Fe 2 O 3 /MgFe 2 O 4 Nanosheet on Nickel Foam for High-Performance Asymmetric Supercapacitors

: In this paper, the effects of nickel foam with different thicknesses, as a ﬂuid collector, on the morphology and properties of electrode materials were explored. The Fe 2 O 3 material, which is a common active material for supercapacitor electrodes, was used in combination with MgFe 2 O 4 . This combination resulted in better electrochemical performance and cycle stability for the Fe 2 O 3 material. The synthesis ratio of Fe 2 O 3 /MgFe 2 O 4 materials with the best stability, as reported in a previous article, was selected for this study. The electrode with the best performance was then selected and assembled with activated carbon to form an asymmetric supercapacitor. This supercapacitor exhibited a high speciﬁc capacity of 240 C/g, an energy density of 58.75 Wh/kg, and a power density of 200.4 W/kg at a current density of 1 A/g. These ﬁndings provide valuable references for the selection of different ﬂuid collectors with electrodes.


Introduction
As the most common secondary energy, energy storage technologies for electrical energy have been extensively researched.Among the large number of available energy storage technologies, the most promising are lithium-ion batteries and ultracapacitors.Supercapacitors fill the performance gap between batteries and capacitors by offering energy and power densities between them.They can store more energy than conventional capacitors and have a higher cycle life, a higher multiplier performance, and better stability than batteries.These advantages give supercapacitors a wide range of application scenarios and have attracted widespread interest.In the previous article [1], the Fe 2 O 3 /MgFe 2 O 4 electrode was prepared using the hydrothermal method, which can achieve high specific capacity and good cycle stability.The electrochemical testing and material characterization revealed the synergistic effect of the two materials, and the reason for the improvement of electrode cycle stability was analyzed [2][3][4][5].
The choice of fluid collector in hydrothermal processes significantly impacts electrode performance as collector morphology affects material growth [6][7][8][9].Prior research has examined nickel foam thickness and found that a common thickness of 0.3 mm yields Fe 2 O 3 nanosheets and MgFe 2 O 4 nanoparticles, which is important due to the increased active sites with a thicker foam.Therefore, the material choice and structure of fluid collectors are crucial as they have varying conductivity and oxidation resistance, which in turn influence overall electrode performance.Additionally, material structures and porosities also affect growth quality [10][11][12][13].Wang et al. [14] used Fe 2 O 3 nanotube arrays coated with polypyrrole on carbon cloth, which displayed good cyclic stability with 80% retention after 10,000 cycles.However, they achieved only a modest initial specific capacity of 230 F/cm 2 at 1 A/cm 2 .In contrast, Kumar et al. [15] achieved a higher initial specific capacity of Crystals 2023, 13, 1561 2 of 14 600 F/g with Mn 3 O 4 -Fe 2 O 3 /Fe 3 O 4 @rGO, although only 61% was retained after 1000 cycles.Therefore, different carriers have a great influence on the performance of the electrode.
The previous article explored the optimal stability of the Fe 2 O 3 /MgFe 2 O 4 material synthesis ratio.In this paper, the influence of nickel foam with different thicknesses, as a fluid collector, on the morphology and performance of electrode materials will be investigated using the synthesis ratio explored in the previous article, and the synthetic route of the material remains unchanged [1].Nickel foam with different thicknesses will be used in the market common nickel foam.The electrode with the best performance will then be selected as the cathode.Taking into consideration factors such as potential window and specific capacity, the anode of the assembled supercapacitor will be commercial activated carbon [16,17].

Experimental Section 2.1. Preparation of Fe 2 O 3 /MgFe 2 O 4 Powders
The steps for the synthesis of Fe 2 O 3 /MgFe 2 O 4 electrode materials are the same as in the previous paper, except that different thicknesses of the nickel foam are changed as the carrier.Fe 2 O 3 /MgFe 2 O 4 electrodes with 0.3, 0.5, and 1.0 mm thicknesses of nickel foam were prepared, respectively named FM-2, FM-0.5NF, and FM-1.0NF, and their properties were compared using electrochemical tests [18].Then, the reasons for the performance changes were analyzed through the characterization of various materials.The specific parameters of the electrodes are shown in Table 1.The molar ratio of composites is calculated by the ion concentration of ICP-OES.

Preparation of Anode Electrode
To prepare the anode materials for asymmetric supercapacitors, the fluid collecting nickel foam is first cleaned by ultrasound.Then, the foam is cut to the required shape and size.The cleaning process of the foam nickel involves sequentially using 1 M dilute hydrochloric acid, anhydrous ethanol, and deionized water for 3-5 min.This effectively removes the oxide layer, surface oil stains, and other impurities.After the cleaning, the nickel foam is placed in a vacuum drying oven.Vacuuming is conducted, followed by heating the foam up to 60 • C at a heating rate of 2 • C/min.The heating is maintained at 60 • C for 6 h.The mixture consists of GO, ACET, and PVDF in a ratio of 8:1:1.1-methyl-2-pyrrolidone is then slowly dripped until the powder is fully wet.The evenly coated mixture is applied to both sides of the nickel foam using a brush and is dried for 6 h.Subsequently, the nickel foam is pressed by a tablet press at a pressure of 10 MPa for 5 min.This process ensures that the electrode material is firmly packed into the pores of the nickel foam, resulting in the GO electrode.By comparing the weight of the nickel foam before and after the electrode, the load of active material is determined to be 2-4 mg/cm 2 [19][20][21][22].

Materials Characterisation and Electrochemical Measurements
For the preparation, all samples were analyzed in phase by X-ray diffraction (XRD, Bruker D8 Advance, Wuhan, China).The product morphology was characterized using a scanning electron microscope (SEM, Zeiss Gemini 300, Wuhan, China).Chemical composition and material binding mode samples were characterized using transmission electron microscopy (TEM, Tecnai G2 F30, Wuhan, China).A full spectral characterization of the sample and the analysis of the Fe2+/Fe3+ content of samples before and after cycle testing were characterized using X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, Wuhan, China).
The electrochemical properties of all samples were tested using a three-electrode system with the sample electrode as the working electrode, the platinum wire as the counter electrode, the Hg/HgO as the reference electrode, and the electrolyte using 1 M KOH.Cyclic voltammetry (CV), constant current charge/discharge and cyclic stability tests were carried out on all samples.The GCD test is used to calculate the specific capacity and is based on the following equation [23]: where C (C/g) is the specific capacity, I (A) is the discharge current, ∆t(s) is the total discharge time, and m (mg) is the electrode material loading mass.The material loading masses were found using inductively coupled plasma optical emission spectrometer (ICP-OES) testing and ranged from 1.0 mg to 1.2 mg.

