SUPPLEMENTARY INFORMATION

Transcription

1 SUPPLEMENTARY INFORMATION Nanoporous Metal/Oxide Hybrid Electrodes for Electrochemical Supercapacitors Xingyou Lang, Akihiko Hirata, Takeshi Fujita, Mingwei Chen * WPI Advanced Institute for Materials Research, Tohoku University, Sendai , Japan mwchen@wpi-aimr.tohoku.ac.jp a b Au: 91 wt% MnO 2 : 9 wt% Au: 83 wt% MnO 2 : 17 wt% c d Au: 61 wt% MnO 2 : 41 wt% Au: 53 wt% MnO 2 : 47 wt% Figure 1S Energy dispersive X-ray spectroscopy (EDS) spectra of the nanoporous Au/MnO 2 composites with the plating time of (a) 5, (b) 10, (c) 20 and (d) 30 minutes. The Cu peaks are from the copper sample holders. nature nanotechnology 1

2 supplementary information Figure 2S a, HRTEM of NPG plated with MnO 2 for 5 minutes. b, Bright field STEM image of the NPG/MnO 2 interface. Both images show that MnO 2 nanocrystals epitaxially grow on the Au surfaces with a near coherent interface. 2 nature nanotechnology

3 supplementary information Figure 3S Internal resistance of the 20 minute plated NPG/MnO 2 electrode in a 2M Li 2 SO 4 electrolyte, which is measured by using the discharge current densities of 0.33, 0.43, 0.53, 1.3, 3.3, 6.7, 10.0, 13.3, 16.7 and 20.0 A/g. nature nanotechnology 3

4 supplementary information Figure 4S Top-view (a) and cross-sectional (b and c) SEM images of MnO 2 plated Ag 65 Au 35 films with the plating time of 10 minutes. d, CV curves of the electrochemical capacitors using the MnO 2 plated Ag 65 Au 35 films as the electrodes. The electrochemical plating time of MnO 2 is 5, 10, 20, and 30 minutes, respectively. The electrochemical performance of these electrodes is consistent with those of MnO 2 films, i.e., the thicker the electro-active films, the lower the capacitance relative to the MnO 2 contents. 35 The cross-sectional SEM micrograph (c) shows that the plated MnO 2 layer is porous. It should be noted that assuming 100% current efficiency via the reaction Mn H 2 O MnO 2 + 4H + + 2e -, the mass of the electro-active material (m) (as MnO 2 ) was calculated on the basis of the charge passed during electrolysis m = 91Q/( ) with Q being the charge nature nanotechnology

5 supplementary information Figure 5S Specific capacitance vs discharge current plots. Here specific capacitance and discharge current are normalized with the mass including both the 40 um separator and the NPG or NPG/MnO 2 electrodes. The mass of the separator is two orders of magnitude heavier than these of the NPG and NPG/MnO 2 electrodes, which gives rise to the much smaller specific capacitance values. The drawback of the nanoporous Au/MnO 2 hybrid electrodes, similar to MnO 2 /CNT, 22 is that they are too thin as compared to the thickness of the cotton paper separators. Although the specific capacitance of the hybrid electrodes is very high, the specific capacitance of the whole devices after considering the mass of the separators is not attractive because the mass of the 40 μm thick separator is about two orders of magnitude larger than that of the nanoporous Au/MnO 2 electrodes (Fig. 5S). However, this shortage can be technically overcome using ultrathin separators and/or thick nanoporous Au/MnO 2 electrodes. With these feasible solutions the outstanding specific capacitance of the hybrid electrodes is expected to be fully exploited for practical applications. nature nanotechnology 5

6 supplementary information Figure 6S CV curves of the aqueous SCs using NPG/MnO 2 as the electrodes at different scanning rates. The MnO 2 plating time of a, 0 min; b, 5 min; and c, 10 minutes. 6 nature nanotechnology

