Highly Ordered Mesoporous Carbon Support Materials for Air

Electrochemistry The Electrochemical Society of Japan

Received: August 30, 2016 Accepted: December 13, 2016 Published: March 5, 2017 http://dx.doi.org/10.5796/electrochemistry.85.128

Article

Electrochemistry, 85(3), 128–132 (2017)

Highly Ordered Mesoporous Carbon Support Materials for Air Electrode of Lithium Air Secondary Batteries Yuhki YUI,a,b Shuhei SAKAMOTO,a Masaya NOHARA,a Masahiko HAYASHI,a,* Jiro NAKAMURA,b,c Kota SUZUKI,b,c Masaaki HIRAYAMA,b,c Ryoji KANNO,b,c and Takeshi KOMATSUa a

NTT Device Technology Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan b Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502, Japan c Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502, Japan * Corresponding author: [email protected] ABSTRACT The electrochemical properties of a lithium air secondary battery (LAB) cell incorporating CMK-3 or carbon replica (CR) as a highly ordered mesoporous carbon support material were examined under the condition of a current density of 0.1 mA/cm2 with a voltage range of 2.0 to 4.2 V in a dry air atmosphere. The first discharge capacities of the LAB cell incorporating Pt10Ru90 electrocatalyst/CMK-3 and CR were 103 and 1000 mAh/g, respectively. The cycle properties of the LAB cell incorporating Pt10Ru90 electrocatalyst/CMK-3 was poor; in contrast, the one incorporating CR showed better cycle stability (828 mAh/g up to 9 cycles). These superior properties with CR are due to its larger surface area and larger total pore volume than those of CMK-3. © The Electrochemical Society of Japan, All rights reserved.

Keywords : Lithium Air Secondary Battery, CMK-3, Carbon Replica

1. Introduction In response to the great demand for power sources in mobile devices, electric vehicles and stationary power storage systems, research on various next-generation batteries has been actively conducted.1–6 Among these batteries, the lithium air secondary battery (LAB) has been attracting much attention because it has the highest theoretical energy density (³3,505 Wh/kg).7–10 The reason for such high energy density is that the battery consists of lithium metal and oxygen supplied from air as a negative and a positive active material, respectively, and a nonaqueous solution as an electrolyte. The discharge reaction of an LAB produces Li2O2 from lithium ions and oxygen on the air (positive) electrode. That is, because it is not necessary to install a positive active material in the battery, the LAB exhibits a very high energy density. However, LABs have issues with their electrochemical properties, such as cyclability and rate capability, which need further improvement to put LABs into practical use.7–10 One of the causes of the problems is large solid discharge product Li2O2 formed on the air electrode diminished reversibility for the positive electrode reaction due to the formation of non-uniform and large solid discharge product Li2O2.11–13 Another is that insulation properties of Li2O2 degrade the electrochemical properties. Carbon black particles, Ketjen-black EC600JD (KB) (surface area of 1270 m2/g; pore volume of 1.2 cm3/g), with nano-sized and unarranged shapes have been widely used as carbon support materials for air electrodes.11,14 As a result, non-uniform and micrometer-order discharge product Li2O2 forms on the air electrode, and it is not decomposed completely in the charge process because of the poor contact between carbon and Li2O2. Therefore, it is important to control the size of discharge product Li2O2 and to uniformly deposit it on air electrode. As reported in Ref. 15, nanoporous gold with 30–50 nm pores showed discharge capacities of about 300 mAh/g for 100 cycles, and it was 128

