Effect of MXene on Co₃O₄–LaVO₄ nanocomposites for synergistic charge transport enhancement and high-performance VARTM assisted solid-state supercapacitor devices using woven carbon fiber

Abstract

This study investigates the synthesis of LaVO₄ (LaVO), Co₃O₄–LaVO₄ (Co–LaVO), and Co₃O₄–LaVO₄/MXene (Co–LaVO/Mx) nanocomposites, focusing on optimizing the MXene concentration in Co–LaVO/Mx for high-performance supercapacitor electrodes. The optimal MXene concentration in Co–LaVO/Mx was identified and utilized to fabricate high-performance supercapacitor devices using the vacuum-assisted resin transfer molding (VARTM) technique. Among the tested compositions in a three-electrode system, the Co–LaVO–Mx3 nanocomposite exhibited the highest electrochemical performance, achieving an outstanding specific capacitance of 1287.80 F g⁻¹ at a current density of 1 A g⁻¹. This remarkable performance significantly surpasses that of LaVO (575.67 F g⁻¹), Co–LaVO (610.66 F g⁻¹), Co–LaVO/Mx1 (783.56 F g⁻¹), and Co–LaVO/Mx5 (1196.45 F g⁻¹), demonstrating the crucial role of optimized MXene concentration in improving charge storage, conductivity, and overall electrochemical efficiency. The optimized Co–LaVO/Mx3 nanocomposite was integrated onto woven carbon fibres (WCFs) and employed to fabricate high-performance solid-state supercapacitor devices using the VARTM technique. The resulting device demonstrated an impressive specific capacitance of 317.57 F g⁻¹ at 2 A g⁻¹ and achieved a remarkable energy density of 74.85 W h kg⁻¹ at 1000 W kg⁻¹. Furthermore, it exhibited exceptional cycling stability, retaining 71% of its initial capacitance after 50 000 cycles, highlighting its robustness and long-term operational reliability for advanced energy storage applications.

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1. Introduction

The rapid global consumption of energy has outpaced its production, emphasizing the critical demand for clean and sustainable power sources. This demand has propelled research into efficient energy transformation and storage technologies. Among these, supercapacitors have emerged as a promising solution, bridging the gap between conventional capacitors and lithium-ion batteries.¹ Supercapacitors stand out due to their exceptional power density and energy density, surpassing those of batteries and fuel cells, making them a viable and growing choice in the energy storage market. Supercapacitors primarily store energy through two mechanisms: electrochemical double-layer capacitors (EDLCs) and faradaic pseudocapacitors. EDLCs rely on the physical storage of energy through electrostatic interactions at the electrode–electrolyte interface, offering high power density and remarkable cycling stability.² On the other hand, pseudocapacitors store energy through rapid and reversible faradaic redox reactions, both at the surface and within the bulk of electrode materials, resulting in higher specific capacitance and energy density compared to EDLCs.³ Despite their advantages, traditional supercapacitors often remain standalone components, requiring additional housing and separate integration into systems. This adds bulk and increases the overall weight of devices, making them less space-efficient and limiting their application in systems where compactness and weight optimization are critical. To address these limitations, structural supercapacitors have emerged as an innovative solution, integrating energy storage with structural functionality. This approach eliminates the need for separate frameworks, reducing weight and optimizing space without compromising performance. The growing demand for compact and efficient systems has driven the development of structural supercapacitors, a significant advancement in multifunctional material research. These devices enable energy storage within load-bearing components, integrating functionality in a way that is particularly advantageous for industries such as aerospace and automotive engineering, where weight reduction directly enhances performance and fuel efficiency.^4,5

Early innovations in supercapacitors include the work of researchers who developed devices incorporating carbon fiber prepreg layers insulated by paper dielectric materials. Further advancements introduced composite efficiency metrics to evaluate both mechanical and electrical performance, highlighting the potential of these systems to revolutionize energy storage and materials science.^6–9 Woven carbon fiber (WCF) offers a unique combination of properties that make it highly suitable for supercapacitors. Its exceptional specific strength and stiffness enable superior mechanical performance while maintaining a lightweight structure. These characteristics are particularly advantageous in applications requiring a balance of durability and weight reduction. Additionally, WCF's high electrical conductivity enhances charge transport, while its mechanical durability ensures long-term stability and reliability in energy storage devices. These attributes position WCF as an excellent choice for multifunctional applications where mechanical and electrochemical performance are equally critical. These properties make WCF a preferred material for supercapacitors, combining its high specific strength, stiffness, and multifunctionality. It is extensively favored in industries requiring lightweight yet durable materials, as it facilitates faster charge movement and ensures long-term device reliability.¹⁰

