of 34
S
1
Atomic H
-
Induced
Mo
2
C
Hybrid as an Active and Stable
Bifunctional Electrocatalyst
Supporting Information
Xiujun Fan,
*
Yuanyue Liu,
¶ς
Zhiwei Peng,
Z
henh
ua
Zhang,
#
Haiqing Zhou
,
Xianming
Zhang,
Boris I. Yakobson,
§
William A. Goddard III,
Xia Guo,
*
Robert H. Hauge
1
and
James M. Tour
§
*
Institute of Crystalline Materials, Shanxi University, Tai
y
uan, Shanxi 030006, China
College of Electronic Information and Control Engineering
,
#
Institu
t
e of Microstructures and
Properties of Advanced Materials
,
Beijing University of Technology, Beijing 100124, China
Department of Ch
emistry,
NanoCarbon Center,
§
Department of Materials Science and
NanoEngineering, Rice University, Houston, Texas 77005, United States
Materials and Process Simulation Center,
ς
The
Resnick Sustainability Institute, California
Institute of Technology, Pasadena, CA 91125, USA
E
-
mail
:
tour@rice.edu
,
guo@bjut.edu.cn
,
fxiu
jun@gmail.com
1
Deceased March 17, 2016
S
2
Figure S
1
.
SEM images of VA
-
GNR.
S
3
Figure S
2
.
TEM images of VA
-
GNR showing that with atomic hydrogen treatment, VA
-
CNTs
were unzipped and transformed into VA
-
GNR.
S
4
Figure S3.
Photograph of Mo@
Si
(left) and
Mo@VA
-
GNR (right)
.
S
5
Figure S
4
. SEM images of
Mo
2
C
-
GNR h
ybrid
grown
with various growth time
(a,
b)
for
3 h
and
(
c
,
d
)
for
9 h
.
S
6
Figure S
5
.
SEM image of Mo
2
C
on Si
.
S
7
500
1000
1500
2000
2500
3000
G
Intensity (a.u.)
Raman shift
(
cm
-1
)
294
223
342
779
931
D
1340
1577
2660
2D
D+G
2943
Mo@VA-GNR
a
10
20
30
40
50
60
(101)
(112)
(042)
(171)
(002)
(220)
(210)
(060)
(111)
(020)
(141)
:
Carbon
:
MoO
3
:
Mo
Intensity (a.u.)
2
/
(
o
)
(002)
Mo@VA-GNR
b
Figure S
6
.
(a)
Raman
spectra of VA
-
GNR with molybdenum deposited on the top layers.
Mo@VA
-
GNR has characteristic peaks at 223, 294, 342, 779, and 931 cm
1
that can be assigned
to MoO
3
.
(b)
XRD patterns of
Mo@VA
-
GNR.
S
8
294
292
290
288
286
284
282
280
Intensity (a.u.)
(a)
284.5 eV
C1s peak
Mo@VA-GNR
Mo
2
C-GNR

Binding energy (eV)
538
536
534
532
530
528
Intensity (a.u.)
(b)
Mo
2
C
-GNR
O1s
Binding energy (eV)
Mo@VA-GNR
Figure
S
7
.
XPS
spectrum
of Mo@VA
-
GNR and Mo
2
C
-
GNR hybrid for (
a
) C
1s and (
b
)
O
1s.
The O
1s spectrum (
b
) for the Mo@VA
-
GNR contained a c
haracteristic signal at 530.4 eV
that is
assigned to O
2
-
in MoO
3
.
1
For Mo
2
C
-
GNR, the O
1s peak becomes prominent and shifts to 532.8
eV, which can be attributed to physisorbed
O
.
S
9
0
2
4
6
8
10
Intensity (au)
O
C
Mo
Mo
Mo@VA-GNR
Mo
2
C-GNR
O
C
Energy (KeV)
Figure S
8.
The results of qualitative EDS of (
black
curve)
Mo@VA
-
GNR
and (
red
curve)
Mo
2
C
-
GNR
.
S
10
Table
S1
.
Mo content determined by ICP
-
MS
and quantitative surface analysis by
EDS
.
Samples
Mo loading
(wt%)
Surface atomic concentration (at%)
C
O
Mo
Mo@VA
-
GNR
3
1
.5
21.0
5
0.6
2
8.4
Mo
2
C
-
GNR
3
1
.3
6
6.3
3
.5
30
.2
S
11
Figure S
9
.
TEM images of
Mo
2
C
.
S
12
Figure S
10
.
The TEM images of Mo
2
C
-
GNR
grown with various growth tim
e
,
(a
-
b) for 3 h
and
(c
-
d) for 9 h.
