Supporting Information. Bimetal-Organic Framework Self-Adjusted Synthesis of Support-Free Nonprecious Electrocatalysts for Efficient Oxygen Reduction

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1 Supporting Information Bimetal-Organic Framework Self-Adjusted Synthesis of Support-Free Nonprecious Electrocatalysts for Efficient Oxygen Reduction Bo You, Nan Jiang, Meili Sheng, Walter S. Drisdell, Junko Yano,, and Yujie Sun * Department of Chemistry and Biochemistry, Utah State University, 0300 Old Main Hill, Logan, Utah (USA) Joint Center of Artificial Photosynthesis, Berkeley, CA (USA) Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA (USA). 1. Chemicals 2-Methylimidazole (MeIM), potassium hydroxide, and perchloric acid were purchased from Alfa Aesar. Cobalt nitrate hexahydrate, zinc nitrate hexahydrate, Nafion, sodium monobasic dihydrogen phosphate, and sodium dibasic monohydrogen phosphate were purchased from Sigma-Aldrich. Methanol and ethanol were purchased from DECON LABORATORIES. Commercial Pt/C catalyst (20% Pt on Vulcan XC-72) was purchased from Premetek. All chemicals were used as received without any further purification. Water deionized (18 M ) with a Barnstead E-Pure system was used in all experiments. 1 of 19

2 2. Supplemental data Figure S1 SEM images of (a, b) Zn 0.8Co 0.2(MeIM) 2 bi-mof and (c, d) their derived fresh-prepared Co- N-C. (e) STEM image of the fresh-prepared Co-N-C. Inset of (e) is the statistical size distribution of Co nanoparticles in fresh-prepared Co-N-C. 2 of 19

3 Figure S2 EDX results of (a) Zn 0.8Co 0.2(MeIM) 2 bi-mof and (b) fresh-prepared Co-N-C. The Al peak is due to the sample holder. 3 of 19

4 Figure S3 XRD patterns of (a) Zn xco 1-x(MeIM) 2 bi-mof (x = 0~1) and (b) their derived fresh-prepared, Co-N-C-x electrocatalysts, wherein x represents the molar content of Zn ions in the bi-mof precursors, Zn xco 1-x(MeIM) 2 (x = 0~1). The Co-N-C-0.8 was denoted as Co-N-C for brevity in main text and carbonization temperature is 900 o C. 4 of 19

5 Figure S4 (a, c, e, g, and i) SEM and (b, d, f, h, and j) the corresponding STEM images of (a, b) carbonized ZIF-67 (Co-N-C-0), (c, d) Co-N-C-0.5, (e, f) Co-N-C-0.67, (g, h) Co-N-C-0.8, and (i, j) Co- N-C The number ( x = 0, 0.5, 0.67, 0.8 and 0.89) represents the molar content of Zn ions in the bi-mof precursors, Zn xco 1-x(MeIM) 2. Duo to the very low Co content in Co-N-C-0.89 NPHs, the Cobased nanoparticles are not visible in Figure j. 5 of 19

6 Figure S5 N 2 adsorption-desorption isotherms of the self-supported porous Co-N-C-x, carbonized ZIF- 67, and carbonized ZIF-8 (without Co). Wherein x represents the molar content of Zn ions in the initial bi-mof precursor, Zn xco 1-x(MeIM) 2, and the carbonization temperature is 900 o C. 6 of 19

7 Figure S6 XPS spectra for the (a) survey scan, (b) Co 2p, (c) N 1s, (d) C 1s, and (e) Zn 2p regions of carbonized ZIF-8, Co-N-C, and carbonized ZIF of 19

