Evaluating Zn ferrite (Zn x Fe 3-x O 4 ; 0 ≤ x ≤ 1) for alkaline water oxidation: electrochemical and operando spectro- electrochemical study

Evaluating Zn ferrite (Zn x Fe 3-x O 4 ; 0 ≤ x ≤ 1) for alkaline water oxidation: electrochemical and operando spectro- electrochemical study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Evaluating Zn ferrite (Zn x Fe 3-x O 4 ; 0 ≤ x ≤ 1) for alkaline water oxidation: electrochemical and operando spectro- electrochemical study Amisha Soni, Manisha Malviya, B. Lal, Dhanesh Tiwary This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3970277/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The present research work describes the fabrication of zinc ferrite nanoparticles with varying stoichiometric compositions (ZnxFe3-xO4; x= 0.25, 0.5, 0.75, and 1) and their electrocatalytic performance for the oxygen evolution reaction (OER). Egg white was employed as a precursor material during the thermal decomposition process to produce the catalysts. OER performances of four synthesized catalysts in the alkaline medium (1.0 M KOH) were investigated by physicochemical (XRD, FTIR and SEM) and electrochemical (CV, EIS, Tafel polarization) techniques. Among four Zn ferrite catalysts of different stoichiometry, just Zn0.25Fe2.75O4 exhibited the optimum catalytic activity, with the current density of 1 mA cm-2 at the overpotential of 454 mV, and with Tafel slope of 107 mVdec-1. The Arrhenius plot was applied to determine thermodynamic parameters such as activation energy and electrochemical entropy of reaction, which were found to be 54.22 kJ mol-1 and -74 J K-1 mol-1, respectively. Oxygen evolution reaction alkaline water oxidation electrocatalysts zinc ferrite nanoparticles. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Highlights Solution combustion technique for the synthesis of zinc ferrite utilising egg white as a precursor. Various electrochemical and thermodynamic parameters were measured such as current density, double layer capacitance, Tafel slope, activation energy, order of reaction, and entropy of the reaction by using techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization. Operando spectro-electrochemical study provides the absorption spectra of the species generated during the electrocatalysis. A best fit of Randle’s circuit analysis was observed. 1. Introduction Due to the wide range of use going from basic research to commercial usage, magnetic oxide nanoparticles are now generating a lot of attention. Because of their electronic, optical, electrical, magnetic, and catalytic capabilities, spinel ferrite nanocrystals are recognized as one of the most significant inorganic nanomaterials. The structure of spinel ferrite is AFe 2 O 4 , where A and B represent the tetrahedral and octahedral cation sites, respectively, and O denotes the oxygen anion site [ 1 ]. Metal spinel ferrite nanoparticles have a face-centered-cubic (fcc) compact packing structure and the general molecular formula MFe 2 O 4 ( e.g ., M = Zn, Ni, Co, Mn, or Mg). Zinc ferrite (ZnFe 2 O 4 ) has gained the most attention among the spinel ferrite compounds because of its excellent chemical stability, robust electromagnetic performance, mechanical toughness, low coercivity, and mild saturation magnetization [ 2 – 4 ]. The main emphasis of the associated research and development operations is now put on the various methods for producing zinc ferrite nanocrystals. Numerous production techniques, such as the ball-milling process and sol-gel approaches, have been described to produce spinel zinc ferrite nanocrystals [ 5 ], co-precipitation [ 6 ], the aerogel process [ 1 ], the hydrothermal method [ 7 ], the reverse micelles process [ 8 ], and the micro-emulsion method [ 9 ]. Different precipitation agents, such as metal hydroxide in the co-precipitation approach, surfactant and ammonia in the reverse micelles process, different micro-emulsion methods, and organic matrices in the sol-gel method, have all been utilized to create specified size to form zinc ferrite nanocrystals. The majority of these techniques have produced particles with necessary sizes and shapes, but because of their costly and complex processes, high reaction temperatures, lengthy reaction times, toxic reagents and by-products, and potential environmental harm, they are challenging to use on a large scale. Numerous proteins found in egg white, including globulin, ovomucin, and ovalbumin that have great nutritional value, strong gelling, foaming and emulsifying properties, and are soluble in water and readily amalgamate with metals. The ability of egg white proteins to foam aids in the creation of ferrites nanocrystals [ 10 ]. Egg white has been utilized as a binder combining gel for shaping material, especially bulk and porous ceramics, because of its solubility in water and capacity to combine with metal ions in solution [ 11 ]. The use of egg white streamlines, and the procedure offers a different method as an option for the quick and affordable production of Zn ferrites [ 12 ]. Alternative energy sources are not a novel idea for humans, but in the twenty-first century, energy has emerged as the world's top worry. Fossil fuel reserves are finite, and by the middle of this century, they would be depleted [ 13 ]. The hunt for alternative and clean energy sources has quickened, especially as efforts are made to limit CO 2 emissions to lessen the effects of global warming. As an alternative, methods like photocatalytic water splitting have also been suggested as a potential method for creating pure hydrogen using solar energy [ 14 , 15 ]. This discussion has led to the discovery that producing hydrogen will be an essential part of our future energy systems [ 16 ], because the hydrogen and oxygen generated by water oxidation have no adverse effects on the environment [ 17 ]. It is challenging to produce minimal electrical energy consumption in the electrolytic cell, which is necessary for effective water electrocatalysis [ 18 ]. In order to do this, the right electrocatalysts must be used, and the hunt for materials that can lower overpotential value of both anodic and cathodic reactions has been increased [ 19 ]. Hydrogen energy is produced by the electrochemical water splitting. RuO x and IrO x , two metal oxide-based electrocatalysts used in this approach, exhibit strong OER activity [ 20 ], even if they are less economical. Perovskites as electrocatalysts, also demonstrate the encouraging catalytic activity [ 21 – 23 ]. Therefore, the creation of an accessible, affordable metal-oxide based electrocatalyst is necessary. Considering many electrocatalytic uses of synthetic zinc ferrite-based materials, the present work describes the use of Zn ferrite as an electrocatalyst in water splitting electrocatalysis. This material performs better when compared to other synthetic zinc ferrite-based material classes, other spinels, and perovskite oxide. 2. Experimental 2.1. Materials Egg white, zinc nitrate hexahydrate (Zn(NO 3 ) 2 .6H 2 O) (AR, Sigma Aldrich, 99.9%), ferrous sulphate (FeSO 4 ) (AR, Merck, 99.9%). 2.2. Synthesis of zinc ferrite Zn x Fe 3−x O 4 (x = 0.25, 0.5, 0.75, and 1.0) nano-sized zinc ferrites were produced via auto combustion method utilizing egg white as a precursor [ 24 ]. In 20 mL of double-distilled water, the stoichiometric ratios of pure zinc nitrate hexahydrate (Zn(NO 3 ) 2 ⋅6H 2 O) and ferrous sulphate (FeSO 4 ) as metal precursors were dissolved (Table S1 ). The metal salts solution was then added dropwise into the egg white solution while vigorous stirring. The solution (30 mL) of egg white was agitated at room temperature until the solution turned milky white. At 100 o C, the resulting gel precursors were broken down and evaporated to create the light solid powder. The fluffy powder was thermally decomposed into the required oxide nanoparticles over the course of five hours in an electrical muffle furnace at 550°C (Fig. 1 ). 2.3. Preparation of working electrode An electrode made of glassy carbon served as support for the working electrode catalyst ink. To make the catalyst ink, 1 mg of the prepared catalyst (zinc ferrite nanoparticles) was dissolved in a solution of 20 µL Nafion (5%) and 40 µL ethyl alcohol, and then ultrasonicated for about an hour. The total resulting oxide ink (60 µL) was then dropwise-casted with the smallest droplet each followed by drying at room temperature. Before the drop casting, the GCE surface was cleaned and polished using alumina powder of sizes 1, 0.3, and 0.05 µm, respectively, for about 15 to 20 minutes. The prepared electrodes were dried at room temperature. 2.4. Electrode preparation for spectro-electrochemical study The obtained ink from the aforementioned method is used to prepare the working electrode for the operando spectro-electrochemical study. By immersing the platinum grid in the catalyst ink and then drying it at room temperature, the platinum grid is made ready to be used as a working electrode. 3. Characterizations 3.1. Physicochemical characterization In order to examine the structure of the ZnFe 2 O 4 nanoparticles, diffraction patterns were made from powder crystalline samples at room temperature in the diffraction angle range of 5° to 80° using Shimadzu XRD 6000 diffractometer. FT-IR spectra were recorded in the range of 400–4000 cm –1 using a PerkinElmer model 1650 FT-IR spectrometer. The morphology of oxide powder was further studied by scanning electron microscope using Nova Nano-SEM 450 [FESEM] at different magnifications. 