SUPPORTING INFORMATION

Enhancing by Nano-engineering: Hierarchical Architectures as Oxygen

Reduction/ Evolution Reactions for Zinc-Air Batteries

Tayyaba Najam1, Syed Shoaib Ahmad Shah1, Wei Ding*, Jianghai Deng, and Zidong Wei*

Chongqing Key Laboratory of Chemical Process for Clean Energy and Resource Utilization, School of Chemistry and

Chemical Engineering, Chongqing University. Shazhengjie 174, Chongqing 400044, China.

1. EXPERIMENTAL SECTION

1.1 Synthesis of CoAl-LDH and NS-CoOxAlOy/C:

Typically, CoCl2 ·6H2O (5 mM), urea (17.5 mM) and AlCl3 ·6H2O (2.5 mM) were added in 400 mL of

deionized water. The mixture was then reflux at 95 0C for 48 h under a nitrogen flow. The resultant product

was filtered, washed with deionized water and ethanol and dried in an oven. Then, as-synthesized CoAl-

LDH was pyrolyzed at heating of 3 ⁰C/min to 435 °C and kept at this temperature for 1 hour followed by

further increasing the temperature up to 900 ⁰C at 5 °C/min for 2 hours under nitrogen atmosphere to

obtained NS-CoOxAlOy. The NS-CoOxAlOy and Vulcan carbon (1:1) were homogeneously mixed to form

NS-CoOxAlOy/C.

1.2 Synthesis of ZnAl-LDH:

Typically, ZnCl2 ·6H2O (5 mM), urea (17.5 mM) and AlCl3 ·6H2O (2.5 mM) were added in 400 mL of

deionized water. The mixture was then reflux at 95 °C for 48 h under nitrogen flow. The resultant product

was filtered, washed with deionized water and ethanol and dried in an oven.

1.3 Synthesis of ZIF-67/ CoAl-LDH, Co-CNTs/ NS-CoOxAlOy and Co-NPs/ NS-CoOxAlOy:

CoAl-LDH (0.1g) sonicated in 50 ml of methanol and 0.8 M solution of 2-MeIM (2-methylimidazol) was

rapidly added, followed by stirring for 5 minutes. Then, Co(NO3)2.6H2O (0.1 M) in 50 ml of methanol

was added into the above mixture, followed by stirring for 30 minutes. The resultant product was filtered,

washed with deionized water and ethanol and dried in an oven. Then, as-synthesized ZIF-67/ CoAl-LDH

was pyrolyzed at heating of 3 ⁰C/min to 435/120 °C and kept at this temperature for 1 hour followed by

further increasing the temperature up to 900 ⁰C at 5 °C/min for 2 hours under nitrogen atmosphere to

obtained Co-CNTs/ NS-CoOxAlOy (435/900 °C) and Co-NPs/ NS-CoOxAlOy (120/900 °C).

1.4 Synthesis of ZIF-67/ ZnAl-LDH and Co-NS/ NS-AlOy:

ZnAl-LDH (0.1g) sonicated in 50 ml of methanol and 0.8 M solution of 2-MeIM (2-methylimidazol) was

rapidly added, followed by stirring for 5 minutes. Then, Co(NO3)2.6H2O (0.1 M) in 50 ml of methanol

was added into the above mixture, followed by stirring for 30 minutes. The resultant product was filtered,

washed with deionized water and ethanol and dried in an oven. Then, as-synthesized ZIF-67/ ZnAl-LDH

was pyrolyzed at heating of 3 ⁰C/min to 435°C and kept at this temperature for 1 hour followed by further

increasing the temperature up to 900 ⁰C at 5 °C/min for 2 hours under nitrogen atmosphere to obtained

Co-NS/ NS-AlOy.

1.5 Synthesis of ZIF-67 and Co-CNTs:

0.1 M methanolic solution of Co(NO3)2.6H2O (50 ml) and 0.8 M solution of 2-MeIM (2-methylimidazol)

were added, followed by stirring for 30 minutes. The resultant product was filtered, washed with deionized

water and ethanol and dried in an oven. Then, as-synthesized ZIF-67 was pyrolyzed at heating of 3 ⁰C/min

to 435°C and kept at this temperature for 1 hour followed by further increasing the temperature up to 900

⁰C at 5 °C/min for 2 hours under nitrogen atmosphere to obtained Co-CNTs.

