3D hierarchical porous indium catalyst for highly efficient electroreduction of CO2

Article abstract of DOI:10.1039/c8ta11645h

The electrochemical reduction of CO₂ requires highly active, selective as well as stable electrocatalysts. Herein, we report a three-dimensional hierarchical porous indium catalyst for the electroreduction of CO₂ to formate. In aqueous bicarbonate solution, the catalyst exhibits a high faradaic efficiency for formate (～90%) in the potential range of -1.0 to -1.2 V (vs. reversible hydrogen electrode) and reaches an unprecedented formate production rate of 1.14 mmol cm^-2 h^-1 at -1.2 V. Additionally, the catalyst also displays a long-term stability (24 h). Density functional theory calculations reveal the catalytically selective nature of In for formate production. Independent of the crystal facet, In surfaces stabilise ?OCHO, a key intermediate for the formate pathway, much more effectively than the ?H (for the H₂ pathway) and ?COOH (for the CO pathway) intermediates. Experimental results demonstrate that the improved CO₂ reduction selectivity on the porous In catalyst originates from the reduced evolution of H₂, which is induced by the high local pH in the vicinity of the electrode. Furthermore, the porous In can also serve as a template to synthesise a porous Pd-In catalyst for tuning the selectivity of formate and CO, demonstrating its promising potential for CO₂ electroreduction.

Full text of DOI:10.1039/c8ta11645h

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ISSN 2050-7488
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Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
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ARTICLE
3
D Hierarchical Porous Indium Catalyst for Highly Efficient
Electroreduction of CO2
Wen Luo, * Wei Xie, Mo Li, Jie Zhang,a,b Andreas Züttela,b
a,b
c
a,b
Received 00th January 20xx,
Accepted 00th January 20xx
The electrochemical reduction of CO
three-dimensional hierarchical porous indium catalyst for the electroreduction of CO
solution, the catalyst exhibits a high faradaic efficiency for formate (~ 90%) in the potential range of −1.0 to −1.2 V (vs.
2
requires highly active, selective as well as stable electrocatalysts. Herein, we report a
DOI: 10.1039/x0xx00000x
2
to formate. In aqueous bicarbonate
www.rsc.org/
‑
2
–1
reversible hydrogen electrode) and reaches an unprecedented formate production rate of 1.14ꢀmmolꢀcm ꢀh at −1.2 V.
Additionally, the catalyst also displays a long-term stability (24 h). Density functional theory calculations reveal the
catalytically selective nature of In for formate production. Independent of the crystal facet, In surfaces stabilise *OCHO, a
key intermediate for the formate pathway, much more effectively than the *H (for the H
pathway) intermediates. Experimental results demonstrate that the improved CO reduction selectivity on the porous In
catalyst originates from the reduced evolution of H , which is induced by the high local pH in the vicinity of the electrode.
Furthermore, the porous In can also serve as a template to synthesise a porous Pd–In catalyst for tuning the selectivity of
formate and CO, demonstrating its promising potential for CO electroreduction.
2
pathway) and *COOH (for the CO
2
2
2
2
desirable to develop a CO -to-formate electrocatalyst that
1
. Introduction
works at a relatively low overpotential while exhibiting high
activity and selectivity.
Electrochemical reduction of carbon dioxide (CO
chemicals and carbon-based fuels using renewable sources of
electricity is a promising strategy to reduce CO emissions by
replacing existing petrochemical-based processes. Among
CO RR products, formic acid (or formate) is an attractive
chemical that has been widely used in cleaning products, for
feed preservation, and in the leather processing industry.
Additionally, the electrochemical formate production process
can also be integrated with biological formate conversion
process to generate higher alcohols. However, despite that
the equilibrium potential for this 2-proton/electron reaction
2
RR) into useful
Early studies have identified several transition and post-
transition metals, including Cd, Hg, In, Sn, Tl, Pb, and Bi, as
2
4
,5
2
selective catalysts for CO -to-formate. Among them, In is
suggested as a potential catalyst for practical formate
production, since it is less toxic and more environmentally
2
2
–6
benign than many of its neighbours. Recent researches have
shown that In-based catalysts can readily reduce CO to formate
1
2
in an aqueous electrolyte with faradaic efficiencies (FE) >80%;
however, with limited current density at reasonable
overpotentials. For example, oxidised In foil and In
2
,3
nanoparticles were found to reduce CO
2
to formate with a
(
2
CO → HCOOH) at pH 7 is approximately 0 V (compared to a
selectivity of >90%, but the current densities were lower than
reversible hydrogen electrode, RHE; all potentials in this paper
are versus RHE unless otherwise specified), at low
overpotentials the reaction efficiency is limited by sluggish
kinetics. Moreover, the poor selectivity due to the myriad
possible reaction pathways for CO RR and, in particular, the
2
competitive hydrogen evolution reaction (HER) also represents
a significant challenge for this reaction. Therefore, it is highly
–2
7,8
1
0 mAꢀcm at the potentials of highest formate FEs. On a
dendrite In electrode, the maximum FE (~ 86%) was achieved at
–2 9
−
0.86 V with a current density of 5.8 mA cm . Even on a gas
diffusion In/carbon electrode, the total current density only
–2
10
reached 6.2 mAꢀcm at −1.2 V. Moreover, the stability of In-
based catalysts has not yet been extensively evaluated and no
9
,11
catalyst with more than 2 h stability has been reported. Thus,
the performance of In-based catalysts, in terms of selectivity,
activity and stability, needs to be greatly improved before any
practical applications.
a. Laboratory of Materials for Renewable Energy (LMER), Institute of Chemical
Sciences and Engineering (ISIC), Basic Science Faculty (SB), École Polytechnique
Fédérale de Lausanne (EPFL) Valais/Wallis, Energypolis, Rue de l’Industrie 17, CH-
Manipulating the structure of the electrode, particularly
creating a highly porous structure, has been recently recognized
as an effective means to enhance the catalytic performance.
1
951 Sion, Switzerland
b.
c.
Empa Materials Science & Technology, CH-8600 Dübendorf, Switzerland
INAMORI Frontier Research Center, Kyushu University, 744 Motooka, Nishiku,
Fukuoka 819-0395, Japan.
Corresponding author: wen.luo@epfl.ch
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
1
2
13
14
While porous metal electrodes, such as Cu, Ag, and Au
have been fabricated and demonstrated as promising CO RR
2
*
catalysts, a porous In electrode may also be designed.
Nevertheless, the special physical and chemical properties of In,
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for example, its soft nature (Young's modulus is 11 GPa), low acetone, water, and 2 M HNO
melting point (156.5 C) and easy to oxidise properties, limit the washed with Milli-Q water and dried in a flow of N
3
for 5 min, sequentially, and then
View Article Online
DOI: 10.1039/C8TA11645H
o
2
. The working
engineering of its nanostructure. Indeed, not only is such a electrolyte was prepared with a 1.5 M (NH
4 2 4
) SO and 0.03 M
porous In catalyst still lacking, the reaction mechanisms of CO In (SO aqueous solution. The hp-In was deposited on the Cu
2
-
2
4 3
)
–2
to-formate over In-based catalysts are also not clear. For mesh at a constant current density of 1.0 mAꢀcm (normalised
instance, Bocarsly et al. suggested that the oxidised In layer on to the geometric surface area) for 120 s. After the deposition,
the surface of an In electrode may be involved in the CO
reaction by forming a metal carbonate species, which is then subsequently dried in a N
2
RR the as-prepared hp-In was carefully washed with Milli-Q water,
flow, and then used as an electrode
2
7
,15
reduced to formate.
that an In/In composite catalyst produces CO, rather than In foil (Figure S1), used as a reference sample, was cleaned
formate, at a selectivity near 100%. Alternatively, for a sequentially with acetone, water, and 2 M HCl for 5 min and
dendritic In catalyst, the high local CO concentration near the then washed with Milli-Q water and dried in a N flow.
electrode induced by the local electric field was proposed as the The two additional porous In electrodes used in control
2
In contrast, Shaughnessy et al. found for CO RR.
