Highly Effective Bifunctional Electrocatalysts: Synthesizing NiCo 2 O 4 Nanostructures via Chemical Precipitation for Enhanced Oxygen Evolution and Reduction Reaction

doi:10.21203/rs.3.rs-4092883/v1

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Highly Effective Bifunctional Electrocatalysts: Synthesizing NiCo 2 O 4 Nanostructures via Chemical Precipitation for Enhanced Oxygen Evolution and Reduction Reaction

https://doi.org/10.21203/rs.3.rs-4092883/v1

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In this investigation, we successfully produced NiCo₂O₄ nanostructures using a simple chemical precipitation method, wherein we adjusted molarity concentration of sodium bicarbonate (NaHCO₃) and precursor ratios of Ni and Co. Analysis of surface features revealed a diverse range of shapes, including particles, flowers, rods, and flakes. Notably, the NiCo₂O₄ nanorods (NCO3) demonstrated a significant threefold increase in BET surface area compared to NCO5. The alterations observed in the physical and chemical characteristics significantly influenced the electrocatalytic efficacy in alkaline environments for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In the context of the oxygen reduction reaction, NCO5 displayed a commencement potential of 0.72 V compared to the reversible hydrogen electrode (RHE), surpassing NCO4 by 110 mV, albeit falling short by 90 mV when compared to Pt/C, the standard benchmark material with a potential of 0.82 V. In terms of OER, NCO3 displayed a potential difference of 152 mV@10mA/cm² compared to other NiCo₂O₄ materials and Pt/C. The increased level of activity observed can be attributed not only to the increased surface area but also to enhancements in electrical properties. This is supported by the lower charge transfer resistance measured in NCO3 (215.2 Ω.cm²) compared to NCO5 (350.2 Ω.cm²) as revealed by electrochemical impedance spectroscopy (EIS).

Inverse spinel

bi-functional

oxygen evolution and oxygen reduction

Lately, there has been a noticeable escalation in the imperative concerning energy consumption and environmental degradation. [1–2]. To mitigate our reliance on fossil fuels, innovative approaches to green energy storage and conversion are imperative [3]. However, a significant obstacle emerges from the slow reaction rates experienced during the process of oxygen reduction at the cathode and oxygen evolution at the anode during the charging of batteries. [4–6]. Fuel cells and air batteries present promising solutions to this challenge [7]. Historically, noble metals such as platinum have been esteemed for their efficacy in catalyzing the oxygen reduction reaction (ORR), while iridium oxide and ruthenium oxide have been favored for the oxygen evolution reaction (OER). However, their substantial cost, restricted availability, and insufficient durability in alkaline conditions have hindered their widespread commercial application [8–12].

In contemporary research endeavors, considerable focus is directed towards minimizing platinum (Pt) loading in catalysts [13]. One prominent approach involves the development of alloys utilizing metals such as Cobalt (Co), Nickel (Ni), and Iron (Fe), alongside the synthesis of core-shell structures [14–16]. These strategies aim to employ the non-noble metal as the active catalyst core, thereby reducing the necessity for Pt content [17–20]. However, the continued dependence on Pt as the principal electroactive substance presents an enduring obstacle, predominantly attributed to its exorbitant expense and constrained accessibility. Consequently, there is a pressing need for alternative methodologies to engineer highly efficient materials [21–24]. Transition metal oxides (TMOs) emerge as a promising substitute in this context. TMOs, exhibiting diverse oxidation states, demonstrate heightened activity in oxygen reactions attributed to enhanced electron transport capabilities [25]. Moreover, their inherent ability to seamlessly integrate within a single material matrix is a crucial attribute for electrocatalysts [26–28]. The continuous oxidation and reduction processes within electrochemical cells necessitate materials capable of swift interconversion between oxidation states, a requirement fulfilled by TMOs [29–30]. Additionally, TMOs offer versatility, allowing for their utilization either in combination with other TMOs to create mixed transition metal oxides or as standalone electrocatalysts (MTMOs). Notably, compounds like spinels and perovskites exhibit well-ordered crystalline structures. Spinels, characterized by the general chemical formula AB₂X₄, offer particularly enticing prospects due to their potential for amalgamating the catalytic properties of various oxides within a single crystal lattice [31].