3.2. Electrochemical characterization A three-electrode, single compartment pyrex glass cell with 8 cm 2 area of Pt foil (Aldrich 99.9% pure) as a counter electrode, a working electrode of GC/oxide with a 0.07cm 2 area, and a reference electrode of Hg/HgO/1M KOH, was used for all electrochemical studies. The Luggin capillary salt bridge was prepared using agar-agar and KCl. It connected the cell electrolyte to the reference electrode. All potentials provided in this study apply to the Hg/HgO/1M KOH reference electrode, having standard potential ( E 0 Hg/HgO ) equal to 105.3 mV vs. NHE [ 24 ]. Using CHI-608C (CH instrument, USA), all electrochemical characterizations were performed using the same approaches as described above. These include cyclic voltammetry, impedance measurements, and Tafel polarization investigations [ 25 – 27 ]. According to the following Eq. 1, all potential values measured by the Hg/HgO reference were converted to the reversible hydrogen electrode (RHE): E RHE = E Hg/HgO + 0.0592×pH + E 0 Hg/HgO (1) 3.3. Spectro-electrochemical characterization During spectro-electrochemical studies in a quartz cuvette, the catalyst ink immersed platinum grid served as the working electrode, platinum wire served as the counter electrode, and Hg/HgO in 1M KOH served as the reference electrode. The Luggin capillary salt bridge, which connected the reference electrode to the cell electrolyte, was built using agar-agar and KCl. During cyclic voltammetry, the spectra were captured at a 20 mVs − 1 scan rate closest to the onset potential. The operando spectro-electrochemical studies were carried out on ocean optics, FLAME-T-XR1-ES Assembly, 200 nm to 1025 nm range. 4. Results and discussion 4.1. Structural and morphological analysis The produced zinc substituted ferrite functional groups are visible in the FT-IR spectra in the 400–4000 cm –1 wave number range. Figure 2 shows the recorded FT-IR spectra and displayed the typical absorption peaks at 422 cm − 1 and 579 cm − 1 , which are attributed to M-O stretching vibrations in octahedral and tetrahedral voids, respectively. Another absorption band at 1110 cm − 1 is attributed to a tetrahedral Fe 3+ -O 2− stretching vibration. Water molecules were found on the surface of ZnFe 2 O 4 nanoparticles as shown by the wide band absorption peak at 3590 cm − 1 (bending mode of H 2 O). The stretching vibration of the C = C atom on the surface of the ZnFe 2 O 4 nanoparticles was responsible for the extremely tiny band seen at 1620 cm − 1 . Tetrahedral and octahedral modes of ZnFe 2 O 4 are shown by the prominent signal at 579.16 cm − 1 [ 28 , 29 ]. By using X-ray powdered diffraction patterns of oxides synthesized at 550 o C for 5 hours, the development of the spinel phase was determined. In accordance with JCPDS file No. 89-1009 of ZnFe 2 O 4 , the XRD powder patterns of zinc substituted oxides (Fig. 3 ) reveal the development of crystalline spinel phase with peaks corresponding to (220), (311), (222), (400), (422), (511) and (440) planes. The remaining peaks adhere to the typical pattern of ZnFe 2 O 4 , with the exception of the impure phases of α-Fe 2 O 3 and ZnO, which are present in all calcined samples and naturally exist as hematite and zincite, respectively [ 27 ]. SEM micrographs of zinc ferrite (ZnFe 2 O 4 ) obtained at various magnifications are shown in Fig. 4 . The uneven aggregation of oxide nanoparticles can be seen in micrographs. Zinc was substituted in the Fe 3 O 4 matrix to increase crystallinity, and the result was formation of nanoparticles [ 30 ]. 4.2. Electrochemical analysis Inks of catalysts deposited on glassy carbon (GCE) conductive substrates, i.e. , zinc ferrites, Zn x Fe 3−x O 4 (x = 0.25, 0.5, 0.75, 1) were examined for their electrocatalytic activity. To detect the occurrence of redox reaction on the oxide/electrolyte interface, the cyclic voltammogram of each oxide on a GCE support was recorded in the potential range of 0.9 to 1.6 V vs. RHE at 20 mVs − 1 scan rate in 1M KOH. Typical cyclic voltammograms of GCE/Zn x Fe 3−x O 4 , which show the lack of redox peaks in the chosen potential area, are shown in Fig. 5 . On a Ti support, cyclic voltammograms of Fe 3 O 4 showed a similar appearance [ 31 ]. Linear polarization ( i - E ) curves of GCE/Zn x Fe 3−x O 4 measured at 0.5 mV/s in the range of OER within 1.4 and 1.8 V vs. RHE with scan rate of 0.5 mV/s are shown in Fig. 6 . Again, the highest activity for OER, seen as the highest current density values is observed for GC/Zn 0.25 Fe 2.75 O 4 , and the lowest for GC/ZnFe 2 O 4 electrode. The Tafel polarization curve was used to determine the electrocatalytic activity in terms of log current density (log j ) at overpotential ( η ). The formal overpotential, commonly referred to as the anodic overpotential, was established by the relationship η = E – E O2/OH − [ 32 ], where E and E O2/OH − = 0.303 V vs. Hg/HgO, are the applied potential across the electrocatalyst/1M KOH interface and the theoretical equilibrium Nernst potential vs. Hg/HgO in 1M KOH at 25°C, respectively. The overpotential was further calculated from the following Eq. 2 after converting the potentials to RHE: η = Ε RHE – 1.23 V (2) Tafel polarization curves are shown in Fig. 7 . Among all stoichiometrics of spinel ferrite, just Zn 0.25 Fe 2.75 O 4 coated on GCE showed the best electrocatalytic activity with Tafel slope 107 mVdec − 1 and overpotential ( η ) of 537mV at current density at 3 mAcm − 2 . To normalize the material loading on the substrate, the activity was also calculated in terms of current density per mg (specific current density) [ 33 ]. Apparent current density ( j app ) and specific current density ( j spec ) values, together with the estimated values of overpotential (at denoted current densities) and Tafel slope values, are for four prepared zinc ferrite samples listed in Table 1 . Table 1 Electrode kinetic parameters for OER on GC/Zn x Fe 3−x O 4 (0 ≤ x ≤ 1) electrodes in 1M KOH at 25 ο C Catalyst Overpotential (mV) at 1 mAcm − 2 Current density at E = 893mV (mAcm − 2 ) C dl (µFcm − 2 ) R f ECSA (cm 2 ) Tafel Slope (mVdec − 1 ) j app j true j specific Zn 0.25 Fe 2.75 O 4 480 3.4 0.44 3.4 309.5 7.7 0.539 107 Zn 0.5 Fe 2.5 O 4 590 (0.67mAcm − 2 ) 0.67 0.335 0.67 80 2 0.14 112 Zn 0.75 Fe 2.25 O 4 530 1.3 0.16 1.3 325.5 8.1 0.569 137 ZnFe 2 O 4 596 (0.45mAcm − 2 ) 0.45 0.3 0.45 59.5 1.5 0.104 143 Either apparent current density ( j app ) or true current density ( j true ), normalized by the geometric surface area of the electrode or the oxide roughness factor, could be used to represent the rate of electrochemical oxygen evolution. By conducting cyclic voltammetry experiments in 1M KOH at various scan rates within the potential region of 0.975 to 1.025 V ( vs. RHE) at 25 o C, the surface roughness factor ( R f ) of each oxide electrode was ascertained. According to Fig. 5 , only capacitive currents due to double-layer charging-discharging predominate in this potential region. Representative cyclic voltammograms at varying scan rates and a plot of current density vs. scan rate are given in Fig. 8 (A) and (B), respectively. By assuming the double layer capacitance value of a smooth oxide surface equal to 40 µFcm − 2 , the oxide roughness factors ( R f ) of Zn ferrite samples were determined [ 34 ]. R f values are together with C dl values (equation S3 & S4) and ESCA values (equation S5), also listed in Table 1 . The Tafel slope of Zn 0.25 Fe 2.75 O 4 is lower than for other samples, suggesting high improvement in electrocatalytic activity. Changes in the electrical and magnetic characteristics of the oxide catalyst cause an increase in electrocatalytic activity when metal ions are substituted in the Fe 3 O 4 lattice [ 35 ]. Additionally, Iwakura et al. discovered that metal substitution in the Fe 3 O 4 lattice increased saturation magnetization [ 36 , 37 ]. They also noticed that when Bohr magneton levels rose, so did the electrocatalytic activity for oxygen evolution reaction. To explain the reaction mechanism, the anodic Tafel polarization curves of GC/Zn x Fe 3−x O 4 electrodes were recorded at various KOH concentrations (0.25 M − 1.5 M), maintaining the mediumionic strength constant (µ = 1.5), in order to determine the order of reaction (p) with regard to [OH − ]. When determining the value of reaction order, the slope of the log j vs. log [OH − ] plot (Fig. 9 ) across the oxide film/KOH interface at the lower overpotential region particularly at potentials 1.55 V, 1.60 V, and 1.65 V vs. RHE was measured, and observed to be almost 2. This confirms the 4e − OER mechanism in strongly alkaline medium [ 38 ]. Figure 10 shows Bode plots of Zn 0.25 Fe 2.75 O 4 recorded in the frequency range of 100 kHz to 1 Hz, at the constant potential of 0.95 V vs. RHE. Any contribution from a faradaic process is observed to be minimal at this potential [ 33 ]. The measured impedance spectra of interface was analyzed by fitting appropriate Randles circuit, R(Q(R(C(R(RW)))))(CR). The agreement between measured and simulated data was excellent. The chi-squared value of 10 − 4 speaks for the quality of the model [ 39 ]. The first part of Bode plots at the highest frequencies corresponds to the solution resistance of the electrolyte, R s , and the second part at other frequencies shows mainly capacitive impedance response, as is expected for the electrode at potentials without faradaic reaction(s). In that a case, the impedance due to double layer charging/discharging would dominate in the impedance spectrum. The corresponding phase angles in Fig. 10 , however, are much lower than expected − 90°, which is usually related to not ideal electrode response due to interfacial irregularities such as porosity, roughness, and geometry [ 43 , 44 ], or possible influence of some other impedance. A clear deep in the phase angle response seen at low frequencies suggests a possible contribution of some additional impedance (resistive-capacitive combination due to oxide film perhaps) which parameters could eventually be estimated by curve fitting procedure of a proper model [ 41 ]. [ 41 ][ 41 ][ 41 ]The capacitance value roughly estimated from the impedance magnitude |Z| of 500 Ωcm 2 at 1Hz is 318 µF/cm 2 , what is good agreement with C dl value in Table 1 for Zn 0.25 Fe 2.75 O 4 . Zn ferrite electrodes were tested for the measurement of standard electrochemical activation energies (Δ H el 0≠ ), entropies (Δ S 0≠ ), and enthalpies (Δ H 0≠ ) in order to understand the impact of temperature on OER. With this goal in mind, anodic polarization curves were recorded in 1M KOH at various temperatures ranging from 25 to 55 0 C (Fig. 11 ). For this purpose, Tafel polarization curves were recorded in the potential range of 1.4 V to 1.8 V vs. RHE at a scan rate of 0.5 mV s − 1 at different temperatures. The temperature of the reference electrode was maintained constant during conducting of this experiment (25 0 C). Each curve current density data was recorded for a certain potential (1.60 V and 1.65 V vs. RHE), and an Arrhenius plot of log j vs. 1/T (Fig. 11 (B)) was created. The result of calculating the slopes of straight lines produced in the Arrhenius plots to determine values of