Ammonia Oxidation Enhanced by Photopotential Generated by Plasmonic Excitation of a Bimetallic Electrocatalyst

Article abstract of DOI:10.1002/anie.202007202

We study how visible light influences the activity of an electrocatalyst composed of Au and Pt nanoparticles. The bimetallic composition imparts a dual functionality: the Pt component catalyzes the electrochemical oxidation of ammonia to liberate hydrogen

Full text of DOI:10.1002/anie.202007202

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
International Edition Chemie
www.angewandte.org
Accepted Article
Title: Ammonia oxidation enhanced by photopotential generated by
plasmonic excitation of a bimetallic electrocatalyst
Authors: Jun Wang, Jaeyoung Heo, Changqiang Chen, Andrew
Wilson, and Prashant K. Jain
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202007202
Link to VoR: https://doi.org/10.1002/anie.202007202

Angewandte Chemie International Edition
10.1002/anie.202007202
COMMUNICATION
Ammonia oxidation enhanced by photopotential generated by
plasmonic excitation of a bimetallic electrocatalyst
[a]
[b]
[c]
[a]
[ad]
Jun Wang, Jaeyoung Heo, Changqiang Chen, Andrew J. Wilson, and Prashant K. Jain *
[a]
Dr. J. Wang, Dr. A. J. Wilson, Prof. P. K. Jain
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801 USA
E-mail: jain@illinois.edu
[b]
[c]
[d]
Mr. J. Heo
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801 USA
Dr. C. Chen
Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
Prof. P. K. Jain
Materials Research Laboratory, Department of Physics, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-
Champaign, Urbana, IL, 61801 USA
Supporting information for this article is given via a link at the end of the document.
Abstract: We study how visible light influences the activity of an
electrocatalyst composed of Au and Pt nanoparticles. The bimetallic
composition imparts a dual functionality: the Pt component catalyses
the electrochemical oxidation of ammonia to liberate hydrogen and
the Au component absorbs visible light by the excitation of localized
surface plasmon resonances. Under visible-light excitation, this
catalyst exhibits enhanced electrochemical ammonia oxidation
kinetics, outperforming previously reported electrochemical schemes.
We trace the enhancement to a photochemical potential resulting from
electron–hole carriers generated in the electrocatalyst by plasmonic
excitation. The photopotential responsible for enhanced kinetics
scales linearly with the light intensity–a general design principle for
eliciting superlative photoelectrochemical performance from catalysts
comprised of plasmonic metals or hybrids. We also determine a
photochemical conversion coefficient.
the surface. In this tandem nanostructure, which we refer to as
Au@Pt NPs, the Pt NPs act as electrocatalytic sites, while the Au
NPs serve as strong visible-light absorbers. Although Pt itself has
broadband light absorption, the response of Au NPs is
characterized by a resonant interaction with visible light through
the excitation of localized surface plasmon resonances (LSPRs).
LSPRs have been exploited for visible-light harvesting as well as
for driving chemical reactions that are otherwise sluggish or do
not take place in the dark, such as CO
2 2 4
reduction, C H
epoxidation, and NH
3
synthesis.[5] Thus, the dual plasmonic–
catalytic function[6] of our catalyst is meant to enable the utilization
of visible light for driving the AOR. This objective is shown to be
realized: the bimetallic catalyst exhibits higher catalytic current
densities for the AOR under LSPR excitation. This photo-
enhancement makes the catalyst superior to previously reported
ones. We show that the enhancement in AOR performance stems
from energetic electron−hole carriers generated by LSPR
excitation and the resulting photochemical potential sustained on
the Au@Pt NPs. The photochemical potential increases linearly
with increasing light intensity, in line with the prediction of a
general model of the steady-state effect of continuous LSPR
excitation.
