Electrode
Surface
Heating
with
Organic
Films
Improves
CO
2
Reduction
Kinetics
on
Copper
Nicholas
B. Watkins,
∥
Yungchieh
Lai,
∥
Zachary
J. Schiffer,
Virginia
M. Canestraight,
Harry
A. Atwater,
Theodor
Agapie,
*
Jonas C. Peters,
*
and John M. Gregoire
*
Cite
This:
ACS Energy
Lett.
2024,
9, 1440−1445
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*
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Supporting
Information
ABSTRACT:
Management
of
the
electrode
surface
temperature
is an
understudied
aspect
of
(photo)electrode
reactor
design
for
complex
reactions,
such
as
CO
2
reduction.
In
this
work,
we
study
the
impact
of
local
electrode
heating
on
electrochemical
reduction
of
CO
2
reduction.
Using
the
ferri/ferrocyanide
open
circuit
voltage
as
a reporter
of
the
effective
reaction
temperature,
we
reveal
how
the
interplay
of
surface
heating
and
convective
cooling
presents
an
opportunity
for
cooptimizing
mass
transport
and
thermal
assistance
of
electrochemical
reactions,
where
we
focus
on
reduction
of
CO
2
to
carbon-coupled
(C
2+
)
products.
The
introduction
of
an
organic
coating
on
the
electrode
surface
facilitates
well-behaved
electrode
kinetics
with
near-ambient
bulk
electrolyte
temperature.
This
approach
helps
to
probe
the
fundamentals
of
thermal
effects
in
electrochemical
reactions,
as
demonstrated
through
Bayesian
inference
of
Tafel
kinetic
parameters
from
a suite
of
high
throughput
experiments,
which
reveal
a decrease
in
overpotential
for
C
2+
products
by
0.1
V
on
polycrystalline
copper
via
60
°
C
surface
heating.
D
ecarbonization
of the
chemical
industry
is an
important
step
toward
halting
the
progress
of
anthropogenic
climate
change.
Electrochemical
re-
actions
driven
with
solar
power
and other
renewable
energy
sources
to manufacture
commodity
chemicals,
such
as
ammonia,
ethylene,
and hydrogen,
have
been
recent
targets
to achieve
this goal.
1
While
these
commodity
chemicals
are
currently
being
produced
by well-established
thermochemical
processes,
such
as the Haber-Bosch
process,
each
product
has a
clear
alternative
electrochemical
synthetic
pathway.
2
Ammonia
can be produced
via nitrogen
reduction
(or Haber
−
Bosch
with
electrochemically
produced
hydrogen),
ethylene
can
be
produced
via CO
2
reduction
(CO
2
R), and hydrogen
can be
produced
via water
reduction
(Scheme
1).
3,4
In addition,
while
the simplest
operation
is to drive
these
processes
using
grid-
based
renewable
electricity
alone,
eventual
electrolyzers
can be
integrated
with
solar-driven
cells
to afford
photoelectrochem-
ical (PEC)
devices
that directly
harness
the sun’s
energy
and
enable
distributed
chemical
manufacturing.
While
these
processes
historically
have
not been
economically
viable,
the
development
of improved
catalysts,
membranes,
photovoltaics,
and government
incentives
drive
forward
their
feasibility.
5
Thermocatalysis
involves
thermally
activated
traversal
of a
reaction
barrier,
which
is well
described
by the Arrhenius
expression
for the rate constant
k
(eq 1).
6,7
Here,
A
is a pre-
exponential
factor,
E
a
is the activation
energy
for the reaction,
R
is the universal
gas constant,
and
T
is the temperature
of the
reaction.
Since
lowering
the activation
energy
is not always
possible,
methodologies
for increasing
reaction
temperature
are therefore
desirable.
=
k
Ae
E
RT
/
a
(1)
The electrochemical
analogue
to eq 1 is the simplified
Butler
−
Volmer
expression
for the kinetic
current
(
i
k
) at high
driving
forces
where
the reverse
reaction
is negligible,
often
termed
the
Tafel
equation:
=
+
i
Ae
k
E
E
RT
/
a
(2)
In the Tafel
equation,
in addition
to the same
temperature-
dependent
exponential
with
an activation
energy,
there
is also a
linear,
potential-dependent
term
in the exponential.
More
complex
theories
expand
on Butler
−
Volmer
by, for example,
adding
a quadratic
potential
term
to the exponential,
as is done
with
the Marcus
theory.
