Morphology Regulated Hierarchical Rods-, Buds-, and Sheets-like CoMoO₄ for Electrocatalytic Oxygen Evolution Reaction

Abstract

One of the hugely focused areas of research for addressing the world’s energy and environmental challenges is electrochemical water oxidation. Morphological modulation of nanomaterials is essential for producing efficient electrocatalysts to achieve the required results. The purpose can be achieved by controlling synthesis parameters, and this is a key factor which greatly influences the oxygen evolution reaction (OER) performance during electrochemical water splitting. In this study, synthesis of cobalt molybdate (CoMoO₄) through a simple and low-cost hydrothermal/solvothermal strategy with tunable morphology is demonstrated. Different morphologies, namely rods-like, buds-like, and sheets-like, referred to as R-CMO, B-CMO, and S-CMO, respectively, have been obtained by systematically varying the solvent media. Their catalytic activity towards OER was investigated in 1.0 M aqueous KOH medium. R-CMO nanoparticles synthesized in an aqueous medium demonstrated the lowest overpotential value of 349 mV to achieve a current density of 10 mA cm⁻² compared with other as-prepared catalysts. In contrast, the B-CMO and S-CMO exhibited overpotential values of 369 mV and 384 mV, respectively. Furthermore, R-CMO demonstrated an exceptional electrochemical stability for up to 12 h.

1. Introduction

Clean, renewable, and environmentally friendly energy systems that use conversion and storage technologies include water splitting, fuel cells, metal–air/oxygen batteries, and carbon dioxide/nitrogen fixation. These systems offer promising solutions for the current energy crisis and environmental issues. For instance, electrochemical methods in conjunction with energy conversion technologies can be used to produce sustainable chemicals and fuels such as H₂, CH₄, NH₃, and HCOOH. Prominently, the Earth’s atmosphere supplies the feedstock of water, air/oxygen, carbon dioxide, and nitrogen. However, a large overpotential that is above thermodynamic criteria still hinders the development of these promising technologies. As a result, developing high-performance electrocatalysts is critical. The oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), nitrogen reduction reaction (N2RR), and carbon dioxide reduction reaction are the main reactions in heterogeneous electrocatalysis [1,2,3].

Electrochemical water splitting with high purity hydrogen production without CO₂ emissions is one of the best methods for establishing a sustainable energy landscape. Because of the abundant supply of raw materials such as power and water, electrochemical water splitting outperforms coal gasification and steam–methane reformation in terms of high hydrogen generation. Particularly, the alkaline water electrolysis has drawn a lot of attention due to its attributes of simple construction and inexpensive electrode materials. The viability of these technologies depends on the electrochemical performance of the two half-reactions, namely the oxygen evolution reaction and the hydrogen evolution reaction taking place at the anode and cathode, respectively. Furthermore, the OER is an electron–proton coupled, complicated, stepwise reaction that is thermodynamically uphill. As a result, compared to the HER process, the OER is a bottleneck in the entire process and requires a high overpotential to achieve the appropriate current density.

As a result, more efforts have been put into creating high-performance and affordable electrocatalysts, particularly OER catalysts. The standard electrocatalysts for OER and HER are frequently recognized as Ir/Ru and Pt-based materials, respectively. Unfortunately, because of their high cost, limited availability, and poor stability under harsh reaction circumstances, these materials are not extensively usable in the context of sustainable energy use technologies. As a result, materials based on transition metals that are Earth-abundant have generated a lot of attention as OER and HER electrocatalysts. Metals/alloys, metal oxides, (oxy)hydroxides, single-atom catalysts, and carbon-based compounds are a few examples of these substances [4,5,6]. In this regard, exploring highly active, affordable, and Earth-abundant OER electrocatalysts is extremely desirable. Some of the recently used OER electrocatalysts to replace the precious catalysts are metal oxides/hydroxides [7,8,9], metal sulfides [10,11], metal selenides [12,13], metal nitrides [14,15], and metal phosphides [16,17,18]. In this context, transition-metal molybdates have drawn huge interest among researchers due to their strong electrocatalytic activity, low cost, and environmental compatibility [19].

