Direct Electrochemical Ammonia Synthesis from Nitric Oxide

Article abstract of DOI:10.1002/anie.202002337

NO removal from exhausted gas is necessary owing to its damage to environment. Meanwhile, the electrochemical ammonia synthesis (EAS) from N₂ suffers from low reaction rate and Faradaic efficiency (FE). Now, an alternative route for ammonia synthesis is proposed from exhaust NO via electrocatalysis. DFT calculations indicate electrochemical NO reduction (NORR) is more active than N₂ reduction (NRR). Via a descriptor-based approach, Cu was screened out to be the most active transition metal catalyst for NORR to NH₃ owing to its moderate reactivity. Kinetic barrier calculations reveal NH₃ is the most preferred product relative to H₂, N₂O, and N₂ on Cu. Experimentally, a record-high EAS rate of 517.1 μmol cm^?2 h^?1 and FE of 93.5 percent were achieved at ?0.9 V vs. RHE using a Cu foam electrode, exhibiting stable electrocatalytic performances with a 100 h run. This work provides an alternative strategy to EAS from exhaust NO, coupled with NO removal.

Full text of DOI:10.1002/anie.202002337

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Accepted Article
Title: Direct Electrochemical Ammonia Synthesis from Nitric Oxide
Authors: Jun Long, Shiming Chen, Yunlong Zhang, Chenxi Guo,
Xiaoyan Fu, Dehui Deng, and Jianping Xiao
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202002337
Angew. Chem. 10.1002/ange.202002337
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10.1002/anie.202002337
Angewandte Chemie International Edition
RESEARCH ARTICLE
Direct Electrochemical Ammonia Synthesis from Nitric Oxide
Jun Long,+[a,b,c] Shiming Chen,+[a] Yunlong Zhang,[a] Chenxi Guo,[a] Xiaoyan Fu,[a,b,c] Dehui Deng*[a] and
Jianping Xiao*[a]
D.D. supervised the experiments and J.X. supervised all the theoretical works and conceived the project. J.L. carried out all the
theoretical calculations and wrote the manuscript. S.C. carried out the experiments and wrote the experimental section of manuscript.
J.L. and S.C have equal contribution. C.G. contributed to the microkinetic simulation. All the authors contributed to the data analysis
and the final version of the paper.
[a]
J. Long, S. Chen+, Y. Zhang, C. Guo, X. Fu, Prof. D. Deng, Prof. J. Xiao
State Key Laboratory of Catalysis
Dalian Institute of Chemical Physics
Zhongshan Road 457, Dalian 116023, P. R. China.
E-mail: dhdeng@dicp.ac.cn and xiao@dicp.ac.cn
These authors contributed equally to this work
J. Long, X. Fu
[+]
[b]
School of Science
Westlake University
Hangzhou, 310024, P. R. China.
J. Long, X. Fu
[c]
Department of Chemistry
Zhejiang University
Hangzhou 310058, P.R. China.
Supporting information for this article is given via a link at the end of the document.
Abstract: NO removal from exhausted gas is necessary due to its
damage to environment. Meanwhile, the electrochemical ammonia
synthesis (EAS) from N2 is suffering from a low reaction rate and
Faradaic efficiency (FE). Herein, we propose an alternative route for
ammonia synthesis from exhausted NO via electrocatalysis. Density
functional theory calculations indicate electrochemical NO reduction
(NORR) is more active than N2 reduction (NRR). Via a descriptor-
based approach, Cu was screened out to be the most active
transition metal catalyst for NORR to NH3 due to its moderate
reactivity. Moreover, kinetic barrier calculations reveal NH3 is the
most preferred product relative to H2, N2O and N2 on Cu.
Experimentally, a record-high EAS rate of 517.1 μmol·cm-2·h -1 and
FE of 93.5% were achieved at -0.9 V vs. RHE using a Cu foam
electrode, exhibiting stable electrocatalytic performances with 100
hours run. The present work provides an alternative strategy to EAS
from exhausted NO, coupled with NO removal.
Haber-Bosch process in industry, while it suffers from a high
temperature of 300~500 ℃ and pressure of 200~300 atm[3]. To
overcome the drawbacks, electrochemical N2 reduction reaction
(NRR) has been proposed to produce NH3 at ambient
conditions[4], which mimics the biological nitrogen fixation.
Electrochemical ammonia synthesis (EAS) can be driven
by renewable electrical energy, generated by solar or wind.
However, two major problems limit the development of this
strategy. One is the low NRR activity. The best transition metal
catalysts (Ru and Mo) for NRR[4b] exhibit experimental NH3 yield
rates only 0.08 and 0.11 μmol·cm-2·h -1, respectively[4a, 5]. Another
problem is the low NH3 selectivity. For N2 electroreduction in
aqueous solution, the competing hydrogen evolution reaction
(HER) is more preferred than NRR on all the transition metals
due to its higher limiting potential[6]. Hence, the Faradaic
efficiencies (FE) of NH3 on pure transition metal catalysts are
very low[5, 7]. Besides, an isotope labelling[8] is often needed to
determine the trace amount of NH3 production.
