Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2013. Supporting Information for Adv. Mater., DOI: 10.1002/adma.201205064 Large Areal Mass, Flexible and Free-Standing Reduced Graphene Oxide/Manganese Dioxide Paper for Asymmetric Supercapacitor Device Afriyanti Sumboja, Ce Yao Foo, Xu Wang, and Pooi See Lee*
Submitted to Supporting Information Large Areal Mass, Flexible and Free-Standing Reduced Graphene Oxide/Manganese Dioxide Paper for Asymmetric Supercapacitor Device By Afriyanti Sumboja, Ce Yao Foo, Xu Wang, and Pooi See Lee* [*] A. Sumboja, C. Y. Foo, X. Wang, Prof. P. S. Lee School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore 639798 E-mail: pslee@ntu.edu.sg 1. The top view of RGO/MnO2 paper Figure S1. Top view high magnification SEM images of RGO/MnO2 paper (a) curved structure; (b) presence of MnO2; (c) edge of hybrid paper showing the open sheets arrangement; (d) edge view of hybrid paper with the presence of MnO2; (e) TEM image of the edge of hybrid paper. High magnification SEM images of the surface of RGO/MnO2 paper shows wrinkled and curves structure (Figure S1). The presence of MnO2 on the surface of RGO/MnO2 paper is i
Submitted to shown at Figure S1b and S1d. Figure S1c, S1d and S1e show the edge of RGO/MnO 2 paper from the top view observation. It was shown that RGO sheets have an open sheets arrangement similar to cross section view provided in the main text. The loosely packed arrangement of RGO sheets helps the diffusion of electrolyte ions during charge discharge process, leading to low charge transfer resistance and high capacitance of the electrode. 2. Weight percentage of MnO 2 in RGO/MnO 2 paper Figure S2. Thermogravimetric analysis of RGO/MNO 2 paper. Thermo Gravimetric Analysis (TGA) was performed by using TGA (TA Instruments Q500) by heating the sample for up to 900 o C with the ramp rate of 10 o C min -1. By assuming the final residue after heating at 900 o C consists of metal oxide only, [1,2] the weight percentage of MnO 2 in RGO/MnO 2 paper is estimated to be 20 wt%. 3. Mechanical properties of RGO/MnO 2 paper RGO/MnO 2 paper electrodes were cut into size of 5 x 16 mm 2. Mechanical properties of the RGO/MnO 2 paper were studied using a dynamic mechanical analyser (DMA Q800) with 2
Submitted to controlled strain rate mode with a preload of 0.001 N at a strain ramp rate of 0.05 % min -1. Young s modulus (E) of free-standing RGO/MnO 2 paper is calculated by taking the slope of linear portion at the elastic region such as shown in the blue dot curve in the Figure S3 below. The resultant Young s modulus is calculated to be 9.84 GPa and the measured tensile strength is about 8.79 MPa. Figure S3. (a) Stress strain curve of RGO/MnO 2 paper and initial linear portion of the curve that is used to measure Young s modulus (dotted line); (b) The initial, linear portion of the corresponding stress-strain curve. 2D Young s modulus (E 2D ) of single sheet MnO 2 /RGO is estimated by taking the thickness of the reported monolayer RGO sheet ( 1.7 nm). [3] It is estimated to be about to be 16.73 N m -1. This number is lower than E 2D of epitaxial and free standing monolayer graphene ( 340 N m - 1 ) and graphene oxide membrane ( 145 N m -1 ), [4-6] which is due to the presence of more defects in chemically reduced graphene oxide as compared to epitaxially grown or mechanically cleaved monolayer graphene sheet. Furthermore, the presence of scattered nanoparticles MnO 2 on RGO sheets induces local heterogeneities across the paper, resulting in the low mechanical properties of RGO/MnO 2 hybrid paper. 3
