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Insight into the catalytic mechanism of bimetallic platinum-copper core-shell nanostructures for nonaqueous oxygen evolution reactions Lu Ma, Xiangyi Luo, A. Jeremy Kropf, Jianguo Wen, Xiaoping Wang, Sungsik Lee, Deborah J. Myers, Dean J. Miller, Tianpin Wu, Jun Lu, and Khalil Amine Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.5b04794 • Publication Date (Web): 28 Dec 2015 Downloaded from http://pubs.acs.org on December 29, 2015

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Insight into the catalytic mechanism of bimetallic platinum-copper core-shell nanostructures for nonaqueous oxygen evolution reactions Lu Ma,1‡ Xiangyi Luo,2‡ A. Jeremy Kropf,3 Jianguo Wen,4 Xiaoping Wang,3 Sungsik Lee,1 Deborah J. Myers,3 Dean Miller,4 Tianpin Wu,1* Jun Lu3*, and Khalil Amine3* 1

X-ray Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439.

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Material Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439.

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Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue,

Argonne, IL 60439. 4

Electron Microscopy Center - Center for Nanoscale Materials, Argonne National Laboratory, 9700

South Cass Avenue, Argonne, IL 60439.

KEYWORDS: bimetallic catalysts, oxygen evolution reaction, X-ray absorption spectroscopy, nanostructures, alloys ABSTRACT The oxygen evolution reaction (OER) plays a critical role in multiple energy conversion and storage applications. However, its sluggish kinetics usually results in large voltage polarization and unnecessary energy loss. Therefore, designing efficient catalysts which could facilitate this process has become an emerging topic. Here, we present a unique Pt-Cu core-shell nanostructure for catalyzing the non-aqueous OER. The catalysts are systematically investigated with comprehensive spectroscopic techniques, and applied in non-aqueous Li-O2 electrochemical cells, which exhibited dramatically reduced charging overpotential (< 0.2 V). The superior performance is explained by the robust Cu (I) surface sites stabilized by the Pt core in the nanostructure. The insights into the catalytic mechanism of the unique Pt-Cu core-shell nanostructure gained in this work are expected to serve as a guide for future design of other nanostructured bimetallic OER catalysts.

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Designing efficient catalysts for advanced energy applications is crucial for the effective and versatile use of energy. Particularly, the oxygen evolution reaction (OER) is a key step in many energy storage processes, such as water splitting1 and rechargeable metal-air batteries.2, 3 However, due to the multiple electron transfer nature, the sluggish kinetics of the OER usually leads to large voltage polarization and hinders its practical applications in commercialized devices.4, 5 Owing to the electronic and geometric structures, bimetallic nanostructured catalysts typically exhibit unusual catalyzing properties.6 Through the rational compositional and structural design, the catalytic activity can be significantly tuned and improved towards specific reactions.7 In fact, bimetallic catalysts have already been widely applied to energy storage, such as the oxygen reduction reaction (ORR) in fuel cells8-17, and the OER18 and hydrogen evolution reactions (HER)19 in water splitting. In this work, we have systematically examined the catalytic activity and mechanism of the platinum-copper (Pt-Cu) core-shell bimetallic nanostructures in non-aqueous condition. A facile strategy to prepare Pt-Cu bimetallic catalysts with the core-shell structure was demonstrated. The composites in the catalyst was characterized by High-Energy X-ray Diffraction (HEXRD) and X-ray absorption near edge structure (XANES) spectroscopy, indicating that the Cu was oxidized to Cu(II) and Pt was partially oxidized in the whole particle level. The core-shell structure of the Pt-Cu catalyst was determined by extended X-ray absorption fine structure (EXAFS) spectroscopy in bulk quantity, as well as confirmed then by scanning transmission electron microscopy (STEM). The particle sizes of the Pt-Cu catalyst was analyzed by small angle X-ray scattering (SAXS), which showed narrow size distributions in the diameter range of 2-4 nm. Those nanostructures exhibited excellent catalytic performance towards the non-aqueous


