Next Article in Journal
Aggregation of Amyloidogenic Peptide Uperin—Molecular Dynamics Simulations
Next Article in Special Issue
Sodium Storage Properties of Carbonaceous Flowers
Previous Article in Journal
Photocatalysis in Water-Soluble Supramolecular Metal Organic Complex
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Molecules
Volume 28
Issue 10
10.3390/molecules28104069
molecules-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Magnetic CoFe2O4 and NiFe2O4 Induced Self-Assembled Graphene Nanoribbon Framework with Excellent Properties for Li-Ion Battery

by
Xiyu Zhao
1,2,
Chunyang He
1,
Qiujv Bai
1,
Xiangwen Miao
1,
Cheng Cao
1 and
Tianli Wu
2,*
1
Key Laboratory of Hexi Corridor Resources Utilization of Gansu, School of Chemistry and Chemical Engineering, Hexi University, Zhangye 734000, China
2
Henan Key Laboratory of Photovoltaic Materials, Henan University, Kaifeng 475001, China
*
Author to whom correspondence should be addressed.
Molecules 2023, 28(10), 4069; https://doi.org/10.3390/molecules28104069
Submission received: 12 April 2023 / Revised: 9 May 2023 / Accepted: 10 May 2023 / Published: 12 May 2023
(This article belongs to the Special Issue Nanomaterials for Energy Storage and Conversion)
Browse Figures
Versions Notes

Abstract

:
A magnetically induced self-assembled graphene nanoribbons (GNRs) method is reported to synthesize MFe2O4/GNRs (M = Co,Ni). It is found that MFe2O4 compounds not only locate on the surface of GNRs but anchor on the interlayers of GNRs in the diameter of less than 5 nm as well. The in situ growth of MFe2O4 and magnetic aggregation at the joints of GNRs act as crosslinking agents to solder GNRs to build a nest structure. Additionally, combining GNRs with MFe2O4 helps to improve the magnetism of the MFe2O4. As an anode material for Li+ ion batteries, MFe2O4/GNRs can provide high reversible capacity and cyclic stability (1432 mAh g−1 for CoFe2O4/GNRs and 1058 mAh g−1 for NiFe2O4 at 0.1 A g−1 over 80 cycles).

Graphical Abstract

1. Introduction

Rechargeable lithium-ion batteries (LIBs) are widely used to meet the ever-increasing demand for fast charging and high-capacity energy storage [1,2,3]. It is particularly important to search for novel anode materials with both high capacity and outstanding safety for high-performance LIBs. Nowadays, graphite is the most commercial anode material for LIBs owing to its abundant natural resources. However, the relatively low theoretical specific capacity (372 mAh g−1) and the lithium diffusion coefficient (10−7~10−10 cm2 s−1) restrict the further application of high-power LIBs [4,5,6]. The choice of magnetic transition metal oxides (TMOs) as anodes for LIBs has received considerable attention due to their high energy density and natural abundance. Apart from binary TMOs, ternary TMOs comprising mixed valence in a single crystalline structure have drawn enormous research attention [7,8]. Regarding cobalt ferrite and nickel ferrite (MFe2O4, M = Co, Ni), as one of the representative ternary TMOs, better electrical conductivity arises because Co2+/Ni2+ and 1/2 the Fe3+ cation occupy the octahedral sites. In comparison to conventional spinel oxides, MFe2O4 with a unique inverse spinel structure has higher Li+ ion incorporation [9,10]. As a result, MFe2O4 is expected to become an appealing anode material for LIBs. Nevertheless, MFe2O4 suffers from huge volume expansion and material cracking problems during the periodic charge–discharge process, which results in rapid fading capability [11,12]. Two common approaches have been proposed to address the above issues. One is to prepare variously nanostructured (such as hollow nanospheres, nanowires, nanotubes) [13,14,15,16] composite. Nanostructured MFe2O4 can shorten the diffusion paths of Li+ ion, leading to higher electrochemical activity.
The other route is to introduce carbon materials, such as carbon nanotubes (CNTs) and graphene, to fabricate MFe2O4/carbon composites [17,18,19]. Among them, nest structure MFe2O4/carbon composites, due to their porous structure, can increase the efficiency of electron transport and the contact area with electrolytes. Moreover, a network carbon framework can not only effectively accommodate volume change in the MFe2O4 and prevent the pulverization, which will enable nest MFe2O4/carbon composites to maintain high conductivity and reversible capacity, but also provide nucleation sites that regulate MFe2O4 crystal morphology [20,21,22,23].
Nest structure MFe2O4/carbon composites can be prepared by hydrothermal, chemical vapor deposition, polymer-assisted methods, and so on [24,25,26]. The 3D framework prepared by the polymer-assisted method is stable in structure and simple in operation. However, the poor-conductivity nature of the polymer would affect the electron transport among the composites. Nest MFe2O4/carbon composites with high electron conductivity can be obtained by replacing the polymer with magnetic MFe2O4; thus, MFe2O4 will not only act as the active material but also as the “binder agent” to stabilize the carbon framework. The common carbon framework is mainly created by graphene or CNTs [26,27]. Compared to them, graphene nanoribbons (GNRs) are more beneficial for improving the electrochemical performance of the composites owing to their high active open edges and specific surface area [28].
Based on our previous work [29], a facile magnetically induced self-assembled graphene nanoribbons (GNRs) method is reported to synthesize MFe2O4. The key feature for our synthesis route is taking advantage of the magnetic attraction of MFe2O4, which cross-link GNRs in the intersections. By means of this procedure, the self-aggregated phenomenon takes place in magnetic nanomaterials owing to more active sites at the GNRs’ junction; MFe2O4 particles tend to link to each other and accumulate at the joints. After a following heating treatment, MFe2O4/GNRs can be easily achieved. MFe2O4/GNRs present excellent cycle performance or LIBs and particularly excellent high reversible capacity and rate capacity, resulting from their unique network structure and the synergy effect of each component. Additionally, research on magnetism indicates that the MFe2O4/GNRs are also promising for magnetic devices.

