Electrochemical Properties of LaMO₃(M=Cr, Mn, and Co) Perovskite Materials

Abstract

The utilization of lanthanide perovskite oxides as electrode materials for supercapacitors has garnered significant interest owing to their excellent electrical conductivity, low cost, and excellent thermal stability. In this study, LaMO₃(M=Cr, Mn, and Co) nanoparticles were prepared by the sol–gel method coupled with a calcination process. To evaluate the microstructures, morphologies, and electrochemical properties of the samples, a variety of techniques were employed, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area measurements, cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) cycling, and electrochemical impedance spectroscopy (EIS). The results revealed that the LaCoO₃ electrodes exhibited a maximum specific capacitance of 118.4 F/g at a current density of 1 A/g, attributed to its higher concentration of oxygen vacancy, larger specific surface area, and lower charge transfer resistance. This discovery substantiates the notion that the electrochemical efficacy is enhanced with the diminishing B-site cation radius in the perovskite LaMO₃ system. The charge–discharge process was employed to investigate the anion-intercalation mechanism of LaMO₃(M=Cr, Mn, and Co).

1. Introduction

The exponential growth in population and rapid advancement of industrialization have resulted in a heightened need for power and energy. Supercapacitors, being efficient and sustainable energy storage devices, have garnered attention due to their higher power density, longer electrochemical cycle stability, rapid charge/discharge rates, and safe operational characteristics [1,2]. According to the charge storage mechanism, supercapacitors can be broadly divided into two categories: pseudocapacitors and electrical double-layer capacitors. Typically, carbonaceous materials are used as electrodes for the former, which operates primarily by adsorption and desorption of ions. Alternatively, the latter involves reversible Faradaic redox reactions occurring on the surface of the active materials, which are typically electroded with conducting polymers and transition metal oxides/hydroxides [3,4]. The functionality of supercapacitors is heavily influenced by the electrode materials. Carbon materials, metal oxides, and conductive polymers have been extensively studied as electrode materials for supercapacitors [5,6]. Transition metal oxides, in particular, have attracted considerable attention due to their higher energy density [7,8]. Nevertheless, the application of transition metal oxides in supercapacitors is hindered by challenges related to their limited conductivity, cycling stability, and voltage window [9,10,11]. Consequently, there is a pressing need for novel transition metal oxides that can overcome these aforementioned limitations.

Perovskite oxides have garnered considerable interest as electrode materials for supercapacitors owing to their unique structure, adaptability in composition, presence of oxygen vacancies, exceptional oxygen storage capabilities, and superior ionic conductivity. Consequently, they represent a promising class of transition metal oxides for this particular application [12,13,14,15,16]. Tyler Mefford et al. proposed an oxygen-embedding mechanism to provide a theoretical basis for the energy storage of perovskite materials [17]. Subsequently, the researchers reported some perovskite oxide materials as electrode materials for supercapacitors, such as strontium-based materials [18,19,20], nickel-based materials [21,22], cerium-based materials [23,24,25], and lanthanum-based materials [26,27,28,29,30]. Lanthanide perovskite oxides have attracted significant attention because they have a stable crystal structure, high thermal stability, fantastic electrical conductivity, low cost, and excellent thermal stability. In comparison to other perovskite oxides, lanthanum-based materials offer a diverse range of synthetic routes, rendering them valuable assets in the realm of energy storage. Lanthanum chromate perovskite oxides have garnered significant attention in recent times due to their distinctive stable crystal structure, remarkable high-temperature structure stability, exceptional catalytic activity, infrared emissivity, and superior chemical stability. These characteristics make them highly suitable for utilization in various memory devices, fuel cells, catalyst electrodes in ORR/HER, electrochemical gas sensors, as well as optical and electrochemical applications [31]. The electrochemical performance of LaCrO₃ perovskite oxide material was initially documented by Shahid Hussain et al. [31], who reported a specific capacitance of up to 1268 F/g in a neutral LiCl aqueous electrolyte. Conversely, Nadarajan Arjun et al. [32] reported specific capacitances of 56.78 F/g and 24.40 F/g for LaMnO₃ and LaCrO₃ perovskite oxide materials, respectively, in a 3 M LiOH electrolyte. V. V. Deshmukh et al. reported that the specific capacitance of LaMnO₃ nanoparticles prepared by sol–gel method was 27.68 F/g [33]. LaCoO₃ is a significant composite utilized in solid oxide fuel cells due to its intricate and temperature-sensitive electronic and magnetic characteristics [34]. Because cobalt atoms exist in multiple oxidation states (Co²⁺, Co³⁺, and Co⁴⁺), it exhibits exceptional electrochemical redox properties, making it a highly promising material for supercapacitor electrodes [35]. The specific capacitance of LaCoO₃ nanofibers reported by Hu et al. [34] is about 95 F/g, while the specific capacitance reported by Fawzi Hadji et al. [35] is only 75.36 F/g. The results indicated that the electrochemical properties of lanthanide perovskite oxides prepared with different B-site cations by different methods and processes were quite different. Few studies have been reported on the effects of different B-site cations on the electrochemical properties of lanthanide perovskite oxides.