Rare-earth metal orthovanadates have garnered significant attention due to their exceptional stability, low toxicity, oxygen vacancies, tunable band gaps, and ability to exhibit multiple valence states. These properties make them suitable for applications such as energy storage, gas sensors, solar cells, and supercapacitors. Transition metal-based vanadates like CeVO₄, PrVO₄, and LaVO₄ stand out for their high reversible capacity, structural stability, and environmentally friendly nature. Among them, lanthanum orthovanadate (LaVO₄) has shown significant promise for supercapacitor applications due to its unique 4f-orbital structures, solid atomic magnetic moments, and spin–orbit coupling characteristics. These attributes enable varied oxidation states and redox activity (V⁵⁺/V⁴⁺), enhancing its energy storage capabilities. However, pristine LaVO₄ faces challenges such as reduced conductivity and increased resistivity caused by electron–hole pair blockage. These shortcomings limit its electrochemical activity, making it less effective for high-performance supercapacitors. To address these limitations, doping or integrating LaVO₄ with transition-metal oxides has been proposed as an effective strategy. Transition-metal oxides, such as Co₃O₄, MnO₂, NiO, ZnO and RuO₂ (ref. 11) are renowned for their high theoretical capacitance, variable valence states, and strong redox activity. Among these, Co₃O₄ is a particularly promising candidate due to its spinel crystal structure, rich valence states, and environmentally friendly nature.¹² Co₃O₄ offers high electroactivity, low cost, and ease of synthesis, making it a widely studied material for energy storage devices. Its high theoretical capacitance, derived from multiple oxidation states (Co²⁺/Co³⁺), makes it an excellent electrode material for supercapacitors.¹³ However, despite its potential, pure Co₃O₄ suffers from several drawbacks, including poor electronic conductivity and limited ion diffusion, which restrict its practical capacitance to values far below its theoretical limit. These limitations arise from structural and electronic bottlenecks that hinder fast electron transfer and ion transport during charge/discharge processes.^14,15 To mitigate these issues, researchers have explored various strategies, such as the formation of composites with other materials like RGO–Co₃O₄–MnO₂,¹⁶ CNT–Co₃O₄,¹⁷ graphene-wrapped and Co₃O₄-intercalated hybrids,¹⁸ 3D Co₃O₄@MMoO4 (M = Ni, Co),¹⁹etc. The integration of LaVO₄ with Co₃O₄ addresses several shortcomings of pristine LaVO₄ by introducing improved electrochemical activity and conductivity. Co₃O₄ enhances the redox properties of LaVO₄ through its rich valence states and contributes additional active sites for charge storage. However, despite these improvements, the LaVO₄–Co₃O₄ composite still faces challenges such as insufficient conductivity and suboptimal long-term cycling stability. These issues can limit its ability to fully realize the synergistic potential of the two components. To overcome these residual challenges and further enhance the composite's performance, the incorporation of MXene (Ti₃C₂T_x) into the system presents a transformative solution.

MXenes, a class of 2D layered materials, have recently gained attention as high-performance materials for energy storage due to their unique combination of properties. MXenes exhibit exceptional electrical conductivity (∼6000–8000 S cm⁻¹), mechanical stability, fast ion transport, hydrophilic surfaces, and abundant active sites for redox reactions. Their layered structure facilitates rapid ion intercalation and deintercalation, while the surface terminations (–F, –OH, and –O) provide additional stability and tunability for electrochemical applications. In the context of LaVO₄–Co₃O₄ composites, MXenes play a dual role. Firstly, MXene acts as a highly conductive matrix, resolving the issue of poor electron transport in LaVO₄ and Co₃O₄. Secondly, its layered structure enhances ion mobility and prevents the aggregation of Co₃O₄ and LaVO₄ nanoparticles, ensuring uniform dispersion and maintaining structural integrity during cycling. The inclusion of MXene further leverages synergistic effects between the components. For instance, the redox-active sites of LaVO₄ and Co₃O₄ are complemented by the superior electronic properties of MXene, leading to enhanced charge transfer and faster ion diffusion. Additionally, MXene prevents self-restacking of its layers through strong van der Waals interactions, preserving its high surface area and facilitating efficient ion intercalation. Studies on similar MXene-based composites, such as MXene–WO₃ systems, have demonstrated remarkable improvements in cycle stability, capacitance retention, and electrochemical performance. For example, MXene–WO₃ nanocomposites have shown more that 90% capacitance retention, highlighting the role of MXene in enhancing durability and long-term performance.^20–22 NiFe-LDH/MXene composites, synthesized hydrothermally, show high specific capacitance (720.2 F g⁻¹), excellent stability (86% after 1000 cycles), and enhanced energy and power density.²³ MXene–NiCo₃S₄ nanocomposites synthesized via a hydrothermal process achieved optimal capacitance (0.862 F cm⁻²), high energy density (69.42 W h kg⁻¹), and excellent stability (91% retention over 10 000 cycles).⁴ The integration of MXene with LaVO₄–Co₃O₄ not only addresses the conductivity limitations but also improves the electrochemical kinetics and charge storage efficiency. MXene's ability to provide additional capacitance, stabilize the composite structure, and extend the voltage window positions the LaVO₄–Co₃O₄–MXene system as a next-generation material for energy storage applications. Furthermore, MXene's compatibility with high-temperature conditions enhances its suitability for real-world applications, where external factors like thermal energy influence ion mobility, conductivity, and surface characteristics. At elevated temperatures, MXene maintains its mechanical stability and accelerates electrolyte diffusion, enabling faster ion intercalation and improved charge storage efficiency.

