Boosting the Bifunctional Catalytic Activity of La_0.85Y_0.15Ni_0.7Fe_0.3O₃ Perovskite Air Electrode with Facile Hybrid Strategy of Metallic Oxide for Rechargeable Zn–Air Batteries

Abstract

Developing cost-effective, sustainable, and high-performance air electrode catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a significant challenge in the advancement of rechargeable zinc–air batteries (ZABs). Herein, we successfully construct a vacancy-rich heterogeneous perovskite La_0.85Y_0.15Ni_0.7Fe_0.3O₃ (LYNF) hybridized with Co₃O₄ spinel nanoparticles using a simple chemical bath-assisted method. The Co₃O₄ composite LYNF material is systematically evaluated as the bifunctional catalyst for ZABs in the proportion of 25 wt%, 50w t%, and 75 wt% (denoted as LYNF-xCo₃O₄, x = 0.25, 0.5, 0.75). The results confirm an intimate coupling between the perovskite and spinel phases, along with a significant increase in oxygen vacancy concentration. Among the composites, LYNF-0.5Co₃O₄ exhibits the best performance, achieving an ORR onset potential of 0.813 V vs. RHE at −0.1 mA cm⁻² and a lower OER overpotential of 441 mV at 10 mA cm⁻². When applied as the air electrode catalyst in ZABs, LYNF-0.5Co₃O₄ displays the highest discharge voltage and a peak power density of 115 mW cm⁻², representing a 20% improvement over pristine LYNF. The enhanced performance of the LYNF-0.5Co₃O₄ composite is attributed to the accumulation of Co₃O₄ nanoparticles within the LYNF matrix, which introduces numerous electrochemically active sites and facilitates the charge and mass transport during the catalytic process in ZABs.

1. Introduction

The global energy crisis, coupled with the escalating greenhouse effect, has presented formidable challenges to sustainable development worldwide. Given these critical issues, substantial research efforts have been devoted to advancing clean and renewable energy technologies as viable alternatives to conventional fossil fuels [1]. Among the emerging technologies, metal–air batteries [2,3], water splitting [4,5], and carbon dioxide reduction have garnered substantial attention. Metal–air batteries, in particular, stand out due to their fuel-cell-like configuration, in which atmospheric oxygen acts as the cathodic reactant and metals such as zinc, lithium, aluminum, or magnesium serve as anodes [6]. ZABs, owing to their high theoretical energy density, have emerged as focal points of research interest [7]. Nevertheless, the commercial viability of rechargeable ZABs faces challenges such as poor cycle stability, pronounced charge–discharge polarization, and suboptimal energy efficiency [8]. Mitigating these challenges necessitates enhancing the kinetic efficiency of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at air electrodes. Accordingly, the development of efficient bifunctional oxygen electrocatalysts is vital for improving the overall performance of ZABs.

Perovskites are a class of crystalline materials with the general formula ABO₃, whose unique crystal structure endows them with excellent physicochemical properties, thus attracting extensive attention in the fields of catalysis, energy storage, and conversion. Among them, rare-earth transition metal-based perovskites have emerged as a research hotspot in the field of electrocatalysis due to their favorable electrical conductivity, stable structure, and tunable electronic properties [9,10]. Notably, recent studies have elucidated the molecular orbital principles underlying the intrinsic OER and ORR activities in alkaline solutions, highlighting the potential role of LaNiO₃ with an e_g electron configuration in enhancing both ORR and OER activities Strategies to enhance perovskite catalytic activity include cationic and anionic doping [10], the construction of hybrid or composite structures [11,12], and the adoption of diverse preparation methods [13].