2. Results and Discussion

2.1. SEM and TEM Analysis

Figure 1a illustrates the synthesis route of CoFe2O4/GNRs composites by simple refluxing. CNTs were unzipped to obtain GNRs [30]. After that, both GNRs and cobalt organic salt were dispersed in benzyl ether solution under agitation. Thereafter, aqueous solution was refluxed at 220 °C for 0.5 h, during which Co(acac)3 decomposed to some CoFeO nanoclusters. Then, borders of GNRs filled with dangling C-C bonds were occupied by the CoFeO nanoclusters. Along with the reaction, CoFeO nanoclusters in situ grew and agglomerated as CoFe2O4 in the surface, interlayers, and edges of GNRs. After drying, the magnetically induced attraction of CoFe2O4 began to focus on the GNRs joints, causing CoFe2O4/GNRs composites to self-assemble. The synthesis procedure of NiFe2O4/GNRs is similar to CoFe2O4/GNRs, except nickel organic is used. The structure of the products was first investigated by SEM. Figure 1b–g represents the SEM images for MFe2O4/GNRs composites. The hybrids possessed a porous structure in the low-magnified SEM. From the high-magnification SEM (Figure 1c,f), the surface of the GNRs was anchored by metal oxide nanoparticles, and it can be clearly seen that some aggregates of MFe2O4 were in the junctions of GNRs. The aggregates of MFe2O4 acted as a “crosslink agent” that fitted together the GNRs to build a 3D porous structure. As presented in Figure 1b,e, the morphology of CoFe2O4/GNRs and MFe2O4/GNRs seemed very similar, indicating that preparation of porous MFe2O4/GNRs was controllable and universal. The SEM images of CoFe2O4 and NiFe2O4 nanocomposite without GNRs are shown in Figure S1 (Supplementary Materials). CoFe2O4 and NiFe2O4 are irregular spheres (20–50 nm) and tend to agglomerate together to form large particles without GNRs. The elemental mapping images of MFe2O4/GNRs are shown in Figure 1d,g, demonstrating that the C, Ni, Co, Fe, and O are gathered in the junction of GNRs and distributed uniformly along GNRs.
The microstructure and composition of the MFe2O4/GNRs were confirmed by the TEM. As shown in Figure 2a,d, there are numerous agglomerated metal oxide nanoparticles at the joints of GNRs. With the cross-linking function of these metal oxide nanoparticles, the GNRs self-assembled into a 3D structure. Additionally, it can be observed from Figure 2b,e that the MFe2O4 in an average size of 3–8 nm was uniformly distributed on both exteriors and interior layers of the GNRs in the hybrids (Figure S2). It was noted that suspended particles of MFe2O4 were found at the borders of GNRs in Figure 2c,f. It was proven that the unsaturated C-C bond at the edge of the GNRs can facilitate the nucleation and growth of MFe2O4. Figure 2c showed the high-resolution lattice images of CoFe2O4/GNRs nanoparticles in CoFe2O4/GNRs composite. The lattice fringes with a lattice spacing of 0.30 nm and 0.25 nm corresponded to the (220) and (311) planes of CoFe2O4, respectively [31]. Figure 2f showed the high-resolution lattice images of NiFe2O4 nanoparticles. The lattice fringes with a lattice spacing of 0.25 nm were assigned to the (311) planes of NiFe2O4 [32].

2.2. XRD, Raman, and XPS Analysis

An X-ray diffraction (XRD) analysis was performed to assess the structure, crystallization, and purity of MFe2O4/GNRs. As shown in Figure 3a, for CoFe2O4/GNRs composite, the diffraction peaks at 18.3, 30.2, 35.5, 43.2, 57.1, and 62.7 correspond to the lattice planes (220), (311), (400), (511), and (440), respectively, of cubic spinel structure (JCPDS No. 22-1086 and NiFe2O4 with JCPDS card no. 86-2267). In addition, there was also a diffraction peak at 26.5°(star symbol in Figure 3a), which was assigned to the GNRs [31,32]. Raman measurement was performed in Figure 3b,c. D, G, and 2D bands at 1340, 1582, and 2678 cm−1 stand for GNRs [32] on account of the strong disorder carbon’s in-plane vibrations and graphitic carbon’s in-plane vibrations. The three peaks of GNRs in MFe2O4/GNRs are basically in the same position as those in GNRs alone, but the strength of all three peaks is significantly reduced since GNRs are combined with MFe2O4. In the enlarged part of the figure, both the composites show three major peaks. CoFe2O4 shows at 680, 532, and 320 cm−1. Further, the peaks of NiFe2O4 are at 672, 470, and 323 cm−1 due to the low Raman-intensity nature of MFe2O4 [33,34], which are all consistent with the XRD results. XPS measurements were performed to further study the surface chemical state of the composites (Figure 3d). For MFe2O4/GNRs, there were several major peaks, assigned to C, O, Fe, Co, and Ni, respectively. In the high-resolution XPS spectra, C1s of CoFe2O4/GNRs had a graphitic C-C/C=C peak at 286.7 eV, together with C=O (287.4 eV), as revealed in Figure 3e [32]. The C-C/C=C and C-O peak of NiFe2O4/GNRs are located at 285.4 eV and 287.6eV, respectively (Figure 3i). The Co 2p3/2 and Co2p1/2 peaks of the CoFe2O4/GNRs were located at 779.4 and 795.8 eV with a 16.4 eV peak-to-peak separation (Figure 3f), indicating the Co(II) oxidation state [35]. The locations of the Fe2p peaks (Fe2p1/2 at 724.5 eV and Fe2p3/2 at 710.4 eV) in Figure 3g verify the presence of Fe3+ cations in CoFe2O4. The O1s spectrum in Figure 3h demonstrates two oxygen attributions. The peaks of 529.7 and 531.2 eV represent a metal-oxygen bond and some surface defect sites, respectively. The deconvolution of the Ni2p spectrum demonstrates four peaks in Figure 3j. At binding energies of 855.7 eV and 876.3 eV are two main peaks followed by two shake-up satellites. Moreover, the signals of Fe2p3/2 and Fe2p1/2 in NiFe2O4 peaks were found at 724.7 eV and 711.9 eV, respectively, indicating that the Fe is in the typical trivalent oxidation state (Figure 3k). Peaks of O1s of NiFe2O4 are denoted as crystal lattice oxygen and chemisorbed oxygen in Figure 3l [36,37].

2.3. BET and TGA Analysis

The nitrogen adsorption-desorption isotherm and pore-size distribution curves are shown in Figure S3a,b. The Brunauer-Emmett-Teller (BET) specific surface areas of CoFe2O4/GNRs and NiFe2O4/GNRs were measured to be 47.7 m2g−1 and 27.5 m2g−1, respectively. The sample exhibits a representative type IV curve, indicating a mesoporous structure with distributions ranging from 2 to 10 nm. The foam structure will help the rapid travel of electrolytic ions for accessing the interior MFe2O4 in the lithiation-delithiation process.
The TGA curves for MFe2O4/GNRs were shown in Figure S4. TGA is performed to analyze the mass ration of MFe2O4 and GNRs. There were several stages of weight loss in Figure S4. The drop in weight below 200 °C can be ascribed to the evaporation of water. The typical weight loss between 200 °C and 550 °C can be ascribed to the oxidation of the GNRs. The one after 550 °C was mainly due to the oxidation of MFe2O4 in air. Based on the weight loss in Figure S4, the weight percentages of CoFe2O4 and NiFe2O4 in MFe2O4/GNRs were estimated to be ~41% and ~23%, respectively.

