High-capacity Sodium Peroxide Based Na-O2 Batteries with Low

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High-capacity Sodium Peroxide Based Na-O Batteries with Low Charge Overpotential via a Nanostructured Catalytic Cathode Lu Ma, Dongzhou Zhang, Yu Lei, Yifei Yuan, Tianpin Wu, Jun Lu, and Khalil Amine ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.7b01143 • Publication Date (Web): 21 Dec 2017 Downloaded from http://pubs.acs.org on December 21, 2017

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ACS Energy Letters

High-capacity Sodium Peroxide Based Na-O2 Batteries with Low Charge Overpotential via a Nanostructured Catalytic Cathode Lu Ma†, Dongzhou Zhang‡, Yu Lei §, Yifei Yuan∥, Tianpin Wu*†, Jun Lu*∥, and Khalil Amine*∥ †

X-ray Science Division and ∥Chemical Sciences and Engineering Division, Advanced Photon

Sources, Argonne National Laboratory, Lemont, Illinois 60439, United States ‡

Partnership for Extreme Crystallography, University of Hawaii at Manoa, Honolulu, Hawaii

96822, United States §

Department of Chemical and Materials Engineering, University of Alabama in Huntsville,

Huntsville, AL 35899, United States AUTHOR INFORMATION Corresponding Author [email protected] (T.Wu), [email protected] (J.Lu), and [email protected] (K. Amine)

Abstract

The superoxide based Na-O2 battery has circumvented the issue of large charge overpotential in Li-O2 batteries, however the one-electron process leads to limited capacity. Herein, A sodium

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peroxide based low overpotential (~0.5 V) Na-O2 battery with a capacity as high as of 7.5 mAh/cm2 is developed with Pd nanoparticles as catalysts on the cathode.

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Rechargeable metal-air batteries, especially the non-aqueous Li-O2 batteries, are recognized as one of the most promising techniques for next-generation energy storage owing to their high


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theoretical specific energy.1 However, one of the biggest challenges facing the Li-O2 battery is the large charge overpotential, which results in low round-trip efficiency and poor cycle life.2 Therefore, an efficient oxygen evolution reaction (OER) catalyst is required to reduce the charge overpotential in the Li-O2 system, which has been the major effort in this field during the past decade.

Alternatively, via substitution of lithium by sodium, Hartmann et al. reported a

rechargeable Na-O2 battery with a very low charge overpotential of 0.2 V, even without any catalyst employed on the cathode support.3 Such low overpotential is mainly due to the relatively high conductivity of the discharge product, sodium superoxide (NaO2). In contrast, the formation of LiO2 in a Li-O2 cell is very difficult due to its unfavorable thermodynamics.4 The formation of NaO2 is accomplished in a one-electron transfer reaction, as shown below: + + → = 2.27 1 From energy density point of view, the one-electron transfer process (forming superoxide) has a drastically lower theoretic specific energy (1108 Wh kg-1) than that of a cell with peroxide as discharge product via a two-electron manner (1605 Wh kg-1):5 + + 2 → = 2.33 2 With almost equal Gibbs free energy of formation shown in Reactions 1 and 2, NaO2 and Na2O2 are both thermodynamically possible discharge products in a Na-O2 cell, Na2O2 being slightly more favorable at standard condition. In fact, sodium peroxide (mostly as hydrates) based Na-O2 batteries have been reported. However the results are ambiguous and the overpotentials are large (~1.6 V).6-8 In this work, we have applied Pd nanoparticles as catalysts to promote the formation/decomposition of the sodium peroxide, and substantially reduced the charge overpotential of such Na2O2-based cell to ~0.5 V.


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The cell cathodes were fabricated by the atomic layer deposition (ALD) technique. ZnO was first deposited on the graphitized carbon black to passivate potential defect sites (denoted as ZnO/C).9 Pd nanoparticles were then grown on the ZnO-coated cathodes (denoted as Pd/ZnO/C). The average size of the Pd nanoparticles is around 5nm (Figure 1a and Figure S1) and the metallic character was confirmed by both the consistency to the diffraction peaks of palladium (ICSD# 41517) by High-resolution X-ray diffraction (HRXRD) (Figure 1b) and the characteristic d-spacing of Pd-(1 1 -1) and atomic structure along Pd-[0 1 1] zone axis obtained from scanning transmission electron microscope (STEM) (Figure 1a). No diffraction peak from ZnO was observed on the Pd/ZnO/C or ZnO/C, possibly due to the small domain-size or the amorphous nature of such ALD-deposited ZnO.10 X-ray absorption spectroscopy was applied to probe the chemical and coordination information. The X-ray absorption near edge structure (XANES) spectra at Zn K-edge (Figure S2a) indicate that the oxidation state of the Zn in the Pd/ZnO/C or the ZnO/C is ~2+, but the ZnO has lost its long-range order, forming amorphous phase (see detailed analysis in SI). The XANES spectra at Pd K-edge (Figure S2b) show that the majority of the Pd is metallic, with a small amount on the surface being oxidized (Table S2). It is believed that such oxidized Pd may enhance the catalytic activity of the Pd nanoparticles.11 The oxidation state of Pd is also influenced by the its interaction with the ZnO layer, which was studied by extended X-ray absorption fine structure (EXAFS) spectra. To avoid the influence of the oxygen, the Pd/ZnO/C sample was reduced by H2 at 250 oC. As shown in Figure 1c, due to the surface oxidation, the Pd-O peak at ~1.5 Å of Pd/ZnO/C cathode was much stronger than that of Pd foil. However, after reduction, instead of being metallic, the intensity of the Pd-O peak of the Pd/ZnO/C was still noticeably higher, reflecting that the Pd formed Pd-O bond with the oxygen in ZnO, which couldn’t be reduced at this condition. The bond between Pd and ZnO