Δ H el 0≠ are shown in Table 2 . As anticipated, Zn 0.25 Fe 2.75 O 4 has a lower electrochemical activation energy value than any other synthesized Zn ferrite sample of different stoichiometry. The average value of calculated transfer coefficient (α) using the relation α = 2.303RT/ b F was quite close to one. Using the relations (3) and (4), other thermodynamic parameters, such as standard enthalpy of activation (Δ H 0≠ ), and standard entropy of activation (Δ S 0≠ ) were determined. Δ H el 0≠ = Δ H 0≠ - αFη (3) Δ S 0≠ = 2.3 R [log j + Δ H el 0≠ / 2.3 RT – log (nFω C OH - )] (4) The Tafel slope (in mVdec − 1 ) is calculated from the polarization curve recorded at various temperatures, and the values of R, F, and T are the gas constant, the Faraday constant, and absolute temperature, respectively. The Boltzmann constant (k B ) and Planck's constant (h) are two constants that make up the frequency term ω, respectively. The very negative value of Δ S 0≠ seen in Table 2 , illustrates the adsorption events that precede the electrochemical production of oxygen. Table 2 lists average values of these thermodynamic parameters [ 42 ]. The slope of Arrhenius plot (log j versus 1/T) was used to compute the value of Δ H el 0≠ , and the reaction entropy in each instance is strongly negative, confirming that electrochemical oxygen evolution happens via adsorption of reactive intermediate species. Table S1 Required stoichiometric amounts of metal precursors used for the synthesis of zinc ferrite nanoparticles. Catalysts Zn(NO 3 ) 2 .6H 2 O FeSO 4 No. of moles Amount (g) No. of moles Amount (g) Zn 0.25 Fe 2.75 O 4 0.008 1.655 0.109 16.6748 Zn 0.5 Fe 2.5 O 4 0.017 3.2583 0.098 15.006 Zn 0.75 Fe 2.25 O 4 0.025 4.917 0.088 13.505 ZnFe 2 O 4 0.034 6.556 0.079 12.004 Table 2 Thermodynamic parameters for OER on GC/Zn x Fe 3−x O 4 (0 ≤ x ≤ 1.0) electrodes in 1 M KOH Catalyst Standard electrochemical energy of activation (Δ H el 0≠ ) (kJmol − 1 ) Standard electrochemical entropy of activation (-Δ S el 0≠ ) (JK − 1 mol − 1 ) Transfer coefficient (α) Standard enthalpy of activation (Δ H 0≠ ) (kJmol − 1 ) Zn 0.25 Fe 2.75 O 4 54.22 74.96 0.70 92.36 Zn 0.5 Fe 2.5 O 4 85.98 172.16 0.65 120.24 Zn 0.75 Fe 2.25 O4 73.87 136.12 0.48 98.37 ZnFe 2 O 4 105.28 237.12 0.56 135.3 4.3. Spectro-electrochemical analysis It is interesting to note that UV-vis–NIR spectroscopy experiments conducted under OER circumstances have shown a rise in absorbance with applied voltage at the onset potential in the region of OER. Conway conducted the first investigation onto the impact of oxidized species on OER in the late 1950s. He found that the evolution of oxygen occurred concurrently with the potential decay from OER-relevant potentials to open-circuit potentials, indicating that oxidized states could be reduced to form molecular oxygen [ 43 ]. Oxo species on nearby Zn centers may chemically interact to form molecular oxygen, following a similar process to the OER predicted on Co in phosphate electrolyte [ 44 – 46 ] and CoOOH [ 47 , 48 ]. Operando UV-vis spectroscopy measurements were carried out to investigate the mechanism for OER and explain the activity patterns [ 49 ]. Figure 12 depicts the operando UV-Vis spectroscopy before and during the cyclic voltammetry for the Zn 0.25 Fe 2.75 O 4 electrode performed at 25 0 C in 1M KOH at scan rate of 20 mV s − 1 , respectively. Upon stepping the electrode potential from 1.6 V to 1.8 V vs. RHE in 0.1 V increments, the formation of absorption peaks from 300–440 nm and a small peak from 850–900 nm were observed, and these absorbance peaks broadened and intensified with increase of applied potential. These may correspond to FeOOH species [ 50 ] when O 2 evolution is proceeding on the electrode. 5. Conclusion The characteristics of four synthesized samples of Zn ferrite (Zn x Fe 3−x O 4 ) with different stoichiometry (0 ≤ x ≤ 1.0) were evaluated up to the point of their possible use as electrocatalysts for active oxygen evolution processes in an alkaline medium (1 M KOH). According to the results of the performed experiments, zinc ferrites may be produced inexpensively and easily by auto combustion utilizing egg ovalbumin, resulting in nano-sized oxides that have greater spinel phase crystallinity. Tafel slope is found to be minimum for Zn 0.25 Fe 2.75 O 4 , for which the maximum electrocatalytic activity towards OER in an alkaline medium and nearly 2nd order kinetics is observed for the OER process. Among all four samples with different stoichiometry, Zn 0.25 Fe 2.75 O 4 showed the lowest standard electrochemical energy of activation which supports our findings. Operando spectro-electrochemical study revealed the active sites of OER, i.e ., formation of absorption peaks from 300–440 nm that corresponds to FeOOH species. Further exploration in NIR region is needed to understand the role of redox active sites. The study showed that more than one redox species is forming during the OER which are responsible for electrocatalytic activity of Zn x Fe 3−x O 4 and the absorbance intensity is maximum for x = 0.25 (Zn 0.25 Fe 2.75 O 4 ). Furthermore, these materials may be employed as electrode materials for energy storage devices and other applications. Using OER catalysts, large-scale practical water splitting operations may be carried out, supplying the clean and efficient energy which has been generally required. Declarations Data availability The corresponding author may provide the data used to support the conclusions of this study upon reasonable request. Funding The authors have not disclosed any funding. Authors and affiliations Department of Chemistry, IIT(BHU), Varanasi, U.P., 211005, India Amisha Soni, Manisha Malviya, & Dhanesh Tiwary Department of Chemistry, Institute of Applied Sciences and Humanities, GLA University, Mathura, 281406, India Dr. Basant Lal Contributions AS: investigation, data curation, conceptualization, methodology, writing the original draft, review and editing. MM: formal analysis, validation, data curation, editing, supervision. BL: formal analysis, supervision. DT: formal analysis, supervision. Corresponding author Correspondence to M. Malviya Declaration of competing Interest The authors affirm that they have no known financial or interpersonal conflicts that would have seemed to have an impact on the research presented in this study. Acknowledgements The authors like to express their sincere thanks to Department of material science and engineering, Advance Imaging Center, IIT Kanpur for providing SEM of our samples and CIF, IIT (BHU) for other physicochemical characterizations. References Naseri MG, Saion EB, Hashim M et al (2011) Synthesis and characterization of zinc ferrite nanoparticles by a thermal treatment method. Solid State Commun 151:1031–1035. https://doi.org/10.1016/j.ssc.2011.04.018 Gangopadhyay P, Kesavamoorthy R, Bera S et al (2005) Optical absorption and photoluminescence spectroscopy of the growth of silver nanoparticles. 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Proc Natl Acad Sci U S A 114:13380–13384. https://doi.org/10.1073/PNAS.1711836114 Moysiadou A, Lee S, Hsu, CS HC-J of the A (2020) U (2020) Mechanism of oxygen evolution catalyzed by cobalt oxyhydroxide: cobalt superoxide species as a key intermediate and dioxygen release as a rate-determining step. ACS Publ 142:11901–11914. https://doi.org/10.1021/jacs.0c04867 Wang LP, Van Voorhis T (2011) Direct-coupling O2 bond forming a pathway in cobalt oxide water oxidation catalysts. J Phys Chem Lett 2:2200–2204. https://doi.org/10.1021/JZ201021N Rao RR, Corby S, Bucci A et al (2022) Spectroelectrochemical Analysis of the Water Oxidation Mechanism on Doped Nickel Oxides. J Am Chem Soc 144:7622–7633. https://doi.org/10.1021/JACS.1C08152 . /ASSET/IMAGES/LARGE/JA1C08152_0005.JPEG Mashiko H, Yoshimatsu K, Oshima T, Ohtomo A (2016) Fabrication and Characterization of Semiconductor Photoelectrodes with Orientation-Controlled α-Fe2O3 Thin Films. J Phys Chem C 120:2747–2752. https://doi.org/10.1021/ACS.JPCC.5B10838 Additional Declarations No competing interests reported. Supplementary Files ESIZnferrite.docx Graphicalabstract.png Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3970277","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":273869902,"identity":"01a01f06-e9bc-4461-8943-afffc183dbc4","order_by":0,"name":"Amisha Soni","email":"","orcid":"","institution":"Indian Institute of Technology (BHU)","correspondingAuthor":false,"prefix":"","firstName":"Amisha","middleName":"","lastName":"Soni","suffix":""},{"id":273869903,"identity":"1c4329f8-f174-4fd3-a0d5-1a5718255791","order_by":1,"name":"Manisha Malviya","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIie3QP0vDQBjH8V8IxCXB9ab6CoRHApnE1/IEwSmUQhfBQaFw3dzFN6Gb44WDdqm4BrzBLJk6pIs04OBprFuSjoL3Xe447sP9AVyuP5rybr5H742huF2j/YhPzHsS/JBA4Jf0dDx/zvPm6QyH97PqstyaMSm/rDExnSRZjVlHq3MIs0gK5mpKKogFqOomKiPtSR8ossASnT4oJPYtupu8rClv5DWOLJm05OC9nxQZqUhqkCVoSThwSrEmHclleGIWseCLKr3T4VRw78WyeNPIq9HodVZutqcmvV3OH+v6o5vsCiF2U/sV4EHwlRje4nK5XP+0T7heX2bZ/+xaAAAAAElFTkSuQmCC","orcid":"","institution":"Indian Institute of Technology (BHU)","correspondingAuthor":true,"prefix":"","firstName":"Manisha","middleName":"","lastName":"Malviya","suffix":""},{"id":273869904,"identity":"57e38192-2b8b-489b-8436-d557df412c5b","order_by":2,"name":"B. 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1","display":"","copyAsset":false,"role":"figure","size":216680,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation showing the thermal decomposition process used to create zinc ferrite nanoparticles from egg white\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/bacca4d55826271d55bf050f.png"},{"id":51467550,"identity":"1d4a233d-a2a2-469c-afcd-57925bb23dbc","added_by":"auto","created_at":"2024-02-22 06:47:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":120506,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR spectra for Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3-x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (x = 0.25, 0.5, 0.75 and 1.0) nanoparticles synthesized at 550\u003csup\u003e0\u003c/sup\u003eC: \u003cstrong\u003ea)\u003c/strong\u003e Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003eb)\u003c/strong\u003e Zn\u003csub\u003e0.5\u003c/sub\u003eFe\u003csub\u003e2.