2 3
O
1
6
2
2
9
,17
reason for the high catalytic performance observed.
ambiguous CO RR mechanism greatly impedes the for hp-In but under different conditions: sample 1, 0.125
development of advanced In catalysts; thus, systematic studies mAꢀcm for 500 s (named hp-In-0.125) and sample 2, 0.5
The experiments were prepared by the same method as that used
2
–2
–2
using experimental and theoretical methods are urgently mAꢀcm for 200 s (named hp-In-0.5).
required to gain further insights into the reaction mechanisms. Porous In on Ni mesh electrode was prepared using a 1.5 M
In this work, we developed a three-dimensional (3D) (NH
hierarchical porous In catalyst (hp-In) for CO RR using a facile deposited on Ni mesh at 2.0 Aꢀcm for 180 s.
electrochemical deposition method. Under a high current Porous Pd electrode was prepared using a 2.0 M H
deposition condition, bubbles generated from the PdCl and 50 mM NaCl aqueous solution. Pd was deposited on
accompanying HER serve as a geometric template. The as- Cu mesh at 2.0 Aꢀcm for 200 s.
prepared hp-In electrode exhibits a high faradaic efficiency for Pd–In electrodes were prepared by dipping the fresh hp-In into
4 2 4 2 4 3
) SO and 0.03 M In (SO ) aqueous solution. In was
–2
2
2 4
SO , 2 mM
H
2
2
1
8
–2
19
formate (~90%) and reaches the highest formate production 1.0 mL PdCl
2
aqueous solutions for 5 min. PdCl
2
solutions with
rate (1.14 mmol cm–2
h
–1
at −1.2 V) among the state-of-the-art different concentrations (0.1, 0.5, 1.0 and 2.0 mM) were
. After Pd
theory (DFT) calculations combined with detailed experimental deposition, the as-prepared electrodes were carefully washed
studies revealed that the high formate selectivity over hp-In is with Milli-Q water and sequentially dried under N flow. The Pd-
catalysts in aqueous solution reported. Density functional prepared with 0.1 M NaCl and certain amount of PdCl
2
2
attributed to the strong adsorption of an *OCHO intermediate In electrodes were denoted as Pd-In-0.1, Pd-In-0.5, Pd-In-1.0
on In facets and the high local pH near the highly roughened and Pd-In-2.0 respectively, according to the concentration of
2
-
4
electrode surface. Furthermore, the hp-In electrode was also [PdCl ] in the solutions.
applied as a template to synthesise a porous Pd–In catalyst for
tuning the CO
2
RR selectivity.
2.3 Characterisation. Scanning electron microscopy (SEM) images
were taken on an FEI Teneo system and X-ray diffraction (XRD)
patterns were obtained from a Bruker D8 Advance equipped
with a Cu Kα X-ray source at 40 kV and 40 mA. The X-ray
2
. Experimental part
2
(
.1 Materials. Cu mesh (80 mesh), Ni mesh (100 mesh), In foil photoelectron spectroscopy (XPS) results were recorded using a
0.127 mm, 99.99% metal basis), In (SO
(99.99% metal basis), Phoibos 100 (SPECS) hemispherical electron analyser with Mg
(2.0 N standardised solution) Kα X-ray source (hv = 1253.6 eV). The XPS spectra were
(65%) were purchased from Alfa Aesar. (NH SO
recorded at a pass-energy of 90 eV for the survey and 20 eV for
SO (75%) and KHCO (99.5%) were purchased from the narrow scans in the fixed analyser transmission mode. The
2
4 3
)
2 3
PdCl (99.9% metal basis), HNO
and HNO
99.5%), H
3
)
4 2
4
(
2
4
3
Carl Roth. NaCl (99.5%) was purchased from Fluca. HCl (32%)
was purchased from Reactolab SA. A Ag/AgCl reference
electrode (3ꢀM NaCl) was purchased from ALS Corporation,
samples are conductive, and thus no charge compensation was
needed. The ICP-OES measurements were taken using an
Agilent 5110 inductively coupled plasma optical emission
spectrometry (ICP-OES) system. All the samples were dissolved
2 2
Japan. High-purity CO (99.999%) and N (99.999%) were
supplied by Cabagas, Switzerland. All chemicals were used as
received without further purification. Electrolyte solutions were
prepared using Milli-Q water (Millipore, 18.2 MΩ cm).
in 65% HNO
standard solutions with different concentrations were prepared
with PdCl and In (SO in 2% HNO , respectively. The obtained
mass loadings of Pd and In were listed in Table S1.
3
and then diluted with Milli-Q water. Pd and In
2
2
)
4 3
3
2
.2 Sample preparation. The hp-In was prepared by an
electrochemical deposition method modified from previous
2
.4 Electrochemical measurements. All electrochemical
measurements were performed with a two-compartment cell
H-Cell) and the working and counter electrode compartments
reports.1
2,18
The electrodeposition was performed in a two-
electrode cell using the Cu mesh as the working electrode (and
also providing a substrate for the hp-In) and Pt wire as the
counter electrode. The Cu mesh (0.4ꢀcmꢀ×ꢀ0.5 cm, with a
(
were separated with a Nafion membrane (212, DuPont). An
Autolab PGSTAT 204 potentiostat was used to record the data.
0
.2ꢀcmꢀ×ꢀ0.5 cm rectangular tip for holding) was sonicated in
2
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A piece of platinum gauze (2.5ꢀcm × 2.5 cm) and a Ag/AgCl approximation (GGA) and Perdew, Burke, and ErnzVeierwhAorftic(lPeBOEnl)i n2 e9
electrode were applied as the counter and reference exchange-correlation function. Four In surDfaOcI:e1s0,.1in0c39lu/Cd8inTgA1(1160415H),
electrodes, respectively.
(002), (110), and (112), were modelled using three-layer (2 × 2)
The the electrochemical surface area (ECSA) of the electrode periodic unit cells, with the bottom layer fixed during
was determined by measuring the double-layer capacitance optimisation while the remaining atoms relaxed. Projector
3
0
(
0
C
dl). Cyclic voltammetry (CV) was performed at scan rates of augmented wave pseudopotentials were used to describe the
.1, 0.15, 0.2, 0.25, and 0.3 Vꢀs– in a N
1
-bubbled 0.1 M KHCO
interactions between the ions and the electrons in expanding
2
3
electrolyte. The potential window of CV was selected to be plane waves with a cutoff energy of 400 eV and a (5,5,1) k-point
3
1
between −0.34 and −0.44 V, where only double-layer charging sampling Monkhorst-Pack grid.
