Letter Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
pubs.acs.org/journal/ascecg
Integrated Flexible Electrode for Oxygen Evolution Reaction: Layered Double Hydroxide Coupled with Single-Walled Carbon Nanotubes Film Hengjie Liu,†,# Jing Zhou,‡,# Chuanqiang Wu,† Changda Wang,† Youkui Zhang,†,§ Daobin Liu,† Yunxiang Lin,† Hongliang Jiang,*,† and Li Song*,† †
National Synchrotron Radiation Laboratory, CAS Center for Excellence in Nanoscience, University of Science and Technology of China, Hezuohua Sourth Road 42, Hefei, Anhui 230029, China ‡ Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jialuo Road 2019, Jiading District, Shanghai 201800, China § School of National Defense Science & Technology, Southwest University of Science and Technology, Qinglong Road 59, Mianyang, Sichuan 621010, China S Supporting Information *
ABSTRACT: The integration of active components and conductive supports forming free-standing electrodes is highly desirable for a series of energy storage and conversion devices. Herein, a facile hydrothermal method is developed to achieve the coupling of NiFe layered double hydroxide (LDH) and single-walled carbon nanotubes (SWNT) film, forming an integrated flexible electrode for oxygen evolution reaction (OER). The electrode requires a low overpotential of 250 mV to reach a current density of 10 mA cm−2 in 1 M KOH, and shows rapid reaction kinetics with a Tafel slope of 35 mV dec−1. Advanced soft X-ray absorption near-edge structure measurements efficiently indicate strong interfacial electron coupling between the LDH and SWNT, which authentically contributes to superior OER performance. This work provides a new strategy to design binder-free and flexile electrodes for practical application. KEYWORDS: Electronic structure, Flexible electrode, X-ray absorption spectroscopy, Oxygen evolution reaction
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INTRODUCTION Increasing concerns about environment and energy issues stimulate global researchers to seek clean energy to replace fossil fuels.1−3 Water splitting is a promising way to produce hydrogen, which is regarded as one of potential clean energy candidates.4−6 However, oxygen evolution reaction (OER), a half reaction of water splitting, remains as the bottleneck in the water splitting process owing to a complicated multielectron process and high overpotential.7−9 With this regard, a lot of efforts have been devoted to develop high active electrocatalysts toward OER. Precious metal-based materials, typically RuO2 and IrO2,10,11 have been identified as the state-of-the-art electrocatalysts for OER to date. Nonetheless, the high costs and low durability hinder their large-scale applications.12 Transition metals with high abundance, such as Fe, Ni, Mn and Co, have been widely studied to serve as potential alternatives to noble metal catalysts.13−16 Layered double hydroxides (LDHs), such as NiFe-LDH, NiCo-LDH, CoMn-LDH, are found to show comparable OER performance to the best precious-metal catalysts.17−19 Moreover, the OER performance of LDHs could be significantly improved by combining LDHs with carbon-based nanomaterials, such as graphene, multiwalled carbon nanotubes and carbon quantum dots.20−25 More recently, for batteries and electrochemical reactions, free-standing electrodes through the © XXXX American Chemical Society
integration of active components and current collectors attract extensive interest. For instance, Duan et al. reported that the OER catalytic activities of NiFe-LDH could be enhanced by directly growing onto Ni foam. The 3D architecture and the macroscopic conductive network of Ni foam are generally considered as the main promoting factor.26 Until now, the interaction of active components and metal current collectors is not well-understood. On the other hand, according to our previous work, flexible single-walled carbon nanotubes (SWNT) film consists of numerous SWNTs forming a macroscopic conductive network, and also provides abundant sites for the introduction of guest materials due to its unique nanostructure.27−29 Therefore, we believe that the integration of SWNT film and LDH hybrids would show significantly enhanced OER performance. Herein, a facile hydrothermal method was proposed to directly grow NiFe-LDH onto the SWNT film (denoted as NiFe-LDH@SWNT). Thanks to the in situ growth process, the NiFe-LDH efficiently grows onto the surface of each SWNT bundle unit, forming unique integration of the LDH and SWNT. Applied as the electrode for OER, the NiFe-LDH@ Received: January 7, 2018 Revised: January 28, 2018 Published: February 5, 2018 A
DOI: 10.1021/acssuschemeng.8b00084 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering SWNT achieves an overpotential of 250 mV at 10 mA cm−2 and a Tafel slope as low as 35 mV dec−1. Impressively, elaborate X-ray absorption near-edge structure (XANES) results reveal the evident interfacial electron coupling through the formation of rich metalOC bonds, which authentically contributes to superior OER performance.