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003ec)\u003c/strong\u003e Zn\u003csub\u003e0.75\u003c/sub\u003eFe\u003csub\u003e2.25\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003ed)\u003c/strong\u003e ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/898b9308ef01cc9a80452ec9.png"},{"id":51467560,"identity":"86f67d25-73b0-43a0-857b-c32b4c2e78ac","added_by":"auto","created_at":"2024-02-22 06:47:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":180902,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of zinc ferrites prepared at 550\u003csup\u003e0\u003c/sup\u003eC: \u003cstrong\u003ea)\u003c/strong\u003e Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003eb)\u003c/strong\u003e Zn\u003csub\u003e0.5\u003c/sub\u003eFe\u003csub\u003e2.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003ec)\u003c/strong\u003e Zn\u003csub\u003e0.75\u003c/sub\u003eFe\u003csub\u003e2.25\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003ed)\u003c/strong\u003e ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/04096c83ef49b3a9ce4de358.png"},{"id":51467559,"identity":"5006aa99-0480-405b-81da-4436b67beee7","added_by":"auto","created_at":"2024-02-22 06:47:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":401775,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of zinc ferrite (ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) at different magnifications: A) ´ 50000 and B) ´ 150000\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/72fa90e57dc3b22f2ca0df11.png"},{"id":51467548,"identity":"d4985242-e488-43d8-8e8f-3eb41110075a","added_by":"auto","created_at":"2024-02-22 06:47:10","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":100473,"visible":true,"origin":"","legend":"\u003cp\u003eIR corrected cyclic voltammograms of GC/Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3-x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode at 20 mVs\u003csup\u003e-1\u003c/sup\u003e in 1M KOH at 25\u003csup\u003e0\u003c/sup\u003eC: \u003cstrong\u003ea)\u003c/strong\u003e Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003eb)\u003c/strong\u003e Zn\u003csub\u003e0.5\u003c/sub\u003eFe\u003csub\u003e2.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003ec)\u003c/strong\u003e Zn\u003csub\u003e0.75\u003c/sub\u003eFe\u003csub\u003e2.25\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003ed)\u003c/strong\u003e ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/4a08ef28c1cf24a7031e71d9.png"},{"id":51467555,"identity":"f19ca6ae-a0cc-4953-afb2-65de8e88284d","added_by":"auto","created_at":"2024-02-22 06:47:11","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":60928,"visible":true,"origin":"","legend":"\u003cp\u003eIR corrected linear polarization curves for GC/Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3-x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrodes at 0.5 mV s\u003csup\u003e-1\u003c/sup\u003e in 1M KOH at 25\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/6029d9398e0370785d780990.png"},{"id":51468001,"identity":"d08ad6f0-3a1b-4622-b669-56e8d0c526fe","added_by":"auto","created_at":"2024-02-22 06:55:10","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":95873,"visible":true,"origin":"","legend":"\u003cp\u003eTafel polarization curves of GC/Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3-x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrodes in 1M KOH at 25\u003csup\u003e0\u003c/sup\u003eC: \u003cstrong\u003ea)\u003c/strong\u003e Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003eb)\u003c/strong\u003e Zn\u003csub\u003e0.75\u003c/sub\u003eFe\u003csub\u003e2.25\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003ec)\u003c/strong\u003e Zn\u003csub\u003e0.5\u003c/sub\u003eFe\u003csub\u003e2.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, \u003cstrong\u003ed)\u003c/strong\u003e ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/967018bbbc8164d2723caa0e.png"},{"id":51467561,"identity":"d905cb08-9b08-4a96-be52-5081519cc913","added_by":"auto","created_at":"2024-02-22 06:47:11","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":124503,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA)\u003c/strong\u003e Cyclic voltammograms in non-faradaic region of GC/Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode at different scan rates in 1M KOH at 25\u003csup\u003e0\u003c/sup\u003eC and \u003cstrong\u003eB)\u003c/strong\u003e capacitive current density vs. scan rate plot of GC/Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/10fd2d525242402aab4967a2.png"},{"id":51467552,"identity":"a9e6a661-3e7e-42d1-ae85-8be68c8f6c6b","added_by":"auto","created_at":"2024-02-22 06:47:10","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":79163,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA)\u003c/strong\u003e Tafel polarization curves of Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e at different concentrations of KOH and 25°C; \u003cstrong\u003eB)\u003c/strong\u003e plots of log j vs. log [OH\u003csup\u003e-\u003c/sup\u003e]\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/c53fa205db01930617f365ae.png"},{"id":51467554,"identity":"583e312f-6dc3-4f43-a1cf-d2fbadfcd17c","added_by":"auto","created_at":"2024-02-22 06:47:10","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":82571,"visible":true,"origin":"","legend":"\u003cp\u003eTypical Bode plot: Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in 1M KOH at 0.95V vs. RHE\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/39a76f28d999a8e5576c36b9.png"},{"id":51467562,"identity":"6a3005e5-eaf5-4f4a-9119-6b7d58133624","added_by":"auto","created_at":"2024-02-22 06:47:11","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":96891,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA)\u003c/strong\u003e iR corrected Tafel polarization curves (5 mVs\u003csup\u003e-1\u003c/sup\u003e) of Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e at different temperatures; \u003cstrong\u003eB)\u003c/strong\u003e Arrhenius plots for GC/Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/d7e2dc7eb41313cee357bf40.png"},{"id":51467558,"identity":"976250be-7bcf-490f-8f46-d96c4eb124b5","added_by":"auto","created_at":"2024-02-22 06:47:11","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":152082,"visible":true,"origin":"","legend":"\u003cp\u003eOperando UV-vis spectra during cyclic voltammetry at scan rate of 20 mVs\u003csup\u003e-1\u003c/sup\u003e\u003cem\u003e.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/e78e87ed6a33821799b9a042.png"},{"id":52379633,"identity":"8fc6d1df-4bf7-430b-8e1d-9987819ab3db","added_by":"auto","created_at":"2024-03-10 15:56:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2008960,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/151bd93a-97be-4255-b155-dda91db9abce.pdf"},{"id":51467557,"identity":"d32ccffe-b139-42dd-8aef-1692e4fb0e65","added_by":"auto","created_at":"2024-02-22 06:47:11","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3714399,"visible":true,"origin":"","legend":"","description":"","filename":"ESIZnferrite.docx","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/21b0090ed514dd8e7690af5b.docx"},{"id":51468002,"identity":"a2f4e072-55f9-470e-a7df-619d65348f33","added_by":"auto","created_at":"2024-02-22 06:55:11","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":122919,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.png","url":"https://assets-eu.researchsquare.com/files/rs-3970277/v1/39cbc0c7248d206c026feb59.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Evaluating Zn ferrite (Zn x Fe 3-x O 4 ; 0 ≤ x ≤ 1) for alkaline water oxidation: electrochemical and operando spectro- electrochemical study","fulltext":[{"header":"Highlights","content":"\u003col\u003e\n \u003cli\u003eSolution combustion technique for the synthesis of zinc ferrite utilising egg white as a precursor.\u003c/li\u003e\n \u003cli\u003eVarious electrochemical and thermodynamic parameters were measured such as current density, double layer capacitance, Tafel slope, activation energy, order of reaction, and entropy of the reaction by using techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization.\u003c/li\u003e\n \u003cli\u003e\u003cem\u003eOperando\u003c/em\u003e spectro-electrochemical study provides the absorption spectra of the species generated during the electrocatalysis.\u003c/li\u003e\n \u003cli\u003eA best fit of Randle\u0026rsquo;s circuit analysis was observed.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eDue to the wide range of use going from basic research to commercial usage, magnetic oxide nanoparticles are now generating a lot of attention. Because of their electronic, optical, electrical, magnetic, and catalytic capabilities, spinel ferrite nanocrystals are recognized as one of the most significant inorganic nanomaterials. The structure of spinel ferrite is AFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, where A and B represent the tetrahedral and octahedral cation sites, respectively, and O denotes the oxygen anion site [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Metal spinel ferrite nanoparticles have a face-centered-cubic (fcc) compact packing structure and the general molecular formula MFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (\u003cem\u003ee.g\u003c/em\u003e., M\u0026thinsp;=\u0026thinsp;Zn, Ni, Co, Mn, or Mg). Zinc ferrite (ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) has gained the most attention among the spinel ferrite compounds because of its excellent chemical stability, robust electromagnetic performance, mechanical toughness, low coercivity, and mild saturation magnetization [\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe main emphasis of the associated research and development operations is now put on the various methods for producing zinc ferrite nanocrystals. Numerous production techniques, such as the ball-milling process and sol-gel approaches, have been described to produce spinel zinc ferrite nanocrystals [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], co-precipitation [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], the aerogel process [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], the hydrothermal method [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], the reverse micelles process [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], and the micro-emulsion method [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Different precipitation agents, such as metal hydroxide in the co-precipitation approach, surfactant and ammonia in the reverse micelles process, different micro-emulsion methods, and organic matrices in the sol-gel method, have all been utilized to create specified size to form zinc ferrite nanocrystals. The majority of these techniques have produced particles with necessary sizes and shapes, but because of their costly and complex processes, high reaction temperatures, lengthy reaction times, toxic reagents and by-products, and potential environmental harm, they are challenging to use on a large scale.