Oxygen vacancy engineering of yttrium ruthenate pyrochlores as an

efficient oxygen catalyst for both proton exchange membrane water

electrolyzers and rechargeable zinc-air batteries

Qi Feng a, b, Zhiliang Zhao b, c, Xiao-zi Yuan e, Hui Li b, c *, Haijiang Wang c, d *

a School of Materials Science and Engineering, Harbin Institute of Technology,

Harbin 150001, China

b Department of Materials Science and Engineering, Shenzhen Key Laboratory of

Hydrogen Energy, Southern University of Science and Technology, Shenzhen 518055,

Guangdong, China

c Guangdong Provincial Key Laboratory of Energy Materials for Electric Power,

Shenzhen 518055, China

d Department of Mechanical and Energy Engineering, Southern University of Science

and Technology, Shenzhen, 518055, China

e Research Center of Energy, Mining and Environment, National Research Council

Canada, 4250 Wesbrook Mall, V6T1W5, Canada

* Corresponding author:

E-mail address: hui.li@sustech.edu.cn, wanghj@sustech.edu.cn

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Figure S1. The crystalline structure of pyrochlore oxides (A2B2O7) 1

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Figure S2. The XRD pattern of the YCRO-0.4 sample.

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Figure S3. The SEM images of (a) YRO, (b) YCRO-0.15, and (c) YCRO-0.4 samples.

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Figure S4. N2 adsorption-desorption isotherm curves of (a) YRO, (b) YCRO-0.15, (c)

YCRO-0.25, (d) YCRO-0.4 and (e) commercial IrO2. (f) Comparison of BET surface

area of YRO, YCRO-0.15, YCRO-0.25, YCRO-0.4 and commercial IrO2.

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Figure S5. The full XPS spectra of (a) YRO, (b) YCRO-0.15, (c) YCRO-0.25, and (d) YCRO-0.4.

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Figure S6. The high-resolution XPS spectra of Ca 2p of (a) YRO, (b) YCRO-0.15, (c) YCRO-0.25, and (d) YCRO-0.4.

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Figure S7. The high-resolution XPS spectra of Y 3d of (a) YRO, (b) YCRO-0.15, (c) YCRO-0.25, and (d) YCRO-0.4.

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Table S1. The area ratio obtained from the deconvolution of the O 1s and Ru 3p3/2

XPS spectra

Oads (O 1s)

(%)

Olatt (O 1s)

(%)

Oads/Olatt Ru5+ (Ru 3p3/2)

(%)

Ru4+ (Ru 3p3/2)

(%)

Ru5+/

Ru4+

YRO 63 37 1.7 0 100 0

YCRO-0.15 79 21 3.8 40.4 59.6 0.67

YCRO-0.25 83 17 4.9 38.2 61.8 0.63

YCRO-0.4 67 33 2.0 39.6 60.4 0.65

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Figure S8. (a) HR-TEM and (b) STEM images of the YRO nanoparticle. (c-e) individual and (f) overlapped EDS mapping images of Y, O, Ru in the YRO

nanoparticle.

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Figure S9. Polarization curves of RuO2 in Ar-saturated 0.5 M H2SO4 with a scan rate of 10 mVs-1. RuO2 catalysts lose its most activity after the second LSV scan in 0.5 M

H2SO4.

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Figure S10. The relationship between Tafel slope and oxygen vacancy concentration.

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Figure S11. The relationship between polarization resistance and oxygen vacancy

concentration.

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Figure S12. (a) The CV curves of YCRO-0.25 and YRO in Ar-saturated 0.5 M H2SO4

at 50 mV s-1. (b) Magnified image of (a).

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Figure S13. TEM and HRTEM measurements after the CP test. (a) HR-TEM and (b) STEM images of the YCRO-0.25 sample. (c-f) Individual EDS mapping images of Y,

O, Ru Ca in YCRO-0.25.

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Figure S14. OER curves of YRO and YCRO-x (x=0.15, 0.25, 0.4) in 0.1 M KOH at a scan rate of 10 mV s-1.

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Figure S15. (a) Comparison of OER curves of YCRO-0.25 before and after 3000th CV cycles in 0.1 M KOH at a scan rate of 10 mV s-1. (b) CP stability test of YCRO-0.25 at

10 mA cm-2 in 0.1 M KOH.

