Supporting information

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1 Supporting information Enhancing electrocatalytic activity of perovskite oxides by tuning cation deficiency for oxygen reduction and evolution reactions Yinlong Zhu, Wei Zhou*, Jie Yu, Yubo Chen, Meilin Liu*, and Zongping Shao Figure S1. Rietveld refinement of XRD patterns of La1-xFeO3-δ (0 x 0.1) powders. Results indicate that all the A-site cation deficient La1-xFeO3-δ perovskites exihibited a pure orthorhombic structure with a space group of Pnma. Figure S2. XRD patterns of La0.8FeO3-δ powder.

2 Figure S3. Nitrogen adsorption-desorption isotherm curves of (a) LF, (b) L0.98F, (c) L0.95F, and (d) L0.9F samples. Figure S4. Potential calibration of the reference electrode in 0.1 M KOH solution. The calibration was performed in a high purity hydrogen-saturated electrolyte with a platinum rotating disk electrode (PINE, 4 mm diameter, cm2) as the working electrode. Cyclic voltammetry (CV) was run at a scan rate of 1 mv s-1, and the average of the two potentials at which the current crossed zero was taken to be the thermodynamic potential for the hydrogen electrode reaction. In 0.1 M KOH solution, ERHE = EAg/AgCl V.

3 Figure S5. LSV curves of (a) LF, (b) L0.98F (c) L0.95F and (d) L0.9F on RDE at various rotation speeds in O 2 -saturated 0.1 M KOH solution at a scan rate of 5 mv s -1. Figure S6. The kinetic current density (J k ) normalized by the surface area at 0.25 V for LF, L0.98F, L0.95F, and L0.9F catalysts.

4 Figure S7. LSVs curves on the RDE (1600 rpm) for other recent well-known perovskite-type materials with high OER activity in O 2 -saturated 0.1 M KOH solution, such as Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF), SrNb 0.1 Co 0.7 Fe 0.2 O 3-δ (SNCF), PrBaCo 2 O 5+δ (PBC) and LaNiO 3-δ (LN). These catalysts were tested under the same condition as LF0.95, ruling out the influence of different electrode preparation details and electrode composition varied in literatures. Figure S8. XRD patterns of the BSCF, SNCF, PBC, and LN powders. BSCF possess a cubic perovskite structure with a space group of Pm-3m. [S1] SNCF possess a tetragonal perovskite structure with a space group of P4/mmm. [S2] PBC possess a tetragonal double-perovskite structure with a space group of P4/mmm. [S3] LN possess a rhombohedral perovskite structure with a space group of R-3c. [S4] The BSCF, PBC, and LN powders in this study for comparison, were synthesized by a standard combined EDTA-citrate complexing sol-gel process as described in

5 detail in the Experimental Section. The solid precursors provided by this method were calcined as follows: 1) in air at 1000 C for 5 h for BSCF, 2) in air 1050 C for 5 h for PBC, and 3) in air 800 C for 5 h for LN. The SNCF powders were synthesized by a traditional solid-state reaction route and calcined at 1200 C in air for 10 h. Figure S9. Oxygen electrode activities of LF, L0.98F, L0.95F, and L0.9F catalysts within the ORR and OER potential window in O 2 -saturated 0.1M KOH solution at 1600 rpm. Figure S10. LSV curves at different scan rates for (a) ORR and (b) OER on the RDE (1600 rpm) of L0.95F catalyst in O 2 -saturated 0.1M KOH solution. The scan rates (5 mv/s or 10 mv/s) had minimal effect on the ORR/OER activity.

