Electrocatalytic Reduction of Nitrate via Co3O4/Ti Cathode Prepared by Electrodeposition Paired With IrO2-RuO2 Anode

1 Introduction

Nitrate (NO₃⁻) contamination of surface water and groundwater is a global environmental problem associated with increasing populations, and its hazards have attracted much attention (Jasper et al., 2014; Khalil et al., 2016; Serio et al., 2018). The accumulation of plant nutrients such as NO₃⁻ and phosphate in water can accelerate eutrophication, a process that increases the biomass of a water body as its biological diversity decreases, for example, due to increases in invertebrates and fish. In the extreme, a state of hypoxia can exist, resulting in the loss of the aquatic ecosystems (Kubicz et al., 2018; Zhang et al., 2021). Although NO₃⁻ is chemically stable, it can be microbially reduced to reactive nitrite in the oral cavity and stomach, which has been linked to liver damage, methemoglobinemia, and cancer in animals (Spalding and Exner, 1993; Elmidaoui et al., 2001; Barakat et al., 2020).

Currently, microbial denitrification is widely used for the large-scale remediation of NO₃⁻ pollution (Clauwaert et al., 2007; Della Rocca and Belgiorno V Meriç, 2007). Many other methods of NO₃⁻ removal have been explored such as reverse osmosis, ion exchange, ammonia stripping, electrodialysis, catalytic reduction, and electrocatalytic reduction (Kapoor and Viraraghavan, 1997; Yang and Lee, 2005; Della Rocca and Belgiorno V Meriç, 2007). Among these techniques, the electrocatalytic reduction of NO₃⁻ is a promising and clean technology because the electron reductants neither introduce pollutants nor adversely affect the environment (Garcia-Segura et al., 2018; Gayen et al., 2018).

The mechanism of the electrochemical NO₃⁻ reduction reaction (NO₃⁻-RR) involves anodic oxidation and cathodic reduction in which NO₃⁻ is reduced to NO₂⁻, NH₄⁺, and N₂ on the active sites of the cathode according to Eqs 1–3 (Zhang et al., 2021):

$\mathrm{N}{\mathrm{O}}_3^{-}+2{\mathrm{e}}^{-}+{\mathrm{H}}_2\mathrm{O}\to \mathrm{N}{\mathrm{O}}_2^{-}+2\mathrm{O}{\mathrm{H}}^{-},(1)$

$\mathrm{N}{\mathrm{O}}_2^{-}+6{\mathrm{e}}^{-}+6{\mathrm{H}}_{2}O\to \mathrm{N}{\mathrm{H}}_4^{+}+8\mathrm{O}{\mathrm{H}}^{-},(2)$

$2\mathrm{N}{\mathrm{O}}_3^{-}+10{\mathrm{e}}^{-}+6{\mathrm{H}}_2\mathrm{O}\to {\mathrm{N}}_2+12\mathrm{O}{\mathrm{H}}^{-}.(3)$

The choice of the cathode material is important in this process. To date, most studies have used high-cost noble metal cathodes, such as Pt, Rh, and Pd, which may limit their commercial application (Taguchi and Feliu, 2007; Yang et al., 2014; Soto-Hernández et al., 2019). Co₃O₄ is a cost-effective catalyst, and the preparation of a CuO-Co₃O₄/Ti electrode by the sol-gel method for electrochemical reduction of NO₃⁻ was recently reported (Yang et al., 2020). The system demonstrated the complete removal of NO₃⁻ after 3 h at a current density of 20 mA/cm².

NO₂⁻ and NH₄⁺ generated at the cathode (Eqs. (1) and (2)) diffuse to the anode where they are adsorbed onto the surface and subsequently oxidized to NO₃⁻ and N₂ (Eqs. (4) and (5)) (Zhang et al., 2021):

$\mathrm{N}{\mathrm{O}}_2^{-}+{\mathrm{H}}_2\mathrm{O}\to \mathrm{N}{\mathrm{O}}_3^{-}+2{\mathrm{e}}^{-}+2{\mathrm{H}}^{+},(4)$

$2\mathrm{N}{\mathrm{H}}_4^{+}\to {\mathrm{N}}_2+6{\mathrm{e}}^{-}+6{\mathrm{H}}^{+}.(5)$

When Cl⁻ is present in the electrolyte, the following reactions also occur at the anode (Eqs. 6–9) (Zhang et al., 2021):