\u003c/p\u003e \u003cp\u003eNumerous proteins found in egg white, including globulin, ovomucin, and ovalbumin that have great nutritional value, strong gelling, foaming and emulsifying properties, and are soluble in water and readily amalgamate with metals. The ability of egg white proteins to foam aids in the creation of ferrites nanocrystals [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Egg white has been utilized as a binder combining gel for shaping material, especially bulk and porous ceramics, because of its solubility in water and capacity to combine with metal ions in solution [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The use of egg white streamlines, and the procedure offers a different method as an option for the quick and affordable production of Zn ferrites [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlternative energy sources are not a novel idea for humans, but in the twenty-first century, energy has emerged as the world's top worry. Fossil fuel reserves are finite, and by the middle of this century, they would be depleted [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The hunt for alternative and clean energy sources has quickened, especially as efforts are made to limit CO\u003csub\u003e2\u003c/sub\u003e emissions to lessen the effects of global warming. As an alternative, methods like photocatalytic water splitting have also been suggested as a potential method for creating pure hydrogen using solar energy [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. This discussion has led to the discovery that producing hydrogen will be an essential part of our future energy systems [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], because the hydrogen and oxygen generated by water oxidation have no adverse effects on the environment [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. It is challenging to produce minimal electrical energy consumption in the electrolytic cell, which is necessary for effective water electrocatalysis [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In order to do this, the right electrocatalysts must be used, and the hunt for materials that can lower overpotential value of both anodic and cathodic reactions has been increased [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHydrogen energy is produced by the electrochemical water splitting. RuO\u003csub\u003ex\u003c/sub\u003e and IrO\u003csub\u003ex\u003c/sub\u003e, two metal oxide-based electrocatalysts used in this approach, exhibit strong OER activity [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], even if they are less economical. Perovskites as electrocatalysts, also demonstrate the encouraging catalytic activity [\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Therefore, the creation of an accessible, affordable metal-oxide based electrocatalyst is necessary.\u003c/p\u003e \u003cp\u003eConsidering many electrocatalytic uses of synthetic zinc ferrite-based materials, the present work describes the use of Zn ferrite as an electrocatalyst in water splitting electrocatalysis. This material performs better when compared to other synthetic zinc ferrite-based material classes, other spinels, and perovskite oxide.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eEgg white, zinc nitrate hexahydrate (Zn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO) (AR, Sigma Aldrich, 99.9%), ferrous sulphate (FeSO\u003csub\u003e4\u003c/sub\u003e) (AR, Merck, 99.9%).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Synthesis of zinc ferrite\u003c/h2\u003e \u003cp\u003eZn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (x\u0026thinsp;=\u0026thinsp;0.25, 0.5, 0.75, and 1.0) nano-sized zinc ferrites were produced via auto combustion method utilizing egg white as a precursor [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In 20 mL of double-distilled water, the stoichiometric ratios of pure zinc nitrate hexahydrate (Zn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO) and ferrous sulphate (FeSO\u003csub\u003e4\u003c/sub\u003e) as metal precursors were dissolved (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe metal salts solution was then added dropwise into the egg white solution while vigorous stirring. The solution (30 mL) of egg white was agitated at room temperature until the solution turned milky white. At 100\u003csup\u003eo\u003c/sup\u003eC, the resulting gel precursors were broken down and evaporated to create the light solid powder. The fluffy powder was thermally decomposed into the required oxide nanoparticles over the course of five hours in an electrical muffle furnace at 550\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Preparation of working electrode\u003c/h2\u003e \u003cp\u003eAn electrode made of glassy carbon served as support for the working electrode catalyst ink. To make the catalyst ink, 1 mg of the prepared catalyst (zinc ferrite nanoparticles) was dissolved in a solution of 20 \u0026micro;L Nafion (5%) and 40 \u0026micro;L ethyl alcohol, and then ultrasonicated for about an hour. The total resulting oxide ink (60 \u0026micro;L) was then dropwise-casted with the smallest droplet each followed by drying at room temperature. Before the drop casting, the GCE surface was cleaned and polished using alumina powder of sizes 1, 0.3, and 0.05 \u0026micro;m, respectively, for about 15 to 20 minutes. The prepared electrodes were dried at room temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Electrode preparation for spectro-electrochemical study\u003c/h2\u003e \u003cp\u003eThe obtained ink from the aforementioned method is used to prepare the working electrode for the \u003cem\u003eoperando\u003c/em\u003e spectro-electrochemical study. By immersing the platinum grid in the catalyst ink and then drying it at room temperature, the platinum grid is made ready to be used as a working electrode.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Characterizations","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Physicochemical characterization\u003c/h2\u003e \u003cp\u003eIn order to examine the structure of the ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles, diffraction patterns were made from powder crystalline samples at room temperature in the diffraction angle range of 5\u0026deg; to 80\u0026deg; using Shimadzu XRD 6000 diffractometer. FT-IR spectra were recorded in the range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e using a PerkinElmer model 1650 FT-IR spectrometer. The morphology of oxide powder was further studied by scanning electron microscope using Nova Nano-SEM 450 [FESEM] at different magnifications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Electrochemical characterization\u003c/h2\u003e \u003cp\u003eA three-electrode, single compartment pyrex glass cell with 8 cm\u003csup\u003e2\u003c/sup\u003e area of Pt foil (Aldrich 99.9% pure) as a counter electrode, a working electrode of GC/oxide with a 0.07cm\u003csup\u003e2\u003c/sup\u003e area, and a reference electrode of Hg/HgO/1M KOH, was used for all electrochemical studies. The Luggin capillary salt bridge was prepared using agar-agar and KCl. It connected the cell electrolyte to the reference electrode. All potentials provided in this study apply to the Hg/HgO/1M KOH reference electrode, having standard potential (\u003cem\u003eE\u003c/em\u003e\u003csup\u003e0\u003c/sup\u003e\u003csub\u003eHg/HgO\u003c/sub\u003e) equal to 105.3 mV \u003cem\u003evs.\u003c/em\u003e NHE [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Using CHI-608C (CH instrument, USA), all electrochemical characterizations were performed using the same approaches as described above. These include cyclic voltammetry, impedance measurements, and Tafel polarization investigations [\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAccording to the following Eq.\u0026nbsp;1, all potential values measured by the Hg/HgO reference were converted to the reversible hydrogen electrode (RHE):\u003c/p\u003e \u003cp\u003e \u003cem\u003eE\u003c/em\u003e \u003csub\u003eRHE\u003c/sub\u003e = \u003cem\u003eE\u003c/em\u003e\u003csub\u003eHg/HgO\u003c/sub\u003e + 0.0592\u0026times;pH\u0026thinsp;+\u0026thinsp;\u003cem\u003eE\u003c/em\u003e\u003csup\u003e0\u003c/sup\u003e\u003csub\u003eHg/HgO\u003c/sub\u003e (1)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Spectro-electrochemical characterization\u003c/h2\u003e \u003cp\u003eDuring spectro-electrochemical studies in a quartz cuvette, the catalyst ink immersed platinum grid served as the working electrode, platinum wire served as the counter electrode, and Hg/HgO in 1M KOH served as the reference electrode. The Luggin capillary salt bridge, which connected the reference electrode to the cell electrolyte, was built using agar-agar and KCl. During cyclic voltammetry, the spectra were captured at a 20 mVs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e scan rate closest to the onset potential. The \u003cem\u003eoperando\u003c/em\u003e spectro-electrochemical studies were carried out on ocean optics, FLAME-T-XR1-ES Assembly, 200 nm to 1025 nm range.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Results and discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.1. Structural and morphological analysis\u003c/h2\u003e \u003cp\u003eThe produced zinc substituted ferrite functional groups are visible in the FT-IR spectra in the 400\u0026ndash;4000 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e wave number range. