Atomic species derived CoO x clusters on nitrogen doped mesoporous carbon as advanced bifunctional electro-catalyst for Zn-air battery 1. Experimental Section 1.1 Materials. Cobalt(II) chloride hexahydrate (CoCl 2 ·6H 2 O, 99.998% Co metal basis, Alfa Aesar), sodium borohydride (NaBH 4 , 99.5%, Sinopharm Chemical Reagent Co. Ltd.), potassium hydroxide (KOH, 85%, Sinopharm Chemical Reagent Co. Ltd.), absolute ethanol (C 2 H 5 OH, 99.8%, Aladdin), nitrogen-doped mesoporous carbon (NMC) powders (8.0 at.% Nitrogen, XFNANO) and Ultrathin carbon film on holey carbon (400mesh, Cu, Ted Pella Inc.) were used as received without any further purification. 1.2 Preparation of clustered CoO x /NMC sample. Firstly, 1g NaBH 4 powder was directly dissolved in a mixed solvent system (10 ml of ultrapure water and 30 ml of absolute ethanol) at - 40 o C (solution A). Then, 10 ml of solution B (CoCl 2 in water, 2 mg ml -1 ) was added dropwise into solution A with an injection rate of 50 uL min -1 controlled by a syringe pump system at room temperature (RT). By mixing with 40 mL of NMC dispersion (1.75 mg ml -1 , V ultrapure water /V absolute ethanol =1:3) for another 12 h under stirring at -40 o C, we
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Atomic species derived CoOx clusters on nitrogen doped
mesoporous carbon as advanced bifunctional electro-catalyst
for Zn-air battery
1. Experimental Section
1.1 Materials.
Cobalt(II) chloride hexahydrate (CoCl2·6H2O, 99.998% Co metal basis, Alfa Aesar), sodium
All electro-catalytic tests were conducted in a conventional three-electrode electrochemical system
containing 1 M KOH solution electrolyte at room temperature, using an Autolab PGSTAT-204
potentiostat equipped with the Nova 1.11 software. A rotating-disk glassy-carbon (area 0.196 cm 2)
electrode coated with the catalyst ink served as the working electrode, an Ag/AgCl (3 M KCl, +0.214 V
vs. standard hydrogen electrode) and a graphite rod were used as a reference and a counter electrode,
respectively. All potentials applied herein were calibrated to the RHE using the following equation:
ERHE = EAg/AgCl + 0.214 + 0.059×pH. The working electrode was prepared by the following procedure:
catalysts (5 mg for cobalt-based nonprecious catalyst while 2 mg for Pt/C and Ir/C commercial
catalysts) was dispersed in a mixture of alcohol (250 μL), water (700 μL), and Nafion solution (50 μL,
5%) for 20 min to form homogeneous catalyst inks. Then certain amount of the catalyst ink was
pipetted onto the GC surface by several times, with the loading of nonprecious catalyst, Pt/C (20%) and
Ir/C (20%) were 1.0, 0.2 and 0.4 mg cm-2. For oxygen reduction reaction (ORR), RDE tests were
performed in O2-saturated 1 M KOH solution at 1600 rpm with a sweep rate of 10 mV s -1 at room
temperature, after cyclic voltammetry (CV) activation for 30 cycles with a scan rate of 50 mV s -1 in N2-
saturated electrolyte. The accelerated durability test (ADT) were carried out at the voltage range of
0.57 to 1.07 V (vs. RHE) for 1000 cyclic voltammetry cycles with a scan rate of 100 mV s -1. Nyquist
plots obtained from EIS measurements at 0.85 V (vs. RHE) in O2-saturated electrolyte. For oxygen
evolution reaction (OER), RDE tests were performed in N2-saturated 1 M KOH solution at 1600 rpm
with a sweep rate of 10 mV s-1 at room temperature, after cyclic voltammetry (CV) activation for 30
cycles with a scan rate of 50 mV s-1. The accelerated durability test (ADT) were carried out at the
voltage range of 1.02 to 1.72 V (vs. RHE) for 1000 cyclic voltammetry cycles with a scan rate of 100
mV s-1. Nyquist plots obtained from EIS measurements at 1.55 V (vs. RHE) in N2-saturated electrolyte.
1.5 Zn-air batteries experiments.
The Zn-air battery tests were performed with a homemade cell configuration using a NEWARE CT-
3008 system to carry out the cycling test (1 h for each discharge and charge period), where a mixed
solution of 0.2 M ZnCl2 + 6 M KOH and a fresh polished Zn plate (1 mm thick) were used the
electrolyte and anode, respectively. The air cathode consisted of a hydrophobic carbon paper with a gas
diffusion layer (1.5 cm in diameter) on the air-facing side and a catalyst layer on the water-facing side.
The catalyst layer was made by loading catalyst ink onto the carbon paper by drop-casting with a
loading of 10 mg cm-2 for all catalysts.
2. Supplementary Figures
Figure S1. Selective STEM images of CoOx/NMC at different magnifications
Figure S2. (a) HAADF-STEM images image of CoOx/NMC and (b) the
corresponding size distribution of CoOx clusters.
Figure S3. (a) HAADF-STEM and the corresponding EDS elemental mapping images
of CoOx/NMC, (b) Co, (c) O e and (d) Co and O overlay.
Figure S4. (a) SEAD pattern and (b) EDS spectrum of CoOx/NMC.