To fabricate supercapacitor devices, the VARTM method was employed. Renowned for its environmental sustainability, cost-efficiency, and versatility, VARTM is a pivotal method in composite manufacturing. It is particularly advantageous for fabricating supercapacitor devices, as it seamlessly combines energy storage capabilities with load-bearing functions. These advancements present groundbreaking possibilities by decreasing weight, boosting effectiveness, and improving the overall capability of composite materials. VARTM enables seamless integration of structural components into the supercapacitor design, packing electrodes and separator materials directly within the composite structure to preserve the harmonious balance between energy storage and mechanical stability. This method facilitates complex, application-tailored designs while ensuring cost efficiency for large-scale production compared to other fabrication techniques.²⁴ In this research, a hydrothermal technique was employed for synthesizing 3% MXene-modified Co–LaVO₄ (Co–LaVO/Mx3) on the surface of woven carbon fibers (WCFs). These coated WCFs were subsequently introduced into the VARTM chamber, where the PVA–Na₂SO₄ gel electrolyte separator, was carefully packed along with the Co–LaVO/Mx3 coated WCF electrodes. The assembled composite was cured at room temperature for 48 h to stabilize the structure and ensure uniform packing (Scheme 1). The resulting Co–LaVO/Mx3-based supercapacitor device demonstrated exceptional characteristics, including high specific capacitance, superior rate capability, and outstanding cycling stability, maintaining performance for up to 50 000 cycles. This innovative approach showcases the potential of combining advanced materials with efficient manufacturing techniques to create high-performance supercapacitor applications.

Scheme 1 A schematic representation of the Co–LaVO/Mx3 based device fabrication process using the VARTM technique.

2. Experimental

2.1 Synthesis of LaVO₄

To synthesize LaVO₄ nanoparticles, 5 mmol of NH₄VO₃ and 5 mmol of NaOH were dissolved in 10 mL of deionized water to prepare a NaVO₃ solution. Then, 5 mmol of La(NO₃)₃ solution was slowly added drop by drop to the NaVO₃ solution.²⁵ The mixture was transferred to a 100 mL Teflon-lined autoclave and heated at 180 °C for 48 hours. The resulting product was washed several times with distilled water and ethanol and dried overnight at 100 °C.

2.2 Synthesis of Co₃O₄–LaVO₄

To synthesize Co₃O₄–LaVO₄, 5 mmol of Co(NO₃)₂·6H₂O and 15 mmol of CO(NH₂)₂ were dissolved in a 0.5 M NaOH solution with magnetic stirring for 30 minutes.²⁶ Afterward, 100 mg of the previously prepared LaVO₄ nanoparticles were added to the mixture. The prepared solution was placed in a Teflon-lined autoclave and heated at 180 °C for 48 h. After gradual cooling, the resulting precipitate was collected and thoroughly washed multiple times with distilled water and absolute ethanol. Finally, the product was dried overnight at 60 °C.

2.3 Synthesis of Co₃O₄–LaVO₄/Mx

Prior to synthesizing Co₃O₄–LaVO₄/Mx, MXene was meticulously prepared following the renowned method outlined by Yury Gogotsi et al., ensuring high quality and consistency for advanced material fabrication.²⁷ For the preparation of Co₃O₄–LaVO₄/Mx composites, varying quantities of MXene (2 mg, 10 mg, and 20 mg) were added in 70 mL of DI water and stirred until a homogeneous solution was formed. The subsequent steps followed the same procedure as described for the preparation of Co–LaVO in Section 2.2. The resulting powder samples were designated as Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 for 2 mg, 10 mg, and 20 mg of MXene, respectively. Fig. S1† and 1 show the schematic synthesis of LaVO and Co–LaVO and Co₃O₄–LaVO₄/Mx composites, respectively.

Fig. 1 (A) The schematic diagram for the synthesis of Co₃O₄–LaVO₄/Mx (Co–LaVO/Mx) composites; (B) XRD of LaVO, Co–LaVO, Mx, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5; (C) Raman spectra of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5; (D) TGA of Co–LaVO and Co–LaVO/Mx3.