Submitted to 4. Charge discharge curves of RGO and RGO/MnO 2 papers at high applied current Figure S4. Charge discharge curve of (a) 1) RGO/MnO 2 and 2) RGO paper at 500 ma g -1 ; (b) 1) RGO/MnO 2 and 2) RGO paper at 1000 ma g -1 ; (c) RGO paper at (1) 500 and (2) 1000 ma g -1 at different time scale to give a better observation on ir drop of RGO paper. ir drop of each paper at 500 ma g -1 is shown in the arrow while the diamond arrow shows the ir drop for each paper at 1000 ma g -1. Figure S4 shows that both paper electrodes have similar ir drop at high applied current. The ir drop of both RGO and RGO/MnO 2 paper becomes more significant at high applied current as there is more voltage drop at the beginning of high discharge current in accordance to Ohm s law. 5. Charge discharge curves of asymmetric supercapacitor device Figure S5. Charge discharge curves of the asymmetric device based on RGO and RGO/MnO 2 paper tested in its bent state at (1) 1000, (2) 500, (3) 250 ma g -1. 4
Submitted to 6. Performance of flexible carbon-based electrodes in the literature Table 1. Literature on flexible carbon-based electrodes for supercapacitor application Material / Reference Mass (mg) Capacita nce (mf cm -2 ) Capacita nce (F g -1 ) Graphene Paper (Free-standing) Graphene Cellulose Paper Flexible Supercapacitors - 81 120 Ref [7] Flexible Pillared Graphene-Paper Electrodes for High- Performance Electrochemical Supercapacitors Facilitated Ion Transport in All-Solid-State Flexible Supercapacitors Folded Structured Graphene Paper for High Performance Electrode Materials Bioinspired Effective Prevention of Restacking in Multilayered Graphene Films: Towards the Next Generation of High-Performance Supercapacitors 0.41 56.6 138 - - 62.3 - - 172 0.45 94.5 210 [8] [9] [10] [11] A Leavening Strategy to Prepare Reduced Graphene Oxide Foams MnO 2 /Carbon-based Paper Solution-Processed Graphene/MnO 2 Nanostructured Textiles for High-Performance Electrochemical Capacitors - 110 0.3 94.5* 315 [12] [13] Flexible Graphene/MnO 2 Composite Papers for Supercapacitor Electrodes (Free-standing) High-Performance Nanostructured Supercapacitors on a Sponge 0.07 17.9* 256 < 0.1 0.9 1230 [14] [15] Flexible Solid-State Supercapacitors Based on Carbon Nanoparticles/MnO 2 Nanorods Hybrid Structure 0.562 109 165 [16] Freestanding Three-Dimensional Graphene/MnO2 Composite Networks As Ultralight and Flexible Supecapacitor Electrode Mass of electrode in 3 electrode test Mass of active material in Device 9.8 0.8 1420 0.024 F* 130 29.8 [17] This work Mass of electrode in 3 electrode test Mass of active material in Device 3.7 15 Flexible and/or carbon-based Electrode Origami Fabrication of Nanostructured, Three- Dimensional Devices: Electrochemical Capacitors with Carbon Electrodes 897 0.34 F 243 22.7-0.008 15 [18] 5
Fiber Supercapacitors Made of Nanowire-Fiber Hybrid Structures for Wearable/Flexible Energy Storage Submitted to - 2 - [19] Ultrathin Planar Graphene Supercapacitors - 0.9 - [20] Ultrahigh-Power Micrometre-Sized Supercapacitors Based on Onion-Like Carbon Direct Laser Writing of Micro-Supercapacitors on Hydrated Graphite Oxide Film 2.8 x 10-4 0.394 247-0.51 - [21] [22] Monolithic Carbide-Derived Carbon Films for Micro- - 32 - Supercapacitors *value is calculated from the information provided by the author in the respective paper. [23] 7. Calculations Specific capacitance of the paper electrode tested in three electrode configuration is calculated from its discharge curve. The discharge specific capacitance (gravimetric capacitance) in F g -1 is calculated according to this calculation: C sp = (I x Δt)/(m х ΔV). I is the applied current, Δt is the discharge time, m is the mass of the paper electrode, and ΔV is the potential window of the test. The areal capacitance of the paper electrode in F cm -2 is calculated as the following: C = (C sp x m)/a A is the area of the paper electrode that immersed in the electrolyte ( 1 cm 2 ). The electrochemical measurements of the RGO-RGO/MnO 2 asymmetric device are calculated according to the following formulas: [1] c= I/-[ΔV/Δt] C=c/A Where c is the measured capacitance of the device, I is the applied current during charge discharge test and ΔV/Δt is the slope of the discharge curve after ir drop. C is areal capacitance of the device in F cm -2 and A is the footprint area of the device ( 3 cm 2 ). Calculations for the areal power and energy specifications are as the following: [24] 6
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