Here,
α
is the transfer
coefficient,
which
is a function
of the pre-equilibrium
electron
transfers
and
the rate-determining
step,
and
E
is the electrostatic
potential
with
respect
to a reference
potential.
7,8
We note
that
the pre-exponential
factor
A
may
also vary
with
temperature,
Received:
January
19, 2024
Revised:
February
24, 2024
Accepted:
March
7, 2024
Published:
March
11,
2024
Letter
http://pubs.acs.org/journal/aelccp
© 2024
The Authors.
Published
by
American
Chemical
Society
1440
https://doi.org/10.1021/acsenergylett.4c00204
ACS Energy
Lett.
2024,
9, 1440
−
1445
This article is licensed under CC-BY 4.0
which
is not considered
in the present
work.
In this case,
the
Tafel
equation
retains
the qualitative
form
of the traditional
Arrhenius
expression,
and elevated
temperatures
will increase
the kinetic
current.
9
Since
elevated
temperature
will improve
reaction
kinetics,
the question
remains
how
to efficiently
heat
the system.
Industrial
water
splitting
and CO
2
reduction
processes
heat the
entire
electrolyzer
to 40
−
60
°
C and
operate
at current
densities
of or above
500 mA/cm
2
.
10,11
It is of note
that the
limitation
for these
operating
temperatures
is typically
the
stability
of the membrane
and not of the catalyst.
12
While
uniform
heating
is beneficial
for homogeneous
reactions
associated
with
many
traditional
thermochemical
processes,
electrochemistry
is localized
to the electrode
surface;
heating
the bulk
may
therefore
result
in wasted
energy.
Additionally,
resistive
heating
at industrially
relevant
current
densities
causes
electrode
surface
temperature
variation
from
the bulk
by more
than
10
°
C.
13,14
In photoelectrochemically
driven
systems,
irradiative
heating
can cause
local
heating
of the electrode
surface
by a similar
margin.
15
Given
the
sensitivity
of
electrochemistry
to changes
in temperature,
these
differences
between
set point
and actual
electrode
temperature
may
have
significant
impacts
on catalysis.
Bulk
heating
experiments
in electrochemical
CO
2
reduction
on copper
have
shown
variable
results.
While
all reports
show
increasing
hydrogen
and
decreasing
methane
at elevated
temperatures,
ethylene
promotion
has
varied
between
studies.
16
−
19
We expect
that this discrepancy
may
be due to
variable
convective
mass
transport
between
systems,
which
has
been
shown
to have
a significant
effect
on selectivity
at 25
°
C
and would
become
especially
important
at elevated
temper-
atures
due to decreased
CO
2
solubility.
20
−
22
There
is evidence
from
the electrochemical
sensor
literature
that
enhanced
reactivity
can be achieved
by using
local
heating.
23
−
25
In the
case
of CO
2
reduction,
this would
overcome
the trade-off
associated
with
decreasing
bulk
CO
2
solubility.
20
Recently,
this
concept
has been
applied
to CO
2
R catalysis
with
both
surface
heating
and cooling,
achieving
altered
performance
without
significantly
affecting
the bulk
temperature.
26,27
In these
works,
Bi rotating
disk electrodes
(RDEs)
increased
their
activity
for
formate
by a factor
of 1.7 upon
raising
surface
temperatures
to
65
°
C and
planar
Cu electrodes
boosted
their
methane
selectivity
to 80%
by cooling
the electrode
to
−
4.4
°
C (and
applying
pulsed
electrolysis).
In contrast
to previous
works,
surface
heating
on copper
showed
no clear
trend
in ethylene
or
methane
Faradaic
efficiencies
with
respect
to temperature,
especially
in the
absence
of supporting
EDTA
in the
electrolyte,
supporting
the
fact
that
hydrodynamics
can
significantly
impact
performance.
27
In this work,
we evaluate
how
mass
transport
and electrodeposited
organic
films
affect
the performance
of heated
electrodes
for ferricyanide
and CO
2
reduction
to C
2+
products.
To establish
a system
with
variable
electrode
temperature
and
hydrodynamics,
we expanded
the
high
throughput
analytical
electrochemistry
(HT-ANEC)
screening
system
to
include
a Peltier
heating
element
that
is electrically
isolated
and
thermally
coupled
to a planar
working
electrode.
To
characterize
the behavior
of the cell with
a heated
working
electrode
and
electrolyte
flow,
we invoked
multiphysics
modeling
to establish
the distribution
of electrolyte
flow
rate
Scheme
1.