6 Figure S11. XPS spectra of Fe for LF, L0.98F, L0.95F, and L0.9F samples. Table S1. Reitveld refinements results of XRD patterns of LF, L0.98F, L0.95F, and L0.9F powders Sample Structure Space Lattice parameters group a (Å) b (Å) c (Å) V(Å 3 ) R p R w χ 2 LF Orthorhombic Pnma L0.98F Orthorhombic Pnma L0.95F Orthorhombic Pnma L0.9F Orthorhombic Pnma LF Site Np x y z Atom Occ La La+3 1 Fe Fe+3 1 O O-2 1 O O-2 1 L0.98F Site Np x y z Atom Occ La La Fe Fe+3 1 O O-2 1 O O-2 1 L0.95F Site Np x y z Atom Occ La La Fe Fe+3 1 O O-2 1 O O-2 1

7 L0.9F Site Np x y z Atom Occ La La Fe Fe+3 1 O O-2 1 O O-2 1 Table S2. Chemical composition of the prepared La 1-x FeO 3-δ (0 x 0.1) samples. ICP-MS analysis iodometric titration The concentrations of Nominal metal ions (mg L -1 ) ICP-MS oxygen nonstoichiometry (δ) oxidation state Iron composition composition La Fe LaFeO 3-δ La FeO 3-δ 0 3 La 0.98 FeO 3-δ La FeO 3-δ La 0.95 FeO 3-δ La FeO 3-δ La 0.9 FeO 3-δ La FeO 3-δ Table S3. Comparison of the bifunctional catalytic activity for LF, L0.98F, L0.95F, and L0.9F catalysts. Catalysts E ORR (V, ma cm -2 E OER (V, ma cm -2 E (V, E OER -E ORR ) LF L0.98F L0.95F L0.9F Table S4. Comparison of the bifunctional catalytic activity for L0.95F catalyst, precious-metalbased and some other reported excellent perovskite-based bifunctional catalysts in the literatures. All the catalysts in the table were tested in a 0.1 M KOH solution. Catalysts Scan rate E ORR (V) E OER (V) E (V, E OER ma cm ma cm -2 E ORR ) L0.95F 5 mv/s 0.58 vs. RHE 1.64 vs. RHE 1.06 L0.95F 10 mv/s 0.58 vs. RHE 1.64 vs. RHE 1.06 Pt/C [S5] 10 mv/s 0.97 vs. RHE 2.19 vs. RHE 1.22 [S5] IrO 2 10 mv/s 0.38 vs. RHE 1.70 vs. RHE 1.32 [S5] RuO 2 10 mv/s 0.54 vs. RHE 1.64 vs. RHE 1.10 [S6] LaNi 0.85 Mg 0.15 O 3 10 mv/s vs. SCE ~0.84 vs. SCE ~1.15 [S7] LaNi 0.8 Fe 0.2 O 3 10 mv/s ~-0.33 vs. SCE ~0.69 vs. SCE ~1.02 [S8] vs vs. Ball milled La 0.6 Sr 0.4 CoO 3-δ 5 mv/s Hg/HgO Hg/HgO 1.08 CaMnO2.77 nanoparticle [S9] 5 mv/s ~0.86 vs. RHE >1.95 vs. RHE >1.09 [S10] Oxygen-deficient BaTiO 3-x N. A. ~0.72 vs. RHE >1.90 vs. RHE >1.18 Hierarchical mesoporous [S11] La 0.5 Sr 0.5 CoO 2.91 nanowire 5 mv/s ~0.78 vs. RHE ~1.84 vs. RHE ~1.06 BaMnO 3 Nanorods@5% ~-0.28 vs. ~-0.90 vs. Carbon [S12] 10 mv/s Ag/AgCl Ag/AgCl ~1.18 La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O [S13] nitrogen-doped graphene 10 mv/s 0.67 vs. RHE 1.72 vs. RHE 1.05 LaTi 0.65 Fe 0.35 O nitrogendoped carbon nanorods (Air) [S14] 5 mv/s ~0.78 vs. RHE ~1.81 vs. RHE ~1.03