Phase Composition, Microstructure and Surface Chemistry
Figure 1 shows the XRD characterization of FM-2-0.5NF-andFM-2-1.0NF-loadedmaterials compared with FM-2 samples.As can be seen from the figure, the sample loads all have obvious diffraction peaks, which proves that the crystal structure is intact.Through comparison, it can be found that, for FM-0 sample load material [1], these peaks at 2θ angles of 24.125  , and 63.948 • can be observed in the X-ray diffraction pattern, it is completely consistent with the standard card JCPDS NO.89-0597 of Fe2O3 material.For FM-2--0.5NF and FM-2-1.0NFsamples, there are diffraction peaks at 2θ = 30.212material standard card JCPDS NO.73-1960 is consistent with that of the FM-2 sample, and the intensity of these peaks relative to Fe 2 O 3 diffraction peaks is greater than that of the FM-2 sample.From a certain level, it can be shown that the MgFe 2 O 4 content in these samples accounts for a larger proportion [24,25].X-ray photoelectron spectroscopy analysis was performed on FM-2-0.5NF and F 2-1.0NF electrodes.The broad spectrum scanning patterns of samples in the range of 1400 eV are shown in Figure 2. As can be seen from the figure, in the binding energy ran of 0-1400 eV, similar to the FM-2 sample, the spectra of C 1s, O 1s, Fe 2p, Ni 2p, and 1s can also be clearly observed.The diffraction peak intensity of Mg 1s increases with increase of nickel foam thickness, which indicates that the relative content of Mg increa to a certain extent, which is consistent with the change of molar ratio of Fe2O3/MgFe and the peak intensity of XRD obtained by the ICP-OES test.XRD and XPS wide-scan patterns further show that Fe2O3/MgFe2O4 loaded in FM-2-0.5NFand FM-2-1.0NFsamp have been successfully synthesized.Figure 3 shows the SEM characterization of FM-0.5NF and FM-1.0NF.As can be s from the figure, the supporting material morphology prepared by nickel foam with thi nesses of 0.5 and 1.0 mm under the same initial conditions is similar to that obtained nickel foam with a thickness of 0.3 mm, both of which are the composite of nanoshe and nanoparticles.Figure 3a,c show the SEM images of FM-0.5NF and FM-1.0NF samp at 10,000 ratios, where the load material of the FM-2-1.0NFsample grows more dens which is consistent with the conclusion that the load material of the FM-2-1.0NFsam is heavier by ICP-OES.The growth of both materials is relatively uniform, and there is obvious agglomeration of nanosheets.Figure 3b,d shows the SEM characterization 100,000 times of the two samples, in which the spherical substances in both samples significantly increased and the gaps of the Fe2O3 nanosheets are filled in, indicating th under the same initial preparation conditions, the MgFe2O4 material on the growth is s nificantly increased with a larger thickness of nickel foam as the base.Although the thic nickel foam brings more growth sites of materials and increases the load material, the s of Fe2O3 nanosheets does not increase accordingly, and the thickness remains about nm, similar to that of the MF-2 sample.The retention of the Fe2O3 nanosheet in a sm size makes it less affected by volume change, which is also conducive to the retention performance.More spherical MgFe2O4 increases the contact between Fe2O3 nanoshe which may be helpful for electron conduction to some extent, while enhancing the e tron exchange ability of the material.Fm-0.5 NF and FM-2-1.0NFhave better stability th FM-2.According to SEM characterization, compared with FM-2 samples, FM-0.5NF a FM -1.0NF samples can support more MgFe2O4 material, and more material loading d not increase the size of Fe2O3 nanosheets.This makes the contact between Fe2O3/MgFe materials better, thus enhancing the electron exchange and further improving the stabi Figure 3 shows the SEM characterization of FM-0.5NF and FM-1.0NF.As can be seen from the figure, the supporting material morphology prepared by nickel foam with thicknesses of 0.5 and 1.0 mm under the same initial conditions is similar to that obtained by nickel foam with a thickness of 0.3 mm, both of which are the composite of nanosheets and nanoparticles.Figure 3a,c show the SEM images of FM-0.5NF and FM-1.0NF samples at 10,000 ratios, where the load material of the FM-2-1.0NFsample grows more densely, which is consistent with the conclusion that the load material of the FM-2-1.0NFsample is heavier by ICP-OES.The growth of both materials is relatively uniform, and there is no obvious agglomeration of nanosheets.Figure 3b,d shows the SEM characterization of 100,000 times of the two samples, in which the spherical substances in both samples are significantly increased and the gaps of the Fe 2 O 3 nanosheets are filled in, indicating that, under the same initial preparation conditions, the MgFe 2 O 4 material on the growth is significantly increased with a larger thickness of nickel foam as the base.Although the thicker nickel foam brings more growth sites of materials and increases the load material, the size of Fe 2 O 3 nanosheets does not increase accordingly, and the thickness remains about 15 nm, similar to that of the MF-2 sample.The retention of the Fe 2 O 3 nanosheet in a small size makes it less affected by volume change, which is also conducive to the retention of performance.More spherical MgFe 2 O 4 increases the contact between Fe 2 O 3 nanosheets, which may be helpful for electron conduction to some extent, while enhancing the electron exchange ability of the material.Fm-0.5 NF and FM-2-1.0NFhave better stability than FM-2.According to SEM characterization, compared with FM-2 samples, FM-0.5NF and FM -1.0NF samples can support more MgFe 2 O 4 material, and more material loading does not increase the size of Fe 2 O 3 nanosheets.This makes the contact between Fe 2 O 3 /MgFe 2 O 4 materials better, thus enhancing the electron exchange and further improving the stability of the material, which is also the reason for the retention of the electrochemical impedance of the material [26].