2.4. Electrochemistry Performance

Cyclic voltammetry (CV) tests were investigated in half-cell configurations to assess the Li+ ion storage properties of the as-prepared MFe2O4/GNRs. Figure 4a–b showed the CV curves of the CoFe2O4/GNRs and NiFe2O4/GNRs in the first three cycles. Two cathodic peaks were observed at 0.57 and 0.53 V in the first cycle, corresponding to multistage electrochemical reduction reactions (lithiation) of MFe2O4/GNRs with a Li+ ion and a partially irreversible solid electrolyte interphase (SEI) layer [32]. The main anodic peaks at 1.5–2.0 V for the two composites were ascribed to the oxidation reactions (delithiation) of MFe2O4; in addition, the lithiation and delithiation peaks of GNRs were at 0.13–0.25 V and 0.15–0.24 V, proving that GNRs were helpful for Li+ ion storage. The above reactions are as follows [38,39,40,41]:
CoFe2O4 + 8Li+ + 8e−↔ 2Fe + Co + 4Li2O
NiFe2O4 + 8Li+ + 8e− ↔ 2Fe + Ni + 4Li2O
6C + xLi+ + xe−↔ LixC6
Figure 4c,d displays the charge-discharge process of MFe2O4/GNRs at a current density of 0.1 A g−1. In agreement with the CV curves, the potential platform at ~0.79 V can be found during the first discharge (lithiation) process. CoFe2O4/GNRs and NiFe2O4/GNRs electrodes delivered initial discharge capacities of 1735 mAh g−1 and 1621 mAh g−1and initial charge capacities of 1573 mAh g−1 and 1502 mAh g−1, with cycle efficiency of 90% and 92%, respectively. The irreversible capacity losses of the two electrodes in the following cycles were probably associated with the formation of SEI and irreversible lithium loss. It was observed that the second and third cycles of the current curve almost overlapped with each other, proposing that the Li+ ion storage of the electrodes was reversible in the following cycles (Figure S5).
To evaluate the rate capability of MFe2O4/GNRs, the electrodes were cycled under various current densities from 0.2 to 10 A g−1, and the results were described in Figure 5a and Table S1. With the increase in current density, the specific capacity of the composites decreases. Because of the slow transportation of Li+ ions and insufficient lithiation-delithiation process, a number of “dead” Li+ ions are generated, leading to a decrease in the capacity of the electrodes. However, when the current density exceeded 5 A g−1, the capacity increased instead. This phenomenon was interpreted by the activation process to facilitate Li+ ion pathways between the electrolyte and the electrode under small current density cycling [42]. Meanwhile, the capacity of CoFe2O4, NiFe2O4, CoFe2O4/GNRs, and NiFe2O4/GNRs composites can be measured to 937, 867, 1475, and 1235 mA h g−1, respectively, when the current density returned to 0.2 A g−1, indicating high reversible rate capability. Even at the higher current density of 5 A g−1, the discharge capacities of CoFe2O4/GNRs and NiFe2O4/GNRs composite remain high at stable values of 1330 and 960 mAh g−1, respectively. However, pure CoFe2O4 and NiFe2O4 cannot maintain capacity in such a high rate due to the lack of GNRs skeleton. In addition, we discovered that the CoFe2O4/GNRs electrode shows better rate performance than NiFe2O4/GNRs, CoFe2O4, and NiFe2O4 electrode. The reason might be associated with more stable states and more negative adsorption energy of CoFe2O4/GNRs, which could produce extra capacity through the pseudo-capacitive behavior. Moreover, the larger BET surface area and more metal oxides component of CoFe2O4/GNRs contribute to better performance in the rate test and the following tests.
The cycling performance of CoFe2O4, NiFe2O4, CoFe2O4/GNRs, and NiFe2O4/GNRs electrodes at the current density of 0.1 A g−1 is presented in Figure 5b. The CoFe2O4/GNRs electrode expresses the best cycle performance after 80 discharge/charge cycles with a reversible capacity of 1432 mAh g−1. CoFe2O4 (715 mAh g−1), NiFe2O4 (569 mAh g−1), and NiFe2O4/GNRs (1085 mAh g−1) electrodes with relatively smaller specific capabilities exhibited cycle stability similar to CoFe2O4/GNRs. When we increased the current density to 1 A g−1, the results were shown in Figure 5c. After 100 cycles, the discharge capacity of CoFe2O4/GNRs and NiFe2O4/GNRs was 1720 mAh g−1 and 1414 mAh g−1, respectively, while CoFe2O4 and NiFe2O4 were 300 mAh g−1 and 201 mAh g−1, respectively. Compared to the previously reported MFe2O4 electrodes, the discharge capacity and cycle stability of the electrode materials were superior (Table S2). Furthermore, the capacities that increased gradually in the initial cycles could be the interfacial Li+ ion storage or the reversible polymer film produced by Co-, Ni-, and Fe-activated electrolyte degradation [32,42]. In the cycles, network GNRs can be used as the support of MFe2O4/GNRs, which can inhibit the volume changes in MFe2O4 during the charge-discharge process. In the meantime, the embedded MFe2O4 in the interlayers of GNRs would prevent the re-stacking and provide extra Li+ ion storage accommodation. Moreover, the transport channels in porous GNRs can speed up the conduction of electrons/ions. Figure S6 showed the SEM images of MFe2O4/GNRs electrodes after 100 cycles at 1A g−1, illustrating that the network remains intact in the process of cycles, which ensured excellent electrochemical performance. However, the CoFe2O4 and NiFe2O4 electrodes detached from the substrate and seriously agglomerated.
To obtain better insight into the mechanism of the electrode reactions in the unique MFe2O4/GNRs architectures, we performed electrochemical impedance spectroscopy (EIS) for both electrodes, as shown in Figure 5d,e. Rct, RSEI, and Rs correspond to the semicircle in the high-frequency region of typical Nyquist plots; CPE relates to the constant phase element [15] on the basis of equivalent electrical circuit mode. The Rct of the CoFe2O4/GNRs and NiFe2O4/GNRs electrodes is 9.5 Ω and 16.8 Ω, respectively, which is smaller than CoFe2O4 and NiFe2O4 electrodes, showing that GNRs can effectively reduce the resistance of the anode. In the low-frequency region, the sloping line refers to the Warburg impedance (Zw); the slope of the CoFe2O4/GNRs electrode is higher than that of the NiFe2O4/GNRs, CoFe2O4, and NiFe2O4 electrodes, which implies that the CoFe2O4/GNRs electrode has lower Li+ ion diffusion resistance [31] (Table S3).