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OER, as demonstrated by the substantially reduction of the charging overpotential in Li-O2 batteries to less than 0.2 V, compared to a typical 1 V overpotential. The X-ray photoelectron spectroscopy (XPS) indicated that the robust catalytic activity can be attributed to the active surface Cu(I) sites which were stabilized by the Pt core. The results of this study have proved that such Pt-Cu core-shell nanostructures are efficient catalysts for non-aqueous OER and our protocol can be generalized to guide the design of other bimetallic catalysts. The Pt-Cu catalyst (2.5% Pt+5% Cu, in weight percentage), pure Cu (5% Cu) and pure Pt (2.5% Pt) samples were prepared by wet-impregnation method. (For experimental details, see Supporting Information, SI.) The crystalline components in Pt-Cu catalyst were characterized by HEXRD (Figure 1a). The diffraction pattern was consistent with CuO. No peak related to Pt, PtO2 or Pt-Cu alloy phases (e.g. Cu3Pt and CuPt) was detected, which implies that Pt may exist either in an amorphous state or in a very small domain. XANES spectra, which are sensitive to the oxidation state of the elements, were then recorded at both Cu K and Pt L3-edges. The oxidation state of Cu was determined by comparing the Cu K-edge positions of Pt-Cu catalyst to the standard Cu(I) oxide and Cu(II) oxide (Figure 1b). The Pt-Cu catalyst showed the same edge position corresponding to Cu(II), in agreement with the HEXRD result. Quantitative calculation of the bulk-scale oxidation state was performed by the linear combination fitting (LCF), which reveals that the Cu was oxidized to Cu(II) (SI, Table S1). The oxidation state of Pt was determined by the white line intensities (Figure 1c). The Pt L3-edge jump is attributed to the transition from 2p3/2 to 5d3/2 and 5d5/2. Since the oxidized Pt has more vacancy in the d-orbital, the white line intensity increased with the platinum oxidation number. The linear relationship of the O/Pt ratio and the white line intensity has also been reported.20 Here, the Pt in both the bimetallic Pt-Cu catalyst and the pure Pt samples had white line intensities between that of Pt


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and PtO2, indicating that they still keep some metallic character even in air. The white line intensities were also quantitatively analyzed via curve fitting (SI, Table S2).

Figure 1. (a) HEXRD of Pt-Cu catalyst; (b) Cu K-edge XANES spectra of Pt-Cu catalyst and the standard Cu(I) oxide and Cu(II) oxide; (c) Pt L3-edge XANES spectra of Pt-Cu catalyst and the standard Pt foil and PtO2. The size distributions of the Pt-Cu catalyst, pure Pt and pure Cu samples were obtained through fitting the integrated 1D plot of the SAXS data that had the carbon background subtracted. Schulz-Zimm was chosen as the distribution shape with spheroid form factor in a dilute system. As shown in Figure S2, pure Cu sample had a broad size distribution from 1 nm to ~20 nm; while pure Pt sample has a very narrow size distribution (1-3 nm). Similar to the pure Pt sample, the size distribution of the Pt-Cu catalyst was also within a narrow range of 2-4 nm. TEM was utilized to provide direct evidence on the structural and morphological characteristics of the catalysts. The Pt-Cu nanoparticles were uniformly distributed on the carbon support (Figure 2a). The particles with diameters of 2-4 nm were observed from the TEM images. The size histogram by statistical analysis of TEM images (SI, Figure S3) was consistent with the SAXS results. Individual Pt-Cu nanoparticle was identified by high resolution TEM (HRTEM) with cuboctahedron shape (Figure 2b). Cuboctahedron (Figure 2b, inset) is one of the


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stable nuclei structures for platinum21 and copper22, which is enclosed by the low-index {100} and {111} facets of the close packed cubic structure.

Figure 2. (S)TEM images of for 2.5%Pt+5%Cu sample. (a)Low magnification TEM image. (b) HRTEM image with lattice fringes. Inset is the scheme of the cuboctahedron structure. (c) HAADF-STEM image with false color. Because these as-prepared Pt-Cu bimetallic nanoparticles possess unique features on porous carbon matrix with high specific surface area, they can provide more active sites for the electrochemical reactions. Consequently, catalytic activity for OER is expected to be increased, as demonstrated next in the tests with Li-O2 cells. The Pt-Cu catalysts were tested in Li-O2 electrochemical cells. During charging, the desired discharge product, Li2O2, decomposes and releases oxygen with the following OER occurring: Li2 O2 → 2Li 2e O2 . Due to the sluggish kinetic of the OER, typical Li-O2 batteries suffer from large overpotentials, which causes the low round-trip efficiency.23-29 As shown in Figure 3a, the Li-O2 cells with bare carbon, pure Pt or pure Cu on carbon as air electrode had a high charging voltage of above 4V