Electrochemical Characterizations
Electrochemical tests were conducted on FM-2-0.5NF and FM-2-1.0NF,and the results are shown in Figures 4 and 5. Figure 4a,b show the CV patterns of FM-2-0.5NF and FM-2-1.0NF at a scanning rate of 10-50 mV/s.Both electrodes have obvious REDOX peaks, showing pseudocapacitance.The reduction peak has a large response current, but the current magnitude is different from the peak current of the oxidation peak, showing a quasireversible reaction.The CV patterns of FM-2-0.5NF and FM-2-1.0NFsamples vary with the scanning rate, and the shape and position of the REDOX peaks are still well maintained.For FM-2-0.5NF samples, at a scanning rate of 10 mV/s, the oxidation peak and reduction peak potentials are 0.47 V and 0.36 V, respectively, with a difference of 0.11 V.At a scanning rate of 50 mV/s, they were offset to 0.60 V and 0.33 V, respectively, and the difference increased to 0.27 V.At 10mV/s, the reduction peaks of FM-2-1.0NFsamples were 0.5 V and 0.32 V, respectively, with a difference of 0.18 V; at 50 mV/s, they were 0.55 V and 0.29 V, with a difference of 0.26 V.The results show that both 0.5 mm and 1.0 mm thick nickel foam electrodes have good reversibility, and 1.0 mm nickel foam electrodes have better reversibility.Figure 4c,d show the GCD patterns of FM-2-0.5NF and FM-2-1.0NF.A 1-8 A/g current density was also selected for each constant-current charge-discharge test.As can be seen from the figure, the specific capacity of FM-2-0.5NF and FM-2-1.0NFsamples decreases with the increase of current density.At a 1 A/g current density, the specific capacity is 372.5 C/g and 379.5 C/g, respectively, which is slightly reduced compared with the FM-2 sample.Among them, FM-2-1.0NFsamples have a better magnification performance than FM-2-0.5NFsamples.At a 1-8 A/g current density, the specific capacities are 379, 348.5, 327.5, and 291 C/g, respectively.When the current density reaches a high magnification of 8 A/g, the specific capacitors can still reach 77% of the specific capacitors when the current density is 1 A/g, 67% higher than FM-2-0.5NFand 73% higher than FM-2.Since the electrolyte is used consistently, this increase in magnification performance may be due to load material variations.Among them, the FM-0.5-NFsample has