$2\mathrm{C}{\mathrm{l}}^{-}\to \mathrm{C}{\mathrm{l}}_2+2{\mathrm{e}}^{-},(6)$

$\mathrm{C}{\mathrm{l}}_2+{\mathrm{H}}_2\mathrm{O}\to \mathrm{H}\mathrm{O}\mathrm{C}\mathrm{l}+\mathrm{C}{\mathrm{l}}^{-}+{\mathrm{H}}^{+},(7)$

$\mathrm{H}\mathrm{O}\mathrm{C}\mathrm{l}\to \mathrm{C}\mathrm{l}{\mathrm{O}}^{-}+{\mathrm{H}}^{+},(8)$

$2\mathrm{N}{\mathrm{H}}_4^{+}+3\mathrm{C}\mathrm{l}{\mathrm{O}}^{-}\to {\mathrm{N}}_2+3{\mathrm{H}}_2\mathrm{O}+2{\mathrm{H}}^{+}+3\mathrm{C}{l}^{-}.(9)$

The electrochemical NO₃⁻-RR involves NO₃⁻ reduction at the cathode and ammonium nitrogen (NH₄⁺-N) oxidation at the anode. Cl₂ generated at the anode (Eq. (6)) immediately forms hypochlorite (Eq. (7)), which selectively oxidizes NH₄⁺ to N₂ (Su et al., 2017). Hence, the efficient anodic oxidation of chloride ions is a key requirement for this process, and the anode materials used in the chlor-alkali industry, which obtain Cl₂ by electrolysis of sodium chloride, provide a useful reference (Yi et al., 2007). Among these materials, IrO₂-RuO₂ is a good choice due to its low overpotential, high chlorine selectivity, and long-term stability (Chen et al., 2007). In addition, the electrocatalytic reduction of NO₃⁻-N is also affected by reaction potential, current, solution pH, battery structure, and anode material.

Here, a catalytic cathode was prepared by the in situ electrodeposition of Co₃O₄ on a titanium substrate (Co₃O₄/Ti) to obtain improved electrocatalytic performance. IrO₂-RuO₂/Ti was employed as the anode for the effective removal of NH₄⁺-N and TN. The aim of this study was to obtain simultaneous electrochemical NO₃⁻ reduction and oxidation of the in situ-generated NO₂⁻ and NH₄⁺ into N₂ gas. The morphology and structure of Co₃O₄/Ti were characterized using conventional methods, and its performance in NO₃⁻ removal was evaluated under different operating conditions. The current efficiency (CE) and energy consumption (EC) of the system were also measured to assess its commercial application.

2 Experimental Section

2.1 Chemicals and Materials

The Ti mesh and Ti plate (99.5% purity, 0.6 mm, 10 mesh) were purchased from Lanruiyinde Electrochemical Materials Co., Ltd. (China). The Pt plate was obtained from Aidahengsheng Co., Ltd., (Tianjin, China). All chemicals were of analytical grade. Potassium nitrate and sodium hydroxide were purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Cobalt nitrate hexahydrate, sodium eicosyl, hexachloroiridic acid, and ruthenium (III) chloride were obtained from Macklin Biochemical Technology Co., Ltd. (Shanghai, China). Solutions were prepared using deionized water (>15 MΩ cm) obtained from an Elix^® 3 purification system (Millipore, United States). Simulated wastewater was prepared by adding potassium nitrate to deionized water.

2.2 Preparation of Co₃O₄/Ti Cathode and IrO₂-RuO₂/Ti Anode

Samples of the Ti mesh and Ti plate (3 × 4 cm, 12 cm²) were degreased with NaOH solution (40 wt%) at 95°C for 2 h before etching by boiling in oxalic acid solution (10 wt%) for 2 h. The treated samples were then rinsed with deionized water and stored in ethanol until further use.

As shown in Figure 1, the Co₃O₄/Ti electrode was prepared using an electrodeposition method. A three-electrode system was employed in a single compartment cell using the pretreated Ti mesh as the cathode, the Pt plate as the anode, and an Ag/AgCl reference electrode. The electrodeposition solution comprised boric acid (0.5 M), cobalt nitrate hexahydrate (0.1 M), and sodium eicosyl sulfonate (2.0 g/L). Following electrodeposition at a current of 0.25 A for 5 min, the electrode was cleaned with deionized water and oven-dried (60°C) before heating at 5°C/min to 500°C (hold 2 h) in a muffle furnace to effect calcination. The treated samples were allowed to cool naturally to room temperature.

