Study on Electrochemical Stability and Charge Transfer Efficiency for the Development of High-Performance Supercapacitors Using Iron Oxide (Fe2O3) Nanorods
Vijay Ramrao Khawale | Mayank | Ravi Kumar | P. Satishkumar* | Barun Haldar | B. Deepa | Rajasekaran Saminathan | P. Veeramanikandan | Azhagu Saravana Babu Packirisamy | Mayakannan Selvaraju
© 2024 The authors. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
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A novel electrode material for electrochemical supercapacitors is introduced in this study: hydrothermally produced permeable iron oxide (Fe2O3) nanorods (NRs). The Fe2O3 nanorods exhibit exceptional crystallinity and phase purity, and X-ray diffraction (XRD) studies validated their cubic crystalline structure inside an Ia3 space collective. An examination of the morphology of the Fe2O3 NRs uncovered their nanostructured characteristics, such as a rod-shaped structure with an average dimension of about 30 nm. A record specific capacitance of 489 F/g was attained by conducting electrochemical performance studies using Fe2O3 NRs electrodes for supercapacitors at 10 mVs-1 scan rate. The effective series resistance (ESR) was determined using electrochemical impedance spectroscopy (EIS). It measured 3.26 Ω, indicating a low resistance and efficient charge transport kinetics. Fe2O3 NRs electrodes exhibited exceptional chemical stability, maintaining excellent capacitance even after 500 charge-discharge cycles at a current density of 6 Ag-1. This study presents a scalable method for creating high-performance supercapacitors using Fe2O3 NRs to improve the development and design of upcoming energy storage devices.
charge–discharge cycles, permeable Fe2O3 nanorods, specific capacitance, effective series resistance, electrochemical super capacitors
There has been a mad dash to find new ways to store and convert energy due to the ever-increasing demand for it and growing worries about the sustainability of conventional energy sources. Because renewable power output is not always consistent, energy storage is essential in this context for meeting modern energy demands. In the pursuit of better energy management and usage, a great deal of research and development has gone into two primary forms of energy storage: batteries and supercapacitors [1, 2].
The ever-increasing need for energy is putting a heavy burden on batteries, a well-established technology for energy storage. For instance, there are a number of major drawbacks to lithium-ion batteries that are so pervasive despite their widespread use: a low power density, a short lifespan, safety concerns and a dependence on finite lithium resources. These factors make them inefficient when it comes to storing big amounts of energy [3, 4].
Supercapacitors are a novel and perhaps revolutionary kind of energy storage technology due to its capacity to provide huge power outputs in comparatively short durations of time [5]. There are a lot of advantages to using supercapacitors, such as the fact that they are environmentally friendly, last a long time, work in a wider range of temperatures, and have exceptional power densities. A lot of people are interested in supercapacitors (SCs) since they are a great energy storage option with many great features, including as a long cycle life, low cost, safety, specific capacity, and high-power density. A supercapacitor's versatility stems from its exceptional capacity to swiftly release electrical energy [6-8]. They can be utilized autonomously or in conjunction with batteries to supply extra power as necessary. They are beneficial for applications requiring quick energy discharge and recharge cycles, as they may link high-power demand with inconsistent energy sources. Supercapacitors' energy storage technologies mainly fall into two categories: pseudo-capacitors and electrical double-layer capacitors (EDLC) [9]. The reported capacitance in pseudo-capacitors is due to faradic processes that involve electro-active species within the electrode material. These species could be surface functional groups or transition metal oxides. Because of their role in reversible redox reactions, these species improve electrical energy storage capabilities. The selection of electrode materials is a significant focus of supercapacitor research and development since it defines their capabilities and efficiency [10-12]. As a rule, the electrode materials of supercapacitors include carbon-based materials, conducting polymers, oxides of transition metals, and comparable compounds. Attractive electrode materials for supercapacitors include transition metal oxides due to their widespread availability, low cost and high redox activity [13, 14]. Cobalt oxide $\left(\mathrm{CO}_3 \mathrm{O}_4\right)$, ruthenium dioxide $\left(\mathrm{RuO}_2\right)$, vanadium pentoxide $\left(\mathrm{V}_2 \mathrm{O}_5\right)$, Nickel oxide $(\mathrm{NiO})$, titanium dioxide $\left(\mathrm{TiO}_2\right)$, iron dioxide $\left(\mathrm{Fe}_2 \mathrm{O}_2\right)$ and molybdenum trioxide $\left(\mathrm{MoO}_3\right)$ are all instances of transition metal oxides presented in the literature [15-17]. Because of their exceptional electrochemical properties and redox capacities, they have garnered interest in enhancing the performance of supercapacitors [18, 19].
