed i

nte

nsi

ty (

a.u

.)

2 (degree)

500oC

Fe2N FeN

0.056

10 20 30 40 50 60

Norm

aliz

ed i

nte

nsi

ty (

a.u

.)

2 (degree)

1000oC

900oC

800oC

700oC

600oC

500oC

Fe2N FeN

0.056

• 2 NH3(g) → N2(g) + 3 H2(g)

• 2 Fe(s) + 2 NH3(g) → 2 Fe2N(s) + 3 H2(g)

• Fe2N (700 ℃) → FeN0.056 (1000 ℃) + x N2

N-doped Graphene; NG (0 D) N-doped BP; NBP (0 D)

7100 7110 7120 7130 7140 7150 7160

7110 7115 7120

Norm

ali

zed

ab

sorb

an

ce

(a.u

.)

Energy (eV)

Fe

Fe(II)

500oC

600oC

700oC

800oC

900oC

1000oC

7100 7110 7120 7130 7140 7150 7160

7110 7115 7120

Norm

ali

zed

ab

sorb

an

ce

(a.u

.)

Energy (eV)

Fe

Fe(II)

500oC

600oC

700oC

800oC

900oC

1000oC

Fe K-edge 7112 eV 1s →4p

Niwa et al., J. Power Sources, 2009, 187, 93.

0.0 0.2 0.4 0.6 0.80

20

40

60

80

100

NBP700

NG700

Potential (V vs. RHE)

H2O

2 y

ield

(%

)

2.0

2.5

3.0

3.5

4.0

Ele

ctr

on

nu

mb

er

Sample Temp. ℃ H2O2%* n*

NG 500 14.68 3.71

600 13.68 3.73

700 2.03 3.96

800 2.23 3.96

900 6.18 3.88

1000 21.37 3.57

NBP 500 2.45 3.95

600 2.03 3.96

700 1.98 3.96

800 2.77 3.94

900 5.23 3.90

1000 11.68 3.77

* Calculate at 0.1V

n: Electron number

Ir: Ring current (H2O2 oxidation)

Id: Disk current (ORR)

N: Collection efficiency

Fe2N

Fe2N

FeN0.056

FeN0.056

NG NBP

700℃

800℃

0.0 0.2 0.4 0.6 0.8 1.0-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

Cu

rren

t d

ensi

ty (

mA

cm

-2)

Potential (V vs. RHE)

500C

600C

700C

800C

900C

1000C

0.0 0.2 0.4 0.6 0.8 1.0-0.2

-0.1

0.0

0.1

0.2

Cu

rren

t d

ensi

ty (

mA

cm

-2)

Potential (V vs. RHE)

500C

600C

700C

800C

900C

1000C

Oxidation

Reduction

N2-saturated condition in 0.5 M sulfuric acid

N-doped graphene; NG (2D) N-doped BP; NBP (0D)

Oxidation

Reduction

394 396 398 400 402 404

Inte

nsi

ty (

a.u

.)

Binding energy (eV)

Raw

Sum

Background

N-pyridinic

N-Metal

N-pyrrolic

N-Graphite

NG700

SampleGraphite-like N %

NG NBP

500 14.8 16.9

600 20.6 16.7

700 21.8 17.2

800 24.0 18.8

900 16.5 -

1000 12.3 -

Fe-N

More graphite-like N

Ozaki et al., J. Phys. Chem. C, 2008, 112, 14706.

0.0 0.2 0.4 0.6 0.8 1.0 1.2-6

-4

-2

0

0.00

0.05

0.10

0.15

0.20

Dis

k c

urr

ent

den

sity

(m

A c

m-2

)

Potential (V vs. RHE)

500C

600C

700C

800C

900C

1000C

Rin

g c

urr

ent

den

sity

(m

A c

m-2

)

500C

600C

700C

800C

900C

1000C

0.0 0.2 0.4 0.6 0.8 1.0 1.2-2.0

-1.5

-1.0

-0.5

0.00.00

0.02

0.04

0.06

0.08

Dis

k c

urr

ent

den

sity

(m

A c

m-2

)

Potential (V vs. RHE)

500C

600C

700C

800C

900C

1000C

Rin

g c

urr

ent

den

sity

(m

A c

m-2

)

500C

600C

700C

800C

900C

1000C

O2-saturated condition in 0.5 M sulfuric acid

Best temperature:

700℃Catalytic phase:

Fe2(N,C)

More graphite-like N

ORR activity:

0D > 2D

N-doped graphene; NG (2D) N-doped BP; NBP (0D)