Hydrogen is being explored as a carbon-emissions-free
replacement for fossil fuels in a variety of energy sectors including
fuel cells for vehicles. But deployment of hydrogen is limited by its
low volumetric energy density and safety hazards, which make
storage and transportation challenging and cost-ineffective.[
1]
3
Ammonia (NH ) may be a promising alternative as a hydrogen
carrier because of its high hydrogen content, easy liquidation,
safer storage and transportation, and carbon-free combustion
Au@Pt NPs were synthesized by a seed-mediated growth
method using HAuCl
ascorbic acid as the reducing agent. In this synthesis, Au NPs
4
and K
2
PtCl
6
as the metallic precursors and
[7]
profile.[ In addition, NH
2]
can be used directly as an energy
fuel cells.[3] In both cases, the
liberation of hydrogen or energy from NH requires the oxidation
of NH . The ammonia oxidation reaction (AOR) is however
3
formed first by the rapid reduction of HAuCl
served as seeds for the epitaxial deposition of Pt NPs by the
slower reduction of K PtCl . Transmission electron microscopy
TEM) images of the synthesized colloid (Figure S1a) showed Au
4
. Then, the Au NPs
source in so-termed direct NH
3
3
2
6
3
(
kinetically sluggish and electrocatalytic means are required to
drive the reaction. Pt is the most active electrocatalyst for the AOR;
however, for practical deployment of electrochemical AOR, it is
necessary to boost the catalytic activity of Pt, so that the process
is more energy-efficient and/or reliant on lower amounts of
expensive Pt. Some improvement in AOR activity has been
achieved by crystal orientation engineering, second-metal
alloying, and modification with oxides. Here, we demonstrate
the use of visible light-excitation for enhancing the AOR activity of
a Pt-based electrocatalyst in a systematic manner.
NPs of a nominal diameter of 30 nm decorated with a constellation
of Pt NPs of a nominal diameter of 5 nm. High-angle annular dark-
field scanning transmission electron microscopy (HAADF–STEM)
images and elemental mapping and line-scan based on X-ray
energy dispersive spectroscopy confirmed the core–satellite
morphology of the Au@Pt NPs (Figure S2). The Au:Pt molar ratio
was measured to be 2.01 by elemental analysis conducted by
inductively coupled plasma–optical emission spectrometry (ICP–
OES). The X-ray diffraction pattern of Au@Pt NPs showed
characteristic peaks of both fcc Au and fcc Pt (Figure S3),
indicating the presence of crystalline Au and Pt domains. The
diffraction peaks for Pt were considerably broadened, which is in
line with the smaller size of the Pt crystallites in the Au@Pt NPs.
[
4]
To impart the AOR electrocatalyst with a strong visible-light
response, we employ a bimetallic composition comprised of Au
nanoparticles (NPs) that bear smaller Pt NPs grown epitaxially on
1
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202007202
COMMUNICATION
The diffraction peaks of the Au@Pt NPs show no shift relative to
those of their monometallic Au and Pt counterparts, which
indicates that the Au@Pt NPs have a non-alloyed structure. The
Au@Pt NPs exhibit in extinction spectra (Figure S1d) a LSPR
band centered at 551 nm. This band is red-shifted and broadened
relative to the LSPR band of Au NPs, which is an effect of the
contribution of the complex dielectric function of Pt in the visible
spectrum range as well as other factors such as non-resonant
plasmonic coupling[8] between the Au and Pt domains, interfacial
electronic hybridization, and charge transfer[9] between the two
domains. The Pt NPs show a featureless absorption in the visible
spectrum range with no LSPR band. The structural and
crystallographic characteristics of the Au NPs and Pt NPs are
described in the Supporting Information (Figures S1 and S3)
Working electrodes were prepared by coating glassy carbon
electrodes (GCEs) with the synthesized NPs, as described in the
Supporting Information. The electrocatalytic activity of each
catalyst toward the AOR was examined by cyclic voltammetry in
a single-compartment three-electrode cell with an aqueous
anodic current peak in the 0.6–0.8 V potential region. This peak
can be attributed to the catalytic oxidation of NH
confirmed by the absence of this peak in a NH -free electrolyte
(Figure S5). We determined from the NH peak the peak current
3
, which is
3
3
density, which is a measure of the specific AOR activity of the
electrocatalyst. In the dark, the peak current density of Au@Pt
-2
NPs is measured to be 0.42 mA cm , which is higher than that of
-2
Pt NPs (0.25 mA cm ). The higher activity of the Au@Pt NPs
compared to the monometallic NPs is indicative of a synergistic
