Supporting Information (SI) for

Transcription

1 Supporting Information (SI) for Component-Controlled Synthesis and Assembly of Cu-Pd Nanocrystals on Graphene for Oxygen Reduction Reaction Yulin Zheng, Shulin Zhao, Suli Liu, Huanhuan Yin, Yu-Yun Chen, Jianchun Bao, Min Han,*,, and Zhihui Dai*, Jiangsu Key Laboratory of Biofunctional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing , P. R. China State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Solid State Microstructures, Nanjing University, Nanjing , P. R. China * To whom correspondence should be addressed @njnu.edu.cn (M. Han); daizhihuii@njnu.edu.cn (Z. Dai) Tel/Fax: This information contains: (1) Composition identification of Cu x Pd y NCs by EDS and ICP (Table S1) (2) XRD patterns of the obtained Cu x Pd y NCs (Figure S1) (3) TEM images of pure Cu and pure Pd control samples (Figure S2) (4) XPS spectra of the Cu x Pd y NCs (Figure S3) and the detailed discussion (5) TEM image and Raman spectrum of pure G control sample (Figure S4) (6) Magnified Raman spectrum for G-Cu 3 Pd NCPs (Figure S5) (7) Composition characterization of G-Cu 4 Pd, G-CuPd, G-CuPd 3 and G-CuPd 4 NCPs (Figure S6 and Figure S7) (8) EIS spectra for pure Cu x Pd y NCs (Figure S8) (9) Equivalent circuits for fitting the EIS data of G-Cu x Pd y NCPs (Figure S9) and pure Cu x Pd y NCs (Figure S10) and parameters of the best-fitted results of EIS spectra for G-Cu x Pd y NCPs (Table S2) and pure Cu x Pd y NCs (Table S3) (10) Comparison of the R et values of the G-Cu x Pd y NCPs and pure Cu x Pd y NCs (Table S4) Page S1

2 (11) Magnified CVs for G-Cu 3 Pd NCPs (Figure S11) (12) The mass specific activities of the G-Cu x Pd y NCPs that calculated according to the amount of pure Pd in the NCPs (Figure S12) (13) The plots for the size of Cu x Pd y NCs and the mass activities of the G-Cu x Pd y NCPs (based on per mg of Pd) at V versus the atomic percentage of Pd (Figure S13) (14) Magnified durability test curves for G-Cu 3 Pd NCPs and commercial Pt/C catalyst (Figure S14) Table S1. The composition of the Cu x Pd y NCs identified from EDS and ICP analysis sample alloy composition from EDS alloy composition from ICP Cu 4 Pd Cu 78 Pd 22 Cu 81 Pd 19 Cu 3 Pd Cu 74 Pd 26 Cu 74 Pd 26 CuPd Cu 48 Pd 52 Cu 50 Pd 50 CuPd 3 Cu 23 Pd 77 Cu 24 Pd 76 CuPd 4 Cu 19 Pd 81 Cu 21 Pd 79 Page S2

3 Figure S1. The XRD patterns of the obtained Cu 4 Pd, Cu 3 Pd, CuPd, CuPd 3 and CuPd 4 NCs, respectively. Figure S2. (A) TEM image of pure Cu NCs control sample synthesized under the same experimental conditions. (B) TEM image of pure Pd NCs control sample prepared using the same synthetic conditions. Figure S3. (A) Fine XPS spectra of Cu 2p regions for the obtained Cu 4 Pd, Cu 3 Pd, CuPd, CuPd 3 and CuPd 4 NCs as well as pure Cu NCs. (B) Fine XPS spectra of Pd 3d regions for the obtained Cu 4 Pd, Cu 3 Pd, CuPd, CuPd 3 and CuPd 4 NCs as well as pure Pd NCs. Page S3