Iron oxide and similar oxides are among the most promising materials among the various metal oxides available for use as electrodes in supercapacitors. For instance, $\mathrm{Fe}_2 \mathrm{O}_3$ has remarkable physical and chemical stability over a range of electrolytes, is non-toxic, and can be architecturally bent to suit different needs. Because of its durability and lack of environmental impact, $\mathrm{Fe}_2 \mathrm{O}_3$ is a great material for supercapacitor electrodes. Despite being compatible with both acidic and alkaline electrolytes, there is still a lot of untapped potential for improving the capacity and energy storage capacities of electrodes based on $\mathrm{Fe}_2 \mathrm{O}_3$ [20-22].
Chemical advancements, integration with conductive materials having a high surface area and the creation of nanostructures are only a few examples of the many optimization efforts that have been applied to electrodes based on $\mathrm{Fe}_2 \mathrm{O}_3$. By capitalizing on $\mathrm{Fe}_2 \mathrm{O}_3$'s inherent strengths and mitigating its potential weaknesses, these endeavors aim to enhance the material's performance as an electrode substance for supercapacitors [23, 24]. Due to its limited porosity, low ionic conductivity, unstable morphology, and lack of cyclic stability, $\mathrm{Fe}_2 \mathrm{O}_3$ supercapacitor electrodes have not achieved success thus far. An increase in $\mathrm{Fe}_2 \mathrm{O}_3$ due to the development of cyclic stability reduced the efficiency of the supercapacitor devices. In order to make $\mathrm{Fe}_2 \mathrm{O}_3$ a potent material for supercapacitor electrodes, many ways have been devised to overcome these constraints. To get the most out of $\mathrm{Fe}_2 \mathrm{O}_3$ in materials used as supercapacitor electrodes, it's best to increase the particular surface area and change the morphological properties [25-27].
This work focuses on the production of permeable $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods using hydrothermal methods for application in supercapacitors. We plan to do a thorough examination of the electrochemical behavior and efficiency of these permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs to find out if they are good electrode materials for supercapacitors. To contribute to ongoing endeavors to enhance supercapacitor technology and address the growing challenges of contemporary energy storage, we want to illuminate their electrochemical characteristics and capacities.
2.1 Fabrication and descriptions
Iron oxide $\left(\mathrm{Fe}_2 \mathrm{O}_3\right)$ nanorods (NRs) were meticulously synthesized according to a well-designed technique as part of our investigative efforts. The synthesis procedures and ingredients are detailed below:
A solution containing 5 mM iron acetate ($\mathrm{Fe}\left(\mathrm{CH}_3 \mathrm{CO}_2\right)_2$, Sigma-Aldrich) and $2.5 \mathrm{mM}$ $\mathrm{C}_2 \mathrm{H}_2 \mathrm{O}_4$ in 100 ml of deionized water is used in composition of the iron oxide nanorod at work. The solution turned a very brown color first, but its pH was reduced to 10 by adding a 2M NaOH solution. The solution changed color from a light brown to a darker brown due to the pH change. A tightly sealed Teflon beaket was used to transfer the reaction suspension in order to carry out the hydrothermal reaction. The reaction was then carried out at a temperature of 120℃ for a duration of 16 hours. Filtration was used to properly recover the precipitates once the autoclave had cooled to the proper temperature. The obtained precipitates were removed using a three-stage washing technique including ethanol and DI water. Afterwards, the precipitates were left to dry overnight in an oven set at 80℃. Following that, a threehour calcination procedure was performed at 350℃ to remove residual impurities, yielding in creation of dark, delicately powdered material. The $\mathrm{Mn}(\mathrm{CH}_3 \mathrm{CO}_2)_2$ precursor, in its asprepared state, was heated further to produce $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods using a hydrothermal procedure. We have used spectroscopic approaches to detect the as-synthesized forms of both the iron acetate precursor and the final product.