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(vs Li/Li+). Surprisingly, with the Pt-Cu catalysts on the air electrode, the charge potential was dramatically reduced to about 3.2 V (Figure 3a). The discharge product showed toroid shape (Figure 3b), which is typical for Li2O2 formed in a Li-O2 cell.30-32 After 36 cycles, the discharge product Li2O2 was still completely charged back, leaving a clean air electrode surface (Figure 3c). This result proves that the Pt-Cu catalysts can efficiently facilitate the decomposition of the Li2O2 during the charging process, i.e., facilitate the OER.

Figure 3. (a) The comparison of voltage profile of Li-O2 electrochemical cells with different PtCu catalysts (b) SEM image of discharge product with 2.5% Pt+ 5% Cu on carbon as cathode. (c) SEM image after cycling under 5-hour time control till its specific capacity dropped to 100 mAh/g carbon and stopped at the end of charge (36 cycles). Regarding the catalytic mechanism, since neither pure Pt nanoparticle nor pure Cu nanoparticle has the contribution to lowering the charge overpotential, it is believed that the


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unique core-shell structure of the Pt-Cu catalyst played a crucial role on the catalytic activity towards the OER. The fact that in the Pt-Cu catalyst, all Cu was oxidized but the Pt maintains a certain degree of metallic property is attributed to the unique arrangement of the Pt and Cu atoms. In addition, the SAXS results indicate that the size distribution of the Pt-Cu catalyst was dominated by Pt. A plausible assumption is that Cu acted as shell to protect the Pt from oxidation and the Pt core determined the size distribution of the Pt-Cu catalyst. To support our hypothesis, EXAFS was employed to determine the coordination structure of the Pt-Cu catalyst. The Pt-Cu catalyst, pure Cu and pure Pt samples were fully reduced by H2 to avoid the influence of the oxygen on resolving the structure. Fourier transform (FT) of the EXAFS and the related scattering paths at Cu K-edge and Pt L3-edge are shown in Figure 4a and 4b, respectively. The spectrum of the pure Cu sample contains one peak related to the Cu-Cu scattering path. With Pt in the bimetallic catalyst, the peak became slightly wider due to the emergence of the Cu-Pt scattering, resulting from the formation of Cu-Pt alloy at the interface. A similar trend was also observed at the Pt L3edge. The FT of the EXAFS of the pure Pt sample shows two peaks which associate with the PtPt scattering. For the bimetallic catalyst, the intensity of the Pt-Cu scattering, which is located between the two Pt-Pt scattering peaks, increased and led to the evolution of the overall peak shape. Therefore, with the FT results we conclude that the Pt-Cu alloy was formed at the Pt/Cu interface in the bimetallic catalysts and the homoatomic interactions (Cu-Cu and Pt-Pt) are stronger than the bimetallic heteroatomic interaction (Pt-Cu).


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Figure 4. (a, b) Magnitude of the Fourier transform of Pt-Cu catalysts: (a) At Cu K-edge in comparison with monometallic 5%Cu sample (orange dashed line: Cu-Cu patch and purple dash dotted line: Cu-Pt path); (b) At Pt L3-edge in comparison with pure Pt sample (orange dashed line: Pt-Pt path and purple dash dotted line: Pt-Cu path). (c, d) First-shell model EXAFS fit of the k3-weighted Fourier transform of 5%Pt+5%Cu catalyst: (c) Cu K-edge (∆k=2.0-13.4 Å-1 and ∆R=1.4-2.8 Å) and (d) Pt L3-edge (∆k=3.0-14.5 Å-1 and ∆R=1.5-3.2 Å). FT magnitude in solid line and imaginary in dashed line, data in black and fit in red. The nearest-neighbor coordination numbers around Cu and Pt atoms were extracted from fitting the EXAFS of the Pt-Cu catalysts with first-shell model. Figure 4c and 4d show the