Due to synergistic association between the high redox behavior of Cobalt (Co) and the strong electrical conductivity of Molybdenum (Mo), CoMoO₄ behaves as a remarkable OER electrocatalyst [20,21,22]. However, because of the small number of active sites, it exhibits relatively poor charge transport efficiency and structural coarsening. During long cycles, the OER activity of CoMoO₄ is still not sufficient [23]. In this regard, an efficient plan to increase the OER activity of CoMoO₄ catalysts is highly anticipated. Morphology tuning is one of the effective methods for addressing the issue by increasing the specific surface area to enhance the number of active sites. For example, B. Paul et al. synthesized morphology controlled Co₃O₄ nanoparticles using facile hydrothermal strategy by varying the reaction time over 6, 12 and 24 h. The Co₃O₄-24 h catalyst is reported to show an overpotential of 296 mV to achieve a current density of 10 mA cm⁻² [24]. X. Lv et al. synthesized a morphology controlled Cu₂S/CF composite by varying the ratio of solvents in a hydrothermal reaction containing alcohol and water in a ratio of 1:9 and exhibited an overpotential of 239 mV to achieve a current density of 10 mA cm⁻² [25].

W. Xie et al. synthesized Fluorine doped CoMoO₄ on graphene felt to achieve an enhanced number of active sites and delivered an overpotential of 256 mV at the current density of 10 mA cm⁻² [26]. Using a simple hydrothermal process, M.Q. Yu et al. synthesized CoMoO₄ that resembled porous flowers to show an overpotential of 312 mV at a current density of 10 mA cm⁻² [20]. Y. Xu et al. also used a simple hydrothermal process to construct Ni(OH)₂ nanosheets wrapped around CoMoO₄ nanoplate arrays supported on Ni foam to reveal an overpotential of 349 mV at a current density of 100 mA cm⁻² [27]. A hybrid of cobalt oxide nanoparticles anchored on CoMoO₄ nanorods synthesized by S. Xun et al. exhibited good oxygen evolution catalytic activity with a low overpotential of 253 mV at a current density of 10 mA cm⁻² [19]. The hierarchical CoMoO₄ nanoparticle-decorated nanoplate arrays that X. Guan et al. grew on Ni foam showed an overpotential of 317 mV to achieve a current density of 100 mA cm⁻² [28]. Hollow nanocages of Co₃O₄-CoMoO₄ heterostructures synthesized by J. Luo et al. showed an overpotential of 248 mV to afford a current density of 10 mA cm⁻² [29]. CoMoO₄ nanofilms on ZnCo₂O₄ nanosheets grown on Ni foam were synthesized by W.D. Yang et al. using a simple two-step hydrothermal technique and showed a low overpotential of 237 mV at 20 mA cm⁻² [30]. Using a simple hydrothermal process, L. Xia et al. synthesized hollow porous Co₃O₄/CoMoO₄ and showed good oxygen evolution reaction performance with an overpotential of 342 mV at 100 mA cm⁻² [31].

Despite the fact that many studies using various CoMoO₄ morphologies and composites for the oxygen evolution reaction have been published, there are still numerous ways to modify the morphology of the catalysts to improve their performance. In this work, a novel strategy to synthesize morphology controlled CoMoO₄ nanoparticles is proposed. Different nanoparticles of CoMoO₄ with rods-like, buds-like, and sheets-like morphologies were synthesized using a facile hydrothermal/solvothermal method utilizing water, water/ethanol and water/ethyleneglycol (in 1:1, v/v) as solvent media, respectively. The material’s physicochemical properties were studied using different analytical techniques. The electrocatalytic activity of the prepared electrodes with regard to oxygen evolution reaction was systematically studied. The R-CMO electrode outperformed the other two electrodes with an overpotential of 349 mV to achieve a current density of 10 mA cm⁻², whereas the B-CMO and S-CMO exhibited an overpotential of 369 and 384 mV, respectively. Thus, the R-CMO electrode is anticipated to be a viable electrode material with appreciable electrocatalytic activity for oxygen evolution reaction.

2. Experimental

2.1. Materials

Analytical grade chemicals were employed in the experiment exactly as they were received. Sigma Aldrich Co., South Korea provided the Co(NO₃)₂·6H₂O (cobalt nitrate hexahydrate), and Na₂MoO₄·2H₂O (sodium molybdate dihydrate). Daesung Chemicals in South Korea supplied the ethanol and ethyleneglycol.