Comparison
of
the
Thermal
and
Electrochemical
Pathways
for
the
Production
of
Ammonia,
Ethylene,
and
Hydrogen
a
a
In the electrochemical
transformations,
the reductive
reaction
listed
is implicitly
paired
with
an oxidative
reaction
such
as oxygen
evolution
from
water.
Figure
1.
(A)
Schematic
of
the
high
throughput
analytical
electrochemistry
(HT-ANEC)
screening
system
utilized
in
this
report.
The
working
electrode
is placed
on
top
of
a Peltier
heating
element
to
accurately
modulate
surface
temperature,
and
the
internal
temperature
can
be
monitored
using
a thermocouple
inserted
in
the
top
of
the
cell.
In
the
inset
are
cross
sectional
images
of
the
simulated
velocity
and
temperature
profiles
within
the
cell
given
a flow
rate
of
150
μ
L
s
−
1
and
a surface
temperature
of
60
°
C.
In
the
thermal
inset,
we
indicate
the
position
of
the
thermocouple
in
the
cathodic
chamber.
ACS
Energy
Letters
http://pubs.acs.org/journal/aelccp
Letter
https://doi.org/10.1021/acsenergylett.4c00204
ACS Energy
Lett.
2024,
9, 1440
−
1445
1441
and temperature
throughout
the working
electrode
chamber
(Figure
1).
28
The
design
of the cell varies
slightly
from
our
previous
report
on the effects
of hydrodynamics
on Tafel
slopes
to allow
for a thermocouple
to be placed
inside
the
working
compartment
to monitor
internal
temperature.
22
We
measured
internal
and outlet
temperatures
at five temperature
points
with
surface
heating
(SH)
to evaluate
the degree
of
global
heating
of the system.
At a surface
temperature
of 60
°
C,
we experimentally
measure
an internal
temperature
of 36
±
1.1
°
C and an outlet
temperature
of 26.8
±
0.1
°
C, which
supports
our goal of mitigating
bulk
electrolyte
heating.
Our simulations
further
support
this claim,
with
the average
temperature
in the
cell showing
Gaussian
temperature
distributions
at temper-
atures
far below
the surface
temperature
(Figure
S1 and Table
S1).
To characterize
the effective
temperature
of electrochemical
reactions
under
the condition
with
a heated
working
electrode
and ambient
recirculating
electrolyte,
we measured
the open
circuit
potential
with
an electrolyte
containing
equal
concentrations
of potassium
ferri/ferrocyanide,
whose
temper-
ature-dependent
equilibrium
potential
is well established.
29
We
performed
open
circuit
voltage
(OCV)
measurements
at our
standard
flow
rate of 150
μ
L s
−
1
as well as a reduced
flow
rate
(Figure
2A).
While
the observed
temperatures
reflect
the
expectation
that rapidly
flowing
ambient
electrolyte
lowers
the
effective
reaction
temperature
with
respect
to the electrode
temperature,
these
deviations
are within
ca. 5
°
C (Figure
2B,
Table
S2, and
Figure
S2)
and
demonstrate
our ability
to
systematically
vary
with
reaction
temperature
via electrode
heating.
To further
understand
the differences
between
surface
and
bulk
heating,
we identified
the mass
transport
limited
current
for each
heating
system
by performing
constant
potential
electrolyses
at variable
temperatures
and using
Fick’s
second
law to determine
the average
concentration
boundary
layer
(
δ
C
) thickness
(Figure
S3
−
5).
30
Upon
changing
the
temperature,
we find that the
δ
C
decreases
in thickness
for both
systems
but marginally
less with
SH, which
we expect
is due to
incomplete/inhomogeneous
heating
of the
concentration
boundary
layer
with
SH (Figure
S6).
Partial
heating
is also
consistent
with
the changes
in cell resistance,
since
we observe
slightly
lower
resistances
with
BH than
SH. (Figure
S7).
Applying
surface
heating
in electrocatalytic
CO
2
R trials,
we
observe
an increase
in activity
for both
CO
2
R and HER,
which
is consistent
with
all previous
reports
(all FEs in Figure
S8,
Table
S3).
16
−
19
With
respect
to carbon-coupled
products,
we
see a 2
×
increase
in partial
current
density
and up to 10%
increase
in Faradaic
efficiency
at
−
1.03
V vs RHE
(Figure
3A).
16,19
We observe
no appreciable
improvement
in C
2+
partial
current
density
heating
the surface
from
43 to 60
°
C,
supporting
the hypothesis
from
Koper
et. al that other
factors,
such
as structural
changes,
may
be significant
factors
at these
elevated
temperatures.
