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

borohydride (NaBH4, 99.5%, Sinopharm Chemical Reagent Co. Ltd.), potassium hydroxide (KOH,

85%, Sinopharm Chemical Reagent Co. Ltd.), absolute ethanol (C2H5OH, 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 CoOx/NMC sample.

Firstly, 1g NaBH4 powder was directly dissolved in a mixed solvent system (10 ml of ultrapure water

and 30 ml of absolute ethanol) at -40 oC (solution A). Then, 10 ml of solution B (CoCl2 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,

Vultrapure water/Vabsolute ethanol=1:3) for another 12 h under stirring at -40 oC, we collected atomically dispersed

CoOOH species on NMC substrates (CoOOH/NMC) sample by rinsing, vacuum filtration and followed

naturally drying at RT. According to previous work, CoOx cluster on NMC substrates (CoOx/NMC) was

transformed from CoOOH/NMC by annealing at 500 oC for 1 h with a heating rate of 1 oC min-1 under

flowing Ar gas. For comparison, we also performed a control experiment by varying the temperature

from -40 oC to RT through the synthesis process.

1.3 Characterizations of as-prepared samples.

Powder XRD patterns were acquired at room temperature using an X-ray diffractometer (D/max

2500V), a typical scan range of a scanning speed of 8 o min-1, an operating voltage of about 40 kV and

corresponding current of 150 mA were employed. Aberration-corrected HAADF-STEM images were

acquired using a JEM-ARM200F transmission electron microscope operated at 200 kV. XPS

measurements were obtained using an X-ray photoelectron spectrometer (Escalab 250Xi) equipped

with an Al Kα radiation source (1487.6 eV) and hemispherical analyzer with pass energy of 30.0 eV

and an energy step size of 0.05 eV. The binding energy of the C 1s peak at 284.8 eV was considered as

an internal reference. Spectral deconvolution was performed by Shirley background subtraction by

using a Voigt function convoluting the Gaussian and Lorentzian functions. Inductively coupled plasma-

mass spectrometry (ICP-MS, ELAN DRC-e) measurements were obtained, confirming the final Co

loading contents on NMC of CoOx/NMC was 11.51%. XAFS measurements at the Co K-edge (7709

eV) in both transmission (for Co foil) and fluorescence (for samples) mode were performed at the

BL14W1 in Shanghai Synchrotron Radiation Facility (SSRF). The electron beam energy was 3.5 GeV

and the stored current was 260 mA (top-up). A 38-pole wiggler with the maximum magnetic field of

1.2 T inserted in the straight section of the storage ring was used. XAFS data were collected using a

fixed-exit double-crystal Si(111) monochromator. A Lytle detector was used to collect the fluorescence

signal, and the energy was calibrated using Co foil. The photon flux at the sample position was

2.1×1012 photons per second. The raw data analysis was performed using IFEFFIT software package

according to the standard data analysis procedures. The spectra were calibrated, averaged, pre-edge

background subtracted, and post-edge normalized using Athena program in IFEFFIT software package.

The Fourier transformation of the k3-weighted EXAFS oscillations, k3·χ(k), from k space to R space was

performed over a range of 2.55-11.76 Å-1 (2.62-12.81 for CoOOH/NMC) to obtain a radial distribution

function. And data fitting was done by Artemis program in IFEFFIT. The position of E0 is identified as

the corresponding energy at 0.5 of normalized absorption spectra. The valence of Co is zero and E0 is

7709eV, the cobalt in CoO is bivalent and E0 is 7717.5eV, the valence of Co in Co3O4 is 2.67 and E0 is

7719.5eV. Then, we perform a linear fitting between valence and E0. At last, the valence of samples are

obtained according to the relationship between E0 and valence. E0 of CoOx is 7718.34eV，and E0 of

CoOOH is 7719.56eV.

1.4 Oxygen electrode electrochemical measurements.

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

KOH. (a) Bifunctional ORR polarization curves, (b) Tafel Plots of ORR, (c)

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.

Catalyst Electrolyte

Ej10

(V vs.

RHE)

OER Tafel

Slope

(mV dec-1)

E1/2

(V vs.

