Supplementary Information N-doped porous carbon under … · 2019-10-25 · S1 Supplementary...
Transcript of Supplementary Information N-doped porous carbon under … · 2019-10-25 · S1 Supplementary...
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Supplementary Information
Electrochemical reduction of N2 to ammonia on Co single atoms embedded
N-doped porous carbon under ambient conditions
Yanming Liu,a Qi Xu,a Xinfei Fan,b Xie Quan,*a Yan Su,c Shuo Chen,a Hongtao Yu,a Zhengjun Cai a
aKey Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of
Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.bCollege of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China.cSchool of Physics and Opto-Electronic Technology, Dalian University of Technology, Dalian 116024,
China.
Corresponding author E-mail: [email protected]
This file includes:Fig. S1. SEM of ZIF and TEM images of CSA/NPCs.Fig. S2. Structure characterization of CSA/NPCs.Fig. S3. Cyclic voltammograms and chronoamperometric curves.Fig. S4. Hydrazine detection.Fig. S5. 1H-NMR spectra for 14NH4
+ and 15NH4+ detection.
Fig. S6. NH3 production rates of CSA/NPC-700.Fig. S7. H2 efficiency of CSA/NPC-750.Fig. S8. SEM images before and after N2 reduction.Fig. S9. XPS spectra before and after N2 reduction.Fig. S10. Potentiostatic stability of CSA/NPC-750.Fig. S11.SEM and TEM images for NPC-750 and Co/NPC-750.Fig. S12. XPS spectra of CSA/NPCs.Fig. S13. N2 adsorption comparison.Fig. S14. Free energy for ammonia synthesis.Table S1. The EXAFS fitting results of CSA/NPC-750.Table S2. Comparison of NH3 synthesis performance between CSA/NPC-750 and electrocatalysts reported.Table S3. The N/C and Co/C ratios for CSA/NPC-750 before and after N2 reduction.Table S4. The metal and N contents of CSA/NPCs, NPC-750 and Co/NPC-750.
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2019
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1. Supplementary Figures
5 nm
5 nm 5 nm
B
C D
500 nm
A
Fig. S1 (A) SEM image of Zn/Co bimetallic ZIF precursor, TEM images of (B) CSA/NPC-750, (C)
CSA/NPC-850 and (D) CSA/NPC-950.
0 5 10 15 20 250.0
0.1
0.2
0.3
CSA/NPC-750 CSA/NPC-850 CSA/NPC-950
dV/d
D (c
m3 g
-1 n
m-1)
Pore size (nm)20 40 60 80
C(002)
CSA/NPC-950
CSA/NPC-850
CSA/NPC-750
Inte
nsity
(a.u
.)
2 theta (deg.)
A B
Fig. S2 (A) X-ray diffraction spectra and (B) pore size distribution of CSA/NPC-750, CSA/NPC-850 and
CSA/NPC-950 (DFT method).
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-0.6 -0.4 -0.2 0.0 0.2 0.4-3
-2
-1
0
1
Ar N2
Curr
ent d
ensit
y (m
A cm
-2)
Potential (V vs RHE)0 1000 2000 3000 4000
-4
-3
-2
-1
0
0.0 V -0.1 V -0.2V -0.3V -0.4V
Curr
ent d
ensit
y (m
A cm
-2)
Time (s)
A B
Fig. S3 (A) Cyclic voltammograms of CSA/NPC-750 on glassy carbon in N2 or Ar saturated 0.05 M
Na2SO4 with scan rate of 20 mV s-1, (B) Chronoamperometric curves for electrochemical reduction of N2
on CSA/NPC-750 at 0.0~-0.4 V (vs RHE).