3. Results and discussion

The XRD patterns of LaVO, Co–LaVO, and MXene-modified Co–LaVO composites (Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5) are shown in Fig. 1B. The patterns are consistent with the standard JCPDS card numbers for LaVO₄ (00-023-0324) and Co₃O₄ (01-078-1970), confirming the successful formation of a composite structure where both LaVO₄ and Co₃O₄ phases coexist. The sharp diffraction peaks of LaVO₄, observed at 2θ values of 18.58°, 24.53°, 30.97°, 33.13°, 34.95°, 37.52°, 39.87°, 44.37°, 47.36°, 48.81°, 50.28°, 51.34°, 53.81°, 56.52°, 57.76°, 61.27°, 63.68°, 65.74°, 69.18°, and 72.54°, correspond to the (101), (200), (211), (112), (220), (202), (301), (103), (321), (312), (400), (213), (411), (420), (004), (332), (204), (431), (224), and (512) planes of the tetragonal LaVO₄ structure with a P2₁/n space group. These peaks confirm the high crystallinity of LaVO₄. The incorporation of Co₃O₄ into LaVO₄ introduces additional peaks at 14.35°, 32.63°, 39.74°, 44.37°, 49.80°, 60.12°, and 72.67°, corresponding to the (111), (220), (311), (400), (422), (511), and (440) planes of Co₃O₄. These peaks confirm the successful integration of Co₃O₄ with LaVO₄, forming a robust composite structure. The simultaneous presence of LaVO₄ and Co₃O₄ peaks confirms the structural integrity of both components in the composite. The XRD pattern of the synthesized pristine Ti₃C₂ MXene reveals distinct diffraction peaks at 2θ values of 8.34°, 18.36°, 23.74°, 27.82°, 34.52°, 41.83°, and 60.75°, which are in good agreement with the standard JCPDS card no. 00-052-0875.^4,28 Among these, the most prominent peak at 8.34° corresponds to the (002) plane, which is a characteristic reflection of Ti₃C₂ MXene, indicating the successful etching of the Al layer from the parent Ti₃AlC₂ MAX phase and the formation of a well-ordered layered structure. This low-angle peak also suggests an expanded interlayer spacing, typically associated with the incorporation of surface terminations (–OH, –O, and –F) and possible intercalated species such as water or cations. The additional reflections at 18.36°, 23.74°, and 27.82° can be assigned to the (004), (006), and (008) planes, respectively, which further support the preservation of the layered 2D morphology. Peaks observed at higher angles, such as 34.52°, 41.83°, and 60.75°, correspond to (101), (103), and (110) planes, affirming the hexagonal symmetry of the Ti₃C₂ structure. Notably, the absence of any intense diffraction peaks around 39°, which is typically associated with the (104) plane of the Ti₃AlC₂ MAX phase, confirms the complete or near-complete removal of aluminum during the selective etching process. Overall, the XRD results validate the successful synthesis of phase-pure Ti₃C₂ MXene with a highly ordered 2D lamellar structure. When MXene is incorporated into the Co₃O₄–LaVO₄ system (Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5), noticeable modifications occur in the XRD patterns, including peak broadening, shifting, and splitting. The broadening of peaks is associated with a reduction in crystallite size, as confirmed by Scherrer's equation. The crystallite sizes of LaVO₄, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 were calculated to be approximately 11.64 nm, 18.34 nm, 16.87 nm, 14.91 nm, and 13.45 nm, respectively, highlighting the gradual reduction in crystallite size with increasing MXene content. This reduction suggests that MXene incorporation introduces structural modifications and disrupts the crystalline order. The incorporation of MXene also causes a consistent shift in diffraction peaks toward higher 2θ angles, indicating strain generation within the crystal lattice. This strain led to a slight compression of the unit cell. Despite these alterations, the overall crystal structure of the composite remains unchanged. This structural modification, particularly evident in Co–LaVO/Mx1 and Co–LaVO/Mx3, demonstrates the ability of MXene to act as a lattice modifier, enhancing structural interaction without compromising the stability of the composite. At higher MXene concentrations, as in Co–LaVO/Mx5, noticeable splitting of certain peaks is observed. This splitting can be attributed to increased strain and lattice distortion caused by the higher MXene content. Such distortion indicates strong interactions between MXene and the Co₃O₄–LaVO₄ matrix, leading to anisotropic stress and structural modification. The enhanced intensity of the diffraction peaks with increasing MXene content reflects improved structural alignment and interaction between MXene and the composite matrix. This increase in intensity may result from better phase alignment, increased electron density from MXene, or stronger scattering effects due to the incorporation of MXene nanosheets. While MXene peaks are not distinctly visible due to their low intensity and overlap with the dominant peaks of Co₃O₄–LaVO₄, their influence is evident through these structural changes. These observations demonstrate that MXene incorporation modifies the polymorphic properties of the Co₃O₄–LaVO₄ system while preserving its primary crystal structure. The strain generation, reduction in crystallite size, peak broadening, and splitting highlight the role of MXene as a structural enhancer. These modifications improve the interaction between MXene and the Co₃O₄–LaVO₄ phases, enhancing the composite's potential for electrochemical applications. Among the samples, Co–LaVO/Mx3 achieves the best balance between structural modification and crystallinity, making it an optimal candidate for advanced functional materials requiring enhanced ion diffusion and charge transfer capabilities.