effective in promoting decomposition of Li2O2. We believe that one of the reasons for the effective decomposition of Li2O2 on nanoporous gold is that the size of Li2O2 can be controlled by the nanopores with gold. However, gold is not suitable for practical use because it’s too expensive. In addition, although not explicitly reported in Ref. 15, since the specific surface area of nanoporous gold would be low, the capacity of the cell appears to be smaller. As reported in Refs. 16, 17, mesoporous MnO2 which is prepared by hard template method showed good electrocatalitic activity, which leads to high discharge capacity and good cyclability. LAB cells with Au-Pd nanoparticle-supported mesoporous B-MnO2 as an air electrode showed good cyclability of 714 mAh/g at 12 cycles.17 Highly ordered mesoporous carbon consists of a carbon matrix arranged with regularly patterned mesopores.18–23 This kind of carbon was synthesized by using an ordered mesoporous silica template coated on a carbon precursor. CMK-3, which is synthesized by using rod-shaped silica SBA-15 as the template, has stacks of hollow rod-shaped pores. As reported in Ref. 23, the pores size of CMK-3 is 5 nm, and the total pore volume and the specific surface area are comparable to those of KB. In addition, the cell with CMK-3 exhibited a better cycle property (about 1000 mAh/g up to 15 cycles) than the one with conventional carbon (Super P).23 Carbon replica (CR), which is synthesized using silica nanospheres (SNSs), has close cubic packing of sphere-shaped pores and the pore size is adjustable in the range of about 10–100 nm. As reported in Ref. 21, the specific surface area of CR is 919 m2/g in the case of pore size of 11 nm. Since CMK-3 and CR have properties similar to KB, which is conventionally used for LABs,14 a cell incorporating CMK-3 or CR should show large capacity and better cycle performance because the shape of discharge product Li2O2 can be regulated by controlling the pore structure. In addition, CMK-3 and CR are suitable materials to evaluate how pore size and shape on a carbon support affect the discharge and charge properties.


2. Experimental 2.1 Synthesis of highly ordered mesoporous carbon, CMK-3 and CR CMK-3 was synthesized by using SBA-15 silica as a template.18–20 SBA-15 silica was prepared using a triblock copolymer (EO20PO70EO20 (P-123), 5 g, Sigma-Aldrich Co. LLC.) as a surfactant, tetraethyl orthosilicate (TEOS, 10.41 g, Tokyo Chemical Industry Co., 96%) as a silica source, and HCl (31.28 g) as an acid catalyst. These materials were mixed in distilled water and left to stand for 24 h at 100°C. Then, the mixture was dried at 100°C. Finally, SBA15 silica was obtained by heating the mixture material for 5 h at 550°C in air. CMK-3 was synthesized by coating SBA-15 silica as a template with furfuryl alcohol (Sigma-Aldrich Co. LLC.) as a carbon source.18–20 The mixture of SBA-15, furfuryl alcohol, and oxalic acid was polymerized for 48 h at 100°C. Then, the mixture was carbonized for 3 h at 800°C in Ar. Next, the carbonized material was soaked in 20 wt% HF to remove the silica template. Finally, CMK-3 was obtained after washing it with distilled water and ethanol. CR was synthesized using the parent SNSs as a template.21 Larginine (Kanto Chemical Co., 0.174 g, 98%) as a base catalyst and TEOS (10.45 g) as a silica source were mixed in distilled water. After the mixture had stood for 24 h at 70°C, it was dried at 100°C. The dried material was heated for 10 h at 550°C, and SNSs (14 nm in diameter) was obtained. Then, CR was obtained from the SNSs by removing the silica template in the same manner as for CMK-3. 2.2 Synthesis of air-electrode material, Pt10Ru90/CMK-3 or CR Pt10Ru90/mesoporous carbon was prepared by the formic acid reduction method, as reported previously.24 The mesoporous carbon was dispersed in formic acid solution by sonication, and then a mixed solution (Pt:Ru = 10:90) of H2PtCl6·6H2O (Kanto Chemical Co.) and RuCl3 (Furuya Metal Co., Ltd.) was dropped into the mesoporous carbon/formic acid solution, which was then stirred overnight. Then, dried Pt10Ru90/mesoporous carbon was obtained by heattreating the mixture at 300°C for 12 h in Ar. Pt10Ru90/mesoporous carbon was synthesized in the ratio of 80 to 10 by weight. 2.3 Characterization of mesoporous carbon and Pt10Ru90/ CMK-3 or CR The porosity of the mesoporous carbon was determined by BET measurements with nitrogen gas (BEL JAPAN INC., BELSORPmini). The pore distribution of carbon was refined by the BJH method. The crystalline phases of mesoporous carbon and Pt10Ru90/ mesoporous carbon were identified with a powder X-ray diffractometer (XRD) (Rigaku Corp., Ultima-IV) using CuKA radiation. The dispersion state of Pt10Ru90 over mesoporous carbon was observed with a field-emission transmission electron microscope (FE-TEM) (JEOL Ltd., JEM-2100F) with an accelerating voltage of 200 kV. To analyze the morphology of discharge products with a scanning electron microscope (SEM, JEOL Ltd., JEM-2100F) with accelerating voltage of 200 kV, the cells were opened after discharge/ charge in dry air with a dew point of less than ¹50°C and the air electrodes were washed with dimethyl carbonate and dried.