In the field of electrocatalysis, hybridization strategies that integrate multiple functional materials have proven effective in modulating active sites and tailoring electronic structures at the atomic level. Such approaches can yield synergistic effects that surpass the performance of individual components, offering a powerful route to design high-performance electrocatalysts [14,15]. Co₃O₄, with its typical spinel structure, is widely recognized as a highly suitable catalyst material for both ORR and OER due to its possession of dual valence states [16,17]. Quan et al. [18] demonstrated the synthesis of SrCo_0.5Fe_0.3Mo_0.2O_3-δ/Co₃O₄ via a simple mixture, achieving overpotential as low as 328 mV. The hybridization of Co₃O₄ with perovskite materials results in biphasic synergies, increasing the number of active sites. Zhang et al. [19] exhibited the fabrication of Co₃O₄-modified blood powder doped with mesoporous carbon, demonstrating impressive ORR and OER potentials of 0.83 V and 380 mV, respectively. In our previous study, Y and Fe co-doped LaNiO₃ perovskite oxide (La_0.85Y_0.15Ni_0.7Fe_0.3O₃, LYNF) showed a better OER performance with overpotential of 510 mV [20]. However, the effect of coupling LYNF with Co₃O₄ spinel has not been thoroughly investigated in ZABs.

This research identifies the high polarization arising from sluggish ORR and OER kinetics as the core bottleneck hindering the commercialization of rechargeable ZABs, leading to poor stability and low energy efficiency. To address this fundamental challenge, we developed a high-performance bifunctional catalyst, LYNF-xCo₃O₄. Utilizing a facile chemical bath-assisted composite strategy [21,22], we successfully constructed a LYNF-xCo₃O₄ heterostructure featuring abundant interfaces, a high concentration of oxygen vacancies, and strong synergistic effects. This design significantly enhanced intrinsic ORR and OER activity, increased the density of active sites, improved charge transport capability, and ultimately boosted catalyst stability [23,24]. Experimental results demonstrate that the optimal composite, LYNF-0.5Co₃O₄, achieves remarkably low ORR and OER overpotentials and Tafel slopes, exhibits improved stability, and enhances overall energy efficiency. These findings provide an effective material solution for overcoming the key challenges facing rechargeable ZABs. In this work, LYNF is hybridized with Co₃O₄ spinel nanoparticles using a simple chemical bath-assisted method. A series of LYNF-xCo₃O₄ composites (x = 0, 0.25, 0.5, 0.75) are synthesized and evaluated for their ORR/OER performance. Furthermore, their applicability as air electrode catalysts in ZABs is systematically investigated.

2. Results and Discussion

2.1. Material Structure and Analysis

The samples of LYNF, Co₃O₄, and LYNF-xCo₃O₄ (x = 0.25, 0.5, 0.75) were analyzed by powder XRD. As shown in Figure 1, the diffraction peaks located at 31.3°, 36.8°, 38.6°, 44.8°, 55.6°, 59.4°, 65.2°, 74.1°, and 77.3° can be well detected as Co₃O₄ [25,26]. The XRD Rietveld image of LYNF-Co₃O₄ is shown in Figure S4. The XRD pattern reveals excellent agreement between the observed diffraction peaks (red “obs.”) and the calculated peaks (black “calc.”) derived from the crystal structures of LYNF and Co₃O₄. The characteristic peak positions for LYNF and Co₃O₄ (indicated by vertical markers) correspond well to the experimental pattern. The absence of any unidentified diffraction peaks confirms the high phase purity of the sample, with no detectable impurity phases. All perovskite phases exhibit a cubic structure with a space group of Pm-3m. Importantly, in all composite samples, the characteristic diffraction peaks of the perovskite phase match those of LYNF, and the characteristic peaks of the spinel phase align with those of Co₃O₄. This indicates that the chemical bath-assisted composite process does not alter the composition of the spinel and perovskite phases [27]. The increasing intensity of the Co₃O₄-related peaks with higher Co₃O₄ content further suggests a uniform and controllable incorporation of spinel nanoparticles into the LYNF matrix.