Electrochemical Characterizations
Electrochemical tests were conducted on FM-2-0.5NF and FM-2-1.0NF,and the results are shown in Figures 4 and 5. Figure 4a,b show the CV patterns of FM-2-0.5NF and FM-2-1.0NF at a scanning rate of 10-50 mV/s.Both electrodes have obvious REDOX peaks, showing pseudocapacitance.The reduction peak has a large response current, but the current magnitude is different from the peak current of the oxidation peak, showing a quasi-reversible reaction.The CV patterns of FM-2-0.5NF and FM-2-1.0NFsamples vary with the scanning rate, and the shape and position of the REDOX peaks are still well maintained.For FM-2-0.5NF samples, at a scanning rate of 10 mV/s, the oxidation peak and reduction peak potentials are 0.47 V and 0.36 V, respectively, with a difference of 0.11 V.At a scanning rate of 50 mV/s, they were offset to 0.60 V and 0.33 V, respectively, and the difference increased to 0.27 V.At 10mV/s, the reduction peaks of FM-2-1.0NFsamples were 0.5 V and 0.32 V, respectively, with a difference of 0.18 V; at 50 mV/s, they were 0.55 V and 0.29 V, with a difference of 0.26 V.The results show that both 0.5 mm and 1.0 mm thick nickel foam electrodes have good reversibility, and 1.0 mm nickel foam electrodes have better reversibility.Figure 4c,d show the GCD patterns of FM-2-0.5NF and FM-2-1.0NF.A 1-8 A/g current density was also selected for each constant-current charge-discharge test.As can be seen from the figure, the specific capacity of FM-2-0.5NF and FM-2-1.0NFsamples decreases with the increase of current density.At a 1 A/g current density, the specific capacity is 372.5 C/g and 379.5 C/g, respectively, which is slightly reduced compared with the FM-2 sample.Among them, FM-2-1.0NFsamples have a better magnification performance than FM-2-0.5NFsamples.At a 1-8 A/g current density, the specific capacities are 379, 348.5, 327.5, and 291 C/g, respectively.When the current density reaches a high magnification of 8 A/g, the specific capacitors can still reach 77% of the specific capacitors when the current density is 1 A/g, 67% higher than FM-2-0.5NFand 73% higher than FM-2.Since the electrolyte is used consistently, this increase in magnification performance may be due to load material variations.Among them, the FM-0.5-NFsample has the lowest specific capacity, which may be due to the fact that 0.5 mm nickel foam does not have advantages for the growth of materials.Further analysis was conducted through subsequent tests and characterization.the lowest specific capacity, which may be due to the fact that 0.5 mm nickel foam do not have advantages for the growth of materials.Further analysis was conducted throu subsequent tests and characterization.After the GCD cycle, the specific capacity of FM-2-0.5NFdeclin to 312.5 C/g, which is 83.9% of the initial specific capacity.In comparison, the speci capacity of the FM-5 sample after the cycle is 344.5 C/g.This confirms that the Fm-2-NF sample exhibits a slower decay rate, indicating an increase in the thickness of the nick foam and a decrease in the initial specific capacity of the hydrothermal electrode.Ho ever, this trade-off leads to improved cycle stability.Furthermore, even though the speci capacity of FM-2-1.0NF is initially slightly lower than that of FM-2, it consistently rema at 375.5 C/g after approximately 400 cycles, which is consistently higher than the FM sample.The improved stability can be attributed to the larger size and pore size of t nickel foam.On the other hand, Figure 5b shows the electrochemical impedance curv before and after the FM-2-0.5NFand FM-2-1.0NFcycles, and Table 2 lists the results of t electrical conductivity test.Prior to the cycle, Fm-2-0.5NF,Fm-2-1.0NFsamples exhibit Faraday impedance of 1.1 Ω and 0.6 Ω, and the exhibit electrical conductivity values 1429 s/cm and 1250 s/cm, respectively, with Fm-2-1.0NFsamples having the lowest init impedance.After 1000 cycles for both electrodes, the Faraday impedance increased to Ω for the FM-2-0.5NFsample and 0.9 Ω for the FM-2-1.0NFsample.These results sugg that the 1.0mm nickel foam electrode has the lowest impedance after circulation, rep senting the minimal degree of material deactivation and, hence, the best stability.
Figure 6 shows the XPS characterization pattern before and after FM-2-0.5NF a FM-2-1.0NFcycles.Figure 6a shows the O 1s spectra of FM-2-0.5NF and FM-2-1.0NFb fore and after the cycle.All curves can also be fitted to three components correspondi to lattice oxygen (OⅠ), chemisorbed oxygen (OⅡ), and physical adsorption oxygen (O which are similar to FM-0 and FM-2.The content of the three oxygen elements is sho in Figure 6b.It can be seen from the figure that the chemisorbed oxygen ratio of FM 1.0NF after cycling is higher than that of FM-2-0.5NF,indicating that the FM-2-1.0NFe trode has better activity.The chemisorption oxygen ratio of FM-2-0.5NF and FM-2-1.0decreased after 1000 cycles, and the initial OⅡ percentage of FM-2-1.0NF was about 61 which remained at 68% after 1000 cycles.However, the chemisorbed oxygen ratio of F 2-0.5NF samples decreased significantly before and after the cyclic charge-discharge t accounting for 33% after the cycle, which was the lowest among the four samples.The fore, it can be inferred that FM-2-1.0NFelectrode materials have more oxygen vacanc at the initial stage and have the best electrochemical activity [27,28].Figure 6c,d shows the spectrum of Fe2p before and after the cycle of the FM-2-1.0sample.It can be seen from the figure that Fe2p has two different characteristic peak 710.8 eV and 724.4 eV, which can correspond to the peaks of Fe 2p3/2 and Fe 2p1/2.T location of the peak value can correspond to that of the FM-2 sample.After partial p fitting, FM-2-0.5NFsamples had a relatively high Fe 2+ /Fe 3+ ratio of 1.19 before the cy After 1000 cycles, Fe 2+ /Fe 3+ decreased to 0.68, indicating a loss of material activity, wh was also consistent with the assumption of oxygen vacancy.Figure 6c,d show the Fe spectra of FM-2-1.0NFsamples before and after cycling.Before the cycle, Fe 2+ /Fe 3+ was and, after the cycle, it remained at 0.94, indicating that FM-2-1.0NFsamples had be activity preservation, which was due to the better reversible reaction during the charg and discharging process [29]. A larger thickness of nickel foam will have more material forming sites.Therefo Figure 5a depicts the cyclic stability pattern of FM-2, Fm-2-0.5 NF, and Fm-2-1.0NF.It can be observed that the overall specific capacity of FM-2-0.5NF and FM-2-1.0NFdecreases during the cycle.After the GCD cycle, the specific capacity of FM-2-0.5NFdeclines to 312.5 C/g, which is 83.9% of the initial specific capacity.In comparison, the specific capacity of the FM-5 sample after the cycle is 344.5 C/g.This confirms that the Fm-2-1.0NF sample exhibits a slower decay rate, indicating an increase in the thickness of the nickel foam and a decrease in the initial specific capacity of the hydrothermal electrode.However, this trade-off leads to improved cycle stability.Furthermore, even though the specific capacity of FM-2-1.0NF is initially slightly lower than that of FM-2, it consistently remains at 375.5 C/g after approximately 400 cycles, which is consistently higher than the FM-2 sample.The improved stability can be attributed to the larger size and pore size of the nickel foam.On the other hand, Figure 5b shows the electrochemical impedance curves before and after the FM-2-0.5NFand FM-2-1.0NFcycles, and Table 2 lists the results of the electrical conductivity test.Prior to the cycle, Fm-2-0.5NF,Fm-2-1.0NFsamples exhibited Faraday impedance of 1.1 Ω and 0.6 Ω, and the exhibit electrical conductivity values of 1429 s/cm and 1250 s/cm, respectively, with Fm-2-1.0NFsamples having the lowest initial impedance.After 1000 cycles for both electrodes, the Faraday impedance increased to 1.7 Ω for the FM-2-0.5NFsample and 0.9 Ω for the FM-2-1.0NFsample.These results suggest that the 1.0 mm nickel foam electrode has the lowest impedance after circulation, representing the minimal degree of material deactivation and, hence, the best stability.Figure 6 shows the XPS characterization pattern before and after FM-2-0.5NF and FM-2-1.0NFcycles.Figure 6a shows the O 1s spectra of FM-2-0.5NF and FM-2-1.0NFbefore and after the cycle.All curves can also be fitted to three components corresponding to lattice oxygen (O I ), chemisorbed oxygen (O II ), and physical adsorption oxygen (O III ), which are similar to FM-0 and FM-2.The content of the three oxygen elements is shown in Figure 6b.It can be seen from the figure that the chemisorbed oxygen ratio of FM-2-1.0NFafter cycling is higher than that of FM-2-0.5NF,indicating that the FM-2-1.0NFelectrode has better activity.The chemisorption oxygen ratio of FM-2-0.5NF and FM-2-1.0NFdecreased after 1000 cycles, and the initial O II percentage of FM-2-1.0NF was about 61%, which remained at 68% after 1000 cycles.However, the chemisorbed oxygen ratio of FM-2-0.5NFsamples decreased significantly before and after the cyclic charge-discharge test, accounting for 33% after the cycle, which was the lowest among the four samples.Therefore, it can be inferred that FM-2-1.0NFelectrode materials have more oxygen vacancies at the initial stage and have the best electrochemical activity [27,28].
Figure 6c,d shows the spectrum of Fe2p before and after the cycle of the FM-2-1.0NFsample.It can be seen from the figure that Fe2p has two different characteristic peaks at 710.8 eV and 724.4 eV, which can correspond to the peaks of Fe 2p 3/2 and Fe 2p 1/2 .The location of the peak value can correspond to that of the FM-2 sample.After partial peak fitting, FM-2-0.5NFsamples had a relatively high Fe 2+ /Fe 3+ ratio of 1.19 before the cycle.After 1000 cycles, Fe 2+ /Fe 3+ decreased to 0.68, indicating a loss of material activity, which was also consistent with the assumption of oxygen vacancy.Figure 6c,d show the Fe 2p spectra of FM-2-1.0NFsamples before and after cycling.Before the cycle, Fe 2+ /Fe 3+ was 1.1 and, after the cycle, it remained at 0.94, indicating that FM-2-1.0NFsamples had better activity preservation, which was due to the better reversible reaction during the charging and discharging process [29].
A larger thickness of nickel foam will have more material forming sites.Therefore, these sites will increase the overall load of the material, but they will not have a significant impact on the nanometer size of the material.The electrode prepared by nickel foam with a 0.5 mm thickness has a similar growth material proportion and mass compared to 0.3 mm, but its conductivity is greatly reduced.On the other hand, the conductivity of the electrode prepared with 1.0 mm thick nickel foam is similar, but the quality and proportion of the material is lower, indicating that 0.5 mm thick nickel foam does not offer any advantage.Although the 1.0 mm thickness of nickel foam exhibits worse conductivity, it provides better contact between the composites, leading to lower electrochemical impedance and better stability.Thus, the initial specific capacity of the FM-2-1.0NFsample is smaller, but the retention rate of the capacitor is better during cycling.Consequently, in this follow-up study, the FM-2-1.0NFelectrode prepared with foam nickel of a 1.0mm thickness was chosen as the research choice [30].
smaller, but the retention rate of the capacitor is better during cycling.Consequently, in this follow-up study, the FM-2-1.0NFelectrode prepared with foam nickel of a 1.0mm thickness was chosen as the research choice [30].The GO electrode was tested.The cyclic voltammetry test pattern is shown in Figure 7a.As can be seen from the figure, at a low scanning rate, the CV pattern is close to a rectangle, showing double electric layer capacitance dominated by physical adsorption.The shape of the rectangle is irregular, indicating the existence of a REDOX reaction, which may be attributed to the functional groups on the GO surface.At the scanning rate of 10-30 mV/s, the shape of the CV pattern remains basically unchanged, showing good magnification performance.When the scanning rate reaches 50 mV/s, part of the shape changes due to the great influence of the functional group pseudo-capacitance, but the shape is very symmetrical, indicating good reversibility.Figure 7b shows the comparison of CV patterns of the GO anode and the Fe2O3/MgFe2O4 electrode at a scanning rate of 10 mV/s.It can be found that the reduction peak of the GO electrode as an anode is higher, The GO electrode was tested.The cyclic voltammetry test pattern is shown in Figure 7a.As can be seen from the figure, at a low scanning rate, the CV pattern is close to a rectangle, showing double electric layer capacitance dominated by physical adsorption.The shape of the rectangle is irregular, indicating the existence of a REDOX reaction, which may be attributed to the functional groups on the GO surface.At the scanning rate of 10-30 mV/s, the shape of the CV pattern remains basically unchanged, showing good magnification performance.When the scanning rate reaches 50 mV/s, part of the shape changes due to the great influence of the functional group pseudo-capacitance, but the shape is very symmetrical, indicating good reversibility.Figure 7b shows the comparison of CV patterns of the GO anode and the Fe 2 O 3 /MgFe 2 O 4 electrode at a scanning rate of 10 mV/s.It can be found that the reduction peak of the GO electrode as an anode is higher, which is slightly lower than that of the cathode, but can be compensated by the increase of load mass.which is slightly lower than that of the cathode, but can be compensated by the increa of load mass.The electrochemical test shows that graphene oxide, as an anode, has a good doub layer performance at −0.65-0 V potential and less pseudo capacitance performance.In t 1 A/g GCD test, it can show a high specific capacity of 169.6 C/g, and the GO electrode h good cyclic stability.After 3000 cycles, 90% of the initial specific capacity can be ma tained.The electrode and Fe2O3/MgFe2O4 cathode can be adapted for the assembly of pacitor batteries.
The potential size of the whole battery is determined by the potential window of t anode and the cathode and the degree of adaptation of the poles.In this whole batte because the anode uses the graphene oxide electrode, it has a large potential window.T cathode Fe2O3/MgFe2O4 electrode potential window is 0-0.65 V.In order to adapt the ca ode potential, the anode potential window is first selected as −0.65-0V. Therefore, t potential window of the whole battery is tested from 0-1.3 V, and the potential window successively increased, and the appropriate working potential is selected based on speci capacity, charging, and discharging efficiency and other factors.Figure 7c shows the GCD curve of the GO anode at −0.65-0 V.The curve is basically straight, with only a slight stagnation platform, showing obvious double-layer characteristics.The charge and discharge curve has a certain curvature, which comes from the pseudo capacitance of functional groups.At a high scanning rate, the Faraday response is delayed due to fast scanning, which leads to rapid potential change in the charge-discharge curve.At a current density of 1, 2, 4, and 8 A/g, the specific capacity of the electrode is 169.6, 160.5, 140.4,and 107.25 C/g respectively, which has a good performance.Figure 7d shows the cycle stability pattern of the GO electrode.The electrode increases slightly from 141.7 C/g to 148.85 C/g at 0-500 cycles, due to the exposure of more active sites during the cycle.After 3000 cycles, the electrode specific capacity drops to 127.4 C/g, which is 90% of the initial specific capacity.GO electrodes show good cyclic stability.