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allows the stable anchoring of Pd catalysts on the cathode and improves the battery cycle life, which was demonstrated by the improved cyclability (discussed in SI).

Figure 1. (a) Annular bright-field scanning transmission electron microscopy (ABF-STEM) showing Pd-(1 1 -1) lattice fringes (white arrows) and Pd-[0 1 1] zone axis atomic structure (yellow dots and the inserted model) of Pd/ZnO/C sample. (b) HEXRD patterns of Pd/ZnO/C and ZnO/C samples (blue dashed line: Pd, ICSD # 41517 and green dashed line: ZnO, ICSD # 67848). (c) EXAFS spectra at Pd K-edge of Pd/ZnO/C sample. The catalytic effect of such Pd/ZnO/C cathode was examined in a Na-O2 cell. Compared to the cell with a ZnO/C-structured cathode (Figure S3a), a significant reduction of the charge overpotential (to ~0.5 V) was obtained with the Pd/ZnO/C cathode (Figure 2a), which validates the electrocatalytic role of the Pd nanoparticles. High energy X-ray diffraction (HEXRD) pattern under operando conditions was collected during the first cycle, which confirmed the formation/decomposition of Na2O2·2H2O (Figure 2b). Raman spectra were used to investigate the surface of the discharge product Na2O2·2H2O (Figure S4). Instead of the characteristic Raman peaks of Na2O2·2H2O (Ref. 7), a peak at 1126 cm-1 appeared, falling in the range of superoxide strength.4 And the peak at 1502 cm-1 is attributed to the strong interaction between the superoxides and the porous carbon surface.12 Overall, the Raman spectra have reflected the


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formation of an oxygen-rich superoxide-like product by the Pd nanoparticles, which is a plausible reason for the reduction of the charge overpotential.13-15

Figure 2. (a) Voltage profiles of Na-O2 batteries cycled under capacity control mode with Pd/ZnO/C as cathode. (b) In-situ X-ray diffraction spectra of the Na-O2 battery with Pd/ZnO/C as cathode. The structural and morphological properties of the discharge product are also profoundly affected by the Pd/ZnO/C cathode due to the increasing active sites by the Pd nanoparticles. As shown in Figure S5a, after 6-hour discharge, feather-like structures formed on the cathode. The “feathers” became thinner (Figure S5b) and cracked into nanowires (Figure S5c) after 18 hours, which developed a lot of holes and prevented the pores of the cathode from clogging. Such highly porous framework allowed the oxygen to access the inside of the cathode facilely. Meanwhile, more discharge product can be stored on the cathode. Consequently, the battery with Pd/ZnO/C cathodes exhibits an extremely large discharge capacity of 7.5 mAh/cm2 (Figure S6). In contrast, the discharge product on ZnO/C merged together and formed a thicker layer on the


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ACS Energy Letters

cathode (Figure S5d-f). The pores of the cathode were blocked quickly by the discharge product, leading to the cell failure. In summary, we have developed a cathode structure with Pd nanoparticles on the ZnO passivated porous carbon for Na2O2-based cells with a low charge overpotential and high capacity. The Pd nanoparticles have promoted the formation/decomposition of the oxygen-rich superoxide-like Na2O2·2H2O with porous structure under a two-electron electrochemical process. The charge overpotential is reduced to ~0.5 V and a high capacity of 7.5 mAh/cm2 is achieved. This study demonstrates a new direction to achieve high-performance peroxide based Na-O2 batteries through the rational design of electrode structures.

ASSOCIATED CONTENT Supporting Information. Experimental methods, low magnification TEM, size distribution, XANES spectra of the Pd/ZnO/C sample, the voltage profile of the Na-O2 battery with bare carbon, ZnO/C and Pd/C as cathodes, Raman spectra and SEM images of the discharge products, deep discharge profile of the Pd/ZnO/C and ZnO/C cell. AUTHOR INFORMATION Corresponding Author *To whom correspondence should be addressed. Jun Lu: Email: [email protected]; Phone: 630-252-4485 Khalil Amine, Email: [email protected], phone: 630-252-3838


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Tianpin Wu: Email: [email protected]; Phone: 630-252-1482

Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the U.S. Department of Energy under Contract DEAC0206CH11357 from the Vehicle Technologies Office, Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE). Use of the Advanced Photon Source (9-BM, 20-BM and 11BM) was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357. Part of the experiments were performed at the 13BM-C experimental station of the GSECARS facility at the APS. 13BM-C operation is supported by COMPRES through the Partnership for Extreme Crystallography (PX^2) project, under NSF Cooperative Agreement EAR 11-57758.