Although many progresses have been made recently,[9]
the EAS from N2 is still far from practice. The difficulties can be
attributed to the chemical inertness of N2 molecule. Can we
directly electrochemically reduce NO from exhausted gas to
ammonia by coupling NO removal and ammonia synthesis (as
proposed in Scheme 1)? Is it possible to overcome the
difficulties in present EAS route from N2? In fact, electrochemical
NO reduction reaction (NORR) has been investigated widely in
Introduction
Nitric oxide (NO) is one of the major air pollutants, which
has caused serious environmental issues, such as acid rain,
photochemical smog, and ozone depletion. The NO pollutant
mainly comes from the combustion of fossil fuels in power plants,
vehicles and factories[1]. At present, the most popular way of NO
removal is the selective catalytic reduction (SCR) technology, by
which NO can be converted into harmless nitrogen (N2) and
released[2]. However, it’s not the ideal way because it will
consume valuable ammonia (NH3) or hydrogen (H2) as the
reductant. In the meanwhile, the artificial N2 fixation to NH3 is
another challenged chemical process. As an essential chemical
substance to produce fertilizers, NH3 was mainly produced via
nitrate, nitrite and NO conversion for wastewater treatment[10]
,
while the catalysts were usually designed to produced N2,
instead of NH3.
In this work, density functional theory (DFT) calculations
were performed to screen an efficient NORR catalyst. It was
found that Cu exhibit higher activity for NORR than NRR, as well
as superior NH3 selectivity relative to H2 production.
1
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10.1002/anie.202002337
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RESEARCH ARTICLE
Experimental study of NORR on a Cu foam electrode achieved a
record-high EAS rate of 517.1 μmol·cm-2·h -1 with a FE of 93.5%
at -0.9 V vs. RHE. This work suggests an alternative EAS route
from NO, coupled with NO removal, which is appealing due to
the high ammonia production rate and selectivity.
We first calculated the adsorption energies of all the
intermediates involved in NORR, NRR, and HER on the terrace
surfaces of 10 transition metals (see details in Figure S3 and
Table S2). All the energies of intermediates show good scaling
relations with N* binding energy (Figure S4). Therefore, the N*
adsorption free energy [Gad(N)] was chosen as the descriptor.
For A-T mechanism, the four specific pathways (distal-O, distal-
N, alternating-O, and alternating-N) were first studied and
compared. As shown in Figure S5a~d, the ΔG-determining step
(GDS) is the same (H+ + e- →H*) in the right leg, while different
for the left leg. Among them, the alternating-N pathway is more
favorable (Figure S5e), which was chosen to analyze the A-T
mechanism in the following. For A-H (Figure S6), the distal-O
pathway is preferred near the optimum and representative. The
D-T, D-H, A-T (alternating-N pathway) and A-H (distal-O
pathway) mechanisms were plotted vs. Gad(N), as shown in
Figure 1a~d. The activity trends among them are compared in
Figure S7. As the A-H with distal-O pathway (AHDO) is more
preferred as Ead(N) < 2.4 eV, the NORR will be analyzed in
detail for this mechanism. For AHDO (Figure 1d), as the
reactivity is weak, the total reaction is limited by the NO
protonation, while the NH* → NH2* turns to be the limiting step
for strong reactive metals. Among all studied transition metals,
Pd and Pt are most active in D-T and A-T mechanism, while Cu
is optimal in D-H and A-H (Figure 1a~d). The most important
AHDO pathway for NORR to NH3 over copper as following:
Nitric oxide
Electric energy
NORR
H*
H+
O* N*
HxNOHy*
NH3
H+
Crops
Fuel cell
Automobile
Scheme 1. Illustration of the proposed electrochemical ammonia synthesis
route from NO. The nitrogen source (NO) is supposed from exhausted gases
from thermal power stations, factories, or vehicles. Electrical energy can be
generated from renewable solar, wind energy, or the hydro power. The
produced ammonia can be used as the chemical energy carrier and feedstock
of fertilizers. The middle region shows the possible reaction mechanisms (red
arrows) for NORR to NH3.
NO(g) + (H+ + e-) → NOH*
NOH* + (H+ + e-) → N* + H2O
N* + (H+ + e-) → NH*
(1)
(2)
(3)
(4)
(5)
NH* + (H+ + e-) → NH2*
NH2* + (H+ + e-) → NH3(g)
Results and Discussion
The NRR and HER were also studied to compare with the
NORR. For NRR, the associative alternating pathway is more
favorable than the distal for both A-T (Figure S8) and A-H
(Figure S9) mechanism. As Ead(N) < -0.58 eV, the D-H
mechanism is most favorable around the optimum (Figure S11).
The comparison among NORR, NRR, and HER is shown in
Figure 1e. A Pt was found close to the activity optimum of HER,
consistent with the observed facts over transition metal catalysts
for hydrogen evolution[12]. Ru and Rh are the best candidates for
NRR, agreeing well with the previous study[4b]. The NRR activity
is always lower than HER for all the transition metals, resulting
in low NH3 selectivity. However, the NH3 selectivity is more
preferred than HER by ~0.65 V in limiting potential for the NORR
scenario, where Cu(111) is the best candidate. Furthermore, the
activities of transition metal step surfaces were also studied and
compared with terrace ones, as shown in Figure S12. Although
the limiting step (NH2→NH3) for strongly reactive metals turn to
be different from terrace surfaces, the Cu(211) is still close to
the activity optimum. As well-known, the scaling relation of
adsorption energies always limit the rate of a given chemical
reaction, while the NORR activity over copper is pretty close to
the activity optimum, as shown in Figure 1f. However, the NRR
activities were found far from the theoretical optimum over
transition metal catalysts[6].
