Electronic Supplementary Information

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1 Electronic Supplementary Material (ESI) for CrystEngComm. This journal is The Royal Society of Chemistry 2017 Electronic Supplementary Information Facile synthesis of self-assemblies of ultrathin round Pd nanosheets or nanorings and their enhanced electrocatalytic activities Huan Wang, a Xing He, a Yanxi Zhao, a Jinlin Li, a Tao Huang,* a and Hanfan Liu ab a Key Laboratory of Catalysis and Material Science of the State Ethnic Affairs Commission & Ministry of Education, Hubei Province, College of Chemistry and Material Science, South- Central University for Nationalities, Wuhan , China b Institute of Chemistry, Chinese Academy of Science, Beijing , China * huangt208@163.com 1

2 Fig. S1 TEM image with different scales of the as-prepared self-assemblies of ultrathin round Pd nanosheets. The molar ratio of Pd(acac)2/PVP/KI/NaAc was 1/9/4/4 and the concentration of Pd(acac)2 was 6.8mM 2

3 Intensity (a.u.) (111) (200) 200 (220) (311) 100 (222) theta(degree) 500 (111) 400 Intensity (200) (220) (311) Theta/degree Fig. S2 XRD patterns of the self-assemblies of round ultrathin Pd nanosheets 3

4 Pd 3d 5/ Intensity counts/s Pd 3d 3/ Pd 0 Pd Binding energy/ev Fig. S3 XPS spectrogram of the self-assemblies of round ultrathin Pd nanosheets 4

5 (a) (b) Fig. S4 TEM images of Pd nanoparticles obtained at different temperatures. (a) 80 C; (b) 120 C 5

6 Fig. 5S TEM images of Pd nanoparicles prepared in the absence of CO. 6

7 (a) CO ox on Pd(111) J/(mA cm -2 ) V Potential/V(SCE) J/(mA cm -2 ) (b) Potential/V(SCE) J/(mA cm -2 ) (c) CO ox on Pd(111) 0.857V Potential/V(SCE) Fig. S6 CO stripping voltammetry of the Pd nanosheet self-assemblies in 0.1 M H2SO4 solution. (a) The freshly-prepared Pd nanosheet self-assemblies without introducing any additional CO; (b) the second potential scanning; (c) after dosing CO for 15 min for clean Pd nanosheet self-assemblies. 7

8 (a) (b) Fig. S7 TEM images of the products prepared in the presence of sodium benzoate (a) or sodium oxalate (b) instead of sodium acetate. 8

9 (a) (b) Fig. S8 HAADT-STEM image (a) of a single Pd nanosheet self-assembly and the corresponding EDX mapping image of I ions (b). 9

10 (a) (b) Fig. S9 TEM images of the products obtained with adding different amount of KI. The molar ratio of Pd(acac)2/PVP/KI/NaAc: (a) 1/9/2/4; (b) 1/9/8/4. 10

11 (a) (b) Fig. S10 TEM images of the Pd nanocrystals with adding others halogen. (a) KCl; (b)kbr 11

12 Fig. S11 TEM image of the product prepared under CO reducing atmosphere at a reaction of 4 h. 12

13 Pd(II) 0.5 h 3 h, 100 C 2 h 70 C etching Fig. S12 Schematic illustrations of the formation procedure and shape evolution of selfassemblies of ultrathin Pd nanosheets and nanorings. 13

14 Fig. S13 TEM image of small Pd nanoparticles. The mean size was 5 nm. 14

15 Current/mA assemblied Pd nanosheets assemblied Pd nanorings Pd nanoparticles Potential/V(SCE) Fig. S14 Cyclic voltammograms of different Pd catalysts in 0.5 M H2SO M HCOOH solution at a scan rate of 50 mv s 1 between -0.2 and 1.0 V. 15

16 (a) (b) (c) (d) J/(mA cm -2 ) monodispersed Pd nanosheets monodispersed Pd nanorings Potential/V(SCE) Fig. S15 TEM images of monodispersed Pd nanosheets (a and b) and monodispersed Pd nanorings (c and d); (e) CV curves for the electrocatalytic oxidation of formic acid by the monodispersed Pd nanosheets, monodispersed Pd nanorings and Pd black. The formic acid oxidation was recorded in 0.5 M H2SO4 solution at a scan rate of 50 mv s 1 between -0.2 and 1.0 V. The current densities were measured to be 6.41 ma cm -2 at V on the monodispersed Pd nanorings and 5.82 ma cm -2 at V on the monodispersed Pd, nansheets, respectively. 16