Co₃O₄, a widely studied spinel electrocatalyst renowned for its efficacy and durability in oxygenevolution reaction (OER) and oxygen reduction reaction (ORR) in basic mediums, has undergone enhancement with the incorporation of Ni atoms to form NiCo₂O₄ [32–34]. This modification aims to bolster electrical conductivity and augment the electroactive sites, thereby improving the overall electrochemical performance [35]. In contrast, nickel oxide, a transition metal oxide (TMO), though less explored, exhibits commendable conductivity, barrier properties, and superior stability compared to precious metals [36]. While demonstrating promising OER capability, it falls short in ORR performance, rendering it unsuitable for standalone ORR applications. However, when combined with other oxides, it holds potential as a bifunctional material. The incorporation of nickel oxides into the spinel structure gives rise to the NiCo2O4 spinel, presenting a notable potential as an electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in various applications [37]. Notably, the electrical conductivity of Co, Ni, and their compositions follows the sequence: Co₃O₄ < NiO < NiCo₂O₄ [38]. Despite its inherent advantages such as high impact strength, corrosion resistance, and abundance, NiCo₂O₄ faces limitations due to its poor conductivity and large structure [39–40]. Various strategies including compositional modification, valence control, defect generation, and morphology optimization have been explored to enhance its electrochemical performance. Diverse morphologies such as nanoparticles, nanowires, nanoneedles, and urchin-like structures have been synthesized via hydrothermal methods, albeit with scalability challenges for commercial applications [41]. In this investigation, we introduce a facile chemical precipitation approach to fabricate NiCo₂O₄ nanostructures by varying molarity of concentration of NaHCO₃ and precursor ratios of Ni and Co chloride source. The effectiveness of electrocatalysis for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) was evaluated using experiments performed utilizing a rotating disk electrode. Our contribution lies in the facile synthesis of this ternary compound as a bifunctional electrocatalyst, crucial for "air electrode" applications in various energy systems, and exploring the influence of Ni incorporation on cobalt oxides in forming NiCo₂O₄ spinel, elucidating structural and electrocatalytic modifications. This study utilizes synthesized NiCo2O4 nanostructures to investigate their electrocatalytic activity for the oxygen reduction and oxygen evolution processes, which were notably influenced by changes in morphology and electrical properties in a systematics approach.

2.1. Chemicals required

Nickel chloride hexahydrate (NiCl₂.6H₂O), cobalt chloride hexahydrate (CoCl₂.6H₂O) and sodium bicarbonate (NaHCO₃) were of analytical grade and employed without additional purification.

2.2. Synthesis of NiCo₂O₄ nanomaterials

The chemicals were employed immediately upon acquisition without the need for further refinement or purification processes. For a conventional preparation procedure, solutions of 0.05 M NiCl₂·6H2O, 0.1 M CoCl₂·6H₂O, and 1.5 M NaHCO₃ were prepared in advance. Subsequently, 80 mL of the NiCl₂·6H₂O solution was mixed with the NaHCO₃ solution under continuous stirring, leading to a 20-minute reaction to form a homogenous suspension. Subsequently, 80 milliliters of the CoCl₂·6H₂O solution were added to the previously mentioned suspension and agitated for a duration of 8 hours. The resulting precipitate was collected via centrifugation, subjected to multiple washes with acetone and water to eliminate residual impurities, and finally dried by maintaining at 70°C in hot-oven. To synthesize the nanostructured NiCo₂O₄ material, the carbonate precursor underwent annealing in an air environment at 300°C for a duration of 3 hours, employing a gradual heating rate of 5°C/min.