The X-ray diffraction (XRD) measurements were then conducted to further study the crystal structure of the hybrid (Figure 2a). The XRD patterns of NiFe-LDH@SWNT and
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RESULTS AND DISCUSSION The pure SWNT film was first prepared using a floating catalyst chemical vapor deposition (FCCVD) method according to our previous work.28 Subsequently, the NiFe-LDH@SWNT was synthesized using a facile hydrothermal method as schematically shown in Figure 1a (see Experimental section in the
Figure 2. (a) XRD patterns of NiFe-LDH and NiFe-LDH@SWNT. (b) Raman spectrum of NiFe-LDH@SWNT and pure SWNT film. High-resolution XPS spectra of NiFe-LDH@SWNT in the Ni 2p (c) and Fe 2p (d) regions.
pure NiFe-LDH match well with previous reports about NiFeLDH,30,31 except that broader diffraction peaks of NiFe-LDH@ SWNT are observed compared to that of the bare NiFe-LDH. This phenomenon probably originates from the inhibited LDH growth process due to the existence of SWNT. The Raman spectrum of pure SWNT (Figure 2b) consists of two main groups of peaks. The small peak below 300 cm−1 (inlet of Figure 2b) is regarded as the radial breathing modes (RBMs) of the SWNT.32 The peaks at 1345 and 1590 cm−1 are assigned to the D-band and G-band of SWNT, which depends on the graphitization degree of SWNT.33,34 The low intensity of Dband and high intensity of G-band reveal the high quality of most carbon nanotubes in SWNT, ensuring its high electron conductivity.35 The Raman spectrum of NiFe-LDH@SWNT is similar to that of pure SWNT, indicating that the structure of SWNT is always kept well after the hydrothermal process. These results suggest the successful synthesis of NiFe-LDH@ SWNT hybrid without the framework damage of SWNT. The X-ray photoelectron electron spectroscopy (XPS) measurements were performed to investigate the surface chemical states of the NiFe-LDH@SWNT. The XPS survey of NiFe-LDH@SWNT reveals the coexistence of Ni, Fe, O and C in the as-synthesized hybrid, obviously different from the pure SWNT film (Figure S4, elements content shown in Table S1). The high-resolution Ni 2p core level XPS (Figure 2c) presents two peaks that could be divided into two parts: spin− orbit doublet of 2p orbital, which could be recognized as Ni2+ 2p3/2 (about 856.8 eV), and Ni2+ 2p1/2 (about 874.3 eV), as well as two corresponding shakeup satellites.36,37 With respect to the Fe 2p spectrum in Figure 2d, the two peaks occurred at about 724.0 and 713.7 eV, indicating the +3 oxidation state of Fe species in
[email protected] The chemical states of Ni and Fe are consistent with previous reports of NiFe-LDH.39 High-resolution C 1s XPS spectra were further conducted to analyze the carbon elements with different chemical environments on the surface of NiFe-LDH@SWNT compared to the
Figure 1. (a) Schematic illustration of the synthesis process of NiFeLDH@SWNT (b,c) SEM images of NiFe-LDH@SWNT in different magnifications. (d) TEM image of NiFe-LDH. (e) HRTEM image of NiFe-LDH@SWNT.
