Volume 4, Issue 4, Pages 896-910 (April 2018) Graphene Thin Films by Noncovalent-Interaction-Driven Assembly of Graphene Monolayers for Flexible Supercapacitors  Guo-Fei Wang, Haili Qin, Xiang Gao, Yi Cao, Wei Wang, Feng-Chao Wang, Heng-An Wu, Huai-Ping Cong, Shu-Hong Yu  Chem  Volume 4, Issue 4, Pages 896-910 (April 2018) DOI: 10.1016/j.chempr.2018.01.008 Copyright © 2018 Elsevier Inc. Terms and Conditions

Chem 2018 4, 896-910DOI: (10.1016/j.chempr.2018.01.008) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 1 Schematic Illustrations for the Fabrication of Freestanding GO Film Step 1: a GO monolayer was deposited on the cellulose membrane by the LB technique. Step 2: the GO monolayer was wrinkled as a result of the shrinkage of the cellulose membrane during the drying process. Step 3: melamine molecules were adsorbed on the surface of the GO monolayer. Step 4: the GO film with the desired thickness was prepared by repetition of the above three steps. Note that the last layer of the assembled film was deposited with GO nanosheets. Step 5: the freestanding GO film was formed by dissolution of the cellulose membrane in acetone. After the floating GO film was captured with a metal grip from acetone and removed from the grip, the flexible GO film was fabricated. See also Figures S1–S5 and Movie S1. Chem 2018 4, 896-910DOI: (10.1016/j.chempr.2018.01.008) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 2 Physical Properties of Freestanding, Transparent GO2 Film (A–D) Photographs showing the freestanding GO2 film of various shapes, including a square (A), triangle (B), pentagon (C), and circle (D), demonstrating its good processability. (E) Photograph of the transparent GO2 film floating in the air. (F and G) Photographs of the GO2 film still retaining its structural integrity after being immersed in 1 M HCl (F) or NaOH (G) solutions for 24 hr and then lifted with tweezers. (H) AFM image of freestanding GO2 film and the corresponding height profile. See also Movie S2. Chem 2018 4, 896-910DOI: (10.1016/j.chempr.2018.01.008) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 3 Compositional Characterization of Freestanding GO6 Film (A–D) TEM image of GO6 film (A) and elemental mappings of C (B), O (C), and N (D). (E) Cross-sectional SEM image of GO6 film. (F) EDX spectrum of GO6 film. See also Figures S6–S11. Chem 2018 4, 896-910DOI: (10.1016/j.chempr.2018.01.008) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 4 Single-Molecule AFM Experiments Directly Measure the Binding Strength between Different Organic Molecules and GO Surfaces (A) Schematic of the single-molecule experiments. Melamine was linked to the AFM cantilever tip through a PEG linker by one of the amino groups. Shorter mPEG was used to minimize nonspecific tip-surface interactions. (B) Three representative force-extension curves for the rupture of melamine-GO interactions. The peak value measured the force at which melamine detached from the GO surface. Because we used a soft cantilever (spring constant of ∼50 pN/nm) for the force measurement, the cantilever was slow to return to the resting flat conformation after each rupture event. Therefore, the force curves show a descending slope after each force peak, reflecting the gradual conformational change of the cantilever. (C) Histogram of the rupture forces for 11 different adhesion molecules with GO surfaces, including fatty amines (ethylenediamine [EDA], diethylenetriamine [DETA], triethylenetetramine [TETA], and tetraethylenepentamine [TEPA]), aromatic amines (aniline and three phenylenediamine derivatives: o-PDA, m-PDA, and p-PDA), and amino-group triazines (2-amino-1,3,5-triazine [ATA], 2,4-diamino-1,3,5-triazine [DATA], and melamine). Error bars show the SD with a sample size of 3. (D) The rupture force distributions for melamine, EDA, and ATA with GO surfaces at a pulling speed of 1,000 nm s−1. The insets show the corresponding molecular structures (gray, carbon; blue, nitrogen; white, hydrogen). (E) The linear-log plots of rupture forces versus loading rates for melamine, EDA, and ATA. The lines correspond to the fits to the Bell-Evans model. Error bars show the SD with a sample size of 3. See also Figures S12–S18. Chem 2018 4, 896-910DOI: (10.1016/j.chempr.2018.01.008) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 5 Optical, Mechanical, and Electromechanical Properties of GO and RGO Films (A) Transmittance spectra of GO2 film and RGO2 film. The inset shows the RGO2 film. (B) Typical tensile stress-strain curves of GO3 film and the corresponding RGO3 film. (C) Photographs of RGO3 film under a continuous bending deformation. (D) Resistance variation of RGO3 film at a bending radius up to 1.5 mm during the first bending cycle. (E) Variation of the electrical resistance of RGO3 film during ten bending cycles. For each cycle, the film was gradually bent to a radius of 1.5 mm and then straightened to its original state. (F) Variation of the resistance of RGO3 film as a function of a long-term bending cycle at a bending radius of 1.5 mm. The inset shows the resistance changes after 10, 100, 1,000, and 10,000 bending cycles. See also Figures S19–S23. Chem 2018 4, 896-910DOI: (10.1016/j.chempr.2018.01.008) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 6 Electrochemical Performance of RGO Film Electrodes Using a Two-Electrode Cell (A) CV curves at a scan rate of 50 mV/s. (B) Galvanostatic charge-discharge curves at a current density of 500 mA/cm3. (C) Volumetric capacitances at different current densities. (D) Electrochemical impedance spectra for RGO films with different thicknesses as supercapacitor electrodes. (E) Variations of current densities of 30-nm-thick RGO film electrodes during charge and discharge with different scan rates at a constant voltage of 0.4 V. (F) Cycling stability of 30-nm-thick RGO film electrodes at a current density of 2,000 mA/cm3. Chem 2018 4, 896-910DOI: (10.1016/j.chempr.2018.01.008) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 7 Electrochemical Performance of an All-Solid-State Flexible Supercapacitor Assembled from 30-nm-Thick RGO Films (A) CV curves at a scan rate of 50 mV/s at different bending degrees. The inset shows the all-solid-state flexible supercapacitor assembled from 30-nm-thick RGO films. (B) CV curves at different scan rates. (C) Galvanostatic charge-discharge curves at different current densities. (D) Cycling stability at a current density of 2,000 mA/cm3. See also Figures S24–S26 and Table S1. Chem 2018 4, 896-910DOI: (10.1016/j.chempr.2018.01.008) Copyright © 2018 Elsevier Inc. Terms and Conditions