Single-Site Active Iron-Based Bifunctional Oxygen Catalyst for a Compressible and Rechargeable Zinc-Air Battery Longtao Ma 1, Shengmei Chen 1, Zengxia Pei 1 *, Yan Huang 2, Guojin Liang 1, Funian Mo 1, Qi Yang 1, Jun Su 3, Yihua Gao 3, Juan Antonio Zapien 1, Chunyi Zhi 1, 4 *. 1 Department of Materials Science and Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong 999077, PR China. 2 School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, PR China. 3 Center for Nanoscale Characterization and Devices, Wuhan National Laboratory for Optoelectronics,School of Physics,School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, PR China. 4 Shenzhen Research Institute, City University of Hong Kong, Nanshan District, Shenzhen 518057, PR China. *Corresponding Authors: Prof. Chunyi Zhi E-mail: c.y.zhi@cityu.edu.hk Dr. Zengxia Pei E-mail: zengxipei2-c@my.cityu.edu.hk 1
Figure S1. Schematic diagram of synthesizing FeN x -embedded in porous nitrogen-doped carbon. In detail, the graphene is coated with polypyrrole (PPy) through polymerizing pyrrole monomers in the existence of iron chlorinum. Then, the ZIF-8 polyhedrons are immobilized on both side of PPy coated graphene uniformly. The PPy could act as a binder, which is favorable to form nucleus of the ZIF-8. After that, coordination of iron ions with 2, 2-bipyridine is dispersed on the surface of ZIF-8 polyhedrons. Finally, the products are calcined under argon atmosphere at 1000 o C for 5 hours, which further subject to leaching by 0.5 M H 2 SO 4 overnight (the resulted catalyst is denoted as FeN x- embedded PNC). During pyrolysis process, the zinc oxide is reduced to elemental zinc in the presence of carbon and simultaneously the zinc is evaporated. 2
Figure S2. TEM images of (a) graphene and (b) PPy-coated graphene. The insets are the highmagnification images for (a) and (b), respectively. (c, d) low- and high-magnification of SEM images for PPy-coated-graphene @ZIF-8. Scale bar for (a) and (b) 100 nm, the inset is10 nm; (c) 1 µm and (d) 500 nm. 3
Figure S3. Low- and high-magnification SEM images of graphene@zif-8 without a binder of PPy. Figure S4. SEM image of FeNx-embedded PNC to characterize the thinness of porous nitrogendoped carbon. 4
Figure S5. XRD spectra of NC, PNC and FeN x -embedded PNC. 5
Figure S6. Raman spectrum of NC, PNC and FeN x -embedded PNC. 6
Figure S7. (a) Nitrogen absorption-desorption isotherm of NC, PNC and FeN x -embedded PNC. (b) Corresponding the pores distribution. 7
Figure S8. Cyclic voltammograms (CV) curves of (a) NC, (e) PNC and (h) Pt/C (20 wt%). ORR polarization curves of (b) NC, (f) PNC and (i) Pt/C at different rotation speeds. The K-L plots at different potentials including electron transfer number (n) per oxygen of (c) NC, (g) PNC and (j) Pt/C. 8
Figure S9. FeN x -embedded PNC without a binder of PPy: (a) Cyclic voltammograms (CV) curves, (b) ORR polarization curves and (c) K-L plots at different potential including electron transfer number (n) per oxygen. 9
Figure S10. ORR polarization of PPy-coated-graphene@ZIF-8/Fe-Bipy treated at different temperature under argon atmosphere in oxygen-saturated 0.1 M KOH aqueous solution at 1600 rpm. 10
Figure S11. (a) ORR polarization curves of FeN x -embedded PNC at different rotating speeds, (b) K-L plots at different potentials including electron transfer number (n) per oxygen. (c) RRDE voltammograms of FeN x -embedded PNC and Pt/C (20 wt%) catalyst at 1600 rpm. 11
Figure S12. CV curves in the region of 0-0.2 V at scan rate from 2 to 10 mv s -1 and corresponding linear fitting of capacitive current. (a) and (b) for NC; (c) and (d) for PNC; (e) and (f) for FeN x -PNC; (g) and (h) for FeN x -PNC without PPy. 12
Figure S13. The A.C impedance plots of NC, PNC, FeN x -PNC and FeN x -PNC without PPy layer. 13
Figure S14. (a) Polarization curves of FeN x -embedded PNC catalyst at 1600 rpm in oxygensaturated 0.1 M KOH electrolyte before and after 10000 cycles to determine stability of catalyst. (b) Chronoamperometric response of as-developed FeN x -embedded PNC catalyst in oxygensaturated 0.1 M KOH aqueous solution at 1600 rpm. 14