2. ELECTROCHEMICAL MEASUREMENTS

Autolab electrochemical work station was used to carry out all the tests for ORR, and OER. The

electrochemical measurements were taken by three electrode method in which working electrode (glassy

carbon rotating disk), counter electrode (graphitic carbon rod) and reference electrode (vs Ag/AgCl) were

used in ultrapure alkaline medium (0.1 M KOH for ORR, 1M KOH for OER). For working electrode,

uniform catalyst ink was prepared by isolating 2 mg of sample in 400 µL ethanol and 5 µL of Nafion (5%)

under sonication for 20 minutes. Then, homogeneous catalyst ink was deposited on a glassy carbon

surface (0.19625 cm2) followed by drying before the performance of tests. The loading of catalysts were

~0.5 mg cm-2. For ORR measurements, cyclic voltammetry (CV), and linear sweep voltammetry (LSV)

were taken in 0.1M KOH solution at 50 and 10 mV s−1 of voltage sweeping rate, respectively. For OER

measurements, LSV with a scan rate of 5 mV s-1 was used to measure the performances. The RRDE

experiments during ORR-pathway was also performed in oxygen-saturated solution at a standard three-

electrode cell at room temperature. In general, the as-prepared catalysts were decorated on the electrode

surface. The total electron-transfer number (n) and hydrogen peroxide yield (%H2O2) were determined

from RRDE-test.

Electrochemical impedance spectroscopy was carried out at 0.8 V vs RHE for ORR, and 0.3 V vs RHE

for OER with frequency from 10 kHz to 0.01 Hz and ac potential of 10 mV. The ECSA was characterized

according to a reported method. Specifically, cyclic voltammograms were collected in a narrow potential

window (1.20 to 1.30 V vs RHE for OER) where no faradaic reactions occurred. A series of scan rates

(from 5 to 30 mV s-1 at an internal of 5 mV s-1; five cycles for each scan rate) were collected and a linear

relationship was obtained between Janodic - Jcathodic (1.25 V vs RHE for OER) and scan rate, in which the

slope is proportional to the electrochemical surface area.

For the liquid zinc-air battery, home-built electrochemical cell was used which typically comprise of two

electrode configuration assembly. The carbon paper supported catalyst works as O2 catalysis electrode

and air diffusion layer, Zn foil as the anode and 6M KOH as the electrolyte (galvanostatic discharge tests).

The area of the electrodes exposed to the electrolyte is 1.0 cm2. A Ni foam was used as current collector.

While electrolytic solution of 6 M KOH + 0.2 M zinc acetate was used for cycling test. The specific

capacity was calculated according to the equation below:

Service hours * Current

Weight of consumed Zinc.

The energy density was calculated according to the equation below:

Service hours * Current *Average discharge voltage

Weight of consumed Zinc.

3. FIGURES AND TABLES

Fig. S1 SEM images (a) ZIF-67, (b) Co-CNTs.

Fig. S2 EDS spectrum of Co-CNTs/ NS-CoOxAlOy

Fig. S3 TGA-DTA curves of; (a) NS-CoOxAlOy (435/ 900), (b) NS-CoOxAlOy (120/ 900), (c)

NS-AlOy (435/ 900), (d) Co-CNTs (435/ 900), (e) Co-CNTs/ NS-CoOxAlOy, (f) Co-NPs/NS-

CoOxAlOy, (g) Co-NS/NS-AlOy.

Fig. S4 N2 adsorption–desorption isotherms (inset; pore diameter distribution curves).

Fig. S5 XRD Comparison plots before (red) and after (blue) acid washing of Co-CNTs/ NS-

CoOxAlOy.

Fig. S6 High resolution XPS spectra; (a) C1s, (b) O1s.

Fig. S7 ORR-CV curves under N2 and O2 saturated solutions in 0.1 M KOH.

Fig. S8 (a) Electron transfer number, (b) Tafel slopes calculated from ORR-LSV at 1600 rpm, (c)

Nyquist plots.

Fig. S9 (a) Tafel slopes derived from OER-polarization curves, (b) Scan-rate dependence of

current densities, (d) Nyquist plots.

Fig. S10 CVs were measured in non-faradic region from 1.20-1.30 vs RHE at different scan

rates.

Fig. S11 LSV curves at 1600 rpm in 0.1 M KOH before and after acid leaching of Co-CNTs/ NS-

CoOxAlOy; (a) ORR-LSV curves, (b) OER-LSV curves.

Fig. S12 (a) Specific capacity curves of primary Zn–air battery with Co-CNTs/ NS-CoOxAlOy

and Pt/C + IrO2 at 10 mA cm−2, (b) Open-circuit plot of Zn–air battery, (c) Energy density

calculated at 10 mA cm−2.

Table S1. Electrocatalytic comparative studies of Co-CNTs/ NS-CoOxAlOy catalyst with

reported catalysts. (OER in 1M KOH, ORR in 0.1 M KOH).