The compositional, optical, vibrational, structural, and morphological features of the produced $\mathrm{Fe}_2 \mathrm{O}_3$ were investigated using a range of characterization techniques. This made it possible to characterize the material in great detail. The crystal structures and phases of the generated composite were revealed through the use of XRD Bruker D8 ADVANCE examination at a $10-80^{\circ}$ diffracting angle with $\mathrm{Cu}-\mathrm{K} \alpha$ radiation (λ=1.54Å). Researchers utilized Raman spectroscopy to find contaminants and flaws in the structure of the permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs. A Hitachi-Japan S-3000H apparatus was utilized for the investigation. Using the $400 \mathrm{~cm}^{-1}$ to $4000 \mathrm{~cm}^{-1}$ range of the Fourier transform infrared spectroscopy (FTIR)-VERTEX 70, we investigated the vibrational characteristics and chemical interactions. It is possible to compress the synthetic material with milled KBr (1wt%) and place it on a pallet in order to prepare it for FTIR tests. Because it could interfere with the procedure if it was still damp, the KBr was dehydrated at 100℃ in an air oven before use.
2.2 Electrochemical analysis
A sequence of examinations was conducted at room temperature to evaluate the electrochemical performance of the produced $\mathrm{Fe}_2 \mathrm{O}_3$ NRs. The experiment employed a threeelectrode cell arrangement and electrochemical analysis. A functional electrode was created by thoroughly mixing finely ground $\mathrm{Fe}_2 \mathrm{O}_3$ NRs, polyvinyl fluoride (PVDF) binder and acetylene black in a precise weight ratio of 85: 10: 05. The ingredients were combined with the N-methyl pyrrolidone (NMP) solvent to create a homogeneous paste. The material was cured in a hot air oven at 80℃ for 12 hours after being utilized to a $1 \times 1 \mathrm{~cm}^2$ nickel foam substrate. The $\mathrm{Fe}_2 \mathrm{O}_3$ NRs composite's working electrodes were constructed using NF substrates. The experiment utilized a platinum wire counter electrode and an aqueous electrolyte solution containing 1 M KOH as the reference and counter electrodes, respectively. The active ingredient was utilized in a milligram form. In order to gain aimproved understanding of the performance characteristics and potential suitability of the generated $\mathrm{Fe}_2 \mathrm{O}_3$ NRs as electrode materials for supercapacitors, we conducted electrochemical performance tests in strict accordance with experimental protocols.
3.1 Classifications and its properties of permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs
The structural properties of the produced permeable $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods (NRs) were thoroughly examined utilizing XRD analysis, which provided valuable information about the material's crystallographic features. The XRD pattern appears to have distinct diffraction peaks at $19.4^{\circ}, 26^{\circ}, 34.8^{\circ}, 39.3^{\circ}$, $46.4^{\circ}, 55.9^{\circ}$, and $66.6^{\circ} 2 \theta$ angles, as shown in Figure 1(a). Peaks at 200, 211, 222, 400, 332, 440, and 622 nm, respectively, represent the crystallographic planes of $\mathrm{Fe}_2 \mathrm{O}_3$ [28-30]. The found peaks clearly show the cubic phase structure of $\mathrm{Fe}_2 \mathrm{O}_3$ with unit cell factors =9.5 Å, which belongs to the space group Ia3.
The FTIR analysis was used to study the chemical make-up, chemical bonding characteristics, and purity of the substance. The $\mathrm{Fe}_2 \mathrm{O}_3$ NRs sample's FTIR spectra, spanning 400 to 4000 $\mathrm{cm}^{-1}$, are displayed in Figure 1(b). Peaks and characteristics can be seen in the infrared spectra obtained by using the Fourier transform. When water molecules are present, a strong signal at about $3450 \mathrm{~cm}^{-1}$ shows the existence of hydroxyl OH groups. Possibility of a peak at $1670 \mathrm{~cm}^{-1}$ provides additional proof of C-C stretching. Alcohol molecules' C-H and O-H bond stretching are associated with two peaks at 1520 and $1392 \mathrm{~cm}^{-1}$ respectively. Two significant infrared peaks at 705 and $612 \mathrm{~cm}^{-1}$ further confirm the occurrence of Mn-O stretching vibrations [31].
Raman spectroscopy was utilized to examine the crystalline characteristics and potential structural alterations of the $\mathrm{Fe}_2 \mathrm{O}_3$ NRs (Figure 1(c)). When $\mathrm{Fe}_2 \mathrm{O}_3$ NRs are synthesized, their Raman-scattering spectra take on distinctive features. A strong Raman band is present at $651 \mathrm{~cm}^{-1}$ while2smaller and weaker bands may be found at $389 \mathrm{~cm}^{-1}$ and $508 \mathrm{~cm}^{-1}$. The Raman band at $668 \mathrm{~cm}^{-1}$ and stretching bridge Mn-O-Mn caused by the Ia3 crystal structure of $\mathrm{Fe}_2 \mathrm{O}_3$. The 2 weak Raman bands at 389 and $508 \mathrm{~cm}^{-1}$ respectively in $\mathrm{Fe}_2 \mathrm{O}_3$ and its companion compounds show the presence of out-of-plane bending modes [32].