Supporting Information for details). For comparison, the pure NiFe-LDH was also synthesized using the same method without the introduction of the SWNT film. Electron microscopy was employed to investigate the microstructure of the NiFe-LDH@SWNT. Figure 1b,c shows the scanning electron microscopy (SEM) images of NiFeLDH@SWNT with different magnifications. The NiFe-LDH nanosheets uniformly grow on the entangled SWNT bundles which connect with each other and form a conductive 3D crosslinked network (optical photograph and SEM image of pure SWNT film is shown in Figures S1 and S2). Typical transmission electron microscopy (TEM) images of the NiFe-LDH@SWNT (Figure 1c and Figure S3) indicate that the NiFe-LDH are efficiently grown around the SWNT units, in accordance with the SEM results. High-resolution TEM imaging (Figure 1e) shows lattice fringes of 0.25 nm corresponding the (012) lattice plane of NiFe-LDH.30 B
DOI: 10.1021/acssuschemeng.8b00084 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering pure SWNT. For pure SWNT (Figure 3a), a strong peak is located at 284.6 eV, which is assigned to the sp2-hybridized
SWNT as well as commercial IrO2 are shown in Figure 4a. It is apparent that the NiFe-LDH@SWNT shows higher OER
Figure 3. (a) High-resolution C 1s XPS spectra of NiFe-LDH@ SWNT and pure SWNT film. (b) C K-edge XANES of pure SWNT and NiFe-LDH@SWNT. (c) Ni 2p core-level XPS comparison of NiFe-LDH@SWNT and NiFe-LDH. (d) Ni L2, 3-edge XANES of NiFe-LDH@SWNT and NiFe-LDH.
Figure 4. (a) LSV polarization curves of NiFe-LDH@SWNT, IrO2, NiFe-LDH and SWNT for OER. (b) Corresponding linear fitting of Tafel plots of NiFe-LDH@SWNT, IrO2, NiFe-LDH and SWNT. (c) EIS of NiFe-LDH@SWNT, SWNT and NiFe-LDH at 1.53 V versus RHE. (d) Chronopotentiometry curves of NiFe-LDH@SWNT and NiFe-LDH at a constant current density of 10 mA cm−2.
graphitic carbons in the SWNT. A weak peak situated at 286.2 eV belongs to CO bonds, confirming the high quality of asprepared SWNT.40 However, in the NiFe-LDH@SWNT hybrid, the intensity of CO bonds is obviously enhanced compared to that of pure SWNT. Meanwhile, a new peak (288.9 eV) assigned to carboxyl groups is observed, implying the interactions between NiFe-LDH and SWNT in the hybrid.41 To further investigate the interactions between NiFe-LDH and SWNT, C K-edge XANES measurements were carried out, considering that it is sensitive to electronic structure and coordination environment. As shown in Figure 3b, the C K-edge XANES shows two peaks at about 285.3 and 291.6 eV, which are assigned to π*CC and σ*CC, respectively. Notably, the NiFe-LDH@SWNT shows a distinct increase of peak intensity at about 288.4 eV compared to pure SWNT, clearly indicating the formation of MOC bonds (MNi/Fe).42 The intense peak at about 290.2 eV is assigned to carbonate, which originates from the interlayer carbonate in the NiFe-LDH, consistent with previous reports.21 The strong electron coupling as well as the interaction could also be observed from Ni sites. Impressively, compared to NiFe-LDH, the binding energies show a noticeable 0.4 eV upshift in the high-resolution Ni 2p XPS spectrum of NiFe-LDH@SWNT hybrid (Figure 3c), indicating the electron transfer from metal sites to carbon sites. Moreover, the feature A in the Ni L-edge XANES of the hybrid shows an increase compared to that of pure NiFe-LDH, suggesting an decreased occupied electron density states, forcefully confirming the electron coupling above.43 To evaluate the electrocatalytic performance of NiFe-LDH@ SWNT under the influence of strong electron coupling between NiFe-LDH and SWNT, electrochemical OER properties of the hybrid were further investigated using a typical threeelectrode system in 1 M KOH solution (see Experimental section in the Supporting Information for details). Linear sweep voltammetry (LSV) curves of NiFe-LDH@SWNT, NiFe-LDH,
activity than NiFe-LDH, SWNT and even commercial IrO2. The NiFe-LDH@SWNT requires a potential of about 1.48 V versus the reversible hydrogen electrode (RHE) to reach a current density of 10 mA cm−2, which is much lower than that of NiFe-LDH (1.59 V), SWNT (1.67 V) and even commercial IrO2 (1.52 V) (Figure S5). What is more, the potential (1.54 V) for NiFe-LDH@SWNT to reach the current density of 50 mA cm−2 is lower than that of NiFe-LDH (1.68 V) and IrO2 (1.57 V), further confirming the superior catalytic performance of NiFe-LDH@SWNT (Figure S6). NiFe-LDH@SWNT also shows comparable OER performance to other recently reported no-noble-metal catalysts (Table S2). The Tafel slopes of these samples are further compared to estimate their reaction kinetics (Figure 4b). Linear fitting of Tafel plots for NiFe-LDH@ SWNT shows a Tafel slope of about 35 mV dec−1; whereas the Tafel slopes of NiFe-LDH, SWNT and commercial IrO2 are 58, 108 and 47 mV dec−1, respectively. The substantially improved reaction kinetics of NiFe-LDH@SWNT could be attributed to the strong interaction as well as electron coupling between NiFe-LDH and SWNT, which was also confirmed by the electrochemical impedance spectroscopy (EIS) measurements as shown in Figure 4c. The electrons transfer from metal sites to carbon sites leads to the holes gathering at the NiFe-LDH, which is favorable for OER as evidenced by previous studies.44 As shown in Figure 4d, NiFe-LDH@SWNT keeps its OER activity even after 20 h chronopotentiometry test. The SEM images, XRD and XPS results of NiFe-LDH@SWNT after OER (Figures S9−S11) did not show obvious change except that slightly surface oxidization was observed (Figure S11), which make it a potential candidate for practical applications.