19
Unexpectedly,
we did not observe
a
noticeable
shift
in onset
potential
for C
2+
products.
Since
the
shift
in
J
CO2R
with
respect
to temperature
is only
slight,
we
expect
that
the more
significant
increase
in
J
HER
at more
positive
potentials
convolutes
the system’s
CO
2
R response
to
temperature,
for example
via competition
for active
sites
(Figure
S9).
Temperatures
above
80
°
C were
unable
to be
tested
on bare
copper
due
to the total
current
density
exceeding
the limitations
of the HT-ANEC
screening
system.
28
In our previous
work,
we determined
organic
films
improve
CO
2
R performance
toward
multicarbon
products
by decreas-
ing the
availability
of water
while
increasing
the
local
concentration
of CO.
22
We hypothesized
that the addition
of
an organic
coating
in this work
would
eliminate
convoluting
effects
from
competing
hydrogen
evolution
and
enable
investigation
of temperature-dependent
CO
2
R. While
previous
investigations
with
organic
coatings
in this electrochemical
cell
were
derived
from
N,
N
′
-ethylenephenanthrolinium
dibromide,
Figure
2.
(A)
OCV
measurements
at
variable
electrode
temper-
atures
over
time
changing
from
a fast
electrolyte
recirculation
rate
to
a slower
one
at
300
s. (B)
Comparison
of
measured
temperature
values
for
the
two
recirculation
rates
compared
to
the
set
temperatures.
Error
bars
indicate
the
variance
between
the
two
measurements
for
each
temperature.
Electrochemistry
was
performed
using
a sputtered
platinum
film
working
electrode,
a
platinum
wire
counter
electrode,
and
a leakless
Ag/AgCl
reference
electrode,
in
0.5
M
KCl
with
5
mM
K
3
Fe(CN)
6
and
5
mM
K
4
Fe(CN)
6
.
Figure
3.
Electrochemical
CO
2
reduction
performance
(A)
without
and
(B)
with
organic
films
in
0.1
M
KHCO
3
. Each
data
point
corresponds
to
an
individual
experiment.
The
organic
film
was
deposited
via
a 10
min
predeposition
of
10
mM
diphenyliodonium
triflate
at
−
1.2
V vs
RHE
in
CO
2
-sparged
0.1
M
KHCO
3
. 10
mM
diphenyliodonium
was
present
during
electrolysis
in
the
case
of
the
additive
film
as
well
to
heal
minor
delamination,
as
reported
previously.
31
ACS
Energy
Letters
http://pubs.acs.org/journal/aelccp
Letter
https://doi.org/10.1021/acsenergylett.4c00204
ACS Energy
Lett.
2024,
9, 1440
−
1445
1442
herein
we investigate
films
from
the
reductive
electro-
deposition
of diphenyliodonium
triflate
due to their
increased
robustness
(Scheme
2).
31
Upon
the incorporation
of an
organic
film,
we observe
a boost
in C
2+
FE and a systematic
increase
in activity
for CO
2
reduction
with
the temperature.
Notably,
we observe
a clearer
positive
trend
in
J
CO2R
with
respect
to temperature
with
additives
than
without
(Figure
S10).
Since
we observe
little
change
in concentration
boundary
layer
thickness
with
respect
to surface
temperature
(Figure
S6),
this
result
supports
that
the CO
2
concentration,
or
chemical
potential,
is unchanged.
Consequently,
we infer
that
the observed
temperature-dependent
partial
current
densities
reflect
changes
to the activation
energy
barriers
in traditional
reaction
rate models,
such
as eqs 1 and 2.
7
Commensurate
with
this hypothesis,
we observe
a positive
shift
in onset
potential
for carbon-coupled
product
formation
(Figure
3B; all FEs in
Figure
S11
and
Table
S3).
The
highest
activity
for C
2+
products
was observed
at
−
1.02
V vs RHE
and SH = 60
°
C,
where
we obtained
a FE
C2+
of 44% and a partial
current
density
of 6.61
mA cm
−
2
. At ambient
temperature,
an additional
0.1 V
of overpotential
is needed
to obtain
comparable
C
2+
activity,
highlighting
how
temperature-based
improvements
to elec-
trode
kinetics
enable
operation
at lower
overpotentials.
We
observe
a change
in slope
for the response
in current
with
respect
to potential
with
and
without
molecular
additives,
which
is consistent
with
our previous
report
on how
transport
affects
the electrode
kinetics
observed
on polycrystalline
copper.
