Supplementary material for

Electrochemical behavior of Ru nanoparticles as catalysts in

aprotic Li–O2 batteries

Xing Xin, Kimihiko Ito, Yoshimi Kubo*

GREEN, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan

* Corresponding author:

Dr. Yoshimi Kubo

Tel.: +81-029-8604773

Email: KUBO.Yoshimi@nims.go.jp

Present Addresses: GREEN, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-

0044, Japan

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Fig. S1. TEM images of RGO nanosheets.

Fig. S2. TGA curves of RGO/Ru and KB/Ru composites.

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Fig. S3. (a) STEM-ADF image and corresponding EELS maps of RGO/Ru, (b) C, (c) O, and (d)

Ru.

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Fig. S4. (a) SEM image of KB particles. (b) SEM image of the KB/Ru composite. (c) STEM-

ADF image and corresponding EELS map of the KB/Ru composite. (d) XRD pattern of the

KB/Ru composite.

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Table S1

RGO/Ru-1 RGO/Ru-2 RGO/Ru-3 RGO/Ru-4 RGO/Ru-5

Ru content 82.7% 72.9% 56.9% 37.2% 10.0%

Pore

volume(cm3/g)

0.065 0.105 0.178 0.275 0.435

Surface Area

(m2/g)

59.8 71.5 75.2 98.8 149.6

Fig. S5. (a) Nitrogen isotherm adsorption–desorption curves and (b) pore-size distributions for

RGO/Ru composites with different Ru contents.

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Fig. S6. SEM images of RGO/Ru nanocomposites with different Ru contents: (a) RGO/Ru-1, (b)

RGO/Ru-2, (c) RGO/Ru-3, (d) RGO/Ru-4, and (e) RGO/Ru-5. (f) TGA curves of RGO/Ru with

different Ru contents.

Nitrogen isotherm adsorption–desorption curves and pore-size distributions (Fig. S5) for

RGO/Ru show that the surface area and pore volume decrease with increasing Ru content. The

pore-size distributions clearly show that pores of several tens of nanometers are dominant and

markedly reduced with increasing Ru content. It is found in Fig. S6 that, at a high Ru content of

82.7% (RGO/Ru-1, Figure S6a), Ru particles attached to the surface of graphene are obviously

aggregated. When the Ru content is decreased, the density of Ru on the graphene sheets

gradually decreases, and the extent of aggregation also declines. When the weight ratio of Ru is

lower than 10%, the sheet thickness is obviously thinner and is similar to bare graphene.

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Fig. S7. (a) Discharge curves during the first cycle for RGO/Ru composites with different Ru

contents at a cut-off voltage of 2.0 V and a current of 0.1 mA. (b) Discharge/charge curves of

RGO/Ru composites with different Ru contents at a cut-off voltage of 2.4–4.5 V and a current of

0.1 mA. The cathode area is 2 cm2.

Note that the cells were totally discharged at a cut-off voltage of 2.0 V will make the cathodes

to be fully filled with the discharge products (mainly Li2O2, insulated) which will further

influence the charge process. Therefore, we investigated the charge process by adopting the

discharge cut-off voltage at 2.4 V (as shown in Figure S7b).

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Fig. S8. SEM images of (a) RGO, (b) KB, (c) RGO/Ru, and (d) KB/Ru after discharge of 2 mAh

at a current of 0.1 mA. The cathode area is 2 cm2.

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Fig. S9. (a) Schematic of in situ XAFS measurement for a Li–O2 cell. (b) Discharge and charge

profiles of the Li–O2 cell during in situ XAFS measurement. EXAFS oscillations during

discharging (c) and charging (d).

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Fig. S10. Discharge-charge curves of Li-O2 cells with RGO/Ru cathodes (area is 2 cm2) at

different cycles, the current is 0.1 mA. Ru content is (a) 82.7%, (b) 72.9%, (c) 56.9% and (d)

10%.

Fig. S11. SEM image (a) and XRD pattern (b) of RGO/Ru (37.2% Ru) after 109 cycles (charged

state) at 0.1 mA with a fixed capacity of 1mAh. Area of cathode is 2 cm2.

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