Based on this, LaCrO₃, LaMnO₃, and LaCoO₃ nanoparticles were prepared by the sol–gel method. The effects of different B-site cations (R_Cr3+ = 0.62 Å, R_Mn3+ = 0.58 Å, R_Co3+ = 0.52 Å) on the electrochemical properties of lanthanide perovskite materials were studied by testing the microstructure, morphology, specific surface area, and electrochemical properties of three perovskite oxide materials. LaCrO₃, LaMnO₃, and LaCoO₃ have specific capacitances of 86.4, 99.2, and 118.4 F/g, respectively, and LaCoO₃ has the best electrochemical performance.

2. Experimental Section

2.1. Synthesis of LaMO₃(M=Cr, Mn, and Co) Powders

LaMO₃(M=Cr, Mn, and Co) powders were prepared by the sol–gel method coupled with a calcination process. The specific process is as follows: First of all, C₆H₈O₇·H₂O (≥99.5%), La(NO₃)₃·6H₂O (≥99.9%), Cr(NO₃)₃·9H₂O (≥99%), MnCl₂·4H₂O (≥99%), and Co(NO₃)₂·6H₂O (≥98.5%) were placed in a beaker of volume 30 mL to stir the substance (for 24 h) and obtain transparent solution of a certain molar ratio. Then, the transparent solution underwent a drying process in a blast drying oven set at 80 °C for 72 h. Subsequently, the desiccated sample was extracted and transferred into a crucible for subsequent calcination within a muffle furnace. The muffle furnace was gradually heated to 700 °C at a rate of 5 °C/min and maintained within an air atmosphere for 2 h, resulting in the formation of black powders after grinding. The synthesis progress of LaMO₃(M=Cr, Mn, and Co) powders is shown in Figure 1.

2.2. Characterization of LaMO₃(M=Cr, Mn and Co) Powders

LaMO₃(M=Cr, Mn, and Co) powders underwent phase analysis using an X-ray powder diffractometer (XRD, Bruker D8 Advance, Karlsruhe, Germany) with a scanning range of 20–70° and a scanning speed of 4°/min. Field emission scanning electron microscopy (Merlin Compact, Carl Zeiss, Oberkochen, Germany) was used to analyze the microstructure of the samples. Thermo Scientific K-Alpha (XPS, Waltham, MA, USA) was used to analyze the elemental composition and chemical valence, as well as a specific surface area tester (BET, ASAP 2020, Micromeritics, Norcross, GA, USA) to determine the specific surface area.

2.3. Electrochemical Test

The electrode is fabricated in the following manner: Initially, a mixture of LaMO₃(M=Cr, Mn, and Co) powders, polyvinylidene fluoride (PVDF), and acetylene black are combined at a ratio of 8:1:1 in a specific quantity of N-methyl pyrrolidone (NMP) and subjected to stirring for a designated duration. Subsequently, the resulting paste is uniformly spread onto a nickel foam sheet measuring 15 × 10 mm, with a coating area of 100 mm². Finally, the electrode is obtained by subjecting the coated sheet to heat treatment in a vacuum oven at 80 °C for 24 h. The electrochemical properties of the LaBO₃ materials were investigated using a CHI 660E electrochemical workstation. Cyclic voltammetry (CV) was conducted with a potential window from 0.1 to 0.55 V at various scan rates (10–100 mV/s). Galvanostatic charge-discharge (GCD) experiments were performed at different current densities (1–5 A/g). Additionally, electrochemical impedance spectroscopy (EIS) was carried out at the open circuit potential, covering a frequency range of 10 MHz to 100 kHz with a potential amplitude of 10 mV. A conventional three-electrode electrochemical cell was used to investigate the impact of the different B-position elements. In this cell, LaBO₃ materials served as the working electrode, Hg/HgO served as the reference electrode, platinum served as the counter electrode, and 3 M KOH solution served as the electrolyte.