22
The
systematic
improvement
to C
2+
activity
is
observed
up to 60
°
C, above
which
we suspect
that the loss in
enhancement
may be from
delamination
of the organic
coating
or the
restructuring
of copper.
19
The
data
up to this
temperature
provide
the opportunity
to model
the temper-
ature-dependent
Tafel
equation
(eq
2) while
remaining
cognizant
of noise
in the data,
which
may
arise
from,
for
example,
inhomogeneities
in mass
transport
across
the
electrode
surface.
In the present
work,
we are ultimately
not
concerned
with
the uncertainty
in the performance
at a given
electrochemical
condition
but rather
the uncertainty
in the
parameters
of a model
that describes
the performance
across
all
electrochemical
conditions.
We thus turn to Bayesian
methods
to infer
the
uncertainty
in model
parameters
under
consideration
of the scatter
in the experimental
data.
We
present
an anecdotal
characterization
of single-condition
reproducibility
in Figure
S12.
While
the Tafel
expression
is analogous
to a traditional
Arrhenius
rate constant
expression,
calculating
the activation
energy
for an electrochemical
reaction
is nontrivial
because
any
temperature-dependent
analysis
(such
as plotting
log
10
(
i
k
) vs
1/
T
)
will result
in the calculation
of a convolution
of activation
energy,
transfer
coefficient,
and applied
potential.
Specifically,
the slope
on a log
10
(
i
k
) vs 1/
T
plot is not the activation
energy
as it is with
a thermochemical
reaction
but instead
is the
quantity
(
−
E
a
+
α
E
).
Thus,
to calculate
the apparent
activation
energy
of an electrochemical
reaction,
a comprehensive
analysis
of a range
of potentials
and temperatures
is necessary,
which
is seldom
done
due
to limitations
in sufficient
data
collection
for rigorous
parameter
estimation
procedures.
This
consideration
guided
our design
of combinatorial
experimen-
tation
to characterize
the transition
in onset
potential
across
temperatures
and
fit the resulting
data
to a temperature-
dependent
Tafel
model
coupled
with
a mass-transfer
limiting
current
(Figure
S13).
8,22
Using
the data collected
with
organic-
coated
Cu at a range
of temperatures
and
potentials,
we
established
a Bayesian
model
for the posterior
distributions
for
all model
parameters
(see the SI for discussion
and derivation).
The result
is an apparent
activation
energy
of 1.0
±
0.2 eV for
the reduction
of CO
2
to C
2+
products
(Figure
4a),
which
differs
from
previously
reported
values
(ca. 0.5 eV) that were
established
with
different
methodology.
Herein
we explicitly
model
E
a
, while
previous
analyses
report
the value
of the
expression
(
−
E
a
+
α
E
).
18
We
note
that
carbon-coupled
products
are aggregated
in this analysis
due to their
presumed
common
rate-determining
step
and corresponding
activation
barrier.
In addition
to the apparent
activation
energy,
we
concomitantly
model
the rate of change
of the onset
potential
with
a changing
temperature
(Figure
4B)
and
the rate
of
change
of the current
with
a changing
temperature
(Figure
4C).
These
derivatives
reveal
that with
increasing
temperature,
Scheme
2.
Under
Reductive
Bias,
Diphenyliodonium
Polymerizes
on
the
Electrode
Surface
to
Form
a Robust
Polyaromatic
Coating
That
Is
Electronically
Insulating
but
Permeable
to
Reactants
and
Solvent
31
Figure
4.
Probability
distributions
of
the
(A)
activation
energy,
E
a
, for
CO
2
reduction
with
molecular
films
using
surface
heating,
(B)
observed
change
in
applied
potential
with
respect
to
temperature
given
a fixed
kinetic
current,
and
(C)
observed
change
in
kinetic
current
with
respect
to
temperature
given
a fixed
applied
potential.
ACS
Energy
Letters
http://pubs.acs.org/journal/aelccp
Letter
https://doi.org/10.1021/acsenergylett.4c00204
ACS Energy
Lett.
2024,
9, 1440
−
1445
1443
the overpotential
at fixed
C
2+
current
is lowered
at a rate of ca.
2 mV K
−
1
. At fixed
overpotential,
the C
2+
current
increases
exponentially
at a rate of 0.02
dec K
−
1
. Overall,
the estimation
of these
values
and
derivatives
for CO
2
reduction
is only
possible
with
the breadth
of data achievable
with
HT-ANEC
as
well as comprehensive
analysis
of the complete
data set with
an
accurate
model
for the current
as a function
of temperature
and voltage.