2.2. Synthesis of CoMoO₄ Nanostructured Materials

Different nanostructured particles of CoMoO₄ were synthesized via simple hydrothermal and solvothermal methods with subsequent annealing treatment. In a typical synthesis procedure, 50 mmol of cobalt nitrate hexahydrate and 50 mmol of sodium molybdate dihydrate were dissolved in 150 mL of DI water, and continuously stirred until a homogeneous mixture was formed. The solution was then transferred to a 200 mL Teflon tube and placed in stainless steel autoclave unit and heated to a temperature of 180 °C for 12 h. Post synthesis, the autoclave unit was allowed to cool down to ambient temperature. The resultant precipitate formed in the autoclave unit was thoroughly washed with water and ethanol to remove undesired particles. Then, the powders were dried at a temperature of 80 °C overnight followed by annealing at an elevated temperature of 400 °C in air for 4 h to obtain rods-like CoMoO₄. For synthesizing buds-like CoMoO₄ and sheets-like CoMoO₄, mixtures of water and ethanol (1:1, v/v), and water and ethyleneglycol (1:1, v/v) were used as solvents, respectively, keeping all the remaining reaction parameters unchanged. The detailed synthesis procedure is illustrated in Scheme 1.

2.3. Materials Characterization

X-ray diffractometry (XRD, PANalytical X’Pert Pro with Cu K radiation source of wavelength = 1.540 A°) was used to analyze the crystal structures and phase purity of the prepared samples. Fourier transform infrared spectroscopy (FT-IR, Perkin Elmer, Waltham, MA, USA) was used to analyze the chemical bonds present in the materials. A field-emission scanning electron microscopy (FESEM, S-4800, Hitachi, Japan) with an X-ray column attached was used to examine the samples’ surface morphology and elemental composition. High-resolution transmission electron microscopy was performed using (HRTEM, Tecnai G² F20 S-Twin, Hillsboro, OR, USA) with a field-emission electron gun in Schottky mode set to 200 kV. The composition and oxidation states of the materials were examined using X-ray photoelectron spectroscopy (XPS, K-alpha, Thermo Scientific, Waltham, MA, USA) with Al K X-ray as monochromatic radiation source (1486.6 eV).

2.4. Electrochemical Characterization

In a 1.0 M KOH aqueous electrolyte that had been nitrogen-purged, all electrochemical experiments were conducted using a Biologic VSP-150 electrochemical workstation in a three-electrode cell, using the Hg/HgO as reference electrode, Platinum (Pt) mesh as counter electrode, and as-prepared CoMoO₄ material as working electrode. The working electrode was prepared using a slurry comprising active material, conductive carbon block, and poly(vinylidene fluoride) with a weight percentage of 80:10:10. Then, the obtained slurry was coated onto a pretreated Ni foam (1 × 1 cm²) and dried at 80 °C overnight. The mass of the active material present on the electrodes was determined by weighing before and after coating and determined to be ~2 mg cm⁻².

The following Nernst equation was used to modify all of the potentials in this work in relation to the reversible hydrogen electrode (RHE) [32]:

$$E_{RHE}=0.095+E_{Hg/HgO}+0.0591 p^H$$

(1)

The polarization curves were measured at 5 mV s⁻¹ and the double-layer capacitance ($C_{dl}$) values were determined using cyclic voltammetry (CV) measurements in the non-faradaic potential region between 1.15 and 1.25 V vs. RHE at various scan rates of 10, 20, 30, 40, 50, 60, and 70 mV s⁻¹. The value of $C_{dl}$ in mF is obtained from the linear slope values obtained by graphing the current density differences (ΔJ) against the scan rates. Electrochemical active surface area (ECSA) is calculated using the Equation (2):

$$ECSA=\frac{C_{dl}}{C_s}$$

(2)

where the $C_s$ value is 0.04 mF cm⁻² in alkaline electrolyte [33], and $C_{dl}$ is the double-layer capacitance. Electrochemical impedance spectroscopy (EIS) is measured in the frequency range of 100 MHz to 100 mHz.