effect. The junctions between the Au and Pt NPs may be sites of
high activity, as further supported by the significantly lower activity
-2
(0.04 mA cm ) of the physical mixture of Au and Pt NPs, which
lack an adjoined/proximal placement of the Au and Pt domains. In
the Au@Pt NPs, charge re-equilibration at the junctions resulting
from the difference in the work functions of the two metals may be
a factor responsible for modulation of the activity.[11]
Under excitation of light of a wavelength of 532 nm and an
-2
intensity of 0.89 W cm , the AOR activity is enhanced relative to
the activity in the dark for both Pt NPs and Au@Pt NPs. The peak
current density (Figure 1b) is enhanced by ~2-fold and ~3-fold to
3 2
electrolyte consisting of 1 M NaOH and 0.05 M NH ·H O. The
-2
-2
AOR activity was measured both in the dark and under light
directly incident upon the working electrode. The light excitation
source was a continuous-wave (CW) laser with a wavelength of
reach a value of 0.53 mA cm and 1.20 mA cm for Pt NPs and
Au@Pt NPs respectively. The larger photo-enhancement factor of
Au@Pt NPs can be attributed to the plasmon-resonant absorption
532 nm that overlaps with the LSPR absorption of the Au@Pt NPs. of 532 nm light by the Au component, which the Pt NPs lack
Such LSPR photoexcitation has been found to facilitate
electrochemical oxidation reactions.[10] As described in the
Supporting Information, all applied potentials in cyclic
voltammogram (CVs) are presented with respect to the reversible
hydrogen electrode (RHE). The current measured by cyclic
voltammetry was normalized by the electrochemically active
surface area (ECSA) of the electrode (Figure S4 and Table S1) to
yield a current density.
despite their broadband absorption (Figure S1d). Au NPs despite
Figure 1. (a) CVs of electrocatalysts comprised of GCEs coated with Au@Pt
NPs (black), a mixture of Au and Pt NPs (orange), Pt NPs (red), and Au NPs
(
blue) in the dark at room temperature (dashed lines) and under 532 nm, laser
-
2
excitation of a incident intensity of 0.89 W cm (solid lines). The CVs were
measured at a scan rate of 20 mV s- under electrochemical AOR conditions,
1
3 2
i.e., an aqueous solution containing 1 M NaOH and 0.05 M NH ·H O. (b) The
peak current density and peak potential for the AOR measured under dark
conditions (black dots) are compared (as shown by the dotted arrow) with those
Figure 2. CVs of an electrocatayst comprised of a GCE coated with Au@Pt NPs
-
1
measured at a scanning rate of 20 mV s in an aqueous solution containing 1
M NaOH and 0.05 M NH ·H O (a) under 532 nm laser excitation at different
cm- laser excitation (red dots) for
2
measured under 532 nm, 0.89
W
3
2
electrocatalysts comprised of GCEs coated with Au@Pt NPs, a mixture of Au
and Pt NPs, and Pt NPs. Each data point represents the average of
measurements on three different but identically prepared electrocatalysts and
the standard deviation is shown by the error bar.
incident light intensities and (b) in the dark at different temperatures of the bulk
electrolyte. Each of these temperatures corresponds to the local steady-state
temperature measured at the electrode surface under 532 nm laser excitation
of a specific intensity from the set used for the study presented in (a): 23.6, 25.3,
-
2
27.7, 30.1, 32.6, and 34.9 °C at 0, 0.13, 0.38, 0.64, 0.89, and 1.15 W cm ,
respectively. All potentials are presented with respect to the RHE. (c) Peak
current density plotted as a function of the incident light intensity in the laser
excitation study (panel a) and plotted as a function of the incident light intensity
corresponding to the temperature employed in the dark control study (panel b).
In panel c, each data point is an average of measurements on three different
but identically prepared electrocatalysts and the standard deviation is shown by
the error bar.
The CVs in Figure 1a compare the electrochemical
performances of the catalysts under AOR conditions in the dark
and under light irradiation. The Au NPs showed no measurable
activity. The CVs of the other three catalysts each exhibit a major
2
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202007202
COMMUNICATION
their LSPR absorption show no AOR activity even under light
excitation because of the lack of the catalytically functional Pt
component. The physical mixture of Au and Pt NPs shows little to
no enhancement under light excitation, which shows that the
tandem structure with interfacial contact is critical not only for
synergistic electrocatalytic performance but also for the photo-
enhancement of electrocatalytic activity.