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CONCLUSION In conclusion, we have developed a facile route to achieve the integration of highly active NiFe-LDH and flexible SWNT film as highly efficient OER catalyst. A series of characterizations, C
DOI: 10.1021/acssuschemeng.8b00084 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering
(3) Cook, T. R.; Dogutan, D. K.; Reece, S. Y.; Surendranath, Y.; Teets, T. S.; Nocera, D. G. Solar Energy Supply and Storage for the Legacy and Non Legacy Worlds. Chem. Rev. 2010, 110, 6474−6502. (4) Liu, G.; Li, P.; Zhao, G.; Wang, X.; Kong, J.; Liu, H.; Zhang, H.; Chang, K.; Meng, X.; Kako, T.; et al. Promoting Active Species Generation by Plasmon-Induced Hot-Electron Excitation for Efficient Electrocatalytic Oxygen Evolution. J. Am. Chem. Soc. 2016, 138, 9128− 9136. (5) Liu, P. F.; Li, X.; Yang, S.; Zu, M. Y.; Liu, P.; Zhang, B.; Zheng, L. R.; Zhao, H.; Yang, H. G. Ni2P(O)/Fe2P(O) Interface Can Boost Oxygen Evolution Electrocatalysis. ACS Energy Lett. 2017, 2, 2257− 2263. (6) Zou, X. X.; Zhang, Y. Noble Metal-Free Hydrogen Evolution Catalysts for Water Splitting. Chem. Soc. Rev. 2015, 44, 5148−5180. (7) Zhang, B.; Zheng, X.; Voznyy, O.; Comin, R.; Bajdich, M.; García-Melchor, M.; Han, L.; Xu, J.; Liu, M.; Zheng, L. Homogeneously Dispersed Multimetal Oxygen-Evolving Catalysts. Science 2016, 352, 333−337. (8) Zeng, Z.; Tan, C.; Huang, X.; Bao, S.; Zhang, H. Growth of Noble Metal Nanoparticles on Single-Layer TiS2 and TaS2 Nanosheets for Hydrogen Evolution Reaction. Energy Environ. Sci. 2014, 7, 797− 803. (9) Zhao, Y.; Nakamura, R.; Kamiya, K.; Nakanishi, S.; Hashimoto, K. Nitrogen-Doped Carbon Nanomaterials as Non-Metal Electrocatalysts for Water Oxidation. Nat. Commun. 2013, 4, 2390. (10) Petrykin, V.; Macounova, K.; Shlyakhtin, O. A.; Krtil, P. Tailoring the Selectivity for Electrocatalytic Oxygen Evolution on Ruthenium Oxides by Zinc Substitution. Angew. Chem., Int. Ed. 2010, 49, 4813−4815. (11) Lee, Y.; Suntivich, J.; May, K. J.; Perry, E. E.; Shao-Horn, Y. Synthesis and Activities of Rutile IrO2 and RuO2 Nanoparticles for Oxygen Evolution in Acid and Alkaline Solutions. J. Phys. Chem. Lett. 2012, 3, 399−404. (12) Vesborg, P. C. K.; Jaramillo, T. F. Addressing the Terawatt Challenge: Scalability in the Supply of Chemical Elements for Renewable Energy. RSC Adv. 2012, 2, 7933−7947. (13) Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y. A Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital Principles. Science 2011, 334, 1383− 1385. (14) Zhou, W.; Wu, X.-J.; Cao, X.; Huang, X.; Tan, C.; Tian, J.; Liu, H.; Wang, J.; Zhang, H. Ni3S2 Nanorods/Ni Foam Composite Electrode with Low Overpotential for Electrocatalytic Oxygen Evolution. Energy Environ. Sci. 2013, 6, 2921−2924. (15) Ponce, J.; Rehspringer, J.