RHE)

ORR Tafel

Slope

(mV dec-1)

Ref

CoOx/NMC 1M KOH 1.499 59.8 0.907 71.5This

work

1nm CoOx/N-

RGO0.1M KOH 1.50 76 0.896 NA 1

CoOx/NC 0.1M KOH 1.578 NA 0.80 NA 2

Co@CoOx/

NCNT0.1 M KOH NA NA 0.80 80 3

Co-CoO/N-

rGO 0.1M KOH 1.62 68 0.780 NA 4

single-crystal

CoO

nanorods

1M KOH 1.56 NA 0.85 NA 5

CoO/N-

graphene1M KOH 1.57 71 0.81 NA 6

Ni-doped

CoO NSs1M KOH NA NA 0.825 121 7

Co/

Co3O4@PGS0.1M KOH 1.58 76.1 0.89 52.6 8

Co3O4/MnO2- 0.1M KOH 1.62 NA ~0.86 NA 9

CNTs -350

Co3O4-doped

Co/CoFe-9000.1M KOH ~1.57 72.8 0.79 NA 10

Co@C

o3O4@NC-

900

1M KOH

OER

0.1M KOH

ORR

1.60 94 0.80 NA 11

CeO2/

Co3O4@NC-

600

0.1M KOH 1.504 58.3 0.86 65.3 12

N-

Co3O4@NC1M KOH 1.56 NA 0.77 NA 13

Table S8. The fitted data of Nyquist plots. Corresponding equivalent circuits

[Rs(Rct1Q1)(R2Q2)]. Rs is the solution resistance, the high-frequency (Rct1, Q1) element

is associated with the charge-transfer process through electrode-electrolyte interface,

and the low frequency (R2, Q2) element can be attributed to the O2 mass-transport.

Sample OER ORR

Rs (Ω) Rct1 (Ω) R2 (Ω) Rs (Ω) Rct1 (Ω) R2 (Ω)

CoOx/NMC 2.12 1.38 19.90 9.02 37.70 78.60

CoOOH/NMC 2.18 1.56 21.10 10.10 47.00 98.60

Pt/C (ORR)

Ir/C (OER)2.16 2.16 25.30 9.30 80.50 151.50

Table S9. Comparison between CoOx/NMC and other previously reported

bifunctional oxygen catalysts for cathode of Zn-Air Battery.

Catalyst ΔE (V)

Open circuit

potential

(V)

Maximum power density

(mW cm-2)

High energy density

(mW h g-1)

1st Over

potenial (V)

Over potenial

after cycling (V)

Ref

CoOx/NMC-500 0.592 1.476 195.3 849.60.74 @

10mA cm-2

1.03 @ 10mA cm-2

(400h)

This work

Pt/C 0.693 1.410 152.9 806.80.69 @

10mA cm-2

1.12 @ 10mA cm-2

(400h)

This work

Co9S8@MoS2 NA 1.384 NA NA0.8 @ 10mA

cm-2NA 14

Co2P@CNF ~0.89 1.393 121 NA0.81 @

10mA cm-2

1.1 @ 10mA cm-2 (150th)

15

Co-N,B-CSs 0.83 1.430 100.4 NA~1.15 @ 5mA cm-2

1.35 @ 10mA cm-2

(128th)16

P,S-CNS 0.69 1.510 198 8450.8 @ 25mA

cm-2NA 17

NiO/CoN PINWs 0.85 1.460 79.6 9450.84 @

50mA cm-2NA 18

NiFe-LDH/Co,N-CNF

0.752 NA NA NA1 @ 25mA

cm-2NA 19

CoSx@PCN/rGO 0.79 1.380 NA NA1.5 @ 50mA

cm-2NA 20

Co/Co3O4@PGS 0.69 1.450 118.27 NA0.91 @

10mA cm-2

0.92 @ 10mA cm-2

(370h)8

NOGB-800 0.78 NA 111.9 NA0.72 @

10mA cm-2NA 21

CuS/NiS2 INs 0.79 1.440 172.4 NA 0.57 @ NA 22

25mA cm-2

CoZn-NC-700 0.78 1.420 152 NA0.73 @

10mA cm-2

1.1 @ 5mA cm-2 (200th)

23

CuCo2O4/N-CNTs NA 1.360 83.83 653.90.36 @

20mA cm-2NA 24

Mo–N/C @MoS2 0.81 1.46 196.4 846.070.75 @ 5mA

cm-2

1.02 @ 5mA cm-2 (12h)