There is a corollary effect of light excitation: the peak
potentials shift in the positive direction (Figure 1b) as shown
further in Figure S6. For an anodic oxidation reaction, the
requirement of a larger potential implies a higher energy input and
a lower efficiency, which is undesirable. But the peak potential
shift is marginal (~2% in Figure 1b) for Au@Pt NPs and therefore
not detrimental to performance. In fact, the electrocatalytic AOR
activity of Au@Pt NPs under LSPR excitation is large enough to
shown by a control study performed in the dark (Figure S9); the
photochemical effect of LSPR excitation plays a minor role.
This photochemical enhancement of the AOR is attributed to
charge carriers generated by LSPR excitation, similar to what has
been observed in other chemical and electrochemical redox
reactions.[
5-6, 10]
In Au, electron–hole pairs are formed primarily by
interband damping of LSPRs. The electron occupies an empty sp
band state above the Fermi level, while the hole lies deep within
the d-band. In chemical redox reactions, typically one of these
carriers–the electron or the hole–is removed on a faster timescale
by
a scavenger. This effectively achieves charge carrier
separation. The other carrier is stored on the NP and can
participate on a slower timescale in the redox reaction. In an
electrochemical reaction under LSPR excitation, an analogous
process can take place. Under an applied positive potential,
make this catalyst superior to previously reported ones (Table S2). excited electrons generated by LSPR excitation are rapidly
In a long-term reaction, it is also confirmed that gaseous N is removed into the external circuit, leaving behind excess holes on
generated as the primary product with a Faradaic efficiency of ~93% the NP.[10] Consequently, under CW laser excitation, there is a
2
(
Figure S7). Following a 15-h long reaction, the core–satellite
steady-state accumulation of holes on the NPs, i.e., an anodic
photopolarization of the electrode that supplements the applied
external potential. The effectively higher anodic potential results
in an increased rate of hole transfer from the electrode to solution-
phase reactants and consequently in enhanced AOR kinetics.
The photo-induced enhancement of the kinetics of charge transfer
is verified by electrochemical impedance spectroscopy (Figure
S10).
morphology of the Au@Pt NPs is found to be maintained (Figure
S8); however elemental analysis showed that the Au:Pt molar
ratio decreased to 1.84, indicating a small loss of Au.
The origin of the LSPR enhancement is elucidated by an
additional study. LSPRs excited in the metal NPs decay to form
excited electron–hole pairs, which are known to enhance the
kinetics of redox reactions.[5a-h, 10] However, there is a process that
occurs in parallel: excited electron–hole pairs decay non-
radiatively by electron-phonon coupling, which results in heating
of the NP lattice, and subsequently by phonon–phonon coupling,
which results in the transfer of heat from the heated NP lattice to
the surrounding medium. This photothermal heating of the local
medium around the NP surface is a potential contributor to the
acceleration of reaction kinetics.[6b, 10] To determine the role of
these two factors–photogenerated charge carriers and
photothermal heating–in the measured photo-enhancement, we
studied the AOR activity of Au@Pt NPs under laser excitation of
different incident light intensities ranging from 0 to 1.15 W cm-2
(
Figure 2a). The peak current density increases with increasing
light intensity in a superlinear manner (red data points in Figure
c). We also measured at each of these laser intensities the local
2
steady-state temperature at the electrode surface. The local
temperature increases from 23.6 to 34.9 oC linearly with
increasing light intensity (Figure S6a). This modest rise in the
local temperature under light excitation is a manifestation of
photothermal heating. To account for this photothermal heating, a
separate control study was performed where the AOR activity was
measured in the dark with the bulk electrolyte temperature set to
each of these measured temperatures (Figure 2b). This control
study shows that only a small portion of the photoinduced
increase in the peak current density is due to a photothermal rise
in the local temperature (black data points in Figure 2c). The
increased local temperature likely enhances the kinetics of charge
transfer, surface chemical reactions, and solution-phase diffusion,
resulting in the modest increase in AOR activity. However, as
seen from the results in Figure 2c, a major portion of the
photoinduced enhancement of the peak current density is not
accounted for by this photothermal effect. In other words, the
primary cause of the photoinduced enhancement of AOR activity
of Au@Pt NPs is photochemical in nature. Unlike the case for
Au@Pt NPs, for Pt NPs, the photoinduced enhancement is in
large part due to a photothermal rise of the local temperature, as
Figure 3. A plot of RTln(jpeak) as a function of the incident light intensity for
electrochemical AOR on Au@Pt NPs under 532 nm laser excitation. RTln(jpeak
)
scales linearly with the incident light intensity as seen from a linear fit to the
data-points (dashed line) with a slope of 2.73×103 s cm2 mol . The value of
-1
RTln(jpeak) at each light intensity is based on the peak current density, jpeak
,
measured in the study presented in Figure 2a. Each data point is the average
value of RTln(jpeak) from three different but identically prepared electrocatalyst
samples; the standard deviation is indicated by the error bar.