Computational screening of catalysts
According to the scaling relations of adsorption energies[11]
a descriptor-based method was used in this work to screen the
promising transition metal catalysts systematically. In principle,
the NO reduction to NH3 and H2O can follow either a dissociative
or associative pathway, as NRR[4b]. In the former pathway, the
N-O bond can be broken at the first step. The resulting N* and
O* can be then protonated, respectively. In the latter case,
,
however, NO can be first hydrogenated to HxNOHy intermediates,
which will be continually reduced to NH3 and H2O. For each
pathway, the hydrogenation process can either undergo a Tafel-
type route, namely, where the solvated protons first adsorb on
catalysts forming adsorbed H*, followed by surface
hydrogenation, or a Heyrovsky-type route, where a NO molecule
and intermediates are protonated directly. Consequently, there
are four categories of NORR mechanisms including dissociative-
Tafel (D-T), Heyrovsky (D-H), associative-Tafel (A-T), and
Heyrovsky (A-H) mechanisms, as shown in Scheme 1 (red
arrows). In addition, the A-T and A-H include four specific
pathways, named distal-O, distal-N, alternating-O, and
alternating-N, respectively (Figure S2). For distal-O (or N)
pathway, the O (or N) atom in NO can be first hydrogenated fully
to H2O (or NH3), followed by another atomic reduction. For the
alternating-O (or N) pathway, the
O and N should be
hydrogenated alternately. All the considered reaction
mechanisms are summarized in Table S1.
2
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10.1002/anie.202002337
Angewandte Chemie International Edition
RESEARCH ARTICLE
(a)
(b)
*
V
O
*
Ag
Cr
2
2
1
0
Ag
O
*+
Mo
O
V
N
*+
H
* →
Cr
N
→
Mo
* →
H
g)
O
→
(
1
0
H
2 O
Ru
g)
O
(
Ru
H
Rh
N
O
N
2 O
Cu
Rh
H
Pt
N
* →
Pd
Pd
Pt
Cu
-
N
H
*
++e
H
→
N
H
H
* →
*
2
N
H
*
2
-1
-2
-1
-2
D-T
-2
D-H
-1
0
1
2
3
-2
-1
0
1
2
3
Gad(N) / eV
Gad(N) / eV
(c)
(d)
2
1
2
1
V
Cr
Mo
V
Au
Cr
Mo
NH
Au
2 * →
Ru
Ag
Ag
Ru
*
N
Rh
H
O
Rh
Cu
H
N
H
* →
Pt
(
Pd
Pt
Pd
g)
N
3
-
*
N
+ +e
H
H
→
→
0
0
Cu
*
H
g)
(
2
O
N
-1
-2
-1
-2
A-T
A-H
-2
-1
0
1
2
3
-2
-1
0
1
2
3
Gad(N) / eV
Gad(N) / eV
-0.48
0.00
0.48
0.96
1.44
1.92
2.40
2.88
3.36
3.84
(e)
(f)
*
Au
H
N
H
O
Ag
* →
2N*
→
N
1
0
1
0
N
H
→
Cu
*
g)
2
g)
(
(
O
2
Pt
N
N
H
Pd
*+
H +
+e
Ru
*
-
-
H
Rh
+ +e
→
→
H
H
(
Pt
g)
Ru
2
Rh
-1
N
H
* →
N
Mo
Cr
NORR
NRR
HER
Cu
H
-2
-3
*
2
V
-1
ΔG / eV
-2
-1
0
1
2
3
-2
-1
0
1
2
3
Gad(N) / eV
Gad(N) / eV
Figure 1. Thermodynamic estimation of NORR to NH3 and screening of catalysts. (a-d) ΔG plotted versus Gad(N) for D-T, D-H, A-T, and A-H mechanisms, where
the red and solid lines are the ΔG-limiting steps. (e) Comparison of the ΔG-determining steps between NORR, NRR, and HER. (f) A two-dimensional activity map
for ammonia production. All the reaction free energies are shown at 0V vs. RHE.
NORR on Cu(111)
In this section, we will systematically study the NORR
kinetics over a Cu(111) surface, combined with the calculations
of potential-dependent barriers via ‘charge-extrapolation’
Pt(100) via the pathway of NO → HNO* → NH* + O* → NH3 +
H2O (denoted as HNO-dissociative pathway), where the HNO*
dissociation is thermodynamically determined. Hence, this
pathway was also explicitly studied on Cu(111), compared with
the AHDO pathway. The free energy diagrams at 0 V vs. RHE
and corresponding structures of IS, TS and FS are shown in
Figure S14 and S15, respectively. For the HNO-dissociative
pathway, the rate-determining step (RDS) is HNO* → NH* + O*,
with a free energy barrier of 0.60 eV. For the AHDO pathway,
the most difficult step is protonation of NOH* (0.54 eV), which is
slightly lower than the former pathway and surmountable at
room temperature[15]. Besides, the barrier of NOH* protonation
will decrease under more negative potential in electrocatalysis,
while the barrier of thermochemical HNO* dissociation remains
with potential. Hence, the AHDO pathway should be more
preferred on Cu(111) under experimental conditions.
a
method, proposed by Nørskov and coworkers[13]. The ab initio
calculations of electrochemical charge transfer reactions are
commonly performed at constant charge, which lead to dramatic
potential shifts along the reaction path. However, the real
electrochemical reactions are operated at constant potential. In
finite model system, as the charge transfer (q) and potential (U)
at initial (IS), transition (TS), and final state (FS) are usually
correlated linearly, therefore, a capacitor model can be used to
calculate the real barrier at a given potential (see Supporting
Information for more details).
