SUPPLEMENTARY INFORMATION Supplementary information … · SUPPLEMENTARY INFORMATION ... Supplementary information for Nanoporous Metal/Oxide Hybrid Electrodes for Electrochemical

SUPPLEMENTARY INFORMATIONdoi: 10.1038/nnano.2011.13

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Supplementary information for

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 980-8577,

Japan

E-mail: [email protected]

a

Au: ∼91 wt% MnO2: ∼9 wt%

b

Au: ∼83 wt% MnO2: ∼17 wt%

cAu: ∼61 wt% MnO2: ∼41 wt%

Au: ∼53 wt% MnO2: ∼47 wt%

d

Figure 1S Energy dispersive X-ray spectroscopy (EDS) spectra of the nanoporous

Au/MnO2 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.

1

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SUPPLEMENTARY INFORMATION doi: 10.1038/nnano.2011.13

Figure 2S a, HRTEM of NPG plated with MnO2 for 5 minutes. b, Bright field STEM

image of the NPG/MnO2 interface. Both images show that MnO2 nanocrystals

epitaxially grow on the Au surfaces with a near coherent interface.

2© 2011 Macmillan Publishers Limited. All rights reserved.



Figure 3S Internal resistance of the 20 minute plated NPG/MnO2 electrode in a 2M

Li2SO4 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.

3

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Figure 4S Top-view (a) and cross-sectional (b and c) SEM images of MnO2 plated

Ag65Au35 films with the plating time of 10 minutes. d, CV curves of the

electrochemical capacitors using the MnO2 plated Ag65Au35 films as the electrodes.

The electrochemical plating time of MnO2 is 5, 10, 20, and 30 minutes, respectively.

The electrochemical performance of these electrodes is consistent with those of MnO2

films, i.e., the thicker the electro-active films, the lower the capacitance relative to the

MnO2 contents.35 The cross-sectional SEM micrograph (c) shows that the plated

MnO2 layer is porous. It should be noted that assuming 100% current efficiency via

the reaction Mn2+ + 2H2O → MnO2 + 4H+ + 2e-, the mass of the electro-active

material (m) (as MnO2) was calculated on the basis of the charge passed during

electrolysis m = 91Q/(2×1.6×6.02×104) with Q being the charge.25




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/MnO2 electrodes. The mass of the separator is two

orders of magnitude heavier than these of the NPG and NPG/MnO2 electrodes, which

gives rise to the much smaller specific capacitance values.

The drawback of the nanoporous Au/MnO2 hybrid electrodes, similar to MnO2/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/MnO2 electrodes (Fig. 5S). However,

this shortage can be technically overcome using ultrathin separators and/or thick

nanoporous Au/MnO2 electrodes. With these feasible solutions the outstanding

specific capacitance of the hybrid electrodes is expected to be fully exploited for

practical applications.




Figure 6S CV curves of the aqueous SCs using NPG/MnO2 as the electrodes at

different scanning rates. The MnO2 plating time of a, 0 min; b, 5 min; and c, 10

minutes.




Figure 7S The Ragone plot, the cycling stability and the Coulombic efficiency of

the NPG/MnO2 electrodes. a, The Ragone plot of the power (P) and energy (E)

densities of the NPG/MnO2-based supercapacitors ( , , for the plating time of 5,

10 and 20 minutes, respectively) in the 2M Li2SO4 aqueous electrolyte. Here the

gravimetric P and E are calculated by P = V2/(4RM) and E = 0.5CV2/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/MnO2 electrodes, and R = ΔVIR/(2i) with

ΔVIR 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 MnO2 based electrodes (pink

symbols): MnO2 electrodes ( ,36 ,37 38), coaxial CNT/MnO2 ( 19),




Au-CNT/MnO2 ( 19), activated carbon-MnO2 hybrid electrodes ( ,39 ,40 412),

MnO2/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/MnO2 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 MnO2 in NPG/MnO2 electrode shows the highest

specific capacitance of ∼1145 F/g.

________________________________________

References:

36 Zolfaghari, Z., Ataherian, F., Ghaemi, M., Gholami, A. Capacitive behavior of

nanostructured MnO2 prepared by sonochemistry method. Electrochim. Acta 52,

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37 Cottineau, T., Toupin, M., Delahaye, T., Brousse, T., Bélanger, D. Nanostructured

transition metal oxides for aqueous hybrid electrochemical supercapacitors. Appl.

Phys. A 82, 599-606 (2006).

38 Wu, Z.S. et al. High-energy MnO2 nanowire/graphene and graphene asymmetric

electrochemical capacitors. ACS Nano 4, 5835-5842 (2010).

39 Brousse, T., Toupin, M., Bélanger, D. A hybrid activated carbon-manganese

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SUPPLEMENTARY INFORMATION Supplementary information … · SUPPLEMENTARY INFORMATION ... Supplementary information for Nanoporous Metal/Oxide Hybrid Electrodes for Electrochemical