1
Supporting Information
for
Reduction of Aqueous CO
2
to
1
-
Propanol at
MoS
2
Electrodes
Sonja A. Francis
†,a
,1
, Jesus M. Velazquez
†a,
,2
, Ivonne M. Ferrer
a
, Daniel A. Torelli
a
, Dan Guevarra
a
, Matthew T. McDowell
a,
3
, Ke Sun
a
, Xinghao Zhao
b
, Fadl
H.
Saadi
b
, Jimmy John
a
, Matthias Richter
a
,
Forrest P. Hyler
c
,
Kimberly M.
Papadantonakis
a
, Bruce S. Brunschwig
d
, Nathan S. Lewis*
,a,d
a
Division of Chemistry and Chemical Engineering,
b
Division of Engineering and Applied Sciences,
and
d
Beckman
Institute, California Institute of Technology, Pasadena, California 91125, United
States
c
Department of Chemistry,
University of California, Davis, California 95616, United States
Corresponding Author
* Email: nslewis@caltech.edu.
Present Addresses
1
De
partment of Chemistry, Princeton University.
2
Department of Chemistry, University of California, Davis.
3
G. W. Woodruff School of Mechanical Engineering and School of Ma
terials Science and Engineering
,
Georgia Institute of Technology.
Author contribution
s
†
These authors contributed equally to this work.
2
Table of Contents
Figure S1.
Photograph of a MoS
2
single crystal with mask
ed
edge
-
dense areas
............
3
Figure S2.
GC
-
HS chromatograms of
liquid aliquot from the electrochemical cell
...........
4
Figure S3.
NMR spectrum for electrolysis
with
a single crystal of MoS
2
..........................
5
Figure S4.
GC
-
TCD chromat
ograms showing the retention time for
H
2
S
........................
6
Figure S5.
Potential
-
dependent Faradaic efficiencies and partial current densities on
MoS
2
single crystals with masked edge sites.
................................
................................
...
7
Figure S6
.
Potential
-
dependent Faradaic efficiencies and partial current densities on
30
-
MoS
2
thin films
................................
................................
................................
...................
8
Figure S7.
Potential
-
dependent Faradaic efficiencies and partial current densities on
180
-
MoS
2
thin films
.
................................
................................
................................
..........
9
Figure S8.
NMR spectra in the 6H,s t
-
butanol region
................................
.....................
10
Figure S9.
C
hromatogram for the GC
-
MS analysis of gas products from CO reduction
on a MoS
2
terrace
................................
................................
................................
............
11
Figure S10
.
Representative chromatogram for the GC
-
MS analysis of gaseous products
from CH
4
reduction on a MoS
2
terrace.
................................
................................
...........
12
Figure S11
.
X
-
ray photoelectron spectroscopy of single crystals of MoS
2
before and
after CO
2
R
.
................................
................................
................................
......................
13
Figure S12
.
Scanning tunneling microscopy images showing sulfur vacancies on
terraces of MoS
2
single crystals.
................................
................................
.....................
14
Figure S1
3
.
O
pen circuit voltages
and GC
-
FID
data for bulk single crystal MoS
2
held at
open circuit
...............................................15
Figure S1
4
.
Schematic of the sealed custom H
-
cell
................................
.....................
16
6
Figure S1
5
.
NMR spectrum showing chemical shifts of standards
..............................
17
7
Table S1
.
Chemical shifts of NMR
spectroscopy
peaks
................................
...............
18
8
3
Figure S
1
.
Photograph of
a
MoS
2
single crystal
with
electroplating tape
applied
to
mask
edge
-
dense
areas
(left) and
an
un
-
masked crystal
with large amounts of
edges
(right)
.
1 cm
4
Figure S
2
.
Representative GC
-
HS chromatograms of a liquid aliquot removed
from the electrochemical cell after electrolysis
at
-
0.59 V vs. RHE
in 0.1
0
M Na
2
CO
3
acidified to pH 6.8 with 1 atm CO
2
on (
top
) MoS
2
single crystals and (
center
) 30
-
MoS
2
showing production of alcohols, compared to standard solutions
(
B
ottom
)
.