400 420 440 460 480 500
CSA/NPC-750, -0.2 V 0.05M Na2SO4
Abso
rban
ce
Wavelength (nm)
Fig. S4. UV-Vis curves of 0.05 M Na2SO4 and the sample for N2 reduction on CSA/NPC-750 (1 h, -0.2 V,
0.05 M Na2SO4) measured by p-dimethylaminobenzaldehyde method.
To find out whether hydrazine can be produced, electrochemical reduction of N2 was conducted on
CSA/NPC-750 at -0.2 V in 0.05 M Na2SO4 for 1 h and hydrazine concentration of the solution was
measured by p-dimethylaminobenzaldehyde spectrophotometric method. Details as follows: 2.0 g p-
dimethylaminobenzaldehyde, 100 mL ethanol and 10 mL HCl (12.0 mol/L) were mixed and used as color
reagent. 0.8 mL color reagent was added into a mixture of 2.0 mL solution (taken from electrochemical cell
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after N2 reduction for 1 h) and 2.0 mL HCl (0.24 mol/L). After mixing thoroughly, the resulting solution
sat for 20 min. Its absorbance was measured at 458 nm. The absorbance of 0.05 M Na2SO4 was used as
reference. As shown in Fig. S4, the absorbance of the sample obtained from N2 reduction on CSA/NPC-750
at -0.2 V is 0.0211, which is similar to that of 0.05 M Na2SO4 (0.0209). Therefore, hydrazine is not produced
during N2 reduction on CSA/NPC-750.
To confirm ammonia is produced from N2 reduction, 15N2 reduction has been performed on CSA/NPC-
750 at 0.05 M Na2SO4. Details as follows: Ar purge was undertaken for 30 min to remove 14N2 in the cell
and electrolyte, followed by 15N2 purge for 20 min. Electrochemical reduction of 15N2 was conducted on
CSA/NPC-750 at -0.2 V with 15N2 flow. After 15N2 reduction for 1 h, the sample was collected and adjusted
to pH 2 with HCl for ammonia quantification by H-NMR on Bruker 700 MHz spectrometer with DMSO
as internal standards. The sample was mixed with 0.2 mM DMSO (D2O was used as solvent) with ratio of
9:1. H-NMR measurement was performed for 2500 scans with water suppression. As reference, electrolysis
was also conducted under Ar on CSA/NPC-750 (-0.2 V, 1 h) and the solution was collected for 1H-NMR
measurement with the same method mentioned above. As reference, the 1H-NMR spectrum of 0.5 mM 14NH4Cl (pH 2) was measured by the same method with 250 scans. Calibration curve for 15NH4
+ was tested
using 15NH4Cl with concentrations of 0-300 uM. As shown in Fig. S5A, doublet at 6.93 ppm and 7.08 ppm
can be observed on the 1H-NMR spectrum for 15N2 reduction sample, while triplet around 6.91-7.09 ppm
appear on the 1H-NMR spectrum for 14NH4+
standard sample and no discernable peak can be observed for
electrolysis under Ar. The doublet (6.93 ppm and 7.08 ppm) for 15N2 reduction sample can be attributed to
the signal of 15NH4+,1 and the triplet (6.91-7.09 ppm) arises from 14NH4
+. The 15N labelling and Ar
electrolysis experiments indicate the detected ammonia in this work is produced from N2 reduction. To
confirm it, the 15NH4+ produced from 15N2 reduction is quantified with the calibration curve in Fig. S5B,
which shows the peak area ratio of 15NH4+/DMSO versus 15NH4
+ concentration. The obtained 15NH4+
production rate is 0.82 μmol cm-2 h-1, consistent with result of 0.86 μmol cm-2 h-1 from 14N2 reduction.
These results confirm the ammonia detected in this work is produced from N2 reduction.
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0 100 200 3000.0
0.1
0.2
0.3
0.4
S15 N
H+ 4/S
DM
SO
15NH4+ concentration (M)
y=0.00119x-0.00807
7.1 7.0 6.9
7.1 7.0 6.9
7.1 7.0 6.9
Under 15N2
14NH4+
Under Ar
H (ppm)
A B
Fig. S5 1H-NMR spectra for (A) 0.5 mM NH4+ standard (250 scans), 15N2 reduction and Ar electrolysis on
CSA/NPC-750 at -0.2 V (2500 scans), (B) calibration curve for 15NH4+: the peak area ratio of
15NH4+/DMSO versus 15NH4
+ concentration.