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the recorded FT-IR spectra and displayed the typical absorption peaks at 422 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 579 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which are attributed to M-O stretching vibrations in octahedral and tetrahedral voids, respectively. Another absorption band at 1110 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to a tetrahedral Fe\u003csup\u003e3+\u003c/sup\u003e-O\u003csup\u003e2\u0026minus;\u003c/sup\u003e stretching vibration. Water molecules were found on the surface of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles as shown by the wide band absorption peak at 3590 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (bending mode of H\u003csub\u003e2\u003c/sub\u003eO). The stretching vibration of the C\u0026thinsp;=\u0026thinsp;C atom on the surface of the ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles was responsible for the extremely tiny band seen at 1620 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Tetrahedral and octahedral modes of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e are shown by the prominent signal at 579.16 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBy using X-ray powdered diffraction patterns of oxides synthesized at 550\u003csup\u003eo\u003c/sup\u003eC for 5 hours, the development of the spinel phase was determined. In accordance with JCPDS file No. 89-1009 of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, the XRD powder patterns of zinc substituted oxides (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) reveal the development of crystalline spinel phase with peaks corresponding to (220), (311), (222), (400), (422), (511) and (440) planes. The remaining peaks adhere to the typical pattern of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, with the exception of the impure phases of α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and ZnO, which are present in all calcined samples and naturally exist as hematite and zincite, respectively [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSEM micrographs of zinc ferrite (ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) obtained at various magnifications are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The uneven aggregation of oxide nanoparticles can be seen in micrographs. Zinc was substituted in the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e matrix to increase crystallinity, and the result was formation of nanoparticles [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.2. Electrochemical analysis\u003c/h2\u003e \u003cp\u003eInks of catalysts deposited on glassy carbon (GCE) conductive substrates, \u003cem\u003ei.e.\u003c/em\u003e, zinc ferrites, Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (x\u0026thinsp;=\u0026thinsp;0.25, 0.5, 0.75, 1) were examined for their electrocatalytic activity. To detect the occurrence of redox reaction on the oxide/electrolyte interface, the cyclic voltammogram of each oxide on a GCE support was recorded in the potential range of 0.9 to 1.6 V \u003cem\u003evs.\u003c/em\u003e RHE at 20 mVs\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e scan rate in 1M KOH. Typical cyclic voltammograms of GCE/Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, which show the lack of redox peaks in the chosen potential area, are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. On a Ti support, cyclic voltammograms of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e showed a similar appearance [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eLinear polarization (\u003cem\u003ei\u003c/em\u003e-\u003cem\u003eE\u003c/em\u003e) curves of GCE/Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e measured at 0.5 mV/s in the range of OER within 1.4 and 1.8 V \u003cem\u003evs.\u003c/em\u003e RHE with scan rate of 0.5 mV/s are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Again, the highest activity for OER, seen as the highest current density values is observed for GC/Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and the lowest for GC/ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode.\u003c/p\u003e \u003cp\u003eThe Tafel polarization curve was used to determine the electrocatalytic activity in terms of log current density (log \u003cem\u003ej\u003c/em\u003e) at overpotential (\u003cem\u003eη\u003c/em\u003e). The formal overpotential, commonly referred to as the anodic overpotential, was established by the relationship \u003cem\u003eη\u003c/em\u003e = \u003cem\u003eE\u003c/em\u003e \u0026ndash; \u003cem\u003eE\u003c/em\u003e\u003csub\u003eO2/OH\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], where \u003cem\u003eE\u003c/em\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003eO2/OH\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e = 0.303 V \u003cem\u003evs.\u003c/em\u003e Hg/HgO, are the applied potential across the electrocatalyst/1M KOH interface and the theoretical equilibrium Nernst potential \u003cem\u003evs.\u003c/em\u003e Hg/HgO in 1M KOH at 25\u0026deg;C, respectively. The overpotential was further calculated from the following Eq.\u0026nbsp;2 after converting the potentials to RHE:\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003e \u003cem\u003eη\u003c/em\u003e = \u003cem\u003eΕ\u003c/em\u003e\u003csub\u003eRHE\u003c/sub\u003e \u0026ndash; 1.23 V (2)\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eTafel polarization curves are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Among all stoichiometrics of spinel ferrite, just Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e coated on GCE showed the best electrocatalytic activity with Tafel slope 107 mVdec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and overpotential (\u003cem\u003eη\u003c/em\u003e) of 537mV at current density at 3 mAcm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. To normalize the material loading on the substrate, the activity was also calculated in terms of current density per mg (specific current density) [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Apparent current density (\u003cem\u003ej\u003c/em\u003e\u003csub\u003eapp\u003c/sub\u003e) and specific current density (\u003cem\u003ej\u003c/em\u003e\u003csub\u003espec\u003c/sub\u003e) values, together with the estimated values of overpotential (at denoted current densities) and Tafel slope values, are for four prepared zinc ferrite samples listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElectrode kinetic parameters for OER on GC/Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (0\u0026thinsp;\u0026le;\u0026thinsp;x\u0026thinsp;\u0026le;\u0026thinsp;1) electrodes in 1M KOH at 25\u003csup\u003eο\u003c/sup\u003eC\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCatalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverpotential (mV) at\u003c/p\u003e \u003cp\u003e1 mAcm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eCurrent density at\u003c/p\u003e \u003cp\u003eE\u0026thinsp;=\u0026thinsp;893mV\u003c/p\u003e \u003cp\u003e(mAcm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eC\u003csub\u003edl\u003c/sub\u003e (\u0026micro;Fcm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eR\u003csub\u003ef\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eECSA (cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eTafel Slope (mVdec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ej\u003csub\u003eapp\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ej\u003csub\u003etrue\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ej\u003csub\u003especific\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e480\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e309.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e7.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.539\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e107\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.5\u003c/sub\u003eFe\u003csub\u003e2.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e590\u003c/p\u003e \u003cp\u003e(0.67mAcm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.335\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e112\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.75\u003c/sub\u003eFe\u003csub\u003e2.25\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e530\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e325.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e8.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.569\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e137\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e596\u003c/p\u003e \u003cp\u003e(0.45mAcm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e59.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.104\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e143\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eEither apparent current density (\u003cem\u003ej\u003c/em\u003e\u003csub\u003eapp\u003c/sub\u003e) or true current density (\u003cem\u003ej\u003c/em\u003e\u003csub\u003etrue\u003c/sub\u003e), normalized by the geometric surface area of the electrode or the oxide roughness factor, could be used to represent the rate of electrochemical oxygen evolution. By conducting cyclic voltammetry experiments in 1M KOH at various scan rates within the potential region of 0.975 to 1.025 V (\u003cem\u003evs.\u003c/em\u003e RHE) at 25\u003csup\u003eo\u003c/sup\u003eC, the surface roughness factor (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e) of each oxide electrode was ascertained. According to Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, only capacitive currents due to double-layer charging-discharging predominate in this potential region.\u003c/p\u003e \u003cp\u003eRepresentative cyclic voltammograms at varying scan rates and a plot of current density \u003cem\u003evs.\u003c/em\u003e scan rate are given in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(A) and (B), respectively. By assuming the double layer capacitance value of a smooth oxide surface equal to 40 \u0026micro;Fcm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the oxide roughness factors (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e) of Zn ferrite samples were determined [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. \u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e values are together with C\u003csub\u003edl\u003c/sub\u003e values (equation S3 \u0026amp; S4) and ESCA values (equation S5), also listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe Tafel slope of Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e is lower than for other samples, suggesting high improvement in electrocatalytic activity. Changes in the electrical and magnetic characteristics of the oxide catalyst cause an increase in electrocatalytic activity when metal ions are substituted in the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e lattice [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Additionally, Iwakura \u003cem\u003eet al.