While the aforementioned explanation is qualitative, we
develop it into
a simple quantiative model and test it
experimentally. There is a linear free-energy relationship between
the activation free energy of a reaction and the reaction free
energy, as a result of which the rate of a reaction depends on the
reaction free energy as:
ꢄꢅꢆꢇ
ꢀ
ꢁꢂꢃ � ꢈ ꢉ = −∆ꢊ (1)
where R is the gas constant (8.314 J mol-1 K ), T is the
-1
temperature (in units of K), A is a constant with units of rate, and
∆G is the standard Gibbs free energy of the reaction (in units of J
3
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202007202
COMMUNICATION
-
1
mol ). For an electrochemical half-reaction, the applied electrode
exhibits an activity that outperforms other electrochemical AOR
schemes. The AOR activity increases exponentially with
increasing light intensity, which matches the prediction of a simple
model that attributes the photo-enhanced electrochemical activity
to a steady-state photopotential induced on the NPs by the
accumulation of d-band holes. This photopotential is linearly
tunable by variation of the light intensity. The principles developed
here will promote widespread usage of plasmonic light absorbers
for harvesting light energy for electrochemical conversions,
thereby aiding the electrification of chemical processes.
potential, E, contributes a free energy. As a result:
ꢋ
ꢀ
ꢁꢂꢃ � ꢉ = −∆ꢊ + ꢌꢃꢍꢎ (2)
ꢈ′
Here the electrochemical current density, j, is a measure of the
reaction rate. A’ is a constant with units of the current density, θ
is a phenomenological constant that incorporates the charge
transfer coefficient, n is the number of electrons involved in the
electrochemical reaction, and F is the Faraday constant. Eq. (2)
is a rendition of the Butler-Volmer relationship. While eq. (2) is
applicable in the dark, under CW LSPR excitation, there is an
additional free energy contribution,
G
photo
,
due to the
Acknowledgements
photopotential induced on the NPs. If we assume no coupling
between the photochemical perturbation and the applied
electrochemical potential, we obtain:
P.K.J. acknowledges funding in the form of the Discovery Award
from UIUC Department of Chemistry. Funding for this work was
provided in part by the Energy & Biosciences Institute (EBI)
through the EBI-Shell program. TEM, STEM, and X-ray EDS
characterization were carried out in the Materials Research
Laboratory Central Research Facilities, University of Illinois.
ꢋphoto
ꢀꢁꢂꢃ �
ꢉ = −∆ꢊ + ꢌꢃꢍꢎ + ꢊꢏꢐꢑꢒꢑ (3)
ꢈ′
which combined with (2) gives:
ꢋphoto
ꢈ′
ꢋ
ꢉ = ꢀꢁꢂꢃ � ꢉ + ꢊ
ꢈ′
ꢀꢁꢂꢃ �
(4)
ꢏꢐꢑꢒꢑ
Keywords: catalysis • electrochemistry • localized surface
Thus, due to the contribution, ꢊꢏꢐꢑꢒꢑ, of the photopotential, the
current density under LSPR excitation, jphoto, is predicted to be
enhanced relative to the value, j, in the dark, which is in line with
the experimental observations (Figure 1). Yu and Jain[12] have
found that the free energy contribution of electron–hole pairs
generated by LSPR excitation scales linearly as the incident light
intensity, I. Using a similar light-intensity dependent free energy
contribution, we get:
plasmon resonance • photochemistry
[1]
a) L. Schlapbach, A. Zuttel, Nature 2001, 414, 353-358; b) T. He, P.