To investigate the internal microstructure and element distribution of perovskite catalysts, transmission electron microscopy (TEM) characterization was performed. The TEM images of LYNF-0.5Co₃O₄ in Figure 2a reveal a heterogeneous architecture, with darker regions assigned to Co₃O₄ nanoparticles and brighter regions corresponding to the perovskite matrix. High-resolution TEM (HRTEM), as seen in Figure 2b, shows clear lattice fringes with interplanar spacings of 0.245 nm and 0.293 nm, which can be indexed to the (311) plane of Co₃O₄ and the (110) plane of LYNF, respectively. The intimate contact at the interface suggests strong phase interaction without significant agglomeration or phase separation, which is expected to benefit charge transfer and interfacial electron transport. The SEM-EDS images in Figure 3a–g show the uniform distribution of Co, Fe, Y, La, Ni, and O elements in the LYNF-0.5Co₃O₄ sample, indicating homogeneity of the hybrid structure, which is beneficial for improving the OER performance. The SEM images in Figure S2 show microstructures of LYNF-Co₃O₄ composites with different Co₃O₄ doping levels. LYNF-0.25Co₃O₄ (a) has notable agglomeration and dense structure. LYNF-0.5Co₃O₄ (b) exhibits a loose structure, uniform and rich pores, and good particle dispersion, optimal for exposing active sites and mass transfer. LYNF-0.75Co₃O₄ (c) has enhanced agglomeration and squeezed pores. Thus, LYNF-0.5Co₃O₄ has the best morphology, benefiting catalytic reactions via structural advantages.

X-ray photoelectron spectroscopy (XPS) was conducted to further probe the electronic structures and surface chemistry of the samples. Figure 4a shows the Ni 2p spectra of LYNF and LYNF-0.5Co₃O₄. The peaks at 854.3 and 872.1 eV are assigned to Ni³⁺ 2p_3/2 and Ni²⁺ 2p₁/₂, respectively, confirming the coexistence of Ni²⁺ and Ni³⁺ oxidation states [28,29,30]. A positive shift of 0.2 eV in the Ni 2p_3/2 binding energy in the composite indicates an increase in Ni³⁺ content, suggesting enhanced oxidation states due to interaction with Co₃O₄. Figure 4b shows that the peaks at 710.1 and 723.8 eV correspond to Fe 2p_3/2 and Fe 2p_1/2, respectively [31,32]. Compared to LYNF, the Fe 2p_3/2 peaks of LYNF-0.5Co₃O₄ shift from 710.4 eV to 711.1 eV.

In the O 1s spectra in Figure 4c, four distinct oxygen species are deconvoluted. The peak at 528.5 eV (O1) is attributed to lattice oxygen (O²⁻), while the peaks at 530.4 eV (O2), 531.7 eV (O3), and 533.0 eV (O4) are assigned to oxygen vacancies, surface-adsorbed oxygen species (e.g., −OH or O²⁻), and weakly bound surface species (such as carbonates or adsorbed H₂O), respectively [33,34]. Notably, the proportion of the O2 component in LYNF-0.5Co₃O₄ reaches 31.5%, which is significantly higher than that in pristine LYNF (16.8%). This substantial increase in oxygen vacancy content suggests that the introduction of Co₃O₄ effectively promotes the generation of surface defects. XPS shows a 0.2 eV positive shift in Ni 2p₃/₂ binding energy for LYNF-0.5Co₃O₄, indicating increased Ni³⁺ content-critical active sites for ORR and OER, enhancing adsorption and activation of oxygen intermediates. Higher Fe oxidation states strengthen affinity for oxygen-containing intermediates, accelerating rate-determining steps in both reactions (e.g., * OOH formation in OER, O = O cleavage in ORR). Oxygen vacancies, significantly increased with Co₃O₄, act as O₂ adsorption sites, reducing dissociation energy for ORR and facilitating lattice oxygen participation in OER via redox mechanisms [35,36].

Such structures not only facilitate the adsorption and activation of oxygen intermediates but also enhance the electronic conductivity of the composite, thereby contributing to improved electrocatalytic performance. The synergistic effect between the spinel Co₃O₄ and the perovskite LYNF is essential for optimizing the surface electronic environment and boosting the overall catalytic activity.