8 High-resolution Co 2p spectra of Co-N-C and carbonized ZIF-67 (Figure S6b) exhibit two peaks at binding energies (B.E.) of ~793.8 and ev, assignable to metallic Co 2p 1/2 and 2p 3/2. The ~15 ev binding energy difference due to spin-orbit split and the asymmetric Co 2p 3/2 peak implies the metallic state of Co (New J. Phys. 2008, 10, ). No cobalt signal was detected in carbonized ZIF-8, consistent with its precursor of Zn(MeIM) 2 only. High-resolution N 1s spectrum (Figure S6c) could be fitted by three sub-peaks corresponding to pyridinic N, pyrrolic N, and oxidized N. The high-resolution C 1s spectrum (Figure S6d) could be deconvoluted into three different peaks with the binding energies corresponding to adventitious C, C=C, C=N, and C-N, respectively (Angew. Chem. Int. Ed. 2012, 52, ), which indicates that the N dopants were successfully incorporated into the carbon framework. The featureless spectrum in the Zn 2p regions of carbonized ZIF-8 and Co-N-C (Figure S6e) demonstrates the complete evaporation of Zn, consistent with the element mapping (Figure 1d in the main text) and EDX (Figure S2b) results. 8 of 19

9 Figure S7 RDE polarization plots measured with Co-N-C-x-y samples (wherein x represents the molar content of Zn ions in the initial bi-mof precursors, Zn xco 1-x(MeIM) 2, and y represents the carbonization temperature) in O 2-saturated 0.1 M KOH at 1600 rpm and 10 mv s -1 as a function of (a) the carbonization temperature and (b) the molar content of Zn in the initial bi-mof precursor. 9 of 19

10 Figure S8 (a) RDE polarization curves and (b) the corresponding K-L plots of Pt/C in O 2-saturated 0.1 M KOH. (c) Rotating ring-disk electrode voltammograms of carbonized ZIF-67 (black), Co-N-C (red) and Pt/C (blue) in O 2-saturated 0.1 M KOH at 1600 rpm and 5 mv s -1. (d) RDE polarization curves of Pt/C before and after 5,000 potential cycles in O 2-saturated 0.1 M KOH at 1600 rpm. 10 of 19

11 Figure S9 (a) SEM and (b) the corresponding STEM images of Co-N-C, (c) XPS survey, (d) Co 2p and (e) N 1s spectra of Co-N-C before and after 5000 potential cycles in 0.1 M KOH. After 5000 consecutive potential cycles in O 2-saturated 0.1 M KOH, the Co-N-C still maintained the overall polyhedron-like morphology (Figure S9a). The corresponding STEM image (Figure S9b) shows that the Co nanoparticles are still well dispersed, confirming the good stability of Co-N-C for ORR. XPS spectra (Figure S9c) of Co-N-C after stability test verify the presence of Co and N. The presence of F element is due to the utilization of Nafion for drop casting the catalyst on the working electrode. High-resolution N 1s spectrum of Co-N-C after stability test is almost same as that of the fresh prepared Co-N-C and the Co 2p spectrum of Co-N-C after stability test exhibits slight oxidation of Co due to the exposure in O 2 environment (O 2-saturated 0.1 M KOH). Collectively, the SEM, STEM, XPS, and the electrocatalytic results demonstrate the strong robustness of our Co-N-C for ORR electrocatalysis. 11 of 19

12 Figure S10 (a) RDE polarization curves and (b) the corresponding K-L plots of Pt/C in O 2-saturated 0.1 M HClO 4. (c) RDE polarization curves of Pt/C before and after 5,000 potential cycles in O 2- saturated 0.1 M HClO 4 at 1600rpm. 12 of 19

13 Figure S11 (a) RDE polarization curves and (b) the corresponding K-L plots of Pt/C catalyst in O 2- saturated 0.1 M neutral phosphate buffer. (c) RDE polarization curves of Pt/C before and after 5,000 potential cycles in O 2-saturated 0.1 M neutral phosphate buffer at 1600 rpm. 13 of 19

14 Figure S12 (a) Co K-edge XANES of Co foil, CoO, Co 3O 4, carbonized ZIF-67 and Co-N-C. (b) Co L- edge of carbonized ZIF-67 and Co-N-C. 14 of 19