Table S1. Comparison single-site Fe-Nx/porous nitrogen-doped carbon electrocatalyst with the state-of-art electrocatalysts and commercial Pt/C in alkaline medium. Electrocatalyst Half-wave potential (V vs RHE) Loading mass µg cm -2 Reference FeN x /porous nitrogendoped carbon 0.86 140 This work Pt/C 0.84 140 This work N/S hierarchically porous carbon from silica 0.85 140 Energy Environ. Sci., 2017, 10, 742. template LDH@ZIF-67-800 0.83 200 Adv. Mater., 2016, 28, 2337. Fe-N/C-800 0.809 100 J. Am. Chem. Soc., 2014, 136, 11027. N-doped carbon cubes from NaCl salt 0.80 400 Nanoscale, 2017, 9, 1059. Fe-N-C 0.85 800 Nat. Commun., 2015, 10, 444. ZIF-67 derived NCNTF 0.87 200 Nat. Energy., 2016, 1, 15006. Nitrogen doped carbon 0.84 600 Ange. Chem. Int. Ed., 2014,126, 1596. N-Fe/CNs-700-800-NH 3 0.859 100 Adv. Mater. 2017, 29, 1700707. N-Fe/CNs-700-800-N 2 0.855 100 Adv. Mater. 2017, 29, 1700707. Fe N/C 0.88 800 J. Am. Chem. Soc., 2016, 138, 15046. Fe 3 N encapsulated in graphitic layers Atomically dispersed S, N-Fe/N/C-CNT 0.86 400 Adv. Mater., 2015, 27, 2521. 0.85 600 Angew. Chem. Int. Ed., 2017, 56, 610. Atomically dispersed Zn-N 4 0.84 390 Adv. Funct. Mater. 2017, 27, 1700802. 15
Figure S15. Open circuit voltage of zinc-air battery using FeN x -PNC as cathodes for 12 h. 16
Figure S16. (a) Battery discharge polarization and corresponding power density curves of zincair battery using FeN x -PNC as cathode. (b) Charge and discharge polarization curves. (c) Galvanostatic discharge curves of primary zinc-air battery at current density from 2 to 50 ma cm -2. (d) Rechargeability cycling measurement of the zinc-air battery at a current density of 10 ma cm -2. (e) Digital image of the as-assembled zinc-air battery to display open-circuit voltage and several LED lights powered by two our zinc-air battery connected in series. 17
Figure S17. SEM images of electrodeposited Zn in different magnification. Scale bar for left: 10 µm, right 3 µm. 18
Figure S18. Photographs of as-assembled compressible zinc-air battery: (a) initial device (b) under compression strain. Bending at (c) 60 o and (d) 90 o. 19
Figure S19. Comparison of compression strain under different compressing loading for (a) compressible PAM electrolyte and (b) traditional PVA electrolyte. 20
Figure S20. Open circuit voltage of as-assembled zinc-air battery, the inset is a photograph of zinc-air battery with an open` -circuit voltage of 1.436 V. 21
Figure S21. The A. C impedance plots of compressible device under 0, 18%, 32% and 54% compression strains. 22
Figure S22. Discharge-charge polarization curves of compressible zinc-air battery after different compression times under 50% compression strain. 23
Table 2. Comparison of the zinc-air battery utilizing FeN x /porous nitrogen-doped carbon with commercial Pt/C and other reported electrocatalysts. Battery performance (Maximum Electrocatalyst electrolyte power density, current density@ Reference 1.0 V ) FeN x /porous nitrogendoped carbon FeN x /porous nitrogendoped carbon Pt/C N/S hierarchically porous Co 4 N/CNW/CC 6 M KOH aqueous solution PAM Hydrogel (All-solid state) 6 M KOH aqueous solution 6 M KOH aqueous solution 6 M KOH aqueous solution 278 mw cm -2, 195 ma cm -2 This work 118 mw cm -2, 59 ma cm -2 This work 162 mw cm -2, 95 ma cm -2 This work Energy Environ. Sci., 2017, 151 mw cm -2, 72 ma cm -2 10, 742. J. Am. Chem. Soc. 2016, 138, 174 mw cm -2, 125 ma cm -2 10226. sulfur-enriched conjugated polymer nanosheet 6 M KOH aqueous solution 0.69 mw cm -2, N/A Adv. Funct. Mater. 2016, 26, 5893. Atomically dispersed S, N-Fe/N/C-CNT Co 3 O 4 -NCNT/ SS LaNiO 3 /NCNT Co 3 O 4 /NPGC 6 M KOH aqueous solution porous cellulose film porous-gelled PVA electrolyte membrane 6 M KOH aqueous solution Angew. Chem. Int. Ed. 2017, 102.7 mw cm -2, 72 ma cm -2 56, 610. 160.7 mw cm -2, 76mA cm -2 Adv. Mater. 2016, 28, 6421. 60 mw cm -2, 8 ma cm -2 Adv. Mater. 2015, 27, 5617. Angew.Chem.Int. Ed. 2016, N/A, 22 ma cm -2 55, 4977. 24