The electrochemical test shows that graphene oxide, as an anode, has a good double layer performance at −0.65-0 V potential and less pseudo capacitance performance.In the 1 A/g GCD test, it can show a high specific capacity of 169.6 C/g, and the GO electrode has good cyclic stability.After 3000 cycles, 90% of the initial specific capacity can be maintained.The electrode and Fe 2 O 3 /MgFe 2 O 4 cathode can be adapted for the assembly of capacitor batteries.
The potential size of the whole battery is determined by the potential window of the anode and the cathode and the degree of adaptation of the poles.In this whole battery, because the anode uses the graphene oxide electrode, it has a large potential window.The cathode Fe 2 O 3 /MgFe 2 O 4 electrode potential window is 0-0.65 V.In order to adapt the cathode potential, the anode potential window is first selected as −0.65-0V. Therefore, the potential window of the whole battery is tested from 0-1.3 V, and the potential window is successively increased, and the appropriate working potential is selected based on specific capacity, charging, and discharging efficiency and other factors.
Figure 7 shows CV patterns and GCD patterns of different potentials of the whole battery at a scanning rate of 10 mV/s. Figure 8a shows the CV patterns of the whole battery with the maximum potential of 1.3-1.7 V.It can be seen from the figure that all CV patterns have obvious REDOX peaks with similar peak current heights, showing good reversibility.
With the increase of the potential window, the response current also increased gradually, Crystals 2023, 13, 1561 10 of 14 and the CV pattern shifted to the right and maintained a good shape.In the pattern of the highest potential 1.3-1.7 V, the peak current density of the reduction peak is 5.55, 5.56, 6.15, 6.24, and 6.52 A/g, respectively.It can be seen that the circuit density of the reduction peak increases the most when the potential window reaches 0-1.5 V, indicating that the material activity increases greatly in this potential window.When the maximum potential reaches 1.7 V, it can be seen that the CV pattern has a large tail, which is due to the severe polarization caused by excessive potential.This polarization will cause electrolytic water reaction and damage to the electrode, so the maximum potential is limited below 1.7 V.
Figure 7 shows CV patterns and GCD patterns of different potentials of the who battery at a scanning rate of 10 mV/s. Figure 8a shows the CV patterns of the whole batte with the maximum potential of 1.3-1.7 V.It can be seen from the figure that all CV patter have obvious REDOX peaks with similar peak current heights, showing good reversib ity.With the increase of the potential window, the response current also increased grad ally, and the CV pattern shifted to the right and maintained a good shape.In the patte of the highest potential 1.3-1.7 V, the peak current density of the reduction peak is 5. 5.56, 6.15, 6.24, and 6.52 A/g, respectively.It can be seen that the circuit density of t reduction peak increases the most when the potential window reaches 0-1.5 V, indicati that the material activity increases greatly in this potential window.When the maximu potential reaches 1.7 V, it can be seen that the CV pattern has a large tail, which is due the severe polarization caused by excessive potential.This polarization will cause elect lytic water reaction and damage to the electrode, so the maximum potential is limit below 1.7 V. Figure 8b shows the GCD at a 1 A/g current density in different potential window It can be seen from the CV pattern that the maximum potential is limited to 1.7 V, so t maximum potential from 1.3 V to 1.6 V is selected.As can be seen from the figure, t charge-discharge capacitance increases with the increase of the potential window.In t 0-1.3 V potential window, the material exhibits low activity, with a specific capacity 63.7 C/g.When the potential window expanded to 0-1.4 V, an obvious plateau of patte stagnation was observed, indicating the occurrence of the Faraday reaction.The chargi specific capacity is increased to 233.8 C/g, while the discharge specific capacity reach 219.8 C/g, and the charging and discharging efficiency is 94%.When the potential windo is 0-1.5 V, the charge-discharge capacitance is further increased, the charge-dischar specific capacity is 297 C/g, the discharge specific capacity is 241.5 C/g, and the charg discharge efficiency drops slightly to 91%.When the potential window reaches 0-1.6 V can be found that the charge-discharge pattern has a serious stagnant platform.The cha ing specific capacity reaches 606.4 C/g, but the discharge specific capacity is still only 2 C/g, and the charge-discharge efficiency is only 49%.Excessive potential leads to difficu in charging the electrode after reaching a certain potential, resulting in severe polarizati of the electrode, and an irreversible Faraday reaction, releasing the same amount of el tricity as the charged amount.Such high potential can cause serious deactivation of el trode material, damage of material morphology, and a decrease of electrode performan Therefore, in order to take into account the specific capacity, charge-discharge efficien and electrode stability of the electrode, a potential window of 0-1.5 V was selected in t study.Figure 8b shows the GCD at a 1 A/g current density in different potential windows.It can be seen from the CV pattern that the maximum potential is limited to 1.7 V, so the maximum potential from 1.3 V to 1.6 V is selected.As can be seen from the figure, the charge-discharge capacitance increases with the increase of the potential window.In the 0-1.3 V potential window, the material exhibits low activity, with a specific capacity of 63.7 C/g.When the potential window expanded to 0-1.4 V, an obvious plateau of pattern stagnation was observed, indicating the occurrence of the Faraday reaction.The charging specific capacity is increased to 233.8 C/g, while the discharge specific capacity reaches 219.8 C/g, and the charging and discharging efficiency is 94%.When the potential window is 0-1.5 V, the charge-discharge capacitance is further increased, the chargedischarge specific capacity is 297 C/g, the discharge specific capacity is 241.5 C/g, and the charge-discharge efficiency drops slightly to 91%.When the potential window reaches 0-1.6 V, it can be found that the charge-discharge pattern has a serious stagnant platform.The charging specific capacity reaches 606.4 C/g, but the discharge specific capacity is still only 296 C/g, and the charge-discharge efficiency is only 49%.Excessive potential leads to difficulty in charging the electrode after reaching a certain potential, resulting in severe polarization of the electrode, and an irreversible Faraday reaction, releasing the same amount of electricity as the charged amount.Such high potential can cause serious deactivation of electrode material, damage of material morphology, and a decrease of electrode performance.Therefore, in order to take into account the specific capacity, charge-discharge efficiency, and electrode stability of the electrode, a potential window of 0-1.5 V was selected in this study.
Figure 9c shows that the supercapacitor exhibits the highest energy density, measuring 58.75 Wh/kg, at a current density of 1 A/g.Additionally, the power density is recorded at 200.4 W/kg.As the current density increases, it results in a reduction in charging and discharging time, leading to a substantial increase in power density but a decrease in energy density.The energy density-power density curve presented in the figure indicates a slight downward trend, illustrating the overall magnification performance of supercapacitors.
Figure 9c shows that the supercapacitor exhibits the highest energy density, mea ing 58.75 Wh/kg, at a current density of 1 A/g.Additionally, the power density is recor at 200.4 W/kg.As the current density increases, it results in a reduction in charging discharging time, leading to a substantial increase in power density but a decrease in ergy density.The energy density-power density curve presented in the figure indicat slight downward trend, illustrating the overall magnification performance of superca itors.It can be observed from Figure 9c that the supercapacitor exhibits the highest ene density of 58.75 Wh/kg at a current density of 1 A/g, along with a power density of 2 W/kg.As the current density increases, the charging and discharging time decreases, l ing to a significant increase in power density but a decrease in energy density.The ene density-power density curve in the figure demonstrates a slight downward trend, refl ing the overall performance characteristics of supercapacitors.
The cycle stability pattern of the whole battery for 3000 cycles is shown in Figure It can be observed that the supercapacitor demonstrates good cycle stability.The spe capacity is maintained at 222 C/g, which is 92% of the initial specific capacity, after 1 cycles.After 2000 cycles, the specific capacity decreases to 216 C/g, accounting for 90% the initial specific capacity.Moreover, during the period from 2000 to 3000 cycles, the percapacitors experience a faster decay in specific capacity.The specific capacity after 3 cycles is 198 C/g, which corresponds to 83% of the initial specific capacity.Comparativ the cycle stability of the whole battery of the supercapacitor is better than that of the c ode.This is attributed to two factors.Firstly, the high stability of the anode contribute an improvement in the overall battery stability.Secondly, the presence of errors in adaptation between the anode and cathode limits the utilization of the cathode mater activity, thereby enhancing the electrode's lifespan.Figure 10b shows the CV cu changes after different cycles.It can be seen from the figure that the electrode has It can be observed from Figure 9c that the supercapacitor exhibits the highest energy density of 58.75 Wh/kg at a current density of 1 A/g, along with a power density of 200.4 W/kg.As the current density increases, the charging and discharging time decreases, leading to a significant increase in power density but a decrease in energy density.The energy density-power density curve in the figure demonstrates a slight downward trend, reflecting the overall performance characteristics of supercapacitors.
The cycle stability pattern of the whole battery for 3000 cycles is shown in Figure 10a.It can be observed that the supercapacitor demonstrates good cycle stability.The specific capacity is maintained at 222 C/g, which is 92% of the initial specific capacity, after 1000 cycles.After 2000 cycles, the specific capacity decreases to 216 C/g, accounting for 90% of the initial specific capacity.Moreover, during the period from 2000 to 3000 cycles, the supercapacitors experience a faster decay in specific capacity.The specific capacity after 3000 cycles is 198 C/g, which corresponds to 83% of the initial specific capacity.Comparatively, the cycle stability of the whole battery of the supercapacitor is better than that of the cathode.This is attributed to two factors.Firstly, the high stability of the anode contributes to an improvement in the overall battery stability.Secondly, the presence of errors in the adaptation between the anode and cathode limits the utilization of the cathode material's activity, thereby enhancing the electrode's lifespan.Figure 10b shows the CV curve changes after different cycles.It can be seen from the figure that the electrode has the maximum response current density before the cycle starts, indicating that the supercapacitor has the best activity before the cycle.After 1000 cycles, the REDOX peak height of CV patterns decreased slightly, indicating partial deactivation of the material.By comparing with the reduction peak of the pre-cycle pattern, it can be found that the reduction peak of the supercapacitor decreases significantly at the potential range of 1.1-1.4V, indicating that the supercapacitor is first deactivated from this range at the beginning of the cycle.After 2000 cycles, it can be found that the CV pattern does not change much compared with 1000 cycles, indicating that the loss of electrochemical activity is small.This conclusion can correspond to Figure 10a.According to the cycle stability pattern, the specific capacity decreases by only 6 C/g after 1000 cycles.After Crystals 2023, 13, 1561 12 of 14 3000 cycles, compared with CV patterns of 2000 cycles, it can be seen that the reduction peak value decreased significantly in the range of 0.8-1.1 V potential, while there was little change in the range of 1.1-1.4V.This indicates that, in the late cycle, the supercapacitor was seriously deactivated at 0.8-1.1 V potential, while the activity of 1.1-1.4V potential basically no longer declined.The sequence of deactivation may be related to the time of deactivation of the two materials in Fe 2 O 3 /MgFe 2 O 4 , respectively [31,32].
itor has the best activity before the cycle.After 1000 cycles, the REDOX peak height of patterns decreased slightly, indicating partial deactivation of the material.By compa with the reduction peak of the pre-cycle pattern, it can be found that the reduction p of the supercapacitor decreases significantly at the potential range of 1.1-1.4V, indica that the supercapacitor is first deactivated from this range at the beginning of the cy After 2000 cycles, it can be found that the CV pattern does not change much compa with 1000 cycles, indicating that the loss of electrochemical activity is small.This con sion can correspond to Figure 10a.According to the cycle stability pattern, the spe capacity decreases by only 6 C/g after 1000 cycles.After 3000 cycles, compared with patterns of 2000 cycles, it can be seen that the reduction peak value decreased significa in the range of 0.8-1.1 V potential, while there was little change in the range of 1.1-1.This indicates that, in the late cycle, the supercapacitor was seriously deactivated at 1.1 V potential, while the activity of 1.1-1.4V potential basically no longer declined.sequence of deactivation may be related to the time of deactivation of the two materia Fe2O3/MgFe2O4, respectively [31,32].By selecting appropriate cathodes for Fe2O3/MgFe2O4 electrodes and performing formance tests in a two-electrode system, it is found that the whole battery has a h specific capacity of 240 C/g, an energy density of 58.75 Wh/kg, and a power densit 200.4 W/kg at a current density of 1 A/g.The asymmetric supercapacitor compose Fe2O3/MgFe2O4//GO has a good electrochemical performance and can be used as a ch and high-performance energy storage device.