Different adsorption
and discharging is relevant. The total charging current at a given configurations were considered and only those adsorbate
scan rate was determined as the difference between the anode configurations with the lowest energy were used for the final
current and the cathode current at −0.39 V. These capacitive free energy diagrams.
currents were plotted against the scan rate, and the slope of All thermodynamic properties were calculated based on the
this plot was divided by 2 to obtain the value of Cdl. The ECSAs molecular vibration analysis from the DFT calculations. The
of the porous samples were then calculated using their Cdl Gibbs free energies were calculated at 298 K and 1 atm.
2
0
98
values divided by 30.5 μF cm– (the Cdl of the In foil, which is according to G = EDFT + EZPE + ∫
2
C dT ― TS, where EDFT is
V
2
0,21
very similar to the value of other planar metal surfaces
Electrochemical CO
with the H-Cell. Each compartment of the cell was filled with thermal capacity ∫
0 mL of 0.1 M KHCO
CO was introduced into the cathodic compartment at a flow system. For the gas molecules, including H
).
the DFT total energy, EZPE is the zero-point vibrational energy
2
reduction experiments were conducted (ZPE) obtained from the calculated vibrational frequencies, the
2
0
98
C dT was calculated from the heat
V
3
3
solution with 15 mL left as dead volume. capacity, T is the temperature, and S the entropy of the studied
, CO , CO, H O, and
2
2
2
2
‑
1
rate of 21 mLꢀmin (controlled by a mass flow controller, (EL- HCOOH, the ideal gas approximation was used, and for the
Flow, Bronkhorst)) during the experiments. Prior to the start of adsorbates, the harmonic approximation was used. Corrections
each experiment, the catholyte was saturated with CO
2 2
for at for CO , CO, and HCOOH were applied using the values for the
least 30 min (the pH value was measured to be 6.8). To enhance PBE function to describe accurately the free energy of the
3
2
2 2
the mass transport of CO during electrolysis, the catholyte was reaction for CO RR. An approximate solvation correction to
stirred continuously using magnetic agitation. All potentials account for the effect of water was applied for *COOH
were recorded against the Ag/AgCl reference electrode and (stabilised by 0.25 eV). Free energy diagrams were generated
3
3
then converted into RHE values using: E (vs. RHE) = E(vs. using the CHE method. Additional details of the DFT
Ag/AgCl) + 0.21 V + 0.0591 V × pH. The uncompensated ohmic calculations are provided in the Supporting Information.
loss (iRu) was corrected in situ via the current interrupt method,
and compensation levels were set to 85% of the measured
iRu.
2
2–26
3. Results and discussions
The same protocol was used for the stability test; however, in
order to avoid the accumulation of formate in the catholyte, a
multi-channel peristaltic pump (ISMATEC, REGLO Digital MS-4/8
3
.1 Synthesis and characterizations of hp-In.
The hp-In catalyst was synthesised by a facile one-step
template-free electrodeposition method at a constant current
8
34) was used to exchange the catholyte. That is, fresh CO
2
-
−2
density of −1.0 A cm for 120 s (Figure 1a and Figure S2). The
concomitant hydrogen bubbles generated during the
electrodeposition served as a geometric template, accounting
for the formation of hierarchical porous structures. (NH
was used as solvent to facilitate H evolution over the initial
deposited In layer, since In has a high hydrogen overpotential.
A copper mesh was selected as a support rather than a foil, as it
allows the transport of electrolyte around the mesh to
compensate the concentration gradient caused by
electrodeposition, and therefore ensures the uniform growth of
porous In. As revealed by the SEM images (Figure 1c–e), the In
layer was deposited homogeneously on the support with
uniformly interconnected macropores (~150 μm, Figure 1c)
which were inherited from the Cu mesh (Figure 1b). Close
observation revealed that densely packed In ‘leaves’ were
formed uniformly and vertically on the Cu wire, and between
the leaves, smaller macropores with diameters of 10 to 30 μm
were observed (Figure 1c–e). In addition, each of the In leaves
was fully covered by
saturated 0.1 M KHCO was pumped into the cathode
3
–1
compartment at a speed of 23 mLꢀmin while, concurrently, the
catholyte was also pumped out and collected at the same flow
rate to maintain a constant level of catholyte (30 mL) in the
cathode compartment.
4 2 4
) SO
2
4
2
.5 Product distribution analysis. The gas-phase products were
detected online with a gas chromatograph (GC, SRI instruments
610C) equipped with a thermal conductivity detector (TCD)
and a flame ionisation detector (FID, with a methaniser). The
CO gas flow, together with the products from the cathodic
8
2
compartment, was vented directly into the sampling loop of the
GC. Aliquots were collected every 20 min during the reaction,
and at least three injections were measured for each
experiment. Liquid products were collected after the reaction
and were detected by high-performance liquid chromatography
(
HPLC, Thermo Scientific, Dionex UltiMate 3000 Standard
2
7
System).
2
.6 DFT models and calculations. All plane-wave DFT
calculations were carried out with the Vienna ab initio
2
8
Simulation Program (VASP) using the generalised gradient
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DOI: 10.1039/C8TA11645H
(
a)
(b)
(d)
(e)
+
-
2
50 μm
150 μm
(
c)
Pt foil Cu mesh
250 μm
20 μm
(
f)
(g)
Figure 1 (a) Schematic illustration for the synthesis of hp-In. (b) SEM image of Cu mesh. (c)-(e) SEM images of hp-In at different magnifications. (f) XRD patterns of In
foil and hp-In. (g) XPS In 3d spectra of In foil and hp-In.
interconnected micro-gullies of appropriately 1 μm width The electrochemical performance of the hp-In was initially
(
Figure 1e). These morphological features clearly demonstrate investigated by CV measurements in 0.1 M KHCO
the successful electrodeposition of hp-In onto the Cu mesh with with N or CO (Figure 2a and Figure S5). The In foil was also
a structure consisting of three sizes of progressively larger tested under identical conditions for the purpose of
3
saturated
2
2
pores.
comparison. As shown in Figure 2a, in all cases, oxidation peaks
0
The crystal structure of the hp-In catalyst was examined by XRD. appeared at ca. −0.1 V, corresponding to the oxidation of In to
As shown in Figure 1f, diffraction peaks located at In .
