Oxygen Reduction. Platinum(II) 2,4-pentanedionate (Pt, 49.6%), Cobalt(II) 2,4-pentanedionate (Co(acac) 2, 98%) and Nickel(II)

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1 Supplementary Information Carbon-Supported PtCo 2 Ni 2 Alloy with Enhanced Activity and Stability for Oxygen Reduction Ya-Rong Zheng 1, Min-Rui Gao 1, Hui-Hui Li 1, Qiang Gao 1, Muhammad Nadeem Arshad 2,3, Hassan A. Albar 3, Tariq R. Sobahi 3, and Shu-Hong Yu 1 * 1. Division of Nanomaterials and Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, Collaborative Innovation Center of Suzhou Nano Science and Technology, Department of Chemistry, University of Science and Technology of China, Hefei, Anhui , P. R. China. 2. Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589, Saudi Arabia. 3. Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia Experimental Section Chemicals. Platinum(II) 2,4-pentanedionate (Pt, 49.6%), Cobalt(II) 2,4-pentanedionate (Co(acac) 2, 98%) and Nickel(II) 2,4-pentanedionate (Ni(acac) 2, 95%) were purchased from Alfa Aesar. Oleylamine (CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 8 NH 2, 70%) and Nafion solution (5 wt%) were purchased from Aldrich. Oleic acid (CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 COOH, 99%), perchioric acid (HClO 4, 70.0%-72.0%) and other solvents such as ethanol and hexane were purchased from Shanghai Chemical Reagent Co., Ltd.. All chemicals were of analytical grade and were used as received without further purification. Synthesis of PtCo 2 Ni 2 /C alloyed composite. In a typical procedure, a molar ratio of Pt(acac) 2 : Co(acac) 2 : Ni(acac) 2 (defined as R) = 1:2:2, defined amount of Vulcan XC-72R (the metal loading ca. 20 wt%), 1 ml oleic acid and 9 ml oleylamine were added into a 25-mL three-neck flask. The mixture was sonicated for 1 h under ambient conditions. After the suspension was purged with N 2 for 30 min, the solution was slowly heated to 230 C at a rate of 3 C min -1 and kept at reflux for 40 min under magnetic stirring and N 2 protection. After cooling the reaction solution to room temperature naturally, the black precipitate was collected by repeated centrifugation and washed several times by hexane and ethanol, and dried under a vacuum at 60 C for 8 h. Synthesis of PtCoNi/C and Pt 2 CoNi/C alloyed composites. S1

2 To synthesize PtCoNi/C and Pt 2 CoNi/C composite, the procedure is the same as that of PtCo 2 Ni 2 /C composite. The only difference is that adjust the molar ration R to 1:1:1, and 2:1:1. Synthesis of PtCo/C and PtNi/C alloyed composites. To prepare PtNi/C and PtCo/C composite, the procedure is the same as PtCo 2 Ni 2 /C composite, by adjust the molar ration of Pt(acac) 2, Co(acac) 2 to 1:2, and Pt(acac) 2 : Ni(acac) 2 to 1:2. Thermal treatment. All samples were treated in a tube furnace using a quartz tube. The as-prepared PtCoNi/C were firstly heated at 260 C in N 2 for 60 min, and then treated at 400, 600, and 800 C in 5% H 2 balanced with Ar for 120 min, respectively. Electrochemical measurement. Electrochemical measurements were performed at room temperature using a rotating disk working electrode made of glassy carbon (PINE, 5 mm diameter, cm 2 ) connected to a Multipotentiostat (IM6ex, ZAHNER elektrik, Germany). Pt wire and AgCl/Ag/KCl (4 M) were used as counter and reference electrodes, respectively. All potentials were converted to reversible hydrogen electrode (RHE) through RHE calibration (see Supporting Information). The electrolyte used for all the measurements was 0.1 M HClO 4, diluted from 70% double-distilled perchloric acid with DIW. The catalyst ink was fabricated as follows: 5 mg catalysts powder were dispersed in 1 ml of a solution of isopropanol with 5 μl Nafion solution (5 wt%). Then the mixtures were ultrasonicated for 30 min, and take 10 μl catalyst ink transferred onto the glassy carbon disk (geometric area: cm 2 ) to obtain a Pt loading amount of 20 μg cm -2 for these catalysts. Finally, the as-prepared RDE was dried at room temperature. Before the electrochemical measurement, the electrolyte (0.1 M HClO 4 ) was degassed by bubbling O 2 or Ar for 30 min. The polarization curves were obtained by sweeping the potential from 0 to 1.2 V vs. RHE, with a scan rate of 5 mvs -1 and at a rotation rate of 1600 rpm in the positive direction. All the data were recorded after applying a number of potential sweeps until which were stable. RHE Calibration. In the all electrochemical tests, AgCl/Ag/KCl (4 M) was used as reference electrode. It was calibrated with regard to RHE. The calibration was performed in 0.1 M HClO 4 solutions under H 2 -saturated condition with a Pt-foil as the working electrode. CV curve was obtained at the scan rate of 1 mv s -1, and the average potential S2