Pachfule, H. Wu, Q. Xu, P. Chen, Nat. Rev. Mater. 2016, 1, 16059-16075.
a) A. Klerke, C. H. Christensen, J. K. Norskov, T. Vegge, J. Mater. Chem.
[2]
2008, 18, 2304-2310; b) R. F. Service, Science 2018, 361, 120-123.
[
3]
4]
C. Zamfirescu, I. Dincer, J. Power Sources 2008, 185, 459-465.
a) Y. Katayama, T. Okanishi, H. Muroyama, T. Matsui, K. Eguchi, J. Phys.
Chem. C 2015, 119, 9134-9141; b) N. Sacre, M. Duca, S. Garbarino, R.
Imbeault, A. Wang, A. H. Youssef, J. Galipaud, G. Hufnagel, A. Ruediger,
L. Roue, D. Guay, ACS Catal. 2018, 8, 2508-2518; c) H. S. Pillai, H. L.
Xin, Ind. Eng. Chem. Res. 2019, 58, 10819-10828.
[
ꢋphoto
ꢈ′
ꢋ
ꢀꢁꢂꢃ �
ꢉ = ꢀꢁꢂꢃ � ꢉ + ∅ꢓ (5)
ꢈ′
where I has units of W cm-2 and Φ is a photochemical conversion
[5]
a) Y. Kim, D. D. Torres, P. K. Jain, Nano Lett. 2016, 16, 3399-3407; b)
Y. Kim, A. J. Wilson, P. K. Jain, ACS Catal. 2017, 7, 4360-4365; c) S. J.
Yu, A. J. Wilson, G. Kumari, X. Q. Zhang, P. K. Jain, ACS Energy Lett.
2
-1
coefficient (with units of s cm mol ) that is a measure of the free
energy contributed to the electrochemical reaction by LSPR
2
017, 2, 2058-2070; d) S. J. Yu, A. J. Wilson, J. Heo, P. K. Jain, Nano
Lett. 2018, 18, 2189-2194; e) S. Yu, P. K. Jain, Nat. Commun. 2019, 10,
022; f) S. J. Yu, P. K. Jain, ACS Energy Lett. 2019, 4, 2295-2300; g) X.
-2
excitation of an incident intensity of 1 W cm . Eq. (5) predicts that
the electrochemical activity, measured in the form of the current
density, ꢔꢏꢐꢑꢒꢑ , will increase exponentially with increasing light
intensity, which is consistent with the behaviour of the peak
current density, jpeak, measured for the AOR on Au@Pt NPs under
2
Q. Zhang, G. Kumari, J. Heo, P. K. Jain, Nat. Commun. 2018, 9, 3056;
h) A. J. Wilson, V. Mohan, P. K. Jain, J. Phys. Chem. C 2019, 123,
29360-29369; i) X. Zhang, X. Q. Li, D. Zhang, N. Q. Su, W. T. Yang, H.
O. Everitt, J. Liu, Nat. Commun. 2017, 8, 14542; j) C. Y. Hu, X. Chen, J.
B. Jin, Y. Han, S. M. Chen, H. X. Ju, J. Cai, Y. R. Qiu, C. Gao, C. M.
Wang, Z. M. Qi, R. Long, L. Song, Z. Liu, Y. J. Xiong, J. Am. Chem. Soc.
532 nm laser excitation (red data points in Figure 2c).
Furthermore, as per eq. (5), RTln(ꢔꢏꢐꢑꢒꢑ) ought to scale linearly
with the light intensity. We plotted RTln(ꢔꢏeak) as a function of the
incident light intensity (Figure 3) and found the dependence to be
linear, which is in accordance with eq. (5). Since, RTln(ꢔꢏeak) is
also a measure of the photopotential induced by LSPR excitation
of the NPs, the observation implies that the photopotential scales
linearly with the light intensity. The linear dependence may break
2019, 141, 7807-7814; k) S. Mukherjee, F. Libisch, N. Large, O.
Neumann, L. V. Brown, J. Cheng, J. B. Lassiter, E. A. Carter, P.
