Rational Design of Hybrid Fe7S8/Fe2N Nanoparticles as

Effective and Durable Bifunctional Electrocatalysts for

Rechargeable Zinc-air Batteries

Shilei Xie*, a, Jiajin Lin a, Shoushan Wang a, Dong Xie a, Peng Liu a, Guiping Tan a, Min Zhang a,

Dongliang Ruan a, Chao Zhen b and Faliang Cheng* a

a Guangdong Engineering and Technology Research Centre for Advanced Nanomaterials, School

of Environment and Civil Engineering, Dongguan University of Technology, Dongguan 523808,

China. E-mail: xieshil@dgut.edu.cn; chengfl@dgut.edu.cn.

b Dongguan Arun Industrial Co., Ltd, Dongguan 523000, Guangdong, China.

Cost analysis of the MIL-101(Fe) precursor:

Preparing around 1 g MIL-101(Fe) precursor requires:

FeCl3 6H2O: $1.2 g, 0.03 USD (AR, Aladdin, China);

Terephthalic acid (PTA): $5.1 g, 0.51 USD (AR, Aladdin, China);

DMF: 115 mL, $1.74 USD (AR, Aladdin, China);

Ethanol: 100 mL, $1.2 USD (AR, Aladdin, China).

Therefore, it takes about $3.48 USD for the raw-materials to prepare 1 g MIL-101(Fe) precursor.

Figure S1. (a) SEM image of MIL-101(Fe). (b) XRD patterns of simulated MIL-101(Fe) and as-

prepared MIL-101(Fe).

Figure S2. SEM images of Fe7S8/Fe2N NPs.

Figure S3. (a) TEM and (b) HR-TEM image of Fe2N NPs. EDS mapping images of Fe2N: (c) Fe

and (d) N.

Figure S4. Nitrogen adsorption-desorption isotherms for (a) Fe7S8/Fe2N and (b) Pt/C+RuO2. CV

curves of (c) Fe2N, (d) Fe7S8/Fe2N and (e) Pt/C+RuO2 electrodes collected at the scan rate range

from 10 mV s-1 to 50 mV s-1. (f) Surface charging current densities plotted against scan rates of

Fe2N and Fe7S8/Fe2N electrodes in 1.0 mol L-1 KOH electrolyte.

Figure S5. EIS spectra of Fe2N, Fe7S8/Fe2N and mixed Pt/C+RuO2 electrodes.

Figure S6. IR-corrected polarization curves of mixed Pt/C+RuO2, Fe2N and Fe7S8/Fe2N electrodes

in (a) 0.1 mol L-1 and (b) 6 mol L-1 KOH.

Figure S7. (a) LSV curves of Fe7S8/Fe2N at different srotation rates. (c) K-L plots of Fe7S8/Fe2N at

different potentials. (c) RRDE LSV curves for Fe7S8/Fe2N and mixed Pt/C+RuO2 at a rotating

speed of 1600 rpm. All the measurements were carried in a solution of O2-saturated 0.1 M KOH.

Figure S8. (a) Voltage-capacity curve of ZAB with Fe7S8/Fe2N electrode at the discharge current

density of 10 mA cm-2. (b) Cycling performance of ZABs with Fe7S8/Fe2N electrode and

Pt/C+RuO2 electrode at the discharge current density of 10 mA cm-2.

Table S1. Electrochemical catalytic performance of some representative iron-based

electrocatalysts in 1.0 mol L-1 KOH. Ej=10 is the OER potential reaching the current density of 10

mA cm-2.

CatalystsEj=10 (V vs.

RHE)

Tafel slope

(mV dec-1)Reference

Fe7S8/Fe2N 1.45 38.3 This work

Pt/C+RuO2 1.50 101.2 This work

NiFe-LSH/Co,N-CNF 1.542 60 [1]

Ni3Fe/N-C 1.60 77 [2]

Ni3FeN 1.585 70 [3]

Fe3O4–CoPx/TiN 1.561 122 [4]

Ni0.76Fe0.24Se 1.427 56 [5]

FeSe2@CoSe2/rGO 1.59 36 [6]

Fe3O4/Co3S4 1.50 56 [7]

FeP@GPC 1.508 87 [8]

hcp-NiFe@NC 1.456 41 [9]

AT NiFe2O4 QDs 1.492 37 [10]

Table S2. Comparison of the ORR and OER performance of Fe7S8/Fe2N with recently reported

bifunctional electrocatalysts in 0.1 M KOH solution. E1/2 was the ORR half-wave potential and

Ej=10 was the potential to reach the anodic current density of 10 mA cm-2. ΔE= Ej=10 - E1/2.

