Supporting Information Highly Stretchable and Transparent Supercapacitor by Ag-Au Core Shell Nanowire Network with High Electrochemical Stability Habeom Lee 1, Sukjoon Hong 2, Jinhwan Lee 1, Young Duk Suh 1, Jinhyeong Kwon 1, Hyunjin Moon 1, Hyeonseok Kim 1, Junyeob Yeo 3 *, Seung Hwan Ko 1 * [1] H. Lee, Dr. J. Lee, Dr. Y. D. Suh, Dr. J. Kwon, H. Moon, H. Kim, Prof. S.H. Ko*, Applied Nano and Thermal Science Lab, Department of Mechanical Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Korea [2] Dr. S. Hong Laser Thermal Lab, Department of Mechanical Engineering, University of California, Berkeley, 94720, USA [3] Prof. J. Yeo* Novel Applied Nano Optics Lab, Department of Physics, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Korea [*] To whom correspondence should be addressed. Prof. Seung Hwan Ko (maxko@snu.ac.kr) Prof. Junyeob Yeo (junyeob@knu.ac.kr) [ ] Habeom Lee and Sukjoon Hong contributed equally to this work. S-1
Figure S1. Porous Au nanotube resulted from galvanic replacement of Ag NW In galvanic replacement, the Ag atoms of Ag NW are replaced by Au atoms to form porous Au nanotube. S-2
Figure S2. TEM-EDX line profile of the Ag-Au core shell NW. (a) There is a clear contrast difference between center and either edge. (b) For further examination, TEM-EDX line profile is measured following the yellow line of the TEM image. It is proved by the EDX analysis that the dark contrast at both edges is resulted from Au layer on the Ag NW surface. S-3
Figure S3. Thickness variation of Au shell layer depending on the Au precursor amount. In the Au coating process, the total amount of Au precursor is controlled to determine the thickness of the Au shell of the Ag-Au core shell NW. Except for the amount of the injected precursor solution, all the other experimental conditions are same in both (a) thin and (b) thick cases. 6mL and 12mL of 0.15 mm HAuCl 4 solution is used respectively in each case. S-4
Figure S4. Average diameter change during the Au deposition process. Diameter change of the NWs during the Au deposition process is measured and calculated from multiple SEM images (a) before and (b) after the deposition process. The average diameter change (increase) of the NW is 5.5 nm and this value is nearly 2 times of the estimated thickness of the Au shell from the Figure S3(a). It means that the core Ag NW sustain its initial diameter without any atomic loss by galvanic replacement during the Au deposition process. S-5
Figure S5. CV curves showing difference between pristine Ag NW based electrode and Ag-Au core shell NW based electrode. At the 2 nd cycle of CV measurement, the pristine Ag NW based electrode shows irregular and unstable current value as displayed by red line due to the destruction of the Ag NWs by rapid oxidation at the first CV cycle. In contrast, even at the 50 th cycle, the Ag-Au core shell NW based electrode shows typical rectangular CV curve except for a pair of peaks around 0.17 V and 0.32 V. These peaks are originated from the property of Au. S-6
Figure S6. Fabrication process of highly stretchable and transparent supercapacitor. (a) The Ag- Au core shell NW based electrode is cut into 1 cm x 2 cm square and one side of the electrode is connected to copper tape with silver paste. (b) The electrode is immersed in polymer electrolyte solution for 1 minute except the copper tape. (c) A pair of electrode are kept in fume hood for 4 hours after the electrolyte deposit process to dry the residual water of the electrolyte layer. In this step, the electrolyte gel layer changes to colorless transparent polymer film. (d) The two identical electrodes are attached together by the solidified electrolyte film acting as a glue. Mild pressure is applied on the both sides for another 1 minute. Through this process, a transparent and stretchable supercapacitor is fabricated. S-7
Figure S7. The 500 times charge-discharge measurement results of the Ag-Au core shell NW based supercapacitor. The Charge-discharge test is conducted at fixed input current density 50 µa/cm 2 for 500 times. During the repeated charge and discharge process, the supercapacitor continue operating well without any degradation or failure. The charge-discharge curves in the first 3 cycles and last 3 cycles both have triangular shape with negligible IR drop. This result implies that the Au shell successfully prevents direct contact between the core Ag NW and polymer electrolyte. S-8
Figure S8. CV measurement of the Ag-Au core shell NW based supercapacitor. (a) The CV test is conducted at various voltage scan rate from 50 mv/s to 500 mv/s. At every scanning condition, the CV curve shows nearly rectangular shape which indicates properties of the ideal supercapacitor. (b) Even at the 10 times faster voltage scan rate, the Ag-Au core shell NW based supercapacitor keeps its capacitance over 78%. S-9
Figure S9. Galvanostatic charge-discharge measurement of the Ag-Au core shell NW based supercapacitor. (a) The charge-discharge measurement is conducted with various input current from 10 µa/cm 2 to 200 µa/cm 2. With every input current, the charge-discharge curve shows nearly triangular shape which indicates the properties of the ideal supercapacitor. (b) Even with the 20 times larger input current, the Ag-Au core shell NW based supercapacitor keeps its capacitance over 65%. S-10
Figure S10. CV test of the series connected highly stretchable and transparent supercapacitors. CV test of the series connected supercapacitors is conducted by two electrode method. Upper limit of voltage window varied from 0.8V to 2.4 V. The voltage scan rate is fixed to 500 mv/s in all cases. The series connected supercapacitor is well operated in the large voltage scan range which exceed the turn on voltage of a red LED. S-11