3. Results and Discussion

3.1. Microstructure and Morphology

The XRD results of LaCrO₃, LaMnO₃, and LaCoO₃ are shown in Figure 2a. Analysis of the figure reveals that the diffraction peaks of the three materials correspond to those of the standard cards PDF#75-0441, PDF#50-0297, and PDF#48-0123, respectively, with no impurity peaks observed. This indicates the successful synthesis of LaCrO₃, LaMnO₃, and LaCoO₃ powders. The crystallite size (D), dislocation density (δ), and strain (ε) of LaCrO₃, LaMnO₃, and LaCoO₃ in XRD can be calculated using Equations (1)–(3). The calculated results are shown in

Table 1. The calculated crystallite size (D), dislocation density (δ), and strain (ε) of LaCrO₃, LaMnO₃, and LaCoO₃.

	LaCrO3	LaMnO3	LaCoO3
D (nm)	19.76	11.82	10.70
δ × 10−3 (nm−2)	2.56	7.15	8.73
ε × 10−3	6.19	10.36	11.26

. The SEM images of LaCrO₃, LaMnO₃, and LaCoO₃ materials are presented in Figure 2b–d. Analysis of the SEM images reveals that the particles of these materials exhibit a uniform distribution, with nanoparticles of small grain size being densely packed. The size of these nanoparticles is approximately in the range of tens of nanometers. The advantageous aspect of a small grain size lies in its ability to enhance the contact area between the materials and the electrolyte during electrochemical testing.

$$D=\frac{\kappa \lambda }{\beta \cos \theta }$$

(1)

$$\delta =\frac{1}{D^2{}_{{}^{}}}$$

(2)

$$\epsilon =\frac{\beta }{4\tan \theta }$$

(3)

The electrochemical properties of LaMO₃(M=Cr, Mn, and Co) nanoparticles are influenced by their specific surface area. To determine this specific surface area, the N₂ adsorption–desorption method was employed. Figure 3a–c display the N₂ adsorption–desorption isotherm curves for the LaCrO₃, LaMnO₃, and LaCoO₃ nanoparticle samples, respectively. Notably, the curves exhibit a distinct hysteresis loop. This phenomenon can be attributed to the condensation of N₂ gas molecules and their subsequent filling of mesoporous channels under the influence of capillary condensation at low pressure. The initiation of N₂ adsorption triggers capillary condensation on the liquid surface of the annular adsorption film formed on the pore wall. The desorption process commences at the spherical meniscus surface located at the orifice, thereby indicating that the observed curve conforms to a type IV curve [36]. Consequently, the nanoparticles of LaCrO₃, LaMnO₃, and LaCoO₃ exhibit mesoporous characteristics. The pore size distribution diagram in Figure 3d–f reveals that the average pore size of the nanoparticle samples of LaCrO₃, LaMnO₃, and LaCoO₃ is predominantly distributed within the range of 2–10 nm, thereby confirming the mesoporous nature of the samples. The specific surface area of the nanoparticle samples of LaCrO₃, LaMnO₃, and LaCoO₃ was determined using the specific surface area calculation formula, resulting in values of 35.01 m² g⁻¹, 38.11 m² g⁻¹, and 41.9 m² g⁻¹, respectively. Notably, the LaCoO₃ nanoparticles exhibited the highest specific surface area among the three materials. Typically, an increase in the specific surface area of a sample corresponds to an increase in its specific capacitance. Consequently, it is plausible that the LaCoO₃ nanoparticle exhibits the highest specific capacitance [37].

XPS tests were conducted on nanoparticle samples of LaCrO₃, LaMnO₃, and LaCoO₃ to investigate their components and elemental valence states. The results are presented in Figure 4. Figure 4a displays the XPS full spectrum of the aforementioned nanoparticle samples. The figure reveals the presence of Cr, Mn, and Co elements, in addition to La and O elements, which correspond to the three materials. This observation confirms that the elemental composition of the materials aligns with the intended design. The peak splitting fitting of the O1s was conducted due to the significant presence of oxygen vacancies in perovskite oxide materials. As per the research conducted by Sadayappan Nagamuthu [38], the O element was categorized into three distinct peaks, namely O1 (representing lattice oxygen), O2 (representing adsorbed oxygen), and O3 (representing oxygen-containing groups).

Table 2. Relative concentrations of the three oxygen of O 1s in LaMO₃(M=Cr, Mn, and Co) nanoparticles.