CatalystsE1/2

(V vs.RHE)

Ej=10 (V vs. RHE)

ΔE (mV) Ref.

Fe7S8/Fe2N 0.792 1.503 711 This work

Pt/C+RuO2 0.811 1.554 733 This work

Ni3FeN/Co,N-CNF 0.81 1.50 690 [3]

NiFe/N-CNT 0.75 1.52 770 [11]

Co-NX-C N/A N/A 950 [12]

Mo-N/C@MoS2 0.81 1.62 810 [13]

NCNFs 0.82 1.84 1020 [14]

Meso-CoNC@GF 0.87 1.66 790 [15]

FeCo@NC 0.80 1.49 690 [16]

N-GCNT/FeCo 0.92 1.73 810 [17]

NiFe@NCx 0.86 1.55 690 [18]

N-Fe/N/C-CNT 0.85 1.60 750 [19]

References:

[1] Q. Wang, L. Shang, R. Shi, X. Zhang, Y. Zhao, G.I.N. Waterhouse, L.-Z. Wu, C.-H. Tung, T. Zhang,

Adv. Energy Mater., 7 (2017) 1700467.

[2] G. Fu, Z. Cui, Y. Chen, Y. Li, Y. Tang, J.B. Goodenough, Adv. Energy Mater., 7 (2017) 1601172.

[3] Q. Wang, L. Shang, R. Shi, X. Zhang, G.I.N. Waterhouse, L.-Z. Wu, C.-H. Tung, T. Zhang, Nano

Energy, 40 (2017) 382-389.

[4] B. Guo, J. Sun, X. Hu, Y. Wang, Y. Sun, R. Hu, L. Yu, H. Zhao, J. Zhu, ACS Appl. Nano Mater., 2

(2019) 40-47.

[5] J. Yu, G. Cheng, W. Luo, Nano Res., 11 (2018) 2149-2158.

[6] G. Zhu, X. Xie, X. Li, Y. Liu, X. Shen, K. Xu, S. Chen, ACS Appl. Mater. Interfaces, 10 (2018)

19258-19270.

[7] J. Du, T. Zhang, J. Xing, C. Xu, J. Mater. Chem. A, 5 (2017) 9210-9216.

[8] Y. Yao, N. Mahmood, L. Pan, G. Shen, R. Zhang, R. Gao, F.-e. Aleem, X. Yuan, X. Zhang, J.-J.

Zou, Nanoscale, 10 (2018) 21327-21334.

[9] C. Wang, H. Yang, Y. Zhang, Q. Wang, Angew. Chem. Int. Ed., 58 (2019) 6099-6103.

[10] H. Yang, Y. Liu, S. Luo, Z. Zhao, X. Wang, Y. Luo, Z. Wang, J. Jin, J. Ma, ACS Catal., 7 (2017)

5557-5567.

[11] H. Lei, Z. Wang, F. Yang, X. Huang, J. Liu, Y. Liang, J. Xie, M.S. Javed, X. Lu, S. Tan, Nano

Energy, (2019) 104293.

[12] C. Tang, B. Wang, H.F. Wang, Q. Zhang, Adv. Mater., 29 (2017) 1703185.

[13] I.S. Amiinu, Z. Pu, X. Liu, K.A. Owusu, H.G.R. Monestel, F.O. Boakye, H. Zhang, S. Mu, Adv.

Funct. Mater., 27 (2017) 1702300.

[14] S. Li, C. Cheng, X. Zhao, J. Schmidt, A. Thomas, Angew. Chem. Int. Ed., 57 (2018) 1856-1862.

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

Chen, Sci. Adv., 2 (2016) e1501122.

[16] P. Cai, S. Ci, E. Zhang, P. Shao, C. Cao, Z. Wen, Electrochim. Acta, 220 (2016) 354-362.

[17] S.H. Ahn, A. Manthiram, Small, 13 (2017) 1702068.

[18] J. Zhu, M. Xiao, Y. Zhang, Z. Jin, Z. Peng, C. Liu, S. Chen, J. Ge, W. Xing, ACS Catal., 6 (2016)

6335-6342.

[19] P. Chen, T. Zhou, L. Xing, K. Xu, Y. Tong, H. Xie, L. Zhang, W. Yan, W. Chu, C. Wu, Angew.

Chem. Int. Ed., 56 (2017) 610-614.