Note that standards of acetone (not shown) have similar retention times to 2
-
pro
panol
.
5
Figure S
3
.
Representative
NMR
spectrum
for electrolysis at
-
0.59 V vs
.
RHE for
a single crystal of MoS
2
in 0.1
0
M Na
2
CO
3
acidified to pH
6.8
with 1 atm CO
2
.
Peak
chemical shifts are identified in
Table S
1
.
-
0
.
5
0
.
0
0
.
5
1
.
0
1
.
5
2
.
0
2
.
5
3
.
0
3
.
5
4
.
0
4
.
5
5
.
0
5
.
5
6
.
0
6
.
5
7
.
0
7
.
5
8
.
0
8
.
5
9
.
0
9
.
5
1
0
.
0
1
0
.
5
p
p
m
0
.
8
4
0
.
8
5
0
.
8
7
1
.
0
9
1
.
2
4
1
.
9
0
2
.
2
2
3
.
6
9
3
.
9
3
7
.
9
2
8
.
4
4
Formate
,
H
COO
-
DMF, (CH
3
)
2
NC(O)
H
Internal standard
(C
H
3
)
2
NC(O)H
Ethylene glycol, HOC
H
2
C
H
2
OH
Ethanol, CH
3
C
H
2
OH (
trace)
Acetone
, C
H
3
(O)C
H
3
Acetate
, C
H
3
COO
-
t
-
Butanol, (C
H
3
)
3
COOH
1
-
Propanol
, C
H
3
CH
2
CH
2
OH
6
Figure S
4
.
Representative
GC
-
TCD
chromatogram
s
showing the retention time
for
(A)
a
H
2
S standard
made in situ from FeS and HCl in inert nitrogen atmosphere,
and
(B)
H
2
S
produced during bulk electrolysis
in 0.1
0
M Na
2
CO
3
acidified to pH
6.8 with 1 atm CO
2
at
-
0.59 V vs. RHE at a MoS
2
single crystal terrace.
7
Figure S
5
.
Potential
-
dependent Faradaic efficiencies (left) and partial current
densities (right) for major (A,B), and minor CO
2
R products (C,D), and proton
reduction (E,F) on MoS
2
single crystals with masked edge sites. The electrolyte
was 0.10 M Na
2
CO
3
(aq) acid
ified to pH 6.8 with 1 atm CO
2
. Standard deviations
are indicated for CO
2
R products.
8
Figure
S6
.
Potential
-
dependent Faradaic efficiencies (left) and partial current densities
(right) for major (A,B), and minor CO
2
R products (C,D), and proton reductio
n (E,F) on
3
0
-
MoS
2
.
The electrolyte was 0.10 M Na
2
CO
3
(aq) acidified to pH 6.8 with 1 atm CO
2
.
Standard deviations are indicated for products at the least reducing potential evaluated.
9
Figure S
7
.
Potential
-
dependent Faradaic efficiencies (left) and
partial current densities
(right) for major (A,B), and minor CO
2
R products (C,D), and proton reduction (E,F) on 180
-
MoS
2
. The electrolyte was 0.10 M Na
2
CO
3
(aq) acidified to pH 6.8 with 1 atm CO
2
.
Standard deviations are indicated for products.
10
Figure
S
8
.
Representative NMR spectra in the 6H,s t
-
butanol region
showing (A)
t
-
butanol produced during unlabelled CO
2
R on MoS
2
single crystal terraces, (B)
labelled t
-
butanol production from
13
CO
2
R on MoS
2
single crystal terraces
.
Electrolyses were performed at
-
0.59V vs. RHE in 0.1
M Na
2
CO
3
electrolyte
acidified to pH 6.8 with 1 atm of reactant gas.
11
Figure
S
9
.
Representative chromatogram for the GC
-
MS analysis of gas products
from CO reduction on a MoS
2
terrace
. Electrolysis was performed at
-
0.59 V vs.
RHE in 0.1
0
M K
2
HPO
4
(aq) buffered to pH 6.8 with KH
2
PO
4
(aq) and purged with
CO
(g)
.
