Supporting Information. Epitaxial Growth of Multimetallic (M = Ni, Rh, Ru) Core-Shell Nanoplates Realized by in situ-produced CO from

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1 Supporting Information Epitaxial Growth of Multimetallic (M = Ni, Rh, Ru) Core-Shell Nanoplates Realized by in situ-produced CO from Interfacial Catalytic Reactions Yucong Yan, Hao Shan, & Ge Li, Fan Xiao, Yingying Jiang, Youyi Yan, Chuanhong Jin, Hui Zhang,,* Jianbo Wu, &,* and Deren Yang,* State Key Laboratory of Silicon Materials, School of Materials Science & Engineering, and Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou, Zhejiang , People s Republic of China & State Key Laboratory of Metal Matrix Composites, School of Materials Science & Engineering, Shanghai Jiao Tong University, Shanghai, , People s Republic of China Department of Forensic Analytical Toxicology, West China School of Basic Science and Forensic Medicine, Sichuan University, Chengdu, Sichuan , People s Republic of China *Correspondence to: msezhanghui@zju.edu.cn, jianbowu@sjtu.edu.cn, mseyang@zju.edu.cn. 1

2 Experimental section Materials. Palladium(II) acetylacetonate (Pd(acac) 2, 99%), platinum(ii) acetylacetonate (Pt(acac) 2, 97%), nickel(ii) acetylacetonate (Ni(acac) 2, 95%), rhodium(iii) acetylacetonate (Rh(acac) 3, 97%), ruthenium(iii) acetylacetonate (Ru(acac) 3, 97%), poly(vinylpyrrolidone) (PVP, MW 29000), oxalic acid (OA), hexadecyltrimethylammonium bromide (CTAB), oleylamine (OAm) and tungsten hexacarbonyl (W(CO) 6 ) were all purchased from Sigma Aldrich. Commercial Pt black and Pt/C (20 wt%) were purchased from Alfa Aesar. Benzyl alcohol (BA), dimethylformamide (DMF), formaldhyde, ethanol, acetone, chloroform and toluene were purchased from Sinopharm Chemical Reagent. All syntheses were carried out in a glass flask (25 ml, Shuniu) or home-made 15 ml Teflon-lined stainless steel autoclave. Synthesis of 18 nm Pd nanoplates. The Pd nanoplates with average edge length of ~18 nm and thickness of ~1.1 nm were synthesized by using a modified protocol based on our previous report. [1] In a typical synthesis, 18 mg of Pd(acac) 2, 30 mg of PVP, 60 mg of CTAB and 30 mg of OA were dissolved in 10 ml of DMF and stirred for 1 h at room temperature. The homogeneous solution was then transferred into a 25 ml glass flask and 100 mg of W(CO) 6 were added into the flask. These processes were carried out in argon atmosphere. The sealed flask was heated at 60 o C under magnet stirring for 3 h and then cooled to room temperature. Due to the use of a large amount of CO derived from W(CO) 6, the overgrowth of the nanoplates along <111> direction perpendicular to the basal {111} planes was greatly inhibited, leading to the thin thickness of Pd nanoplates. The resulting dark blue solution was preserved in argon atmosphere for further use. Synthesis of 10 nm Pd octahedra. The octahedral Pd nanocrystals were synthesized by using a modified protocol based on a previous report. [2] Pd nanocubes with an average edge length of 6 nm were first synthesized. In a typical synthesis, 105 mg of PVP, 300 mg of KBr, 60 mg of AA, and 8 ml of deionized (DI) water were mixed together in a vial and pre-heated under magnetic stirring at 80 o C for 10 min. Then 57 mg of Na 2 PdCl 4 was dissolved in 3 ml of DI water and subsequently added to the pre-heated solution. After the vial was capped, the reaction was maintained at 80 o C for another 3 h. After being collected by centrifugation and being washed three times with DI water, the final product was re-dispersed in 11 ml of DI 2