Figure S5. HAADF-STEM images at different magnifications of (a, b) CoOOH/NMC-RT
and (c, d) CoOx/NMC-RT.
Figure S6. HAADF-STEM images of (a-b) CoOx/NMC-750 and (c-d) CoOx/NMC-
900.
Figure S7. XRD patterns of (a) CoOOH/NMC, CoOOH/NMC-RT and pure NMC
substrate and (b) CoOx/NMC, CoOx/NMC-RT with respect to pure NMC substrate.
Figure S8. High-resolution B 1s XPS spectra of CoOx/NMC and CoOOH/NMC.
Figure S9. High-resolution C 1s XPS spectra of CoOx/NMC and CoOOH/NMC.
Figure S10. High-resolution N 1s XPS spectra of CoOx/NMC and CoOOH/NMC.
Figure S11. Normalized X-ray absorption pre-edge structure spectra at Co K-edge for
different samples.
Figure S12. Fourier transformed k3 weight EXAFS oscillations measured at Co K-edge and fitted by different model. (a)Co K edge of CoOx/NMC fitted by structure of CoO. (b) Co K edge of CoOOH/NMC fitted by structure of Co and CoOOH. (c) Co K edge of CoOOH/NMC fitted by structure of CoOOH.
Figure S13. The fitting line of the valence of different samples.
Figure S14. Oxygen electrode catalytic performance of different catalysts in 1 M
Bifunctional OER polarization curves and (d) Tafel Plots of OER for CoOx/NMC,
CoOOH/NMC, CoOx/NMC-RT and CoOOH/NMC-RT.
Figure S15. Oxygen electrode catalytic performance of various catalysts in 1 M
KOH. (a) ORR polarization curves, (b) OER polarization curves.
Figure S16. LSV curves of (a) CoOOH/NMC and (b) Pt/C before and after 10,00 potential cycles under ORR conditions. LSV curves of (a) CoOOH/NMC and (b) Pt/C before and after 10,00 potential cycles under OER conditions.
Figure S17. Discharge demonstration to power the LED using two primary Zn-air
batteries in series using CoOx/NMC as the cathode catalyst.
Figure S18. The galvanostatic discharge curves of different Zn-air batteries at a
current density of 10 mA cm−2.
Table S1. EXAFS structural fitting parameters for CoOx/NMC. CN, coordination
number; R, distance between absorber and backscatter atoms; σ2, the Debye-Waller
factor value; The Fourier transformation of the k3-weighted EXAFS oscillations, k3·
χ(k), from k space to R space was performed over a range from 2.55 to 11.76 Å -1 to
obtain a radial distribution function.
Path CN R (Å) σ2
1 Co-O 3.99 2.08 0.01
2 Co-Co 5.63 3.03 0.01
3 Co-O 3.25 3.59 0.01
4 Co-Co 7.34 4.39 0.009
5 Co-O 10.46 4.58 0.01
Table S2. EXAFS structural fitting parameters for CoOOH/NMC. CN, coordination
number; R, distance between absorber and backscatter atoms; σ2, the Debye-Waller
factor value; The Fourier transformation of the k3-weighted EXAFS oscillations, k3·
χ(k), from k space to R space was performed over a range from 2.62 to 12.81 Å-1 to
obtain a radial distribution function (red part belong to Co).
Path CN R (Å) σ2
1 Co-O 3.94 1.90 0.006
1 Co-Co 0.79 2.56 0.0053
2 Co-H 10.17 2.58 0.01
3 Co-Co 3.19 2.81 0.008
4 Co-O 5.43 3.43 0.005
2 Co-Co 1.81 3.68 0.007
5 Co-O 6.40 3.79 0.009
6 Co-H 18.36 4.094 0.008
Table S3. Structural parameters for CoO standard sample. CN, coordination number;
R, distance between absorber and backscatter atoms.
Path CN R (Å)
1 Co-O 6 2.13
2 Co-Co 12 3.01
3 Co-O 8 3.69
4 Co-Co 6 4.26
5 Co-O 24 4.77
6 Co-Co 24 5.22
Table S4. Structural parameters for Co3O4 standard sample. CN, coordination
number; R, distance between absorber and backscatter atoms.
Path CN R (Å)
1 Co-O 12 1.93
2 Co-O 12 2.73
3 Co-O 12 3.04
4 Co-Co 12 3.38
5 Co-Co 4 3.53
6 Co-O 24 4.51
7 Co-O 24 4.71
8 Co-O 24 4.9
9 Co-O 24 5.09
Table S5. Structural parameters for CoOOH standard sample. CN, coordination
number; R, distance between absorber and backscatter atoms.
Path CN R (Å)
1 Co-O 6 1.90
2 Co-H 6 2.75
3 Co-Co 6 2.86
4 Co-O 6 3.43
5 Co-O 6 3.83
6 Co-H 6 3.94
7 Co-Co 2 4.40
8 Co-O 12 4.46
9 Co-O 6 4.77
10 Co-H 12 4.89
Table S6. Structural parameters for Co foil. CN, coordination number; R, distance
between absorber and backscatter atoms.
Path CN R (Å)
1 Co-Co 12 2.49
2 Co-Co 6 3.52
3 Co-Co 24 4.31
4 Co-Co 12 4.98
Table S7. Comparison between CoOx/NMC and other recently reported bifunctional
cobalt oxides nanocatalysts for oxygen-electrode activity.