A layer of water with a solvated proton was added on a
Cu(111) slab to explicitly model the electrochemical solid−liquid
interface (Figure S13). In addition to electrochemical processes
of proton transfer, some thermochemical steps are also possibly
important in electrocatalysis. For example, Rosca et al.[14]
proposed that a NO molecule was reduced to ammonia on
According to the previous reports[10a, 16], the possible
products of NORR include H2, NH3, N2O and N2. The formation
of N2O was proposed to follow a Eley–Rideal (E-R) mechanism
on Pt(111)[15b], where a solvated NO first couples with an
3
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10.1002/anie.202002337
Angewandte Chemie International Edition
RESEARCH ARTICLE
adsorbed NO* to form a trans-ONNO* dimer (limiting step),
followed by the protonation to ONNOH*. Different from Pt(111),
the most difficult step of E-R mechanism on Cu(111) is the
protonation of ONNOH* to form N2O, with a barrier of 0.73 eV at
0V vs. RHE (Figure S16). Besides, the N* can be formed easily
with a barrier of 0.54 eV in the AHDO pathway (Figure S14), and
NH3 is produced through the continually hydrogenation of N*.
However, there are two competitive processes for N2O (N-NO
coupling) and N2 (N-N coupling) production (Figure 2a). The
limiting steps for N2 and N2O formation are N-N and N-NO
coupling, with the barriers of 0.92 and 0.60 eV, respectively. The
highest barrier to continually reduce N* to NH3 is 0.50 eV, lower
than the N-NO and N-N coupling. Moreover, the N* protonation
to NH3 is totally electrochemical reaction and the barriers will
decrease at more negative potential, whereas the
thermochemical N-N and N-NO coupling barriers remain intact,
suggesting the NH3 selectivity will be quite high at negative
potential. In addition, the hydrogen evolution needs to overcome
a barrier of 0.98 eV, which is most unfavorable compared to
other products. Overall, the NORR to NH3 should exhibit high
activity and selectivity over copper electrode.
The high HER barriers compared to NH3 production are
also elucidated well. For NOH* + (H++e-) → N* + H2O, the
transition states are initial-state-like (Figure 2b), resulting in a
small barrier, so does the N* + (H++e-) → NH* (Figure 2c). For
NO + (H++e-) → NOH*, NH* + (H++e-) → NH2*, and NH2* +
(H++e-) → NH3, we have analyzed the projected density of states
(PDOS) and electronic localization functions (ELF) for the
transition states. As the transferring protons have strong
electronic interactions with O in water layer and intermediates
simultaneously, as indicated by the ELF and hybridized peak α,
β and γ of DOS (Figure 2d~f), suggesting the new H-O or H-N
bond with adsorbates have been formed partially before H2O∙∙∙H
bond breaking, which stabilize the transition states. For the
proton adsorption reaction (Figure 2g), however, the H2O∙∙∙H
bond has been broken before the H approaching to the surface.
Therefore, the transition state is not well stabilized, and the
kinetic barrier is relatively higher.
IS
TS
FS
(a)
(b)
(c)
0.97
0.54
NH3
N2O
N2
H2
0.98
H++e-
NO(g)
H2
H*
0.92
0.60
0.42
0
-2
-4
-6
H2O
NOH*
0.50
N*
0.47
NH2*
IS
TS
FS
NH*
N2O
N2
NH3
Cu(111)
0V vs. RHE
Reaction Coordinate
(d)
(e)
0.6
0.6
0
H 1s
H 1s
O 2p
N 2p
γ
γ
O1
O1 2p
O2 2p
O
H
H
O2
N
N
Cu
0
β
α
α
β
-20
-10
0
-20
-10
0
Energies / eV
Energies / eV
(f)
(g)
0.6
0.6
H 1s
O 2p
Cu 3d
H 1s
O 2p
N 2p
γ
O
O
H
H
N
α
Cu
Cu
0
0
α
β
-20
-10
0
-20
-10
0
Energies / eV
Energies / eV
Figure 2. NORR over Cu(111). (a) Free energy diagrams for HER, NORR to NH3, N2O, and N2 under 0 V vs. RHE, the kinetic barriers shown in eV. (b)
Geometries of the IS, TS, and FS for NOH* + (H+ + e-) → N* + H2O and (c) N* + (H++e-) →NH*; the light red, red, blue, and white atoms are Cu, O, N and H,
respectively; the green balls represent the hydrogen participating in the proton transfer. Projected Density of States (DOS) and electron localization function (ELF)
for the transition states are shown in (d) NO + (H++e-) → NOH*, (e) NH* + (H++e-) → NH2*, (f) NH2* + (H++e-) → NH3 and (g) proton adsorption.