2.5. DFT Analysis

To further explain the effect of GNRs, we performed DFT calculations focused on the adsorption abilities towards Li+ ions and charge distribution after intercalation of Li+ ion [43,44]. CoFe2O4 and NiFe2O4 are semiconductors with band gaps of about 1.2 and 1.4 eV, respectively (Figure 6a–d). Since VASP is considered as a pseudopotential, the calculated value is relatively small. After the wrapping of GNRs, the hybrid orbitals appear near the Fermi level, leading to better electrical conductivity, which is consistent with the EIS results. According to Bader charge analysis, the number of transferred electrons for CoFe2O4 and NiFe2O4 is 0.23 and 0.26, respectively, while CoFe2O4/GNRs transfer 0.41 e− and NiFe2O4/GNRs transfer 0.33 e−, indicating the more stable state of CoFe2O4/GNRs. Moreover, Li atoms adsorption models of MFe2O4 and Mfe2O4/GNRs were constructed to calculate the corresponding adsorption energy (ΔEads). As can be seen in Figure 6e, the ΔEads of lithium adsorption in the CoFe2O4/GNRs is remarkably higher than that of NiFe2O4/GNRs, CoFe2O4, and NiFe2O4/GNRs, exhibiting that the CoFe2O4/GNRs can propel the lithium process. Accordingly, the theoretical analysis and experimental results are In a great consistence that the charge/discharge kinetics can be enhanced via GNRs assembling CoFe2O4 and NiFe2O4 to boost the electric conductivity and the advanced intrinsic Li+ storage.
The excellence electrochemical performance of MFe2O4/GNRs electrodes is probably due to the following reasons [17,45]: (1) as an elastic buffer layer, GNRs in the composites can not only avoid the volume expansion of CoFe2O4 and NiFe2O4 during lithiation and delithiation but also efficiently prevent the cracking or crumbling of anode materials [46,47]; (2) GNRs have premium electrical conductivity and are regarded as the electron transport path among CoFe2O4 and NiFe2O4, reducing the inner resistance of Li+ ion batteries; (3) the nano-sized active materials act as nanospacers to refrain the re-stacking of GNRs and therefore maintain their high active surface area, which is beneficial for enhancing the capacity of the composites.

2.6. Magnetic Performance Analysis

CoFe2O4 and NiFe2O4 nanoparticles are typical ferromagnetic nanomaterials. To clarify the effect of magnetism of CoFe2O4/GNRs and NiFe2O4/GNRs, the magnetic properties were studied by vibrating sample magnetometer system (VSM) at room temperature, as shown in Figure 7. Each CoFe2O4 and NiFe2O4 exhibited superparamagnetic behavior with little remanence and coercivity, implying that there is no remaining magnetization when the applied magnetic field is removed [48]. However, the saturation magnetization (Ms) values of CoFe2O4/GNRs and NiFe2O4/GNRs nanocomposites were 11.8 emu/g and 40.4 emu/g, respectively. The saturation magnetization intensity is lower than that of their bulk material. The main reason for the low saturation magnetization could be the size effect of magnetic nanoparticles; the surface spin coupling of nanoparticles is weaker than that of bulk materials. The saturation magnetization of all MFe2O4/GNRs composites is much higher than that of MFe2O4 and GNRs. It is noted that the saturation magnetization of NiFe2O4 nanoparticles in the NiFe2O4/GNRs is improved 10 times as much as that on their own. The improved saturation magnetization of NiFe2O4/GNRs is probably due to the increased electron conductivity by the aid of GNRs. In addition, we also calculated the magnetism enhancement after recombination of GNRs; the reason may be the influence of the built-in electromagnetic field on lithium storage (Table S4).
The CoFe2O4/GNRs and NiFe2O4/GNRs have maintained the dispersion and paramagnetism of magnetic nanoparticles, demonstrating their promising applications in magnetic devices.

3. Materials and Methods

3.1. Synthesis

The synthesis processes of GNRs and MFe2O4/GNRs were shown in supporting information [30].

3.2. Electrochemical Measurement

Coin cells (CR2430) were used to characterize the electrochemical properties of the sample. The working electrode was prepared by dropping the suspension of composites into a carbon nanofiber paper (CFP, d~16 mm, S~2 cm2) without any binder, then dried in vacuum. Cyclic voltammetry (CV) was carried out on an electrochemical workstation (Solartron Metrology 1260 + 1287, Bognor Regis, UK) with the scanning rate of 0.1 mV s−1 (0.00–3.00 V vs. Li/Li+). Arbin BT (2000, College Station, TX, USA) was used to measure charge–discharge properties of the samples. All the capacities showed in this work have deducted the contribution from the substrate.

3.3. Sample Characterization

X-ray diffraction (XRD, DMAX-2500PC, Tokyo, Japan) was used to record the phase structure of the samples using Cu/Kα radiation (kα = 0.15406 nm). Raman spectra were obtained by a Renishaw Invia Raman Microprobe (Wotton-under-Edge, UK) (100–3000 cm−1) using argon ion laser (514 nm). The morphologies of the as-obtained samples were studied using a field emission scanning electronic microscope (FE-SEM, Hitachi S-4800, Tokyo, Japan) and transmission electron microscope (TEM, Zeiss LIBRA 220 FEG, Oberkochen, Germany). X-ray photoelectron spectroscopy (XPS, ESCALAB 250 Thermo Fisher Scientific, Waltham, MA, USA) was carried out to study the surface chemical state of the composites. Brunner–Emmet–Teller (BET) measurements were operated on a Micromeritics ASAP 2020, USA. The content of the sample was analyzed by the thermogravimetric analysis (TGA Perkin ELMER TGA7, Waltham, MA, USA). The measurement of magnetic hysteresis loop was performed using a vibrating sample magnetometer (VSM Lake Shore 7400, Lake Shore Cryotronics, Westerville, OH, USA). All calculations were completed within the framework of the density functional theory (DFT) within the projector’s enhanced plane wave method.