\u003c/em\u003e discovered that metal substitution in the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e lattice increased saturation magnetization [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. They also noticed that when Bohr magneton levels rose, so did the electrocatalytic activity for oxygen evolution reaction.\u003c/p\u003e \u003cp\u003eTo explain the reaction mechanism, the anodic Tafel polarization curves of GC/Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrodes were recorded at various KOH concentrations (0.25 M \u0026minus;\u0026thinsp;1.5 M), maintaining the mediumionic strength constant (\u0026micro;\u0026thinsp;=\u0026thinsp;1.5), in order to determine the order of reaction (p) with regard to [OH\u003csup\u003e\u0026minus;\u003c/sup\u003e]. When determining the value of reaction order, the slope of the log \u003cem\u003ej vs.\u003c/em\u003e log [OH\u003csup\u003e\u0026minus;\u003c/sup\u003e] plot (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e) across the oxide film/KOH interface at the lower overpotential region particularly at potentials 1.55 V, 1.60 V, and 1.65 V \u003cem\u003evs.\u003c/em\u003e RHE was measured, and observed to be almost 2. This confirms the 4e\u003csup\u003e\u0026minus;\u003c/sup\u003e OER mechanism in strongly alkaline medium [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows Bode plots of Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e recorded in the frequency range of 100 kHz to 1 Hz, at the constant potential of 0.95 V \u003cem\u003evs.\u003c/em\u003e RHE. Any contribution from a faradaic process is observed to be minimal at this potential [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The measured impedance spectra of interface was analyzed by fitting appropriate Randles circuit, R(Q(R(C(R(RW)))))(CR). The agreement between measured and simulated data was excellent. The chi-squared value of 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e speaks for the quality of the model [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe first part of Bode plots at the highest frequencies corresponds to the solution resistance of the electrolyte, \u003cem\u003eR\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e, and the second part at other frequencies shows mainly capacitive impedance response, as is expected for the electrode at potentials without faradaic reaction(s). In that a case, the impedance due to double layer charging/discharging would dominate in the impedance spectrum. The corresponding phase angles in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, however, are much lower than expected \u0026minus;\u0026thinsp;90\u0026deg;, which is usually related to not ideal electrode response due to interfacial irregularities such as porosity, roughness, and geometry [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], or possible influence of some other impedance. A clear deep in the phase angle response seen at low frequencies suggests a possible contribution of some additional impedance (resistive-capacitive combination due to oxide film perhaps) which parameters could eventually be estimated by curve fitting procedure of a proper model [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e][\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e][\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]The capacitance value roughly estimated from the impedance magnitude |Z| of 500 Ωcm\u003csup\u003e2\u003c/sup\u003e at 1Hz is 318 \u0026micro;F/cm\u003csup\u003e2\u003c/sup\u003e, what is good agreement with \u003cem\u003eC\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e value in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e for Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eZn ferrite electrodes were tested for the measurement of standard electrochemical activation energies (Δ\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eel\u003c/em\u003e\u003c/sub\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e), entropies (Δ\u003cem\u003eS\u003c/em\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e), and enthalpies (Δ\u003cem\u003eH\u003c/em\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e) in order to understand the impact of temperature on OER.\u003c/p\u003e \u003cp\u003eWith this goal in mind, anodic polarization curves were recorded in 1M KOH at various temperatures ranging from 25 to 55\u003csup\u003e0\u003c/sup\u003eC (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e). For this purpose, Tafel polarization curves were recorded in the potential range of 1.4 V to 1.8 V \u003cem\u003evs.\u003c/em\u003e RHE at a scan rate of 0.5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at different temperatures. The temperature of the reference electrode was maintained constant during conducting of this experiment (25\u003csup\u003e0\u003c/sup\u003eC). Each curve current density data was recorded for a certain potential (1.60 V and 1.65 V \u003cem\u003evs.\u003c/em\u003e RHE), and an Arrhenius plot of log \u003cem\u003ej vs.\u003c/em\u003e 1/T (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e (B)) was created. The result of calculating the slopes of straight lines produced in the Arrhenius plots to determine values of Δ\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eel\u003c/em\u003e\u003c/sub\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAs anticipated, Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e has a lower electrochemical activation energy value than any other synthesized Zn ferrite sample of different stoichiometry.\u003c/p\u003e \u003cp\u003eThe average value of calculated transfer coefficient (α) using the relation α\u0026thinsp;=\u0026thinsp;2.303RT/\u003cem\u003eb\u003c/em\u003eF was quite close to one. Using the relations (3) and (4), other thermodynamic parameters, such as standard enthalpy of activation (Δ\u003cem\u003eH\u003c/em\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e), and standard entropy of activation (Δ\u003cem\u003eS\u003c/em\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e) were determined.\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eΔ\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eel\u003c/em\u003e\u003c/sub\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e = Δ\u003cem\u003eH\u003c/em\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e \u003cem\u003e- αFη \u003c/em\u003e (3)\u003c/p\u003e\u003cp\u003eΔ\u003cem\u003eS\u003c/em\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e = 2.3\u003cem\u003eR\u003c/em\u003e [log \u003cem\u003ej\u003c/em\u003e\u0026thinsp;+\u0026thinsp;Δ\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eel\u003c/em\u003e\u003c/sub\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e / 2.3\u003cem\u003eRT\u003c/em\u003e \u0026ndash; log (nFω\u003cem\u003eC\u003c/em\u003e\u003csub\u003eOH\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e)] (4)\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe Tafel slope (in mVdec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is calculated from the polarization curve recorded at various temperatures, and the values of R, F, and T are the gas constant, the Faraday constant, and absolute temperature, respectively. The Boltzmann constant (k\u003csub\u003eB\u003c/sub\u003e) and Planck's constant (h) are two constants that make up the frequency term ω, respectively. The very negative value of Δ\u003cem\u003eS\u003c/em\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e seen in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, illustrates the adsorption events that precede the electrochemical production of oxygen.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e lists average values of these thermodynamic parameters [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. The slope of Arrhenius plot (log \u003cem\u003ej\u003c/em\u003e versus 1/T) was used to compute the value of Δ\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eel\u003c/em\u003e\u003c/sub\u003e\u003csup\u003e\u003cem\u003e0\u0026ne;\u003c/em\u003e\u003c/sup\u003e, and the reaction entropy in each instance is strongly negative, confirming that electrochemical oxygen evolution happens \u003cem\u003evia\u003c/em\u003e adsorption of reactive intermediate species.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable S1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRequired stoichiometric amounts of metal precursors used for the synthesis of zinc ferrite nanoparticles.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCatalysts\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eZn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eFeSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNo. of moles\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAmount\u003c/p\u003e \u003cp\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo. of moles\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAmount\u003c/p\u003e \u003cp\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.655\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.109\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e16.6748\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.5\u003c/sub\u003eFe\u003csub\u003e2.