The Raman spectrum of LaVO exhibits distinct vibrational modes indicative of its monoclinic crystalline structure. A sharp and intense peak centered at 871 cm⁻¹ corresponds to the symmetric stretching (ν₁) vibration of the VO₄³⁻ tetrahedral unit, the signature Raman-active mode for orthovanadates. A broad shoulder observed around 378 cm⁻¹ is assigned to asymmetric bending (ν₄) modes of the VO₄³⁻ group. Additional weak bands near 154 cm⁻¹ and 258 cm⁻¹ are attributed to La–O lattice vibrations and translational phonon modes. The sharpness and high intensity of these peaks confirm the phase purity and high crystallinity of the synthesized LaVO₄.²⁹ The Co–LaVO spectrum retains the VO₄³⁻ stretching peak at 869 cm⁻¹, confirming that the orthovanadate structure is preserved upon cobalt oxide incorporation. New peaks emerge at 478 cm⁻¹, 519 cm⁻¹, and 682 cm⁻¹, which are characteristic of Co₃O₄. These correspond to the F₂g and A₁g vibrational modes of the spinel Co₃O₄ phase, associated with Co–O stretching vibrations in both octahedral and tetrahedral sites.³⁰ Additionally, the low-frequency region shows enhanced intensity around 185 cm⁻¹ and 292 cm⁻¹, attributed to mixed La–O and Co–O lattice interactions. This confirms the formation of a biphasic composite with strong vibrational coupling between LaVO₄ and Co₃O₄ domains. Upon MXene incorporation in Co–LaVO/Mx1, the spectrum shows the VO₄³⁻ stretching peak slightly shifted to 866 cm⁻¹, while the Co–O peaks remain discernible at 482 cm⁻¹ and 676 cm⁻¹, albeit slightly broadened. New bands appear in the 200–250 cm⁻¹ range, corresponding to Ti–C vibrations and Ti–O terminations (–OH, –O, and –F) from the MXene surface.³¹ These shifts and broadenings suggest strong interfacial interactions and local structural distortion induced by MXene integration. In the Raman spectrum of Co–LaVO/Mx3, the VO₄³⁻ stretching peak further shifts to 863 cm⁻¹ and becomes broader with reduced intensity, indicative of partial lattice distortion or altered electronic environments. Co–O peaks remain identifiable at 486 cm⁻¹ and 667 cm⁻¹, but exhibit increased spectral overlap. Ti₃C₂T_x-related features are more pronounced, especially in the 150–250 cm⁻¹ region, reflecting a higher contribution from MXene vibrations. The overall broadening in the 300–800 cm⁻¹ region indicates enhanced phonon coupling and increased interface interactions.³² In the Raman spectrum of Co–LaVO/Mx5, the spectrum exhibits significantly broadened and merged peaks. The VO₄³⁻ symmetric stretch appears at 859 cm⁻¹, with considerable loss of intensity and definition. Co–O features become further overlapped and less distinct, appearing as broad bands near 472 cm⁻¹ and 654 cm⁻¹. The Ti–C related modes dominate the low-wavenumber region (∼210 cm⁻¹), and the spectrum shows increased baseline intensity, which may arise from enhanced electronic conductivity or defect-related scattering from MXene sheets. These spectral changes not only suggest strong interfacial charge delocalization but also imply a partial loss of long-range crystalline order.

The thermal stability of the synthesized nanocomposites was evaluated by thermogravimetric analysis (TGA) under a nitrogen atmosphere, as illustrated in Fig. 1C. The TGA curves of both Co–LaVO and Co–LaVO/Mx3 were recorded in the temperature range of 30–800 °C to assess the impact of MXene incorporation on the thermal behavior of the composite. The Co–LaVO sample exhibited excellent thermal stability, with a total weight loss of only ∼3.2% up to 800 °C. The slight initial weight loss observed below 150 °C can be attributed to the evaporation of physically adsorbed water and trace moisture retained from synthesis or ambient exposure. Beyond this, the curve remains nearly flat, indicating the absence of any significant thermally labile species and confirming the robust thermal resistance of the Co₃O₄ and LaVO₄ phases. In contrast, the Co–LaVO/Mx3 composite showed a slightly higher overall weight loss of approximately ∼9.3% over the same temperature range. The first distinct weight loss step, occurring between 150 °C and 350 °C, corresponds to the removal of intercalated water and the decomposition of surface terminations (–OH, –F, and –O) present on the MXene sheets (Ti₃C₂T_x). These functional groups are known to be thermodynamically less stable and tend to desorb or decompose at moderate temperatures.^33,34 A gradual and continuous weight loss is observed from ∼400 °C to 700 °C, which is attributed to the partial decomposition or structural degradation of the Ti₃C₂ MXene framework itself. This degradation typically involves the breakdown of the carbide layers and release of trapped gases formed from residual organic or surface moieties. Importantly, even at 800 °C, Co–LaVO/Mx3 retains over 90% of its initial weight, indicating that despite the slightly lower thermal stability introduced by the presence of MXene, the composite remains largely intact. Overall, the TGA results confirm that the inclusion of MXene into the Co–LaVO matrix results in a modest reduction in thermal stability due to the thermally sensitive nature of surface terminations and the MXene phase itself. However, this trade-off is justified by the substantial improvements observed in electrochemical performance, making Co–LaVO/Mx3 a viable and thermally tolerant candidate for supercapacitor applications.