Nordlander, N. J. Halas, Nano Lett. 2013, 13, 240-247; l) S. Mukherjee,
L. A. Zhou, A. M. Goodman, N. Large, C. Ayala-Orozco, Y. Zhang, P.
Nordlander, N. J. Halas, J. Am. Chem. Soc. 2014, 136, 64-67.
a) S. Mubeen, J. Lee, N. Singh, S. Kramer, G. D. Stucky, M. Moskovits,
Nat. Nanotechnol. 2013, 8, 247-251; b) F. Wang, C. H. Li, H. J. Chen, R.
B. Jiang, L. D. Sun, Q. Li, J. F. Wang, J. C. Yu, C. H. Yan, J. Am. Chem.
Soc. 2013, 135, 5588-5601; c) Z. K. Zheng, T. Tachikawa, T. Majima, J.
Am. Chem. Soc. 2014, 136, 6870-6873; d) Z. K. Zheng, T. Tachikawa, T.
Majima, J. Am. Chem. Soc. 2015, 137, 948-957; e) T. Oshikiri, K. Ueno,
H. Misawa, Angew. Chem. Int. Ed. 2016, 55, 3942-3946; f) J. H. Yang,
Y. Z. Guo, R. B. Jiang, F. Qin, H. Zhang, W. Z. Lu, J. F. Wang, J. C. Yu,
J. Am. Chem. Soc. 2018, 140, 8497-8508; g) H. L. Jia, A. X. Du, H. Zhang,
J. H. Yang, R. B. Jiang, J. F. Wang, C. Y. Zhang, J. Am. Chem. Soc.
2019, 141, 5083-5086.
[6]
down at higher light intensities where multi-carrier processes
become dominant;[5a, 5d, 13] but this regime does not appear to be
reached within the intensity range of our study. The slope of the
linear plot yields a photochemical conversion coefficient of ~3000
s cm2 mol , which implies that LSPR excitation of an incident
-1
-2
-1
intensity of 1 W cm contributes 3 kJ mol to the free energy of
the reaction, or equivalently a photopotential of 30 mV.
In summary, we have designed a Au@Pt electrocatalyst for
AOR that combines plasmon-resonant light absorption with
electrocatalytic sites for the AOR. Under LSPR excitation of
[7]
H. Ataee-Esfahani, L. Wang, Y. Nemoto, Y. Yamauchi, Chem. Mater.
2010, 22, 6310-6318.
-2
moderate light intensity (~1 W cm ), this tandem electrocatalyst
4
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202007202
COMMUNICATION
[8]
a) S. Sheikholeslami, Y. W. Jun, P. K. Jain, A. P. Alivisatos, Nano Lett.
010, 10, 2655-2660; b) H. J. Jang, S. Hong, S. Ham, K. L. Shuford, S.
2
Park, Nanoscale 2014, 6, 7339-7345.
[9]
a) Z. Lou, M. Fujitsuka, T. Majima, ACS Nano 2016, 10, 6299-6305; b)
D. Y. Kim, K. W. Choi, X. L. Zhong, Z. Y. Li, S. H. Im, O. O. Park,
CrystEngComm 2013, 15, 3385-3391.
[10] L. Huang, J. S. Zou, J. Y. Ye, Z. Y. Zhou, Z. Lin, X. W. Kang, P. K. Jain,
S. W. Chen, Angew. Chem. Int. Ed. 2019, 58, 8794-8798.
[11] a) K. Tedsree, T. Li, S. Jones, C. W. A. Chan, K. M. K. Yu, P. A. J. Bagot,
E. A. Marquis, G. D. W. Smith, S. C. E. Tsang, Nat. Nanotechnol. 2011,
6, 302-307; b) S. T. Hunt, M. Milina, A. C. Alba-Rubio, C. H. Hendon, J.
A. Dumesic, Y. Roman-Leshkov, Science 2016, 352, 974-978.
12] S. J. Yu, P. K. Jain, Angew. Chem. Int. Ed. 2020, 59, 2085-2088.
13] Y. Kim, J. G. Smith, P. K. Jain, Nat. Chem. 2018, 10, 763-769.
[
[
5
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202007202
COMMUNICATION
Entry for the Table of Contents
A photochemical potential generated by the excitation of localized surface plasmon resonances of a bimetallic Au@Pt nanoparticle
catalyst boosts electrochemical ammonia oxidation activity.
Institute and/or researcher Twitter usernames: @plasmon @ChemistryUIUC @BeckmanInst @Illinois_Alma
6
This article is protected by copyright. All rights reserved.