FIGURE 1

FIGURE 1. Schematic of the preparation procedure.

The IrO₂-RuO₂/Ti anode was prepared by using a thermal decomposition method. A mixed solution of hexachloroiridic acid and ruthenium (III) chloride in n-butanol (molar ratio, 2:1) was evenly coated onto the surfaces of the pretreated titanium plate, dried at 105°C for 10 min, and then calcined at 500°C for 15 min. The process was repeated until the weight of the titanium plate increased by about 10 g/cm². Finally, the electrode was washed with deionized water before use.

2.3 Characterization of the Co₃O₄/Ti Cathode

Surface morphology and elemental composition were studied by field-emission scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) on a Phenom ProX system (Thermo Fisher Scientific, United States) at an accelerating voltage of 15 kV. The crystal structure of Co₃O₄ was examined by X-ray diffraction (XRD) with an X’pert Powder system (Malvern Panalytical, Malvern, UK) using Cu Kα (λ = 1.5406 Å) irradiation.

2.4 Electrochemical Measurements

NO₃⁻-RR tests were performed in a single chamber electrolytic cell (200 ml) using a three-electrode system, with Co₃O₄/Ti (or Ti as required), Pt plate, and Ag/AgCl as the working, counter, and reference electrodes, respectively. The electrolyte was prepared using Na₂SO₄ (0.1 M) and different concentrations of NO₃⁻-N (KNO₃) as required. Linear sweep voltammetry (LSV), and electrolysis tests were performed in an electrochemical workstation (Metrohm Autolab M204, Switzerland). Prior to the electrochemical test, oxygen was removed by bubbling high-purity N₂ through the electrolyte for ≥20 min, and continuously fed during the experiments.

Electrolysis measurements were performed at an optimum current density of 15 mA/cm², and aliquots of the reaction solutions (2 ml) were removed at predetermined time intervals to measure the concentrations of NO₃⁻-N, NO₂⁻-N, and NH₄⁺-N. The effects of chlorine on NO₃⁻-RR and the stability of the Co₃O₄/Ti cathode electrode were assessed at a current density of 15 mA/cm² for 2 h and an initial NO₃⁻-N concentration of 100 mg/L.

2.5 Analytical Methods

During the NO₃⁻-RR, the formation of NO, N₂O, and NH₃ are negligible, and hence, the generated gaseous products can be considered as N₂ (Teng et al., 2018). UV-Vis spectroscopy was used to measure the concentrations of NO₃⁻-N, NO₂⁻-N, NH₄⁺-N, and total nitrogen (TN) (Evolution 201, Thermofisher Scientific Co., Ltd.), and their removal efficiencies were calculated according to Eqs (10)–(12):

$N{O}_3^{-}-N removal=\frac{C_0\left(N{O}_3^{-}-N\right)-C_t\left(N{O}_3^{-}-N\right)}{C_0\left(N{O}_3^{-}-N\right)}\times 100\%,(10)$

$N{H}_4^{+}-N generation=\frac{C_t(N{H}_4^{+}-N)}{C_0\left(N{O}_3^{-}-N\right)}\times 100\%,(11)$

$TN removal=\frac{C_0\left(TN\right)-C_t\left(TN\right)}{C_0\left(TN\right)}\times 100\%,(12)$

where C₀(NO₃⁻-N) (mg/L) is the initial concentration of NO₃⁻-N, C_t(NO₃⁻-N) (mg/L) is the concentration of NO₃⁻-N at time t, C_t(NH₄⁺-N) (mg/L) is the concentration of NH₄⁺-N at time t, C₀(TN) (mg/L) is the initial concentration of TN, and C_t(TN) (mg/L) is the concentration of TN at time t.

EC was calculated using Eq. 13 (Zhang et al., 2016):

$\mathrm{E}\mathrm{C}=\frac{\mathrm{U}\mathrm{I}\mathrm{t}}{\mathrm{V}\left({\mathrm{C}}_0-{\mathrm{C}}_{\mathrm{t}}\right)},(13)$

where U is the cell potential (V), I is the current (A), t is the reaction time (h), and V is the volume of reaction solution (L).