3 water. The octahedral Pd nanocrystals with an average edge length of 10 nm were synthesized using the as-formed Pd nanocubes as seeds. In a typical synthesis, 105 mg of PVP, 100 µl of formaldhyde, 0.2 ml of an aqueous suspension of the as-prepared Pd nanocubes, and 8 ml of deionized (DI) water were mixed together in a vial and pre-heated at 60 o C for 5 min under magnetic stirring. Then 3 ml of aqueous solution containing 20 mg of Na 2 PdCl 4 was added to the pre-heated solution. After the vial was capped, the reaction was allowed to proceed at 60 o C for additional 3 h. After being collected by centrifugation and being washed three times with DI water, the Pd octahedra were dispersed in BA for further use. Synthesis of Pd@Pt and Pd@PtM (M = Ni, Rh, Ru) nanoplates. In a standard procedure for the synthesis of the Pd@PtNi nanoplates, 300 mg of PVP, mmol of Pt(acac) 2 and mmol of Ni(acac) 2 were dissolved in 10 ml of BA. 4 ml of dark blue solution containing Pd seeds was separated by centrifugation with acetone, and re-dispersed in the above-mentioned reaction solution. After that, the resulting mixture was transferred and sealed into a 15 ml Teflon-lined stainless steel autoclave in argon atmosphere after stirring for 1 h. The autoclave was heated at 200 o C for 12 h and then cooled at room temperature. The final product was collected by centrifugation, washed with ethanol for three times. The Pd@Pt, Pd@PtRh, and Pd@PtRu nanoplates were also synthesized by varying the types of the metal precursors with the same amount under otherwise identical experimental conditions. The thickness of the Pd@PtM (M = Ni, Rh, Ru, none) nanoplates was tuned by varying the amount of the metal precursors to or mmol. Phase-transfer of Pd@PtM (M = Ni, Rh, Ru) nanoplates into hydrophobic solvent. For better observation, the resulting product was precipitated by centrifugation with ethanol, and then dispersed in a mixture of ethanol (toluene for Pd@PtRh nanoplates) and OAm with a volume ratio of 1:4. The mixture was heated at 80 o C for 3 h, then collected by centrifugation with ethanol and re-dispersed in toluene. The washing procedure was repeated three times. Morphological, structural, and composition characterizations. The obtained samples were characterized by X-ray powder diffraction (XRD) using a Rigaku D/max-ga x-ray diffractometer with graphite monochromatized Cu Kα radiation (λ = Å). Transmission electron microscopy (TEM) images of the obtained samples 3

4 were taken using a HITACHI HT-7700 microscope operated at 100 kv. High-resolution transmission electron microscopy (HRTEM) was performed using a FEI Tecnai F30 G2 microscope operated at 300 kv. High-angle annular dark-field scanning TEM (HAADF-STEM) and Energy dispersive X-ray (EDX) mapping analyses were taken on a FEI Titan ChemiSTEM equipped with a probe-corrector and a Super-X EDX detector system. This microscope was operated at 200 kv with a probe current of 50 pa and a convergent angle of 21.4 mrads for illumination. X-ray photoelectron spectrometer (XPS) was performed on ESCALAB 250Xi (Thermo, U.K). The percentages of the elements in the samples were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES, IRIS Intrepid II XSP, TJA Co., USA). GC-MS analysis. Gas chromatography mass spectrometer (GC-MS) measurements were performed on a GC-MS 7890A-5975C (Agilent) with molecular ion selective monitoring. Three kinds of residual solutions for analysis include pure BA, BA containing Pd nanoplates, BA containing Pt salt precursor, Ni salt precursor and Pd nanoplates treated by the typical solvothermal process in an Ar atmosphere at 200 o C for 12 h. For simplicity, no PVP was used in the reaction since PVP only acts as the stabilizing agent, showing no obvious effect on the synthesis of the multimetallic nanoplates (image not shown here). For comparison, a standard sample containing (1) benzene, (2) toluene, (3) benzaldehyde, (4) BA and (5) benzoic acid was prepared to take GC-MS analysis. All of these samples were diluted with acetone in fixed ratio before the GC-MS measurement. FTIR analysis. Fourier Transform infrared spectroscopy (FTIR) was performed on a Vertex 70V (Bruker), operated with a scanning rate of 4 cm -1. Pd nanoplates and Pd@PtNi nanoplates treated or prepared by the typical synthetic protocol in the absence of PVP were cleaned and separated by centrifugation with ethanol for three times and dispersed in ethanol. The samples dispersed in ethanol were loaded on KBr wafers and dried in Ar. These samples were used for the FTIR analysis in Figure 3b. The background was deducted by pure BA treated through the solvothermal process. 4