2.2. Electrochemical Performance

The electrochemical performance of these catalysts was assessed via LSV polarization curves in an O₂-saturated 0.1 M KOH electrolyte using a three-electrode system. As shown in Figure 5a, LYNF-0.5Co₃O₄ exhibits the highest limiting current density and the most positive onset potential (0.813 V) among all samples, outperforming LYNF-0.75Co₃O₄ (0.789 V), LYNF-0.25Co₃O₄ (0.775 V), and pristine LYNF (0.751 V). Moreover, its half-wave potential (0.630 V) surpasses that of LYNF-0.75Co₃O₄ (0.612 V), LYNF-0.25Co₃O₄ (0.608 V), and pristine LYNF (0.584 V). The initial potential of LYNF-0.5Co₃O₄ is also higher (0.813 V) than that of LYNF-0.25Co₃O₄ (0.775 V) and LYNF (0.751 V), indicating a superior ORR performance. Figure S7 is for OER and ORR performance comparison chart. These enhancements can be attributed to the synergistic coupling between the spinel and perovskite phases, which improves electronic conductivity and facilitates oxygen adsorption or activation.

The corresponding Tafel plots in Figure 5b further demonstrate the improved ORR kinetics of LYNF-0.5Co₃O₄, which exhibits the lowest Tafel slope of 91.4 mV dec⁻¹. In comparison, the slopes of LYNF-0.75 Co₃O₄, LYNF-0.25 Co₃O₄, and pristine LYNF are 92.2, 114, and 141 mV dec⁻¹, respectively. A smaller Tafel slope reflects more favorable electron transfer kinetics during the reaction.

As depicted in Figure 5c, the overpotential of LYNF-0.5Co₃O₄ at the current density of 10 mA cm⁻² is 441 mV, which is lower than that of LYNF-0.25Co₃O₄ (455 mV), LYNF-0.75Co₃O₄ (454 mV), and LYNF (510 mV). The OER kinetics were evaluated by calculating the Tafel slope, as shown in Figure 5d. LYNF-0.5Co₃O₄ exhibits a Tafel slope of 57 mV dec⁻¹, which is lower than those of LYNF-0.75Co₃O₄ (64.1 mV dec⁻¹), LYNF-0.25Co₃O₄ (64.5 mV dec⁻¹), and LYNF (96.9 mV dec⁻¹). Figure S8 is overpotentials to afford 10 mA cm⁻² for different electrocatalysts [35,36]. It indicates that LYNF-0.5Co₃O₄ has the lowest overpotential. These results indicate that the integration of LYNF with Co₃O₄ enhances the OER kinetics. This improvement can be attributed to the heterostructures formed upon recombination, which typically exhibit enhanced electron and ion transport pathways. These features reduce charge transfer resistance and thereby promote superior OER performance. The Koutecky–Levich (K-L) plots (Figure S6) of LYNF and LYNF-0.5Co₃O₄ derived from the RRDE measurements showed excellent linearity between J⁻¹ and ω^−1/2, indicating first-order kinetics of ORR for the two materials. Based on the K-L equation, the electron-transfer number (n) of LYNF-0.5Co₃O₄ was calculated to be about 3.95, confirming its favorable four-electron reaction path toward catalyzing ORR.

For the electrochemical impedance spectroscopy (EIS) measurements, the Nyquist plots were analyzed using ZView software (Version 3.5c) to fit the equivalent circuit. The equivalent circuit employed was a typical R_s (R_ctCPE) model, where R_s represents the series resistance, R_ct is the charge transfer resistance, and CPE denotes the constant phase element. The Nyquist plots for LYNF and LYNF-xCo₃O₄ (x = 0, 0.25, 0.5, 0.75) samples are shown in Figure 5e. All plots exhibit typical semicircular profiles in the high-to-mid frequency region, which correspond to the charge transfer resistance (R_ct) at the electrode/electrolyte interface [37,38]. Among the tested samples, LYNF-0.5Co₃O₄ exhibits the smallest semicircle diameter, indicating the lowest R_ct value. In contrast, pristine LYNF shows the largest R_ct, suggesting sluggish electron transfer during the OER process. The trend in R_ct values (LYNF-0.5Co₃O₄ < LYNF-0.25Co₃O₄ ≈ LYNF-0.75Co₃O₄ < LYNF) is consistent with the observed electrocatalytic activity trends from LSV and Tafel analyses. The reduced charge transfer resistance of LYNF-0.5Co₃O₄ can be attributed to the synergistic effect between LYNF and Co₃O₄, which improves the electrical conductivity, enhances electron mobility, and facilitates faster charge transfer at the catalyst surface.