3
+ 7,9,16
The reduction peaks appeared at around −0.4 V, with
approximately 32.7, 36.1, 38.9, 54.2, 56.3, 63.0, 66.8, peak areas similar to the oxidation peaks, which corresponds to
3
+
0 7,9,16
and 68.9 were consistent with those of the In foil and the the reduction of In to In .
metallic In phase (JCPDS card No. 01-80-5354). Additional peaks 2(a) shows that the redox peaks of In foil obtained in CO
were observed at 43.3 and 50.4 on the hp-In pattern, arising lower than those obtained in N , which could be due to the
from the Cu mesh support. The sharp diffraction peaks of the presence of adsorbed species during CO
Interestingly, the inset in Figure
2
are
2
3
4
2
RR. While in case of
hp-In indicate the high crystallinity of the deposited In (the hp-In, the redox peaks are much larger compared with those of
average crystallite size calculated using the Scherrer equation In foil, thus no obvious influence from reaction intermediates is
with full profile fitting was ~60 nm). XPS was performed to observed. At more negative potentials (< −0.6 V), the increase
investigate the surface chemical composition and oxidation in current densities (geometric current density, unless
state of the hp-In. No spectrum from Cu was observed in the otherwise specified) under N
survey spectrum (Figure S3), implying that the Cu mesh was fully the HER, while under CO conditions it is due to the HER and
covered by the porous In layer. Specifically, the In 3d5/2 XP CO RR. Obviously, both the In foil and hp-In electrodes show
spectra of the hp-In and In foil were deconvolved into two peaks higher current densities in CO conditions than those in N
Figure 1g), which were attributable to the metallic In (443.9 eV) demonstrating the active nature of In in reducing CO rather
and In (445.1 eV). The partially oxidised In could be removed than H O. Moreover, due to its porous structure, hp-In exhibits
2
conditions could be attributed to
2
2
2
2
,
(
2
2
+
O
3
2
by Ar sputtering performed in the XPS chamber (Figure S4), much higher current density than that of In foil.
therefore the oxidation of In should be associated with To identify and quantify the reduction products, bulk
oxidation in air prior to the XPS measurement. Such a thin layer electrolysis was conducted in CO -saturated 0.1 M KHCO . The
2 3
of oxidised In could be readily reduced at the beginning of FEs of the reduction products in the potential range of −0.6 to
7
CO
2
RR.
−1.2 V are displayed in Figure 2b–c for In foil and hp-In,
respectively. As shown, only H , CO, and formate were detected
3
.2 CO
2
RR performance over In foil and hp-In.
2
as the reduction products from the two electrodes, with a total
4
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FE of approximately 100%. Figure 2b shows that formate and H
ARTICLE
2
porous structure, the CO RR performance of the In electrode, in
2
View Article Online
are the main products obtained from the In foil electrode, the terms of both current density and formaDtOeI:s1e0l.e10c3ti9v/iCt8yT, Ac1a1n64b5He
FEs of which are strongly dependent on the applied potential, dramatically improved.
whereas the FE for CO is limited to less than 13% over the entire Because of the outstanding current densities and the high
2
potential range. Note that trace amounts of H , CO, and formate formate FEs, the hp-In electrode also delivers superior formate
can also be detected at −0.6 and −0.7 V, but are hardly production rates (FPRs). As shown in Figure 2e, the FPRs of hp-
quantified because of the limits of detection. From −0.8 V, In are plotted against the applied potential and compared with
formate starts to be reliably and reproducibly detected with an those of other state-of-the-art formate-producing catalysts,
FE of 29.9%, while H exhibits an FE of 51.3%. With the decrease including In, Sn, Bi, and Pb etc. At more positive potentials (−0.6
2
in the applied potential, the formate selectivity increases to −1.0 V), the FPRs of the hp-In electrode are among the
dramatically to 64.9% at −1.0 V and reaches a plateau of ca. 70% highest values delivered by the most active formate-producing
2
at −1.2 V. Conversely, the FE for H decreases gradually to catalysts under optimised conditions. As the FPR of the hp-In
1
2.2%. This product distribution agrees well with that observed increases monotonically with the overpotential, it reaches an
‑2 ‑1
on other In-based electrodes, where formate is the dominant unprecedented value of 1.14 mmolꢀcm ꢀh at −1.2 V.
product reduced from CO
2
, while H
2
is the competitive product The durability of a catalyst is essential for practical applications;
from the HER.7 Surprisingly, on the hp-In electrode, the FE for however, the stability of In-based catalysts has not yet been
,9
H
2
is significantly suppressed to less than 10% in the entire extensively evaluated and no catalysts with more than 2 h
potential range, and CO
2
is reduced to formate and CO with FEs stability have been reported.9 Therefore we examined the
,11
of >90% (Figure 2c). Formate is initially detected at −0.6 V with long-term performance of the hp-In electrode in 0.1 M KHCO
3
3
5
an FE of 61.2%, which gradually increases to 88.2% at −1.0 V and at −1.0 V. According to previous results, the accumulation of
is then maintained at ~90% until −1.2 V. In concert with the rise formate in the cathodic compartment of the H-Cell can lead to
of formate FE, the CO FE declines from 29.4% to 2.4% as the a decrease of the formate FE, as also observed in our initial tests
applied potential shifts negatively from −0.6 V to −1.2 V. To (Figure S8). To isolate the influence of the formate
futher confirm that the Cu mesh dese not play a catalytic role accumulation, we exchanged the electrolyte in the cathodic
during CO
a Ni mesh and evaluated its CO
is known to be inactive for CO
2 2 3
RR, we prepared a porous In electrode supported on compartment with fresh CO ‑saturated 0.1 M KHCO at a
–1
2
RR performance. While bulk Ni constant flow rate (23 mLꢀh ) using a peristaltic pump. As
RR, the product distribution of shown in Figure 2f, the current density was maintained at
4
2
porous In on Ni mesh is similar as that of hp-In (Figure S6). This around 33 mA during the 24 h stability test, with no apparent
indicates that the metal meshes only serve as support and signs of activity loss. The formate FE showed an initial decay
current collector, and it also demonstrates the universality of from ~90% to ~78% over the first 9 h, and then stabilised at
our method in preparing supported porous In catalysts.
The total current density of the In foil and the hp-In are also compensated by the CO FE, which increased from ~6% to ~16%,
plotted against the working potential (Figure 2d). Consistent while the FE for H remained at a low level (<10%). We speculate
~76%. Notably, the decrease in the formate FE was
2
with the CV results (Figure 2a), hp-In shows significantly higher that the increase in CO selectivity in the first few hours is due to
current densities than In foil. With an increase in the the access of the electrolyte/gas bubbles at the interface of the
overpotential, the total current on the hp-In reaches a In layer and the Cu mesh, as the Cu-In interface has been
–2
36
remarkably high value of 67.5 mA cm at −1.2 V. This improved suggested to be highly selective for CO
2
-to-CO.
The
current density on hp-In may be attributable to its enlarged morphology of the sample after the stability test had not
surface area. To confirm this, ECSA was calculated from the changed and the porous 3D structure was well preserved, as
double-layer capacitance derived from the CV data (Figure S7 revealed by the SEM results (Figure S9). Taken together, the
and Table S2). The results reveal that hp-In exhibits a 27.6-fold high current density, along with the high formate selectivity and
higher ECSA than In foil due to its highly porous structure. Taken long-term stability, demonstrates the significant potential of
2
together, these results demonstrate that by creating a 3D hp-In for CO RR applications
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DOI: 10.1039/C8TA11645H
(
a)
(b) 100
(c)
In foil (N
In foil (CO
hp-In (N
hp-In (CO
2
)
HCOO-
CO
HCOO-
CO
1
0
5
0
5
100
80
2
)
)
80
H
2
H
2
2
2
)
6
0
60
4
2
0
0
0
-
40
1
0
1
-
-
10
15
2
0
0
-
-0.6 -0.4 -0.2 0.0
0.2
-
0.6
-0.7
-0.8
-0.9
-1.0
-1.1
-1.2
-0.6
-0.7
-0.8
-0.9
-1.0
-1.1
-1.2
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Potential (V vs. RHE)
Potential (V vs. RHE)
Potential (V vs. RHE)
(
d)
(e)
(f)
80
60
40
20
0
hp-In
In foil
This work
-0.6
-0.7
-0.8
-0.9
-1.0
-1.1
-1.2
Potential (V vs. RHE)
Figure 2 (a) Cyclic voltammograms of the In foil and hp-In in N
compensation were not applied during CV scans to avoid a noisy background, which leads to lower total current densities compared with the values shown in (d). (b)
Potential dependent faradaic efficiencies for In foil and (c) hp-In. (d) Comparison of current densities for In foil and hp-In obtained at various applied potentials. (e)
Formate production rate at various applied potentials on the hp-In electrode, along with an overview of the formate production rate on the state-of-the-art CO -to-
and non-metal electrodes
The details are summarised in Figure S10 and Table S3 in the Supporting Information. (f) Catalytic stability performance for hp-In.