4. Conclusions

A general magnetically induced self-assembled graphene nanoribbons method is proposed to prepare network MFe2O4/GNRs. The formation of these MFe2O4/GNRs is due to the surface in situ growth of MFe2O4 on GNRs and aggregation at the joints of GNRs, which is mainly driven by their own magnetic interactions. The unique framework of MFe2O4/GNRs can effectively prevent the shedding of MFe2O4, inhibiting the re-stacking of GNRs layers and shortening the Li+ ion transmission path. Consequently, CoFe2O4/GNRs and NiFe2O4/GNRs composites exhibited large reversible capacities (1432 and 1058 mAh g−1 at 0.1 A g−1, 1720 mAh g−1 and 1414 mAh g−1 at 1 A g−1, respectively), excellent cyclic performance, and good rate capabilities. The reason that the CoFe2O4/GNRs electrode shows better Li-ion battery performance than NiFe2O4/GNRs might be associated with the more stable states and more negative adsorption energy of CoFe2O4/GNRs according to DFT results, which could produce extra capacity through pseudo-capacitive behavior. Additionally, combining GNRs with MFe2O4 helps to improve the magnetism of the MFe2O4, making MFe2O4/GNRs suitable for magnetic applications, such as magnetically mediated targeted drug delivery and magnetic resonance imaging.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules28104069/s1, 1 Synthesis of MFe2O4/GNRs. 2 Computational Method. Figure S1: (a,b) SEM images of as-prepared CoFe2O4; (b–d) SEM images of as-prepared NiFe2O4; Figure S2 (a–e) TEM images of as-prepared CoFe2O4/GNRs; Figure S3: The nitrogen adsorption/desorption isotherms and porosity distribution of (a,b) CoFe2O4/GNRs and (c,d) NiFe2O4/GNRs; Figure S4: TGA curves of CoFe2O4/GNRs and NiFe2O4/GNRs.; Figure S5 (a) CoFe2O4/GNRs and (b) NiFe2O4/GNRs electrodes at a current density of 0.1 A g−1 for the 1st, 2nd, 3rd, 30th, and 50th cycles in the voltage range between 3.00 and 0.01 V; Figure S6 SEM images of (a,b) CoFe2O4/GNRs and (c,d) NiFe2O4/GNRs electrode; Figure S7 SEM images of (a) CoFe2O4/GNRs, (b) NiFe2O4/GNRs, (c) CoFe2O4/GNRs, (d,e) CoFe2O4, and (f) NiFe2O4 electrode after 100 cycles (1 Ag−1). Table S1: Rate capability of the samples; Table S2: Comparison of the electrochemical performance of some Li-ion battery anodes; Table S3: The EIS simulation parameters of as-prepared samples; Table S4: Saturation magnetization of as-prepared samples. References [49,50,51] are cited in the supplementary materials.

Author Contributions

Conceptualization, X.Z. and T.W.; methodology, C.H. and Q.B.; formal analysis, X.M.; investigation, C.C.; writing—original draft preparation, X.Z.; writing—review and editing, T.W.; supervision, X.Z and T.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Young Doctoral Fund of Gansu Province (2022QB-157), College Education Innovation Fund Project of Gansu Province (2022B-196), and National Innovation and Entrepreneurship Training Program for College Students (202210740015).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available from the authors.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Samples of the compounds are available from the authors.