	LaCrO3	LaMnO3	LaCoO3
O1	49.3	47.7	45.3
O2	38.6	47.5	47.5
O3	12.1	6.8	7.2
O2/O1	0.78	0.99	1.05

presents the comparative concentrations of three oxygen species in LaCrO₃, LaMnO₃, and LaCoO₃ nanoparticles. The existence of oxygen vacancies within the electrode material demonstrates a significant association with electrical conductivity. An increased concentration of adsorbed oxygen enhances the capacity for OH adsorption, thereby accelerating the surface REDOX reaction and ultimately improving the electrochemical performance [39]. According to the findings in the literature [40], the O2/O1 value has been identified as a reliable indicator of the concentration of oxygen vacancies. As illustrated in Table 2, LaCoO₃ exhibits the highest O2/O1 value, suggesting that it possesses the highest concentration of oxygen vacancies, which may potentially contribute to its favorable electrochemical performance.

3.2. Electrochemical Performance

The CV curves of LaCrO₃, LaMnO₃, and LaCoO₃ electrodes at different scanning rates are shown in Figure 5a–c. The results show that the CV curves are little affected by scanning rates. Moreover, the results demonstrate that the electrodes derived from LaCrO₃, LaMnO₃, and LaCoO₃ samples exhibit favorable reversibility and stability. Additionally, the observed capacitive behavior suggests the presence of both double-layer capacitors and Faraday pseudocapacitors within the material. The CV curves of LaCrO₃, LaMnO₃, and LaCoO₃ exhibit REDOX peaks at 0.43 and 0.39 V, 0.44 and 0.39 V, and 0.45 and 0.39 V, respectively. These peaks are attributed to the alteration of valence states of B-site cations in the respective samples, specifically Cr³⁺ and Cr⁴⁺ in LaCrO₃; Mn²⁺, Mn³⁺, and Mn⁴⁺ in LaMnO₃; and Co²⁺ and Co³⁺ in LaCoO₃. Furthermore, it is observed that the enclosed area of CV curves for LaCrO₃, LaMnO₃, and LaCoO₃ exhibit an increase at the same scanning rate. Notably, LaCoO₃ demonstrates the largest CV area, followed by LaMnO₃, while LaCrO₃ exhibits the smallest CV area. This finding aligns with the outcomes of the specific surface area analysis and the observed trend in oxygen vacancy concentration.

Drawing from the information presented in the CV and XPS results provided, as well as previous scholarly sources [31,33,35], the electrochemical storage mechanism of LaMO₃(M=Cr, Mn, and Co) perovskite in an alkaline electrolyte may be described as the intercalation of oxygen ions facilitated by the oxidation of B(B=Cr, Mn, and Co) atoms. This phenomenon can be mathematically represented by Equations (4)–(9) [35].

$$\mathrm{L}\mathrm{a}\left[{\mathrm{C}\mathrm{r}}_{2\mathsf{\delta }}^{2+};{\mathrm{C}\mathrm{r}}_{1-2\mathsf{\delta }}^{3+}\right]{\mathrm{O}}_{3-\mathsf{\delta }}+2\mathsf{\delta }{\mathrm{O}\mathrm{H}}^{-}\leftrightarrow {\mathrm{L}\mathrm{a}\mathrm{C}\mathrm{r}}^{3+}{\mathrm{O}}_3+\mathsf{\delta }{\mathrm{H}}_2\mathrm{O}+2{\mathsf{\delta }\mathrm{e}}^{-}$$

(4)

$$\mathrm{L}\mathrm{a}{\mathrm{C}\mathrm{r}}^{3+}{\mathrm{O}}_3+2\mathsf{\delta }{\mathrm{O}\mathrm{H}}^{-}\leftrightarrow \mathrm{L}\mathrm{a}\left[{\mathrm{C}\mathrm{r}}_{2\mathsf{\delta }}^{4+},{\mathrm{C}\mathrm{r}}_{1-2\mathsf{\delta }}^{3+}\right]{\mathrm{O}}_{3+\mathsf{\delta }}+2\mathsf{\delta }{\mathrm{e}}^{-}+\mathsf{\delta }{\mathrm{H}}_2\mathrm{O}$$

(5)

$$\mathrm{L}\mathrm{a}\left[{\mathrm{M}\mathrm{n}}_{2\mathsf{\delta }}^{2+};{\mathrm{M}\mathrm{n}}_{1-2\mathsf{\delta }}^{3+}\right]{\mathrm{O}}_{3-\mathsf{\delta }}+2\mathsf{\delta }{\mathrm{O}\mathrm{H}}^{-}\leftrightarrow {\mathrm{L}\mathrm{a}\mathrm{M}\mathrm{n}}^{3+}{\mathrm{O}}_3+\mathsf{\delta }{\mathrm{H}}_2\mathrm{O}+2{\mathsf{\delta }\mathrm{e}}^{-}$$