5 Three residual solutions including pure BA, BA containing Pt salt precursor, Ni salt precursor and Pd nanoplates and BA containing Pt salt precursor, Ni salt precursor and Pd octahedra were directly loaded on KBr wafers for the FTIR analysis in Figure S11b. Electrochemical Measurements. A three-electrode cell was used to take the electrochemical measurement with a CHI760E electrochemical analyzer (CH Instrument, Shanghai). The working electrode was a glassy-carbon rotating disk electrode (GCE) (diameter: 5 mm and area: cm 2 ) from Pine Instruments. A platinum wire with the length of 5 cm was used as the counter electrode and a reversible hydrogen electrode (RHE) which was calibrated with H 2 oxidation/evolution on a Pt polycrystalline RDE electrode was used as the reference electrode. To prepare the working electrode, water dispersions with 10 µg of pure Pd, Pd@Pt or Pd@PtNi nanoplate catalysts were dropped on the GCE. After the dispersion was dried, 3 µl of Nafion solution (0.05%) was deposited on the working electrode. To prepare the inks of the reference catalysts, 5 mg of commercial Pt black or Pt/C (Alfa Aesar, 20wt%) were dispersed in a 5 ml of mixed solution containing DI water, isopropanol, 5% Nafion in the volume ratio of 4:1: After that, the ink was added onto the GCE by a pipette and dried in flowing argon. Before the electrochemical measurement, all these five catalysts were loaded on glass carbon electrodes (GCEs) with a same mass loading of metal and electrochemically cleaned through a cyclic voltammogram (CV) process in 0.1 M HClO 4 solution for 40 cycles. The metal loading on the GCE for all samples was 10 µg. The electrochemical active surface area (ECSA) was determined by integrating the carbon monoxide oxidation charge via CO stripping measurements. As for CO-stripping measurement, the GCE with catalysts loaded was first immersed in 0.1 M HClO 4 solution with CO bubbling for 15 min and then in 0.1 M argon saturated HClO 4 solution to conduct the stripping voltammogram. Methanol oxidation reaction (MOR) was conducted in a mixture solution containing 0.5 M H 2 SO 4 and 0.5 M MeOH at a scan rate of 50 mv/s. The chronoamperometry (I-t) curves were measured at 0.85 V (vs RHE) for 1500 s. 5

6 References [1] Li, Y.; Yan, Y.; Li, Y.; Zhang, H.; Li, D.; Yang, D. CrystEngComm, 2015, 17, [2] Jin, M.; Zhang, H.; Xie, Z.; Xia, Y. Energ. Environ. Sci. 2012, 5,

7 Table S1. ICP-AES data of the (M = Ni, Rh, Ru) multimetallic nanoplates for only Pt/M ratio. Pt : M (M = Ni, Rh, Ru) molar ratio of the metal precursors atomic ratio of Pt/M Pd@PtNi 50 : : 49.8 Pd@PtRh 50 : : 52.9 Pd@PtRu 50 : :

8 Table S2. ECSAs of these five catalysts including pure Pd nanoplates calculated from CO oxidation charge, and their specific and mass activities for MOR achieved by normalizing with ECSA (CO stripping) and Pt mass, respectively. Samples ECSA CO # (m 2 /g metal ) i s (ma/cm 2 ) i m (ma/g Pt ) Pd nanoplates in terms of Pd mass Pt black Pt/C Pd@Pt nanoplates Pd@PtNi nanoplates # A charge of 420 µc/cm 2 was assumed for carbon monoxide oxidation on the surface of metal samples. 8

9 Figure S1. TEM images of the Pd nanoplates seeds that (a) lay flat on the TEM grid and (c) attached vertically on the carbon nanotubes. The corresponding (b) edge length and (d) thickness distributions of the Pd seeds. 9

Figure S2. (a, b) TEM image of the Pd@PtNi multimetallic nanoplates at lower magnification.

