Supporting Information. Supercapacitors

Transcription

1 Supporting Information Ni(OH) 2 Nanoflower/Graphene Hydrogels: A New Assembly for Supercapacitors Ronghua Wang ab, Anjali Jayakumar a, Chaohe Xu* c and Jong-Min Lee* a [a] School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore , Singapore jmlee@ntu.edu.sg (J.-M. Lee) Tel: [b] College of Materials Science and Engineering, Chongqing University, No. 174 Shazhengjie Road, Chongqing , P.R. China [c] College of Aerospace Engineering, Chongqing University, No. 174 Shazhengjie Road, Chongqing , P.R. China xche@cqu.edu.cn Page S1

2 Figure S1. (a, b) SEM images of Ni(OH)2 precursor. (c, d) TEM images of Ni(OH)2 precursor/go. Figure S2. A digital photograph of Ni(OH)2/GS hydrogel. Page S2

3 Figure S3. TG curves of pure Ni(OH) 2 and freeze-dried Ni(OH) 2 /GS hydrogels with different graphene contents. Figure S4. Core level C 1s spectrum of GO and freeze-dried Ni(OH) 2 /GS hydrogels. Page S3

4 Figure S5. Raman spectra of pure Ni(OH) 2 and freeze-dried Ni(OH) 2 /GS hydrogels. As shown in Figure S5 and Table S1, the spectra of pure Ni(OH) 2 can be well assigned to α-ni(oh) 1 2 (other peaks, such as 195, 654, etc. may due to the signal of intercalated anions). And Raman spectra of Ni(OH) 2 /GS (Table S2) shows both the peaks of α-ni(oh) 2 and GS, confirming the successful formation of α-ni(oh) 2 /GS hydrogels 2. Table S1. Raman peaks for pure Ni(OH) 2. Raman shift Peak assignment 452, 497 α-ni(oh) 2 Lattice mode 928 α-ni(oh) 2 2 nd order lattice mode 1436 α-ni(oh) 2 O-H bend, lattice OH 1615 α-ni(oh) 2 O-H bend, layer H 2 O 2869 α-ni(oh) 2 /surface 2 nd order O-H bend/c-h stretch hydrocarbon 2934 CH 3 COO - /surface C-H stretch hydrocarbon Page S4

5 Table S2. Raman peaks for Ni(OH) 2 /GS. Raman shift Peak assignment 445, 496 α-ni(oh) 2 Lattice mode 929 α-ni(oh) 2 2 nd order lattice mode 1363 GS D band 1434 α-ni(oh) 2 O-H bend, lattice OH 1600 α-ni(oh) 2 and GS G band+(o-h bend, layer H 2 O 2938 CH 3 COO - /surface C-H stretch hydrocarbon Page S5

6 Figure S6. TEM images of pure Ni(OH)2 after the solvothermal reaction. Page S6

7 Figure S7. Charge-discharge curves of pure graphene hydrogels at different current densities. Page S7

8 Figure S8. (a) Discharge curves of Ni(OH) 2 /GS hydrogels with 24.9 % graphene. (b) Specific capacitance of hydrogels with 16.5 % and 24.9 % graphene, respectively. As shown in Figure S8b, the hybrid hydrogel with 24.9 % graphene delivers lower capacitance compared with Ni(OH) 2 /GS (16.5 %). Clearly, excess graphene is harmful for the electrochemical performance. This is because too much graphene will induce the aggregation of graphene sheets and the lower capacitance of graphene ascribe to EDLC behavior compromise the capacitance based on the total mass of the composite 3. Page S8

9 However, when the graphene content was much lower than 16.5 %, the hybrid hydrogels cannot form at all. Therefore, in the manuscript, all of the characterizations are carried out on the sample with 16.5 % graphene. Figure S9. (a) CV curves of the Ni(OH) 2 /GS//Ni(OH) 2 /GS symmetric capacitor at 50 mv s -1. (b) Charge-discharge curves of the Ni(OH) 2 /GS//Ni(OH) 2 /GS symmetric capacitor at different current densities. (c) The corresponding specific capacitances of the Ni(OH) 2 /GS//Ni(OH) 2 /GS symmetric capacitor versus current density. The specific capacitance of a single electrode in a two-electrode cell was calculated based on the following equation 4-5 : Cs = 2I t V m where I, t, V and m represent the discharge current, discharge time, voltage range upon discharging (excluding the IR drop) and the mass of active materials in one electrode. CV and charge-discharge tests were conducted with a symmetrical two-electrode cell, to evaluate supercapacitors performance. According to literatures 6, CV curves were conducted within a -0.3 to 0.3 V voltage window. A pair of redox peaks between -0.1 and 0.1 V was shown in CV curves, which correspond to redox conversions between Ni(OH) 2 and NiOOH. The charge-discharge curves also display two plateaus Page S9

10 between -0.1 V and 0.1 V, in good accordance with the CV curves. As calculated, the two-electrode cell delivered specific capacitances of 328, 229, 176, 151, 128 and 119 F g -1 at current densities of 1, 2, 4, 6, 8 and 10 A g -1, respectively. References: 1. Hall, D. S.; Lockwood, D. J.; Poirier, S.; Bock, C.; MacDougall, B. R., Raman and infrared spectroscopy of α and β phases of thin nickel hydroxide films electrochemically formed on nickel. J. Phys. Chem. A 2012, 116 (25), Wang, R. H.; Wang, Y.; Xu, C. H.; Sun, J.; Gao, L., Facile one-step hydrazine-assisted solvothermal synthesis of nitrogen-doped reduced graphene oxide: reduction effect and mechanisms. Rsc Adv. 2013, 3 (4), Wu, Z.; Huang, X.-L.; Wang, Z.-L.; Xu, J.-J.; Wang, H.-G.; Zhang, X.-B., Electrostatic Induced Stretch Growth of Homogeneous beta-ni(oh) 2 on Graphene with Enhanced High-Rate Cycling for Supercapacitors. Sci. Rep. 2014, 4, Xu, Y.; Lin, Z.; Huang, X.; Liu, Y.; Huang, Y.; Duan, X., Flexible Solid-State Supercapacitors Based on Three-Dimensional Graphene Hydrogel Films. Acs Nano 2013, 7 (5), Xu, Y.; Lin, Z.; Huang, X.; Wang, Y.; Huang, Y.; Duan, X., Functionalized Graphene Hydrogel-Based High-Performance Supercapacitors. Adv. Mater. 2013, 25 (40), Ci, S. Q.; Wen, Z. H.; Qian, Y. Y.; Mao, S.; Cui, S. M.; Chen, J. H., NiO-Microflower Formed by Nanowire-weaving Nanosheets with Interconnected Ni-network Decoration as Supercapacitor Electrode. Sci. Rep. 2015, 5, Page S10