Furthermore, the identical procedure was employed to generate samples with varied molarities of NaHCO₃ precursors, specifically 0.5 M, 1 M, and 2 M, while maintaining consistency in other parameters. The samples synthesized using NaHCO₃ at concentrations of 0.5 M, 1 M, and 2 M were denoted as NCO1, NCO2, NCO3, and NCO4 respectively. Furthermore, two additional materials were created by adjusting the ratio of Ni and Co precursors while maintaining consistent synthesis conditions. These materials, designated as NCO5 and NCO6, were prepared using precursor molar ratios of Ni to Co of 1:0.5 and 1:1 respectively, in accordance with the established protocol.

2.3. Materials Characterizations

The investigation of morphology and surface structure was carried out utilizing scanning electron microscopy (SEM) (LEO FESEM 1530) and transmission electron microscopy (TEM) (Philips CM300). Surface structure and morphology were further analyzed using Fast Fourier Transformation (FFT) and high-resolution TEM (HR-TEM). The crystalline nature of the spinel nanostructure within NiCo₂O₄ was explored employing HR-TEM, FFT, and selected area electron diffraction (SAED) patterns. The surface area and porosity characteristics were determined using a Micromeritics ASAP 2020 surface area and porosity analyzer, with the nitrogen adsorption-desorption isotherm analyzed through the Brunauer-Emmett-Teller (BET) method, and pore size distributions assessed via the Barrett-Joyner-Halenda (BJH) model. The spinel crystal structure of the nanoplatelets in NiCo₂O₄ was confirmed through X-ray diffraction (XRD) (BrukerAXS D8 Advance). Additionally, X-ray photoelectron spectroscopy (XPS) was conducted to ascertain the composition available within the NiCo₂O₄ nanostructure.

2.4. Electrochemical characterization and electrocatalytic evaluation

Cyclic voltammetry (CV) for OER and rotating disc electrode (RDE) voltammogram for ORR were used to examine the electrochemical performances of the nanomaterials used for the current study in 1 M aqueous KOH electrolyte. A potentiostat and a rotation speed controller make up the setup for RDE. All electrochemical tests were performed at room temperature, with Ag/AgCl acting as a reference electrode. The counter electrode was made of platinum wire. The working electrode was a glassy carbon electrode (5 mm OD) coated with 20 mL of 4 mg mL^− 1 suspension produced by combining NiCo₂O₄ and a 0.5 wt% Nafion solution in mixed solution (375 µL H2O + 125 µL IPA). All additional comparative materials were prepared in the same way as the working electrode. ORR curves were recorded from − 0.7 to 1V using an O₂-saturated electrolyte at a scan rate of 5 mV/s at varied electrode rotation speeds (1000, 1200,1400,1600,1800,2000 rpm). In order to spin off the oxygen evolved during voltammetry testing, the OER curves were recorded from 0 to 0.8 V at a scan rate of 5 mV/s with a N₂-saturated electrolyte rotating at 1000 rpm. Linear sweep voltammetry was taken from 0.3 to 0.93 V vs RHE (Reversible Hydrogen Electrode) at a sweep rate of 5 mV/s for ORR in a O₂-rich solution. The experiments of OER were taken by taking potential range from 1 to 1.9 V vs RHE at a sweep rate of 5 mV/s in a N₂-rich solution. The RDE measurement for ORR was carried out by taking different rotation (1000–2000 rpm) from potential range 0 to 0.93 V vs RHE. Moreover, electrochemical impedance spectroscopy (EIS) was taken to check the electrical properties of the NiCo₂O₄ materials, particularly the resistance of charge-discharge (Rct). The measurements were performed at 0.64 V vs. RHE with the frequency ranging from 0.01 HZ to 100 kHZ.