References

  1. Li, M.; Lu, J.; Chen, Z.; Amine, K. 30 Years of Lithium-Ion Batteries. Adv. Mater. 2018, 30, 1800561. [Google Scholar] [CrossRef] [PubMed]
  2. Kim, T.; Song, W.; Son, D.Y.; Ono, L.K.; Qi, Y. Lithium-ion batteries: Outlook on present, future, and hybridized technologies. J. Mater. Chem. A. 2019, 7, 2942–2964. [Google Scholar] [CrossRef]
  3. Lv, W.; Li, Z.; Deng, Y.; Yang, Q.; Kang, F. Graphene-based materials for electrochemical energy storage devices: Opportunities and challenges. Energy Stor. Mater. 2016, 2, 107–138. [Google Scholar] [CrossRef]
  4. Lebrouhi, B.E.; Baghi, S.; Lamrani, B.; Schall, E.; Kousksou, T. Critical materials for electrical energy storage: Li-ion batteries. J. Energy Stor. 2022, 55, 105471. [Google Scholar] [CrossRef]
  5. Chen, M.; Shao, L.L.; Wang, X.Q.; Qian, X.; Yuan, Z.Y.; Fang, L.X.; Ding, A.X.; Lv, X.W.; Wang, Y.N. Controlled synthesis of highly active nonstoichiometric tin phosphide/carbon composites for electrocatalysis and electrochemical energy storage applications. ACS Sustain. Chem. Eng. 2022, 10, 1482–1498. [Google Scholar] [CrossRef]
  6. Chen, J.; Wang, P.F.; Kang, Y.; Zhang, Y.H.; Yang, D.X.; Shi, F.N. Co3O4/LaCoO3 nanocomposites derived from MOFs as anodes for high-performance lithium-ion batteries. Inorg. Chem. Commun. 2022, 140, 109447. [Google Scholar] [CrossRef]
  7. Yang, D.; Feng, Y.; Gao, J.; Wu, K.; He, M. A simple fabrication for nanoscale SnO2-Fe2O3-C lithium-ion battery anode material with tubular network structure. Ionics 2022, 28, 2185–2196. [Google Scholar] [CrossRef]
  8. Dorri, M.; Zamani, C.; Babaei, A. Insights into temperature-induced evolution of spinel MnCo2O4 as anode material for Li-ion batteries with enhanced electrochemical performance. J. Alloys Compd. 2023, 941, 169034. [Google Scholar] [CrossRef]
  9. Alhakemy, A.Z.; Elseman, A.M.; Fayed, M.G.; Ahmed Amine Nassr, A.B.; El-Hady Kashyout, A.; Wen, Z. Hybrid electrocatalyst of CoFe2O4 decorating carbon spheres for alkaline oxygen evolution reaction. Ceram. Int. 2022, 48, 5442–5449. [Google Scholar] [CrossRef]
  10. Du, W.; Zheng, Y.; Liu, X.; Cheng, J.; Chenna Krishna Reddy, R.; Zeb, A.; Lin, X.; Luo, Y. Oxygen-enriched vacancy spinel MFe2O4/carbon (M = Ni, Mn, Co) derived from metal-organic frameworks toward boosting lithium storage. Chem. Eng. J. 2023, 451, 138626. [Google Scholar] [CrossRef]
  11. Zhao, Q.; Xia, Z.; Qian, T.; Rong, X.; Zhang, M.; Dong, Y.; Chen, J.; Ning, H.; Li, Z.; Hu, H.; et al. PVP-assisted synthesis of ultrafine transition metal oxides encapsulated in nitrogen-doped carbon nanofibers as robust and flexible anodes for sodium-ion batteries. Carbon 2021, 174, 325–334. [Google Scholar] [CrossRef]
  12. Yang, T.; Liu, Y.; Yang, D.; Deng, B.; Huang, Z.; Ling, C.D.; Liu, H.; Wang, G.; Guo, Z.; Zheng, R. Bimetallic metal-organic frameworks derived Ni-Co-Se@C hierarchical bundle-like nanostructures with high-rate pseudocapacitive lithium ion storage. Energy Storage Mater. 2019, 17, 374–384. [Google Scholar] [CrossRef]
  13. Song, Y.; Liu, T.; Yao, B.; Kou, T.; Feng, D.; Liu, X.; Li, Y. Amorphous mixed-valence vanadium oxide/exfoliated carbon cloth structure shows a record high cycling stability. Small 2017, 13, 1700067. [Google Scholar] [CrossRef]
  14. Fan, H.; Chen, S.; Chen, X.; Tang, Q.; Hu, A.; Luo, W.; Dou, S.X. 3D Selenium sulfide@carbon nanotube array as long-life and high-rate cathode material for lithium storage. Adv. Funct. Mater. 2018, 28, 1805018. [Google Scholar] [CrossRef]
  15. Liu, J.; Zhu, L.; Ding, Q.; Lin, X.; Han, T.; Hu, C. Free-standing nanowires growing on ginkgo biloba as high areal capacity Li-ion battery anode at high and low temperatures. Appl. Surf. Sci. 2023, 620, 156841. [Google Scholar] [CrossRef]
  16. Chen, Y.M.; Yu, L.; Lou, X.W. Hierarchical tubular structures composed of Co3O4 hollow nanoparticles and carbon nanotubes for lithium storage. Angew. Chem. 2016, 55, 5990–5993. [Google Scholar] [CrossRef] [PubMed]
  17. Jiang, Y.; Jiang, Z.; Yang, L.; Cheng, S.; Liu, M. A high-performance anode for lithium ion batteries: Fe3O4 microspheres encapsulated in hollow graphene shells. J. Mater. Chem. 2015, 3, 11847–11856. [Google Scholar] [CrossRef]
  18. Han, W.; Qin, X.; Wu, J.; Li, Q.; Liu, M.; Xia, Y.; Kang, F. Electrosprayed porous Fe3O4/carbon microspheres as anode materials for high-performance lithium-ion batteries. Nano Res. 2018, 11, 892–904. [Google Scholar] [CrossRef]
  19. Wang, J.; Wu, J.; Wu, Z.; Han, L.; Huang, T.; Xin, H.L.; Wang, D. High-rate and long-life lithium-ion battery performance of hierarchically hollow-structured NiCo2O4/CNT nanocomposite. Electrochim. Acta 2017, 244, 8–15. [Google Scholar] [CrossRef]
  20. Xue, Z.; Li, L.; Cao, L.; Zheng, W.; Yang, W.; Yu, X. A simple method to fabricate NiFe2O4/NiO@Fe2O3 core-shelled nanocubes based on prussian blue analogues for lithium ion battery. J. Alloys Compd. 2020, 825, 153966. [Google Scholar] [CrossRef]
  21. Pham, T.V.; Guo, H.P.; Luo, W.; Chou, S.; Wang, J.; Liu, H. Carbon- and binder-free 3D porous perovskite oxide air electrode for rechargeable lithium–oxygen batteries. Small 2016, 12, 3031–3038. [Google Scholar] [CrossRef]
  22. Yin, Z.; Cho, S.; You, D.; Ahn, Y.; Yoo, J.; Kim, Y.S. Copper nanowire/multi-walled carbon nanotube composites as all-nanowire flexible electrode for fast-charging/discharginglithium-ionbattery. Nano Res. 2017, 11, 769–779. [Google Scholar] [CrossRef]
