In Situ Grown Fe2O3 Single Crystallites on Reduced Graphene Oxide

Article

In-situ grown Fe2O3 single crystallites on reduced graphene oxide nanosheets as high performance conversion anode for sodium-ion batteries Ting Li, Aiqiong Qin, Lanlan Yang, Jie Chen, Qiufan Wang, Daohong Zhang, and Hanxi Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 24 May 2017 Downloaded from http://pubs.acs.org on May 27, 2017

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ACS Applied Materials & Interfaces

In-situ grown Fe2O3 single crystallites on reduced graphene oxide nanosheets as high performance conversion anode for sodium-ion batteries Ting Li, † Aiqiong Qin, †Lanlan Yang,‡ Jie Chen, † Qiufan Wang, † Daohong Zhang* †

†

and Hanxi Yang*‡

Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs

Commission & Ministry of Education, College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan, 430074, P. R. China. ‡

College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072,

China.

*Corresponding author E-mail: [email protected]; [email protected].

ABSTRACT: Electrochemical conversion reactions of metal oxides provide a new avenue to build high capacity anodes for sodium-ion batteries. However, the poor rate performance and cyclability of these conversion anodes remain a significant challenge for Na-ion battery applications because the most of conversion anodes suffer from sluggish kinetics and irreversible structural change during cycles. In this paper, we report a Fe2O3 single crystallites/reduced graphene oxide composite (Fe2O3/rGO), where the Fe2O3 single crystallites with a particle size of ~300 nm were uniformly anchored on the rGO nanosheets, which provide a highly conductive framework to

ACS Paragon Plus Environment


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facilitate electron transport and a flexible matrix to buffer the volume change of the material during cycling. This Fe2O3/rGO composite anode shows a very high reversible capacity of 610 mAh g-1 at 50 mA g-1, a high coulombic efficiency of 71% at the first cycle and a strong cyclability with 82% capacity retention after 100 cycles, suggesting a potential feasibility for sodium-ion batteries. More significantly, the present work clearly illustrates that an electrochemical conversion anode can be made with high capacity utilization, strong rate capability and stable cyclability through appropriate tailoring the lattice structure, particle size and electronic conduction channels for a simple transition-metal oxide, thus offering abundant selections for development of low-cost and high-performance Na-storage electrodes.

KEYWORDS: Fe2O3 single crystal, reduced graphene oxide nanosheets, conversion anode, metal oxide, sodium-ion batteries

1. INTRODUCTION Large-scale energy storage technologies are greatly needed to effectively utilize renewable electricity such as solar panels and wind farms for mobile transportation and smart grids. In the pursuit of these technologies, many new types of electrochemical batteries have been proposed for future electric vehicle and distributed electric storage applications.1,2 Among all the new battery chemistries being developed, sodium-ion batteries (SIBs) are considered to be one of the most attractive candidates because of their similar intercalation chemistry to Li-ion batteries and natural abundance of sodium resources. However, finding suitable


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Na-host materials for battery application is difficult because the larger sized Na+ ions are frustrated to move freely in the rigid oxide lattices.3-5 Up to date, only a few of Na-intercalation anodes are found to have acceptable redox capacity and certain cyclability.6-10 To overcome this difficult circumstance, several types of Na-alloying compounds are developed to demonstrate remarkable high Na-storage capacities, such as Na3.75Sn (847 mAh g-1),11,12 Na3Sb (660 mAh g-1)13,14 and Na3P (2560 mAh g-1).15,16 However, the huge volume changes of these host materials during alloying/dealloying reactions lead to a structural instability, which severely hinder their applications for Na-ion batteries.9,17 Electrochemical conversion reaction provides a new mechanism to realize high Na-storage capacity through reversible structural conversion to utilize the multi-oxidation states of transition-metal elements.18,19 In recent years, many types of metal oxides,20-24 metal sulfides,25,26 metal selenides,27-28 metal nitrides29 and metal phosphides30,31 have been reported for Na-storage anodes. Among them, Fe2O3 seems to be particularly attractive, owing to its natural abundance, environmental benignity, and high theoretical capacity (1007 mAh g-1).32-40 However, most of the Fe2O3 electrodes reported so far suffers from low utilization, inferior cycling performance, and poor rate capability, due to its low electron conductivity and large specific volume change during the electrochemical conversion processes.32,37 To overcome the these problems, many efforts are devoted to tailor the nanostructure of Fe2O334-37 or to coat Fe2O3 nanoparticles with conductive carbon.32,37-40 For example, Zhou’s group reported graphene-supported Fe2O3 nanocrystals with excellent cycling performance



