Supporting Information Scalable Holey Graphene Synthesis and Dense Electrode Fabrication Toward High Performance Ultracapacitors Xiaogang Han, 1 Michael R. Funk, 2,3 Fei Shen, 1 Yu-Chen Chen, 1 Yuanyuan Li, 1 Caroline J. Campbell, 4 Jiaqi Dai, 1 Xiaofeng Yang, 1 Jae-Woo Kim, 4 Yunlong Liao, 4,6 John W. Connell, 3 Veronica Barone, 5 Zhongfang Chen, 6 Yi Lin, *,2,4 and Liangbing Hu *,1 1. Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA 2. Department of Applied Science, The College of William and Mary, Williamsburg, VA 23185, USA 3. Mail Stop 226, Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia 23681, USA 4. National Institute of Aerospace, 100 Exploration Way, Hampton, Virginia 23666, USA 5. Department of Physics and Science of Advanced Materials Program, Central Michigan University, Mount Pleasant, MI 48859, USA 6. Department of Chemistry, Institute for Functional Nanomaterials, University of Puerto Rico, Rio Piedras Campus, San Juan, Puerto Rico 00931 1
Figure S1. Thermogravimetric analysis (TGA) for the starting graphene. The temperature ramp was 10 o C/min in air. 2
Figure S2. A typical TEM image of starting graphene, showing largely intact sheet surface. 3
Differential Pore Volume (cm 3 /g) 6 4 2 h-graphene (430C/10h) Graphene Control 0 1 10 100 Pore Radius (nm) Figure S3. Barrett-Joyner-Halenda (BJH) pore size distribution plot for the starting graphene ( ) and an h-graphene sample obtained from 430 C/10h ( ). 4
C/O from XPS (atom ratio) 60 40 20 0 starting graphene 430 o C/3h 430 o C/10h 480 o C/3h Figure S4. C/O ratio from X-ray photoelectron spectra (XPS) of starting graphene and h- Graphene obtained from 430 o C/3h, 430 o C/10h, and 480 o C/3h. 5
Figure S5. XPS C-1s data for (a) the starting graphene and (b) the h-graphene sample used for electrode fabrication. 6
Figure S6. Fourier transform infrared spectroscopy (FT-IR) of starting graphene and h-graphene obtained from 430 o C/3h, 430 o C/10h, and 480 o C/3h. The oxygen-containing groups adsorption peaks are highlighted with guide lines (they are intrinsically small). FTIR results are supporting evidence to prove the increase of oxygen-groups content under more oxidative conditions. For example, the intensities of the peaks at ~1720 (-COO-), ~1090 (-C-O-), and ~900 cm -1 (-C-O-C-) all increased for h-graphene samples. 7
Figure S7. Contact angle test results for water (top), NMP (middle), and EMI:TFSI (bottom) on graphene and h-graphene film, separately. The corresponding movies M1-4 can be found as separate files in the Supporting Information. 8
Figure S8. Capacitance retention and corresponding Coulombic efficiency for h-graphene ultracapacitor cycling 100 000 at 3 A/g. 9
Current (A/g) 1.5 1.0 0.5 0.0-0.5 h-graphene film 8.9 µm thickness 50 mv/s 30 mv/s 10 mv/s -1.0 0.0 0.5 1.0 1.5 2.0 2.5 Voltage (V) Figure S9. Cyclic voltammetry (CV) at different scan rates for the thick h-graphene film ultracapcitor. Rectangular shapes indicate the capacitive behavior. 10
3 h-graphene film (8.9 µm thickness) 3 A/g 2 Ewe (V) 1 0 1 st cycle 9366 th cycle 0 30 60 90 256650 256700 Time (s) Figure S10. Galvanostatic change/discharge curves of the thick h-graphene film ultracapacitor at a constant current density of 3 A/g. 11
60 Specific capacitance (F/cm 3 ) 50 40 30 20 10 0 3 A/g h-graphene film (8.9 µm thickness) 0 3000 6000 9000 12000 100 80 60 40 20 0 Couloumbic efficiency (%) Cycle Figure S11. Cycling performance with Coulombic efficiency for the thick h-graphene film ultracapacitor at a constant current density of 3 A/g. 12
Figure S12. Nyquist EIS plots of h-graphene, showing the imaginary part versus the real part of impedance. The inset is the highlight of the high-frequency ranges. The frequency is from 1 MHz to 100 mhz. 13
Figure S13. HR-TEM images of h-graphene obtained from 430 C/10h, showing 5-15 layers in the graphene sheets. 14
Figure S14. Model system for the QM/MM calculations employed in this work. We perform QM/MM calculations extending the QM region by including the ion and a larger number of C atoms into the DFT calculations in order to check the validity of our models. For instance, for a hole of 1.3 nm in diameter Model 1 consists of 986 atoms in the low level region and 66 atom plus the molecular system under consideration in the high level region. Model 2 for the same hole consists of 882 atoms in the low level region and 170 atoms plus the molecule under consideration in the high level region. As shown in the figure for EMI + migration through the hole, the results obtained in this way do not present significant differences with each other within the accuracy range considered here. We therefore adopted the smaller QM region model (model 1) due to its reduced computational cost. 15