XPS was performed to further characterize the chemical state and composition of Co–LaVO and Co–LaVO/Mx3. The full spectrum (Fig. 2A) shows the presence of elements La, V, O, and Co in both samples along with Ti, C and F in Co–LaVO/Mx3. The high-resolution XPS spectra of La 3d, V 2p, Co 2p and O 1s corresponding to Co–LaVO are presented in Fig. 2B–E, and those of La 3d, V 2p, Co 2p, O 1s, Ti 2p, C 1s and F 1s corresponding to Co–LaVO/Mx3 are presented in Fig. 2F–L, respectively. For Co–LaVO, the La 3d spectrum (Fig. 2B) displays peaks at 834.31 eV, 838.22 eV, 851.12 eV, and 855.13 eV, corresponding to the spin–orbit splitting of La 3d_5/2 and La 3d_3/2 states. The peaks at 834.31 eV and 851.12 eV represent the primary La 3d_5/2 and La 3d_3/2 states, indicating the presence of La³⁺ in the LaVO₄ lattice. The peaks at 838.22 eV and 855.13 eV are attributed to satellite shake-up peaks of La³⁺ ions. The energy difference between the La 3d_5/2 and La 3d_3/2 states in Co–LaVO is approximately 16.81 eV, which aligns well with the values reported in the literature.³⁵ The XPS spectrum of V 2p (Fig. 2C) shows peaks at 516.46 eV and 523.66 eV, corresponding to the V 2p_3/2 and V 2p_1/2 states, respectively. These peaks are indicative of V⁵⁺ oxidation states present in the LaVO₄ lattice. The observed spin–orbit splitting between the V 2p_3/2 and V 2p_1/2 peaks (∼7 eV) is consistent with expected values for vanadium in the +5-oxidation state. The peaks at 529.37 eV, and 529.60 eV are attributed to lattice oxygen (O²⁻) in the LaVO₄ structure, originating from the vanadate anion (VO₄³⁻). The slight shifts between these two peaks may indicate oxygen atoms in different local chemical environments in the crystal lattice. The peak at 531.58 eV corresponds to surface-adsorbed oxygen species or hydroxyl groups (–OH) present on the surface of the material. Surface oxygen typically appears at higher binding energies due to weaker bonding compared to lattice oxygen. These peaks confirm the presence of vanadium in the +5-oxidation state (V⁵⁺), as indicated by the 2p_3/2 and V 2p_1/2 peaks, and reflect the contributions from both lattice oxygen in the bulk material and surface-adsorbed species. The data confirm the successful formation of LaVO₄ with vanadium in the expected oxidation state and provide insights into the material's surface and bulk composition.³⁶ Based on the XPS analysis, the Co 2p spectrum (Fig. 2D) is resolved into two primary peaks along with two weak satellite features. The spin–orbit doublets corresponding to cobalt oxides appear at binding energies of 779.39 eV and 794.64 eV, representing Co 2p_3/2 and Co 2p_1/2, respectively. The Co 2p_3/2 doublet is further deconvoluted into two peaks at 779.14 eV and 780.66 eV, which are associated with Co³⁺ 2p_3/2 and Co²⁺ 2p_3/2 states. Similarly, the Co 2p_1/2 doublet is split into two distinct peaks at 794.28 eV and 796.22 eV, attributed to Co³⁺ 2p_1/2 and Co²⁺ 2p_1/2 states. The observed energy separation of approximately 15 eV between Co 2p_3/2 and Co 2p_1/2 is characteristic of the Co₃O₄ cubic phase. Additionally, the presence of two satellite peaks (Co_sat.) near the spin–orbit doublets, at binding energies of 786.25 eV and 802.88 eV, further confirms the existence of cobalt oxides.³⁷ In the O 1s spectrum of Co–LaVO (Fig. 2E), the peak at 529.37 eV is attributed to lattice oxygen (O²⁻) in the Co₃O₄ and LaVO₄ structure, which is crucial for preserving the crystalline framework and redox activity. The peak at 530.51 eV is attributed to surface oxygen, particularly hydroxyl groups (O–H), or oxygen associated with vacancies and defects. The peak at 532.39 eV is attributed to chemisorbed oxygen species, such as surface-adsorbed water molecules or oxygen-containing functional groups.