Supporting Information. Oxygen Reduction. School of Mechanical and Power Engineering, East China University of Science and

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1 Supporting Information Ordered Pt 3 Co Intermetallic Nanoparticles Derived from Metal-organic Frameworks for Oxygen Reduction Xiao Xia Wang,,,1 Sooyeon Hwang,,1 Yung-Tin Pan, Kate Chen, Yanghua He, Stavros Karakalos, Hanguang Zhang, Jacob S. Spendelow, Dong Su,, * and Gang Wu, * School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 2237, China Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 1426, United States Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina 2928, United States Corresponding author addresses: gangwu@buffalo.edu (G. Wu); dsu@bnl.gov (D. Su) 1, These two authors contributed equally S

2 Experimental details Preparation of Co-doped ZIF derived carbon supports Co-doped ZIF precursors with different Co contents were synthesized by varying the Co percent against total Co and Zn in a methanol solution during the ZIF crystal formation. Typically, a controlled amount of zinc (Ⅱ) nitrate hexahydrate and cobalt (Ⅱ) nitrate hexahydrate were dissolved in a methanol solution in a round-bottom flask. The other methanol solution contained 2-methylimidazole. Once these two solutions were mixed together, the temperature was increased to 6 C for ZIF nanocrystal synthesis for one hour. Then the precipitate were collected by centrifugation, washed at least three times with ethanol, then dried at 6 C in a vacuum oven for 1 hours. The precursors are designated as nco-zif, where n is defined as the molar percentage of Co against total Zn and Co in the starting materials. The Co-ZIF precursors were subsequently heated at a temperature of 9 C in a tube furnace under N 2 flow for 1 hour to obtain the N and Co co-doped carbon supports, which was labeled as nco-nc. Preparation of Pt 3 Co intermetallic catalysts At first, the Pt nanoparticles with a mass loading of 2 wt.% were deposited on the carbon derived from Co-doped ZIF by using an ethylene glycol (EG) reduction method. Typically, the nco-nc supports were sonicated in EG. Then, a certain amount of chloroplatinic acid (CPA) solution, prepared by dissolving CPA in EG, was added into the slurry and then stirred for 3 minutes. The mixture was heated up to 13 C and refluxed for 3 h under continuous magnetic stirring. After cooling down to room temperature, the catalysts were washed with deionized water several times until no Cl could be detected by AgNO 3 solution and dried at 8 C in a vacuum oven overnight. The as-prepared catalysts are designed as Pt/nCo-NC. In order to obtain structurally ordered PtCo intermetallic catalysts, the as-prepared Pt/nCo-NC was further annealed at 9 C in a tube furnace under vacuum for 3 minutes, referring to as Pt/nCo-NC-9. As the annealing post-treatment is critical to catalyst activity and stability, for a comparison, the as-prepared Pt/nCo-NC was also heat at 7, 8, and 1 C under the same procedure and were designed as Pt/nCo-NC-temperature. Physical characterization The morphology of ZIF precursors and derived supports were studied using scanning electron microscopy (SEM) on a Hitachi SU 7 microscope at a working voltage of 5 kv. The crystal phases present in each progress were identified using powder X-ray diffraction (XRD) on a Rigaku Ultima IV diffractometer with Cu Kα X-rays. Bright field and high-resolution transmission electron microscopy (HRTEM) images were obtained with JEM1F (JEOL) at an accelerating voltage of 2 kv. Atomic resolution high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images and elemental maps were acquired with HD27C STEM (Hitachi) equipped with a probe aberration corrector and Enfina spectrometer (Gatan). X-ray photoelectron spectroscopy (XPS) was performed using a Kratos AXIS Ultra DLD XPS system equipped with a hemispherical energy analyzer and a monochromatic Al Kα source. The source was operated at 15 kev and 15 W; pass energy was fixed at 4 ev for the high-resolution scans. All samples were prepared as pressed powders S

3 supported on a metal bar for the XPS measurements. Electrochemical measurements Electrochemical measurements were carried out by using an electrochemical workstation (CHI76b) coupled with a rotating-ring disc electrode (RRDE, Pine, AFMSRCE 35) in a three-electrode cell. A graphite rod and an Hg/HgSO 4 (K 2 SO 4 -sat.) electrode were used as the counter and reference electrodes, respectively. The reference electrode was calibrated to a reversible hydrogen electrode (RHE) in the same electrolyte before each measurement. A rotating disk electrode with a disk diameter of 5.6 mm covered by a thin film of the catalyst was used as the working electrode. To prepare the working electrode, 5 mg catalyst was ultrasonically dispersed in a 1. ml mixture of methanol and Nafion (5 wt.%) solution to form an ink. Then the ink was drop-casted on the disk electrode with a designed loading of 6 µg Pt /cm 2 and dried at room temperature to yield a thin-film electrode. The catalyst-coated disk working electrode was subjected to cyclic voltammetry (CV) in N 2 -saturated.1 M HClO 4 at a scan rate of 5 mv/s to activate the catalysts. The electrocatalytic activity for ORR was tested by steady-state measurement using staircase potential control with a step of.5 V at intervals of 3 s from to 1. V vs. RHE in O 2 -saturated.1 M HClO 4 solution at 25 C and a rotation rate of 9 rpm. Catalyst and support stability was studied by potential cycling at.6 to 1. V (5 mv/s) and 1. to 1.5 V (5 mv/s) in.1 M HClO 4 electrolyte. S

