of 45
1
Supplementary Materials
1
Enhancing the activity of oxygen
-
evolution and chlorine
-
evolution electrocatalysts by
atomic
2
layer deposition of TiO
2
3
Authors:
Cody E. Finke
1,2
,3
*, Stefan T.
Omelchenko
3
, Justin T. Jasper
1,2
, Michael F.
4
Lichterman
4
,
Carlos G. Read
2,
4
,
Nathan S. Lewis
4
, Michael R. Hoffmann
1,
2,
3
,
*
5
Affiliations:
6
1
The Linde Center for Global Environmental Science,
Caltech, Pasadena, CA 91125, USA.
7
2
The
Resnick Sustainability
Institute
,
Caltech, Pasadena, CA 91125, USA.
8
3
Division of Engineering and Applied Science
, Caltech, Pasadena, CA 91125, USA.
9
4
Division of Chemistry and Chemical Engineering, Caltech, Pasadena, CA 91125, USA.
10
*Corresponding Authors:
finkec@caltech.edu
,
mrh@caltech.edu
11
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Electronic
Supplementary
Material
(ESI)
for
Energy
&
Environmental
Science.
This
journal
is
©
The
Royal
Society
of
Chemistry
2018
2
Table of Contents
26
1
)
Surface Topogrpahy Determination and Surface Homogeneity
,
and Acitve Site Discussion
27
p # S1
S
5
28
a) Transmission Electron
Miscroscopy
29
b
) Atomic Force Microscopy
30
c
) Profilometry
31
d
) Scanning Electron Microscopy
32
e) Active Sit
e
33
2)
Estimation of Electronegativity
, p #
S
6
-
7
34
3)
Electrode Preparation
, p #
S
8
S
10
35
a)
RuO
2
and IrO
2
Sample Preparation
36
b) FTO Sample Preparation
37
c)
Atomic Layer Deposition
38
d
) X
-
Ray Diffraction Spectroscopy
39
4)
Electrochemical
Measurements
, p #
S
10
-
S
1
6
40
a)
Overpotential Calculations
41
b)
Faradaic Efficiency Determination
42
c)
Determination of Solution and System Resistance
43
d) 24 hr Stability Testing
44
e)
Determination of Solution and System Resistance
45
5)
Determination of Specific Activities
, p #
S
1
7
-
S
2
5
46
a)
Determination of
Double
-
Layer Capacitance and Electrochemically Active Surface
47
Area
48
b)
Calculating Specific Activityies Using ECSA and AFM
49
c) Tafel
Analysis
50
6) Determination of
E
ZC
by Electrochemical Impedance Spectroscopy
, p
S
2
5
S
30
51
7
)
X
-
ray
P
hotoelectron
S
pectroscopy
, p #
S
30
S
41
52
a)
Data Collection and Peak Fitting
53
b)
Ti 2p Core
-
level Photoemission
54
c)
Underlying Metal Oxide Photoemission
55
d)
Electrocatalyst
Stability
56
Tables S1
S
7
57
Figures S1
S
2
3
58
Equation S1
-
S3
59
References (
S1
-
S29
)
60
3
Surface Topogr
a
phy Determinatiion and Surface Homogeneity
, and Acitve Site
61
Discussion
62
63
Tr
ansmission Electron miscroscopy
64
65
To better understand the surface morphology
,
TEM images
were aquired
of 10 and 40 ALD cycles
66
of TiO
2
on IrO
2
.
Transmission
-
electron microscopy (TEM) samples of films were prepared using
67
a focused Ga
-
ion beam (FIB) on a FEI Nova
-
600 Nanolab FIB/FESEM, with Pt and C protection
68
layers being applied bef
ore being exposed to the FIB.
High
-
resolution TEM (HRTEM) images and
69
high
-
angle annular dark
-
field scanning transmission electron microscopy (HAADF
-
STEM) images
70
were collected on an FEI Titan G2 S/TEM equipped with spherical aberration correctors on the
71
im
age and probe
-
forming lenses at an accelerating voltage of 200 kV. STEM
-
EDS maps were
72
acquired in the FEI Titan using the Super
-
X EDX quad detector system at a current of 0.1 nA.
73
Standard
-
less Cliff
-
Lorimer quantification was performed on the deconvoluted
EDS line intensity
74
data using the Bruker Esprit software.