3 at which the current crossed zero was regard as the thermodynamic potential for the hydrogen electrode reaction. In 0.1 M HClO 4 solution, E(RHE) = E(Ag/AgCl) V. ECSA Calculation. The electrochemical active surface areas (ECSAs) measurements were estimated by measuring the hydrogen adsorption charge on the cyclic voltammetry (CV) at room temperature in Ar-saturated 0.1 M HClO 4 solutions at a sweep rate of 50 mv/s. By integrating the area of the H-desorption region, the ECSAs can be calculated on the following equation: QH ECSA m 210 Q H (mc/cm 2 ) represents the charge for H-desorption, m is the Pt loading (mg/cm 2 ) in the RDE and 210 (mc/cm 2 ) represent the charge required to adsorb a monolayer of H 2. Characterization. X-Ray powder diffraction patterns (XRD) of the products were obtained on a Japan Rigaku DMax-γA rotation anode X-ray diffractometer equipped with graphite monochromatism Cu-Kα radiation ( λ = Ǻ ). Transmission electron microscope (TEM) images were taken with a Hitachi H7650 transmission electron microscope with CCD imaging system on an acceleration voltage of 120 kv. High resolution TEM (HRTEM) and energy-filtered TEM (EFTEM) mapping were performed using JEM-ARM 200F operating at an accelerating voltage of 200 kv. Elemental mapping were obtained using a Gatan GIF Quantum 965. X-ray photoelectron spectra (XPS) were performed on an X-ray photoelectron spectrometer (ESCALab MKII) with an excitation source of Mg Kα radiation ( ev). Fourier transform infrared (FT-IR) spectrum was measured on a Bruker Vector-22 FT-IR spectrometer from 4000 to 500 cm 1 at room temperature. Actual Pt loadings of the carbon-supported alloy catalysts were determined by the inductively coupled plasma atomic emission spectroscopy (ICP-AES) technique utilizing an Atomscan Advantage (Thermo Jarrell Ash Corporation, U.S.A.) instrument. S3

4 Figure S1 TEM images of carbon-supported alloy catalysts with different composition, the molar ratio (R) of Pt(acac) 2, Co(acac) 2 and Ni(acac) 2 are 1:2:2 (a), 1:1:1 (b), and 2:1:1 (c), respectively. (d, e, and f) show the particle size histograms and (g, h, and i) are the HRTEM images correspond to (a, b, and c), respectively. The inserts of (g, h, and i) show the SAED patterns of the TEM images. (j) XRD patterns of the as-prepared catalysts with different composition. (k) ICP data showing the different Pt loading amount and bulk atomic ratio of PtCo 2 Ni 2, PtCoNi, and Pt 2 CoNi. Figure S2 TEM images of the PtCo 2 Ni 2 /C, which was thermal treated at 400 C (a), 600 C (b) and 800 C (c), respectively. S4

5 Figure S3 XPS spectra of the Pt 4f signals for the as-prepared (a) PtCoNi/C and (b) Pt 2 CoNi/C catalyst treated at 400, 600 and 800 C, respectively. O Intensity / a.u Binding Energy / ev Figure S4 The high-resolution O1s XPS spectrum of as-prepared PtCo 2 Ni 2 /C. Figure S5 XPS spectra of the Ni2p (a) and Co2p (b) for the as-prepared PtCo 2 Ni 2 /C and C400, C600 and C800, respectively. S5

6 Figure S6 CV original data of (a) C400, (b) C600 and (d) C800. The experiments were performed at the scan rate of 250 mv s -1 in 0.1 M HClO 4 solutions under Ar-saturated condition and the data were recorded from the 1st to 250th cycles. (d, e) EDX line-scan profiles of C600 after the dealloying treatment. The initial CV curves (a-c) show weak hydrogen adsorption/desorption between 0-0.4V, with the cycles going on, clear hydrogen adsorption and desorption peaks of the CV curves are observed due to the surface roughness and the exposure of Pt atoms.[1-3] After 250 potential cycles, the resulting CV curves become stable and resemble that of pure Pt, suggesting the increased electrochemical active surface areas (ECSAs) and thus highly active surface sites were obtained. Operated at 200 kv, EDX revealed that the Pt peak is broader than the Ni and Co at both sides of the line scan, indicating that a Pt-enriched surface structure was finally formed after leaching the surface Co, Ni atoms. Figure S7 The energy dispersive X-ray spectroscopy (EDS) spectrum of the catalyst after dealloying treatment, which reveals the molar ratio between Pt, Co, and Ni is 57:20:23. The increased percentage of the Pt element is due to the leaching of the surface Co, Ni atoms. S6

7 0 j / ma cm Pt 2 CoNi PtCo 2 Ni 2 PtCoNi E / V vs. Ag/AgCl Figure S8 The ORR polarization curves of PtCo 2 Ni 2 /C, PtCoNi/C, and Pt 2 CoNi/C, after 250 potential cycles in O 2 -saturated 0.1 M HClO 4 solution with a scan rate of 5 mvs -1 and a rotation rate of 1600 rpm at room temperature. Figure S9 (a, b) TEM images of the PtNi/C and PtCo/C, respectively, which were synthesized by the same method. (c, d) XRD patterns of the PtNi/C and PtCo/C, respectively. (e) CV curves of PtNi/C and PtCo/C were recorded with a scan rate of 50 mvs -1 after 250 potential cycles in Ar-saturated 0.1 M HClO 4 solution. (f) The ORR polarization curves of PtNi/C and PtCo/C, after 250 potential cycles in O 2 -saturated 0.1 M HClO 4 solution with a scan rate of 5 mvs -1 and a rotation rate of 1600 rpm at room temperature. S7

8 References [1] Duong, H. T., Rigsby, M. A.; Zhou, W. P., Wieckowski, A. Oxygen reduction catalysis of the Pt 3 Co alloy in alkaline and acidic media studied by X-ray photoelectron spectroscopy and electrochemical methods. J. Phys. Chem. C 2007, 111: [2] Erlebacher, J., Aziz, M. J., Karma, A., Dimitrov, N., Sieradzki, K. Evolution of nanoporosity in dealloying. Nature 2001, 410: [3] Strasser, P., Koh, S., Anniyev, T. et al. Lattice-strain control of the activity in dealloyed core-shell fuel cell catalysts. Nat. Chem. 2010, 2: S8