School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai , PR China

Transcription

1 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is The Royal Society of Chemistry 2017 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A High area-specific capacitance of Co(OH) 2 /hierarchical nickel/nickel foam supercapacitor and increase with cycling Zheyin Yu, [a] Zhenxiang Cheng*, [a] Xiaolin Wang, [a] Shi Xue Dou, [a] and Xiangyang Kong [b] a Institute for Superconducting and Electronic Materials, University of Wollongong, North Wollongong, NSW 2500, Australia. cheng@uow.edu.au; Fax: ; Tel: b School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai , PR China Experimental Section All chemicals were of reagent quality and used without further purification. The nickel chloride, annonium chloride, ethylenediamine hydrochloride, sodium nitrate, cobalt nitrate, and boric acid were obtained from Bio-Scientific Pty. Ltd. The nickel foam was obtained from Changsha Lyrun Company (China). Preparation of hierarchical nickel/nickel foam (HNNF) In the first step of the, the electrolyte consisted of 0.1 M NiCl 2 and 2 M NH 4 Cl. A piece of clean nickel foam (NF) acted as the working electrode, and a Pt plate acted as the counter electrode. The was carried out under the constant current density of 2 A cm -2 for 320 s. In the second step of the, the electrolyte for electro consisted of 0.85 M NiCl 2, 1.5 M ethylenediamine hydrochloride, and 0.5 M H 3 BO 3. The was carried out under the constant current density of 0.1 A cm -2 for 1080 s. Preparation of Co(OH) 2 /HNNF The electrolyte for of Co(OH) 2 consisted of 0.35 M Co(NO 3 ) 2 6H 2 O and 0.12 M NaNO 3. The HNNF acted as the working electrode, and a Pt plate acted as the counter electrode. The was carried out under a

2 constant current density of 3 ma cm -2 for 600 s, and the mass loading was about 2.3 mg cm -2. To allow comparison with a Co(OH) 2 /nickel foam electrode (Co(OH) 2 /NF), the direct of Co(OH) 2 on nickel foam was carried out under the same experimental conditions, and the mass loading was about 2.2 mg cm -2. Materials Characterization Scanning electron microscope (SEM) images were collected with a field-emission scanning electron microscope (FESEM, JEOL-7500, 2 kev). X-ray diffraction (XRD) patterns were collected on a polycrystalline X-ray diffractometer (RIGAKU, D/MAX 2550 VB/PC, 40 kv/20 ma, λ = Å). Transmission electron microscope (TEM) images and highresolution TEM (HRTEM) images were collected on a transmission electron microscope (JEOL-2100F, 200 kev). Electrochemical performance measurements The performance of the as-prepared electrode was measured using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) testing, and impedance spectroscopy (EIS) on an workstation (VMP-3) with a typical three-electrode system working at ambient temperature. Specifically, the Co(OH) 2 /HNNF and Co(OH) 2 /NF electrodes were used as the working electrodes, respectively, platinum plate was used as the counter electrode, and saturated calomel electrode (SCE) was used as the reference electrode. EIS testing was performed in the frequency range from 100 khz to 10 mhz at open circuit potential. 2.0 M KOH solution was used as the electrolyte. The areaspecific capacitance was calculated according to the following equation: C A = I t / ( V S) (1) Where C A is the area-specific capacitance (F cm -2 ), I is the discharging current (A cm -2 ), t is the discharging time (s), V is the discharging potential range (V), and S is the electrode area (cm 2 ), respectively.

3 Fig. S1 Comparative mechanical strength test. Tape was made to adhere to Ni samples after one-step and two-step (HNNF) (a), and the tape was then peeled off from the Ni samples (b). There was no obvious residue on the peeled-off tape from the Ni sample after the two-step. Fig. S2 Comparison of the morphologies of commercial nickel foam and nickel/nickel foam from two-step (HNNF). SEM images of commercial nickel foam (a) and nickel/nickel foam (HNNF) from two-step (b).