7 supplementary information Figure 7S The Ragone plot, the cycling stability and the Coulombic efficiency of the NPG/MnO 2 electrodes. a, The Ragone plot of the power (P) and energy (E) densities of the NPG/MnO 2 -based supercapacitors (,, for the plating time of 5, 10 and 20 minutes, respectively) in the 2M Li 2 SO 4 aqueous electrolyte. Here the gravimetric P and E are calculated by P = V 2 /(4RM) and E = 0.5CV 2 /M, respectively. Here V is the cutoff voltage, C is the measured device capacitance, M is the total mass of the nanoporous gold or nanoporous gold/mno 2 electrodes, and R = ΔV IR /(2i) with ΔV IR being the voltage drop between the first two points in the voltage drop at its top cutoff. 2,15,20 For comparison, the literature data of other MnO 2 based electrodes (pink symbols): MnO 2 electrodes (, 36, ), coaxial CNT/MnO 2 ( 19 ), nature nanotechnology 7

8 supplementary information Au-CNT/MnO 2 ( 19 ), activated carbon-mno 2 hybrid electrodes (, 39, ), MnO 2 /graphene ( 38 ), and these of carbon nanotube based supercapacitors (violet symbols):, 15, 38, 42, 43, 44, 45, 46, 47 as well as these of commercial supercapacitor devices (cyan symbols): 48 SAFT ( ), PowerSystem PSL ( ), Panasonic UPC ( ), Maxwell PC2500 ( ), CCR3000 ( ), CCR2000 ( ), Panasonic UPA ( ), Ness ( ), EPCOS ( ), Panasonic UPB ( ) are also listed in the plot. b, Cycling stability of the NPG/MnO 2 composite electrode (20 min plating) as a function of cycle number. The measurements of capacitance retention were carried out, respectively, in the galvanostatic charge/discharge at the current density of 1 A/g for over 1000 cycles, and in the Cyclic voltammetry for over 500 cycles at the scan rate of 50 mv/s at which the constituent MnO 2 in NPG/MnO 2 electrode shows the highest specific capacitance of 1145 F/g. References: 36 Zolfaghari, Z., Ataherian, F., Ghaemi, M., Gholami, A. Capacitive behavior of nanostructured MnO 2 prepared by sonochemistry method. Electrochim. Acta 52, (2007). 37 Cottineau, T., Toupin, M., Delahaye, T., Brousse, T., Bélanger, D. Nanostructured transition metal oxides for aqueous hybrid electrochemical supercapacitors. Appl. Phys. A 82, (2006). 38 Wu, Z.S. et al. High-energy MnO2 nanowire/graphene and graphene asymmetric electrochemical capacitors. ACS Nano 4, (2010). 39 Brousse, T., Toupin, M., Bélanger, D. A hybrid activated carbon-manganese dioxide capacitor using a mild aqueous electrolyte. J. Electrochem. Soc. 151, 8 nature nanotechnology

9 supplementary information A614-A622 (2004). 40 Xu, C.J., Du, H.D., Li, B.H., Kang, F.Y., Zeng, Y.Q. Asymmetric activated carbon-manganese dioxide capacitors in mild aqueous electrolytes containing alkaline-earth cations. J. Electrochem. Soc. 156, A (2009). 41 Khomenko, V., Raymundo-Pinero, E., Béguin, F. Optimisation of an asymmetric manganese oxide/activated carbon capacitor working at 2 V in aqueous medium. J. Power Sources 153, (2006). 42 Ma, R.Z. et al. Processing and performance of electric double-layer capacitors with block-type carbon nanotube electrodes. Bull. Chem. Soc. Jpn (1999). 43 Zhou, C.F., Kumar, S., Doyle, C.D., Tour, J.M. Functionalized single wall carbon nanotubes treated with pyrrole for electrochemical supercapacitor membranes, Chem. Mater. 17, (2005). 44 An, K.H. et al. Supercapacitors using single-walled carbon nanotube electrodes. Adv. Mater. 12, (2001). 45 Du, C.S., Pan, N. Supercapacitors using carbon nanotubes films by electrophoretic deposition. J. Power Sources 160, (2006). 46 Kimizuka, O. et al. Electrochemical doping of pure single-walled carbon nanotubes used as supercapacitor electrodes. Carbon 46, (2008). 47 Hu, L.B. et al. Highly Conductive paper for energy-storage devices. Proc. Natl. Acad. Sci. USA 106, (2009). 48 Chu, A., Braatz, P. Comparison of commercial supercapacitors and high-power nature nanotechnology 9

10 supplementary information lithium-ion batteries for power-assist applications in hybrid electric vehicles I. Initial characterization. J. Power Sources 112, (2002). 10 nature nanotechnology