Table S2. Comparison of Co-CNTs/ NS-CoOxAlOy performance with reported electrocatalysts

for zinc-air/ O2 battery.

Catalyst OCP

(V)

Pmax

( mW cm-2)

E

(Wh kg-1)

Ref

Co-CNTs/ NS-CoOxAlOy 1.51 234 874 This work

N-GRW 1.46 65 - [11]

Catalyst OER

(J = 10 mA cm-2)

ORR

(E1/2)

References

Co-CNTs/ NS-CoOxAlOy 1.51 0.835 This work

Defective graphene 1.57 0.760 [1]

Co0.85Se@NC 1.50 0.817 [2]

NS/rGO-Co4 1.49 0.84 [3]

Co3O4 /NCMTs 1.58 0.778 [4]

CoS-Co(OH)2@MoS2+x/NF 1.61 - [5]

CF-NG-Co 1.63 0.85 [6]

N, P, and F tri-doped Graphene 1.80 0.72 [7]

Co/N-C-800 1.60 0.74 [8].

CoS2(400)/N,S-GO 1.61 0.79 [9]

Fe/Fe2O3 @Fe-N-C-1000 1.66 0.79 [10]

3D NCNT array 1.47 190 776.5 [12]

NCNF-1000 1.48 185 776 [13]

CMS/BNC 1.40 258 - [14]

Co4N/CNW/CC 1.40 174 - [15]

Co/CoxSy@SNCF-800 1.37 230 - [16]

ZnCo2O4/ N-CNT 1.47 82.3 595 [17]

[1] Y. Jia, L. Zhang, A. Du, G. Gao, J. Chen, X. Yan, C.L. Brown, X. Yao, Advanced Materials,

28 (2016) 9532-9538.

[2] T. Meng, J. Qin, S. Wang, D. Zhao, B. Mao, M. Cao, Journal of Materials Chemistry A, 5

(2017) 7001-7014.

[3] N. Wang, L. Li, D. Zhao, X. Kang, Z. Tang, S. Chen, Small, 13 (2017) 1701025.

[4] B. Wang, L. Xu, G. Liu, P. Zhang, W. Zhu, J. Xia, H. Li, Journal of Materials Chemistry A, 5

(2017) 20170-20179.

[5] T. Yoon, K.S. Kim, Advanced Functional Materials, 26 (2016) 7386-7393.

[6] Z. Pei, Z. Tang, Z. Liu, Y. Huang, Y. Wang, H. Li, Q. Xue, M. Zhu, D. Tang, C. Zhi, Journal

of Materials Chemistry A, 6 (2018) 489-497.

[7] J. Zhang, L. Dai, Angewandte Chemie International Edition, 55 (2016) 13296-13300.

[8] Y. Su, Y. Zhu, H. Jiang, J. Shen, X. Yang, W. Zou, J. Chen, C. Li, Nanoscale, 6 (2014) 15080-

15089.

[9] P. Ganesan, M. Prabu, J. Sanetuntikul, S. Shanmugam, ACS Catalysis, 5 (2015) 3625-3637.

[10] Y. Zang, H. Zhang, X. Zhang, R. Liu, S. Liu, G. Wang, Y. Zhang, H. Zhao, Nano Research,

9 (2016) 2123-2137.

[11] H.B. Yang, J. Miao, S.-F. Hung, J. Chen, H.B. Tao, X. Wang, L. Zhang, R. Chen, J. Gao,

H.M. Chen, L. Dai, B. Liu, Science Advances, 2 (2016) e1501122.

[12] Z. Li, M. Shao, Q. Yang, Y. Tang, M. Wei, D.G. Evans, X. Duan, Nano Energy, 37 (2017)

98-107.

[13] Q. Liu, Y. Wang, L. Dai, J. Yao, Advanced Materials, 28 (2016) 3000-3006.

[14] Z. Wang, S. Xiao, Y. An, X. Long, X. Zheng, X. Lu, Y. Tong, S. Yang, ACS Applied

Materials & Interfaces, 8 (2016) 13348-13359.

[15] F. Meng, H. Zhong, D. Bao, J. Yan, X. Zhang, Journal of the American Chemical Society,

138 (2016) 10226-10231.

[16] S. Liu, X. Zhang, G. Wang, Y. Zhang, H. Zhang, ACS Applied Materials & Interfaces, 9

(2017) 34269-34278.

[17] Z.-Q. Liu, H. Cheng, N. Li, T.Y. Ma, Y.-Z. Su, Advanced Materials, 28 (2016) 3777-3784.