15 Table S1 Comparison of electrocatalytic ORR activity of various nonprecious catalysts under basic condition (0.1 M KOH). Specific mass Loading E 1/2 J at 0.80 V Catalysts (mg cm -2 ) (V vs RHE) (ma cm -2 ) a J k (ma cm -2 Post-treatment ) activity at 0.80 V b or (A g -1 ) a additives Co-N-C-0.8 NPHs (900 rpm) 39.3 at 0.80 V 35.9 at 0.60 V 44.3 at 0.40 V 44.5 at 0.20 V (900 rpm) none Reference This work CNCo Leaching in 0.5 M H 2SO 4 at 80 o C for Adv. Mater. 2015, 27, h for twice P-CNCo Leaching in 0.5 M H 2SO 4 at 80 o C for 12h for twice and stirring with triphenylphosphine Adv. Mater. 2015, 27, for 24h plus annealing at 800 o C for 2h. NPMC ~3.8 ~25 at 0.65 V - freeze-drying for 24 h Nat. Nanotech. 2015, 10, 444. Ag-Co alloy ~ ~2.0 (900rpm) - <5.0 - Nat. Chem. 2014, 6, 828. FePhen@MOF- Second-annealing in <5.0 - <8.3 ArNH 3 NH 3 Nat. Commun. 2015, 6, LT-Li 0.5CoO < Nat. Commun. 2014, 5, Meso/micro-PoPD ~10 at 0.80 V 43.2 colloidal silica as template Nat. Commun. 2014, 5, Fe 3C/CNT < Leaching in 0.1M H 2SO 4 for 24 h J. Am. Chem. Soc. 2015, 137, CPM-99Co/C <3.0 - <15 none J. Am. Chem. Soc. 2015, 137, FeCo xo y/carbon impregnating with <0.75 < black carbon black J. Am. Chem. Soc. 2014, 136, Co 3O 4/C-NAs Cu foil as support J. Am. Chem. Soc. 2014, 136, CPM-99Fe/C ~4.0 ~8.0 none J. Am. Chem. Soc. 2015, 137, P-Z8-Te <3.0 - <30 Te nanowire as J. Am. Chem. Soc. 2014, 136, of 19

16 Fe-N/C <35 NOSC ~25 at 0.60 V 7.39 MnCo xo y/ncnt <0.75 ~1.0 - ~4.76 N,S,O-OMC <0.75 < at 0.75 V <3.33 NC <0.70 <0.5 - <14.7 N-Fe-CNT/CNP <2.5 (900 rpm) - <12.5 (900rpm) Fe-NT-G Fe, Co-N x/g <0.75 <2.0 - <2.81 N_Fe ~ Fe N x/c <3.90 (900 rpm) Fe 3C/C < template and second-annealing for P doping Leaching in 6 M HCl for 8h colloidal silica as template Leaching in 1.5 M HNO 3 for 72h and second-high temperature oxidation mesoporous silica SBA-15 as template furfuryl alcohol and NH 4OH as additives Leaching in 0.5 M H 2SO 4 at 80 o C for 8 h. concentrated H 2SO 4 and KMnO 4 oxidation Leaching in 0.5 M H 2SO 4 at 80 o C for 8 h. Leaching in 2M H 2SO 4 and secondannealing and activated carbon as support J. Am. Chem. Soc. 2014, 136, J. Am. Chem. Soc. 2014, 136, J. Am. Chem. Soc. 2014, 136, J. Am. Chem. Soc. 2014, 136, J. Am. Chem. Soc. 2014, 136, Nat. Commun. 2013, 4, Nat. Nanotech. 2012, 7, 394. J. Am. Chem. Soc. 2014, 136, 9070 J. Am. Chem. Soc. 2014, 136, at 0.80 V <39 (900 rpm) carbon as support J. Am. Chem. Soc. 2013, 135, Leaching in 0.5 M H 2SO 4 at 85 C for 9h. Angew. Chem. Int. Ed. 2014, 53, of 19