Figure 6a–d presents the CV curves of the various samples recorded within a non-Faradaic region. LYNF-0.5Co₃O₄ exhibits the largest C_dl value of 2.54 mF cm⁻², which is significantly higher than that of pristine LYNF. The LYNF-based composites show slightly lower C_dl values: 1.91 mF cm⁻² for LYNF-0.25Co₃O₄, 1.83 mF cm⁻² for LYNF-0.75Co₃O₄, and 1.59 mF cm⁻² for pristine LYNF. A higher C_dl indicates a larger electrochemically active surface area, which provides more accessible active sites for catalytic reactions. As shown in Figure S5, the BET surface areas of LYNF and LYNF-0.5Co₃O₄ are calculated to be 2.8513 m² g⁻¹ and 7.8153 m² g⁻¹, respectively. This indicates that the introduction of Co₃O₄ significantly increases the BET surface area of the catalyst. To link this with electrochemical performance, the electrochemical surface area (derived from C_dl) of LYNF-0.5Co₃O₄ is larger than that of LYNF, which is consistent with the trend of BET surface area. This consistency supports that the increased BET surface area provides more active sites, contributing to the enhanced electrochemical performance.

The long-term electrochemical stability of the catalysts is also investigated by accelerated aging tests. LYNF-0.5Co₃O₄ displays excellent stability over 2000 CV cycles. As depicted in Figure 7a–d, it is observed that the potential for ORR and OER LYNF-0.5Co₃O₄ decreases by 1 mV and 40 mV at 10 mA cm⁻², respectively. Meanwhile, the values for LYNF are 8 mV and 140 mV. These results further demonstrate that LYNF-0.5Co₃O₄ exhibits promising catalytic stability in alkaline electrolyte, which is essential for practical rechargeable ZAB applications.

2.3. Zn–Air Battery Performance

To further evaluate the practical applicability of LYNF-0.5Co₃O₄, aqueous ZABs were assembled using it as the air cathode catalyst. The battery configuration is schematically illustrated in Figure 8a. The electrochemical performance of the ZABs was evaluated through galvanodynamic discharge and cycling tests. As shown in Figure 8b, the LYNF-0.5Co₃O₄-based ZAB achieved a peak power density of 115 mW cm⁻², which is 20% higher than that of the pristine LYNF-based ZAB (93 mW cm⁻²). The enhanced output reflects the superior ORR and OER bifunctional catalytic activity of the composite catalyst, which facilitates rapid oxygen-related ORR processes and effective charge transfer.

In addition to power output, long-term cycling stability was examined under a constant current density of 5 mA cm⁻² in Figure 8c. The LYNF-0.5Co₃O₄-based ZAB exhibits excellent cycle stability, with a relatively small voltage gap between charge and discharge even after prolonged operation. In contrast, the battery using pristine LYNF shows a pronounced increase in overpotential during cycling, indicating more severe degradation. These results demonstrate that hybridizing LYNF with Co₃O₄ not only enhances catalytic activity but also substantially improves the stability of the air electrode, making LYNF-0.5Co₃O₄ a highly promising candidate for practical rechargeable ZAB applications.