Experimental validations
0.9 V vs. RHE. A Pt foil was also tested for a comparison. The
experiments were performed at an airtight H-shape reactor,
separated by a Nafion membrane 115 at 25 ℃ for 600 s, where
0.25 mol/L Li2SO4 was used as electrolyte. 30 mL/min of NO
flow was introduced to the cathode chamber as reactant. The
According to the theoretical calculations, copper is predicted as
the most active and selective transition metal catalyst for NORR
to NH3. To confirm the prediction, we have first performed
electrocatalytic NORR experiments using a Cu foil electrode at -
4
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10.1002/anie.202002337
Angewandte Chemie International Edition
RESEARCH ARTICLE
gaseous products were detected by gas chromatography (GC)
and ammonia was quantified by ion chromatography (IC), details
were described in Supporting Information. The NH3 production
rate on Pt and Cu foil are 99.4 and 95.0 μmol·cm-2·h -1 (Figure
3a), respectively, which is very close. However, the H2 evolution
rate on the Pt foil (730.7 μmol·cm-2·h -1) is much higher than that
on the Cu foil (135.7 μmol·cm-2·h -1) (Figure 3a), leading to the
NH3 FE of Pt foil much lower (Figure 3b). The higher current
density of Pt foil than Cu foil (Figure 3c) is also attributed to the
dominant HER. Hence, the Cu electrode is more interesting
rather than Pt for electrochemical ammonia synthesis from NO
reactant, considering the selectivity and price of catalysts. To
acquire a better performance, a Cu foam catalyst was prepared
and tested under the same conditions. Consequently, an
excellent NH3 formation rate (517.1 μmol·cm-2·h -1) and FE
(93.5%) were obtained, with a significantly enhanced current
density (Figure 3a~c). In addition, the overpotential for NORR on
Cu foam is only 0.11 V at 10 mA·cm-2, which is competitive to
NRR. The improved NORR performances of Cu foam can be
attributed to its porous structure, which increases the specific
surface area of electrode and promotes the diffusion of NO and
NH3. In addition, the NORR performances of Cu foam were
examined at different potentials (-1.2 ~ 0.3 V vs. RHE).
Ammonia is always the dominant product over all studied
potentials and its production rate gets higher at more negative
potentials (Figure 3d). The NH3 FE increases until the potential =
-0.9 V vs. RHE (Figure 3e), with the maximum of 93.5%.
Therefore, the potential -0.9 V vs. RHE was the optimal for both
activity and selectivity for NORR to NH3 over a Cu foam
electrode. As a comparison, the NRR performance was also
examined on the Cu foam under the same conditions at -0.9V,
while only trace amount of NH3 (< 0.1 μmol·cm-2·h -1) was
produced (Figure 3a). Even compared with some recent NRR
results (Table 1), the NORR with Cu foam still remains as a
record-high EAS activity and selectivity. More strikingly, the
ammonia production rate via NORR (9234 μmol∙g-1∙h-1) at
ambient conditions can even reach the level of Haber-Bosch
process at high temperature[17] (Table S4), suggesting EAS from
NO is promising to be an alternative ammonia synthesis strategy.
NH3
N2O
N2
H2
(a)
NH3
N2O
N2
H2
(b)
100
80
60
40
20
730.7
800
600
400
200
0
35.4
61.9
580.8
517.1
70.8
98.8
93.5
135.7
95.0
NH3
<0.1
99.4
24.1
0.1
0
*
*
2
- NO
2
- NO
Foil - NO
Cu
Foam - NO
Foam - N
Foil - NO
Cu
Foam - NO
Pt Foil
Foam - N
Cu
Cu
Pt Foil
Cu
Cu
NH3
N2O
N2
H2
(c)
(d)
600
500
400
300
200
100
0
0
-30
537.8
517.1
400.7
-60
252.6
-90
Cu Foam Ar
Cu Foam N2
112.4
52.3
Cu Foil NO
Pt Foil NO
Cu Foam NO
99.3
-120
-150
51.8
36.4
68.2
-0.6
53.8
-0.9
11.9
-1.2
-1.2
-0.9
-0.6
-0.3
0.0
0.3
0.6
-0.3
0
0.3
Applied voltage (V vs.RHE)
Applied voltage (V vs.RHE)
NH3
N2O
N2
H2
(e)
(f)
600
500
400
300
200
100
100
80
60
40
20
0
-1.2V
3.9
6.2
-0.9V
-0.6V
9.3
15.8
13.1
21.5
-0.3V
0V
76.6
0.3
83.2
-0.3
84.8
88.0
-1.2
90.6
-0.6
93.5
-0.9
0.3V
0
2000 3000 4000 5000 6000 7000 8000
0
Theoretical TOF (S-1)
Applied voltage (V vs.RHE)
Figure 3. Experiments of NORR and NRR over different catalysts and theoretical microkinetic simulation. Reaction rate (a) and Faradaic efficiency (b) for NORR
on a Pt foil, Cu Foil, and Cu foam for 600 s, and NRR over Cu foam for 2 hours at -0.9 V vs. RHE. (c) Linear Sweep Voltammetry (LSV) for Pt foil, Cu foil and Cu
foam in NO-saturated 0.25 M Li2SO4 Cu foam in Ar or N2 -saturated 0.25 M Li2SO4 acquired with a scan rate of 10 mV s−1 at 25 °C. Reaction rate (d) and Faradaic
efficiency (e) of NORR on Cu foam at varying potentials. (f) The measured ammonia production rates over the Cu foam plotted as theoretical TOF at different
potentials.
5
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10.1002/anie.202002337
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RESEARCH ARTICLE
Table 1. Comparison of NORR on Cu foam with NRR from some recent reports
Potential
NH3 production rate
(μmol∙cm-2∙h-1)
Catalysts
Reactants
Electrolyte
FE (%)
Ref.