References (1) Lee, D. U.; Xu, P.; Cano, Z. P.; Kashkooli, A. G.; Park, M. G.; Chen, Z. W. Recent Progress and Perspectives on Bi-Functional Oxygen Electrocatalysts for Advanced Rechargeable Metal-Air Batteries. J. Mater. Chem. A 2016, 4, 7107-7134. (2) Lu, J.; Li, L.; Park, J. B.; Sun, Y. K.; Wu, F.; Amine, K. Aprotic and Aqueous Li-O2 Batteries. Chem. Rev. 2014, 114, 5611-5640. (3) Hartmann, P.; Bender, C. L.; Vracar, M.; Durr, A. K.; Garsuch, A.; Janek, J.; Adelhelm, P. A Rechargeable Room-Temperature Sodium Superoxide (NaO2) Battery. Nat. Mater. 2013, 12, 228-232.


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(4) Lu, J.; Lee, Y. J.; Luo, X. Y.; Lau, K. C.; Asadi, M.; Wang, H. H.; Brombosz, S.; Wen, J. G.; Zhai, D. Y.; Chen, Z. H. et al. A Lithium-Oxygen Battery Based on Lithium Superoxide. Nature 2016, 529, 377-382. (5) Das, S. K.; Lau, S.; Archer, L. A. Sodium-Oxygen Batteries: A New Class of Metal-Air Batteries. J. Mater. Chem. A 2014, 2, 12623-12629. (6) Sun, Q.; Yadegari, H.; Banis, M. N.; Liu, J.; Xiao, B.; Wang, B.; Lawes, S.; Li, X.; Li, R.; Sun, X. Self-Stacked Nitrogen-Doped Carbon Nanotubes as Long-Life Air Electrode for Sodium-air Batteries: Elucidating the Evolution of Discharge Product Morphology. Nano Energy 2015, 12, 698-708. (7) Ortiz-Vitoriano, N.; Batcho, T. P.; Kwabi, D. G.; Han, B. H.; Pour, N.; Yao, K. P. C.; Thompson, C. V.; Shao-Horn, Y. Rate-Dependent Nucleation and Growth of NaO2 in Na-O2 Batteries. J. Phys. Chem. Lett. 2015, 6, 2636-2643. (8) Yin, W. W.; Yue, J. L.; Cao, M. H.; Liu, W.; Ding, J. J.; Ding, F.; Sang, L.; Fu, Z. W. Dual Catalytic Behavior of A Soluble Ferrocene as An Electrocatalyst and in the Electrochemistry for Na-Air Batteries. J. Mater. Chem. A 2015, 3, 19027-19032. (9) Lu, J.; Lei, Y.; Lau, K. C.; Luo, X. Y.; Du, P.; Wen, J. G.; Assary, R. S.; Das, U.; Miller, D. J.; Elam, J. W. et al. A Nanostructured Cathode Architecture for Low Charge Overpotential in Lithium-Oxygen Batteries. Nat. Commun. 2013, 4, 2383. (10) Libera, J. A.; Elam, J. W.; Pellin, M. J. Conformal ZnO Coatings on High Surface Area Silica Gel Using Atomic Layer Deposition. Thin Solid Films 2008, 516, 6158-6166. (11) Wang, C. X.; Yang, F.; Yang, W.; Ren, L.; Zhang, Y. H.; Jia, X. L.; Zhang, L. Q.; Li, Y. F. PdO Nanoparticles Enhancing the Catalytic Activity of Pd/carbon Nanotubes for 4nitrophenol Reduction. RSC Adv. 2015, 5, 27526-27532. (12) Zhai, D. Y.; Wang, H. H.; Lau, K. C.; Gao, J.; Redfern, P. C.; Kang, F. Y.; Li, B. H.; Indacochea, E.; Das, U.; Sun, H. H. et al. Raman Evidence for Late Stage Disproportionation in a Li-O2 Battery. J. Phys. Chem. Lett. 2014, 5, 2705-2710. (13) Zhai, D.; Lau, K. C.; Wang, H.-H.; Wen, J.; Miller, D. J.; Lu, J.; Kang, F.; Li, B.; Yang, W.; Gao, J. Interfacial Effects on Lithium Superoxide Disproportionation in Li-O2 Batteries. Nano Lett. 2015, 15, 1041-1046. (14) Lu, Y. C.; Shao-Horn, Y. Probing the Reaction Kinetics of the Charge Reactions of Nonaqueous Li-O2 Batteries. J. Phys. Chem. Lett. 2013, 4, 93-99. (15) Peng, Z. Q.; Freunberger, S. A.; Hardwick, L. J.; Chen, Y. H.; Giordani, V.; Barde, F.; Novak, P.; Graham, D.; Tarascon, J. M.; Bruce, P. G. Oxygen Reactions in a Non-Aqueous Li+ Electrolyte. Angew Chem Int Edit 2011, 50, 6351-6355.


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High-capacity Sodium Peroxide Based Na-O2 Batteries with Low

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