4 The surface structure and electronic effects of the obtained Cu 4 Pd, Cu 3 Pd, CuPd, CuPd 3 and CuPd 4 NCs are further characterized by X-ray photoelectron spectroscopy (XPS). Figure S3 shows the XPS spectra of Cu 2p and Pd 3d regions for all alloy NCs. On the whole, the binding energies of Cu 2p peaks (Figure S3A) in the alloy NCs are shifted negatively with the increase of Pd atomic percentage compared with that of pure Cu NCs, implying that the interactions between Cu and Pd are strong and the atomic ensemble effects are obvious in the alloy NCs. In contrast to the relatively monotonous evolution of the binding energies of Cu 2P peaks in the alloy NCs, the corresponding change trend of the binding energies of Pd 3d peaks (Figure S3B) becomes complicated with the increase of Cu atomic percentage in the alloy NCs, indicating that Cu and Pd atoms play different roles on the surface electronic structure of the alloy NCs. When the Cu atomic percentage is increased from 20% to 50%, both the binding energies of Pd 3d5/2 and Pd 3d 3/2 peaks in the alloy NCs are shifted negatively compared with that of pure Pd NCs. While further increasing the Cu atomic percentage from 50% to 80%, both the binding energies of Pd 3d5/2 and Pd 3d 3/2 peaks in the alloy NCs gradually shift to the positive direction in contrast to pure Pd NCs. The largest positive shift phenomenon is observed as the Cu atomic percentage is 75%, revealing that the Cu 3 Pd NCs have unique electronic structure compared with that of other alloy NCs. The obviously positive-shifted Pd 3d peaks in Cu 3 Pd NCs relative to pure Pd NCs reveals that their first surface layers are not dominated by Pd atoms and there may be some Cu atoms that are intercalated to disturb the Pd-Pd interactions. From current XPS binding energy data, it seems that the surface of Pd possesses positive charge formally while that of Cu has negative charge. This abnormal charge distribution gives a hint that the electronic coupling between Cu and Pd in the alloy NCs is very complicated. The detailed reason for this abnormal charge distribution is not fully clear at present. In contrast to the positive-shifted Pd 3d peaks, the nearly unchanged Cu 2P peaks in Cu 3 Pd NCs relative to pure Cu NCs discloses that the subsurface layers are occupied by Cu atoms and there are no Pd atoms to disturb Cu-Cu interactions. That is to say, the Pd-Cu and Cu atomic layer may be alternatively arranged in Cu 3 Pd NCs to form chemically ordered alloy phase structure. Page S4

5 Figure S4. (A) TEM image of the G control sample. The inset shows the corresponding photograph for the dispersion solution of G in DMF. (B) Raman spectrum for the G control sample. Figure S5. Raman spectrum of the G-Cu 3 Pd NCPs magnified from 1000 to 1800 cm -1. For comparison, the Raman spectrum for pure G is also given in this figure. Page S5

6 Figure S6. The EDS patterns of the obtained (A) G-Cu 4 Pd, (B) G-CuPd, (C) G-CuPd 3, and (D) G-CuPd 4 NCPs, respectively. Page S6

7 Figure S7. The XRD patterns of the obtained (A) G-Cu 4 Pd, (B) G-CuPd, (C) G-CuPd 3, and (D) G-CuPd 4 NCPs, respectively. Figure S8. (A) Electrochemical impedance spectra (EIS) or Nyquist curves for Cu 3 Pd (a), Cu 4 Pd (b) and CuPd 3 (c) NCs. (B) Nyquist curves for CuPd (a), and CuPd 4 (b) NCs. Page S7

8 Figure S9. The equivalent circuits for fitting the Nyquist curves of (A) G-Cu 4 Pd, (B) G-Cu 3 Pd, (C) G-CuPd 3, (D) G-CuPd, and (E) G-CuPd 4 NCPs, respectively. Table S2 Parameters of the best-fitted results of EIS spectra for G-Cu x Pd y NCPs modified GCEs CPE W Samples Rs (Ω) Ret (Ω) (Warburg Y o N impedance) G-Cu 4 Pd (nMho) (nmho) G-Cu 3 Pd (μmho) (nmho) G-CuPd (μmho) (nmho) G-CuPd (μmho) (nmho) G-CuPd (nmho) (nmho) Page S8

9 Figure S10. The equivalent circuits for fitting the Nyquist curves of pure (A) Cu 4 Pd, (B) Cu 3 Pd, (C) CuPd 3, (D) CuPd, and (E) CuPd 4 NCs, respectively. Table S3 Parameters of the best-fitted results of EIS spectra for pure Cu x Pd y NCs modified GCEs CPE W Samples Rs (Ω) Ret (Ω) (Warburg Yo N impedance) Cu 4 Pd (μmho) (nmho) Cu 3 Pd (μmho) (μmho) CuPd (nmho) (nMho) CuPd (nmho) (nMho) CuPd (nmho) (nMho) Page S9

10 Table S4. Comparison of the Ret values of G-Cu x Pd y NCPs and pure Cu x Pd y NCs Samples Ret (Ω) Samples Ret (Ω) G-Cu 4 Pd 198 Cu 4 Pd 295 G-Cu 3 Pd 181 Cu 3 Pd 272 G-CuPd 386 CuPd 460 G-CuPd CuPd G-CuPd CuPd Figure S11. The magnified CV plots of the G-Cu 3 Pd NCPs in N 2 - and O 2 -saturated 0.1 M KOH at the potential window of -0.3 to 0 V (vs. SCE). Page S10

11 Figure S12. The mass specific activities of various G-Cu x Pd y NCPs at different potential that calculated according to the mass of pure Pd in the NCPs. Figure S13. The corresponding plots for the size of Cu x Pd y NCs and the mass activities of the G-Cu x Pd y NCPs (based on per mg of Pd) at V versus the atomic percentage of Pd in the Cu x Pd y NCs components of the NCPs. Page S11

12 Figure S14. The magnified durability test plots for (A) G-Cu 3 Pd NCPs and (B) commercial Pt / C catalyst. Page S12