(vs. RHE)
[18]
[9a]
[19]
[9b]
Ru SACs/N-C
Au6/Ni
N2/H2O
N2/H2O
N2/H2O
N2/H2O
NO/H2O
0.05M H2SO4
0.05M H2SO4
0.1M KOH
-0.2
1.81
0.87
0.52
52
29.6
67.8
17.3
66
-0.14
-0.45
-0.6
Zr-TiO2
K-BNC
0.5M K2SO4
0.25M Li2SO4
Cu foam
-0.9
517.1
93.5
This work
Moreover, a microkinetic model was performed to estimate
the turnover frequency (TOF) of NORR to NH3 on Cu(111) under
different applied potentials.[20] The kinetic equations were shown
in Table 2. The reaction constant k is calculated following the
Arrhenius-type based equation with the parameter of potential-
dependent activation barriers (Equation S5). The experimental
NH3 yield rate vs. theoretical TOF was compared in Figure 3f. As
the potential varying from 0.3 to -1.2 V, the TOF increases from
2630 to 7840 S-1, because of the decrease of reaction and
activation energies at more negative potentials. The measured
NH3 production rate exhibits a nice linear correlation with
theoretically calculated activity, confirming our reaction
pathways and mechanisms above.
our experiments. The quantification results are shown in Figure
4b. The average of 128.36 μmol with standard deviation of 0.098
was achieved, which indicate reliable results were obtained with
the IC, NMR, and Indophenol blue Methods. In addition, a 100
hours stability test was performed for the Cu foam at -0.9 V vs.
RHE (see Supporting Information for details). As shown in
Figure 4c, the increment of total charge consumption was linear
with time, with an average current 79 mA/cm2. The FE of NH3
was calculated as the average value within the measured time
slot, which was always higher than 90%. The structure of the Cu
foam retained after 100 hours run, according to the SEM image
as shown in Figure 4d. The crystallographic structure signals
after electrochemical reactions were still consistent with the XRD
pattern for as-prepared samples. The diffraction peak at 2θ of
43.2o, 50.4o and 74.1o correspond to the Cu(111), (200), and
(220) facet, respectively. No other phases were found in the
XRD patterns. The X-ray absorption near-edge structure
(XANES) spectra of Cu K-edge in Cu foam before and after
reaction are basically the same with the Cu foil standard,
indicating the valence state of electrode is metallic Cu, as shown
in Figure S23. The k3-weighted extended X-ray absorption fine
structure (EXAFS) in Figure 4e also shows the Cu-Cu
coordination was dominate structure, which has been confirmed
by XRD profile. Furthermore, the surface species and states
over the Cu foam were studied by X-ray photoelectron
spectroscopy (XPS). There are the sharp peaks at the binding
energy of 933 eV and 953 eV, and no signals around 945 eV,
which means the metallic Cu was dominant species on the
surface. Though some Cu (II) species could be found according
to the two weak satellites peaks at binding energies of 944.8 eV
and 963.2 eV, which is due to the samples oxidized by air for
XPS examination. However, they remain intact before and after
electrochemical reactions, as shown in Figure 4f. All the
characterizations above indicate the Cu foam electrode was
robust enough during the 100 hours run.
Table 2. The kinetic equations for microkinetic model
Elementary reactions
Reaction rate (r)
[a]
NO(g) +H++e- + * ↔ NOH*
NOH* + H++e- ↔ N* + H2O
N* + H++e- ↔ NH*
r = P(NO) · P(H+) ·θ(*) · kf – θ(NOH*) ·kb
r = θ(NOH*) · P(H+) ·kf – θ(N*) ·P(H2O) · kb
r = θ(N*) · P(H+) ·kf – θ(NH*) · kb
NH* + H++e- ↔ NH2*
r = θ(NH*) · P(H+) ·kf – θ(NH2*) · kb
NH2* + H+ + e- ↔ NH3(g)+*
r = θ(NH2*) · P(H+) ·kf – P(NH3*) · θ(*) · kb
[a] * indicates active site. θ and P represent the concentration and pressure of
reactant, respectively. kf and kb are the reaction constant for forward and
backward reaction, respectively.