S
13
10
20
30
40
50
60
9h
6h
2
/
(
o
)
Intensity (a.u.)
: Carbon
: Mo
2
C
: MoO
3
(002)
(100)
(002)
(101)
(101)
(004)
(102)
3h
Figure S
1
1
.
XRD patterns
of
Mo
2
C
-
GNR
grown with
various growth time
, from 3 to 9 h
.
From
this data, it is confirmed that Mo
2
C was successfully synthesized on
GNRs
in the Mo
2
C
-
GNR
hybrid.
S
14
Figure S
1
2
.
(a) TEM,
(
b
) HAADF image of
Mo
2
C
-
GNR
prepared with atomic H treatment for 9
h
and
element maps of (
c
)
C
, (
d
)
Mo
, and (
e
)
O
.
S
15
0.0
0.2
0.4
0.6
0.8
1.0
0
500
1000
1500
2000
Amount absorbed
(
cm
3
g
-1
STP
)
Relative pressure (P/P
0
)
VA-GNR, S
BET
=936.4 m
2
g
-1
Mo
2
C-GNR, S
BET
=641.1 m
2
g
-1
Figure S
1
3
.
Nitrogen sorption
isotherms
of VA
-
GNR and Mo
2
C
-
GNR hybrid.
S
16
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-0.4
-0.2
0.0
0.2
0.4
O
2
j / mA cm
-2
Potential / V vs. RHE
(a)
Ar
0.4
0.6
0.8
1.0
1.2
-4.5
-3.0
-1.5
0.0
1.5
3.0
0.030
0.045
0.060
0.3
0.4
0.5
0.6
Pt/C
n = 4.0
(b)
j
(
mA cm
-2
)
225 rpm
400 rpm
625 rpm
900 rpm
1225 rpm
1600 rpm
E (V vs. RHE)
J
-1
(
mA
-1
cm
2
)
0.70 V
0.75 V
0.80 V
0.85 V
-1/2
(
rpm
-
1/2
)
Figure
S
1
4
.
(a) CV of Pt/C in Ar
-
(red) and
O
2
-
(black) saturated electrolyte
.
(b) LSVs of Pt
/C
in
O
2
-
saturated 0.1 M KOH at a scan rate of 5 mV s
-
1
at different RDE rotation rates (in rpm
)
.
Inset
reveals corresponding Koutecky
-
Levich plots (
J
-
1
v
s
rpm
-
1
-
2
) at different potentials.
S
17
0.2
0.4
0.6
0.8
1.0
-5
-4
-3
-2
-1
0
0.2
0.4
0.6
0.8
3.0
3.2
3.4
3.6
3.8
4.0
Disk
j / mA cm
-2
E / V vs RHE
a
Mo
2
C-GNR
Ring
b
Electron Transfer Number (n)
E / V vs RHE
0
10
20
30
40
Percentage of peroxide (%)
0.2
0.4
0.6
0.8
-5
-4
-3
-2
-1
0
0.2
0.4
0.6
0.8
3.6
3.8
4.0
Pt/C
j / mA cm
-2
E / V vs RHE
Disk
Ring
Electron Transfer Number (n)
E / V vs RHE
c
d
-4
-2
0
2
4
6
8
10
Percentage of peroxide (%)
Figure S1
5
. (
a,c
) Rotating ring disk electrode
(
RRDE
)
voltammograms of ORR on
Mo
2
C
-
GNR
and Pt/C
electrode
, respectively,
with a sweep rate of 5 mv s
-
1
at 1600 rpm
.
(b,d)
Percentage of
peroxide and the
electron transfer number (
n
) of
Mo
2
C
-
GNR and Pt/C
at different potentials
derived from the RRDE data.
S
18
0.2
0.4
0.6
0.8
1.0
-3
-2
-1
0
1
2
3
0.2
0.4
0.6
0.8
1.0
-3
-2
-1
0
1
2
3
0.02
0.03
0.04
0.05
0.06
0.07
0.4
0.6
0.8
1.0
1.2
0.02
0.03
0.04
0.05
0.06
0.07
0.4
0.6
0.8
1.0
1.2
a
0.5 M H
2
SO
4
Mo
2
C-GNR
n = 3.78
j / mA cm
-2
E / V vs RHE
225 rpm
400 rpm
625 rpm
900 rpm
1225 rpm
1600 rpm
2025 rpm
b
j / mA cm
-2
E / V vs RHE
225 rpm
400 rpm
625 rpm
900 rpm
1225 rpm
1600 rpm
2025 rpm
0.5 M H
2
SO
4
Pt/C
n = 3.96
0.60 V
0.55 V
0.50 V
0.45 V
j
-1
/ mA
-1
cm
2
-1/2
/ rpm
-
1/2
0.65 V
0.60 V
0.55 V
0.50 V
j
-1
/ mA
-1
cm
2
-1/2
/ rpm
-
1/2
Figure S
1
6
.