Surface area, pore volume, and internal and external specific surfaces are all enhanced when $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods are synthesized. The visible fine lines on the nanorods' surfaces, which represent an imperfect morphology at their corners, are the source of these increases. Because of their distinct structural properties, $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods should work exceptionally well as electrode materials in supercapacitor systems.
Figure 1. As synthesized hollow Fe2O3 nanorods (a) Ramanscattering spectrum (b) XRD pattern (c) FTIR spectrum
The formation of the distinctive structure of permeable $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods during their hydrothermal production procedure relies on a number of chemical reactions. Here is a comprehensive breakdown:
$\mathrm{Fe}\left(\mathrm{CH}_3 \mathrm{COO}\right) .2 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Fe}^{2+}+2 \mathrm{CH}_3 \mathrm{COO}^{-}+2 \mathrm{H}_2 \mathrm{O}$ (1)
$2 \mathrm{Fe}^{2+}+5 \mathrm{OH}^{-} \rightarrow \mathrm{Fe}(\mathrm{OH})_2+2 \mathrm{Fe}(\mathrm{OH})_3$ (2)
$\mathrm{Fe}(\mathrm{OH})_2+2 \mathrm{Fe}(\mathrm{OH})_3 \xrightarrow[3 h]{350^{\circ} \mathrm{C}} \mathrm{Fe}_2 \mathrm{O}_3+4 \mathrm{H}_2 \mathrm{O}$ (3)
To separate iron and acetate ions from iron acetate, a basic medium is utilized. Iron trihydroxide and iron dihydroxide are the by products of a reaction with hydroxide ions. Iron dihydroxide starts to self-assemble, turning into a distinctive rod-like shape, during the hydrothermal process, which entails heating the particles for a long duration at 120℃. After the hydroxide nanostructures are made, the final step is to anneal them at 350℃ for three hours. At the right temperature, iron hydroxides can have their water molecules removed, allowing them to undergo a phase transition and become permeable $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods. The nanorods produced display a distinct structure, verified using various characterization techniques. The generated nanorods possess intriguing features and have the potential to serve as electrochemical supercapacitors.
Figure 2. Binding energies of (a) Fe2O3 NRs' completely perused XPS spectrum, core regions (b) Fe, and (c) O
Our produced nanorods were thoroughly examined for their chemical composition and electronic states using XPS. Figure 2 shows the high-resolution XPS spectra and the findings of the analysis. The XPS survey spectra of the produced permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs are shown in Figure 2(a). The binding energies of Mn2p and O1s are corresponding to two significant peaks, while a smaller peak appears to represent C1s. This peak is probably induced by residual precursors from the synthesis. The high-resolution XPS spectra of the Mn2p region are displayed in Figure 2(b). The Mn 2p3/2 core region binding energies and $\mathrm{Mn} 2 \mathrm{p} 1 / 2$ core region have been determined to be 642 and 654.1 eV, respectively [33]. Since Mn 2p signals are present, it is probable that the produced permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs contain Mn3+ states. The obtained orbit splitting value of 12.1 eV is also consistent with $\mathrm{Fe}_2 \mathrm{O}_3$ principles found in previous studies [34]. These results validate the production of $\mathrm{Fe}_2 \mathrm{O}_3$ and also show that the cubic crystal structure of $\mathrm{Fe}_2 \mathrm{O}_3$ agrees with the XRD data. Fitting the O1s X-ray photoelectron spectroscopy data to the binding energies is shown in Figure 2(c). There are 531.22 eV for lattice oxygen binding energies with metal (O-Fe-O) and 530.05 eV for adsorbed oxygenated species, like hydroxyl (-OH) created from material surface's adsorbed moisture.
This means that the synthetic material is primarily $\mathrm{Fe}_2 \mathrm{O}_3$, devoid of meaningful oxide impurities, according to the XPS results. A wide range of analytical methods have been used to characterize the synthetic permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs. Due to this, we can deduce their compositional and structural characteristics, which validates their promise as a component of energy storage devices, particularly supercapacitors.
