Department of Chemistry and Chemical Biology, Cornell University, Ithaca 14853

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1 Supporting Information Synthesis of Structurally Ordered Pt 3 Ti and Pt 3 V Nanoparticles as Methanol Oxidation Catalysts Zhiming Cui, # Hao Chen, # Mengtian Zhao, Daniel Marshall, Yingchao Yu, Héctor Abruña and Francis J. DiSalvo* Department of Chemistry and Chemical Biology, Cornell University, Ithaca Experimental Materials: Platinum (IV) chloride (PtCl 4 ), Titanium (IV) chloride (TiCl 4 ), Vanadium (III) chloride (VCl 3 ) and 1.0 M potassium triethylborohydride (KEt 3 BH) in THF were purchased from Sigma-Aldrich. Vulcan XC-72 carbon black is from Cabot Corporation. Synthesis: Pt 3 Ti/C was synthesized as follows: 0.12 mmol PtCl 4 and 0.04 mmol TiCl 4 were weighed out in an argon-filled glove box and dissolved in 10 ml of THF by stirring. The reducing agent KEt 3 BH (1.0 M in THF, Sigma- Aldrich) with 30 mol % excess was mixed with THF to form a 15 ml solution. Then the precursor solution was drawn up into a syringe and injected into a solution of the reducing agent under vigorous stirring. The sample was dried under vacuum until most of the THF was gone. Hexanes were then added to precipitate the Pt 3 Ti-KCl powders. The sample was then washed three times with THF and hexanes without contacting air. The product was then dried under vacuum for 2 h and transferred to the glove box. The product was placed into silica tubes, which were sealed under vacuum and then annealed at 700 o C. The resulted Pt 3 Ti-KCl powders were added in a solution of ethylene S1

2 glycol that contained the carbon support as a well-dispersed suspension. Pt 3 Ti particles were released from the KCl matrix and bound to carbon black support after KCl was dissolved in the solution. Pt 3 V/C and Pt/C were prepared by the similar procedure but was annealed at 650 o C and 600 o C, respectively. In addition, we also prepared disordered Pt 3 Ti/C and disordered Pt 3 V/C by a similar procedure and were annealed at 450 o C for 24 hr without producing the ordered phase. Physicochemical characterization: Finely ground powders were examined with a Rigaku Ultima VI powder X-ray diffractometer (PXRD) with CuK radiation (Kα 1, λ= Å and Kα 2, λ = Å). Crystal structures of the oxides and resultant nitrides were confirmed by PXRD profiles using GSAS. Energy dispersive X-ray analysis (EDX) was performed with a LEO-1550 field emission SEM (FSEM). Transmission electron microscopy (TEM) was performed with a FEI F20 TEM STEM operated at 200 kv. Electrochemical Measurements: Electrochemical measurements were carried out with a potentiostat/galvanostat (WaveNano USB Potentiostat) and a conventional three-electrode test cell. The catalyst ink was prepared by ultrasonically dispersing the mixture of 5 mg catalysts, 1 ml ethanol, and 50 µl 5 wt.% Nafion solutions. 10 µl catalyst inks was pipetted and spread on the glassy carbon disk. A Pt foil and silver/silver chloride (Ag/AgCl) were used as the counter and reference electrodes, respectively. S2

3 Results 1. Scheme Figure S1 Scheme for the synthesis of carbon supported Pt 3 M (Ti and V) bimetallic catalysts. S3

4 2. Calculating the temperature ( G=0) Reaction1: +3 + (Equation S1) Reaction 2: +3 + (Equation S2) The standard enthalpies of formation (H o f) of the solids are all negative, but the change in entropy on reaction is positive due to the formation of a gaseous product, H 2. The free energy ( G) of the forward reaction can then be estimated versus temperature (T) as below: Pt 3 Ti: = (Equation S3) Pt 3 V: = (Equation S4) Equation S3 and S4 assumes that the difference in enthalpy is only weakly temperature dependent and that the temperature dependence can be ignored. Thus the difference in enthalpy equals the difference in free energy at T = 0 K. Table S1 Calculated transition temperatures for alloying Ti and V with Pt from their hydride form Pt-M H MH 2 (kj mol -1 ) H Pt 3 M (kj mol -1 ) S (H 2 ) (J mol -1 K -1 ) T (K) G=0 Pt 3 Ti Pt3V References: (1) Er, S.; Tiwari, D.; de Wijs, G. A.; Brocks, G. Phys Rev B 2009, 79; (2) Bardi, U.; Ross, P. N. J Vac Sci Technol A 1984, 2, 1461; (3) Guo, Q. T.; Kleppa, O. J. J Alloy Compd 1994, 205, 63 S4

5 3. XRD Figure S2 XRD patterns for (a) Pt/C, (b) Pt 3 Ti and (c) Pt 3 V. S5

6 4. Particle size distribution Figure S3 TEM image of (a) Pt/C, (c) Pt 3 Ti and (e) Pt 3 V as well as the corresponding histograms of metal particle diameters for (b) Pt/C, (d) Pt 3 Ti and (f) Pt 3 V. S6

7 5. Simulation Figure S4 Simulated diffraction patterns of Pt 3 Ti (a) and Pt 3 V (b) from [001] zone axis. S7

8 6. TGA Figure S5 Plot of measured TGA for (a) Pt 3 Ti/C, (b) Pt 3 V/C and (c) Pt/C. Thermogravimetric analysis (TGA) of three samples was performed from 40 to 550 o C at a heating rate of 5 o C min -1 under air. The following reactions occurred during TGA. According to these reactions, the actual metal loadings in Pt 3 Ti/C, Pt 3 V/C and Pt/C were calculated. For Pt 3 Ti/C: C+O 2 CO 2 ; Ti+O 2 TiO 2 For Pt 3 V/C: C+O 2 CO 2 ; 4V+5O 2 2V 2 O 5 For Pt/C: C+O 2 CO 2 S8

9 7. EDX Figure S6 EDX spectrum of Pt 3 Ti/C (a) and Pt 3 V/C (b). S9

10 Figure S7 (a) STEM image of Pt3Ti; (b) The mapping image of Pt; (c) The mapping image of Ti; (d) STEM-EDS line spectra of Pt 3 V/C. S10

11 8. Electrochemical tests. Figure S8 CO ad stripping voltammograms of (a) Pt 3 Ti/C, (b) Pt 3 V/C and (c) Pt/C. S11

12 Figure S9 Cyclic voltammograms of the catalysts samples measured in electrolytes of 0.1 M HClO M CH 3 OH solution at a scan rate of 20 mv s -1. S12

13 Figure S10 Current vs. time plots measured by chronoamperometry at 0.6 V (vs. Ag/AgCl) in 0.1 M HClO M CH 3 OH. S13

14 Figure S11 The currents retention at 0.5V versus cycle numbers of linear sweep voltammograms in 0.1 M HClO M CH 3 OH solution at 50 mv s -1. S14

15 Figure S12 Linear sweep voltammograms of (a) ordered and non-ordered Pt 3 Ti/C, and (b) ordered and non-ordered Pt 3 V/C; potential vs. time plots measured by chronopotentiometry for (c) ordered and nonordered Pt 3 Ti/C, and (d) ordered and non-ordered Pt 3 V/C. At a given potential of o.5v, the current densities for non-ordered Pt3Ti/C and non-ordered Pt3V/C are ma mg -1 Pt and ma mg -1 Pt. The potential changes in one hour are 55 mv h -1 and 48 mv h -1 for non-ordered Pt 3 Ti/C and non-ordered Pt 3 V/C. S15