10 Figure S2. (a, b) TEM image of the multimetallic nanoplates at lower magnification. (c) TEM image of the multimetallic nanoplates that partially assembled in a face-to-face way. (d) The thickness distribution of the Pd@PtNi multimetallic nanoplates achieved from (c). 10

11 Figure S3. (a, b) Top view HAADF-STEM images of a planar Pd@PtNi multimetallic nanoplate. (c, d) Cross-section HAADF-STEM image of the vertically standing Pd@PtNi nanoplates and the corresponding EDX line profile. 11

Figure S4. TEM image and thickness distribution of the Pd@PtNi nanoplates prepared using the standard procedure, except for different concentration of the metal precursors: (a, b) 0.

12 Figure S4. TEM image and thickness distribution of the nanoplates prepared using the standard procedure, except for different concentration of the metal precursors: (a, b) mol/l of Pt(acac) 2 and mol/l of Ni(acac) 2 and (c, d) mol/l of Pt(acac) 2 and mol/l of Ni(acac) 2. The insets in (b, d) correspond to TEM images at a higher magnification. The scale bars in insets are 3 nm. 12

13 Figure S5. (a) XRD pattern of the nanoplates with the standard diffraction positions for Pd (black lines), Pt (dash lines), and Ni (dot lines). (b) XRD pattern of nanoplates. 13

14 Figure S6. HAADF-STEM images of the vertically standing nanoplates and EDX mapping images of the planar nanoplates for (a, b) nanoplates, (c, d) nanoplates, and (e, f) nanoplates, respectively. 14

15 Figure S7. TEM images at a lower magnification and thickness distributions of the planar (a, b) Pd@Pt nanoplates, (c, d) Pd@PtRh nanoplates, and (e, f) Pd@PtRu nanoplates, respectively. The insets in (a, c, e) correspond to TEM images of the vertically standing nanoplates. 15

16 Figure S8. TEM images (scale bar of 30 nm) and thickness distributions of the nanoplates prepared using the standard procedure, except for different concentration of the metal precursors: (a, b) mol/l of Pt(acac) 2 and mol/l of Rh(acac) 3 and (c, d) mol/l of Pt(acac) 2 and mol/l of Rh(acac) 3. The insets in (b, d) correspond to TEM images at a higher magnification. The scale bars in insets are 3 nm. 16

17 Figure S9. TEM images (scale bar of 30 nm) and thickness distributions of the nanoplates prepared using the standard procedure, except for different concentration of the metal precursors: (a, b) mol/l of Pt(acac) 2 and mol/l of Ru(acac) 3 and (c, d) mol/l of Pt(acac) 2 and mol/l of Ru(acac) 3. The insets in (b, d) correspond to TEM images at a higher magnification. The scale bars in insets are 3 nm. 17

18 Figure S10. TEM images of (a) (c) (e) nanocrystals prepared by direct inflowing CO at a rate of 50 ml/min. TEM images of (b) Pd@PtNi, (d) Pd@PtRh, (f) Pd@PtRu nanocrystals prepared using the same molar amount of Pd octahedra as the seeds relative to the Pd nanoplates. 18

19 Figure S11. (a) TEM image of Pd octahedral seeds; (b) FTIR spectra of BA, BA containing Pd nanoplates, and BA containing Pd octahedra treated by a solvothermal process at 200 o C for 12 h. 19

20 Figure S12. CO stripping of (a) the nanoplates (red), nanoplates (green), Pt/C (blue), and Pt black (black) and (b) the pure Pd nanoplates in 0.1 M HClO 4 solution at a scan rate of 50 mv/s. 20

21 Figure S13. CV curve of the Pd nanoplates in a mixed solution containing 0.5 M H 2 SO 4 and 0.5 M MeOH solution at a scan rate of 50 mv/s. 21

22 Figure S14. TEM image of (a) nanoplates and (b) nanoplates after electrochemical measurements. 22

Synthesis of Pt Ni Octahedra in Continuous-flow Droplet Reactors for the Scalable Production of Highly Active Catalysts toward Oxygen Reduction

Supporting Information for Synthesis of Pt Ni Octahedra in Continuous-flow Droplet Reactors for the Scalable Production of Highly Active Catalysts toward Oxygen Reduction Guangda Niu,, Ming Zhou, Xuan