The CE for TN removal rates was obtained using Eq. 14:

$\mathrm{C}\mathrm{E}(\%)=\frac{({\mathrm{C}}_0-{\mathrm{C}}_{\mathrm{t}})\times \mathrm{V}}{\mathrm{M}\times \mathrm{Q}}\times \mathrm{n}\times 96485\times 100\%,(14)$

where M is the molar mass of N (14 g/mol), Q is the amount of electricity passing through the electrode, and n is the number of electrons obtained from the complete reduction of NO₃⁻-N (calculated according to the conversion of NO₃⁻ to N, n = 5).

3 Results and Discussion

3.1 Electrode Characterizations and Chemical Tests

SEM was used to depict the electrode surface morphology of Co₃O₄/Ti. Figure 2 shows that spherical particles (3–5 μm) of Co₃O₄ were observed on the surface of Co₃O₄/Ti at different magnifications, confirming its deposition on the Ti mesh. SEM-EDS elemental mapping of a surface region of the Co₃O₄/Ti cathode (Figure 3) gave a value of 26.26 atom% for Co, indicating that the element was successfully deposited on the titanium mesh.

FIGURE 2

FIGURE 2. SEM image of Co₃O₄/Ti at different resolutions.

FIGURE 3

FIGURE 3. EDS elemental analysis of the surface of Co₃O₄/Ti cathode.

Figure 4 shows the XRD patterns of the calcined Co₃O₄/Ti electrode and their comparison with the reference powder patterns of cubic phase Co₃O₄ (PDF#42–1467) and Ti (PDF#44–1294). The characteristic peaks observed at 2θ of 35.1°, 38.4°, 40.2°, 53.0°, 62.9°, 70.7°, 76.2°, and 77.4° correspond to (100), (002), (101), (102), (110), (103), (112), and (201) planes of Ti (PDF#44–1294), respectively (Figure 4A). Inspection of the enlarged pattern obtained from the Co₃O₄/Ti cathode (Figure 4B) showed that the main peaks of Co₃O₄ at 2θ=31.3°, 36.9°, 44.8°, 59.4°, 65.2°, and 74.1°, correspond to the (220), (311), (400), (511), (440), and (620) planes of Co₃O₄, respectively. These results were in good agreement with the standard cubic phase (PDF#42–1467).

FIGURE 4

FIGURE 4. Crystal structure of Co₃O₄/Ti cathode and comparison with the reference XRD powder patterns: (A) XRD patterns of Ti and Co₃O₄/Ti cathodes; (B) enlarged XRD patterns of Co₃O₄/Ti cathode.

LSV was used to evaluate the electrocatalytic performance of the catalysts toward NO₃⁻-RR. Figure 5A shows the LSV curves obtained with Co₃O₄/Ti and Ti in the presence of NO₃⁻-N. The onset potential for NO₃⁻-RR using the Co₃O₄/Ti cathode (-0.7 V) was more positive than that using the Ti mesh (-1.0 V), indicating the improved performance with the composite catalyst. From −0.7 to −1.6 V, Co₃O₄/Ti gave a larger current response at all potentials due to its higher activity toward the NO₃⁻-RR compared with the Ti mesh. Figure 5B shows the effects of increasing NO₃⁻-N (0–500 mg/L) using Co₃O₄/Ti as the cathode. In the absence of NO₃⁻-N, the onset potential (i.e., for the electrolysis of water to produce H₂) was −0.9 V. The addition of NO₃⁻ produced a positive shift in the onset potential, and the corresponding current increased with increasing initial NO₃⁻-N due to the enhanced reduction reaction activity.

FIGURE 5

FIGURE 5. LSV curves illustrating the NO₃⁻-N removal performance of the catalysts (0.1 M Na₂SO₄, 10 mV/s). (A) Effects of different catalysts at constant initial NO₃⁻-N concentration (100 mg/L). (B) Effects of increasing initial NO₃⁻-N concentrations using the Co₃O₄/Ti cathode.

3.2 Effects of Electrochemical Reaction Parameters on NO₃⁻-RR Using the Co₃O₄/Ti Cathode

3.2.1 Catalytic Activity of the Co₃O₄/Ti Cathode

To determine the effect of Co₃O₄ on NO₃⁻RR activity, the NO₃⁻-N (100 mg/L) removal efficiencies of the Co₃O₄/Ti and Ti mesh cathodes were compared at a current density of 15 mA/cm² with a Pt plate as the anode (Figure 6). The results showed that the Co₃O₄/Ti cathode could achieve a NO₃⁻-N removal efficiency of ∼98% in 2 h, compared with 6.4% using the Ti mesh, demonstrating the important role of Co₃O₄ in improving the performance of NO₃⁻-RR.