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and rate capability.32 Chen’s group synthesized a 3D porous γ-Fe2O3@C nanocomposite, which provides a capacity of about 400 mAh g-1 with a high cycling stability over 200 cycles.37 Such nanoarchitectures can indeed enhance the kinetics and performance of Fe2O3 conversion materials. From the thermodynamic point of view, nanosized particles are intrinsically unstable because of their high surface energy, and easy agglomeration during electrochemical cycling is inevitable.41,42 Such an effect becomes even prominent with downsizing the nanoparticles and eventually leads to an unavoidable capacity fading if no special strategy is introduced. On the other hand, the large surface area of nanoparticles causes a high irreversible capacity during the solid electrolyte interface (SEI) formation and results in a low coulombic efficiency at initial cycles.41 As an anode material, the low coulombic efficiency will bring a significant capacity loss at the initial cycle for the batteries. More significantly, such a capacity loss is even larger for SIBs than for Li-ion batteries, as it is revealed that the overall SEI coverage on Fe2O3 electrode is more prominent in the Na-half batteries than in those based on Li-half batteries.33,43 Very recently, it was reported that single crystal metal oxides such as Fe2O3, CuO and V2O5 show excellent electrochemical performance with high Li or Na-storage capacity and satisfactory cyclability.44-47 It was found that the predominantly exposed facets of the single crystals have relatively high surface energy, thus providing active sites for accommodating lithium or sodium ions and then for a fast conversion reaction. Furthermore, it was also observed that although suffered from the structural


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transformation of the electrode material during lithiation/delithiation processes, the conversion products can inherit the crystallographic orientation of single-crystal α-Fe2O3.48 These results suggest that single crystal structure may have a strong resistance to the aggregation of nanoparticles and a strong tendency to keep the electrode structure reversibly changed, thus ensuring the cycling stability. In the present work, we synthesized monocrystalline Fe2O3 particles with a diameter of hundreds nanometer, which are uniformly anchored onto reduced graphene oxide nanosheets (rGO) through one-step solvothermal method, and investigated the electrochemical performance, especially cycling stability of the material. Due to the structural integrity and appropriate size of the Fe2O3 single crystallites along with the abundant 3D electron transport channels provided by rGO sheets, this Fe2O3/rGO composite anode shows a very high reversible capacity of 610 mAh g-1 at 50 mA g-1, a high coulombic efficiency of 71% at the first cycle and a strong cyclability (82% capacity retention over 100 cycles), suggesting a potential feasibility to use this conversion anode for sodium-ion batteries. 2.

EXPERIMENTAL SECTION

2.1. Materials Synthesis Fe2O3/rGO composites were prepared by a one-step solvothermal process. In a typical synthesis, 10 mL of 0.4 mol L-1 Fe(NO3)3 methanol solution was mixed with 60 mL of 1 mg mL-1 GO (Graphene Oxide, 99% purity, Nanjing XFNANO Materials Tech Co., Ltd，Nanjing, China) methanol dispersion under vigorous stirring and ultrasonic surging for 1 h. After dropwise addition of 14 mL aqueous ammonia and



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stirring for 0.5 h, the formed homogeneous mixture was added into a 100 mL Teflon-lined stainless steel autoclave at 180 °C for about 10 h. When cooling down to room temperature, the solid product was centrifuged and washed with distilled water and ethanol, and then dried at 60 °C under vacuum. Pure Fe2O3 and rGO samples were synthesized using the above-mentioned method in the absence of GO or Fe(NO3)3, respectively. 2.2. Structural characterizations The crystalline structural features of the as-prepared samples were characterized by X-ray diffraction (XRD, Bruker, D8-advance, Cu Kα radiation). The morphologies of Fe2O3 monocrystals and as-prepared composite were observed using scanning electron microscopy (SEM, FEI Quanta-200) and transmission electron microscope (TEM, JEOL, JEM-2100FEF). The structures of the GO and rGO in Fe2O3/rGO composite were investigated by confocal Raman microspectroscopy (Renishaw, RM-1000, 514.5 nm excitation). The content of the rGO in Fe2O3/rGO composite was obtained by thermogravimetric analysis (TGA, TA, Q500) in air from room temperature to 800 °C at a heating rate of 10 °C min-1. X-ray Photoelectron Spectroscopy (XPS) was conducted on a VG Multilab 2000 spectrometer. Binding energies were calibrated by setting the C 1s hydrocarbon component peak at 284.6 eV. To characterize the structural changes during cycling, ex-situ XRD and XPS analysis are conducted for the electrode samples, which are taken out from the cycled cells at different depths of charge and discharge (0.01-3.0 V), and rinsed with