3.1. Structural analysis

The X-ray diffraction (XRD) analysis was conducted to assess the crystallinity, structural characteristics, and phase purity of the synthesized nanostructures. Figure 1 illustrates the powder XRD patterns obtained from samples prepared using various concentrations of NaHCO₃ and different precursor ratios of Ni and Co. The synthesis involved chemical co-precipitation followed by calcination at 300°C for 3 hours, employing NaHCO₃ concentrations of 0.5 M, 1 M, and 2 M, and precursor molar ratios of Ni to Co at 1:0.5 and 1:1, respectively. Distinct samples were synthesized with different molarities, including 1.5 M (NCO1), 0.5 M (NCO2), 1 M (NCO3), and 2 M (NCO4), as well as precursor molar ratios of Ni to Co at 1:0.5 (NCO5) and 1:1 (NCO6), respectively. The diffraction peaks observed at 18.6°, 30.9°, 35.5°, 38.3°, 44.4°, 54.9°, 58.8°, and 75.0° correspond to the crystallographic planes of (111), (220), (311), (222), (400), (422), (511), and (440), respectively. These peaks are consistent with the cubic spinel NiCo₂O₄ phase, as confirmed by comparison with the JCPDS file (JCPDS card No.00-20-0781) [42]. The XRD patterns (Fig. 1A) exhibit prominent peaks indicative of well-crystalline samples, while low-intensity peaks remain unindexed. Notably, no characteristic peaks associated with impurities, such as NiO or CoO, were detected, underscoring the high purity of the synthesized NiCo₂O₄ samples [43]. Furthermore, variation in the stoichiometric ratio of precursor concentrations during the synthesis of NCO1, from 1:0.5 (NCO5) to 1:1 (NCO6), revealed consistent formation of the cubic spinel NiCo₂O₄ phase across all XRD peaks. Importantly, no significant alterations in peak position or additional peaks were observed in the XRD patterns of NiCo₂O₄ samples synthesized under different parameters, including molarity and precursor molar ratios.

The FTIR analysis of NiCo₂O₄ revealed significant peaks near 2104 cm^− 1, suggesting potential bending of water molecules. Additionally, the presence of the H–O–H bending vibration mode was indicated by peaks observed at 1602 cm^− 1and 1078 cm^− 1. Weak signals at 640 cm^− 1 and 487 cm^− 1, consistent with all peaks detected in the NiCo₂O₄ nanostructured materials illustrated in Fig. 2, were attributed to metal oxide vibrations [44].

3.2. Morphological analysis

By varying the concentration of sodium bicarbonate and adjusting the precursor molar ratio, the surface characteristics of the produced NiCo₂O₄ nanostructures (as depicted in Fig. 3) were investigated. Figure 3 (NCO1) presents a scanning electron microscope (FESEM) image of nickel cobaltite nanoparticles synthesized using water as the solvent and a concentration of 1.5 M NaHCO₃.Additionally, nanoflowers were produced when the molarity concentration of NaHCO₃ was switched from 1.5 M to 0.5 M (NCO2) while keeping the remaining synthesis parameters constant (Fig. 3(NCO2)). In addition, compared to using little high molarity concentration, the morphology of the sample is significantly changed when using 1 M concentration of sodium bicarbonate (NCO3). Figure 3 (NCO3) shows how nanorods are shaped which have also good electrochemical performance for making efficient electrocatalyst. Using the highest molar concentration of 2 M (NCO4) and keeping the other synthesis variables constant, the shape of nanoparticles similar to those shown in Fig. 3 (NCO4) was found. It is worth emphasised that the solvent is essential for the creation of different NiCo₂O₄ nanostructures with morphologies resembling nanoparticles, nanoflowers, and nanorods [45]. Further, we achieved 1:0.5 and 1:1 NiCl₂.6H₂O and CoCl₂.6H₂O precursor ratios throughout the synthesis of NCO1, while maintaining the other reaction conditions constant. This allowed us to better understand the impact of precursor molar ratio. NiCl₂.6H₂O and CoCl₂.6H₂O were mixed in a 1:0.5 molar ratio to produce nanosheets (Fig. 3, NCO5). CoCl₂.6H₂O and NiCl₂.6H₂O were combined in a 1:1 molar ratio to create encapsulated nanoparticles with the same shape (Fig. 3, NCO6).