FIGURE 6

FIGURE 6. Removal efficiencies of NO₃⁻-N by the Ti and Co₃O₄/Ti cathodes (Pt anode; [NO₃⁻-N], 100 mg/L, 150 ml; current density, 15 mA/cm²; pH, 7.0; reaction time, 2 h).

3.2.2 Effects of Current Density

Figure 7A,B show the rate of NO₃⁻-N removal using the Co₃O₄/Ti cathode and the corresponding fit of the experimental data to first-order kinetics. The increased removal efficiency with increasing current density over 5–15 mA/cm² could be attributed to enhanced electron transfer on the electrode surface of Co₃O₄/Ti, which increased the rate of NO₃⁻-RR. However, when the current density was increased from 15 to 20 mA/cm², the removal efficiency of NO₃⁻-N did not improve significantly. At higher current densities, the competing hydrogen evolution reaction consumes the extra charge, and the NO₃⁻-N removal efficiency decreases. Figure 7C shows that there was good correspondence between the reduction of NO₃⁻-N and the generation of NH₄⁺-N. The reduction products were NH₄⁺-N and N₂, while NO₂⁻-N was not detected (Figure 7D).

FIGURE 7

FIGURE 7. Effects of current density on the NO₃⁻-RR using the Co₃O₄/Ti cathode (Pt anode; [NO₃⁻-N], 100 mg/L, 150 ml; initial pH, 7.0; reaction time, 2 h): (A) and (B) rate of loss of NO₃⁻-N and the fit of the data to first-order kinetics; (C) rate of generation of NH₄⁺-N; and (D) distribution of the products formed.

3.2.3 Effect of Initial NO₃⁻-N Concentration

The effects of initial NO₃⁻N concentration on its removal efficiency using the Co₃O₄/Ti cathode and the generation of reduction products are shown in Figure 8. At initial NO₃⁻-N concentrations of <100 mg/L, the removal efficiency of the system was close to 100% at 2 h; and the corresponding reduction products were NH₄⁺-N (60%) and N₂. At an initial NO₃⁻-N concentration of 200 mg/L, the removal efficiency decreased to ∼58%, while the NH₄⁺-N generation efficiency increased to ∼79%. Under this condition, the higher initial NO₃⁻-N concentration suppressed the competing hydrogen evolution reaction, thus reducing its charge consumption at the electrode.

FIGURE 8

FIGURE 8. Effects of different initial NO₃⁻-N concentrations on NO₃⁻-RR using the Co₃O₄/Ti cathode (Pt anode; reaction solution, 150 ml; current density, 15 mA/cm²; initial pH, 7.0; reaction time, 2 h): (A) and (B) Rate of loss of NO₃⁻-N and the fit of the data to first-order kinetics; (C) generation of NH₄⁺-N; and (D) product distributions.

3.3 Effects of Cl⁻

The main product of electrocatalytic NO₃⁻ reduction is NH₄⁺, which is also a contaminant requiring removal. However, in the presence of Cl⁻, which is widely present in drinking water and industrial water, the active species participating in the oxidative transformation of NH₄⁺-N to N₂ at the anode (Eqs 6–9) will increase TN removal. The IrO₂-RuO₂/Ti electrode is widely employed in the chlor-alkali industry because of its high chlorine evolution performance. To investigate the effects of Cl⁻ on NH₄⁺-N generation and NO₃⁻-N removal, various concentrations of Cl⁻ were presented to a Co₃O₄/Ti/IrO₂-RuO₂/Ti NO₃⁻-N removal system (Table 1). As the concentration of Cl⁻ increased from 0 to 2000 mg/L, the removal efficiencies of NO₃⁻-N were all >90%. At 4,000 mg/L Cl⁻, the removal efficiency decreased to 83.99% due to the oxidation of NH₄⁺ to NO₃⁻ by HClO/ClO⁻. The increase in Cl⁻ concentration increased the amount of HClO/ClO⁻ generated by anodic oxidation to reduce NH₄⁺-N to N₂. Hence, NH₄⁺-N generation decreased and TN removal efficiency increased with increasing Cl⁻ concentration. The TN removal efficiency reached 78.1% with negligible NH₄⁺-N generation (0.34%) and without NO₂⁻-N accumulation.