4 Table S1. Summary of synthesis and ORR activity of previously reported Pt-Co catalysts Catalysts Methods Structures Pt 3 Co-High T Impregnation reduction, heat treatment E 1/2 V vs. RHE V (A/mg Pt ) RDE activity V Stability ( E 1/2, mv) (ma/cm 2 Pt ) ordered Pt 3 Co/C-7 Co-reduction, ordered PtCo/C-7 heat treatment ordered PtCo hollow nanowire Annealed Pt 3 Co Pt 3 Co-8 D-PtCo 3 Electrospinning, reduction by H 2 acid leaching Acid leaching PtCo and annealing Co-reduction, heat treatment Impregnation reduction, heat treatment, acid leaching dealloyed ( V, 5 mv/s, 5 cycles) 2 ( V, 5 mv/s, 5 cycles) (.6. V, 5mV/s, 1 cycles) ordered Partly ordered dealloyed O-PtCo@Pt/C Co-reduction, ordered (.6. V, 5 mv/s, - Fuel cell performance V Ref S

5 heat treatment 5 cycles) PtCo/C Co-reduction, heat treatment disordered PtCo@NC Decomposition (.4.5 V, 5 mv/s, disordered of Pt@ZIF67 2 cycles) -- Heat treatment PtCo/CCCS of Pt supported ordered on Co-doped C Pt 3 Co/C-7 Impregnation 1 (.5. V, 5 mv/s, reduction, heat ordered cycles) treatment -- PtCo/C Co-reduction disordered (.75V) (.75V) PtCo/C-9 Co-reduction, ordered.7 heat treatment (.75V) (.75V) Pt 3 Co.9 nm Heat treatment ordered Pt 3 Co-8.1 nm Heat treatment ordered PtNiCo NWs/C Co-reduction disordered (.6.1 V, 5 mv/s, 3 cycles) -- 5 (square wave potential Fct-TM PtFeCo Impregnation cycling at.6 V for 3s ordered reduction and 1. V for 3s, 5 -- cycles) Pt 2 FeCo/C Impregnation reduction, ordered Pt 75 Co 25 /C(5) CVD technique ordered (5 cycles) S-5

6 (a) Intensity (a.u.) 6Co-NC 4Co-NC 2Co-NC Co JCPDS: Quantity absorbed (cm 3 /g STP) (b) Co-NC 4Co-NC 6Co-NC θ (degree) (c) Increamental volume (cm 3 /g).18 Micropore Mesopore Micropore Co-NC 4Co-NC 6Co-NC Relative pressure (P/P ) Pore width (nm) Figure S1. (a) XRD patterns, (b) isothermal physisorption, and (c) pore size distribution for ZIF derived carbon supports with different Co contents. S-6

7 (a) 2Co-NC (b) 4Co-NC (c) 6Co-NC Figure S2. TEM and STEM images for different supports used for PtCo alloy catalyst preparation. (b) 4Co-NC S-7

8 Pt/6Co-NC Pt/4Co-NC Pt/2Co-NC Co JCPDS: Pt JCPDS: Figure S3. XRD patterns for Pt deposited on different supports with different Co contents. S-8

9 Figure S4. (a-c) TEM images of Pt deposited on 4Co-NC supports. (d) Particle size distribution measured by TEM of more than 2 particles for Pt/4Co-NC (before heat treatment). S-9

10 (a) (b) Normalized Intensity (a.u.) Co Pt (c) (d) Normalized Intensity (a.u.) Distance (nm) Co Pt Distance (nm) Figure S5. Line scan for the particles in Pt/4Co-NC. S

11 (a) (b) (c) (d) Frequency (%) Pt/4Co-NC-9 (e) Normalized Intensity (a.u.) Co Pt (f) Normalized Intensity (a.u.) Co Pt Particle size (nm) (g) Distance (nm) (f) Distance (nm) 2 nm Figure S6. (a)-(c) TEM images of Pt/4Co-NC-9. (d) Particle size distribution measured by TEM of more than 2 particles for Pt/4Co-NC-9 (before heat treatment). (e) and (f) Line-scans for two Pt 3 Co nanoparticles. (g) and (h) STEM images of particles in Pt/4Co-NC-9, with two parallel lines along with arrow marks indicating 17 lattice spacing. S1