Furthermore,
we find
that
organic
modification
was essential
to enable
the calculation
of these
fundamental
parameters.
While
this study
was limited
to CO
2
R on organic
modified
Cu, the integration
of combinatorial
experimentation
and
Bayesian
analysis
can be used
to determine
activation
barriers
for a myriad
of electrochemical
reactions.
The
use of surface
heating
and
organic
coatings
herein
demonstrates
a methodology
for identifying
the apparent
activation
energy
of an electrochemical
transformation
while
mitigating
the influence
of bulk mass
transport.
Combining
this
technique
with
automated
experimentation,
we demonstrate
that
the ensemble
of partial
current
densities
acquired
at
various
potentials
and temperatures
can be modeled
by the
temperature-dependent
Tafel
equation.
By invoking
Bayesian
methods,
the uncertainty
in model
parameters
can also
be
inferred,
which
in the present
work
yields
an apparent
activation
energy
for C
2+
products
of 1.0
±
0.2 eV, which
is
deconvoluted
from
the
transfer
coefficient
and
applied
potential.
With
this methodology,
we enable
future
systematic
catalyst
screening
for lower
C
2+
barriers
and subsequent
system
design
around
low
E
a
catalysts
to achieve
high
activity
and
selectivity
for carbon-coupled
products
at reduced
over-
potentials.
■
ASSOCIATED
CONTENT
*
sı
Supporting
Information
The
Supporting
Information
is available
free
of charge
at
https://pubs.acs.org/doi/10.1021/acsenergylett.4c00204.
Detailed
methods,
modeling
information,
additional
electrochemical
data,
additional
fitting
data,
and a data
table
containing
the temperature-dependent
electro-
chemical
and
product
distribution
data
used
for
parameter
fitting
(PDF)
■
AUTHOR
INFORMATION
Corresponding
Authors
Theodor
Agapie
−
Liquid
Sunlight
Alliance,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Division
of Chemistry
and
Chemical
Engineering,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
orcid.org/0000-0002-9692-7614;
Email:
agapie@caltech.edu
Jonas
C. Peters
−
Liquid
Sunlight
Alliance,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Division
of Chemistry
and
Chemical
Engineering,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
orcid.org/0000-0002-6610-4414;
Email:
jpeters@caltech.edu
John
M. Gregoire
−
Liquid
Sunlight
Alliance,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Division
of Engineering
and
Applied
Science,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
orcid.org/0000-0002-2863-5265;
Email:
gregoire@caltech.edu
Authors
Nicholas
B. Watkins
−
Liquid
Sunlight
Alliance,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Division
of Chemistry
and
Chemical
Engineering,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
orcid.org/0000-0001-7251-9387
Yungchieh
Lai
−
Liquid
Sunlight
Alliance,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Division
of Engineering
and
Applied
Science,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States
Zachary
J. Schiffer
−
Liquid
Sunlight
Alliance,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Division
of Engineering
and
Applied
Science,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Present
Address:
Applied
Physics,
Harvard
John
A. Paulson
School
of Engineering,
Harvard
University,
Cambridge,
Massachusetts
02138,
United
States.
(Z.J.S.)
;
orcid.org/0000-0001-6069-8613
Virginia
M. Canestraight
−
Liquid
Sunlight
Alliance,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Division
of Chemistry
and
Chemical
Engineering,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States
Harry
A. Atwater
−
Liquid
Sunlight
Alliance,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
Division
of Engineering
and
Applied
Science,
California
Institute
of Technology,
Pasadena,
California
91125,
United
States;
orcid.org/0000-0001-9435-0201
Complete
contact
information
is available
at:
https://pubs.acs.org/10.1021/acsenergylett.4c00204
Author
Contributions
∥
N.B.W.
and Y.L. contributed
equally
to this work.
Notes
The authors
declare
no competing
financial
interest.
■
ACKNOWLEDGMENTS
This
material
is primarily
based
on work
performed
by the
Liquid
Sunlight
Alliance,
which
is supported
by the U.S.
Department
of Energy,
Office
of Science,
Office
of Basic
Energy
Sciences,
Fuels
from
Sunlight
Hub
under
Award
Number
DE-SC0021266.
The
Resnick
Sustainability
Institute
at Caltech
is acknowledged
for its support
of enabling
infrastructure
and facilities.
We thank
Florian
Grass
for many
productive
conversations.
■
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