Conclusions
The influence of the fluid collector on the active material and the performance of electrode sheet in an electrode sheet is investigated in this study.The Fe2O3/MgFe2O4 terial mentioned earlier is loaded onto various fluid collectors.Through electrochem testing and material characterization, the impact of the fluid collector is examined, an suitable fluid collector is chosen for electrode preparation.Subsequently, the obtai electrode serves as the cathode, and a suitable GO anode is selected.These compon are then assembled into a hybrid supercapacitor battery.To obtain the parameters of entire battery, appropriate potential window selection and thorough electrochemical ing are conducted.The following specific results are obtained: (1) After selecting the appropriate cathode electrode material, select the appropriate lector for it.Fe2O3/MgFe2O4 electrodes were prepared from nickel foam with diffe thicknesses, and the influence of different fluid concentrations was investigated electrochemical testing and material characterization.It is found that, for electro

Conclusions
The influence of the fluid collector on the active material and the performance of the electrode sheet in an electrode sheet is investigated in this study.The Fe 2 O 3 /MgFe 2 O 4 material mentioned earlier is loaded onto various fluid collectors.Through electrochemical testing and material characterization, the impact of the fluid collector is examined, and a suitable fluid collector is chosen for electrode preparation.Subsequently, the obtained electrode serves as the cathode, and a suitable GO anode is selected.These components are then assembled into a hybrid supercapacitor battery.To obtain the parameters of the entire battery, appropriate potential window selection and thorough electrochemical testing are conducted.The following specific results are obtained: (1) After selecting the appropriate cathode electrode material, select the appropriate collector for it.Fe 2 O 3 /MgFe 2 O 4 electrodes were prepared from nickel foam with different thicknesses, and the influence of different fluid concentrations was investigated by electrochemical testing and material characterization.It is found that, for electrodes, the larger thickness of nickel foam has more material forming sites, so the electrode load increases, but the larger load does not lead to the larger size of Fe 2 O 3 nanosheets.In addition, the content of MgFe 2 O 4 nanoparticles increased with the increase of thickness, indicating that more forming sites were convenient for the growth of MgFe 2 O 4 nanoparticles.The addition of MgFe 2 O 4 nanoparticles leads to better interatrial contact, thus improving electrochemical impedance and increasing the reversibility of the material reaction.Although the larger thickness of the nickel foam leads to poorer conductivity and thus lower initial specific capacity, combined with stability analysis, the larger-thickness nickel foam electrode has a better overall performance.
(2) Fe 2 O 3 /MgFe 2 O 4 electrodes were prepared by an appropriate collecting system as the cathode of the supercapacitor, and an appropriate anode was selected for it.It is found that the potential window of the electrode material is too narrow to be used as an anode.GO was selected as the anode with high performance.The electrode has a high specific capacity of 169.6 C/g and an excellent stability of 90% capacitance retention rate after 3000 cycles.Taking the electrode as the anode, the quality of active material was matched by the performance difference of the anode and cathode, and the whole battery of the supercapacitor was assembled.(3) An electrochemical test was carried out on the assembled full battery of the supercapacitor in the two-electrode system.Firstly, the specific capacity and charge-discharge efficiency of the electrode under different potential windows were selected as 0-1.5 V, and the test showed that the supercapacitor had a high specific capacity of 240 C/g at the current density of 1 A/g, energy density of 58.75 Wh/kg, and power density of 200.4 W/kg.Supercapacitors also have good stability, with an 83% capacitance retention rate for 3000 cycles.The deactivation potential sequence of the supercapacitor was analyzed by the CV curve after the cycle, and the difference of the deactivation process of the cathode composite material was determined.
13,  x FOR PEER REVIEW 5 of 15 of the material, which is also the reason for the retention of the electrochemical impedance of the material[26].