17 Fe-N-CNT/G <0.75 < none Angew. Chem. Int. Ed. 2014, 53, Co 0.50Mo 0.50O yn z/c ~ Angew. Chem. Int. Ed. 2013, 52, Co 3O 4/N-rmGO V <4.0 - <40 NH 4OH additive for N-doping Nat. Mater. 2011, 10, 780. N-doped C/CNTs at 0.80 V 5.67 CNT as supports Angew. Chem. Int. Ed. 2014, 53, Mesoporous silica N-doped carbon as template and nanosheets NaOH etching Angew. Chem. Int. Ed. 2014, 53, Fe/Fe 3Cmelamine/N-KB <5.0 - <17.5 a The current density (J) and specific mass activity were obtained at 1600 rpm unless otherwise stated. b Post-treatment means the additional procedures after the first-annealing. Leaching in 2M H 2SO 4 at 80 o C for 3h and melamine as support Angew. Chem. Int. Ed. 2013, 52, of 19

18 Table S2 Comparison of ORR activity of various nonprecious catalysts in acid solution. Catalysts Loading (mg cm -2 ) E 1/2 (V vs RHE) J at 0.70 V (ma cm -2 ) a J k at 0.7V (ma cm -2 ) Specific mass activity at 0.70 V (A g -1 ) a Post-treatment b or additives Reference Co-N-C-0.8 NPHs none This work CPANI-Fe-NaCl 0.6 <7.40 < Leaching in 0.5 M H 2SO 4 J. Am. Chem. Soc. 2015, 137, at 80 o C and NaCl as template Fe 3C/CNT 1.2 ~0.60 <2.0 - <1.7 Leaching in 0.1M H 2SO 4 J. Am. Chem. Soc. 2015, 137, for 24 h CPM-99Co/C 0.6 <0.55 <1.0 - <1.7 none J. Am. Chem. Soc. 2015, 137, meso/micro-popd 0.5 ~0.70 <2.7 <5.4 colloidal silica as template Nat. Commun. 2014, 5, bngr <0.70 <3.0 - <4.2 Leaching in 0.5 M H 2SO 4 J. Am. Chem. Soc. 2014, 136, 9070 at 80 o C for 8 h. CPM-99Fe/C 0.6 ~0.75 <4.0 - <6.7 none J. Am. Chem. Soc. 2015, 137, Fe N x/c 0.1 < carbon as support J. Am. Chem. Soc. 2013, 135, PpPD-Fe-C <3.0 - <3.3 Leaching in 0.5 M H 2SO 4 Angew. Chem. Int. Ed. 2014, 53, at 80 o C for 8 h. Co-N-C 0.6 < Leaching in 10% HF at 25 o C for J. Am. Chem. Soc. 2013, 135, h and SBA-15 as template Co 0.50Mo 0.50O yn z/c ~0.0 - ~0 NH 3 flow Angew. Chem. Int. Ed. 2013, 52, Fe-N/C ~0.60 ~1.0 - ~10 Leaching in 6 M HCl for J. Am. Chem. Soc. 2014, 136, h Fe-NT-G <5.0 - <10.3 concentrated Nat. Nanotech. 2012, 7, 394. H 2SO 4 and KMnO 4 oxidation Fe 3C/C < Leaching in 0.5 M H 2SO 4 Angew. Chem. Int. Ed. 2014, 53, at 85 C for 9h. NG@H-MMT 0.6 <0.72 < <5.0 Montmorillonite as Angew. Chem. Int. Ed. 2013, 52, template Co 1-xS/RGO <0.60 ~1.2 - ~4.2 graphene as support Angew. Chem. Int. Ed. 2011, 50, PANI-Co-C 0.6 ~0.75 ~3.0 (900 rpm) - - Leaching in 0.5 M H 2SO 4 at 80 o C Science 2011, 332, 443. a The current density (J) and specific mass activity were obtained at 1600 rpm. b Post-treatment means the additional procedures after the first-annealing. 18 of 19

19 Table S3 Physiochemical parameters of Co-N-C, carbonized ZIF-8, and carbonized ZIF-67. Samples S BET Co N content Percentage of Content of pyrrolic and (m 2 g -1 ) content pyrrolic and pyridine pyridine N N Co-N-C % 8.5% 90% 7.65% Carbonized ZIF % 78.3% 6.73% Carbonized ZIF % 1.1% N/A < 1.1% 19 of 19