Fig
.
S1 below shows HAADF
-
STEM images of
10 cycles
75
of TiO
2
exhibited a semicontinuous film where the majority of imaged areas were covered withTiO
2
76
with relatively small gaps of
what appeared to be
uncoat
ed area. 40 ALD cycle exhibited a fully
77
continuous film for at all areas imaged.
78
79
Fig. S1.
High
-
Angle Annular Dark
-
Field Scanning Transmission Electron Microscopy (HAADF
-
80
STEM) images
of different IrO
2
+ 10 ALD cycles of TiO
2
samples. The crystalline sublayer is IrO
2
81
and the hairy top layer is amorphous TiO
2
.
82
83
84
4
Atomic Force Microscopy
85
86
Atomic Force Microscopy (AFM) was used to investigate
the
surface morphology. A Bruker
87
Dimension Icon was used in Peak Force Tunneling AFM
Mode (PF
-
TUNA) for all topography and
88
conductive AFM measurements. Representative surface topology (
Fig. S
2
)
and conduc
tive AFM
89
(TUNA current) (Fig. S
3
) for 0, 3, 10, and 1000 ALD TiO
2
cycles
are shown
for IrO
2
, RuO
2
, and
90
FTO substrates. AFM images of RuO
2
, IrO
2
, FTO, and substrates coated with
1000 cycles of TiO
2
91
were consistent with previou
s
ly reported images of materials grown under similar conditions
1
-
4
.
92
5
93
Fig. S
2
.
Representative t
opographic
atomic force microscopy images of IrO
2
, RuO
2
, and FTO
94
each with 0, 3, 10, and 1000 ALD cycles of TiO
2
.
The red cirle indicates exposed RuO
2
under
95
TiO
2
.
96
6
97
Fig. S
3
.
Representative
c
onductive
atomic force microscopy tun
n
eling current images of IrO
2
,
98
RuO
2
, and FTO each with 0, 3, 10, and 1000 ALD cycles of TiO
2
.
The red cirle indicates
99
exposed RuO
2
under TiO
2
.
100
101
102
103
7
Table S1
.
Surface area (measured by AFM) as a percent of geometric surface area. Dividing
104
these values by 100 yields topographic roughness factors.
105
AFM Measured Surface Area as a
Percentage of Geometric Surface
Area
TiO
2
Cycle
Number
IrO
2
RuO
2
FTO
0
104.52%
107.75%
108.35%
3
103.87%
102.45%
107.98%
6
103.12%
103.93%
110.24%
10
102.94%
104.08%
108.05%
20
103.32%
104.61%
110.60%
30
108.92%
40
102.70%
102.61%
108.27%
50
108.18%
60
103.60%
101.65%
108.10%
500
102.00%
1000
102.01%
111.02%
104.15%
106
The surface area as measured by AFM was at most 112% of the geometric surface area
(Table
107
S1).
It was very difficult to find places in AFM images where the underlying material was exposed
108
even at only 3 ALD cycles of TiO
2
. On FTO and IrO
2,
the base electr
ocatalyst materials did not
109
appear to be exposed even at 3 ALD cycles. However, for RuO
2
, while mostly the sample
110
appeared to be covered by TiO
2
, there was some evidence of holes in the TIO
2
coverage, and we
111
chose to display that image.
For IrO
2
and FTO, the surface topography was similar for all cycle
112
numbers
of TiO
2
. The only observable change as the number of ALD cycles increased was that
113
the
conductivtiy and surface area decreased uniformly as TiO
2
was deposited, suggesting that
114
TiO
2
coat
ed
t
he catalysts’ surface
reasonably
evenly
,
see
Fig.
S1 for TEM images for higher
115
resolution coverage analysis
.
Based on AFM data,
No holes were visible in the TiO
2
coat
ing
at
116
any cycle number for FTO and IrO
2
.
T
he surface topography of bare RuO
2
was
rippled
(0 cycles)
,
117
and
gradually morphed into a
flake
-
like structure (3
-
6 cycles)
,
a columnar structure
similar to
IrO
2
118
(10
-
30 cycles)
,
and then back into flakes similar to FTO (>30 cycles). Furthermore, for RuO
2
at 3
119
ALD cycles some holes in the TiO
2
were clearl
y visible in both the topological and the conductive
120