3. Results and Discussion

3.1. Phase and Microstructural Analysis

An X-ray diffraction (XRD) study was used to analyze the CoMoO₄ material’s crystalline structure and phase purity. According to the typical pattern of CoMoO₄ as shown in Figure 1a, all distinct diffraction peaks are accurately indexed to their respective planes of reflection. Additionally, the XRD pattern reveals that the samples are monoclinic crystals and belong to the space group C2/m with space group number 12 [34]. The diffraction peak positions corresponding to the three CoMoO₄ samples located around the 2θ values of 13.14, 19.04, 23.24, 25.45, 26.42, 27.14, 28.37, 32.01, 33.66, 36.70, 38.75, 40.15, 43.42, 45.17, 47.48, 52.04, 53.46, 58.27, 60.04, and 64.44° are attributed to their respective planes of reflection (hkl) values of (001), (−201), (021), (201), (002), (−112), (−311), (−131), (−222), (400), (040), (003), (−422), (113), (241), (−204), (−441), (024), (−424), and (243). As there are no additional peaks except those characteristic of CoMoO₄ in the XRD pattern, this indicates the as-synthesized samples are phase pure.

In addition, using the following equations (Equations (1) and (2)) the crystallite sizes (D) of the nanostructured materials are determined to be 84.62, 97.16, and 148.09 nm and the cell volumes (v) are 635.51, 637.53, and 644.01 ${Å}^3$, corresponding to R-CMO, B-CMO, and S-CMO, respectively [35,36].

$$\mathrm{Crystallite} \mathrm{size} \left(D\right)=\frac{K\lambda }{Hcos\theta }$$

(3)

$$\mathrm{Cell} \mathrm{volume} \left(v\right)=abc·sin\beta$$

(4)

where D is crystallite size in nm, K is shape factor (0.9), λ is wavelength of the X-rays (0.1540598 nm for Cu K_α1 radiation), H is full width at half maximum intensity in radians, and θ is peak position in degrees. The parameters, a, b, c, and β are lattice constants.

The bonding nature in CoMoO₄ material was assessed using Fourier transform infrared (FT-IR) spectroscopy in the wavenumber range of 500–4000 cm⁻¹ as shown in Figure 1b. The spectra of all the three samples appear almost identical, indicating that the three samples have similar compositions. Peaks appearing at 614 and 700 cm⁻¹ are attributed to the vibrational mode of Mo-O and v₃ vibrational mode of MoO₄ in CoMoO₄. The sharp peaks appearing at 783 and 838 cm⁻¹ represent the stretching vibrations of Mo-O-Mo. The stretching vibration of MoO₄ in CoMoO₄ is represented by the band at 932 cm⁻¹. The bands near 1600 cm⁻¹ and 3400 cm⁻¹ appear due to bending and stretching vibrations of the OH⁻ group on the material’s surface [37,38,39].

The as-synthesized CoMoO₄ samples were further analyzed using SEM, to understand their morphological features and are shown in Figure 2. The utilization of different solvents apparently influenced the morphologies of the nanostructured materials. When DI water was used as a solvent medium, rods-like particles with several micrometre lengths were obtained (Figure 2a–c). Buds-like nanostructured particles were obtained when a mixture of DI water and ethanol was used as a solvent (Figure 2d–f). However, when a mixture of DI water and ethyleneglycol was used as a solvent, sheets-like nanostructured particles were obtained (Figure 2g–i). The rods-like particles appear to be aligned randomly with more void spaces in between. In contrast, the buds-like, and sheets-like particles were formed bulkily with relative fewer void spaces in between. Consequently, the effective contact area of the rods-like particles is greater compared with buds-like, and sheets-like particles. This is anticipated to enhance the utilization of more electroactive sites to interact with the electrolyte and improve the electrocatalytic performance of the electrode [40,41]. Furthermore, the EDS spectrum (Figure 2j) of the R-CMO confirms the presence of the individual elements in CoMoO₄.

The TEM analysis was further used to evaluate the particle formation and self-assembly of the as-prepared CoMoO₄ samples. TEM analysis was performed for the R-CMO catalyst due to its superior electro-catalytic activity compared with the other two electrodes. The low- and high-resolution TEM images are shown in Figure 3a–c. The nanostructured particles, as observed in the TEM image, are primary particles for the formation of rod-like morphologies through the self-assembly process [42]. The interplanar distance was determined to be 0.39 nm corresponding to the lattice plane (021), which is also consistent with the XRD analysis. The selected area electron diffraction (SAED) pattern (Figure 3d) of the sample demonstrates its polycrystalline nature. The lattice planes of the SAED pattern are indexed according to their d-spacing values as determined using ImageJ software.