Figure 3. (a) The pore size dispersion graphs of the synthetic permeable Fe2O3 NRs and (b) the N2 adsorption-desorption isotherms
As displayed in Figure 3, the surface behavior of synthetic permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs was examined by evaluating the nitrogen adsorption-desorption isotherms. A clear hysteresis loop extending from 0.5 to 0.85 relative pressure is observed in the produced permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs, which is represented by a Type II desorption - adsorption. Permeability is demonstrated by the presence of a Type II desorption - adsorption isotherm. With a predicted BET surface area of $74.6 \mathrm{~m}^2 / \mathrm{g}$, the synthetic permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs should perform admirably. So, it seems the structure allowed water to seep through. Figure 4(b) shows pore widths ranging from 5 to 14 nm, which are indicative of mesopores. Thus, $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods created by synthesis with high permeability can accelerate electrochemical processes.
3.2 Application of supercapacitor of as-received permeable $\mathrm{Fe}_2 \mathrm{O}_3$
Electrochemical experimenting with galvanostatic chargedischarge (GCD) and cyclic voltammetry (CV) was performed on $\mathrm{Fe}_2 \mathrm{O}_3$ NRs to determine their potential as a supercapacitor electrode. The studies offered a comprehensive insight into the electrode's ability to store charge under different operating situations.
By increasing the potential window $(\Delta \mathrm{V})$ from -0.2 to 0.6 V, information for the CV measurements were collected at different scan rates. A precise calculation of the $\mathrm{Fe}_2 \mathrm{O}_3$ electrode's specific capacitance (Csp) was performed utilizing CV datasets and data acquired from previous studies in order to assess the electrochemical performance [35]. The produced electrode's Csp was calculated using this equation.
$C_{s p}=\frac{\int i d v}{s \Delta V \cdot m}$ (4)
Eq. (5) can be used to find the particular capacitance value from GCD:
$C_{s p}=\frac{I \Delta t}{m \cdot \Delta V}$ (5)
Figure 4(a) displays individual capacitance values derived from cyclic voltammetry analysis: $489 \mathrm{~F} / \mathrm{g}$ at a scan rate of 10 $\mathrm{mVs}^{-1}, 437 \mathrm{~F} / \mathrm{g}$ at $40 \mathrm{mVs}^{-1}$, $279 \mathrm{~F} / \mathrm{g}$ at $60 \mathrm{mVs}^{-1}$, and $182 \mathrm{~F} / \mathrm{g}$ at $100 \mathrm{mVs}^{-1}$. The significant variations in redox peaks with higher scan rates proved that redox processes were the main charge-storage mechanism. The remarkable reversibility of the electrode material was demonstrated by the cyclic voltammetry curves' ability to maintain the quasi-rectangular shape even at greater scan speeds. Ion diffusion was uniform on both the inner and outer electrode surfaces at lower scan rates, but predominantly on the outer surface at higher scan rates. Interestingly, the scan rate that produced the highest specific capacitance was the one with the lowest value.
Following the addition of $\mathrm{Fe}_2 \mathrm{O}_3$ NRs, we conducted a more thorough investigation of the electrode's charge-discharge behavior using GCD, an approach that is equally significant for evaluating supercapacitor performance. Visualizing the charge-discharge curves for current densities ranging from 1 to 10 Ag-1 and potentials spanning from 0.0 V to 0.4 V is done in Figure 4(b). At various current densities, these profiles show how complicated the charging and discharging processes are. Research has demonstrated that at different current densities, the potential-time curves behave in an almost symmetrical fashion, suggesting a negligible polarization effect and a high charge-discharge Coulombic effectiveness [36-39]. The specific capacitance values (389, 361, 352, 276, 233, and 131 Fg, respectively) for current densities ranging from 1 to 10 Ag-1 validated the electrode's robust behavior.
Scanning rates and current densities are shown by the relevant fluctuations in individual capacitance values in Figures 4(c) and (d). A lower specific capacitance is observed at higher scan rates owing to kinetic constraints on proton transport from the electrolyte to the electrode surface. Reduced rates of ion adsorption and desorption are the result. The specific capacitance drops down sharply as the discharge current density rises with increasing current values.
Figure 4. Plot for (a) evaluation of Scanning rate and Specific Capacitance, (b) evaluation of Current Density and Specific Capacitance, (c) CV, and (d) GCD
Since the electrolyte and electrode surface do not have adequate time to undertake full Faradaic redox reactions, the higher resistance could be the reason behind this. Faradaic reactions dominate the electrochemical activity because $\mathrm{Fe}_2 \mathrm{O}_3$ NRs in the water-based electrolyte indicate pseudocapacitive behavior. The pseudo capacitance can be caused by $\mathrm{Mn}+3 / \mathrm{Mn}+2$ pair.
