Structurally ordered intermetallic platinum cobalt core shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts Deli Wang, Huolin L. Xin, Robert Hovden, Hongsen Wang, Yingchao Yu, David A. Muller, Francis J. DiSalvo, Héctor D. Abruña* *To whom correspondence should be addressed. E-mail: hda1@cornell.edu Table of contents: Table S1: Detailed information for samples in Fig. S1 Fig. S1: Mass activities comparison. Fig. S2: Bright and dark field images of Pt 3 Co/C-700 nanoparticles. Fig. S3: Particle size distribution of Pt 3 Co/C-700 nanoparticles from TEM image. Fig. S4: Low resolution STEM images of Pt 3 Co/C-700 nanoparticles. Fig. S5: Comparison of the ADF-STEM image contrast for ordered and disordered Pt 3 Co. Fig. S6: Particle Comparison of the atomic-resolution ADF-STEM image of the nanoparticle shown in Fig. 1 before and after Richardson-Lucy deconvolution Fig. S7: Comparison of the atomic-resolution ADF-STEM image of the nanoparticle shown in Fig. 1 with multislice simulation of an idealized Pt 3 Co nanoparticle. Fig. S8: Koutecky-Levich plots on Pt/C electrode. Fig. S9: Representative CV curve of Pt 3 Co/C for ECSA calculation Fig. S10: CV curves of Pt 3 Co/C-400 and Pt 3 Co/C-700 during 50 potential cycles. Fig. S11: Low resolution STEM images of Pt 3 Co/C-700 nanoparticles after 5000 potential cycling. NATURE MATERIALS www.nature.com/naturematerials 1
Table S1. Detailed information for samples in Fig. S1. Number catalyst electrolyte Temperature MA@0.9V Ref. o C maµg -1 1 PtCo 3 0.1M HClO 4 RT 0.34 1 2 PtCu 3 Co 0.1M HClO 4 RT 0.37 1 3 PtCu 2 Co 2 0.1M HClO 4 RT 0.37 1 4 PtCuCo 3 0.1M HClO 4 RT 0.49 1 5 Pt 3 Co/C as prepared 0.1 M HClO 4 25 0.136 2 6 Pt 3 Co/C 200 o C annealing 0.1M HClO 4 25 0.129 2 7 Pt 3 Co/C 500 o C annealing 0.1 M HClO 4 25 0.217 2 8 PtCo 3 600 o C annealing 0.1M HClO 4 20 0.23 3 9 PtCo 2.7 600 o C annealing 0.1M HClO 4 20 0.26 3 10 PtCo 3 600 o C annealing 0.1 M HClO 4 20 0.34 3 11 PtCo 2.8 900 o C annealing 0.1M HClO 4 20 0.31 3 12 PtCo 2.8 1000 o C annealing 0.1 M HClO 4 20 0.25 3 13 Acid-treated Pt 3 Co 0.1M HClO 4 RT 0.35 4 14 Annealed Pt 3 Co 0.1 M HClO 4 RT 0.31 4 15 7.3%PtCo 0.5 M H 2 SO 4 60 0.041 5 16 CoCuPt 200 o C annealing 0.1 M HClO 4 RT 0.15 6 17 CoCuPt 200 o C annealing 0.1M HClO 4 RT 0.072 6 18 CoCuPt 200 o C annealing 0.1 M HClO 4 RT 0.05 6 19 PtCo/C-900 0.5 M H 2 SO 4 RT 0.084 7 20 Pt-Co/C-S 1 M HClO 4 RT 0.154 8 21 Pt-Co/C-T 1 M HClO 4 RT 0.109 8 22 Pt-Co/C-SB 1 M HClO 4 RT 0.151 8 23 Pt-Co/C-TB 1 M HClO 4 RT 0.102 8 24 Pt-Co/C-SH 1 M HClO 4 RT 0.054 8 25 Pt-Co/C-TH 1 M HClO 4 RT 0.093 8 26 Pt 3 Co/C 0.1 M HClO 4 25 0.25 9 27 PtCo/C 0.1 M HClO 4 25 0.37 9 28 Pt 3 Co/C-400 0.1 M HClO 4 RT 0.16 this paper 29 Pt 3 Co/C-700 0.1 M HClO 4 RT 0.52 this paper 2 NATURE MATERIALS www.nature.com/naturematerials