12 Table S2. Elemental contents determined by XRF for different PtCo catalysts. Catalyst Pt (at.%) Co (at.%) Pt/Co (at.%) Pt/2Co-NC Pt/4Co-NC Pt/6Co-NC S2

13 Pt/4Co-NC Co 2p O 1s Pt 4p N 1s Pt 4d- Pt 4d C 1s Pt 4f Pt/4Co-NC-9 Intensity (a. u.) Pt/4Co-NC-8 Pt/4Co-NC Binding energy (ev) Figure S7. XPS wide scanning spectra for Pt/4Co-NC catalysts and post treatment at different temperatures Table S3. Elemental quantification determined by XPS for different PtCo catalysts. Samples C (at%) N (at%) Pt (%) Co (%) O (%) Pt/4Co-NC Pt/4Co-NC Pt/4Co-NC Pt/4Co-NC S3

14 (a) Pt/4Co-NC Pt 4f 5/2 Pt 4f 7/2 (b) Pt/4Co-NC Graphitic N Pyridinic N NO x Intensity (a.u.) Pt/4Co-NC-8 Intensity (a. u.) Pt/4Co-NC (c) Pt/4Co-NC Binding energy (ev) C=C C-N, C-C (d) Binding energy (ev) Pt/4Co-NC Co 2p 3/2 Co 2p 1/2 Intensity (a. u.) Carbonates π -π * ) transitions O-C=O C=O Pt/4Co-NC-8 Intensity (a.u.) Pt/4Co-NC Binding energy (ev) Binding energy (ev) Figure S8. XPS analysis of (a) Pt 4f, (b) N 1s, (c) C1s, and (d) Co 2p survey spectra for different PtCo catalysts before and after heat treatment at 8 C and 9 C. S4

15 Table S4. Summary of fitting results for Pt 4f XPS spectra for various catalysts. Samples Pt (%) Pt 2+ (%) Pt/4Co-NC Pt/4Co-NC Pt/4Co-NC Pt/4Co-NC Table S5. Summary of fitting results for N 1s XPS spectra for various catalysts. Samples Pyridinic-N Co-N x (%) Graphitic-N Oxidized (%) (%) pyridinic-n (%) Pt/4Co-NC Pt/4Co-NC Pt/4Co-NC Pt/4Co-NC S5

16 (a) Current density (ma cm ) 2Co-NC 4Co-NC 6Co-NC (b) (c) Pt/2Co-NC Pt/4Co-NC Pt/6Co-NC Currend density (ma/cm 2 ) Pt/2Co-NC Pt/4Co-NC Pt/6Co-NC Figure S9. (a) SCV curves for NC supports heated at 9 ºC with different Co contents, (b) CV, and (c) SCV curves for different Pt catalysts before heat treatment. S6

17 (a) Pt/4Co-8-9 Pt/4Co-NC(9)-9 Pt/4Co-9 Pt/4Co1-9 (b) Intensity (a. u.) C (2) Pt (111) Pt (2) Pt/4Co1-9 Pt (22) Pt (311) (c).1 M HClO4, 9 rpm, 25 C θ (degree) Pt/ZIF8-NC-9 Pt/C Pt/4Co-NC Figure S1. (a) ORR polarization curves for the catalysts deposited on supports derived from various heating temperature, (b) XRD patterns for Pt/4Co1-9, and (c) SCV curves for Pt/ZIF8-NC-9, Pt/4Co-NC-9 and Pt/C catalysts. S7

18 (a) (c) Pt/.4Co-NC 1..5 V, 5mV/s N2-saturated.1M HClO4 Initial After 1k After 5k After 1k After 2k Initial After 1k After 5k After 1k Pt/.4Co-NC.6. V, 5mV/s N2-saturated.1M HClO Figure S11. Cyclic voltammetry curves of Pt/4Co-NC catalyst in N 2 -saturated.1 M HClO 4 solution for various numbers of potential cycling between (a) 1. and 1.5 V, 5 mv/s, (c).6 and 1. V, 5 mv/s. Polarization curves of Pt/4Co-NC catalyst in N 2 -saturated.1 M HClO 4 solution for various numbers of potential cycling between (b) 1. and 1.5 V, 5 mv/s, (d).6 and 1. V, 5 mv/s. (b) -5 (d) -5 Pt/4Co-NC 1..5 V, 5mV/s Cycling in N2-saturated.1M HClO4 Initial After 1k After 5k After 1k After 2k 57 mv loss Pt/4Co-NC.6. V, 5mV/s N2-saturated.1M HClO4 Initial After 1k After 5k After 1k 43 mv loss S8