Figure
Figure5adepicts the cyclic stability pattern of FM-2, Fm-2-0.5 NF, and Fm-2-1.0N It can be observed that the overall specific capacity of FM-2-0.5NF and FM-2-1.0NFd creases during the cycle.After the GCD cycle, the specific capacity of FM-2-0.5NFdeclin to 312.5 C/g, which is 83.9% of the initial specific capacity.In comparison, the speci capacity of the FM-5 sample after the cycle is 344.5 C/g.This confirms that the Fm-2-NF sample exhibits a slower decay rate, indicating an increase in the thickness of the nick foam and a decrease in the initial specific capacity of the hydrothermal electrode.Ho ever, this trade-off leads to improved cycle stability.Furthermore, even though the speci capacity of FM-2-1.0NF is initially slightly lower than that of FM-2, it consistently rema at 375.5 C/g after approximately 400 cycles, which is consistently higher than the FM sample.The improved stability can be attributed to the larger size and pore size of t nickel foam.On the other hand, Figure5bshows the electrochemical impedance curv before and after the FM-2-0.5NFand FM-2-1.0NFcycles, and Table2lists the results of t electrical conductivity test.Prior to the cycle, Fm-2-0.5NF,Fm-2-1.0NFsamples exhibit Faraday impedance of 1.1 Ω and 0.6 Ω, and the exhibit electrical conductivity values 1429 s/cm and 1250 s/cm, respectively, with Fm-2-1.0NFsamples having the lowest init impedance.After 1000 cycles for both electrodes, the Faraday impedance increased to Ω for the FM-2-0.5NFsample and 0.9 Ω for the FM-2-1.0NFsample.These results sugg that the 1.0mm nickel foam electrode has the lowest impedance after circulation, rep senting the minimal degree of material deactivation and, hence, the best stability.Figure6shows the XPS characterization pattern before and after FM-2-0.5NF a FM-2-1.0NFcycles.Figure6ashows the O 1s spectra of FM-2-0.5NF and FM-2-1.0NFb fore and after the cycle.All curves can also be fitted to three components correspondi to lattice oxygen (OⅠ), chemisorbed oxygen (OⅡ), and physical adsorption oxygen (O