3. Experimental Section

3.1. Synthesis of Samples

LYNF was synthesized utilizing the conventional self-propagating combustion method according to our previous study. Initially, La(NO₃)₃·6H₂O, Y(NO₃)₃·6H₂O, Ni(NO₃)₂·6H₂O, and Fe(NO₃)₃·9H₂O in stoichiometric amounts were dissolved in 50 mL of distilled water. Subsequently, ethylenediaminetetraacetic acid (EDTA) and citric acid (CA) were incorporated into the aqueous solution, followed by pH adjustment to 8 using ammonia. The solution was then stirred at 80 °C until gelation occurred. Upon gel formation, the precursor gel was transferred into an electric furnace for spontaneous combustion. The resultant product was subjected to calcination at 800 °C for 5 h. Co₃O₄ was synthesized via a high-temperature calcination method by heating Co(NO₃)₂·6H₂O at 400 °C for 3 h. Subsequently, Co₃O₄ and LYNF were mixed at mass ratios of 75 wt%, 50 wt%, and 25 wt%, respectively, and dispersed in 60 mL of deionized water. The mixtures were stirred and heated in a water bath at 90 °C. Afterward, the resulting suspensions were subjected to calcination at 400 °C for 3 h. The obtained products were denoted as LYNF-0.75Co₃O₄, LYNF-0.5Co₃O₄, and LYNF-0.25Co₃O₄, respectively. The synthesis procedure for LYNF-0.5Co₃O₄ electrocatalysts is schematically illustrated in the Supplementary Materials (Figure S1).

3.2. Characterization

X-ray diffraction (XRD) patterns were acquired utilizing a powder X-ray diffractometer, which employed a Cu K_β source for irradiation, operating at a scan rate of 10° per minute. High-resolution transmission electron microscopy (TEM) images were acquired via a JEOL-Model-JEM-2100F field-emission electron microscope at an accelerating voltage of 200 kV. To investigate the surface chemistry and ascertain the atomic composition, X-ray photoelectron spectroscopy (XPS) was employed.

3.3. Electrochemical Test

The electrochemical characterization was conducted using a three-electrode system, incorporating a Pt wire as the counter electrode, an Ag/AgCl electrode (3.5 M KCl solution) as the reference electrode, and a 0.1 M KOH solution serving as the electrolyte. Initially, a mixture comprising 5 mg of catalyst, 5 mg of Super P Li conductive carbon, 50 µL of Nafion solution (5 wt%), 300 µL of isopropanol, and 700 µL of water was prepared. The suspension was homogenized using ultrasound treatment for 1 h. The glassy carbon electrode was subsequently polished with 0.4 mm and 30 nm Al₂O₃ particles in succession, followed by thorough rinsing with deionized water and ethanol. A precise volume of 5 µL from the homogeneous catalyst suspension was then applied onto a glassy carbon disc electrode, possessing a diameter of 4 mm and a surface area of 0.1256 cm², using a pipette. The ORR/OER polarization curves were recorded via linear sweep voltammetry (LSV) at a sweep rate of 5 mV s⁻¹, with potential windows set to 0 V to 1 V (vs. Ag/AgCl) for OER, respectively. The electrochemical impedance spectroscopy (EIS) potentials were tested at a potential of 0.76 V vs. Ag/AgCl, with frequencies ranging from 100,000 to 0.1 Hz and amplitudes of 5 mV. The capacitive currents were determined using cyclic voltammetry (CV) across varying scan rates of 20, 40, 60, 80, 100, and 120 mV/s to estimate the electric double-layer capacitance (C_dl).

Notably, a lower overpotential signifies superior OER catalytic efficiency and an enhanced rate of mass transfer. The overpotential (η) was derived using the following equation [39]:

$$\mathsf{\eta }={\mathrm{E}}_{\mathrm{j}=10\mathrm{mA}/\mathrm{c}{\mathrm{m}}^2}-1.23\mathrm{V}\mathrm{vs}.\mathrm{RHE}$$

(1)

where 1.23 V represents the equilibrium potential of O₂/H₂O.