2.4 Electrochemical measurements of LAB cells with Pt10Ru90/CMK-3 or CR The air electrodes were prepared by coating a titanium mesh as a current collector with the mixture of mesoporous carbon or Pt10Ru90/mesoporous carbon and PVdF (Kureha Battery Materials Japan Co.) in N-methylpyrrolidone solvent (Tomiyama Pure Chemicals Industries Ltd.), and drying it at 100°C. The composition ratio of an air electrode with a diameter of 5 mm (weight of about 1.3 mg) was mesoporous carbon:PVdF = 90:10 or mesoporous carbon or KB:Pt10Ru90:PVdF = 80:10:10 in weight. The LAB cell (ECC-Air, EL-Cell GmbH) was assembled, incorporating the air electrode loaded with Pt10Ru90/mesoporous carbon, an electrolyte solution (1 mol/l lithium bis(trifluoromethanesulfonyl) amide [LiTFSA]/TEGDME (Tomiyama Pure Chemicals Industries Ltd.), a glass separator, and Li metal sheets (thickness of 600 µm; diameter of 17 mm; weight of about 71 mg) (Honjo Metal Co., Ltd.). Electrochemical measurements were carried out using an automatic galvanostatic discharge-charge system (Hokuto Denko Corp., HJ1001SD8) at a constant current density of 0.1 mA/cm2 between 2.0 and 4.2 V in dry air with a dew point of less than ¹50°C. The LAB cells were cycled with the cut-off capacity of 1000 mAh/g which corresponded to Li usage of about 0.34 mg. The discharge/ charge capacities were normalized by the weight of the mesoporous carbon, Pt10Ru90, and PVdF in the air electrodes. To analyze the discharged/charged electrodes with the XRD, the LAB cells were disassembled after the charge/discharge process, and the air electrodes were washed with dimethyl carbonate and dried in dry air atmosphere. 3. Results and Discussion The XRD patterns of samples of CMK-3, CR, Pt10Ru90/CMK-3 or CR are shown in Fig. 1. All the patterns exhibit broad peaks at around 23.0 and 43.5 deg, which correspond to carbon black (Vulcan XC-72R).25 That is, these mesoporous carbons’ crystal structure is similar to the conventional carbon black, but the particle shape and porosity are different as described below. These carbons have very broad peaks, and this suggests that they have the small crystallites and a low degree of graphitization. In many cases, such small crystallites lead to small particle size and large surface area. Peaks for silica were not observed, which suggests that the silica template had been completely removed. CMK-3 and CR had no differences in terms of crystal structure, and there were no changes in their crystal structures after electrocatalyst (Pt10Ru90) supported them. In our previous report on Pt10Ru90/KB, peaks for ruthenium (PDF#00-006-0663) at 38.4 and 44.0 deg were confirmed.24 However, there are no peaks for platinum and ruthenium as shown in Figs. 1(c) and (d). This is because Pt10Ru90 particles remained small, as will be discussed in the TEM results. The small Pt10Ru90

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In this study, our purpose was to control the size and shape of Li2O2 deposited on the air electrode and consequently improve the cycle properties by using highly ordered mesoporous carbon as support materials. We previously reported that a LAB cell incorporating Pt10Ru90/KB electrocatalyst shows discharge capacities of more than 800 mAh/g for over 8 cycles in an electrolyte solution based on tetraethylene glycol dimethyl ether (TEGDME).24 Thus, we prepared electrocatalyst-supported mesoporous carbons, Pt10Ru90/CMK-3 and Pt10Ru90/CR, and examined the electrochemical properties of LAB cells incorporating them into an air electrode.

