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
퐽
=
1
퐽
퐾
+
1
퐽
퐿
=
1
퐽
퐾
+
1
퐵휔
1
/
2
(
1
)
퐵
=
0
.
62
푛퐹
퐶
0
퐷
0
2
/
3
훾
1
/
6
(
2
)
퐽
퐾
=
푛퐹퐾
퐶
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
퐻
2
푂
2
(
%
)
=
100
2
퐼
푟
푁
⁄
퐼
푑
+
퐼
푟
푁
⁄
(
4
)
S
21
푛
=
4
×
퐼
푑
퐼
푑
+
퐼
푟
푁
⁄
(
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
.