  23. Wang, H.; Liu, C.; Yang, X.; Gu, J.; Niu, M.; Yang, L.; Bai, Z. In situ synthesis of CoFe2O4 nanoparticles embedded in N-doped carbon nanotubes for efficient electrocatalytic oxygen reduction reaction. Int. J. Hydrogen Energy 2022, 47, 6059–6066. [Google Scholar] [CrossRef]
  24. Liu, J.; Li, X.; Huang, J.; Li, J.; Zhou, P.; Liu, J.; Huang, X. Three-dimensional graphene-based nanocomposites for high energy density Li-ion batteries. J. Mater. Chem. A 2017, 5, 5977–5994. [Google Scholar] [CrossRef]
  25. Tabassum, H.; Zou, R.; Mahmood, A.; Liang, Z.; Wang, Q.; Zhang, H.; Guo, S. A universal strategy for hollow metal oxide nanoparticles encapsulated into B/N Co-doped graphitic nanotubes as high-performance lithium-ion battery anodes. Adv. Mater. 2018, 30, 1705441. [Google Scholar] [CrossRef]
  26. Yuan, D.; Ji, C.; Zhuge, X.; Chai, A.; Pan, L.; Li, Y.; Luo, Z.; Luo, K. Organic-inorganic interlayer enabling the stability of PVDF-HFP modified Li metal for lithium-oxygen batteries. Appl. Surf. Sci. 2023, 613, 155863. [Google Scholar] [CrossRef]
  27. Li, H.; Liu, L.; Yang, F. Covalent assembly of 3D graphene/polypyrrole foams for oil spill cleanup. J. Mater. Chem. A 2013, 1, 3446–3453. [Google Scholar] [CrossRef]
  28. Carbonellsanroma, E.; Hieulle, J.; Vilasvarela, M.; Brandimarte, P.; Iraola, M.; Barragan, A.; Pascual, J.I. Doping of graphene nanoribbons via functional group edge modification. ACS Nano 2017, 11, 7355–7361. [Google Scholar] [CrossRef]
  29. Zhao, X.; Li, X.; Zhang, S.; Long, J.; Huang, Y.; Wang, R. A three-dimensional sponge of graphene nanoribbons crosslinked by Fe3O4 nanoparticles for Li+ storage. J. Mater. Chem. A 2017, 5, 23592–23599. [Google Scholar] [CrossRef]
  30. Genorio, B.; Lu, W.; Dimiev, A.M.; Zhu, Y.; Raji, A.O.; Novosel, B. In situ intercalation replacement and selective functionalization of graphene nanoribbon stacks. ACS Nano 2012, 6, 4231–4240. [Google Scholar] [CrossRef]
  31. Li, Y.; Zhu, S.; Yu, Z.; Meng, Q.; Zhang, T.; Liu, Q.; Zhang, D. A facile fabrication of Fe3O4/graphene nanosheets for lithium-ion battery. Sci. Adv. Mater. 2014, 6, 283–289. [Google Scholar] [CrossRef]
  32. Li, L.; Kovalchuk, A.; Fei, H.; Peng, Z.; Li, Y.; Kim, N.D.; Tour, J.M. Enhanced cycling stability of lithium-ion batteries using graphene-wrapped Fe3O4-graphene nanoribbons as anode materials. Adv. Energy Mater. 2015, 5, 1500171. [Google Scholar] [CrossRef]
  33. Agudo, A.L.; Gil, F.J.; Calleja, J.M.; Fernández, V. Raman spectroscopic study of MoO3/γ-Al2O3 and CoO(or NiO)-MoO3/γ-Al2O3 oxide catalysts prepared by different methods. J. Raman Spectrosc. 1981, 11, 454–458. [Google Scholar] [CrossRef]
  34. Li, Y.; Qiu, W.; Qin, F.; Fang, H.; Hadjiev, V.G.; Litvinov, D.; Bao, J. Identification of cobalt oxides with raman scattering and fourier transform infrared spectroscopy. J. Phys. Chem. C 2016, 120, 4511–4516. [Google Scholar] [CrossRef]
  35. Zhang, C.; He, Y.; Wang, Y.; Liang, Y.; Majeed, A.; Yang, Z.; Yao, S.; Shen, X.; Li, T.; Qin, S. CoFe2O4 nanoparticles loaded N-doped carbon nanofibers networks as electrocatalyst for enhancing redox kinetics in Li-S batteries. Appl. Surf. Sci. 2021, 560, 149908. [Google Scholar] [CrossRef]
  36. Wilson, D.; Langell, M.A. XPS analysis of oleylamine/oleic acid capped Fe3O4 nanoparticles as a function of temperature. Appl. Surf. Sci. 2014, 303, 6–13. [Google Scholar] [CrossRef]
  37. Ma, J.; Yang, J.; Jiao, L.; Mao, Y.; Wang, T.; Duan, X.; Zheng, W. NiO nanomaterials: Controlled fabrication, formation mechanism and the application in lithium-ion battery. Crystengcomm. 2011, 14, 453–459. [Google Scholar] [CrossRef]
  38. Chu, Y.; Xiong, S. Mixed transition-metal oxides@carbon core-shell nanostructures derived from heterometallic clusters for enhanced lithium storage. Chin. Chem. Lett. 2022, 33, 486–490. [Google Scholar] [CrossRef]
  39. Ramadevi, P.; Shanmugavadivu, R.; Venkatesan, R.; Mayandi, J.; Sagadevan, S. Photocatalytic dye degradation efficiency and reusability of aluminium substituted nickel ferrite nanostructures for wastewater remediation. Inorg. Chem. Commun. 2023, 150, 110532. [Google Scholar] [CrossRef]
  40. Zhou, J.; Li, J.; Liu, K.; Lan, L.; Song, H.; Chen, X. Free-standing cobalt hydroxide nanoplatelet array formed by growth of preferential-orientation on graphene nanosheets as anode material for lithium-ion batteries. J. Mater. Chem. A 2014, 2, 20706–20713. [Google Scholar] [CrossRef]
  41. Varghese, B.; Reddy, M.V.; Zhu, Y.; Lit, C.S.; Hoong, T.C.; Subba Rao, G.V.; Chowdari, B.V.; Wee, A.T.; Lim, C.T.; Sow, C.H. Fabrication of NiO nanowall electrodes for high performance lithium ion battery. Chem. Mater. 2008, 20, 3360–3367. [Google Scholar] [CrossRef]
  42. Tang, Y.; Zhang, Y.; Li, W.; Ma, B.; Chen, X. Rational material design for ultrafast rechargeable lithium-ion batteries. Chem. Soc. Rev. 2015, 46, 5926–5940. [Google Scholar] [CrossRef] [PubMed]
  43. Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 1999, 59, 1758. [Google Scholar] [CrossRef]
  44. Perdew, J.P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865–3868. [Google Scholar] [CrossRef] [PubMed]
  45. Luo, J.; Liu, J.; Zeng, Z.; Ng, C.F.; Ma, L.; Zhang, H.; Fan, H.J. Three-dimensional graphene foam supported Fe3O4 lithium battery anodes with long cycle life and high rate capability. Nano Lett. 2013, 13, 6136–6143. [Google Scholar] [CrossRef]
  46. Yang, C.; Peng, C.; Chen, P.; Ma, C.; Guo, K.; Cheng, Y. Insights into electrochemical performances of NiFe2O4 for lithium-ion anode materials. J. Alloys Compd. 2022, 896, 163079. [Google Scholar] [CrossRef]