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typical fitting results for the Pt-Cu catalysts, the good fitting quality was verified by the R-factors of ≤0.001 with k1 and k3 weightings for both Cu K and Pt L3-edges. The fitting parameters were summarized in Table S3. Since the amplitude reduction factor S02 was maintained the same during the fitting, the changes in coordination numbers were compared. Here the nearest neighbor M’ atoms around M atom is denoted by NMM’. Because neither NCu-Pt nor NPt-Cu was zero in our catalysts, Pt and Cu didn’t form separate monometallic particles. Instead, they should establish either intermetallic compound or core-shell structure. If an intermetallic compound was formed, the total coordination number of Pt (NPt-M = NPt-Cu+ NPt-Pt) should equal to the total coordination number of Cu (NCu-M = NCu-Cu+ NCu-Pt). But in our case, for the Pt-Cu catalyst, NPt-M ≠ NCu-M. In fact, in a core-shell structure, the Pt was bonded to Cu only at the interface, thus one metal atom has significantly higher possibility to coordinate with the same type of metal atom than the other type. The distinct inequality of NPt-Pt and NCu-Pt provides an evidence supporting the formation of the core-shell structure in the Pt-Cu catalysts. In addition, since the surface atoms have smaller coordination numbers than the bulk, the fact NPt-M ≥NCu-M indicates that Pt was acting as the core while Cu as the shell. The extents of the alloying of Pt and Cu were also calculated from the EXAFS-derived coordination numbers and from the coordination numbers expected for the complete and random alloying (SI, Part 5). The results suggest that both Pt and Cu atoms are preferred to form homoatomic bonds rather than to be alloyed. Apart from the bulk-scale characterizations of the structure of Pt-Cu catalysts by interpreting EXAFS spectra, the core-shell structure of Pt-Cu nanoparticles was further verified by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Due to the Z-contrast effect of STEM (Z is atomic number), Pt have a higher intensity than that


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of Cu. As shown in Figure 2c, the shells of the nanoparticles with a lower intensity than the core validated the core-shell structure of the Pt-Cu catalysts. Since the electrocatalytic OER process only occurs on the electrode surface, X-ray Photoelectron Spectroscopy (XPS), a surface sensitive technique, was employed to investigate the interaction between Pt and Cu on the surface of Pt-Cu catalyst. The results showed a distinct Cu surface was formed, i.e., both Cu (II) and Cu (I) were found on the surface through deconvolution of the Cu 2p peak (Figure 5). Based on the STEM, XAS and XPS results, it seems that the Pt core was covered by the oxidized Cu (CuxO), and espically the Pt-Cu alloy was formed at the interface, as schematically shown in the inset of Figure 2c. It should be noted that the Cu (I) species typically are unstable at room temperature, as evident that only Cu (II) was detected on the pure Cu sample. However, the presence of Cu (I) on the surface of our Cu-Pt catalyst suggests that the unique core-shell structure may stabilize the Cu(I) through the Pt-Cu alloy interface in the particle. Based on the earlier studies on the catalytic activity of Cu (I) on OER in aqueous systems,

33, 34

we believed that such stabilized Cu(I) species on the catalyst

surface played a crucial role to reduce the OER potential in non-aqueous Li-O2 cell, as observed in this study. In fact, the distribution of the active Cu(I) sites were not as uniforme as that of the atomically dispersed dopants in the tranditional carbon-based catalysts, e.g. Fe/N/C.35 The dopants with atmic uniformity produce a higher interfacial boundary with the discharge product Li2O2 to help the electron and mass transfer process, leading to the low charge overpotential in Li-O2 cells.36 Thereby, regarding the high catalytic activity of the Pt-Cu catalysts, the uniformity distribution of the active sites was not the main reason. As calculation results showed that the O2(2-n)- had a lower O2 desorption energy37, the charge-transfer from the O22- to the catalytic surface may play a crucial role on the catalytic activity.


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Cu 2p3/2

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Binding Energy (eV) Figure 5. The spectra of Cu 2p XPS of the Pt-Cu catalyst. In summary, this study reports the electrocatalytic activity of a unique bimetallic Pt-Cu coreshell nanostructured catalyst towards the non-aqueous OER process. The structure characterizations of the catalysts were accomplished via XAS and SAXS. Benefiting from the unique Pt-Cu core-shell structure, Cu (I) has been stabilized on the surface and serves as the key to improve the OER catalytic activity. Consequently, the bimetallic Pt-Cu catalyst exhibited significantly reduced charging overpotential (< 0.2 V) in non-aqueous Li-O2 cells. This interesting finding suggests that our protocol can be generalized to guide the design of other efficient bimetallic catalysts.