The total
c
harge passed
was
60 Coulombs.
12
Figure
S
10
.
Representative chromatogram for the
GC
-
MS
analysis of gas
eous
products
from
CH
4
reduction on a MoS
2
terrace
. Electrolysis was performed
at
-
0.59 V vs. RHE in 0.1
0
M K
2
HPO
4
(aq) buffered to pH 6.8 with KH
2
PO
4
(aq) and
purged with CH
4
gas.
The total c
harge passed
was
60
Coulombs
.
13
Figure
S
11
.
X
-
ray photoelectron spectroscopy of single crystals of MoS
2
before
and after CO
2
R
, respectively
.
14
Figure
S12
. Scanning
t
unneling
m
icroscopy images showing sulfur vacancies on
terraces of MoS
2
single crystals.
The gap voltage was set to 1.3V, the tunneling
current to 0.69
nA, the scan rate to 434
nm/s
(forward scan direction (left to right)
15
Figure S1
3
.
O
pen circuit voltages
and GC
-
FID
data
for
bulk single crystal MoS
2
in 0.1
M Na
2
CO
3
solution purged with high purity CO
2
for one hour
with no
applied voltage
. (A)
Measured open circuit voltage vs.
time.
(B) . GC
-
FID data of
tw
o data sets. The orange chromato
gram
(top) shows a
16.5 hour
r
un with
background subtr
action resulting in no prominent
peaks of interest. The pe
aks at
6
and 7 minutes are caused by water vapor interacting with the column. The
b
lack chromatagram
(bottom)
show
s
1
μ
M calibration solutions of methanol,
ethanol, acetone, and 1
-
propanol.
Chromatograms demonstrate t
hat no key
alcohol products
derived from
CO
2
reduction were formed when no current was
being applied.
16
Figure
S
1
4
.
Schematic of
t
he sealed custom H
-
cell
used for
the
electrochemical
experiments.
Pt CE
MoS
2
WE
Ag/AgCl
RE
stir bar
Selemion
membrane
headspace sample
removal site (septum)
ground glass joint
17
Figure
S
1
5
.
NMR spectrum showing chemical
shifts of standards
~0.002 vol %
in 0.1
0
M Na
2
CO
3
(aq). Dimethyl formamide (DMF) was used as the internal
standard
, with
the aldehydic proton signal at 7.92 ppm used to calibrate the
chemical shift positions. Peak chemical shifts are identified in
Table S
1
.
0
.
0
0
.
5
1
.
0
1
.
5
2
.
0
2
.
5
3
.
0
3
.
5
4
.
0
4
.
5
5
.
0
5
.
5
6
.
0
6
.
5
7
.
0
7
.
5
8
.
0
f
1
(
p
p
m
)
-
5
0
0
0
0
5
0
0
0
1
0
0
0
0
1
5
0
0
0
2
0
0
0
0
2
5
0
0
0
3
0
0
0
0
3
5
0
0
0
4
0
0
0
0
4
5
0
0
0
5
0
0
0
0
2
.
8
5
3
.
0
0
3
.
3
4
3
.
6
5
4
.
0
1
4
.
8
2
7
.
9
2
0
.
8
0
.
9
1
.
0
1
.
1
1
.
2
1
.
3
1
.
4
1
.
5
1
.
6
1
.
7
f
1
(
p
p
m
)
0
5
0
0
0
1
0
0
0
0
0
.
8
6
0
.
8
8
0
.
8
9
1
.
1
5
1
.
1
6
1
.
1
8
1
.
2
3
1
.
5
2
1
.
5
4
3
.
3
3
.
4
3
.
5
3
.
6
3
.
7
3
.
8
3
.
9
4
.
0
f
1
(
p
p
m
)
0
1
0
0
0
2
0
0
0
3
0
0
0
4
0
0
0
5
0
0
0
6
0
0
0
7
0
0
0
8
0
0
0
9
0
0
0
1
0
0
0
0
1
1
0
0
0
3
.
3
4
3
.
5
5
3
.
6
3
4
.
0
1