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.017\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.2583\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.098\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e15.006\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.75\u003c/sub\u003eFe\u003csub\u003e2.25\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.917\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.088\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e13.505\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.034\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.556\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.079\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.004\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThermodynamic parameters for OER on GC/Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (0\u0026thinsp;\u0026le;\u0026thinsp;x\u0026thinsp;\u0026le;\u0026thinsp;1.0) electrodes in 1 M KOH\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCatalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStandard electrochemical energy of activation (Δ\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eel\u003c/em\u003e\u003c/sub\u003e\u003csup\u003e0\u0026ne;\u003c/sup\u003e)\u003c/p\u003e \u003cp\u003e(kJmol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eStandard electrochemical entropy of activation\u003c/p\u003e \u003cp\u003e(-Δ\u003cem\u003eS\u003c/em\u003e\u003csub\u003e\u003cem\u003eel\u003c/em\u003e\u003c/sub\u003e\u003csup\u003e0\u0026ne;\u003c/sup\u003e)\u003c/p\u003e \u003cp\u003e(JK\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003emol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTransfer coefficient (α)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eStandard enthalpy of activation\u003c/p\u003e \u003cp\u003e(Δ\u003cem\u003eH\u003c/em\u003e\u003csup\u003e0\u0026ne;\u003c/sup\u003e)\u003c/p\u003e \u003cp\u003e(kJmol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e54.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e74.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e92.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.5\u003c/sub\u003eFe\u003csub\u003e2.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e85.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e172.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e120.24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.75\u003c/sub\u003eFe\u003csub\u003e2.25\u003c/sub\u003eO4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e73.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e136.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e98.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e105.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e237.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e135.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.3. Spectro-electrochemical analysis\u003c/h2\u003e \u003cp\u003eIt is interesting to note that UV-vis\u0026ndash;NIR spectroscopy experiments conducted under OER circumstances have shown a rise in absorbance with applied voltage at the onset potential in the region of OER. Conway conducted the first investigation onto the impact of oxidized species on OER in the late 1950s. He found that the evolution of oxygen occurred concurrently with the potential decay from OER-relevant potentials to open-circuit potentials, indicating that oxidized states could be reduced to form molecular oxygen [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Oxo species on nearby Zn centers may chemically interact to form molecular oxygen, following a similar process to the OER predicted on Co in phosphate electrolyte [\u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] and CoOOH [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. \u003cem\u003eOperando\u003c/em\u003e UV-vis spectroscopy measurements were carried out to investigate the mechanism for OER and explain the activity patterns [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e depicts the \u003cem\u003eoperando\u003c/em\u003e UV-Vis spectroscopy before and during the cyclic voltammetry for the Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode performed at 25\u003csup\u003e0\u003c/sup\u003eC in 1M KOH at scan rate of 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Upon stepping the electrode potential from 1.6 V to 1.8 V \u003cem\u003evs.\u003c/em\u003e RHE in 0.1 V increments, the formation of absorption peaks from 300\u0026ndash;440 nm and a small peak from 850\u0026ndash;900 nm were observed, and these absorbance peaks broadened and intensified with increase of applied potential. These may correspond to FeOOH species [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] when O\u003csub\u003e2\u003c/sub\u003e evolution is proceeding on the electrode.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThe characteristics of four synthesized samples of Zn ferrite (Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) with different stoichiometry (0\u0026thinsp;\u0026le;\u0026thinsp;x\u0026thinsp;\u0026le;\u0026thinsp;1.0) were evaluated up to the point of their possible use as electrocatalysts for active oxygen evolution processes in an alkaline medium (1 M KOH). According to the results of the performed experiments, zinc ferrites may be produced inexpensively and easily by auto combustion utilizing egg ovalbumin, resulting in nano-sized oxides that have greater spinel phase crystallinity. Tafel slope is found to be minimum for Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, for which the maximum electrocatalytic activity towards OER in an alkaline medium and nearly 2nd order kinetics is observed for the OER process. Among all four samples with different stoichiometry, Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e showed the lowest standard electrochemical energy of activation which supports our findings. \u003cem\u003eOperando\u003c/em\u003e spectro-electrochemical study revealed the active sites of OER, \u003cem\u003ei.e\u003c/em\u003e., formation of absorption peaks from 300\u0026ndash;440 nm that corresponds to FeOOH species. Further exploration in NIR region is needed to understand the role of redox active sites. The study showed that more than one redox species is forming during the OER which are responsible for electrocatalytic activity of Zn\u003csub\u003ex\u003c/sub\u003eFe\u003csub\u003e3\u0026minus;x\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and the absorbance intensity is maximum for x\u0026thinsp;=\u0026thinsp;0.25 (Zn\u003csub\u003e0.25\u003c/sub\u003eFe\u003csub\u003e2.75\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e). Furthermore, these materials may be employed as electrode materials for energy storage devices and other applications. Using OER catalysts, large-scale practical water splitting operations may be carried out, supplying the clean and efficient energy which has been generally required.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe corresponding author may provide the data used to support the conclusions of this study upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have not disclosed any funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors and affiliations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDepartment of Chemistry, IIT(BHU), Varanasi, U.P., 211005, India\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAmisha Soni, Manisha Malviya, \u0026amp; Dhanesh Tiwary\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDepartment of Chemistry, Institute of Applied Sciences and Humanities, GLA University, Mathura, 281406, India\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDr. Basant Lal\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAS:\u0026nbsp;investigation, data curation, conceptualization, methodology, writing the original draft, review and editing.\u003c/p\u003e\n\u003cp\u003eMM: formal analysis, validation, data curation, editing, supervision.\u003c/p\u003e\n\u003cp\u003eBL: formal analysis, supervision.\u003c/p\u003e\n\u003cp\u003eDT: formal analysis, supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence to M. Malviya\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;Declaration of competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors affirm that they have no known financial or interpersonal conflicts that would have seemed to have an impact on the research presented in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors like to express their sincere thanks to Department of material science and engineering, Advance Imaging Center, IIT Kanpur for providing SEM of our samples and CIF, IIT (BHU) for other physicochemical characterizations.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eNaseri MG, Saion EB, Hashim M et al (2011) Synthesis and characterization of zinc ferrite nanoparticles by a thermal treatment method. 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J Phys Chem C 120:2747\u0026ndash;2752. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/ACS.JPCC.5B10838\u003c/span\u003e\u003cspan address=\"10.1021/ACS.JPCC.5B10838\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Oxygen evolution reaction, alkaline water oxidation, electrocatalysts, zinc ferrite nanoparticles.","lastPublishedDoi":"10.21203/rs.3.rs-3970277/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3970277/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"The present research work describes the fabrication of zinc ferrite nanoparticles with varying stoichiometric compositions (ZnxFe3-xO4; x= 0.25, 0.5, 0.75, and 1) and their electrocatalytic performance for the oxygen evolution reaction (OER). Egg white was employed as a precursor material during the thermal decomposition process to produce the catalysts. OER performances of four synthesized catalysts in the alkaline medium (1.0 M KOH) were investigated by physicochemical (XRD, FTIR and SEM) and electrochemical (CV, EIS, Tafel polarization) techniques. Among four Zn ferrite catalysts of different stoichiometry, just Zn0.25Fe2.75O4 exhibited the optimum catalytic activity, with the current density of 1 mA cm-2 at the overpotential of 454 mV, and with Tafel slope of 107 mVdec-1. The Arrhenius plot was applied to determine thermodynamic parameters such as activation energy and electrochemical entropy of reaction, which were found to be 54.22 kJ mol-1 and -74 J K-1 mol-1, respectively.","manuscriptTitle":"Evaluating Zn ferrite (Zn x Fe 3-x O 4 ; 0 ≤ x ≤ 1) for alkaline water oxidation: electrochemical and operando spectro- electrochemical study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-22 06:47:04","doi":"10.21203/rs.3.rs-3970277/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"89071808-6cbd-4d8a-910d-bf037abf4556","owner":[],"postedDate":"February 22nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-03-10T15:48:21+00:00","versionOfRecord":[],"versionCreatedAt":"2024-02-22 06:47:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3970277","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3970277","identity":"rs-3970277","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}