SUPPLEMENTARY INFORMATION Figure S1. Comparison of the mass activities of Pt-Co systems from literature reprints and this work. The numbers in the figure represent the different samples. Detailed information of the samples is shown in Table S1. Figure S2. Bright-field (BF) (a) and annular dark-field (ADF) (b) STEM images of Pt 3 Co/C-700 nanoparticles. NATURE MATERIALS www.nature.com/naturematerials 3
Figure S3. a, Annular dark-field STEM overview image of Pt 3 Co/C-700 made from an extended depth of field reconstruction 10. b, Particle size distribution of more than 150 particles. A log-normal distribution fit to the histogram is shown in red. Figure S4. Two lower resolution STEM images of Pt 3 Co/C-700 nanoparticles a,b, Bright-field (BF) and a,b, annular dark-field (ADF) images. 4 NATURE MATERIALS www.nature.com/naturematerials
SUPPLEMENTARY INFORMATION Figure S5. Comparison of the ADF-STEM image contrast for ordered and disordered Pt 3 Co. Multislice simulation 11 of a, disordered alloy Pt 3 Co. b, L1,2 ordered intermetaltic Pt 3 Co (100 kv, Probe forming angle = 27.8 mrad, ADF collection angle = 98-295 mrad). The disordered Pt 3 Co atom coordination was created from 4- by-4-by-12 supper cell of L1,2 ordered Pt 3 Co by swapping a randomly selected pair of atoms for 2x10 7 times. The simulation thickness for both a and b is 4.6 nm. (xyz structure files are available upon request to HLX) Figure S6. Comparison of the atomic-resolution ADF-STEM image of the nanoparticle shown in Fig. 1 before and after Richardson-Lucy deconvolution (4 iterations) 12. The deconvolution kernel was assumed to be an Airy disk (100 kv, α max = 28 mrad) convolved with a 0.8-Å Gaussian source. The deconvolution was done by a custom-written matlab script utilizing the native deconvlucy(i, PSF) function in the image processing toolbox (scripts are available upon request to HLX). NATURE MATERIALS www.nature.com/naturematerials 5
Figure S7. Comparison of the atomic-resolution ADF-STEM image of the nanoparticle shown in Fig. 1 with multislice simulation of an idealized Pt 3 Co nanoparticle. a, Experimental ADF-STEM image; b, ADF-STEM (100 kv, Probe forming angle = 27.8 mrad, ADF collection angle = 98-295 mrad) image of the idealized nanoparticle as shown in c simulated using a multislice code 11,13. The resulting image was convolved with a 0.8- Å-FWHM Gaussian plus a 0.05-Å-FWHM Lorentzian to simulate the degradation of the image contrast due to a finite source size and chromatic aberrations; c, the idealized atomic structure of the Pt 3 Co core-shell nanoparticle. The distance between the three major facets ({111},{001},{110}) were chosen to match the morphology of the particle shown in a rather than using a Wulff construction. (xyz/cif structure filesare available upon sending request to HLX). Figure S8. a, ORR polarization curves of Pt/C in O 2 -saturated 0.1 M HClO 4 solution at a scan rate of 50 mvs -1 and different rotation rates. b, Corresponding Koutecky-Levich plots at different potentials. 6 NATURE MATERIALS www.nature.com/naturematerials