The comprehensive microstructural analysis of NCO3 was completed utilising TEM in addition to support FESEM. Using a 0.05 M of NiCl₂.6H₂O and 0.1 M of CoCl₂.6H₂O and 1 M of NaHCO₃ in 80 mL of aqueous solution and calcinated at 300°C for 3 hours, NCO3 was synthesised. Figure 4 illustrates the TEM image, selected area electron diffraction (SAED) pattern, and high-resolution transmission electron microscopy (HRTEM) images of NCO3.The TEM picture (Fig. 4a) displays a morphology resembling nanorods made of nanoplates. Moreover, the location of the selected area electron diffraction (SAED) pattern of NCO3 (Fig. 4b) indicates the poly-crystalline structure of the samples. Furthermore, the edge of a nanosheet was used to catch the high-resolution TEM (HRTEM) (Fig. 4c). The (311) crystal plane of the synthesized nanocomposite, identified as the most prominent peak in XRD, corresponds to a fringe spacing of 0.22 nm, as observed in Fig. 1a (NCO3) [46].

3.3. Compositional analysis

X-ray photoelectron spectroscopy (XPS) is employed to gain insights into the elemental composition and chemical states of the prepared NiCo₂O₄ sample.. Figure 5a shows the Ni, Co, and O components present in the survey region from the XPS survey pattern of NiCo₂O₄ nanoflowers (1200-0 eV). Using high resolution Ni, Co, and O spectra, the sample's spinel structure's oxidation condition was determined. In Fig. 5b, the high-resolution Ni 2p spectrum is depicted, delineated into the Ni 2p_3/2 peak at 850.2 eV and the Ni 2p_1/2 peak at 856.6 eV, forming a spin-orbit doublet. The Ni³⁺2p_3/2 and Ni³⁺2p_1/2 states exhibit dual peaks with spin-orbit binding energies of 852.5 and 860.7 eV, correspondingly, while Ni²⁺2p_3/2 and Ni²⁺2p_1/2 display two peaks with binding energies of 848.5 and 856.8 eV, respectively. Additionally, the Co 2p spectrum demonstrates a well-fitted profile with two prominent peaks corresponding to Co 2p_3/2 and Co 2p_1/2, positioned at 772.5 eV and 792.4 eV, as illustrated in Fig. 5c. In the O 1s spectra (depicted in Fig. 5d), the binding energies of 526.1 eV, 528.2 eV, and 529.5 eV are attributed to the metal-oxygen bond in NiCo₂O₄, as well as to defect sites with reduced oxygen coordination and oxygen absorption from the surrounding atmosphere[47].

3.4. BET analysis

The BET technique, founded on the adsorption of particular molar species in their gaseous state on the surface, stands as one of the pivotal methods for accurately determining the total specific area of porous samples [48]. The crucial factor in any electrochemical reaction, the active surface area of the synthesized NiCo₂O₄-based samples, was assessed utilizing the Quantachrome Nova station 100 apparatus through gas adsorption analysis conducted at 77 K. The synthesised NCO3 (Fig. 6(a)) has high surface area of 91.2 m²/g, compared to 30.76 m²/g for the NCO5 (Fig. 6(b)). When compared to NCO3, the nanorod morphology of the synthesized NCO3 substantially enhances the specific surface area. The total pore volume was calculated by assessing the quantity of gas absorbed relative to the applied pressure. The investigation of the pore size distribution of the synthesized NiCo₂O₄ active materials was conducted using non-local density functional theory. The synthesised NCO3 has a pore volume of 2.184 cm³/g, while the synthesised NCO5 has a pore volume of 0.135 cm³/g. Due to high pore volume of as synthesized NCO3, it indicates the superior electrochemical performance.