The cyclic stability of electrode was assessed by monitoring the charge-discharge potentials for 500 cycles at $6 \mathrm{Ag}^{-1}$, as depicted in Figure 5(a). Surprisingly, the permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs retained an astounding 94% of their initial characteristics, demonstrating their exceptional durability and endurance, even after undergoing such lengthy cycling. A promising indicator of the material's long-term stability, the cycle stability test revealed that the form of the permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs remained unchanged. The fact that the shape of the permeable $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods does not alter once the cycling process is complete indicates that the $\mathrm{Fe}_2 \mathrm{O}_3$ electrode did not experience any discernible structural changes. Despite the changing electrochemical conditions that are intrinsic to cycling, this discovery proves that the structural integrity of the electrode remains strong.
Due in large part to electrochemical impedance spectroscopy (EIS), the complex dynamics of electrochemical reactions became better understood. By employing a 10 mV amplitude signal that ranged from 1 Hz to 100 kHz, EIS was able to assess the ion mobility between the electrolyte and electrode surface. Figure 5(b) illustrates the Nyquist curve before and after 500 sets of galvanostatic charge-discharge and it is shown exactly as it is. At higher frequencies, the Nyquist plot displays the ESR which we were able to measure by finding the intersects of the curve with real impedance axis.
Figure 5. (a) The electrochemical impedance spectrum of $\mathrm{Fe}_2 \mathrm{O}_3$ NRs and (b) the cyclic behaviour of $\mathrm{Fe}_2 \mathrm{O}_3$ Nanorods at 6 A/g
For permeable MnO NRs electrode, it is surprising that the ESR value stayed about the same from 3.22 $\Omega$ prior chargedischarging to 3.45 $\Omega$ subsequently 500 sets. Based on the EIS data, the sample of permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs seemed to have a lower electrolytic ion diffusion resistance and steeper slope in middle and lower frequency sections, suggesting a low sequence resistance ($\mathrm{Rs}=3.2 \Omega$). on pages 28 and 29. The Rs value, which remains constant even after 500 GCD cycles, demonstrates that the electrode treated with $\mathrm{Fe}_2 \mathrm{O}_3$ is exceptionally chemically stable, an important property for long-term supercapacitor applications. The specific capacitance performance is listed in Table 1.
Table 1. The specific capacitor results of the permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs electrode
|
S. No |
Specimen |
Electrolyte |
No. of Cycles (Retention) (%) |
Csp (F/g) |
|
1. |
Fe2O3 |
1 M of KOH |
500 (94) |
489 |
This study showcased the hydrothermal production of $\mathrm{Fe}_2 \mathrm{O}_3$ nanoparticles and provided insights into their structural and electrochemical characteristics. Confirming the crystalline clarity of the synthesized permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs, the materials exhibited a clearly specified cubic phase belonging to the Ia3 space group. Confirming the presence of $\mathrm{Fe}_2 \mathrm{O}_3$ and offering further insight within the material's bonding states, extrapolative X-ray photoelectron spectroscopy (XPS) showed unique binding energies for Fe 2 p and O 1 s. The vibrations of metal oxides and other chemical linkages were used by FTIR to gain a deeper understanding the composition of the materials. By using Raman spectroscopy, we were able to confirm the structural stability of the $\mathrm{Fe}_2 \mathrm{O}_3$ NRs by studying how morphological alterations affected their crystal structure. Electrochemical tests demonstrated the exceptional super capacitive performance of permeable $\mathrm{Fe}_2 \mathrm{O}_3$ NRs. Using a 1 M KOH electrolyte solution and a scan rate of $10 \mathrm{mVs}^{-1}$, the specific capacitance was determined to be 489 F/g in CV investigations and $389 \mathrm{~F} / \mathrm{g}$ in GCD testing. The $\mathrm{Fe}_2 \mathrm{O}_3$ NRs' outstanding ion diffusion capabilities were highlighted by the EIS research, which found a minimal ESR of $3.26 \Omega$. Astonishingly, the $\mathrm{Fe}_2 \mathrm{O}_3$ NRs retained 94% of their capacitor during 500 charge-discharge cycles. Because of its outstanding chemical stability, $\mathrm{Fe}_2 \mathrm{O}_3$ treatments produce outstanding performance from electrodes. Overall, these results indicate that permeable $\mathrm{Fe}_2 \mathrm{O}_3$ nanorods show promise as a material for upcoming technological supercapacitors.
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