³⁸ To further elucidate the interactions between Co₃O₄–LaVO₄ and MXene, the high-resolution XPS spectra of La 3d, V 2p, and Co 2p are shown in Fig. 2F–H. The binding energy differences for La 3d_5/2 and La 3d_3/2 in Co–LaVO₄–Mx exhibit a shift of approximately 0.14 eV compared to Co–LaVO₄. Similarly, the binding energies of V 4f_7/2 and V 4f_5/2 shift by around 0.12 eV, while those of Co 2p_3/2 and Co 2p_1/2 experience a shift of approximately 0.915 eV. These shifts arise due to the formation of an interface between Co–LaVO₄ and Mx, leading to alterations in electron density and the local atomic environment. The XPS results confirm that Co–LaVO₄ and Mx interact electronically at the interface, indicating their successful synthesis.³⁹ In the O 1s spectrum of Co–LaVO/Mx3, peaks appear at 529.49 eV, 530.67 eV, and 531.93 eV (Fig. 2I). The peak at 529.49 eV represents lattice oxygen (O²⁻) and is slightly shifted compared to Co–LaVO, indicating electronic interactions between the MXene and Co–LaVO framework. The peak at 530.67 eV is attributed to surface hydroxyl groups and oxygen defects, while the peak at 531.93 eV is due to adsorbed oxygen or oxygen-containing functional groups, introduced or enhanced by the MXene incorporation. The higher intensity of the adsorbed oxygen peak in Co–LaVO/Mx3 suggests increased surface functionalization and defect density due to MXene's contributions. The shifts in binding energies from Co–LaVO to Co–LaVO/Mx3 reflect significant electronic interactions and structural modifications introduced by MXene. Fig. 2J showing the Ti 2p spectrum of the Co–LaVO/Mx3 composite reveals critical details about the titanium chemical states associated with MXene. The spectrum displays well-defined peaks corresponding to the spin–orbit splitting of Ti 2p into Ti 2p_3/2 and Ti 2p_1/2 components, with a characteristic binding energy difference of approximately 6.174 eV, which is consistent with the typical splitting observed for titanium species.⁴⁰ The peaks at 455.45 eV (Ti 2p_3/2) and 461.67 eV (Ti 2p_1/2) are attributed to Ti–C bonds, characteristic of titanium carbide in the MXene core structure. The peaks at 458.60 eV (Ti 2p_3/2) and 464.75 eV (Ti 2p_1/2) correspond to Ti(IV) in titanium dioxide (TiO₂), indicating the presence of surface oxidized titanium species. Additionally, the peaks at 457.41 eV (Ti 2p_3/2) and 465.41 eV (Ti 2p_1/2) represent intermediate oxidation states of titanium, such as Ti(III), which result from partial oxidation during synthesis or environmental exposure. The coexistence of these peaks reflects the dual nature of titanium in the MXene material, with contributions from both titanium carbide (Ti–C) and titanium oxide (Ti–O) bonds. The higher binding energy peaks correspond to oxygen-containing functional groups (e.g., –O and –OH), which are common terminations in MXenes and contribute to their enhanced surface reactivity and hydrophilicity. The XPS spectrum of the C 1s region for the Co–LaVO/MXene composite, as depicted in Fig. 2K, reveals multiple deconvoluted peaks corresponding to different chemical states. The peak at 284.39 eV is attributed to graphitic carbon (C–C/C=C), signifying the existence of sp²-hybridized carbon in the MXene structure. The peak at 285.72 eV is associated with C–O bonds, suggesting surface oxygen functionalities. A smaller peak observed at 288.25 eV corresponds to the O=C–O group, indicating the presence of carboxylic functional groups. Additionally, the peak at 281.04 eV is assigned to the Ti–C bond, characteristic of the MXene core structure. The major components in the F 1s (Fig. 2L) region are C–Ti–F_x and TiO_2−xF_x at BEs of 684.92 eV and 685.5 eV respectively, indicating the presence of fluorine species as a consequence of the HCl + LiF etching process.⁴¹