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Figure 1. (Color online) XRD patterns of (a) CMK-3, (b) CR, (c) Pt10Ru90/CMK-3, and (d) Pt10Ru90/CR. 129

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particle size would improve the electrochemical properties of the cell with the electrocatalyst since the oxygen reduction/evolution reaction was catalyzed on the surface of Pt10Ru90. Figure 2 shows the pore size distributions for CMK-3 and CR. The BJH plot of CMK-3 and CR exhibits sharp peaks at only 3.32 and 12.1 nm, respectively. This suggests that CMK-3 and CR have uniform pores of about 3 and 12 nm, respectively. The pore size is consistent with the following TEM observation, and these results are in good agreement with Refs. 20, 21. The specific surface area and total pore volume of CMK-3 and CR obtained from the analysis by the BET method are shown in Table 1. Both the specific surface area and total pore volume of CR is an order of magnitude greater than those of CMK-3, and the data for CR is comparable to those for KB.14 These results suggest that, compared to CMK-3, CR has a large number of active sites at which discharge products can be deposited. Therefore, the use of CR would increase the capacity. The difference in physical properties between CMK-3 and CR result from the silica template shape. Figure 3 shows TEM images of CMK-3 and CR with/without Pt10Ru90 electrocatalyst. Figures 3(a) and (d) show views from the front of the rod, and Figs. 3(b) and (e) show views from the side surface of the rod. CMK-3 has regularly arranged rods of about 6 nm in diameter and pores with the size of approximately 2–3 nm between the rods, as shown in Figs. 3(a) and (b). The pore size is in good agreement with the value obtained from the BJH (Fig. 2). CR has pores of about 10 nm that are arranged in a regular manner, and the thickness of carbon framework between the pores is about 5 nm as shown in Fig. 3(c). The pore size is also in good agreement with the value obtained from the BJH (Fig. 2). Furthermore, there were no significant structural changes in either CMK-3 or CR due to loading electrocatalyst as shown in Figs. 3(d)–(f ). The particle size of Pt10Ru90 electrocatalyst is about 1–3 nm, which is smaller than the ones in the case of KB.24 In addition, Pt-Ru particles were found to be thoroughly dispersed in both the CMK-3 and CR. The mesoporous structure of CMK-3 and CR would lead to small particles of Pt10Ru90 electrocatalyst. Thus, XRD peaks of Pt-Ru might not be observable because of the nanometer particle size as shown in Figs. 3(c) and (d). Figures 4 and 5 respectively show the first discharge-charge curves and the cycle properties of the LAB cells incorporating

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Figure 5. (Color online) Cycle properties of cells incorporating (a) CMK-3 and (b) CR. CMK-3 and CR without Pt-Ru electrocatalysts in the 2.0 to 4.2 V range. The first discharge capacities are 132 and 811 mAh/g in the cells with CMK-3 and CR, respectively. The discharge capacities are quite different between CMK-3 and CR. This is because the specific surface area and total pore volume of CR are an order of magnitude larger than those of CMK-3 and because there are a large number of reaction sites where the discharge product could be deposited on the CR, as expected from the above discussion. In fact, discharge capacities, specific surface areas, and pore volumes for various kinds

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Figure 7. (Color online) Cycle properties of cells incorporating (a) Pt10Ru90/CMK-3, (b) Pt10Ru90/CR and (c) Pt10Ru90/KB. of carbons as support material have been reported to be closely related linearly.14 In the following charging process, charge capacities were 51 and 509 mAh/g in the cells with CMK-3 and CR, respectively. The coulombic efficiencies for CMK-3 and CR were 39 and 63% at the first cycle, respectively. In Ref. 26, it was found that Li2O2 cannot be fully decomposed for a carbon-only air electrode without a catalyst. This indicates that the discharge product on the electrode remained even when the charging ends. Therefore, the subsequent discharge capacities would decrease gradually. In fact, the cyclability of cells with CMK-3 and CR without the catalysts was poor, as shown in Fig. 5. The discharge capacities of the LAB cells with CMK-3 and CR decresed to 22 and 155 mAh/g in the second cycle, respectively. To improve the cyclability, we tried to enhance the activities for the discharge/charge reactions by using Pt10Ru90 electrocatalyst/mesoporous carbon. Figure 6 shows the first discharge-charge curves of the LAB cells incorporating Pt10Ru90 electrocatalyst/CMK-3, CR or KB in the 2.0 to 4.2 V range, and Fig. 7 shows cycle properties. The first discharge capacities are 103, 1000, and 1000 mAh/g in the ones with Pt10Ru90/CMK-3, CR and KB, respectively. Here, the capacity of 1000 mAh/g cut off the discharge/charge step. In the following charging process for all cells, the charge capacities showed almost the same values as the discharge capacities, and the charging voltage was lower than the ones without the electrocatalyst. The improvement in charging capacity is due to the electrocatalytic activity of Pt-Ru. In addition, compared to the one with KB as a reference, the discharge voltage of the one with CR was higher. This suggests that the pore structure of CR promotes the electrocatalitic activity. Then, the improved charge capacity would lead to good cyclability. The one with Pt10Ru90/CMK-3 showed almost the same discharge