-0.1 -0.2 -0.30.00
0.05
0.10
0.15
0.20
0.25
NH
3 pro
duct
ion
rate
(m
ol c
m-2
h-1
)
Potential (V vs. RHE)
Fig. S6 The NH3 production rates of CSA/NPC-700 for electrochemical reduction of N2 at -0.1~-0.3 V (vs
RHE) and 0.05 M Na2SO4.
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-0.3 V -0.2 V0
20
40
60
80
100
Fara
daic
eff
icie
ncy
(%)
Potential (V vs. RHE)
Fig. S7 The H2 production efficiencies during electrochemical reduction of N2 on CSA/NPC-750 at -0.2 V
and -0.3 V.
Fig. S8 SEM images of CSA/NPC-750 electrode (A) before and (B) after electrochemical reduction of N2
at -0.2 V.
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280 282 284 286 288 290
After
In
tens
ity (a
.u.)
Binding energy (eV)
Before
770 780 790 800 810
Inte
nsity
(a.u
.)
Binding energy (eV)
After
Before
392 396 400 404
Inte
nsity
(a.u
.)Binding energy (eV)
After
Before
A B C
Fig. S9 (A) C 1s, (B) N 1s and (C) Co 2p XPS spectra of CSA/NPC-750 before and after electrochemical
reduction of N2 at -0.2 V.
0 5000 10000 15000 20000 25000-1.2
-0.9
-0.6
-0.3
0.0
Time (s)
Cur
rent
den
sity
(mA
cm
-2)
0
3
6
9
12
15
Far
adai
c ef
ficie
ncy
(%)
Fig. S10 Chronoamperometric curve and NH3 production efficiency during electrochemical reduction of
N2 on CSA/NPC-750 at -0.2 V.
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Fig. S11 SEM images of (A) NPC-750 and (B) Co/NPC-750, (C) low and (D) high resolution TEM images
of Co/NPC-750.
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200 400 600 800 1000
Zn
CoN
O CSA/NPC-750 CSA/NPC-850 CSA/NPC-950
Inte
nsity
(a.u
.)
Binding energy (eV)
C
396 398 400 402 404
Graphitic N
Pyrrolic N
Inte
nsity
(a.u
.)
E (eV)
Pyridinic N
396 398 400 402 404
Graphitic N
Pyrrolic N
Inte
nsity
(a.u
.)
E (eV)
Pyridinic N
396 398 400 402 404
Graphitic N
Pyrrolic N
Inte
nsity
(a.u
.)
E (eV)
Pyridinic N
C D
A B
Fig. S12 (A) XPS survey scan spectra of CSA/NPCs, N 1s XPS spectra of (B) CSA/NPC-750, (C)
CSA/NPC-850 and (D) CSA/NPC-950.
100 200 300 400 500
CSA/NPC-750 NPC-750
Inte
nsity
(a.u
.)
Temperature (ºC)
Fig. S13 N2-TPD curves of CSA/NPC-750 and NPC-750.
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DFT calculation was conducted on Vienna Ab-initio Simulation Package (VASP) with the projector
augmented wave (PAW) potentials, the generalized gradient approximation (GGA) parameterized by
Perdew, Burke and Ernzerhof (PBE) for texchange correlation functional.2,3 The Co single atoms embedded
N-doped carbon (CSA/NPC) with a 7×7 unit cell was used as model (Fig. S14). Both Co atoms coordinated
with four N atoms (Co-N4) and pyridinic N were considered in this model. The kinetic energy cutoff was
set to 400 eV for the plane-wave basis. To eliminate the interaction of periodic images of the system,
vacuum layer above the CSA/NPC plane was selected to be 20 Å. The model structures are optimized by
using thresholds for the total energy of 10−4 eV and force of 0.01 eV/Å. The free energy of possible reaction
pathways for NH3 synthesis was calculated4-6 as follows: ΔG = ΔEDFT + ΔEZPE -TΔS, where ΔEDFT is the
DFT total energy, ΔEZPE is the zero-point energy, and TΔS is the entropy difference between the initial
adsorbed state and final state. During the DFT calculation, the H, N2Hx and NHx adsorbed on CSA/NPC
are optimized by searching all the possible structures and find the lowest energy ones.