As an isotope labelling experiment is useful to exclude the
contamination of nitrogen source,[8a, 8b] we have also performed
isotope labeling experiments for confirmation. 15NO was used as
the reactant for NORR at -0.9 V vs. RHE for 30 minutes. After
reaction, the electrolyte was detected by Ion Chromatography
(IC), NMR, and Indophenol blue methods independently (see
details in SI). As shown in Figure 4a, a typical double peak on
15NH4+ at δ = 6.93 ppm and 7.04 ppm by 15NO reduced product,
well consistent with the 15NH4+ reference. Furthermore, the tipple
peaks signals of 14NH4+ were not found on 15NO reduced product,
demonstrating the produced ammonia is from the NO reactant in
6
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10.1002/anie.202002337
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RESEARCH ARTICLE
130
128
126
124
122
120
(a)
(b)
128.47
128.33
128.28
14NH+4 STD
15NH+4 STD
15NO reduced product
7.2
7.1
7.0
6.9
6.8
6.7
IC
NMR
Indophenol blue
Chemical shift (ppm)
(c)
(d)
NH3
H2
N2
N2O
Fresh Cu Foam
30
SEM
500mm
25
20
15
10
5
111
100
XRD
200
220
80
60
40
20
0
Cu Foam 100 h
SEM
500 mm
111
200
XRD
0
220
0
10 20 35 50
80
100
20
30
40
50
60
70
80
Time (h)
2(Degrees)
(e)
(f)
Cu-Cu
Fresh Cu Foam
Cu Foil STD
Fresh Cu Foam
Cu Foam 100 h
Cu 2p1/2
Cu 2p3/2
satellite
satellite
Cu Foam 100 h
0
2
4
6
8
10
970
960
950
940
930
Distance (Å)
Binding Energy (eV)
+
+
Figure 4. 15NO Isotope labelling experiment, stability test and characterizations for the Cu foam electrode. (a) The 1H NMR spectra of 14NH4 15NH4 and 15NO
,
reduced product; (b) the comparison of quantification results among the Ion Chromatography (IC), NMR and Indophenol blue Methods; (c) the stability of Cu foam
was examined for 100 hours at -0.9 V vs. RHE; (d) the comparison of XRD profile and SEM images for the as-prepared Cu foam samples and those after
lectrochemical reactions; (e) the Fourier transforms of EXAFS signals for the standard Cu Foil samples, as-prepared Cu foam, and the Cu foam after reaction; (f)
the X-ray photoelectron spectroscopy for the as-prepared Cu foam and those after reaction.
electrodes in experiments and examined their electrochemical
NORR performance. A record-high EAS rate (517.1 μmol·h-1·cm-
Conclusion
2) and FE (93.5%) was achieved at -0.9 V vs. RHE over a Cu
foam, which also showed a long-term stability for 100 hours run.
Moreover, the NH3 production rate of NORR over the Cu foam
reached the level of Haber-Bosch process. Hence, we propose
an alternative route for electrochemical ammonia synthesis from
NO over copper, which also open up a new scenario to reuse
the exhausted NO gas in industry.
A new electrochemical strategy to produce ammonia from
NO was proposed in this study, which can be coupled with the
need of NO removal. A thermodynamic estimation based on
DFT calculations suggests the NORR to NH3 is a more effective
scenario rather than NRR. Copper was screened out to be the
optimal metal catalyst. Kinetic barriers calculations confirm the
NH3 selectivity over copper is greater over N2 and N2O
production, as well as compared to hydrogen evolution.
Therefore, we used the commercially available copper as
Acknowledgements
7
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RESEARCH ARTICLE
[15] a) W. Hui-Fang, L. Zhi-Pan, J. Am. Chem.Soc. 2008, 130, 10996-
11004; b) C. Andre, C. Hee-Joon, R. B. Rankin, G. Jeff, Angew. Chem.
Int. Ed. 2015, 127, 8373-8376.
This work was supported by the National Natural Science
Foundation of China (No. 91945302, 21802124, 91845103,
21988101 and 21890753 ) , the National Key R&D Program of
China (No. 2016YFA0204100 and 2016YFA0200200),
Transformational Technologies for Clean Energy and
Demonstration”, Strategic Priority Research Program of the
Chinese Academy of Sciences (No. XDA21010208), the China
Postdoctoral Science Foundation Grant (No. 2019M661140),
LiaoNing Revitalization Talents program (XLYC1907099) and
the DNL Cooperation Fund, CAS (No. DNL180201). We thank
the staff at the BL14W1 beamline of the Shanghai Synchrotron
Radiation Facilities for assistance with the EXAFS and XANES
measurements.
[16] A. C. A. D. Vooys, M. T. M. Koper, R. A. V. Santen, J. A. R. V. Veen,
J. Catal. 2001, 202, 387-394.
[17] a) F. Chang, Y. Guan, X. Chang, J. Guo, P. Wang, W. Gao, G. Wu, J.
Zheng, X. Li, P. Chen, J. Am. Chem. Soc. 2018, 140, 14799-14806; b)
M. Kitano, Y. Inoue, Y. Yamazaki, F. Hayashi, S. Kanbara, S. Matsuishi,
T. Yokoyama, S. W. Kim, M. Hara, H. Hosono, Nat. Chem. 2012, 4,
934-940; c) P. Wang, F. Chang, W. Gao, J. Guo, G. Wu, T. He, P.
Chen, Nat. Chem. 2017, 9, 64-70.
[18] Z. Geng, Y. Liu, X. Kong, P. Li, K. Li, Z. Liu, J. Du, M. Shu, R. Si, J.
Zeng, Adv. Mater. 2018, 1803498.
[19] N. Cao, Z. Chen, K. Zang, J. Xu, J. Zhong, J. Luo, X. Xu, G. Zheng, Nat.
Commun. 2019, 10, 2877.
[20] J.-F. Chen, Y. Mao, H.-F. Wang, P. Hu, ACS Catal. 2016, 6, 7078-7087.
Keywords: Ammonia synthesis • NO removal • Electrocatalysis
• Computational Catalyst Design
[1]
[2]
[3]
T. Lee, H. Bai, Aims Environ. Sci. 2016, 3, 261-289.
M. Koebel, G. Madia, M. Elsener, Catal. Today 2002, 73, 239-247.
T. Kandemir, M. E. Schuster, A. Senyshyn, M. Behrens, R. Schlogl,
Angew. Chem. Int. Ed. 2013, 52, 12723-12726.