-L.; Poillerat, G.; Gautier, J. Electrochemical Study of Nickel-Aluminium-Manganese Spinel NiXAl1‑XMn2O4. Electrocatalytical Properties for the Oxygen Evolution Reaction and Oxygen Reduction Reaction in Alkaline Media. Electrochim. Acta 2001, 46, 3373−3380. (16) Wang, D.; Chen, X.; Evans, D. G.; Yang, W. Well-Dispersed Co3O4/Co2MnO4 Nanocomposites as a Synergistic Bifunctional Catalyst for Oxygen Reduction and Oxygen Evolution Reactions. Nanoscale 2013, 5, 5312−5315. (17) Gong, M.; Dai, H. A Mini Review of NiFe-Based Materials as Highly Active Oxygen Evolution Reaction Electrocatalysts. Nano Res. 2015, 8, 23−39. (18) Song, F.; Hu, X. Ultrathin Cobalt-Manganese Layered Double Hydroxide Is an Efficient Oxygen Evolution Catalyst. J. Am. Chem. Soc. 2014, 136, 16481−16484. (19) Song, F.; Hu, X. Exfoliation of Layered Double Hydroxides for Enhanced Oxygen Evolution Catalysis. Nat. Commun. 2014, 5, 4477. (20) Tang, C.; Wang, H. S.; Wang, H. F.; Zhang, Q.; Tian, G. L.; Nie, J. Q.; Wei, F. Spatially Confined Hybridization of Nanometer-Sized NiFe Hydroxides into Nitrogen-Doped Graphene Frameworks Leading to Superior Oxygen Evolution Reactivity. Adv. Mater. 2015, 27, 4516−4522. (21) Gong, M.; Li, Y.; Wang, H.; Liang, Y.; Wu, J. Z.; Zhou, J.; Wang, J.; Regier, T.; Wei, F.; Dai, H. An Advanced Ni-Fe Layered Double
such as XANES, XPS and EIS, have proved that the superior OER performance could be attributed to the 3D macroscopic conductive network, the strong electron coupling between NiFe-LDH and SWNT. Moreover, the direct growth of NiFeLDH on macroscopic SWNT film also avoids the deactivation of active components, and thus a high durability is delivered. We postulate that this strategy could be extended to develop more binder-free flexible electrodes for catalysis and batteries.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.8b00084. Experimental section, materials characterization and additional data (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*H. Jiang. Tel.: +86-0551-63602017, Email:
[email protected]. cn. *L. Song. Tel.: +86-0551-63602102, Email: song2012@ustc. edu.cn. ORCID
Hongliang Jiang: 0000-0002-5243-3524 Li Song: 0000-0003-0585-8519 Author Contributions #
These authors contributed equally.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is financially supported in partly by MOST (2017YFA0303500, 2014CB848900), NSFC (U1532112, 11574280, 21706248), Innovative Research Groups of NSFC (Grant No. 11621063), China Postdoctoral Science Foundation (BH2310000033), CAS Interdisciplinary Innovation Team and CAS Key Research Program of Frontier Sciences (QYZDB-SSW-SLH018), Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology (2016FXCX003). L.S. acknowledges the recruitment program of global experts, the CAS Hundred Talent Program and Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University (111 project, B12015), Key Laboratory of the Ministry of Education for Advanced Catalysis Materials and Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces (Zhejiang Normal University). We thank the Shanghai synchrotron Radiation Facility (14W1, SSRF), the Beijing Synchrotron Radiation Facility (1W1B and soft-X-ray endstation, BSRF), the Hefei Synchrotron Radiation Facility (Photoemission, MCD and Catalysis/Surface Science Endstations, NSRL), and the USTC Center for Micro and Nanoscale Research and Fabrication for helps in characterizations.