ASSOCIATED CONTENT Supporting Information. Experimental details, fitting result of XAS and SAXS. This material is available free of charge via the Internet at http://pubs.acs.org.


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AUTHOR INFORMATION Corresponding Author *To whom correspondence should be addressed. Jun Lu: Email: [email protected]; Phone: 630-252-4485 Tianpin Wu: Email: [email protected]; Phone: 630-252-1482 Khalil Amine: Email: [email protected]; Phone: 630-252-3838

Author Contributions All authors have given approval to the final version of the manuscript. ‡These authors contributed equally. Notes The authors declare no competing financial interests.

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). MRCAT operations are supported by the U.S. Department of Energy and the MRCAT member institutions. Use of the Advanced Photon Source and the Electron Microscopy Center, Center for Nanoscale Materials was supported by


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the U.S. Department of Energy, Office of Basic Energy Sciences, under contract No. DE-AC0206CH11357. ABBREVIATIONS OER, oxygen evolution reaction; ORR, oxygen reduction reaction; HER, hydrogen evolution reaction; HEXRD, High-Energy X-ray Diffraction; XANES, X-ray absorption near edge structure; EXAFS, X-ray absorption fine structure, STEM, scanning transmission electron microscopy; SAXS, small angle X-ray scattering; HAADF-STEM, high angle annular dark field scanning transmission electron microscopy; XPS, X-ray photoelectron spectroscopy.

REFERENCES 1. Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q. X.; Santori, E. A.; Lewis, N. S. Chem Rev 2010, 110, 6446-6473. 2. Wang, Z. L.; Xu, D.; Xu, J. J.; Zhang, X. B. Chem Soc Rev 2014, 43, 7746-7786. 3. Cao, R.; Lee, J. S.; Liu, M. L.; Cho, J. Adv Energy Mater 2012, 2, 816-829. 4. Shao, Y. Y.; Park, S.; Xiao, J.; Zhang, J. G.; Wang, Y.; Liu, J. Acs Catal 2012, 2, 844-857. 5. Jiao, Y.; Zheng, Y.; Jaroniec, M. T.; Qiao, S. Z. Chem Soc Rev 2015, 44, 2060-2086. 6. Guczi, L. Catal Today 2005, 101, 53-64. 7. Chen, C.; Kang, Y. J.; Huo, Z. Y.; Zhu, Z. W.; Huang, W. Y.; Xin, H. L. L.; Snyder, J. D.; Li, D. G.; Herron, J. A.; Mavrikakis, M.; Chi, M. F.; More, K. L.; Li, Y. D.; Markovic, N. M.; Somorjai, G. A.; Yang, P. D.; Stamenkovic, V. R. Science 2014, 343, 1339-1343. 8. Markovic, N. M.; Schmidt, T. J.; Stamenkovic, V.; Ross, P. N. Fuel Cells 2001, 1, 105-116. 9. Hyun, K.; Lee, J. H.; Yoon, C. W.; Kwon, Y. Int J Electrochem Sc 2013, 8, 11752-11767. 10. Wu, J. B.; Yang, H. Accounts Chem Res 2013, 46, 1848-1857. 11. Ge, X. B.; Chen, L. Y.; Kang, J. L.; Fujita, T.; Hirata, A.; Zhang, W.; Jiang, J. H.; Chen, M. W. Adv Funct Mater 2013, 23, 4156-4162. 12. Neergat, M.; Rahul, R. J Electrochem Soc 2012, 159, F234-F241. 13. Rioux, R. M.; Vannice, M. A. J Catal 2005, 233, 147-165. 14. Koh, S.; Strasser, P. J Am Chem Soc 2007, 129, 12624-12625. 15. Tseng, C. J.; Lo, S. T.; Lo, S. C.; Chu, P. P. Mater Chem Phys 2006, 100, 385-390. 16. Strasser, P.; Koh, S.; Anniyev, T.; Greeley, J.; More, K.; Yu, C. F.; Liu, Z. C.; Kaya, S.; Nordlund, D.; Ogasawara, H.; Toney, M. F.; Nilsson, A. Nat Chem 2010, 2, 454-460. 17. Xiong, L.; Manthiram, A. J Electrochem Soc 2005, 152, A697-A703.