The R-CMO sample was further investigated using X-ray photoelectron spectroscopy (XPS) to study the surface-chemical composition and chemical states attributed to its superior electrochemical performance compared with the other two specimens, as shown in Figure 4. The XPS survey scan is displayed in Figure 4a, indicating the R-CMO sample contained Co, Mo, and O species. Figure 4b depicts the Co 2p core level spectrum. The spin-orbit states of Co 2p_1/2, Co 2p_3/2, and their related satellite peaks were identified in four regions. The +3 and +2 oxidation states of the spectrum were further divided into two peaks. The peaks appearing at 780.3 eV (Co1), and 781.5 eV (Co2) belong to Co 2p_3/2, and 796.1 eV (Co3), and 797.3 eV (Co4) belong to Co 2p_1/2, respectively, and reflect the Co³⁺ and Co²⁺ states of Co. Similarly, Co 2p_3/2 and Co 2p_1/2 have satellite peaks appearing at 787.3 eV and 803.1 eV, respectively [43,44]. Additionally, the presence of the Co²⁺ oxidation state is confirmed by the energy gap of 16.2 eV between the two main peaks [43,45]. In the Mo 3d spectrum, two splitting doublets associated with the Mo 3d_5/2 and Mo 3d_3/2 states are found to appear at 231.9 and 235.1 eV, respectively, as shown in Figure 4c. It demonstrates that the molybdenum in the R-CMO sample is in the Mo⁶⁺ oxidation state. Additionally, it is also confirmed by the difference of ~3.6 V in binding energy between the Mo 3d_5/2 and Mo 3d_3/2 states [43,45]. The XPS spectra of O 1s was depicted in Figure 4d and is fitted into two peaks, designated as O1 and O2, located at 530.2 and 531.7 eV, respectively. The M-O bond and M-OH bond (M = Mo and Co) of the surface-adsorbed water molecules present on the surface of the material, respectively, are represented by the O1 peak and O2 peak, respectively [46,47]. Thus, the XPS study confirms the successful formation of CoMoO₄.

3.2. OER Performance

In a nitrogen gas-saturated solution of 1.0 M aqueous KOH, the electrocatalytic performance of the nanostructured materials towards oxygen evolution reaction was assessed using cyclic voltammetry (CV), linear seep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The OER polarization curves of the R-CMO, B-CMO, and S-CMO catalysts with IR correction are shown in comparison with that of the bare Ni substrate in Figure 5a. The overpotential values of the catalysts are found to be 349, 369, and 384 mV corresponding to R-CMO, B-CMO, and S-CMO, with onset potentials of 1.580, 1.599, and 1.614 V vs. RHE, respectively, to achieve a current density of 10 mA cm⁻². The overpotentials of the three catalysts are observed to be nearly identical, with a small difference of about 20 mV. However, R-CMO catalyst is found to exhibit higher electrocatalytic activity compared with the other two as-prepared catalysts and evidenced by its lower overpotential and onset potential. The smaller crystallite size and higher active surface area of R-CMO are the main factors influencing its performance. These are also the main driving forces in promoting ion transportation across the void spaces and boosting the electrocatalytic OER activity [24]. The overpotential of R-CMO catalyst outperformed many previously reported non-noble metal OER electrocatalysts (

Table 1. Comparison of OER performance of present work with some of the representative non-noble catalysts.

Catalyst	Substrate	Electrolyte	Overpotential (mV) @ Current Density (mA cm−2)	References
R-CMO	Ni foam	1.0 M KOH	349@10	This work
MWCNT/Au/Co3O4	GCE	1.0 M KOH	350@10	[48]
Zn-CoSe2 Nanosheets	Carbon fabric collector	1.0 M KOH	356@10	[49]
Co/CeO2	GCE	1.0 M KOH	365@10	[50]
B-CMO	Ni foam	1.0 M KOH	369@10	This work
Co2P/NPCNTs	GCE	1.0 M KOH	370@10	[51]
Co/ZrO2	GCE	1.0 M KOH	373@10	[50]
NiCo Nanocages	GCE	1.0 M KOH	380@10	[52]
S-CMO	Ni foam	1.0 M KOH	384@10	This work
Co/TiO2	GCE	1.0 M KOH	390@10	[50]
NiCo2O4 Nanoflakes/Ti4O7	GCE	1.0 M KOH	398@10	[53]
CoP Hollow polyhedrons	GCE	1.0 M KOH	400@10	[54]
CeO2/Co(OH)2	GCE	1.0 M KOH	410@10	[55]

).