2 2 3
- and CO -saturated 0.1 M KHCO at a scan rate of 50 mV/s; note that magnetic stirring and ohmic loss
2
6
–9
37–44
1,26,45–48
49,50
51,52
formate catalysts. The catalysts were classified as: In (red), Sn (dark-blue),
Bi (yellow),
Pb (blue),
alloys (black),
5
3–55
(magenta).
+
–
3
.3 Mechanism of CO
2
RR to formate on In facets.
H + e + * → *H
(5)
(6)
(7)
+
–
*
H + H + e → H
2
, or
Calculations using DFT have become a powerful tool for
studying the reaction mechanisms of CO RR on model catalysts.
Computational investigations on metals such as Cu,
Pd and Zn have provided mechanistic insights into the
reaction pathways and predicted appropriate structures for
advanced catalysts. However, no DFT simulation has been
*
H + *H→ H
2
2
3
2,56
17,57 In all of these equations, the asterisk (*) indicates an active
catalytic site. It is generally believed that the selectivity of these
Au,
5
8
59
three products is determined primarily by the relative stability
of their reaction intermediates. Therefore, we calculated here
the free energy changes for the first PCET process.
6
3,64
We
2
conducted for In-based catalysts for CO RR. Therefore, to reveal
considered four different In facets, including (101), (002), (110)
and (112). The (101) facet was chosen because it is the
predominantly exposed crystal plane, as observed in the XRD
results; moreover, it is the energetically most stable low-index
crystal facet of In. Although the (002), (110), and (112) facets
2,60 are less prevalent in the XRD patterns, they were chosen to
study the influence of crystal facet on the reaction
the origin of the preferential selectivity towards formate over
In-based catalysts, we calculated the adsorption energies of the
key reaction intermediates over various In facets. During the
DFT calculation, HCOOH was considered to be a reduction
product rather than formate, since decoupling the proton and
3
electron donations remains computationally unviable.
According to the experimental results, HCOOH and CO are the
3
2,65
pathways.
2
only products reduced from CO over the In electrodes, both of
Figure 3a presents the clean (101) surface (Figure 3a1) and the
stable adsorption geometries of *H (Figure 3a2), *COOH (Figure
which involve two proton-coupled-electron-transfer (PCET)
processes. Theoretical and experimental studies have
3
a3) and *OCHO (Figure 3a4) (adsorption structures on other
suggested that CO
2
-to-HCOOH proceeds through formate
-to-CO proceeds through
facets can be found in the Supporting Information, Table S4).
The computational results suggest that a hollow site is
energetically preferred for the adsorption of H*. For the *COOH
intermediate, C adsorbs on the In atom with O approaching the
neighbouring In atom. In case of the *OCHO intermediate, the
results show that its most energetically favourable
configuration is the binding of two In atoms via two oxygen
intermediate (*OCHO) and CO
carboxyl intermediate (*COOH),
following equations (eqs. 3–4):
2
1
,32,60–62
as shown in the
+
–
CO
*
2
+ H + e + * → *OCHO
(1)
(2)
(3)
(4)
+
–
OCHO + H + e → HCOOH
+
–
2
CO + H + e + * → *COOH
+
–
*
COOH + H + e → CO
1
,66
atoms, similar to the adsorption structure on Bi and Sn.
HER as a competitive reaction of CO
intermediate (eqs 5, 6 or 5, 7):
2
RR proceeds via the *H
Based on these optimised adsorption geometries, we calculated
6
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(a)
(b)
a1
a3
a2
a4
Figure 3 (a) DFT models of (a1) clean (101) surface; (a2) optimised adsorption configuration of *H on (101); (a3) side (top) and top (bottom) views of optimised adsorption
configuration of *COOH on (101); and (a4) side (top) and top (bottom) views of optimised adsorption configuration of *OCHO on (101). (b) Free energy diagrams
calculated for the HER, CO -to-CO, and CO -to-HCOOH on (101), (002), (110), and (112).
2 2
the Gibbs free energy changes (ΔG) at U = 0 V potential using *OCHO intermediate rather than *H and *COOH, which
the computational hydrogen electrode (CHE) model for the rationalises the experimentally observed high formate
3
2
6,9
2
CO RR and HER processes (Figure 3b). For the HER, the selectivity over In-based catalysts.
formation of *H on all the four In facets is significantly uphill in
2
energy (0.80–0.93 eV), indicating that a high overpotential is 3.4 Origin of the improved CO RR selectivity over hp-In.
2 2
needed for the evolution of H . For the CO RR pathways,
While DFT calculations provide reasonable interpretations of
the preferential production of formate over In-based catalysts,
adsorption intermediate on In surfaces, whether the surface is
planar (e.g. (101)) or stepped (e.g. (112)). Thus, the readily
adsorbed *OCHO would occupy the active sites and inhibit the
adsorption of *H and *COOH, leading to a high HCOOH
selectivity. Moreover, the total reaction overpotential is
estimated to be >0.4 V, which agrees reasonably well with our
experimental finding (~0.55 V).
Although all the studied surfaces show similar free energy
diagrams for the specified product, facet-dependent adsorption
energy differences can still be observed. For example,
compared to other facets, the low index (101) surface stabilises
the *OCHO intermediate most effectively but stabilises *H and
further insights into the enhanced CO
still required. As CO RR is performed in an aqueous
environment, the improved CO RR selectivity can be attributed
reduction activity and/or the decrease of
2
RR selectivity on hp-In are
2
2
to the increase of CO
HER activity.