4 Fig. S3 Characterization of HNNF. XRD pattern of HNNF (a), TEM image of HNNF (b), with the inset showing a piece of nickel flake, SAED pattern of HNNF (c), and HRTEM image of HNNF (d). Fig. S4 Optical images of NF, HNNF, Co(OH) 2 /HNNF, and Co(OH) 2 /NF (from left to right). Table S1 This work compared with previous reports on free-standing Co(OH) 2 and other metal hydroxide/oxide materials as supercapacitor electrode fabricated by. Material Current collector fabrication method Active material fabrication method Active material mass loading (mg cm -2 ) Area-specific capacitance (F cm -2 ) Rate capability Cycling performance Ref. co- Co(OH) 2 /Ni/ of Ni-Cu, and then ly dissolving Cu (0.25 ma cm -2 ) 70.69% (15 ma cm -2 ) 1.08 F cm -2 About 100% 2.5 ma cm -2 ) S1 Co(OH) 2 /ITO/Ti foil (0.25 ma cm -2 ) 74.46% 0.38 F cm -2 About 91.5% (1200 cycles, ma cm -2 ) S2 co- Co(OH) 2 /Ni/Ni foil of Ni-Cu, and then ly dissolving Cu (5 mv s -1 ) 93.2% (200 mv s -1 ) F cm -2 About 150% (5 mv s -1 ) S3

5 Co(OH) 2 /TiO 2 /FTO Hydrothermal reaction (0.2 ma cm -2 ) 56.78% (2 ma cm -2 ) 0.11 F cm % 2 ma cm -2 ) S4 Co(OH) 2 /Ni/Ni foil (2 ma cm -2 ) 95% (40 ma cm -2 ) 1.9 F cm % 2 ma cm -2 ) S5 Co(OH) 2 /Cu/Ni foil co of Ni-Cu, and then ly dissolving Cu (0.5 ma cm -2 ) 96% (200 mv s -1 ) F cm % 0.5 ma cm -2 ) S6 Co-Ni mixed hydroxide/ (0.75 ma cm -2 ) 80% (7.5 ma cm -2 ) 0.91 F cm -2 71% (, 7.5 ma cm -2 ) S7 Co-Ni mixed hydroxide/ (0.75 ma cm -2 ) 83.4% (15 ma cm -2 ) 0.91 F cm -2 87% 7.5 ma cm -2 ) S8 Co-Ni mixed hydroxide/ - co (0.24 ma cm -2 ) 73.5 % (6 ma cm -2 ) 0.49 F cm -2 94% 2.4 ma cm -2 ) S9 Ni(OH) 2 / (2 ma cm -2 ) 9% (8 ma cm -2 ) 0.14 F cm -2 48% (3000 cycles, 2 ma cm -2 ) S10 Ni(OH) 2 /graphene/ (0.99 ma cm -2 ) 58.91% (9.9 ma cm -2 ) 0.56 F cm -2 77% 9.9 ma cm -2 ) S11 Ni(OH) 2 /ITO/Ti foil (0.47 ma cm -2 ) 83.51% (9.4 ma cm -2 ) 0.40 F cm -2 93% (500 cycles, 0.47 ma cm -2 ) S12 Co 3 O 4 / (2.8 ma cm -2 ) 54.78% (28 ma cm -2 ) 1.05 F cm -2 99% (3000 cycles, 11.2 ma cm -2 ) S13 NiCo 2 O 4 / - co (1.6 ma cm -2 ) 72% (16 ma cm -2 ) 1.15 F cm -2 94% (2300 cycles, 1.6 ma cm -2 ) S14 NiCo 2 O 4 /CNT/ stainless steel co (0.62 ma cm -2 ) 82.87% (12.4 ma cm -2 ) 0.36 F cm -2 91% (1500 cycles, 2.48 ma cm -2 ) S15 Co(OH) 2 /Ni/ % 2.84 F cm % 5 ma cm -2 ) 9.62 F cm -2 This work Figure S5 TEM image of Co(OH) 2 /HNNF after 2000 cycles (a) and corresponding EDX spectrum with inset analysis (b).

6 Figure S6 SEM images (a and b) and HRSEM image (c) of Co(OH) 2 /HNNF after. Figure S7 Further cycling performance testing for the Co(OH) 2 /HNNF after 2000 cycles under 5 ma cm -2. Table S2 The Co(OH) 2 /HNNF after 2000 cycles compared with previous reports on free-standing electrode with high area-specific capacitance fabricated by hydrothermal reaction. Materials Current collector Area-specific capacitance (F cm -2 ) Rate capability Cycling performance Ref. Ni-Co mixed hydroxide 8.05 (3 ma cm -2 ) 83% 6.68 F cm -2 95% (15 ma cm -2 ) S16 Ni(OH) % 3.38 F cm -2 96% 500 cycles S17 Co(OH) (7mA cm -2 ) 69% (28 ma cm -2 ) 1.35 F cm -2 88% (7 ma cm -2 ) 3000 cycles S18 Co 3 O NiCo 2 O (10 ma cm -2 ) 50% 0.75 F cm -2 87% (7 ma cm -2 ) 1500 cycles S19