capacity as the cell without the electroctalyst, but the first cycle coulombic efficiency for CMK-3 with/without the electrocatalyst was improved from 39 to 78%. The first cycle coulombic efficiency for CR with/without the electrocatalyst was improved from 62 to 100%. Furthermore, the one incorporating CR showed good cycle stability with discharge capacity of 828 mAh/g at the 9th cycle, as shown in Fig. 7. There is not much difference between the cycle properties for CR and KB as shown in this figure. The LAB cell incorporating CR showed higher discharge voltages as shown in Fig. 6 in spite of its lower surface areas than KB, since the catalytic activity of CR was promoted by the pore structure. The cycle properties of CR would be further improved by optimizing the size of the pore diameter. Although the discharge capacities for Pt10Ru90/ CMK-3 are smaller than for Pt10Ru90/CR over the cycle test, the cell with Pt10Ru90/CMK-3 was also slightly improved with respect to cycle performance by the addition of the catalyst. The addition of the electrocatalyst is effective for reducing charge voltage and increasing discharge-charge capacity. Figure 8 show SEM images of the pristine air electrodes incorporating Pt10Ru90/CMK-3, CR, and KB (as reference), after the first discharge and charge. Pristine electrodes incorporating CMK-3 and CR have highly ordered structure as shown in (a-1) and (b-1). In contrast, the one incorporating KB has particles of irregular shapes as shown in (c-1). After discharge, the one incorporating CMK-3 is covered with discharge products as shown in (a-2), and the one incorporating KB is covered with non-uniform and large size discharge products as shown in (c-2). These shapes of discharge products would be difficult to decompose in the charge process. On the other hand, discharge products on the one incorporating CR have a netlike shape, which is affected by the pore structure of CR support materials as shown in (b-2). This shape would be easier to decompose in the charge process since electrolyte solution seep through the discharge products to a deep position. As shown in (a-3), (b-3), and (c-3), all electrodes after the first charge returned to their pristine shape because discharge products were decomposed in the charge process. However, the ease of decomposition of the discharge products by their shape significantly differenced in the long-term cycle, and the one incorporating CR showed good cycle stability as shown in Fig. 7. Figure 9 shows XRD patterns of the air electrode incorporating Pt10Ru90/CR as prepared and after the first discharge/charge shown in Fig. 6. After the first discharge, new peaks appeared at around 131


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and CR, and loading the electrocatalyst did not cause any significant structural changes in either one. While the cell incorporating CMK-3 shows a small capacity (103 mAh/g), the one incorporating CR shows high capacity of 1000 mAh/g. In addition, the electrocatalyst is effective for reducing charge voltage and improving the first coulombic efficiency from 62 to 100%.