2
14,67
To clarify that, we tried to compare the
production for our In
intrinsic activity for formate, CO, and H
2
electrodes. Besides hp-In and In foil, we prepared two
additional lower-porosity In electrodes for better comparison
(
denoted as hp-In-0.125 and hp-In-0.5 since they were
–2
deposited at 0.125 and 0.5 Aꢀcm , respectively. Details can be
found in the experimental section, Figure 4a, and Figure S11–
S13). Specific current densities were calculated by normalising
*
COOH more difficultly, thus is suggested to be highly selective
towards HCOOH, even though a high overpotential is required
0.70 V). In contrast, the stepped (112) surface is more
2
the partial currents of formate, CO, and H to the ECSA of each
electrode (Figure 4a). Figure 4b shows that at a low
(
favourable in stabilising *H and *COOH relative to the other
facets, suggesting that relatively low overpotentials are
required for the H (0.8 V) and CO (0.38 V) pathways. The other
2
two facets, (002) and (110), are proposed to be the most
promising surfaces for the production of HCOOH, since they
have low ΔG for the *OCHO → HCOOH step but relatively high
ΔG for *H and *COOH adsorption steps. Therefore, we can
predict that at low overpotentials, open facets such as (002) and
overpotential range (−0.6 to −0.9 V), the four electrodes exhibit
-
identical specific formate current densities (j(HCOO) /ECSA). At high
overpotentials (>−0.95 V), the In foil catalyst performs better
because mass transfer is limiting the supply of CO to the highly
2
roughened hp-In electrode. Interestingly, the specific CO
current densities (j(CO)/ECSA) in Figure 4c follow a very similar
-
trend to that of specific j(HCOO) /ECSA. In stark contrast, the H
2
evolution curves change dramatically. As shown in Figure 4d,
over the entire potential range, the higher the ECSA, the lower
the specific H current densities (j(H2)/ECSA) observed. These data
2
imply that while the In foil and the hp-In electrodes exhibit
similar intrinsic CO and formate activities, the lower HER activity
(110) are more active towards HCOOH, while at high
overpotentials (101) may play a dominant role in the production
of HCOOH. Together, by comparing the three reaction pathways
on different In facets, we demonstrate that, from a
thermodynamic point of view, In is intrinsically selective for
2
on hp-In leads to the higher CO RR selectivity.
2
CO RR towards formate due to the preferred adsorption of the
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(
a)
(b)
(
c)
(d)
Figure 4 SEM images and ECSA for the In foil, hp-In-0.125, hp-In-0.5, and hp-In samples. Scale bar of SEM image for the In foil is 20 μm, and for the other three samples
is 150 μm. Specific activity for (b) formate, (c) CO, and (d) H for the four electrodes evaluated in CO saturated 0.1 M KHCO electrolyte.
2
2
3
Figure 5 (a) Schematic illustration of local pH effect during CO
added to maintain the K concentration at 0.5 M).
2
RR. (b) CO
2 2 3
RR performance of hp-In, evaluated in CO saturated 0.1− 0.5 M KHCO at −0.8 V (KCl was
+
(
b)
(
a)
(c)
200 μm
In
Figure 6 (a) SEM image of hp-In-1.0 sample and the corresponding elemental mappings of Cu, In, and Pd. (b) Pd/In atomic ratios for the porous Pd-In electrodes,
obtained from XPS and ICP-OES measurements. (c) Total current density and faradaic efficiencies of CO, formate and H for hp-In, porous Pd-In, and porous Pd
electrodes, evaluated in CO saturated 0.1 M KHCO at −0.7 V.
2
2
3
8
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mg cm (Table S1)), Pd could homogenously distribute on the
-2
View Article Online
As the HER activity is strongly correlated to the ECSA of the hp-In electrodes (Figure 6a). This is becDaOuI:s1e0.1P0d39w/Ca8sTAm11a6i4n5lHy
electrode (Figure 4d), we proposed that the reduced HER deposited on the surface of the electrodes. As shown in Figure
activity on a high-surface-area electrode is because of the high 6b, the surface atomic ratios (XPS results) of Pd/In are much
local pH near the electrode. As illustrated in Figure 5a, when higher than the bulk atomic ratios (ICP-OES results).
electrolysing CO
2
in an aqueous solution, the pH rises locally at The CO
2
RR performance of the porous Pd–In electrodes were
saturated 0.1 M KHCO and the
the electrode/electrolyte interface because of the proton investigated at −0.7 V in CO
2
3
consumption for the cathodic reactions (eqs. (1) – (6)). The results are shown in Figure 6c. The performance of the hp-In
highly porous structure of the electrode (i.e. hp-In) and the electrode and an electrodeposited porous Pd electrode was
−
weak buffer capacity of the electrolyte (i.e. CO
prone to induce high local pH.
2
/HCO
3
) are also included for comparison. While hp-In displays a higher FE
1
4,68
Therefore, HER activity is for formate (68.5%) than for CO (23.2%), after Pd deposition the
postulated to be lower over the high-surface-area hp-In formate FE declines systematically with an increase in the
electrode. On the other hand, if we increase the buffer capacity amount of Pd. In the meantime, the FE CO for Pd-In-1.0 sample
2
of the electrolyte, a reduced local pH and consequently an increases to its highest value of ~70% and the total FE for CO RR
6
9
increased HER activity is expected. To verify that, we approaches 90%. In contrast, the porous Pd electrode shows
−
increased the HCO
performed the CO
3
concentration from 0.1 to 0.5 M and high activity towards HER instead of CO
2
RR. Thus, despite the
2
RR on the hp-In electrode. KCl electrolyte, distinct chemical properties between Pd and Cu or Ag, we show
which has no buffering ability, was added to the KHCO
electrolytes to minimise the influence of K on the activity and selective CO
3
here for the first time that Pd-In electrode can also be a highly
+
2
-to-CO catalyst. Furthermore, the deposition of Pd
+
selectivity of CO
0
2
RR by maintaining the total K concentration at also improves the catalytic activity. As shown in Figure 6c, the
.5 M.17 Figure 5b shows that j(H2)/ECSA rises monotonically with total current density dramatically increased from 2.5 mA cm
the crease in HCO concentration, confirming that the higher for hp-In to 10 mA cm for Pd-In-2.0. These results not only
3
−2
−
−2
buffering capacity of the electrolyte promoted the HER activity. indicate that the selectivity of the formate and CO can be tuned
This result is further supported by the data obtained in other by deposition of Pd onto hp-In, but also suggest a promising
electrolytes, including KCl and K HPO , where H selectivity is strategy of using hp-In as a template for preparing other porous
2 4 2
also positively related to the electrolyte buffering ability (Figure In-based bimetallic catalysts.
S14). Moreover, Figure 5b shows that the specific activities of
−
formate and CO are almost unchanged as the HCO
3
4
. Conclusions
concentration increases, indicating that under the current
experimental conditions, CO RR activity is less sensitive to the
local pH compared with HER. These data imply that the
improved CO RR selectivity on hp-In originates from the
reduced H activity, which is induced by the high local pH at the
vicinity of the electrode. It is worth to mention that despite
various nanostructured catalysts have been applied for CO RR,
2
In summary, we have developed a porous 3D hierarchical In
catalyst for selective CO RR by template-free electrodeposition
of porous In onto a Cu mesh. The catalyst exhibits an extremely
high formate production rate (1.14ꢀmmolꢀcm ꢀh at −1.2 V)
and has excellent formate selectivity (~90%, from −1.0 to
2
2
2
–2 –1
2
−
1.2 V) as well as remarkable stability (24 h). The high catalytic
the effect of local pH on the catalytic selectivity is often
overlooked. In such circumstance, the influence of other
factors, such as crystal orientation, defect or oxidation state of
the catalyst, could be overestimated. Therefore, we emphasize
that further consideration of local pH effect needs to be taken
in the interpretation of the reaction mechanisms, as well as the
development of electrode materials and reaction cells.
activity is attributed to the highly porous hierarchical structure,
which offers an enlarged surface area (27.6-fold higher than
that of In foil). DFT calculations reveal that the preferential
reduction of CO
the intrinsic property of In, which prefers the stabilisation of
OCHO for formate production rather than *COOH or *H.