7 % (20 ma cm -2 ) 1.78 F cm % (20 ma cm -2 ) 2000 cycles S20 NiCo 2 O (2 ma cm -2 ) 66% 2.47 F cm % (5 mv s -1 ) 2000 cycles S21 Co 3 O % 2.51 F cm % 2000 cycles S22 Co 3 O 3 O % F cm % (20 ma cm -2 ) S23 NiMoO (4 ma cm -2 ) 65% (32 ma cm -2 ) 3.75 F cm % (8 ma cm -2 ) S24 NiCo 2 S % 4.79 F cm -2 85% (50 ma cm -2 ) S25 Co(OH) 2 /HNNF after 2000 cycles HNNF % 6.93 F cm -2 92% This work References [S1] M.-J. Deng, C.-Z. Song, C.-C. Wang, Y.-C. Tseng, J.-M. Chen and K.-T. Lu, ACS Appl Mater Interfaces 2015, 7, [S2] D. T. Dam and J.-M. Lee, Nano Energy 2013, 2, [S3] C.-M. Wu, C.-Y. Fan, I.-W. Sun, W.-T. Tsai and J.-K. Chang, Journal of Power Sources 2011, 196, [S4] A. Ramadoss and S. J. Kim, Electrochimica Acta 2014, 136, [S5] X. Xia, J. Tu, Y. Zhang, Y. Mai, X. Wang, C. Gu and X. Zhao, The Journal of Physical Chemistry C 2011, 115, [S6] J.-K. Chang, C.-M. Wu and I.-W. Sun, Journal of Materials Chemistry 2010, 20, [S7] T. Nguyen, M. Boudard, M. J. Carmezim and M. F. Montemor, Scientific Reports, 2017, 7, [S8] M. Yang, H. Cheng, Y. Gu, Z. Sun, J. Hu, L. Cao, F. Lv, M. Li, W. Wang and Z. Wang, Nano Research, 2015, 8, [S9] J. Xing, S. Wu and K. S. Ng, RSC Advances, 2015, 5, [S10] G.-W. Yang, C.-L. Xu and H.-L. Li, Chemical Communications, 2008, [S11] X. Wang, J. Liu, Y. Wang, C. Zhao and W. Zheng, Materials Research Bulletin, 2014, 52, [S12] D. T. Dam, X. Wang and J.-M. Lee, Nano Energy, 2013, 2, [S13] C. Yuan, L. Yang, L. Hou, L. Shen, X. Zhang and X. W. D. Lou, Energy & Environmental Science, 2012, 5, [S14] C. Yuan, J. Li, L. Hou, X. Zhang, L. Shen and X. W. D. Lou, Advanced Functional Materials, 2012, 22, [S15] W.-w. Liu, C. Lu, K. Liang and B. K. Tay, Journal of Materials Chemistry A, 2014, 2, [S16] H. Chen, L. Hu, M. Chen, Y. Yan and L. Wu, Advanced Functional Materials, 2014, 24, [S17] Z. Lu, Z. Chang, W. Zhu and X. Sun, Chemical Communications, 2011, 47, [S18] F. Cao, G. Pan, P. Tang and H. Chen, Journal of Power Sources, 2012, 216, [S19] G. Zhang, T. Wang, X. Yu, H. Zhang, H. Duan and B. Lu, Nano Energy, 2013, 2, [S20] C. Zhou, Y. Zhang, Y. Li and J. Liu, Nano Letters, 2013, 13,

8 [S21] J. Hu, F. Qian, G. Song and L. Wang, Nanoscale Research Letters, 2016, 11, 257. [S22] Q. Yang, Z. Lu, X. Sun and J. Liu, Scientific Reports, 2013, 3, [S23] Q. Yang, Z. Lu, Z. Chang, W. Zhu, J. Sun, J. Liu, X. Sun and X. Duan, RSC Advances, 2012, 2, [S24] G. Jiang, M. Zhang, X. Li and H. Gao, RSC Advances, 2015, 5, [S25] M. Yan, Y. Yao, J. Wen, L. Long, M. Kong, G. Zhang, X. Liao, G. Yin and Z. Huang, ACS Applied Materials & Interfaces, 2016, 8,