Fig. S14 The model of CSA/NPC used for DFT calculation.
2. Supplementary tablesTable S1. The EXAFS fitting results of CSA/NPC-750.
Electrocatalysts Bond type N R 2 ∆E0 (eV)CSA/NPC-750 Co-N 4.0 1.89 0.0034 -6.7
N is the coordination number, R is the distance between absorber and backscatter atoms, 2 is the Debye-Waller factor value, ∆E0 is edge-energy shift
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Table S2. Comparison of NH3 synthesis performance between CSA/NPC-750 and electrocatalysts reported recently
Electrocatalysts Production rate(µmol h-1 cm-2)
Efficiency(%) Conditions References
Au/CeOx-RGO 0.098 10.1% -0.2 V, pH 2 Adv. Mater. 2017, 29, 1700001
Au nanorod 0.097 8.11% -0.2 V, pH 13 Adv. Mater. 2017, 29, 1604799
Fe2O3/CNT 0.013 0.18% -1.4 V, pH 7 Angew. Chem. Int. Ed. 2017, 56, 2699
MoS2 0.29 1.17% -0.5 V, pH 7 Adv. Mater. 2018, 30, 1800191
Carbon nitride 0.95 11.59% -0.2 V, pH 1 Angew. Chem. Int. Ed. 2018, 57, 10246
CSA/NPC 0.86 10.5% -0.2 V, pH 7 This work
Table S3. The N/C and Co/C ratios obtained from XPS for CSA/NPC-750 before and after electrochemical reduction of N2 at -0.2 V.
N/C ratio Co/N ratioBefore use 0.319 0.0152After use 0.335 0.0146
XPS is used to quantify CSA/NPC-750 before and after electrochemical reduction of N2 at -0.2 V. As
shown in Figure S11 and Table S3, the atom ratios of N/C and Co/C are 0.319 and 0.0152 before use. After
electrochemical reduction of N2 for six cycles (1 h for each cycle), the N/C ratio is 0.335. The slightly
increased N content could be caused by measurement error and/or adsorbed ammonia. The Co/C ratio is
0.0146 after use, which can be considered as the same before reaction.
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Table S4. The metal and N contents of CSA/NPCs, NPC-750 and Co/NPC-750
Electrocatalysts Co content Zn content N content
CSA/NPC-750 1.4 wt% 4.3 wt% 20.6 at.%
CSA/NPC-850 1.5 wt% 1.8 wt% 15.3 at.%
CSA/NPC-950 1.8 wt% 0.03 wt% 13.0 at.%
NPC-750 0 4.2 wt% 20.7 at.%
Co/NPC-750 8.2 wt% 4.1 wt% 21.8 at.%
Metal content is measured by inductively coupled plasma atomic emission spectroscopy, N content is measured by XPS.
3. References1. F. Zhou, L. M. Azofra, M. Ali, M. Kar, A. N. Simonov, C. McDonnell-Worth, C. Sun, X. Zhang, D. R. MacFarlane, Energy Environ. Sci. 2016, 9, 2545-2549.2. J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett., 1996, 77, 3865-3868.3. G. Kresse and J. Hafner, Phys. Rev., 1993, 47, 558-561.4. Z. Geng, Y. Liu, X. Kong, P. Li, K. Li, Z. Liu, J. Du, M. Shu, R. Si and J. Zeng, Adv. Mater., 2018, 30, 1803498.5. S. Back and Y. Jung, Phys. Chem. Chem. Phys., 2016, 18, 9161-9166.6. X. Yu, P. Han, Z. Wei, L. Huang, Z. Gu, S. Peng, J. Ma and G. Zheng, Joule, 2018, 2, 1610-1622.