[4]
a) V. Kordali, G. Kyriacou, C. Lambrou, Chem. Commun. 2000, 1673-
1674; b) E. Skulason, T. Bligaard, S. Gudmundsdottir, F. Studt, J.
Rossmeisl, F. Abild-Pedersen, T. Vegge, H. Jonsson, J. K. Norskov,
Phys. Chem. Chem. Phys. 2012, 14, 1235-1245; c) C. X. Guo, J. R.
Ran, A. Vasileff, S. Z. Qiao, Energy Environ. Sci. 2018, 11, 45-56.
D. Yang, T. Chen, Z. Wang, J. Mater. Chem. A 2017, 5, 18967-18971.
J. H. Montoya, C. Tsai, A. Vojvodic, J. K. Norskov, ChemSusChem
2015, 8, 2180-2186.
[5]
[6]
[7]
a) L. Hu, A. Khaniya, J. Wang, G. Chen, W. E. Kaden, X. Feng, Acs
Catal. 2018, 8, 9312-9319; b) H. Huang, L. Xia, X. Shi, A. M. Asiri, X.
Sun, Chem. Commun. 2018, 54, 11427-11430; c) J. Wang, L. Yu, L. Hu,
G. Chen, H. Xin, X. Feng, Nat. Commun. 2018, 9, 1795; d) M. M. Shi, D.
Bao, B. R. Wulan, Y. H. Li, Y. F. Zhang, J. M. Yan, Q. Jiang, Adv. Mater.
2017, 29, 1606550.
[8]
a) S. Z. Andersen, V. Colic, S. Yang, J. A. Schwalbe, A. C. Nielander, J.
M. McEnaney, K. Enemark-Rasmussen, J. G. Baker, A. R. Singh, B. A.
Rohr, M. J. Statt, S. J. Blair, S. Mezzavilla, J. Kibsgaard, P. C. K.
Vesborg, M. Cargnello, S. F. Bent, T. F. Jaramillo, I. E. L. Stephens, J.
K. Norskov, I. Chorkendorff, Nature 2019, 570, 504-508; b) J.
Kibsgaard, J. K. Nørskov, I. Chorkendorff, ACS Energy Letters 2019, 4,
2986-2988; c) Y. T. Liu, D. Li, J. Yu, B. Ding, Angew. Chem. Int. Ed.
2019, 58, 16439-16444.
[9]
a) Z. H. Xue, S. N. Zhang, Y. X. Lin, H. Su, G. Y. Zhai, J. T. Han, Q. Y.
Yu, X. H. Li, M. Antonietti, J. S. Chen, J. Am. Chem. Soc. 2019, 141,
14976-14980; b) Y.-C. Hao, Y. Guo, L.-W. Chen, M. Shu, X.-Y. Wang,
T.-A. Bu, W.-Y. Gao, N. Zhang, X. Su, X. Feng, J.-W. Zhou, B. Wang,
C.-W. Hu, A.-X. Yin, R. Si, Y.-W. Zhang, C.-H. Yan, Nat. Catal. 2019, 2,
448-456; c) M. Wang, S. Liu, T. Qian, J. Liu, J. Zhou, H. Ji, J. Xiong, J.
Zhong, C. Yan, Nat. Commun. 2019, 10, 341; d) Y. T. Liu, X. Chen, J.
Yu, B. Ding, Angew. Chem. Int. Ed. 2019, 58, 18903-18907.
[10] a) A. C. A. D. Vooys, M. T. M. Koper, R. A. V. Santen, J. A. R. V. Veen,
Electrochimi. Acta 2002, 46, 923-930; b) V. Rosca, M. Duca, M. T. D.
Groot, M. T. M. Koper, Chem. Rev. 2009, 109, 2209-2244; c) H.-J.
Chun, V. Apaja, A. Clayborne, K. Honkala, J. Greeley, ACS Catal. 2017,
7, 3869-3882; d) M. Duca, M. C. Figueiredo, V. Climent, P. Rodriguez,
J. M. Feliu, M. T. Koper, J. Am. Chem. Soc. 2011, 133, 10928-10939.
[11] F. Abild-Pedersen, J. Greeley, F. Studt, J. Rossmeisl, T. R. Munter, P.
G. Moses, E. Skulason, T. Bligaard, J. K. Norskov, Phys. Rev. Lett.
2007, 99, 016105.
[12] J. K. Nørskov, T. Bligaard, A. Logadottir, J. R. Kitchin, J. G. Chen, S.
Pandelov, U. Stimming, J. Electrochem. Soc. 2005, 152, J23-J26.
[13] a) K. Chan, J. K. Norskov, J. Phys. Chem. Lett. 2015, 6, 2663-2668; b)
K. Chan, J. K. Norskov, J. Phys. Chem. Lett. 2016, 7, 1686-1690.
[14] R. Victor, M. T. M. Koper, J. Phys. Chem. B 2005, 109, 16750.
8
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Table of Contents
Nitric oxide
Electric energy
Cu
Foam
NH3
Automobile
Crops
Wind energy
Fuel cell
We proposed an alternative route for ammonia synthesis from exhausted NO by electrocatalysis, coupled with NO removal. A record-
high electrochemical ammonia synthesis rate of 517.1 μmol·cm-2·h -1 and FE of 93.5% were achieved at -0.9 V vs. RHE using a Cu
foam electrode.
9
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