8 Table S5. O 1s XPS peak deconvolution results. Electrocatalysts lattice O 2- O 2-2 /O - -OH/O 2 H 2 O LF 41.46% % 16.81% L0.98F 52.57% 18.85% 19.3% 9.28% L0.95F 52.98% 20.03% 18.34% 8.65% L0.9F 52.17% 18.91% 20.15% 8.77% Table S6. Mössbauer parameters of LF, L0.98F, L0.95F, and L0.9F samples Samples Profile Isomer shift Quadrupole splitting Half-peak width Area δ (mm/s) Qs (mm/s) FWHM (mm/s) Ratio (%) LF Fe Fe 4+ / / / 0 L0.98F Fe Fe L0.95F Fe Fe L0.9F Fe Fe References S1. Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn. Y. A perovskite oxide optimized for oxygen evolution catalysis from molecular orbital principles. Science 2011, 334, S2. Zhu, Y. L.; Zhou, W.; Chen, Z.-G.; Chen, Y. B.; Su, C.; Tadé, M. O.; Shao, Z. P. SrNb 0. 1 Co 0. 7Fe 0.2 O 3-δ perovskite as a next-generation electrocatalyst for oxygen evolution in alkaline solution. Angew. Chem. Int. Ed. 2015, 54, S3. Grimaud, A.; May, K. J.; Carlton, C. E.; Lee, Y.-L.; Risch, M.; Hong, W. T.; Zhou, J. G.; Shao- Horn, Y. Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution. Nat. Commun. 2013, 4, S4. Zhou, W.; Sunarso, J. Enhancing bi-functional electrocatalytic activity of perovskite by temperature shock: a case study of LaNiO 3-δ. J. Phys. Chem. Lett. 2013, 4, S5. Rincón, R. A.; Masa, J.; Mehrpour, S.; Tietz, F.; Schuhmann, W. Activation of oxygen evolving perovskites for oxygen reduction by functionalization with Fe-N x/c groups. Chem. Commun 2014, 50, S6. Du, Z. Z.; Yang, P.; Wang, L. ; Lu, Y. H.; Goodenough, J. B.; Zhang, J.; Zhang, D. W. Electrocatalytic performances of LaNi 1-x Mg x O 3 perovskite oxides as bi-functional catalysts for lithium air batteries. J. Power Sources 2014, 265, S7. Zhang, D. W.; Song, Y. F.; Du, Z. Z.; Wang, L.; Li, Y. T.; Goodenough, J. B. Active LaNi 1-x Fe x O 3 bifunctional catalysts for air cathodes in alkaline media. J. Mater. Chem. A 2015, 3, S8. Oh, M. Y.; Jeon, J. S.; Lee, J. J.; Kim, P.; Nahm, K. S.; The bifunctional electrocatalytic activity of perovskite La 0.6 Sr 0.4 CoO 3-δ for oxygen reduction and evolution reactions. RSC Adv. 2015, 5, S9. Du, J. Zhang, T. R.; Cheng, F. Y.; Chu, W. S.; Wu, Z. Y.; Chen, J.; Nonstoichiometric perovskite CaMnO 3-δ for oxygen electrocatalysis with high activity. Inorg. Chem. 2014, 53, S10. Chen, C.-F.; King, G.; Dickerson, R. M.; Papin, P. A.; Gupta, S.; Kellogg, W. R.; Wu, G. Oxygen-deficient BaTiO 3-x perovskite as an efficient bifunctional oxygen electrocatalyst. Nano Energy 2015, 13,

9 S11. Zhao, Y. L.; Xu, L.; Mai, L. Q.; Han, C. H.; An, Q. Y.; Xu, X.; Liu, X.; Zhang, Q. J. Hierarchical mesoporous perovskite La 0.5 Sr 0.5 CoO 2.91 nanowires with ultrahigh capacity for Li-air batteries. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, S12. Xu, Y. J.; Tsou, A.; Fu, Y.; Wang, J.; Tian, J.-H.; Yang, R. Z. Carbon-coated perovskite BaMnO 3 porous nanorods with enhanced electrocatalytic properties for oxygen reduction and oxygen evolution. Electrochim. Acta 2015, 174, S13. Park, H. W.; Lee, D. U.; Zamani, P.; Seo, M. H.; Nazar, L. F.; Chen, Z. W. Electrospun porous nanorod perovskite oxide/nitrogen-doped graphene composite as a bi-functional catalyst for metal air batteries. Nano Energy 2014, 10, S14. Prabu, M.; Ramakrishnan, P.; Ganesan, P.; Manthiram A.; Shanmugam, S. LaTi 0.65 Fe 0.35 O 3-δ nanoparticle-decorated nitrogen-doped carbon nanorods as an advanced hierarchical air electrode for rechargeable metal-air batteries. Nano Energy 2015, 15,