(6)

$$\mathrm{L}\mathrm{a}{\mathrm{M}\mathrm{n}}^{3+}{\mathrm{O}}_3+2\mathsf{\delta }{\mathrm{O}\mathrm{H}}^{-}\leftrightarrow \mathrm{L}\mathrm{a}\left[{\mathrm{M}\mathrm{n}}_{2\mathsf{\delta }}^{4+},{\mathrm{M}\mathrm{n}}_{1-2\mathsf{\delta }}^{3+}\right]{\mathrm{O}}_{3+\mathsf{\delta }}+2\mathsf{\delta }{\mathrm{e}}^{-}+\mathsf{\delta }{\mathrm{H}}_2\mathrm{O}$$

(7)

$$\mathrm{L}\mathrm{a}\left[{\mathrm{C}\mathrm{o}}_{2\mathsf{\delta }}^{2+};{\mathrm{C}\mathrm{o}}_{1-2\mathsf{\delta }}^{3+}\right]{\mathrm{O}}_{3-\mathsf{\delta }}+2\mathsf{\delta }{\mathrm{O}\mathrm{H}}^{-}\leftrightarrow {\mathrm{L}\mathrm{a}\mathrm{C}\mathrm{o}}^{3+}{\mathrm{O}}_3+\mathsf{\delta }{\mathrm{H}}_2\mathrm{O}+2{\mathsf{\delta }\mathrm{e}}^{-}$$

(8)

$$\mathrm{L}\mathrm{a}{\mathrm{C}\mathrm{o}}^{3+}{\mathrm{O}}_3+2\mathsf{\delta }{\mathrm{O}\mathrm{H}}^{-}\leftrightarrow \mathrm{L}\mathrm{a}\left[{\mathrm{C}\mathrm{o}}_{2\mathsf{\delta }}^{4+},{\mathrm{C}\mathrm{o}}_{1-2\mathsf{\delta }}^{3+}\right]{\mathrm{O}}_{3+\mathsf{\delta }}+2\mathsf{\delta }{\mathrm{e}}^{-}+\mathsf{\delta }{\mathrm{H}}_2\mathrm{O}$$

(9)

Utilizing LaCoO₃ as a focal point, the preliminary stage of the oxygen intercalation mechanism within the LaCoO₃ electrode involves the assimilation of hydroxide ions (OH⁻) by oxygen imperfections. As a consequence, superoxide ions (O²⁻) and water (H₂O) are produced in the alkaline electrolyte, leading to the transportation of O²⁻ ions across the octahedral lattice to uphold the structural stability of oxygen vacancies. During this process, the neighboring Co²⁺ species undergoes conversion to Co³⁺ and simultaneously releases an electron, ultimately leading to the formation of the neutral LaCo³⁺O₃ compound, as depicted in Equation (8). According to Equation (9), the subsequent step consisted of liberating cobalt from the oxygen octahedron’s central region. This allowed excess oxygen to be absorbed by the surrounding environment, thereby causing a transition in the valence state of the Co cation from Co³⁺ to Co⁴⁺, ultimately resulting in an abundance of oxygen [35].

Figure 5d–f depict the constant current charge and discharge profiles of LaCrO₃, LaMnO₃, and LaCoO₃ electrodes. The graph demonstrates a decrease in discharge duration as current density increases, which can be attributed to the increased internal resistance of the material caused by the higher current density. This subsequently leads to a decrease in specific capacitance. The change in the slope of the graph is associated with the alteration in the valence state of the B-position cations (Cr³⁺ and Cr⁴⁺, Mn²⁺ and Mn³⁺, Co²⁺ and Co³⁺). The specific capacitance values of LaCrO₃, LaMnO₃, and LaCoO₃ samples were determined to be 86.4, 99.2, and 118.4 F/g at a current density of 1 A/g, respectively, which aligns with the observed trends in specific surface area and oxygen vacancy concentration. LaCoO₃ exhibits the highest specific capacitance among the aforementioned materials, owing to its elevated specific surface area and concentration of oxygen vacancies. Notably, the specific capacitance values of LaCoO₃ nanoparticles surpass those of LaCoO₃ nanofibers (95 F/g) as reported by Hu et al. [25]. The interaction between the electrode and electrolyte can be represented by Coulomb efficiency, as evidenced by the charge-discharge curve. Additionally, the performance of the electrode material is determined by the active sites involved in the REDOX reaction [20]. The calculations for Coulomb efficiency and active site determination are as follows [20]:

$$\eta =\frac{t_D}{t_C}\times 100\%$$

(10)

where η is the Coulomb efficiency, t_D is the electrode discharge time, and t_C is the electrode charge time [41].