25

Co–Nx/C NRA 0.65 1.42 193.2 NA0.68 @

50mA cm-2

0.91 @ 50 mA cm-2

(80h)26

S-GNS/ NiCo2S4 0.69 ~1.35 216.3 NA0.8 @ 10mA

cm-2NA 27

Ni0.5Fe0.5@N-GR 0.61 1.482 85 NA0.8 @ 10mA

cm-2NA 28

P-CoSe2/N-C FAs 0.59 1.3 NA NA~0.8 @ 1mA

cm-2

~1.25 @ 1mA cm-2

(20h)29

NCNFs-1000 1.02 1.48 185 8380.73 @

10mA cm-2

0.86 @ 10mA cm-2

(80h)30

Co3FeS1.5(OH)6 0.867 NA NA NA0.86 @

20mA cm-2NA 31

IrMn/Fe3Mo3C 0.63 NA NA NA0.75 @

20mA cm-2

0.86 @ 20mA cm-2

(200h)32

Fe0.5Co0.5Ox 0.74 1.43 86 9040.79 @

10mA cm-2

0.89 @ 10mA cm-2

(60th)33

NGM-Co 0.95 1.44 152 NA1.12 @ 5mA

cm-2

1.15 @ 5mA/cm2

(12h)34

NiS2/CoS2-O NWs

0.765 1.49 NA NA0.95 @ 3mA

cm-2

1.3 @ 3mA cm-2 (25h)

35

Ni6/7Fe1/7S2 NA NA NA NA 0.55 @ ~0.85 @ 36

15mA cm-25mA cm-2

(160th)

1nm CoOx/N-RGO

0.74 1.39 NA NA0.57 @ 6mA

cm-2NA 1

Fe-N4 SAs/NPC 0.775 NA 232 NA1.45 @

50mA cm-2NA 37

Fe3Pt/Ni3FeN 0.665 NA NA NA0.72 @

50mA cm-2

0.97 @ 50mA cm-2

38

meso/micro-FeCo-Nx-CN-30

0.78 ~1.4 150 NA~0.81 @

10mA cm-2

0.8 @ 10mA cm-2 (40h)

39

CoNi/BCF 0.8 1.44 155.1 853.1~0.85 @

10mA cm-2

~0.95 @ 10mA cm-2

(30h)40

Co3O4/Ni foam NA NA 35.7 NA~1.15 @

10mA cm-2

~1.3 @ 10mA cm-2

(20h)41

La2O3/Co3O4/MnO2-CNTs

NA 1.5 295 970~0.7 @

10mA cm-2

~0.8 @ 10mA cm-2

(89h)42

NiCo-air 0.93 1.38 102.08 NA0.98 @

10mA cm-2

1.12 @ 10mA cm-2

(29h)43

U-Fe7C3@NC NA 1.486 105.3 710.3 NA NA 44

Ni1Co3/CN-3 NA 1.16 38.5 NA NA NA 45

Co3O4/MnO2-CNTs -350

0.83 1.47 340 775 NA NA 9

Fe@C-NG/ NCNTs

0.84 1.37 101.2 764.50.89 @

10mA cm-2

1.02 @ 10mA cm-2

(99h)46

Fe/N/C NA NA 250 NA0.66 @ 5mA

cm-2

~1 @ 5mA cm-2

(40h)47

Co@Co3O4@NC-900

0.85 1.06 64 NA~0.7 @

10mA cm-2

<1 @ 10mA cm-2 (98th)

11

Co3O4-doped Co/CoFe-900

0.78 1.43 97 819~0.7 @ 5mA

cm-2

~1.25 @ 10mA cm-2

(65h)10

CeO2/Co3O4@NC-600

0.64 1.41 116.8 805~0.75 @ 5mA cm-2

~1.2 @ 10mA cm-2

(350th)12

CoN4/NG 0.74 1.51 115 6710.84 @

10mA cm-2

0.84 @ 10mA cm-2

(100h)48

(Zn,Co)/NSC NA 1.5 150 NA NA NA 49

Ordered Pd3Pb/C NA NA NA 7100.72 @

10mA cm-2

0.86 @ 10mA cm-2

(135th)50

NPMC 1.02 1.48 55 8351.26 @ 5mA

cm-2NA 51

N-Fe-HPCs NA 1.48 540 >800 NA NA 52

CoNCF-1000-80 0.84 1.44 170 7970.75 @

10mA cm-2

0.83 @ 10mA cm-2

(166h)53

CF-K-A NA 1.4 61.5 NA NA NA 54

Fe-NSDC 0.8 1.53 225.1 NA0.45 @ 4mA

cm-2

0.7 @ 4mA cm-2 (50h)

55

FeNx/C-70020 1.1 1.6 36 NA1.3 @ 5mA

cm-2

1 @ 5mA cm-2 (84h)

56

N, P/CoS2 @TiO2

NP0.78 1.31 NA NA

0.8 @ 10mA cm-2

0.85 @ 10mA cm-2

(133h)57

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