Figure 6 .
Figure 6.(a) XPS spectrum of O1s (b) contents of O I , O II , and O III before and after cycle (c,d) Fe 2p spectrum of FM-2-0.5NFbefore and after cycle (e,f) Fe 2p spectrum of FM-2-1.0NFbefore and after cycle.
13, x FOR PEER REVIEW 9 of

Figure 7 .
Figure 7. (a) CV curve of GO (b) CV comparison between GO anode and Fe2O3/MgFe2O4 cathode GCD curve of GO (d) cyclic stability pattern of GO.

Figure
Figure7cshows the GCD curve of the GO anode at −0.65-0 V.The curve is basica straight, with only a slight stagnation platform, showing obvious double-layer charact istics.The charge and discharge curve has a certain curvature, which comes from t pseudo capacitance of functional groups.At a high scanning rate, the Faraday response delayed due to fast scanning, which leads to rapid potential change in the charge-d charge curve.At a current density of 1, 2, 4 ,and 8 A/g, the specific capacity of the electro is 169.6, 160.5, 140.4,and 107.25 C/g respectively, which has a good performance.Figu 7d shows the cycle stability pattern of the GO electrode.The electrode increases sligh from 141.7 C/g to 148.85 C/g at 0-500 cycles, due to the exposure of more active sites du ing the cycle.After 3000 cycles, the electrode specific capacity drops to 127.4 C/g, which 90% of the initial specific capacity.GO electrodes show good cyclic stability.The electrochemical test shows that graphene oxide, as an anode, has a good doub layer performance at −0.65-0 V potential and less pseudo capacitance performance.In t 1 A/g GCD test, it can show a high specific capacity of 169.6 C/g, and the GO electrode h good cyclic stability.After 3000 cycles, 90% of the initial specific capacity can be ma tained.The electrode and Fe2O3/MgFe2O4 cathode can be adapted for the assembly of pacitor batteries.The potential size of the whole battery is determined by the potential window of t anode and the cathode and the degree of adaptation of the poles.In this whole batte because the anode uses the graphene oxide electrode, it has a large potential window.T cathode Fe2O3/MgFe2O4 electrode potential window is 0-0.65 V.In order to adapt the ca ode potential, the anode potential window is first selected as −0.65-0V. Therefore, t potential window of the whole battery is tested from 0-1.3 V, and the potential window successively increased, and the appropriate working potential is selected based on speci capacity, charging, and discharging efficiency and other factors.

Figure 7 .
Figure 7. (a) CV curve of GO (b) CV comparison between GO anode and Fe 2 O 3 /MgFe 2 O 4 cathode (c) GCD curve of GO (d) cyclic stability pattern of GO.

Figure 8 .
Figure 8.(a) CV patterns of different potential windows of the whole battery.(b) GCD patterns different potential windows of the whole battery.

Figure 8 .
Figure 8.(a) CV patterns of different potential windows of the whole battery.(b) GCD patterns of different potential windows of the whole battery.

Figure 10 .
Figure 10.(a) Cycle stability curve of the whole battery of the supercapacitor.(b) CV pattern different cycles.

Figure 10 .
Figure 10.(a) Cycle stability curve of the whole battery of the supercapacitor.(b) CV pattern after different cycles.By selecting appropriate cathodes for Fe 2 O 3 /MgFe 2 O 4 electrodes and performing performance tests in a two-electrode system, it is found that the whole battery has a high specific capacity of 240 C/g, an energy density of 58.75 Wh/kg, and a power density of 200.4 W/kg at a current density of 1 A/g.The asymmetric supercapacitor composed of Fe 2 O 3 /MgFe 2 O 4 //GO has a good electrochemical performance and can be used as a cheap and high-performance energy storage device.

Table 1 .
Comparison of nickel foam samples with different thicknesses.

Table 2 .
The conductivity results of the sample.

Table 2 .
The conductivity results of the sample.