3.5. Electrocatalytic study on OER/ORR

The electrocatalytic characteristics of NiCo₂O₄ nanostructures were investigated using the polarisation plot of the oxygen evolution reaction (OER) (Fig. 7a). The onset potentials of the NiCo₂O₄ nanostructures (NCO1, NCO2, NCO3, NCO4, NCO5, NCO6, and IrO₂) synthesised using the various parameters stated were 1.52, 1.5, 1.49, 1.52, 1.54, 1.56, 1.57, and 1.6, respectively, vs. RHE. In compared to other nickel cobaltite samples and IrO₂, the NiCo₂O₄ material (NCO3) used 260 mV less energy to conduct the oxygen evolution when a reference current density of 10 mA.cm^− 2 was used. The highest electrocatalytic characteristics for oxygen evolution are defined by the high double layer region in NiCo₂O₄ samples with IrO₂, while NCO3 revealed the low double layer region in Cdl plots (Fig. 7b). The decreased Tafel slope, which denotes a successful charge-transfer process, can be linked to the increased OER activity NCO3 exhibits IrO₂'s Tafel slope indicated that the dissociative water adsorption mechanism was its limiting factor [49]. All of the NiCO₂O₄ samples' tafel slopes were further displayed (SI). In addition to NCO5's outstanding ORR performance in compared to Pt/C, NCO3 also demonstrated strong OER activity. Figure 7(c) shows the Nyquist plot of the synthesized materials using a frequency range of 0–10 kHz and amplitude of 5 kV. In comparison to other NiCo₂O₄ samples, the synthesised materials NCO3 and NCO5 have a lower Rct value, which indicates that they have good electrocatalytic capabilities for oxygen reduction and evolution reactions.

NCO5 was found to achieve a greater current density than other NiCo₂O₄ nanomaterials, it was also discovered. Thus, linear sweep voltammetry curve for the oxygen reduction reaction of NiCo₂O₄ nanoparticles with Pt/C at different rotatory speeds are given in Fig. 7e and the LSV curve of other synthesized NiCo₂O₄ nanomaterials were shown in supporting information (SI, Fig. S1). As can be seen, at all rotational speeds, all materials reached clearly defined diffusion limiting currents. An activity comparison of Pt/C and NiCo₂O₄ nanomaterials at 1600 rpm is shown in Fig. 7(d). While Pt/C displayed 15.8 mA.cm^− 2 at the same potential, NCO5 displayed a highest current density of -12.3 mA.cm^− 2 among all NiCo₂O₄ catalysts. So Changes in surface area cause a shift in the onset potential. With a nearly 2-fold greater surface area than Co₃O₄, NiCo₂O₄ exhibits better activity in terms of current density. As a result, there are more active sites available for oxygen molecule reactions in NiCo₂O₄. The introduction of Ni species into the NiCo₂O₄ catalyst enhanced its activity by boosting surface area and shifting the onset potential. The performance exhibited by the NiCo₂O₄ material surpassed that of comparable reported materials, with the added advantage of being synthesized through a simpler process [50–51]. The presence of nickel (Ni) molecules within the NiCo₂O₄ catalyst facilitated an improvement in the onset potential. Ni played a crucial role in augmenting electrical conductivity, thereby enhancing electronic properties and facilitating electron transfer [52]. The enhancement in onset potential resulting from nickel substitution is attributed to the reduction in activation energy [53].

Because of the enhancement of the electronic characteristics, the NiCo₂O₄ material demonstrated an enhancement in the electrocatalytic performance for ORR. The following equations were used to conduct a Koutecky-Levich correlation and further analyse the ORR mechanism.

$$\frac{1}{J}=\frac{1}{{J}_{L}}+\frac{1}{{J}_{K}}=\frac{1}{B{\omega }^{\frac{1}{2}}}+\frac{1}{{J}_{K}}$$

B = 0.62nFC₀ (D₀)^2/3${\vartheta }^{-1/6}$ (2)

J_K =nFkC₀ (3)