19 (a) (c) Pt/C 1..5 V, 5 mv/s N 2 saturated.1 M HClO 4 Initial After 1k After 5k After 1k After 2k Pt/C.6. V, 5 mv/s N 2 saturated.1 M HClO 4 Initial After 5k After 1k After 2k (b) -5 (d) -5 Pt/C 1..5 V, 5mV/s N 2 -saturated.1m HClO 4 Initial After 1k After 5k After 1k After 2k 11 mv loss Pt/C.6. V, 5mV/s N 2 -saturated.1m HClO 4 Initial After 5k After 1k After 2k 44 mv loss Figure S12. Cyclic voltammetry curves of Pt/C catalyst in N 2 -saturated.1 M HClO 4 solution for various numbers of potential cycling between (a) 1. and 1.5 V, 5 mv/s, (c).6 and 1. V, 5 mv/s. Polarization curves of Pt/C catalyst in N 2 -saturated.1 M HClO 4 solution for various numbers of potential cycling between (b) 1. and 1.5 V, 5 mv/s, (d).6 and 1. V, 5 mv/s. S9

20 (a) Pt/4Co-NC V, 5 mv/s N 2 -saturated.1m HClO 4 Initial After 1k After 5k After 1k After 2k (b) Pt/4Co-NC-9 N 2 -saturated.1 M HClO 4.6.V 5mV s Initial After 1k After 5k After 1k After 14k Figure S13. Cyclic voltammetry curves of Pt/4Co-NC-9 catalyst in N 2 -saturated.1 M HClO 4 solution for various numbers of potential cycling between (a) 1. and 1.5 V, 5 mv/s, (b).6 and 1. V, 5 mv/s. S

21 Figure S14. The TEM bright field images for the Pt/4Co-NC-9 catalyst after potential cycling for 3 cycles. References (1) Koh, S.; Toney, M. F.; Strasser, P. Electrochim. Acta 27, 52, (2) Cai, Y.; Gao, P.; Wang, F.; Zhu, H. Electrochim. Acta 217, 245, 924. (3) Huang, Y.; Garcia, M.; Habib, S.; Shui, J.; Wagner, F.; Zhang, J.; Jorne, J.; Li, J. M. J. Mater. Chem. A 214, 2, (4) Chen, S.; Ferreira, P. J.; Sheng, W.; Yabuuchi, N.; Allard, L. F.; Shao-Horn, Y. J. Am. Chem. Soc. 28, 13, (5) Schulenburg, H.; Müller, E.; Khelashvili, G.; Roser, T.; Bönnemann, H.; Wokaun, A.; Scherer, G. G. J. Phys. Chem. C 29, 113, 469. (6) Jia, Q.; Caldwell, K.; Strickland, K.; Ziegelbauer, J. M.; Liu, Z.; Yu, Z.; Ramaker, D. E.; Mukerjee, S. ACS Catal. 215, 5, 176. (7) Yang, W.; Zou, L.; Huang, Q.; Zou, Z.; Hu, Y.; Yang, H. J. Electrochem. Soc. 217, 164, H331. (8) Loukrakpam, R.; Luo, J.; He, T.; Chen, Y.; Xu, Z.; Njoki, P. N.; Wanjala, B. N.; Fang, B.; Mott, D.; Yin, J. J. Phys. Chem. C 211, 115, (9) Du, N.; Wang, C.; Long, R.; Xiong, Y. Nano Res. 217, 1, (1) Jung, W. S.; Popov, B. N. ACS Appl. Mater. Interfaces 217, 9. (11) Wang, D.; Xin, H. L.; Hovden, R.; Wang, H.; Yu, Y.; Muller, D. A.; DiSalvo, F. J.; Abruña, H. D. Nat. Mater. 213, 12, 81. (12) Min, K. J.; Zhang, Y.; Mcginn, P. J. Electrochim. Acta 21, 55, S1

22 (13) Gummalla, M.; Ball, S. C.; Condit, D. A.; Rasouli, S.; Yu, K.; Ferreira, P. J.; Myers, D. J.; Yang, Z. Catalysts 215, 5, 926. (14) Jiang, K.; Zhao, D.; Guo, S.; Zhang, X.; Zhu, X.; Guo, J.; Lu, G.; Huang, X. Science Advances 217, 3, e (15) Arumugam, B.; Kakade, B.; Tamaki, T.; Arao, M.; Imai, H.; Yamaguchi, T. RSC Advances 214, 4, (16) Tamaki, T.; Minagawa, A.; Arumugam, B.; Kakade, B. A.; Yamaguchi, T. J. Power Sources 214, 271, 346. (17) Choi, D. S.; Robertson, A. W.; Warner, J. H.; Kim, S. O.; Kim, H. Adv. Mater. 216, 28, S2