2
to formate on the In electrodes originates from
*
Additional electrocatalytic studies indicate that the further
improved formate selectivity on hp-In compared to In foil is
strongly correlated with the highly porous morphology, which
induces high local pH and therefore suppresses the evolution of
H . Furthermore, the hp-In can also serve as a template for
2
synthesising porous Pd–In electrodes to tune the formate/CO
selectivity. Thus, the simple approaches for fabricating highly
3
2
.5 Porous Pd–In electrodes for CO RR.
With its highly porous morphology, hp-In can also serve as a
template for synthesising other porous electrodes. Recent
works have shown that In-based bimetallic catalysts, e.g. Cu–In
3
6,70,71
2
and Ag–In, are highly selective for the CO RR to CO.
porous electrodes and the mechanistic insights for CO
2
RR over
Inspired by that, we deposited Pd onto the hp-In electrode via
a facile galvanic replacement method to fabricate a porous Pd–
nanostructured catalysts may provide guidelines for the design
of other porous metal and alloy electrodes for large-scale CO
applications.
2
RR
In electrode for CO
the hp-In into PdCl
2
RR. The catalysts were prepared by dipping
solutions with different concentrations for
2
5
min to partially replace the In on the electrode with Pd. After
deposition, the 3D morphology of the electrodes was well
preserved (Figure S15). Despite that the mass loading of Pd in
the Pd-In electrodes is very low (in the range of 0.014 to 0.099
Conflicts of interest
There are no conflicts to declare.
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Journal Name
2
2
2
3
G. O. Larrazábal, A. J. Martín, S. Mitchell, R. Hauert and J.
Pérez-Ramírez, J. Catal., 2016, 343, 266–277.
Acknowledgements
View Article Online
DOI: 10.1039/C8TA11645H
This research is part of the activities of SCCER HeE, which is
financially supported by Innosuisse-Swiss Innovation Agency.
This research is also supported by SNF (Ambizione Project
PZ00P2_179989). We thank Dr. Gian Luca De Gregorio and Prof.
Raffaella Buonsanti for the analysis of liquid products using
HPLC.
C. M. Gabardo, A. Seifitokaldani, J. P. Edwards, C. T. Dinh,
T. Burdyny, M. G. Kibria, C. P. O’Brien, E. H. Sargent and D.
Sinton, Energy Environ. Sci., 2018, 11, 2531–2539.
J. H. Kim, H. Woo, S. W. Yun, H. W. Jung, S. Back, Y. Jung
and Y. T. Kim, Appl. Catal. B Environ., 2017, 213, 211–215.
Y.-C. Hsieh, S. D. Senanayake, Y. Zhang, W. Xu and D. E.
Polyansky, ACS Catal., 2015, 5, 5349–5356.
2
2
2
4
5
6
Z. Zhang, M. Chi, G. M. Veith, P. Zhang, D. A. Lutterman, J.
Rosenthal, S. H. Overbury, S. Dai and H. Zhu, ACS Catal.,
Notes and references
1
J. H. Koh, D. H. Won, T. Eom, N. K. Kim, K. D. Jung, H. Kim,
Y. J. Hwang and B. K. Min, ACS Catal., 2017, 7, 5071–5077.
H. Li, P. H. Opgenorth, D. G. Wernick, S. Rogers, T. Y. Wu,
W. Higashide, P. Malati, Y. X. Huo, K. M. Cho and J. C. Liao,
Science, 2012, 335, 1596.
2
016, 6, 6255–6264.
2
7
A. Loiudice, P. Lobaccaro, E. A. Kamali, T. Thao, B. H.
Huang, J. W. Ager and R. Buonsanti, Angew. Chemie - Int.
Ed., 2016, 55, 5789–5792.
2
2
2
8
9
G. Kresse and J. Furthmüller, Phys. Rev. B, 1996, 54,
3
C. Gimkiewicz, R. Hegner, M. F. Gutensohn, C. Koch and F.
Harnisch, ChemSusChem, 2017, 10, 958–967.
1
1169–11186.
J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
996, 77, 3865–3868.
4
5
Y. Hori, Mod. Asp. Electrochem., 2008, 42, 89–189.
A. Komatsu, Seiji; Yanagihara, Tetsu; Hiraga, Yuki; Tanaka,
Michie; Kunugi, Denki Kagaku oyobi Kogyo Butsuri Kagaku,
1
3
3
0
1
P. E. Blöchl, Phys. Rev. B, 1994, 50, 17953–17979.
H. J. Monkhorst and J. D. Pack, Phys. Rev. B, 1976, 13,
1
995, 63, 217–224.
5
188–5192.
6
7
8
9
1
1
1
1
1
1
1
1
R. Hegner, L. F. M. Rosa and F. Harnisch, Appl. Catal. B
Environ., 2018, 238, 546–556.
Z. M. Detweiler, J. L. White, S. L. Bernasek and A. B.
Bocarsly, Langmuir, 2014, 30, 7593–7600.
3
3
2
3
A. A. Peterson, F. Abild-Pedersen, F. Studt, J. Rossmeisl and
J. K. Nørskov, Energy Environ. Sci., 2010, 3, 1311.
J. K. Nørskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J. R.
Kitchin, T. Bligaard and H. Jónsson, J. Phys. Chem. B, 2004,
J. L. White and A. B. Bocarsly, J. Electrochem. Soc., 2016,
1
08, 17886–17892.
1
63, H410–H416.
3
4
W. Tang, A. A. Peterson, A. S. Varela, Z. P. Jovanov, L. Bech,
W. J. Durand, S. Dahl, J. K. Nørskov and I. Chorkendorff,
Phys. Chem. Chem. Phys., 2012, 14, 76–81.
D. H. Won, C. H. Choi, J. Chung, M. W. Chung, E. H. Kim and
S. I. Woo, ChemSusChem, 2015, 8, 3092–3098.
W. Luo, W. Xie, R. Mutschler, E. Oveisi, G. L. De Gregorio, R.
Buonsanti and A. Zuttel, ACS Catal., 2018, 8, 6571–6581.
W. Lv, R. Zhang, P. Gao and L. Lei, J. Power Sources, 2014,
Z. Xia, M. Freeman, D. Zhang, B. Yang, L. Lei, Z. Li and Y.
Hou, ChemElectroChem, 2018, 5, 253–259.
Z. Bitar, A. Fecant, E. Trela-Baudot, S. Chardon-Noblat and
D. Pasquier, Appl. Catal. B Environ., 2016, 189, 172–180.
A. Rabiee and D. Nematollahi, Mater. Chem. Phys., 2017,
0
1
2
3
4
5
6
7
3
3
3
3
3
4
4
4
4
5
6
7
8
9
0
1
2
3
1
93, 109–116.
A. Dutta, M. Rahaman, N. C. Luedi, M. Mohos and P.
Broekmann, ACS Catal., 2016, 6, 3804–3814.
Y. Yoon, A. S. Hall and Y. Surendranath, Angew. Chemie -
Int. Ed., 2016, 55, 15282–15286.
A. S. Hall, Y. Yoon, A. Wuttig and Y. Surendranath, J. Am.
Chem. Soc., 2015, 137, 14834–14837.
2
53, 276–281.
J. Yu, H. Liu, S. Song, Y. Wang and P. Tsiakaras, Appl. Catal.
A Gen., 2017, 545, 159–166.
F. Li, L. Chen, G. P. Knowles, D. R. MacFarlane and J. Zhang,
Angew. Chemie Int. Ed., 2017, 56, 505–509.