Where J_d, J_k, and J_l are the disc current density, kinetic current density, and diffusion current density, respectively. Furthermore, n represents the electron transfer number, F represents the Faraday constant (96485 C/mol), CO₂ represents the oxygen concentration in KOH solution (1.4x10^− 6 mol/cm³), DO₂ represents the oxygen diffusion coefficient in KOH (1.73x10^− 5 cm²/s), is the kinematic viscosity of the KOH solution (0.01 cm²/s), and is the electrode rotation rate (rad/s). Figure 7(f) shows the KL plots obtained at two different potentials of NCO5 samples and other plots were shown in Fig S2. This phenomenon can be visually illustrated by contrasting the outcomes with theoretical K–L plots for 2 and 4 electrons, demonstrating a consistent adherence to a 4-electron trend across all materials. The number of transferred electrons was determined using Eq. 2, yielding values of 3.12, 1.2, 1.9, 1.4, 3.3, 1.9, and 4e- for NCO1, NCO2, NCO3, NCO4, NCO5, NCO6, and Pt/C, respectively. Otherwise, KL plots showed linear behaviour, indicating that these materials had a first-order influence on O₂ kinetics [54].

NiCo₂O₄ nanostructures were made using a simple chemical precipitation method followed by callcination, which is a quick and efficient way to produce spinel type oxides. The morphology of the samples transforms when nickel is added, transitioning from particles to a flake-like structure for NiCo₂O₄. X-ray diffraction and X-ray photoelectron spectroscopy, which revealed NiCo₂O₄ in the form of an inverse spinel, corroborated the production of these spinel type structures. These modifications led to a shift in the surface area determined by BET, which was altered to discover areas of 121.26 and 32.27 m²/g for NCO3 and NCO5 materials, respectively. EIS measurements supported the claim that the Ni inclusion also changed the NiCo₂O₄ material's electrical characteristics. When compared to other NiCo₂O₄ material, NCO5's charge transfer resistance dropped from 350.2 cm² to 215.2 cm². The electrocatalytic activity for the oxygen reduction and oxygen evolution processes was significantly impacted by these morphological and electrical alterations. During the ORR, the NCO5 had an onset potential of 0.72 V vs. RHE, which was 110 mV higher than the NCO4 (0.61 V) and 90 mV lower than the Pt/C as reference material (0.82 V). And for the OER, the NCO3 material exhibiting a potential difference of 152 mV@10 mA.cm^− 2 when compared to other NiCo₂O₄ materials and Pt/C.

Author Contributions Statement

Ananta Sasmal: Experimentation, Investigation, Writing – review & editing; Dipankar Gogoi: Conceptualization, Experimentation, Investigation, Methodology, & Writing – original draft; and T.D. Das: Visualization, & Supervision.

Funding

No financial support was provided by any funding agency or organizations for this work.

Declaration of Competing Interest

The authors have no direct or indirect competing interests.

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Highly Effective Bifunctional Electrocatalysts: Synthesizing NiCo 2 O 4 Nanostructures via Chemical Precipitation for Enhanced Oxygen Evolution and Reduction Reaction

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental Section

2.1. Chemicals required

2.2. Synthesis of NiCo₂O₄ nanomaterials

2.3. Materials Characterizations

2.4. Electrochemical characterization and electrocatalytic evaluation

3. Results and Discussions

3.1. Structural analysis

3.2. Morphological analysis

3.3. Compositional analysis

3.4. BET analysis

3.5. Electrocatalytic study on OER/ORR

4. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

Highly Effective Bifunctional Electrocatalysts: Synthesizing NiCo 2 O 4 Nanostructures via Chemical Precipitation for Enhanced Oxygen Evolution and Reduction Reaction

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental Section

2.1. Chemicals required

2.2. Synthesis of NiCo2O4 nanomaterials

2.3. Materials Characterizations

2.4. Electrochemical characterization and electrocatalytic evaluation

3. Results and Discussions

3.1. Structural analysis

3.2. Morphological analysis

3.3. Compositional analysis

3.4. BET analysis

3.5. Electrocatalytic study on OER/ORR

4. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

2.2. Synthesis of NiCo₂O₄ nanomaterials