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References

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1. M. D. Slater, D. Kim, E. Lee, and C. S. Johnson, Adv. Funct. Mater., 23, 947 (2013). 2. Y. Yui, Y. Ono, M. Hayashi, Y. Nemoto, K. Hayashi, K. Asakura, and H. Kitabayashi, J. Electrochem. Soc., 162, A3098 (2015). 3. Y. Yui, M. Hayashi, and J. Nakamura, Sci. Rep., 6, 22406 (2016). 4. T. D. Gregory, R. J. Hoffman, and R. C. Winterton, J. Electrochem. Soc., 137, 775 (1990). 5. M.-C. Lin, M. Gong, B. Lu, Y. Wu, D.-Y. Wang, M. Guan, M. Angell, C. Chen, J. Yang, B.-J. Hwang, and H. Dai, Nature, 520, 324 (2015). 6. H. Wang, Y. Yang, Y. Liang, J. T. Robinson, Y. Li, A. Jackson, Y. Cui, and H. Dai, Nano Lett., 11, 2644 (2011). 7. K. M. Abraham and Z. Jiang, J. Electrochem. Soc., 143, 1 (1996). 8. P. G. Bruce, S. A. Freunberger, L. J. Hardwick, and J.-M. Tarascon, Nat. Mater., 11, 19 (2012). 9. J.-S. Lee, S. T. Kim, R. Cao, N.-S. Choi, M. Liu, K. T. Lee, and J. Cho, Adv. Energy Mater., 1, 34 (2011). 10. R. Padbury and X. Zhang, J. Power Sources, 196, 4436 (2011). 11. S. Higashi, Y. Kato, K. Takechi, H. Nakamoto, F. Mizuno, H. Nishikoori, H. Iba, and T. Asaoka, J. Power Sources, 240, 14 (2013). 12. R. R. Mitchell, B. M. Gallant, Y. S. Horn, and C. V. Thompson, J. Phys. Chem. Lett., 4, 1060 (2013). 13. E. Yilmaz, C. Yogi, K. Yamanaka, T. Ohta, and H. R. Byon, Nano Lett., 13, 4679 (2013). 14. M. Hayashi, H. Minowa, M. Takahashi, and T. Shodai, Electrochemistry, 78, 325 (2010). 15. Z. Peng, S. A. Freunberger, Y. Chen, and P. G. Bruce, Science, 337, 563 (2012). 16. A. K. Thapa, Y. Hidaka, H. Hagiwara, S. Ida, and T. Ishihara, J. Electrochem. Soc., 158, A1483 (2011). 17. A. K. Thapa, T. H. Shin, S. Ida, G. U. Sumanasekera, M. K. Sunkara, and T. Ishihara, J. Power Sources, 220, 211 (2012). 18. M. Nagao, M. Otani, H. Tomita, S. Kanzaki, A. Yamada, and R. Kanno, J. Power Sources, 196, 4741 (2011). 19. M. Nagao, Y. Imade, H. Narisawa, R. Watanabe, T. Yokoi, T. Tatsumi, and R. Kanno, J. Power Sources, 243, 60 (2013). 20. M. Nagao, Y. Imade, H. Narisawa, T. Kobayashi, R. Watanabe, T. Yokoi, T. Tatsumi, and R. Kanno, J. Power Sources, 222, 237 (2013). 21. T. Yokoi, Y. Sakamoto, O. Terasaki, Y. Kubota, T. Okubo, and T. Tatsumi, J. Am. Chem. Soc., 128, 13664 (2006). 22. I. Hwang, G. Lee, and Y. Tak, Int. J. Electrochem. Sci., 10, 8982 (2015). 23. B. Sun, H. Liu, P. Munroe, H. Ahn, and G. Wang, Nano Res., 5, 460 (2012). 24. Y. Yui, M. Nohara, S. Sakamoto, M. Hayashi, J. Nakamura, and T. Komatsu, International Meeting on Lithium Batteries, IMLB, Abst. #365 (2016). 25. M. Carmo, A. R. Santos, J. G. R. Poco, and M. Linardi, J. Power Sources, 173, 860 (2007). 26. T. Ogasawara, A. Debart, M. Holzapfel, P. Novak, and P. G. Bruce, J. Am. Chem. Soc., 128, 1390 (2006).

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Figure 9. (Color online) XRD patterns of air electrodes incorporating Pt10Ru90/CR: Pristine, after first discharge, and after first charge.

32.9 and 58.7 deg, which were assigned to Li2O2. The peaks of Li2O2 are very small and broad, indicating that the crystallinity would be amorphous-like or very small particles. Then, the peaks assigned to Li2O2 disappeared after the first charge. These results suggest that the main discharge product Li2O2 is deposited and that it is decomposed by the charging process. In addition, peaks of TiO2 were detected on the titanium current collector. Since TiO2 has low conductivity, it may possibly inhibit the formation and decomposition reaction of Li2O2. As described above, the cells incorporating Pt10Ru90/CR show a discharge capacity of 1000 mAh/g and have good cycle characteristics. Hence, CR is useful as a carbon support material, and the electrochemical properties of CR are further improved by adding an electrocatalyst. Hereafter, there is a need to further improve the discharge/charge characteristics by optimizing the fine structure of CR. 4. Conclusions We focused on highly ordered mesoporous carbons, CMK-3 and CR, as support material for air electrodes in LABs. CMK-3 and CR were synthesized by using an ordered mesoporous silica template, and these carbons have a low degree of graphitization. CMK-3 with pores of about 2–3 nm arranged regularly and CR with pores of about 10 nm arranged regularly were synthesized. CR has a large specific surface area and large total pore volume, and the values were found to be an order of magnitude larger than those for CMK3. In addition, Pt10Ru90 of 1–3 nm in size was loaded onto CMK-3

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