F. Lei, W. Liu, Y. Sun, J. Xu, K. Liu, L. Liang, T. Yao, B. Pan, S.
Wei and Y. Xie, Nat. Commun., 2016, 7, 1–8.
S. Zhang, P. Kang and T. J. Meyer, J. Am. Chem. Soc., 2014,
J. E. Pander, M. F. Baruch and A. B. Bocarsly, ACS Catal.,
2
016, 6, 7824–7833.
C. I. Shaughnessy, D. T. Jantz and K. C. Leonard, J. Mater.
Chem. A, 2017, 00, 1–7.
M. Liu, Y. Pang, B. Zhang, P. De Luna, O. Voznyy, J. Xu, X.
Zheng, C. T. Dinh, F. Fan, C. Cao, F. P. G. de Arquer, T. S.
Safaei, A. Mepham, A. Klinkova, E. Kumacheva, T. Filleter,
D. Sinton, S. O. Kelley and E. H. Sargent, Nature, 2016, 537,
1
36, 1734–1737.
D. H. Won, C. H. Choi, J. Chung, M. W. Chung, E. H. Kim and
S. I. Woo, ChemSusChem, 2015, 8, 3092–3098.
B. Kumar, V. Atla, J. P. Brian, S. Kumari, T. Q. Nguyen, M.
Sunkara and J. M. Spurgeon, Angew. Chemie - Int. Ed.,
3
82–386.
H. C. Shin, J. Dong and M. Liu, Adv. Mater., 2003, 15, 1610–
614.
J. Liu, L. Cao, W. Huang and Z. Li, J. Electroanal. Chem.,
012, 686, 38–45.
C. W. Li and M. W. Kanan, J. Am. Chem. Soc., 2012, 134,
231–7234.
2
017, 56, 3645–3649.
1
1
2
2
8
9
0
1
4
4
4
4
4
5
6
7
D. Du, R. Lan, J. Humphreys, S. Sengodan, K. Xie, H. Wang
and S. Tao, ChemistrySelect, 2016, 1, 1711–1715.
N. Han, Y. Wang, H. Yang, J. Deng, J. Wu, Y. Li and Y. Li, Nat.
Commun., 2018, 9, 1320.
H. Zhong, Y. Qiu, T. Zhang, X. Li, H. Zhang and X. Chen, J.
Mater. Chem. A, 2016, 4, 13746–13753.
1
2
7
A. D. J. Motheo, S. A. s. Machado, M. H. Van Kampen and J.
N. Han, Y. Wang, H. Yang, J. Deng, J. Wu, Y. Li and Y. Li, Nat.
Commun., 2018, 9, 1–8.
R. S. Jr, J. Braz. Chem. Soc., 1993, 4, 122–127.
1
0 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
Page 12 of 12
Journal Name
ARTICLE
4
8
C. W. Lee, J. S. Hong, K. D. Yang, K. Jin, J. H. Lee, H. Y. Ahn,
H. Seo, N. E. Sung and K. T. Nam, ACS Catal., 2018, 8, 931–
37.
J. Wang, H. Wang, Z. Han and J. Han, Front. Chem. Sci. Eng.,
015, 9, 57–63.
M. Fan, S. Garbarino, G. A. Botton, A. C. Tavares and D.
Guay, J. Mater. Chem. A, 2017, 5, 20747–20756.
W. Luc, C. Collins, S. Wang, H. Xin, K. He, Y. Kang and F.
Jiao, J. Am. Chem. Soc., 2017, 139, 1885–1893.
X. Zhang, F. Li, Y. Zhang, A. M. Bond and J. Zhang, J. Mater.
Chem. A, 2018, 6, 7851–7858.
View Article Online
DOI: 10.1039/C8TA11645H
9
4
5
5
5
5
9
0
1
2
3
2
S. Zhang, P. Kang, S. Ubnoske, M. K. Brennaman, N. Song,
R. L. House, J. T. Glass and T. J. Meyer, J. Am. Chem. Soc.,
2
014, 136, 7845–7848.
5
4
H. Wang, J. Jia, P. Song, Q. Wang, D. Li, S. Min, C. Qian, L.
Wang, Y. F. Li, C. Ma, T. Wu, J. Yuan, M. Antonietti and G.
A. Ozin, Angew. Chemie - Int. Ed., 2017, 56, 7847–7852.
H. Wang, Y. Chen, X. Hou, C. Ma and T. Tan, Green Chem.,
5
5
5
5
5
6
7
8
2
016, 18, 3250–3256.
J. Hussain, H. Jónsson and E. Skúlason, ACS Catal., 2018, 8,
240–5249.
S. Back, M. S. Yeom and Y. Jung, ACS Catal., 2015, 5, 5089–
096.
5
5
W. Sheng, S. Kattel, S. Yao, B. Yan, Z. Liang, C. Hawxhurst,
Q. Wu and J. G. Chen, Energy Environ. Sci., ,
DOI:10.1039/C7EE00071E.
5
6
6
6
9
0
1
2
D. H. Won, H. Shin, J. Koh, J. Chung, H. S. Lee, H. Kim and S.
I. Woo, Angew. Chemie - Int. Ed., 2016, 55, 9297–9300.
B. Jiang, X. G. Zhang, K. Jiang, D. Y. Wu and W. Bin Cai, J.
Am. Chem. Soc., 2018, 140, 2880–2889.
J. S. Yoo, R. Christensen, T. Vegge, J. K. Nørskov and F.
Studt, ChemSusChem, 2016, 9, 358–363.
J. T. Feaster, C. Shi, E. R. Cave, T. Hatsukade, D. N. Abram,
K. P. Kuhl, C. Hahn, J. K. Nørskov and T. F. Jaramillo, ACS
Catal., 2017, 7, 4822–4827.
6
6
3
4
Z. Zhao and G. Lu, ACS Catal., 2018, 3885–3894.
M. Karamad, V. Tripkovic and J. Rossmeisl, ACS Catal.,
2
014, 4, 2268–2273.
S. Back, M. S. Yeom and Y. Jung, ACS Catal., 2015, 5, 5089–
096.
6
6
5
6
5
J. T. Feaster, C. Shi, E. R. Cave, T. Hatsukade, D. N. Abram,
K. P. Kuhl, C. Hahn, J. K. Nørskov and T. F. Jaramillo, ACS
Catal., 2017, 7, 4822–4827.
6
7
E. L. Clark, J. Resasco, A. Landers, J. Lin, L. T. Chung, A.
Walton, C. Hahn, T. F. Jaramillo and A. T. Bell, ACS Catal.,
2
018, 8, 6560–6570.
6
6
7
8
9
0
M. Ma, B. J. Trzesniewski, J. Xie and W. A. Smith, Angew.
Chemie - Int. Ed., 2016, 55, 9748–9752.
A. S. Varela, M. Kroschel, T. Reier and P. Strasser, Catal.
Today, 2016, 260, 8–13.
S. Rasul, D. H. Anjum, A. Jedidi, Y. Minenkov, L. Cavallo and
K. Takanabe, Angew. Chemie - Int. Ed., 2015, 54, 2146–
2
150.
7
1
G. O. Larrazabal, A. J. Martin, S. Mitchell, R. Hauert and J.
Perez-Ramirez, J. Catal., 2016, 343, 266–277.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
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