  47. Ortiz, G.F.; Lavela, P.; Knauth, P.; Djenizian, T.; Alcántara, R.; Tirado, J.L. Tin-based composite materials fabricated by anodic oxidation for the negative electrode of Li-ion batteries. J. Electrochem. Soc. 2011, 158, A1094. [Google Scholar] [CrossRef]
  48. Han, D.H.; Wang, J.P.; Luo, H.L. Crystallite size effect on saturation magnetization of fine ferrimagnetic particles. J. Magn. Magn. Mater. 1994, 136, 176–182. [Google Scholar] [CrossRef]
  49. Kresse, G.; Furthmuller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comp. Mater. Sci. 1996, 6, 15–50. [Google Scholar] [CrossRef]
  50. Surendranath, Y.; Kanan, M.W.; Nocera, D.G. Mechanistic studies of the oxygen evolution reaction by a cobalt-phosphate catalyst at neutral pH. J. Am. Chem. Soc. 2010, 132, 16501–16509. [Google Scholar] [CrossRef]
  51. Peterson, A.A.; Abild-Pedersen, F.; Studt, F.; Rossmeisl, J.; Nørskov, J.K. How copper catalyzes the electroreduction of carbon dioxide into hydrocarbon fuels. Energy Environ. Sci. 2010, 3, 1311. [Google Scholar] [CrossRef]
Molecules 28 04069 g001 550
Figure 1. (a) The schematic illustration of the synthesis of CoFe2O4/GNRs composites. (b,c) SEM images of as-prepared CoFe2O4/GNRs and (d) EDS mapping of CoFe2O4/GNRs. (e,f) SEM images of NiFe2O4/GNRs and (g) EDS mapping of NiFe2O4/GNRs.
Figure 1. (a) The schematic illustration of the synthesis of CoFe2O4/GNRs composites. (b,c) SEM images of as-prepared CoFe2O4/GNRs and (d) EDS mapping of CoFe2O4/GNRs. (e,f) SEM images of NiFe2O4/GNRs and (g) EDS mapping of NiFe2O4/GNRs.
Molecules 28 04069 g001
Molecules 28 04069 g002 550
Figure 2. TEM images of as-prepared (a–c) CoFe2O4/GNRs and (d–f) NiFe2O4/GNRs.
Figure 2. TEM images of as-prepared (a–c) CoFe2O4/GNRs and (d–f) NiFe2O4/GNRs.
Molecules 28 04069 g002
Molecules 28 04069 g003 550
Figure 3. (a) ★ Represents the XRD peaks of graphene nanoribbons (GNRs); XRD patterns and Raman spectra of (b) CoFe2O4/GNRs and (c) NiFe2O4/GNRs. (d) Full XPS spectra of as-prepared CoFe2O4/GNRs and NiFe2O4/GNRs. XPS survey spectra of CoFe2O4/GNRs (e) C 1s. (f) Co 2p. (g) Fe 2p. (h) O1s and NiFe2O4/GNRs. (i) C 1s. (j) Ni 2p. (k) Fe 2p. (l) O1s.
Figure 3. (a) ★ Represents the XRD peaks of graphene nanoribbons (GNRs); XRD patterns and Raman spectra of (b) CoFe2O4/GNRs and (c) NiFe2O4/GNRs. (d) Full XPS spectra of as-prepared CoFe2O4/GNRs and NiFe2O4/GNRs. XPS survey spectra of CoFe2O4/GNRs (e) C 1s. (f) Co 2p. (g) Fe 2p. (h) O1s and NiFe2O4/GNRs. (i) C 1s. (j) Ni 2p. (k) Fe 2p. (l) O1s.
Molecules 28 04069 g003
Molecules 28 04069 g004 550
Figure 4. CV curves of (a) CoFe2O4/GNRs, (b) NiFe2O4/GNRs electrodes, (c) CoFe2O4/GNRs, and (d) NiFe2O4/GNRs electrodes at a current density of 0.1 A g−1 for the 1st, 2nd, and 3rd cycles in the voltage range between 3.00 and 0.01 V.
Figure 4. CV curves of (a) CoFe2O4/GNRs, (b) NiFe2O4/GNRs electrodes, (c) CoFe2O4/GNRs, and (d) NiFe2O4/GNRs electrodes at a current density of 0.1 A g−1 for the 1st, 2nd, and 3rd cycles in the voltage range between 3.00 and 0.01 V.
Molecules 28 04069 g004
Molecules 28 04069 g005 550
Figure 5. (a) Rate capability of the CoFe2O4, NiFe2O4, CoFe2O4/GNRs, and NiFe2O4/GNRs electrodes from 0.2 A g−1 to 10 A g−1. (b) Cycling performance of four electrodes at 0.1 A g−1. (c) Cycling performance of four electrodes at 1.0 A g−1. (d) Nyquist plots of four electrodes in the frequency ranging from 0.01 Hz to 10 kHz. (e) The enlarged part of (d). (f) Equivalent circuit model.
Figure 5. (a) Rate capability of the CoFe2O4, NiFe2O4, CoFe2O4/GNRs, and NiFe2O4/GNRs electrodes from 0.2 A g−1 to 10 A g−1. (b) Cycling performance of four electrodes at 0.1 A g−1. (c) Cycling performance of four electrodes at 1.0 A g−1. (d) Nyquist plots of four electrodes in the frequency ranging from 0.01 Hz to 10 kHz. (e) The enlarged part of (d). (f) Equivalent circuit model.
Molecules 28 04069 g005
Molecules 28 04069 g006 550
Figure 6. The calculated band gap of (a) CoFe2O4 and CoFe2O4/GNRs. (b) NiFe2O4 and NiFe2O4/GNRs. (c,d) Simulated adsorption configurations and (e) corresponding adsorption energy.
Figure 6. The calculated band gap of (a) CoFe2O4 and CoFe2O4/GNRs. (b) NiFe2O4 and NiFe2O4/GNRs. (c,d) Simulated adsorption configurations and (e) corresponding adsorption energy.
Molecules 28 04069 g006
Molecules 28 04069 g007 550
Figure 7. Hysteresis curves of (a) CoFe2O4, (b) NiFe2O4, (c) CoFe2O4/GNRs, (d) NiFe2O4/GNRs, and (e) GNRs (insets are the enlarged part of the samples); (f) saturation magnetization of as-prepared samples.
Figure 7. Hysteresis curves of (a) CoFe2O4, (b) NiFe2O4, (c) CoFe2O4/GNRs, (d) NiFe2O4/GNRs, and (e) GNRs (insets are the enlarged part of the samples); (f) saturation magnetization of as-prepared samples.
Molecules 28 04069 g007
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Zhao, X.; He, C.; Bai, Q.; Miao, X.; Cao, C.; Wu, T. Magnetic CoFe2O4 and NiFe2O4 Induced Self-Assembled Graphene Nanoribbon Framework with Excellent Properties for Li-Ion Battery. Molecules 2023, 28, 4069. https://doi.org/10.3390/molecules28104069

AMA Style

Zhao X, He C, Bai Q, Miao X, Cao C, Wu T. Magnetic CoFe2O4 and NiFe2O4 Induced Self-Assembled Graphene Nanoribbon Framework with Excellent Properties for Li-Ion Battery. Molecules. 2023; 28(10):4069. https://doi.org/10.3390/molecules28104069

Chicago/Turabian Style

Zhao, Xiyu, Chunyang He, Qiujv Bai, Xiangwen Miao, Cheng Cao, and Tianli Wu. 2023. "Magnetic CoFe2O4 and NiFe2O4 Induced Self-Assembled Graphene Nanoribbon Framework with Excellent Properties for Li-Ion Battery" Molecules 28, no. 10: 4069. https://doi.org/10.3390/molecules28104069

Article Metrics

Back to TopTop