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dimethyl carbonate solvent in an Ar-filled glove box. 2.3. Electrochemical measurements Electrochemical performances of the electrode materials were examined by coin cells. The electrodes were fabricated by coating a slurry, which was composed of 80 wt% materials, 10 wt% CMC binder and 10 wt% Super P, onto a copper foil and dried at 60 °C overnight under vacuum. The mass loading of the active material within the film is about 2.5 mg cm-2. Coin cells (2032 type) were assembled in an argon-filled glovebox using the as-prepared electrode as a working electrode, sodium metal disk as the counter and reference electrode, a microporous membrane (Celgard 2400) as the separator. The electrolyte used is prepared by dissolving NaPF6 (1 M) in the solvent of ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1 by volume) with 5% fluoroethylene carbonate (FEC). The galvanostatic discharge/charge measurement was carried out using LAND cycler (Wuhan Kingnuo Electronic Co., China). The charge/discharge specific capacity of the Fe2O3/rGO electrode is calculated based on the mass of Fe2O3/rGO composite. Cyclic voltammetry was conducted using coin cells on an electrochemical workstation (CHI 660e, Chenhua Instruments Co., China) at a scan rate of 0.1 mV s-1. Electrochemical impedance spectra (EIS) were obtained on IM 6e impedance measuring unit (Zahner) with an AC voltage of 5 mV amplitude from 100 kHz to100 mHz.

3.

RESULTS AND DISCUSSION The Fe2O3/rGO nanocomposite was synthesized by a simple one-step solvothermal



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process. As shown in Figure 1, GO methanol dispersion was first mixed with Fe(NO3)3 under vigorous stirring to form a precursor solution, in which Fe3+ cations were adsorbed uniformly on GO platelets through electrostatic interaction of oxygen-containing functional groups such like hydroxyl, carboxyl, and epoxyl. Then Fe(OH)3 crystals were in-situ produced and anchored onto the GO nanosheets after the intervention of aqueous ammonia. During the subsequent solvothermal treatment, GO was converted to rGO with the reduction of methanol and Fe(OH)3 decomposed to form Fe2O3 nanocrystals simultaneously.

Figure 1. Schematic illustration of the Fe2O3/rGO composite formation process. The structure and morphology of the Fe2O3/rGO composites were characterized by XRD, Raman, TGA, SEM and TEM measurements. As shown in Figure 2a, both Fe2O3/rGO composite and pure Fe2O3 sample show strong XRD signals that can all be indexed to α-Fe2O3 (JCPDS No. 33-0664), suggesting high purity and crystallinity of the as-synthesized Fe2O3 particles. The reduction of GO and its content in the


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composite were confirmed by Raman spectra and TGA, respectively. Figure 2b gives the Raman spectra of pristine GO sample and Fe2O3/rGO composite. The two Raman bands observed at about 1355 and 1605 cm-1 in both cases are characterized as D-band and G-band, respectively, due to characteristic Raman shifts of graphite.49 It is obvious that the intensity ratio for the D-band to G-band (ID/IG) of the Fe2O3/rGO composite is higher than that of GO, indicative of the certain reduction of GO in the solvothermal treatment.50,51 As estimated by TGA in air (Figure 2c), the content of rGO in Fe2O3/rGO composite was determined to be 15.7%, in good accordance with the theoretical value (15.79%).

