Electrospun Mat of Polyvinyl Alcohol/Graphene Oxide for Superior Electrolyte Performance

Transcription

1 Supporting Information Electrospun Mat of Polyvinyl Alcohol/Graphene Oxide for Superior Electrolyte Performance Qin Pan, Ningjun Tong, Nanfei He, Yixin Liu, Eunkyoung Shim, Behnam Pourdeyhimi, and Wei Gao * The Nonwovens Institute, North Carolina State University, Raleigh, North Carolina 27606, United States Department of Textile Engineering, Chemistry & Science, College of Textiles, North Carolina State University, Raleigh, North Carolina 27695, United States * (W. G.) wgao5@ncsu.edu Address: 1020 Main Campus Dr. Raleigh, NC, , USA S-1

2 Figure S1. SEM image of (a) PVA, (b) PVA-GO electrospun mat, with PVA:GO=25:1, w/w, (c) PVA-GO mat, with PVA:GO=10:1, w/w, (d) photographs of PVA and PVA-GO mats. S-2

3 Figure S2. X-ray diffraction pattern of PVA and PVA-GO electrospun mat. Figure S3. EIS spectra evolution of (a) CC supercapacitor on PVA-GO mat stored at 25, 45±5% RH over 1 month (high frequency region), inset showing the whole spectra from 0.01 Hz to 1 M Hz, (b) CC supercapacitor on PVA mat stored at the same condition after 1 week. S-3

4 Figure S4. (a) Cyclic voltammetry curves and (b) EIS spectra of PVA-GO-m in 6 M KOH when upon saturation and after stored at 25, 45 ± 5% RH for 1 day. Figure S5. Cross-sectional SEM of monolithic supercapacitor with sandwich geometry on PVA-GO mat, showing the interface between LGO and PVA-GO mats. S-4

5 Figure S6. (a) Cyclic voltammetry curves and (b) EIS spectra of PVA-GO-m before and after bending. The inset picture in (a) shows the measurement during bending. The inset figure in (b) shows the zoom-in region in the high frequency region, indicating after bending the resistance increases slightly. The capacitance exhibited no significant changes (unbent: 4.5 mf cm -2 ; bent: 4.6 mf cm -2 ); while the resistivity showed slight increase upon bending (unbent: 457 kω cm; bent: 469 kω cm), probably due to less intimate contact between the LGO flakes. Figure S7. The equivalent circuit used for fitting the EIS spectra generated in the Z-view software S-5

6 Figure S8. SEM image of GO flakes. Figure S9. Charge-discharge curves of PVA-GO-m at different current densities. S-6

7 Figure S10. Ragone plot of the PVA-GO-m supercapacitor compared with similar LGO micro-supercapacitors reported in the literature. Data adapted from ref [1-4]. Figure S11. Cycling performance of PVA-GO-m supercapacitors in 0.01 M H 2 SO 4. S-7

8 Figure S12. Rate capability of the PVA-GO-m supercapacitor. (a) Overlapped CV curves at various scan rates from 10 to 1000 mv s -1. (b) A plot of areal capacitance vs scan rate -1/2. Figure S12 (a) overlaps the CV curves at different scan rates from 10 to 1000 mv s -1. The shape of CV curves retains rectangular even when the scan rate is high as 400 mv s -1, indicating the excellent ion diffusion of our supercapacitor. Figure S12 (b) shows the plot of areal capacitance vs scan rate -1/2. The separation of diffusion-controlled region and capacitive-controlled region occurs at very high scan rate of 200 mv s -1, corresponding with the good rate capability observed in (a). At the scan rate lower than 200 mv s -1 (region 1), the capacitance is almost independent of the scan rate, indicating that the electrolyte diffusion is not the limiting factor for charge-storage within this time domain. The extrapolated y-intercept yields the infinite sweep-rate capacitance. The capacitance started to deviate far from it when the scan rate is higher than 200 mv s -1, when the electrolyte diffusion becomes the limiting factor for the charge storage. S-8