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18. Forgie, R.; Bugosh, G.; Neyerlin, K. C.; Liu, Z. C.; Strasser, P. Electrochem Solid St 2010, 13, D36-D39. 19. Lu, Q.; Hutchings, G. S.; Yu, W. T.; Zhou, Y.; Forest, R. V.; Tao, R. Z.; Rosen, J.; Yonemoto, B. T.; Cao, Z. Y.; Zheng, H. M.; Xiao, J. Q.; Jiao, F.; Chen, J. G. G. Nat Commun 2015, 6, 6567. 20. Yoshida, H.; Nonoyama, S.; Yazawa, Y.; Hattori, T. Phys Scripta 2005, T115, 813-815. 21. Song, H.; Kim, F.; Connor, S.; Somorjai, G. A.; Yang, P. D. J Phys Chem B 2005, 109, 188193. 22. Salzemann, C.; Lisiecki, L.; Urban, J.; Pileni, M. P. Langmuir 2004, 20, 11772-11777. 23. Lu, J.; Li, L.; Park, J. B.; Sun, Y. K.; Wu, F.; Amine, K. Chem Rev 2014, 114, 5611-5640. 24. Lu, J.; Amine, K. Energies 2013, 6, 6016-6044. 25. Qin, Y.; Lu, J.; Du, P.; Chen, Z. H.; Ren, Y.; Wu, T. P.; Miller, J. T.; Wen, J. G.; Miller, D. J.; Zhang, Z. C.; Amine, K. Energ Environ Sci 2013, 6, 519-531. 26. Luo, X. Y.; Piernavieja-Hermida, M.; Lu, J.; Wu, T. P.; Wen, J. G.; Ren, Y.; Miller, D.; Fang, Z. Z.; Lei, Y.; Amine, K. Nanotechnology 2015, 26, 164003. 27. Kraytsberg, A.; Ein-Eli, Y. Nano Energy 2013, 2, 468-480. 28. Kim, H. J.; Jung, S. C.; Han, Y. K.; Oh, S. H. Nano Energy 2015, 13, 679-686. 29. Peng, S. J.; Hu, Y. X.; Li, L. L.; Han, X. P.; Cheng, F. Y.; Srinivasan, M.; Yan, Q. Y.; Ramakrishna, S.; Chen, J. Nano Energy 2015, 13, 718-726. 30. Mitchell, R. R.; Gallant, B. M.; Thompson, C. V.; Shao-Horn, Y. Energ Environ Sci 2011, 4, 2952-2958. 31. Lu, J.; Cheng, L.; Lau, K. C.; Tyo, E.; Luo, X. Y.; Wen, J. G.; Miller, D.; Assary, R. S.; Wang, H. H.; Redfern, P.; Wu, H. M.; Park, J. B.; Sun, Y. K.; Vajda, S.; Amine, K.; Curtiss, L. A. Nat Commun 2014, 5, 4895. 32. 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.; Albishri, H. M.; Abd El-Hady, D.; Sun, Y. K.; Curtiss, L. A.; Amine, K. Nat Commun 2013, 4, 2383. 33. Kumar, B.; Saha, S.; Ganguly, A.; Ganguli, A. K. Rsc Adv 2014, 4, 12043-12049. 34. Kumar, B.; Saha, S.; Ojha, K.; Ganguli, A. K. Mater Res Bull 2015, 64, 283-287. 35. Shui, J. L.; Karan, N. K.; Balasubramanian, M.; Li, S. Y.; Liu, D. J. J Am Chem Soc 2012, 134, 16654-16661. 36. Li, Q.; Xu, P.; Gao, W.; Ma, S. G.; Zhang, G. Q.; Cao, R. G.; Cho, J.; Wang, H. L.; Wu, G. Adv Mater 2014, 26, 1378-1386. 37. Zhu, J. Z.; Wang, F.; Wang, B. Z.; Wang, Y. W.; Liu, J. J.; Zhang, W. Q.; Wen, Z. Y. J Am Chem Soc 2015, 137, 13572-13579.


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