$$Z=\frac{C_{sp}\times △V\times W}{F}$$

(11)

where the active point site of the REDOX reaction, denoted as Z, represents the extent of participation in the reaction (Z = 1 indicating full participation). Additionally, the specific capacitance of the material is denoted as C_sp, the voltage window is represented by the molecular weight of the material, denoted as W, and the Faraday constant is represented by F [41]. The coulombic efficiency and the number of available REDOX active sites for LaMO₃(M=Cr, Mn, and Co) electrodes were calculated at a current density of 1 A/g, and the results are presented in

Table 3. The Coulombic efficiency and available redox reaction active sites of LaMO₃(M=Cr, Mn, and Co) at the current density of 1 A/g.

	Columbic Efficiency	Available Redox Reaction Active Sites
LaCrO3	92.7%	0.0960
LaMnO3	90.1%	0.1104
LaCoO3	94.6%	0.1360

. LaMO₃(M=Cr, Mn, and Co) electrodes have 9.6, 11.04 and 13.6% participation in the REDOX reaction, respectively, among which the LaCoO₃ electrode has the most REDOX active sites involved in the reaction, indicating that its electrochemical performance is the best [20].

Figure 6 depicts the AC impedance diagram of LaCrO₃, LaMnO₃, and LaCoO₃ electrodes. By fitting the impedance spectrum, an equivalent circuit is derived, as illustrated in Figure 6. In this circuit, R_s represents the electrolyte resistance, R_ct denotes the charge transfer resistance, Z_w signifies the Warburg element, and C_PE represents the constant phase element. The R_ct, R_s, C_PE, Z_W, and Chi² values obtained from the EIS spectra of LaMO₃(M=Cr, Mn and Co) electrodes are shown in

Table 4. The R_ct, R_s, C_PE, Z_W, and Chi² values obtained from the EIS spectra of LaMO₃(M=Cr, Mn and Co) electrodes.

	Rs (Ω)	Rct (Ω)	CPE (Ω)	ZW (Ω)	Chi2
LaCrO3	0.83	5.21	1.68	0.68	0.0030386
LaMnO3	0.76	4.02	0.78	0.69	0.0012108
LaCoO3	0.79	2.56	0.94	0.66	0.0009933

. Upon analysis, the charge transfer resistances of the LaCrO₃, LaMnO₃, and LaCoO₃ electrodes are 5.21, 4.02, and 2.56 Ω, respectively, with corresponding R_s values of 0.83, 0.76, and 0.79 Ω. Notably, the LaCoO₃ electrode displays the lowest impedance, indicating superior electrochemical performance. Figure 6 does not exhibit a discernible semicircular curve, suggesting that the charge transfer resistance of the material is minimal, enabling rapid charge transfer through the mesoporous holes in the electrolyte and electrode samples [42,43].

4. Conclusions

In summary, LaMO₃(M=Cr, Mn, and Co) nanoparticles were successfully synthesized using the sol–gel technique coupled with a calcination process. The utilization of XRD and XPS analyses provide evidence of the formation of a remarkably pure perovskite structure, devoid of any secondary phases. Furthermore, it is observed that the concentration of oxygen vacancies in LaMO₃(M=Cr, Mn, and Co) exhibited an upward trend as the B-site cation radius decreased. SEM and specific surface analysis reveal the presence of polycrystalline structures with diverse sizes, alongside a mesoporous structure. Additionally, the specific surface area of LaMO₃(M=Cr, Mn, and Co) nanoparticles exhibits a gradual increase as the B-site cation radius decreases. Electrochemical measurements reveal that the specific capacitance values of LaCrO₃, LaMnO₃, and LaCoO₃ nanoparticles are 86.4, 99.2, and 118.4 F/g, respectively. The observed pseudocapacitive phenomena in LaBO₃ perovskites are ascribed to the Faradaic redox reactions involving the interchanges between B³⁺ and B²⁺. This investigation provides evidence that a decreased cation radius at the B-site within the LaBO₃ perovskite system shows remarkable electrochemical capabilities.