The Tafel slopes of the polarization curves of the catalytic materials are determined based on LSV curves using equation, $\eta =b\log j+a$, here $\eta$represents overpotential, b stands for Tafel’s slope, j for current density, and a is the constant, as shown in Figure 5b [19]. The Tafel slope of R-CMO is 165 mV decade⁻¹, which is a smaller value compared with 168 mV decade⁻¹ corresponding to B-CMO and 180 mV decade⁻¹ corresponding to S-CMO indicating higher catalytic kinetics towards OER process. The EIS was also used to investigate the reaction kinetics of the catalysts. The EIS measurements were conducted for all the catalysts at the potentials of their corresponding overpotentials vs. Hg/HgO obtained from the respective LSV curves, i.e., 0.63, 0.67, and 0.68 V for R-CMO, B-CMO, and S-CMO, respectively. Figure 5c depicts the Nyquist plots of the catalysts. R-CMO catalyst has a lower charge transfer resistance $\left(R_s\right)$of 1.30 Ω compared with B-CMO (1.37 Ω) and S-CMO (1.44 Ω) catalysts, indicating its faster kinetics towards OER activity [19].

Furthermore, as shown in Figure 5d, CV measurements were performed at various scan rates in the non-faradaic region to determine the electrochemically active surface area (ECSA) and double layer capacitance ($C_{dl}$) using Equation (2). The ECSA and ($C_{dl}$) values of R-CMO, B-CMO, S-CMO are 459, 424, and 385 cm², and 18.4, 16.9, and 15.4 mF cm⁻², respectively. The higher ECSA and $C_{dl}$ values corresponding to R-CMO catalyst indicate the exposure of its large number of electroactive sites to interact with the electrolyte facilitating the OER performance [19].

Furthermore, the chronoamperometric current-time (i-t) stability test was conducted at the overpotentials vs. Hg/HgO of the respective catalysts to evaluate the long-term durability of the catalysts as depicted in Figure 5e. The R-CMO catalyst exhibited a relatively high stability up to 12 h with no apparent change in the current density, compared with the other two catalysts. On the other hand, in the cases of B-CMO and S-CMO catalysts, the current response was observed to be unstable in the beginning because of gradual activation of the electrode material. However, after 5 h, the current response was stable and continued to be stable for up to 12 h. The polarization curves of the three catalysts after i-t stability test exhibit negligible changes as depicted in the inset of Figure 5e. The ECSA curves of the three samples are shown in Figure 6.

The following features can be attributed to the higher performance of the R-CMO catalyst.

• The R-CMO catalyst, which has a hierarchical structure made up of a number of rod-like nanostructures, utilizes the Co and Mo ions’ synergistic effect to encourage adequate exposure of a number of active sites to the electrolyte solution, which enhances electrochemical stability and OER performance.
• Rapid ion transportation is made possible by the catalyst’s high electrochemically active surface area, which also offers readily accessible electroactive sites. By reducing electrode resistance, this feature also improves redox diffusion kinetics.
• The R-CMO catalyst’s void space, adorned with many nanostructured rods, increases internal stress and volumetric fluctuations to shield the active material from structural collapse and loosening of the electrical structure during the chronoamperometric stability test.

Based on the above findings, R-CMO could be used as an efficient and high-performing electrocatalyst for OER applications.

4. Conclusions

In conclusion, we described a simple hydrothermal/solvothermal approach to synthesizing CoMoO₄ nanostructured materials with rods-like, buds-like, and sheets-like morphologies which involves altering the solvent media during the synthesis process. The R-CMO catalyst synthesized using water as the solvent medium exhibits lower overpotential of 349 mV to afford a current density of 10 mA cm⁻² with a Tafel’s slope of 165 mV decade⁻¹. When compared with the performance of other catalysts, R-CMO exhibits higher OER performance, which can be attributed to its smaller crystallite size and higher active surface area. This could be the main factor promoting ion transport across void spaces and boosting electrochemical OER activity. Additionally, the chronoamperometry studies demonstrated the R-CMO catalyst’s exceptional stability compared with other catalysts. Thus, the rods-like CoMoO₄ (R-CMO) with higher electrocatalytic OER performance has a great deal of potential for fabricating effective, inexpensive, and widely accessible alternatives for electrochemical water oxidation in place of expensive noble metal based electrocatalysts.