Supporting Information. Au Aerogels: Three-Dimensional Assembly of Nanoparticles and Their Use as Electrocatalytic Interfaces

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1 1 Supporting Information Au Aerogels: Three-Dimensional Assembly of Nanoparticles and Their Use as Electrocatalytic Interfaces Dan Wen, Wei Liu, Danny Haubold, Chengzhou Zhu, Martin Oschatz, Matthias Holzschuh, André Wolf, Frank Simon, Stefan Kaskel, and Alexander Eychmüller* Physical Chemistry, TU Dresden, Bergstrasse 66b, Dresden, Germany Inorganic Chemistry, TU Dresden, Bergstrasse 66, Dresden, Germany Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, Dresden, Germany (A) Figure S1. UV-vis absorbance spectrum (A) and TEM image of the as-prepared β-cd Au NPs. 1

2 (A) Figure S2. TEM image of the Au assemblies induced by 2.5 (3 months) and 7.5 µm (1 week) 17 dopamine. The insets are photograph of Au sols with interaction of 2.5 µm dopamine for 3 18 months and overview TEM images of Au assemblies derived from 7.5 µm dopamine-induced, 19 respectively. 20 (A) (C) (D) (E) (F) Figure S3. SEM (A-C) and TEM (D-F) images of the Au aerogels induced by dopamine: 10, and 100 µm, respectively. The insets of D-F are TEM images with high magnification. 24 2

3 Figure S4. TGA in the temperature range of C under argon flow (A) and EDS of the Au β-cd. 28 (A) Figure S5. The representative HRTEM images of Au assembly intermediates (t=2 min, A) and final aerogel. 3

4 32 (A) (C) (D) (E) (F) (G) Figure S6. TEM images of the NS Au NPs (A), Cit Au NPs and 5-HSTz Au NPs (C), and 35 TEM (D, E and the insets) and SEM images (F, G) of Au gels from NS Au NPs and Cit Au NPs 36 assembly induced by 20 µm dopamine. 37 4

5 (A) (C) Figure S7. CVs of the Au β-cd (A), Au Cit and Au NS (C) modified electrodes correspond to different concentrations of glucose in the range from 0-30 mm in 0.1 M NaOH at a scan rate of 50 mv s 1. 5

6 (A) (C) Figure S8. CVs of the Au aerogel (black line) and corresponding NPs (red line) modified electrodes with 4 mm glucose in 0.1 M NaOH. The capping ligands are (A) β-cd, Citrate and (C) non-stabilizers, respectively. The scan rate is 50 mv s 1. The active amount (Au) of the Au aerogel and Au NPs were evaluated to be equal by ICP-OES. 47 6

7 (A) Figure S9. (A) CVs of the Au β-cd (black line), Au Cit (red line) and Au NS (blue line) modified GCEs in N 2 -saturated aqueous 1 M NaOH+1 M ethanol solution at a scan rate of 50 mv s 1. Current densities for the ethanol oxidation on three Au aerogel modified electrodes. The Au β-cd modified GCE shows the highest activity towards ethanol oxidation, with a specific activity of 2.39 ma cm 2 and a mass activity of 0.31 A mg 1 at 0.18 V. This is comparable to a commercial Pd/C catalyst (with a specific activity of 1.69 ma cm 2 and a mass activity of 0.67 A mg 1 in Figure S8) and much higher than other nano Au-based catalysts, such as Au nanowires, nanoporous Au, or dendritic Au nanocorals. 1 3 In addition, the amount of the adsorbed poisoning species accumulated on the surface can be evaluated by the ratio of the forward (I f ) to the reverse backward anodic peak current density (I b ). Here an I f /I b of 5.1 on the Au aerogels is much larger than that of Pd- and Pt-based nanocatalysts, indicating that ethanol is more efficiently oxidized with little accumulation of carbonaceous residues on the Au aerogel/gce surface. The development of other Au-based aerogels (e.g., AuPd or AuPt bimetallic aerogels) with high activity and extremely high ethanol oxidation efficiency would be of interest for use in direct alcohol fuel cells. 7

8 Figure S10. CVs of commercial Pd/C modified GCE in N 2 -saturated 1 M NaOH aqueous solution in the absence (black line) and presence (red line) 1 M ethanol at a scan rate of 50 mv s 1. The metal concentration of Pd/C is 1.0 mg ml 1 (evaluated by ICP-OES) Figure S11. CVs at the Au β-cd modified GC electrode in 4 mm glucose+0.1 M NaOH solution before (black line) and after (red line) the addition of 0.2 mm ascorbic acid and 0.2 mm uric acid. The scan rate is 50 mv s

9 74 75 Table S1. Comparison of various Au-based nanomaterials and porous metals used for nonenzymatic glucose oxidation. Electrode materials Medium Linear range (mm) µa mm -1 µa mm -1 cm -2 a sensitivity -1 µa mm cm -2 b - ma mm 1 mg -1 Au β-cd 0.1 M NaOH This work Au cit 0.1 M NaOH This work Au NS 0.1 M NaOH This work Au NPs PBS (ph 9.2) [4] Nanoporous Au [5] gold nanoflower on PDDC c 0.1 M NaOH [6] NiO Au nanobelts [7] Gold micropillar array PBS (7.4) [8] Gold Nanocoral PBS (7.4) [9] Honeycomb nanoau networks 1 M NaOH --- ~75.0 [10] Ref Pt 50 Au 50 NPs/MWNTs d PBS (7.4) Up to [11] Gold NW e array 0.1 M NaOH [12] Gold NW array 0.1 M NaOH [13] Dendritic Au@Pt NPs PBS (7.4) [14] 3D nanoporous Au@Cu composite PBS (7.4) 1-20 ~0.4 [15] NHC Au(I) complex 0.1 M NaOH [16] PtPb nanoporous network PBS (7.4) [17] Mesoporous Pt PBS (7.4) [18] a current density per geometric area; b current density per real area; c PDDC (phosphorus doped diamond-like carbon); d MWNTs (Multi-Walled Carbon Nanotube); e NW (Nanowire)

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