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REFERENCES
(1) McCrory, C. C.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 16977−16987. (2) Dresselhaus, M. S.; Thomas, I. L. Alternative Energy Technologies. Nature 2001, 414, 332−337. D
DOI: 10.1021/acssuschemeng.8b00084 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering Hydroxide Electrocatalyst for Water Oxidation. J. Am. Chem. Soc. 2013, 135, 8452−8455. (22) Tang, D.; Liu, J.; Wu, X.; Liu, R.; Han, X.; Han, Y.; Huang, H.; Liu, Y.; Kang, Z. Carbon Quantum Dot/NiFe Layered DoubleHydroxide Composite as a Highly Efficient Electrocatalyst for Water Oxidation. ACS Appl. Mater. Interfaces 2014, 6, 7918−7925. (23) Jia, Y.; Zhang, L. Z.; Gao, G. P.; Chen, H.; Wang, B.; Zhou, J. Z.; Soo, M. T.; Hong, M.; Yan, X. C.; Qian, G. R.; Zou, J.; Du, A. J.; Yao, X. D. A Heterostructure Coupling of Exfoliated Ni-Fe Hydroxide Nanosheet and Defective Graphene as a Bifunctional Electrocatalyst for Overall Water Splitting. Adv. Mater. 2017, 29, 1700017. (24) Zhou, D.; Cai, Z.; Lei, X.; Tian, W.; Bi, Y.; Jia, Y.; Han, N.; Gao, T.; Zhang, Q.; Kuang, Y.; et al. NiCoFe-Layered Double Hydroxides/ N-Doped Graphene Oxide Array Colloid Composite as an Efficient Bifunctional Catalyst for Oxygen Electrocatalytic Reactions. Adv. Energy Mater. 2017, 1701905. (25) Han, X.; Yu, C.; Zhou, S.; Zhao, C.; Huang, H.; Yang, J.; Liu, Z.; Zhao, J.; Qiu, J. Ultrasensitive Iron-Triggered Nanosized Fe-CoOOH Integrated with Graphene for Highly Efficient Oxygen Evolution. Adv. Energy Mater. 2017, 7, 1602148. (26) Lu, Z.; Xu, W.; Zhu, W.; Yang, Q.; Lei, X.; Liu, J.; Li, Y.; Sun, X.; Duan, X. Three-Dimensional NiFe Layered Double Hydroxide Film for High-Efficiency Oxygen Evolution Reaction. Chem. Commun. 2014, 50, 6479−6482. (27) Song, L.; Ci, L.; Lv, L.; Zhou, Z.; Yan, X.; Liu, D.; Yuan, H.; Gao, Y.; Wang, J.; Liu, L.; et al. Direct Synthesis of a Macroscale Single-Walled Carbon Nanotube Non-Woven Material. Adv. Mater. 2004, 16, 1529−1534. (28) Ma, W.; Song, L.; Yang, R.; Zhang, T.; Zhao, Y.; Sun, L.; Ren, Y.; Liu, D.; Liu, L.; Shen, J.; et al. Directly Synthesized Strong, Highly Conducting, Transparent Single-Walled Carbon Nanotube Films. Nano Lett. 2007, 7, 2307−2311. (29) Xiang, T.; Tao, S.; Xu, W.; Fang, Q.; Wu, C.; Liu, D.; Zhou, Y.; Khalil, A.; Muhammad, Z.; Chu, W.; Wang, Z.; Xiang, H.; Liu, Q.; Song, L. Stable 1T-MoSe2 and Carbon Nanotubes Hybridized Flexible Film: Binder-Free and High-Performance Li-Ion Anode. ACS Nano 2017, 11, 6483−6491. (30) Youn, D. H.; Park, Y. B.; Kim, J. Y.; Magesh, G.; Jang, Y. J.; Lee, J. S. One-Pot Synthesis of NiFe Layered Double Hydroxide/Reduced Graphene Oxide Composite as an Efficient Electrocatalyst for Electrochemical and Photoelectrochemical Water Oxidation. J. Power Sources 2015, 294, 