9 Figure S13. Raman spectra of LGO and GO. After laser treatment I d /I g increases from 0.88 to S-9

10 Figure S14. The chronological evolution of charge-discharge profiles of the PVA-GO-m supercapacitor from D0 (a), D1 (b), D3 (c) to D5 (d). D means the number of storage days, e.g. D0 represents as-made. Table S1 Fitting Results for Nyquist Plot with Equivalent Circuit in Figure S7 R s /Ω R ct / Ω CPE ct W o CPE dll Y 0 /F α R w /W T w /s α Y 0 /F α PVA-GO-m 0D PVA-GO-m 1D PVA-GO-m 2D PVA-GO-m 3D PVA-GO-m 6D PVA-GO-m 12D PVA-GO-m 36D PVA-m 0D PVA-m 3D PVA-m 10D PVA-m 14D S-10

11 PVA-m 36D PVA-gel 0D PVA-gel 1D PVA-GO gel 0D PVA-GO gel 1D Table S2 Ionic conductivities of various polymer electrolytes reported in literature Polymer Electrolyte Proton Testing/Storage Electrode Ref Conductivity (S cm -1 ) Environment Material PVA-GO-m Soaked in 1 M H 2 SO 4 LGO This work PVA-m Soaked in 1 M H 2 SO 4 LGO This work Nafion-117 (commercial) Stored wet over water PPy/PSS 5 Sulfonated commercial PEEK Soaked in 0.25 M H 2 SO 4 before cell assembly activated carbon 6 P(VDF-HFP)-EMIMBF 4 -GO gel 3.5~ EMIMBF 4 as electrolyte activated carbon 7 PVA Borate gel M KCl activated carbon 8 PVA-KOH-K 3 [Fe(CN) 6 ] gel polymer PVA:KOH:K 3 [Fe(CN) 6 ]: 1:1:0.01 activated carbon 9 PAN/PEO 1~ Soaked in 1.0 M LiPF 6 in EC/DMC/DEC PVA-BMIMCl-Li 2 SO PVA:BMIMCl:Li 2 SO 4 : 1:3:0.4 LiFeO 4 /Li battery 10 activated carbon 11 PVA-HClO M HClO 4 black pearl carbon 12 Methylene blue (MB) adsorption method to determine the surface area of LGO and PVA-GO mat. Due to our limited access to BET, the surface area of LGO and PVA-GO mat were measured by methylene blue (MB) adsorption method This method has been used for determining the surface area of clay minerals and activated carbon generally by industries for several decades. In a typical test, certain amount of LGO was stirred in the methylene blue solution S-11

12 continuously at a rate of 300 rpm for a total of 40 hours to reach the maximum adsorption. The mixture was then allowed to settle and centrifuged to remove any suspended material. The concentration of MB in the supernatant was measured by UV-vis spectroscopy at a wavelength of 664 nm, and compared with the initial methylene blue concentration. The specific surface is calculated from the amount of absorbed MB using the following equation: S s = m MB A MB 1 m s where m MB is the amount of absorbed MB, A MB is the area covered by one MB molecule (assumed to be 130 Å 2 ), is the molar molecular weight of MB, m s is the amount of material (LGO). Based on this calculation, for LGO, the surface area is m 2 g -1 ; while for PVA-GO mat, the surface area is 75.1 m 2 g -1. Figure S15 The CV curves of PVA-GO-m supercapacitor with and without the compression of 30 g weight. S-12

13 Figure S16 Comparison of calculating capacitance from CV and charge/discharge curve. (a) The CV curve of PVA-GO-m supercapacitor at the scan rate of 40 mv s -1. (b) the charge/discharge curve at the current of 0.25 ma. The capacitance calculated from the CV curve was 6.2 mf cm -2, while that calculated based on the discharge curve is 7.4 mf cm -2. Here we use the average slope of the entire discharge curve. Generally, the results are comparable, with the value from the discharge curve being slightly higher. S-13

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