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Figure S16. TEM and HRTEM measurements after the OER stability test in 0.1 M KOH. (a) low and high (b) magnification of HR-TEM. (c-d) STEM images of the

YCRO-0.25 sample. (e-i) Individual EDS mapping images of C, Ca, Y, Ru, O, respectively. (j) EDS profiles of the YCRO-0.25 nanoparticles

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Figure S17. ORR curves of YRO and YCRO-x (x=0.15, 0.25, 0.4) in 0.1 M KOH at a scan rate of 10 mV s-1.

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Figure S18. ORR LSV curves of YCRO-0.25 catalyst for the first and 5000 th CV cycles in the potential of 1.1 to 0.6 V in O2-saturated 0.1 M KOH solution.

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Figure S19. TEM and HRTEM measurements after the ORR stability test in 0.1 M KOH. (a) low and high (b) magnification of HR-TEM. (c-d) STEM images of the

YCRO-0.25 sample. (e-i) Individual EDS mapping images of C, Ca, Y, Ru, O, respectively. (j) EDS profiles of the YCRO-0.25 nanoparticles

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Table S2. Comparison of OER activities for YCRO-0.25 with other OER catalysts recently reported in 0.5 M H2SO4

Material ᵑ10

(mV)

Tafel slope

(mV decade-

1)

Electrolyte Mass loading

(mg cm-2)

Reference

YCRO-0.25 275 40.3 0.5 M H2SO4 0.2 mg cm-2 This work

Ba2YIrO6 335 60 0.1 M HClO4 15 ug cm-2 Nature

Communications

2016, 7, 12363

F-doped IrO2 400 N/A 1 M H2SO4 N/A J. Phys. Chem. C, 2013,

117,

20542

IrNiOx/ATO 330 N/A 0.05 M H2SO4 10.2 ug cm-2 Angew. Chem. Int. Ed.,

2015, 54, 2975

Co-IrCu octahedral

nanocarbon

290 N/A 0.1 M HClO4 20 ug cm-2 Adv. Funct.

Mater. 2017, 27,

1604688

IrCo-porous hollow

nanocrystals

303 N/A 0.1 M HClO4 10 ug cm-2 Adv. Mater.2017,

29, 1703798

Ni0.34Co0.46Ir0.2O2-δ 280 40 0.1 M HClO4 0.2 mg cm-2 Applied Catalysis B:

Environmental 244 (2019)

295–302

Ir/Co4N 319 67 0.5 M H2SO4 N/A ACS Catal. 8 (2018) 2615–

2621

Ir6Ag9 NTs/C 285 61.1 0.5 M H2SO4 13.3 ug cm-2 Nano Energy 56 (2019)

330–337

Ru@IrOx 282 69.1 0.05 M H2SO4 0.05 mg cm-2 Chem 5, 445–459,

February 14, 2019

RuO2 297 64 0.5 M H2SO4 0.28 mg cm-2 NATURE

COMMUNICATIONS |

(2019) 10:162

Ir0.3Mo0.7O2 345 57 0.1 M HClO4 N/A ACS Sustain. Chem. Eng.

6 (2018) 4854–4862

IrO2 415 N/A 0.1 M HClO4 0.2 mg cm-2 J. Mater. Chem. A

2018, 6, 21558-21566

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Table S3 Results of EIS analysis at 1.55 V for YRO, YCRO-0.15, YCRO-0.25,

YCRO-0.4 and IrO2 electrocatalysts

Catalysts Rs Rp CPE-T CPE-P

YRO  5.25 12.91 0.00074 0.876

YCRO-

0.15

 5.20 7.74 0.0012 0.84

YCRO-

0.25

 5.09 6.98 0.0013 0.875

YCRO-0.4  5.17 10.88 0.0006 0.862

IrO2 5.32 23.6 0.0003 0.806

*: CPE-P is the Constant Phase Element-P, which is related to the semicircle in the

Nyquist plot, and CPE-T is the Constant Phase Element-T, which is the pseudo

capacitance.

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1. The University of Liverpool, ChemTube 3D, http://www.chemtube3d.com/solidstate/SSPyrochlore.htm, Accessed May 28, 2019.

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