437−443. (31) Chitravathi, S.; Kumar, S.; Munichandraiah, N. NiFe-Layered Double Hydroxides: A Bifunctional O2 Electrode Catalyst for NonAqueous Li-O2 Batteries. RSC Adv. 2016, 6, 103106−103115. (32) Bandow, S.; Asaka, S.; Saito, Y.; Rao, A.; Grigorian, L.; Richter, E.; Eklund, P. Effect of the Growth Temperature on the Diameter Distribution and Chirality of Single-Wall Carbon Nanotubes. Phys. Rev. Lett. 1998, 80, 3779. (33) Jorio, A.; Dresselhaus, G.; Dresselhaus, M.; Souza, M.; Dantas, M.; Pimenta, M.; Rao, A.; Saito, R.; Liu, C.; Cheng, H. Polarized Raman Study of Single-Wall Semiconducting Carbon Nanotubes. Phys. Rev. Lett. 2000, 85, 2617. (34) Dresselhaus, M. S.; Dresselhaus, G.; Saito, R.; Jorio, A. Raman Spectroscopy of Carbon Nanotubes. Phys. Rep. 2005, 409, 47−99. (35) Mattia, D.; Rossi, M.; Kim, B.; Korneva, G.; Bau, H.; Gogotsi, Y. Effect of Graphitization on the Wettability and Electrical Conductivity of CVD-Carbon Nanotubes and Films. J. Phys. Chem. B 2006, 110, 9850−9855. (36) Mansour, A. N. Characterization of NiO by XPS. Surf. Sci. Spectra 1994, 3, 231−238. (37) Kautz, R. L.; Dresselhaus, M. S.; Adler, D.; Linz, A. Electrical and Optical Properties of NiS2. Phys. Rev. B 1972, 6, 2078−2082. (38) Yamashita, T.; Hayes, P. Analysis of XPS Spectra of Fe2+ and Fe3+ Ions in Oxide Materials. Appl. Surf. Sci. 2008, 254, 2441−2449. (39) Nayak, S.; Mohapatra, L.; Parida, K. Visible Light-Driven Novel g-C3N4/NiFe-LDH Composite Photocatalyst with Enhanced Photocatalytic Activity Towards Water Oxidation and Reduction Reaction. J. Mater. Chem. A 2015, 3, 18622−18635.
(40) Datsyuk, V.; Kalyva, M.; Papagelis, K.; Parthenios, J.; Tasis, D.; Siokou, A.; Kallitsis, I.; Galiotis, C. Chemical Oxidation of Multiwalled Carbon Nanotubes. Carbon 2008, 46, 833−840. (41) Long, X.; Li, J.; Xiao, S.; Yan, K.; Wang, Z.; Chen, H.; Yang, S. A Strongly Coupled Graphene and FeNi Double Hydroxide Hybrid as an Excellent Electrocatalyst for the Oxygen Evolution Reaction. Angew. Chem., Int. Ed. 2014, 53, 7584−7588. (42) Kuznetsova, A.; Popova, I.; Yates, J. T.; Bronikowski, M. J.; Huffman, C. B.; Liu, J.; Smalley, R. E.; Hwu, H. H.; Chen, J. G. Oxygen-Containing Functional Groups on Single-Wall Carbon Nanotubes: NEXAFS and Vibrational Spectroscopic Studies. J. Am. Chem. Soc. 2001, 123, 10699−10704. (43) Liang, Y.; Li, Y.; Wang, H.; Zhou, J.; Wang, J.; Regier, T.; Dai, H. Co3O4 Nanocrystals on Graphene as a Synergistic Catalyst for Oxygen Reduction Reaction. Nat. Mater. 2011, 10, 780−786. (44) Jia, Y.; Zhang, L.; Gao, G.; Chen, H.; Wang, B.; Zhou, J.; Soo, M. T.; Hong, M.; Yan, X.; Qian, G.; et al. A Heterostructure Coupling of Exfoliated Ni-Fe Hydroxide Nanosheet and Defective Graphene as a Bifunctional Electrocatalyst for Overall Water Splitting. Adv. Mater. 2017, 29, 170017.
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