LSVs at
5
mV s
-
1
in the presence of oxygen with rotation speed
from
225
to 2
025
rpm in 0.5 M H
2
SO
4
for (a)
Mo
2
C
-
GNR
grown with 6 h and (b) Pt/C.
The i
nset
s in each panel
are
the
corresponding Koutecky
-
Levich plots (
J
-
1
v
s
rpm
-
1
/
2
) at different potentials.
S
19
0.4
0.6
0.8
1.0
-4
-3
-2
-1
0
1
2
3
0.4
0.6
0.8
1.0
-4
-3
-2
-1
0
1
2
3
0.02
0.03
0.04
0.05
0.06
0.07
0.4
0.6
0.8
1.0
0.02
0.03
0.04
0.05
0.06
0.07
0.4
0.6
0.8
1.0
1.2
3 h
n = 3.27
a
j / mA cm
-2
E / V vs RHE
225 rpm
400 rpm
625 rpm
900 rpm
1225 rpm
1600 rpm
2025 rpm
9 h
n = 2.64
b
j / mA cm
-2
E / V vs RHE
225 rpm
400 rpm
625 rpm
900 rpm
1225 rpm
1600 rpm
2025 rpm
0.75 V
0.70 V
0.65 V
0.60 V
j
-1
(
mA
-1
cm
2
)
-1/2
(
rpm
-
1/2
)
0.75 V
0.70 V
0.65 V
0.60 V
j
-1
(
mA
-1
cm
2
)
-1/2
(
rpm
-
1/2
)
Figure S
1
7
.
Rotating
-
disk
voltammograms of
Mo
2
C
-
GNR
grown with various time
in
O
2
-
saturated 0.1 M
KOH at a scan rate of 5 mV s
-
1
at different rotating speeds
,
(a)
3 h and
(b)
9 h
.
Insets are the corresponding Koutecky
-
Levich plots at different potentials.
S
20
ORR Activity Calculations
The working electrode was scanned cathodical
ly at a rate of 5 mV s
1
with varying rotating speed
from 225 to 2025 rpm. Koutecky
Levich plots (
J
1
vs
ω
1/2
) were analyzed at various electrode
potentials. The slopes of their best linear fit lines were used to calculate the number of electrons
transferred (
n
) on the basis
of the Koutecky
Levich eq 1
-
3
:
1
=
1
+
1
=
1
+
1
퐵휔
1
/
2
(
1
)
=
0
.
62
푛퐹
0
0
2
/
3
1
/
6
(
2
)
=
푛퐹퐾
0
(
3
)
where
J
is the measured current density,
J
k
and
J
L
are the kinetic
-
and diffusion
-
limiting current
densities,
ω
is the angular velocity,
n
is transferred electron number,
F
is the Faraday constant
(96 485 C mol
1
),
C
0
is the bulk concentration of O
2
(1.2 × 10
6
mol cm
3
),
and
ν
is the
kinetic
viscosity of the electrolyte (0.01 cm
2
s
1
for both 0.5 M H
2
SO
4
solution
and 0.1 M KOH
solution)
,
D
0
is the O
2
diffusion coefficient (1.9 × 10
5
cm
2
s
1
), and
k
is the electron
-
transfer rate
constant. The number of electrons transferred (
n
) and
J
k
can be obtained from the slope and
intercept of the Koutecky
Levich plots, respec
tively.
For the RRDE measurements, catalyst inks and electrodes were prepared by the same
method as
those of RDE. The disk electrode was scanned at a rate of 5 mV s
-
1
and the
ring potential was
kept constant at 0.5 V vs. Ag/AgCl. The H
2
O
2
eq
4
and
5
2
2
(
%
)
=
100
2
+
(
4
)
S
21
=
4
×
+
(
5
)
H
ere
,
I
d
is disk current,
I
r
is ring current and N = 0.36 is collection efficiency (N).
S
22
-0.3
-0.2
-0.1
0.0
0.1
-100
-80
-60
-40
-20
0
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
0.0
0.1
0.2
0.3
0.4
0.5 M H
2
SO
4
a
3 h
6 h
9 h
j / mA cm
-2
Potential / V vs RHE
0.5 M H
2
SO
4
b
3 h
6 h
9 h
Overpotential / V
Log j / mA cm
-2
93 mV dec
-1
65 mV dec
-1
84 mV dec
-1
Figure S
1
8
.
(a)
HER polarization curves and
(b)
the corresponding Tafel
plots of
Mo
2
C
-
GNR
grown with various growth time
.