Figure 2. (a) XRD patterns of pure Fe2O3, Fe2O3/rGO composite and rGO sample; (b) Raman spectra of the Fe2O3/rGO composite and GO sample; (c) TGA curve of the Fe2O3/rGO composite. The morphology and microstructure of pure Fe2O3 and Fe2O3/rGO composite were observed via SEM and TEM spectrometry. As seen in Figure 3a (SEM), the pure



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Fe2O3 particles are homogeneously distributed with a uniform size. It is further confirmed by TEM image (Figure 3c) that the single Fe2O3 crystallite displays a rhombic structure with a diameter of ~300 nm. On the other hand, for the Fe2O3/rGO composite, it is clearly observed that the Fe2O3 particles are anchored tightly on the rGO sheets (Figure 3b, SEM) and the monodisperse Fe2O3 particles are uniformly wrapped in graphene sheets (Figure 3d, TEM). The high-resolution TEM image of Figure 3e indicates a single Fe2O3 crystallite in the Fe2O3/rGO composite with a particle size of about 300 nm, which is similar to that of the pure Fe2O3 sample. Figure 3f displays the corresponding selected area electron diffraction pattern (SAED) from the above single crystallite. It shows a set of clear diffraction spots, all of which can be well indexed as (104), (110) and (012) planes of pure α-Fe2O3 phase. The results above confirmed that single-crystal Fe2O3 particles with a diameter of ~300 nm were synthesized in both the samples of pure Fe2O3 and Fe2O3/rGO composite (Figure 3f and S-1), and the particle size (~300 nm) is significantly larger than those of previously reported nanosized Fe2O3.32-34,37,39-40


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Figure 3. (a) SEM image of pure Fe2O3 sample, (b) SEM image of Fe2O3/rGO nanocomposite; (c) TEM image of pure Fe2O3 sample, (d) TEM image of Fe2O3/rGO nanocomposite; (e) TEM image of a single crystal of Fe2O3/rGO nanocomposite at high magnification; (f) The corresponding SAED pattern from (e). The electrochemical conversion performances of Fe2O3/rGO electrode were evaluated by cyclic voltammetry (CV) and galvanostatic discharge-charge measurements. Figure 4a shows typical CV curves of the Fe2O3/rGO electrode at a scan rate of 0.1 mV s-1 within the voltage range of 0.01-3.0 V. During the first



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negative scan, two broad cathodic peaks appeared at 1.1 and 0.5 V, respectively, which is different from the subsequent cycles, suggesting the irreversible formation of solid electrolyte interface (SEI) layer in the initial sodiation reaction for the Fe2O3/rGO electrode. At subsequent scans, two cathodic peaks emerged at 0.7 and 1.1 V, following two anodic peaks at 0.8 and 0.4V, respectively, which are reasonably originated from the reversible redox reactions of Fe3+ ↔ Fe2+ and Fe2+ ↔ Fe0 couples.33-34,37 Figure 4b provides the discharge/charge profiles of the Fe2O3/rGO electrode in the voltage range of 0.01-3.0 V at a current density of 50 mA g-1. In good agreement with its CV features, the Fe2O3/rGO electrode displayed sloping discharge/charge profiles with broad voltage plateaus at 0.8-0.4 V and 0.7-1.1 V, respectively, suggesting the reversible conversion reactions of Na+ with Fe2O3 crystallite. The Fe2O3/rGO electrode showed initial discharge/charge capacities of 861 and 611 mAh g-1 (calculated based on the mass of Fe2O3/rGO composite), resulting in a coulombic efficiency of 71% at the first cycle, which is relatively higher than those of the previously reported nanoscaled Fe2O3.32,37,39-40 This is attributed to the relatively larger size (~300 nm) and therefore lower surface area of these Fe2O3 particles, which reduce the irreversible capacity consumed for the formation of the SEI film and elevate the initial coulombic efficiency. After the following cycles, the reversible capacity maintained stable at ~610 mAh g-1. Upon the subtraction of specific capacity of rGO (50 mAh g-1, Figure S-4 and S-5), the reversible conversion capacity of the Fe2O3 crystallites in the electrode is determined to be about 723 mA h g-1,