SUPPLEMENTARY INFORMATION Figure S9. Representative CV curve of Pt 3 Co/Cfor ECSA calculation. The CV curve was recorded from Pt 3 Co/C-700 nanoparticles after 50 potentail cycles between 0.05 to 1.0 V (vs. RHE), in 0.1 M HClO 4 at a scan rate of 50 mvs -1. Figure S10. The changes of CV curve of Pt 3 Co/C-400 and Pt 3 Co/C-700 during 50 petential cycles. The CV curves were recorded between 0.05 to 1.0 V (vs. RHE), in 0.1 M HClO 4 at a scan rate of 50 mvs -1. NATURE MATERIALS www.nature.com/naturematerials 7
Figure S11. Two low resolution STEM images of Pt 3 Co/C-700 nanoparticles after 5000 potential cycles between 0.05 to 1.0 V (vs. RHE), in 0.1 M HClO 4 at a scan rate of 50 mvs -1. a,b, Bright-field (BF) and a,b, annular dark-field (ADF) images. 8 NATURE MATERIALS www.nature.com/naturematerials
SUPPLEMENTARY INFORMATION Reference 1. Srivastava, R., Mani, P., Hahn, N. & Strasser, P. Efficient oxygen reduction fuel cell electrocatalysis on voltammetrically dealloyed Pt-Cu-Co nanoparticles. Angew. Chem. Int. Ed. 46, 8988-8991 (2007). 2. Liu, Z. C., Yu, C. F., Rusakova, I. A., Huang, D. X. & Strasser, P. Synthesis of Pt 3 Co alloy nanocatalyst via reverse micelle for oxygen reduction reaction in PEMFCs. Top.Catal. 49, 241-250 (2008). 3. Schulenburg, H. et al. Heat-Treated PtCo 3 Nanoparticles as Oxygen Reduction Catalysts. J. Phys. Chem. C 113, 4069-4077 (2009). 4. Chen, S. et al. Enhanced activity for oxygen reduction reaction on "Pt 3 CO" nanoparticles: Direct evidence of percolated and sandwich-segregation structures. J. Am. Chem. Soc. 130, 13818-13819 (2008). 5. Bogdanovskaya, V. A., Tarasevich, M. R., Kuznetsova, L. N., Zhutaeva, G. V. & Lozovaya, O. V. Oxygen electroreduction at catalysts PtM (M = Co, Ni, or Cr). Russ. J. Electrochem. 46, 925-933 (2010). 6. Wu, J. B., Peng, Z. M. & Yang, H. Supportless oxygen reduction electrocatalysts of CoCuPt hollow nanoparticles. Phil. Trans. R. Soc.A 368, 4261-4274 (2010). 7. Jeon, M. K., Zhang, Y. A. & McGinn, P. J. A comparative study of PtCo, PtCr, and PtCoCr catalysts for oxygen electro-reduction reaction. Electrochim. Acta 55, 5318-5325 (2010). 8. He, Q. G. & Mukerjee, S. Electrocatalysis of oxygen reduction on carbon-supported PtCo catalysts prepared by water-in-oil micro-emulsion. Electrochim. Acta 55, 1709-1719 (2010). 9. Markovic, N. M., Schmidt, T. J., Stamenkovic, V., Ross, P. N. Oxygen reduction reaction on Pt and Pt bimetallic surfaces: A Selective Review. Fuel cells 1, 105-116 (2001). 10. Hovden, R., Xin, H. L. & Muller, D. A. Extended depth of field for high-resolution scanning transmission electron microscopy. Micros. Microanal. 17, 75-80 (2011). 11. Kirkland, E. Advanced Computing in Electron Microscopy (Springer, 2010). 12. Mkhoyan, K. A., Batson, P. E., Cha, J., Schaff, W. J. & Silcox, J. Direct determination of local Lattice polarity in crystals. Science 312, 1354 (2006). 13. The code is distributed through http://people.ccmr.cornell.edu/~kirkland/ NATURE MATERIALS www.nature.com/naturematerials 9