TABLE 1

TABLE 1. Effects of Cl⁻ on the Co₃O₄/Ti/IrO₂-RuO₂/Ti NO₃⁻-N removal system.

3.4 Long-Term Stability

In addition to the initial activity, the long-term performance of a catalyst is an essential requirement for its commercial application. Figure 9 shows the changes in NO₃⁻-N removal and distribution of generated products over 4 h, and 10 consecutive cycles of 2 h each, using the system. At an initial concentration of 100 mg/L, almost all NO₃⁻-N is converted into N₂ after 4 h (Figure 9A). After 10 cycles (Figure 9B), the removal efficiencies of NO₃⁻-N (∼90%) and TN remained unchanged.

FIGURE 9

FIGURE 9. Changes in NO₃⁻-N removal and the distribution of generated products for the Co₃O₄/Ti/IrO₂-RuO₂/Ti system ([NO₃⁻-N], 100 mg/L, 150 ml; current density, 15 mA/cm²; pH, 7.0; cycle time, 2 h). (A) Changes over 4 h. (B) Changes over 10 cycles.

3.5 EC and CE

EC and CE are key evaluation factors for the commercial electrochemical treatment process (Zeng et al., 2020). The EC and CE under different process conditions using the system were calculated. It can be seen from Figure 10A,B that within 1 h after the start of the reaction, EC is lower and CE is higher than those of the follow-up experiments, but the NO₃⁻-N removal rate is only 58.52%. After 2 h, the NO₃⁻-N removal efficiency reaches 93.39% with an EC of 0.10 kW h/g NO₃⁻-N and a CE of 40.3%. There was no significant improvement in the follow-up, but the EC continued to rise, and the CE continued to decline.

FIGURE 10

FIGURE 10. Effects of reaction time and initial NO₃⁻-N concentrations on the operational efficiency. (A) and (C) EC; (B) and (D) CE (pH, 7.0; current density, 15 mA/cm²; [Cl⁻], 2000 mg/L; reaction time, 2 h).

The effect of the initial NO₃⁻-N concentration is demonstrated in Figures 10C,D. As the NO₃⁻-N concentration increased, the EC decreased and CE increased. This can be explained by the increase in the contact area between NO₃⁻-N and the electrode surface with increasing concentrations, which promotes the reduction reaction. From an economic viewpoint, the results indicate that the Co₃O₄/Ti/IrO₂-RuO₂/Ti electrocatalytic process is more suitable for wastewater with high concentrations of NO₃⁻. The small amount of NO₃⁻ remaining in the electrochemically treated wastewater can be removed by other processes, such as the electrocatalytic removal of NO₃⁻-N, which can be combined with constructed wetlands for wastewater control/remediation.

4 Conclusion

A Co₃O₄/Ti electrode was successfully prepared by electrodeposition, and the material showed good electrocatalytic performance toward NO₃⁻-RR. At an initial concentration of 100 mg/L NO₃⁻-N, the removal rate was ∼98% in 2 h (Pt anode; pH, 7.0; current density, 15 mA/cm²). The corresponding generation of NH₄⁺-N was ∼60%, while NO₂⁻-N was not detected. When IrO₂-RuO₂/Ti was employed as the anode in the presence of Cl⁻ (2000 mg/L), the removal efficiencies for NO₃⁻-N and TN under the same operating conditions were ∼91% and ∼60%, respectively, with an EC of 0.10 kW h/g NO₃⁻-N and a CE of 40.3%. After 4 h of continuous operation, 100% of NO₃⁻-N was converted into N₂. In addition, the system could maintain the removal efficiencies of ∼90% and ∼60% for NO₃⁻-N and TN, respectively, after 10 consecutive cycles (2 h each). This work provides a simple preparation method of electrodeposited Co₃O₄/Ti with good catalytic performance and stability, which provides a new preparation strategy for the Co₃O₄ catalytic electrode.

Data Availability Statement

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

Author Contributions

CW: conceptualization, methodology, data analysis, and writing—original draft. ZC: data curation. HH: validation. HL: resources and funding acquisition. SW: conceptualization, investigation, and writing—review and editing.

Funding

This work was supported by the National Natural Science Foundation of China (grant numbers 51978181, 51808527, 51727812, and 52131003).

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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