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corresponding to 4.3 Na+ conversion with per Fe2O3 unit. The cycling performances of pure Fe2O3 and Fe2O3/rGO composite electrodes were comparatively evaluated to reveal the electrochemical enhancement of graphene matrix for the conversion reactions. As seen in the Figure 4c, the pristine Fe2O3 electrode exhibited a Na storage capacity of 330 mAh g-1 in the initial cycle and maintained a reversible capacity of 235 mAh g-1 after 100 cycles, corresponding to a capacity retention rate of 71.2%. Meanwhile, the Fe2O3/rGO composite electrode delivered a much higher reversible capacity of ~500 mAh g-1 after 100 cycles with a capacity retention rate of 81.8%. Both of the pure Fe2O3 and Fe2O3/rGO electrodes show a satisfactory cyclability. In comparison with the Fe2O3 nanoparticles previously reported,32,37-39 the as-prepared Fe2O3 single nanocrystals did not show a fast capacity fading but a much stable cyclability even they were used directly in its pristine form, demonstrating that the single-crystal structure of the Fe2O3 particles is beneficial to maintain the structural integrity of the electrode and the electrochemical reversibility for the conversion processes. Sluggish kinetics has been a severe issue for battery application of conversion electrodes. However, the Fe2O3 single crystallites demonstrate a strong rate capability, i.e., fast structural conversion during charge/discharge processes. Figure 4d shows the rate performance of pristine Fe2O3 and Fe2O3/rGO electrodes cycled at different current densities from 50 to 2000 mA g-1. The Fe2O3/rGO electrode delivered a reversible capacity of 216 mAh g-1 at a high current density of 2000 mA g-1, and recovered 95% of its original capacity (~500 mAh g-1) when the current density was



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returned to 100 mA g-1. In contrast, the pure Fe2O3 electrode only showed 54 mAh g-1 at a high current density of 2000 mA g-1. The greatly enhanced rate capability of the Fe2O3/rGO composite is obviously attributed to the existent of the rGO nanosheets, which act as a highly conductive and flexible buffering matrix to facilitate the electron conduction and alleviate the structural change of the electrode during the conversion reactions.

Figure 4. (a) CV curves of Fe2O3/rGO electrode at a scan rate of 0.1 mV s-1 between 0.01 and 3.00 V. (b) Charge/discharge curves of Fe2O3/rGO electrode in the voltage range of 0.01-3.00 V at 50 mA g-1; (c) Cycling curves of Fe2O3 and Fe2O3/rGO electrodes at 50 mA g-1; (d) Rate performance of Fe2O3 and Fe2O3/rGO electrodes at different current densities. Electrochemical impedance spectra (EIS) of Fe2O3 and Fe2O3/rGO composite electrodes were measured at different cycles to further confirm the electrochemical enhancement of rGO on the Fe2O3/rGO electrode (Figure 5). The fitted impedance


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parameters on the basis of the equivalent circuit inset (Figure 5a, b) are listed in Table 1. It is observed that charge transfer resistance (Rct) of the Fe2O3 electrode was 441 Ω at the first cycle and increased to 3470 Ω at the 40th cycle. In contrast, the Rct of Fe2O3/rGO electrode is 80.2 and 777.1 Ω at the first and 40th cycles, respectively, suggesting that rGO carbon matrix offers a well-connected electron transport network which significantly accelerates the electronic conduction during the conversion reaction as well as enhance the rate capability of the composite electrode.

Figure 5. Electrochemical impedance spectra (EIS) of Fe2O3 (a) and Fe2O3/rGO (b) electrodes at charge state after 1st and 40th cycles. The equivalent circuits are given as the inset. Table 1 The results of the EIS Simulation based on the equivalent circuit Fe2O3

Fe2O3/rGO

Cycle RSEI(Ω)

Rct (Ω)

RSEI (Ω)

Rct (Ω)

1st Cycle

17.9

441

5.7

80.2

40th Cycle

76.5

3470

7.1

777.1

RSEI and Rct are the resistances of SEI film and charge transfer, respectively.

The structural conversion mechanism can be visualized from ex-situ XRD and XPS



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characterizations of the cycled Fe2O3/rGO electrode at different charge/discharge states. As seen in Figure 6a, the as-prepared electrode shows a clear XRD pattern of Fe2O3 lattice. After discharged to 0.6 V, the Fe2O3 signals almost disappeared, while the main reflection of metal Fe at 20.3° (JCPDS No. 01-1267) was observed. Upon a fully discharged of the electrode to 0.01 V, the XRD signal of Fe became stronger, meanwhile the XRD peaks characteristic of Fe2O3 vanished completely, implying that the Fe2O3 crystallites had entirely transformed into metallic Fe through the electrochemical conversion reaction. The traceable XRD signal from Na2O phase is invisible, possibly due to the poor diffractions of nanosized Na2O produced by conversion reaction. In the reversed charge process, the peak intensity of the Fe phase decreased and completely disappeared at a fully charged state of 3.0 V, while a weak peak of Fe2O3 reappeared, indicating a high reversibility of the structural change during discharge/charge process. This reversible conversion mechanism has also been confirmed by ex-situ XPS analysis of Fe element in the cycled Fe2O3/rGO electrode at different oxidation states. As shown in Figure 6b, the pristine Fe2O3/rGO electrode gives two XPS peaks at 710.7 and 724.3 eV, which are attributed to the binding energies of Fe3+ 2p3/2 and Fe3+ 2p1/2, respectively. Once discharged to 0.01 V, the above-mentioned binding energy peaks vanished and new imperceptible peaks at 706.8 and 720 eV appeared, corresponding to the binding energies of Fe0 2p3/2 and Fe0 2p1/2, respectively, indicative of the reduction of all the Fe3+ ions in the Fe2O3 lattice to Fe0. The binding energies returned to the original values when it recharged to 3.0 V, which suggests a reversible structural conversion of Fe0 to Fe3+ ions in the Fe2O3


