Supporting Information. Concave Rhombic Dodecahedral Au Nanocatalyst with Multiple High-Index Facets for CO 2 Reduction

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1 Supporting Information Concave Rhombic Dodecahedral Au Nanocatalyst with Multiple High-Index Facets for CO 2 Reduction Hye-Eun Lee 1, Ki Dong Yang 1, Sang Moon Yoon 1, Hyo-Yong Ahn 1, Yoon Young Lee 1, Hyejin Chang 2, Dae Hong Jeong 2, Yoon-Sik Lee 3, Mi Young Kim 1 and Ki Tae Nam 1 1 Department of Materials Science and Engineering, Seoul National University, , Korea 2 Department of Chemistry Education, Seoul National University, Seoul , Korea 3 School of Chemical and Biological Engineering, Seoul National University, Seoul , Korea This file includes: Figure S1~S15 SCHEME TABLE Calculation of loading amount of nanoparticle catalysts Calculation of Faradaic efficiency REFERENCE

2 Figure S1. Schematic model of concave RD viewed at different angle. As the location 2 is situated at higher position, more atoms exist in the path of electron beam (blue line-electron beam passing through location1 and red line-location 2). This results in the increased intensity of location 2 in the HAADF STEM image compared to the location 1. Figure S2. SEM image of nanoparticles synthesized with p-phenylenediamine Figure S3. Top: Photograph of solutions containing various concentrations of CTAB (0.1M, 10mM, 1 mm and

3 without) mixed with HAuCl4 (10 mm) Bottom: Photograph of solution containing various concentrations of CTAB (0.1M, 10mM, 1mM and without) mixed with HAuCl4 (10mM) and ascorbic acid (0.1 M). Figure S4. SEM image of nanoparticles synthesized under low concentrations of CTAB (10 mm). Figure S5. SEM images of nanoparticle synthesized with 10 mm of ascorbic acid.

4 Figure S6. Photograph of growth solutions prepared with different concentration of ascorbic acid (1 mm ascorbic acid and without ascorbic acid). Figure S7. SEM image of Au nanoparticles synthesized with 500 mm ascorbic acid. Figure S8. SEM images of Au nanoparticles prepared from different concentrations of 4-ATP: (a) 2 mm 4-ATP, (b) 10 mm 4-ATP

5 Figure S9. SEM images of Au nanoparticles after 2 min of reaction time synthesized under (a) thiophenol and (b) 2-aminethiophenol. Figure S10. SEM images of Au nanoparticles after the growing from (a) 4-ATP attached cubocatahedron seed (b) 4-ATP attached RD seed.

6 Figure S11. Chemical selectivity of the electrodes depending on the loading amount of concave RD. (a) GC results, (b) Faradaic efficiency for CO. Figure S12. SEM images of each Au nanoparticle used in CO 2 reduction. (a) Rhombic dodecahedron, (b) cube, and (c) Au film.

7 Figure S13. Mass activity for carbon monoxide (CO) of concave RD and comparison with RD and Cube Au. Figure S14. Stability test for Au nanoparticle for sec. Figure S15. SEM images of concave RD after 5000 sec of electrolysis.

8 SCHEME Scheme S1. Schematic of three-electrode electrochemical cell system TABLE Table S1. Faradaic efficiencies for chemical products V V V V V V V V F.E. CO F.E. H F.E. HCOOH Total Faradaic efficiency for CH 4 was negligible (less than detection limit of gas chromatography) Calculation of loading amount of nanoparticle catalysts We dropped the solution of gold nanoparticles onto the electrode and dried out the water on the electrode. All nanoparticles in the solution were directly deposited onto the electrode. Therefore, the amount of loaded nanoparticles on the electrode can be determined by the number of nanoparticles in the solution. The concentration of RD and cube were calculated using the method described in the previous report. 1 In the case of concave RD, the number of nanoparticles was calculated from the amount of cuboctahedron seeds. In order to measure the mass of nanoparticles, the gold nanoparticle solution with the known concentration was dehydrated using freeze-dryer and then the dried powder was weighed. Calculation of Faradaic efficiency The Faradaic efficiency for the CO was measured without stirring at a various potential from 270 mv to 870 mv, more negative than the thermodynamic reduction potential of CO 2 to CO ( V vs. RHE). The equation for calculating faradaic efficiency is as follows. Faradaic Efficiency moles of product moles of electron 1 equivalents of electron needed for conversion

9 REFERENCE 1) Anal. Chem. 2007, 79,