Within the non-Faradaic potential regime, the double-layer capacitance (C_dl) was assessed via CV, facilitating the estimation of the electrochemical surface area (ECSA). ECSA serves as an indicator of the catalyst’s effective specific surface area pertinent to the oxygen evolution reaction (OER) and is derived using the following formula [40]:

$$\mathrm{ECSA}={\displaystyle \frac{{\mathrm{C}}_{\mathrm{dl}}}{{\mathrm{C}}_{\mathrm{s}}}}$$

(2)

where C_s represents the specific capacitance of the electrode material in a unit area. Given that ECSA is directly proportional to C_dl under identical conditions, C_dl indirectly reflects the extent of the catalyst’s surface area involved in OER activities.

4. Challenges and Limitations

4.1. Contributions of LYNF-xCo₃O₄

The LYNF-0.5Co₃O₄ catalyst achieves a significant reduction in overpotential for both ORR and OER through optimized electronic structure and enhanced interfacial contacts. Specifically, it exhibits an elevated oxygen vacancy concentration of 31.5%, an ORR onset potential of 0.813 V, and an OER overpotential of 441 mV at 10 mA cm⁻², accompanied by reduced Tafel slopes for both reactions. These features directly enhance charge transfer kinetics, thereby contributing to mitigated charge–discharge polarization and improved energy efficiency. Accelerated aging tests further demonstrate the catalyst’s favorable stability: after 2000 cyclic voltammetry (CV) cycles, the decay in ORR and OER potentials is merely 1 mV and 40 mV, respectively. Moreover, the assembled ZABs with this catalyst shows only a slight increase in the charge–discharge voltage gap during cycling at 5 mA cm⁻², indicating a distinct contribution to short-term cycling stability.

4.2. Limitations of LYNF-xCo₃O₄

With respect to long-term stability, despite the demonstrated stability in 2000 cyclic voltammetry (CV) cycles and approximately 100 h of battery cycling tests, there remains a gap compared to the requirement of thousands of cycles in practical applications. Additionally, the mechanisms underlying active site loss, oxygen vacancy reconstruction, or interactions with electrolytes (e.g., carbonation) during long-term cycling of the catalyst have not been explored. In terms of adaptability to practical operating conditions, the performance of the catalyst was only evaluated in 0.1 M KOH electrolyte, whereas practical ZABs typically utilize higher-concentration electrolytes (e.g., 6 M KOH) and may encounter issues such as zinc dendrite growth and electrolyte drying [41,42]. The stability and catalytic activity of the catalyst under these complex conditions remain unvalidated. Regarding challenges in cost and large-scale preparation, although the chemical bath-assisted method is described as “facile”, the introduction of Co₃O₄ may increase material costs, and the feasibility of this method in large-scale production (e.g., uniformity control, yield) has not been discussed, which limits the evaluation of its commercialization potential. Concerning limitations in mechanistic research, although oxygen vacancies and interfacial electron coupling are hypothesized to be key to performance enhancement, there is a lack of in situ characterization (e.g., in situ XPS, in situ Raman) to directly confirm the dynamic role of these factors in catalytic reactions, and the precise identification of active sites remains unclear. These limitations will be the focus of our future research to further enhance the practical application value of the catalyst [43].

5. Conclusions

In conclusion, this study presents a simple hybrid strategy to further optimize the Y and Fe co-doped perovskite material. Based on LYNF, hybrid samples with different composite ratios were obtained by adjusting only the stoichiometric coefficient of the Co element without changing the composition of the matrix perovskite. Among them, LYNF-0.5Co₃O₄ with a fine heterostructure has a better activity than the original LYNF. It proved that there are a large number of charge transfers and strong electronic coupling in LYNF-0.5Co₃O₄. Meanwhile, the dispersed and compact interface between Co₃O₄ and perovskite generates a synergistic effect, which can provide more active sites and effectively adapt to local environmental changes during the ORR and OER process. This study indicates that the one-step mixing method is an effective approach to preparing high-performance catalysts, providing a new direction for the search of bifunctional electrocatalysts with practical application value.