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crystallite. The above-mentioned XPS and XRD results evidently demonstrate the reversible structural conversion of the Fe2O3 with Na+ during discharge-charge cycles.

Figure 6. (a) Ex situ XRD patterns of Fe2O3/rGO electrodes at different discharge and charge states as labeled in the figure; (b) Ex situ XPS survey of Fe 2p spectra for Fe2O3/rGO electrodes at various discharge and charge states as labeled in the figure. TEM images of Fe2O3/rGO electrode after 100 cycles were observed to evidence the structural stability of the electrode enduring long-term discharge and charge. Compared with the original morphology (Figure 3d, e), the Fe2O3 crystallites in the Fe2O3/rGO electrode (Figure 7a, b) still maintain the single crystal structure without any cracks or aggregations after 100 cycles. The HRTEM image (Figure 7c) of Fe2O3/rGO electrode at fully discharged state shows the lattice fringe with d-space of 0.201 nm, corresponding to the (110) planes of Fe. When the electrode is fully charged, the lattice fringe of Fe2O3 (104) phase was observed (Figure 7d), which is in agreement with the results of ex situ XRD analysis. This outstanding structural stability of the Fe2O3/rGO electrode arose from its single-crystal structure feature, which maintains the mechanical integrity of the electrode during cycling. Moreover, it is also speculated that the stable and conductive rGO carbon matrix wrapped on Fe2O3



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nanograins can not only facilitate the electronic transports but also effectively accommodate the volume changes during the conversion process, resulting in a significantly improved cycling stability.

Figure 7. (a) TEM image of Fe2O3/rGO electrode after 100 discharge/charge cycles at 100 mA g-1; (b) at higher magnification of image (a); (c) HRTEM image of Fe2O3/rGO electrode at a fully discharged state; (d) HRTEM image of Fe2O3/rGO electrode at a fully charged state. 4.

CONCLUSIONS In summary, monocrystalline Fe2O3/rGO composite was prepared by one-step

solvothermal method, in which Fe2O3 single crystallites with a diameter of ~300 nm was uniformly anchored onto rGO nanosheet. The as-prepared Fe2O3/rGO composite exhibits a high reversible Na storage capacity of 610 mAh g-1 at 50 mA g-1 with a


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high coulombic efficiency of 71% at the first cycle, a outstanding rate capability with 216 mAh g-1 at a high current of 2000 mA g-1, and an excellent cycling stability with 82% capacity retention over 100 cycles. It is thought that the single crystal structure of the Fe2O3 particles is favorable to prevent the aggregation of the nanograins during the cycling and enhance the cycling stability, and the relatively large particle size benefits to raise the high initial coulombic efficiency. The rGO nanosheet provides fast electron transport network, which improves the specific capacity and rate capability. The present work indicates that a high capacity utilization and high rate capability of the Fe2O3 nanocrystallites can be realized through electrochemical conversion reaction by tailoring the lattice structure, particle size and building appropriate electronic conduction channels of the Fe2O3 nanocrystals. ASSOCIATED CONTENT Supporting Information Available. Additional figures as mentioned in the text. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Tel: 86-027-67841788. *E-mail: [email protected]. Tel: 86-027-68754526. ACKNOWLEDGMENTS We gratefully acknowledge the financial support of the National Natural Science Foundation of China (21403305) and Hubei Province Natural Science Fund for Distinguished Young Scientists (2014CFA037). .



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Table of contents Graphic 451x331mm (150 x 150 DPI)


In Situ Grown Fe2O3 Single Crystallites on Reduced Graphene Oxide

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