Porous dendritic platinum nanotubes with extremely high. activity and stability for oxygen reduction reaction

Transcription

1 Supplementary Information Porous dendritic platinum nanotubes with extremely high activity and stability for oxygen reduction reaction Gaixia Zhang 1,,, Shuhui Sun 1,,, ei Cai 3, Yong Zhang 1, Ruying Li 1 & Xueliang Sun 1, * 1 Department of echanical and aterials Engineering, the University of Western Ontario, London, Ontario N6A 5B9, Canada Institut National de la Recherche Scientifique-Énergie, atériaux et Télécommunications, Université du Québec, Varennes, QC J3X 1S, Canada 3 General otors Research and Development Center, Warren, ichigan, , USA * xsun@eng.uwo.ca 1

2 (a) (b) Figure S1. (a) SE image of uniform, large-scale synthesis of Ag dendrites. (b) EDX spectrum of Ag dendrites.

3 Figure S. EDX spectrum of Pt dendrites. 3

4 (a) (b) (c) (d) Figure S3. Large-scale synthesis of (a,b,c) Ag dendrites (10 g) and (d) Pt dendritic tubes (1.5 g). Note that, considering the high price of Pt precursor, we did not try to synthesize greater amount of Pt dendritic tubes. However, we believe that a much greater quantity (for the commercialization) of Ag and Pt dendritic structures can be obtained using this simple method when necessary. 4

5 r (Pt) R (Pt) L Figure S4. Schematic of a single branch of a Pt hollow dendrite. Theoretical calculation of the wall thickness of the Pt tubes. Based on the similar diameters (about 40 nm) of most branches of Ag dendrite template, to simplify the calculation, we suppose that one Pt dendrite has N branches of tubes. In addition, it is assumed that the conversion from Ag to Pt is complete and the walls of Pt tubes are fully condensed. Thus, according to the reaction equation 4Ag ( PtCl6 ) Pt 4AgCl Cl, the molar number of Ag is four times of that of Pt. n n 4 ( Pt ) V ( Pt) V 4 ( Pt) ( Pt) N R( Ag ) L ( Pt ) N ( R( Pt ) r( Pt ) ) 4 ( Pt ) L R ( 4 Pt) ( Pt) ( R ( Pt) r ( Pt) ) Where ρ is the density, V is the volume, is the molar mass, N is the branch number of a dendrite, L is the branch length, R (Ag) is the radius of the Ag branch, and r (Pt) and R (Pt) are the inner and outer radii of the Pt tube, respectively. The detailed values are the following: ( Ag) ( Pt) 1. 4 g cm g cm g mol 1 5

6 ( Pt ) g mol 40 R nm 0nm 46 R( Pt ) nm 3nm 1 Therefore, r( Pt ) 1. 0nm. So the wall thickness of Pt nanotubes is R( Pt) r( Pt) 3nm 1nm nm. Considering the fact that Pt dendritic tubes are composed of a large number of Pt nanocrystals with same orientation, rather than fully condensed bulk crystals, it is reasonable that the wall thickness of the as-synthesized Pt tubes (about.5 nm) is slightly larger than the theoretical one (.0 nm). 6

7 Figure S5. HRTE images taken from (a) the stem and the junctions of a dendritic branch and (b) one leaf of the Ag dendrites. Interestingly, all the growth directions are along <111>. This implies that the Ag dendrites grow along a preferential direction. In addition, this HRTE image also shows that, because the stem and the side branch have identical crystal orientation, the total dendrite structure is a single crystal. 7

8 a b 00 nm 00 nm c d 00 nm 00 nm e 00 nm Figure S6. TE images of the morphological evolution from solid Ag dendrites to hollow Pt dendritic tubes, as a function of reaction time, (a) 0 min (Ag dendrites), (b) 1 min, (c) 8 min, (d) 1 min, (e) 4 hours (Pt hollow dendrites). 8

9 Intensity (arb. units) min 1 min AgCl(111) AgCl(00) Ag(111) Pt(111) $ Ag(00) AgCl(0) $ (deg.) Pt(00) AgCl(311) AgCl() Ag(0) Figure S7. Comparison of XRD patterns of the samples taken as a function of reaction time for 8 min and 1 min, respectively. 9

10 a b c d 0 nm 5 µm 5 nm 100 nm Figure S8. (a,b) SE images of the as-received commercial g powder. (c,d) SE image and TE image of Pt urchin-like structures, obtained via the replacement reaction between g and H PtCl 6. 10

11 a Ag branch H PtCl 6 RT AgCl PtCl 6 - b c d Pt tube Figure S9. Schematic illustration of the formation mechanism from Ag wire to Pt tube. 11

12 a b 0.3 nm 00 nm 5 nm Figure S10. TE and HRTE images of Pt dendritic tube catalyst, after 4000 cycles ADT test. 1