Fig. 2 (A) XPS survey of Co–LaVO and Co–LaVO/Mx3; XPS of Co–LaVO (B) La 3d, (C) V 2p, (D) Co 2p, and (E) O 1s; XPS of Co–LaVO/Mx5 (F) La 3d, (G) V 2p, (H) Co 2p, (I) O 1s, (J) Ti 2p, (K) C 1s, and (L) F 1s.

The SEM analysis of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 is shown in Fig. S2A–D† and 3A–L, respectively. The SEM image of LaVO (Fig. S2A†) reveals a spongy morphology characterized by interconnected voids and pores, indicative of a highly porous material. This structure suggests that the LaVO₄ particles have aggregated to form a porous network. The micrograph shows regions of agglomerated particles with a smooth and consistent texture, distributed uniformly across the field of view. Upon closer examination of Fig. S2B† at a magnification of 2 μm, pseudo-circular and interconnected particle morphologies are observed, intricately intertwined to create the distinctive spongy texture of the material. The uniform distribution of these aggregates is critical for maintaining consistent material properties. The spongy nature of the material, coupled with the observed voids and interconnected pores, indicates that LaVO₄ may possess a high surface area. The incorporation of Co₃O₄ into the LaVO₄ network (Fig. S2C and D†) results in tighter particle clustering, reducing the prominence of voids and pores and creating a more compact and rugged structure. The connectivity between particles in Co–LaVO is stronger, enhancing structural integrity and leading to a more robust arrangement. The surface texture becomes rougher with the addition of Co₃O₄, transforming the open, spongy structure of LaVO₄ into a denser and more cohesive composite. These morphological differences emphasize the impact of Co₃O₄ incorporation, which modifies the open, porous structure of LaVO₄ into a denser, interconnected composite with improved structural cohesion and robustness. The SEM image of the MXene-modified Co₃O₄–LaVO₄ (Fig. 3A–L) shows a well-defined layered structure characteristic of MXene sheets, with an accordion-like morphology indicative of successful exfoliation. The Co₃O₄–LaVO₄ particles appear as irregular aggregates distributed across the MXene surface, demonstrating good interfacial contact between the components. The MXene layers exhibit a distinct, stacked configuration with visible edges and interlayer spacing. The Co₃O₄–LaVO₄ particles adhere to the MXene sheets, suggesting effective integration and consistent distribution of components. The structural integrity of the MXene layers is preserved, ensuring stability and a cohesive composite. The SEM images of Co–LaVO/Mx1 (Fig. 3A–C) reveal sparsely distributed MXene sheets, providing limited coverage of the Co₃O₄–LaVO₄ particles. The Co₃O₄–LaVO₄ particles are observed as irregular aggregates that are unevenly distributed, leaving significant portions of the MXene surface exposed. At higher magnification, the MXene layers retain their layered morphology, but the interaction with Co₃O₄–LaVO₄ particles appears less pronounced. The composite demonstrates a partially dispersed structure with gaps between particles, indicating incomplete integration. The optimized Co–LaVO/Mx3 (Fig. 3C–I) shows a significantly improved morphology. At lower magnifications, the MXene sheets are well-dispersed with minimal particle aggregation, forming a uniform and interconnected structure. At moderate magnifications, the interaction between MXene and Co₃O₄–LaVO₄ particles becomes more pronounced, with the MXene layers forming a continuous network and the particles adhering firmly to the surface. The visible interlayer spacing of MXene sheets and the rough texture of Co₃O₄–LaVO₄ particles contribute to the hierarchical architecture. At higher magnifications, fine structural details, including small particles uniformly distributed across the MXene surface, highlight efficient integration and deposition. The composite maintains a balanced and cohesive structure with preserved MXene sheet integrity and strong interfacial interactions. The SEM images of Co–LaVO/Mx5 (Fig. 3J–L) show dense coverage of MXene sheets, resulting in noticeable aggregation. At lower magnifications, overlapping MXene sheets and clustering of Co₃O₄–LaVO₄ particles are evident, leading to reduced porosity. At moderate magnifications, the accordion-like structure of MXene becomes distorted, with uneven particle distribution and partial masking of the MXene layers. At higher magnifications, the MXene sheets exhibit compaction and reduced interlayer spacing. The Co₃O₄–LaVO₄ particles vary in their attachment, with some embedded deeply while others remain loosely adhered. The higher MXene content results in a denser morphology, reduced uniformity, and overlapping of MXene sheets, which could hinder material functionality. Comparatively, the Co–LaVO/Mx3 exhibits the most balanced morphology, with uniform particle distribution, minimal aggregation, and optimal integration of MXene sheets and Co₃O₄–LaVO₄ particles. The 1% MXene content provides limited coverage and incomplete integration, while the 5% MXene content introduces excessive aggregation and overlapping, reducing structural uniformity. The 3% MXene loading achieves a cohesive, well-dispersed, and structurally optimized composite. From BET analysis, the detailed surface characteristics and pore volume of the obtained nanomaterials were ascertained using the nitrogen-sorption isotherm; the outcomes are displayed in Fig. S3.† The isotherm is categorized as a type II isotherm by IUPAC, with a broad range of pore sizes. The surface areas of Co–LaVO and Co–LaVO/Mx3 were found to be 65.82 and 82.35 m² g⁻¹ and pore sizes were 9.20 and 13.50 nm respectively.

Fig. 3 SEM images of Co–LaVO/Mx1 at (A) 5 μm, (B) 2 μm, and (C) 1 μm magnifications; SEM images of Co–LaVO/Mx3 at (D) 10 μm, (E) 5 μm, (F) 3 μm, (G) 2 μm, (H) 1 μm, and (I) 0.5 μm magnifications; SEM images of Co–LaVO/Mx5 at (J) 10 μm, (K) 5 μm, and (L) 2 μm magnifications.

The HRTEM analysis provides an in-depth characterization of the Co–LaVO and Co–LaVO/Mx3 nanocomposites, revealing their structural, compositional, and interfacial features across various magnifications (Fig. 4A–J). These results, supported by SAED patterns, EDAX spectra, and elemental mapping, confirm the successful synthesis, integration, and crystallinity of the composites (Fig. 5A–D). For Co–LaVO, distinct nanostructures with varied morphologies, including rounded and faceted particles, are observed. At 50 nm magnification (Fig. 4A), the particles appear aggregated but maintain distinct boundaries, confirming the structural integrity and successful synthesis of the composite. Higher magnifications at 20 nm (Fig. 4B) and 10 nm (Fig. 4C) reveal semi-spherical to slightly irregular particle shapes with sharp and well-defined interfaces between Co₃O₄ and LaVO₄. These sharp boundaries indicate strong interfacial interactions, which are crucial for achieving synergistic properties. The bright and dark contrasts in the images arise from differences in electron density between Co₃O₄ and LaVO₄, aiding in identifying their distribution. At 2 nm magnification (Fig. 4D), lattice fringes corresponding to well-ordered atomic arrangements and high crystallinity are evident. The SAED pattern (Fig. 4E) displays bright diffraction spots, further confirming the crystalline nature of Co–LaVO. The Co–LaVO/Mx3 nanocomposite, examined at various magnifications, exhibits a hierarchical structure with well-integrated phases. At 20 nm (Fig. 4F), the MXene sheets display their thin, layered structure, confirming exfoliation and a large surface area. Co₃O₄ nanoparticles appear as darker regions uniformly distributed across the MXene surface, while smaller LaVO₄ clusters are embedded within the matrix. These features highlight the structural homogeneity and MXene's role as a conductive backbone for anchoring Co₃O₄ and LaVO₄. At 10 nm magnification (Fig. 4G), finer details of the MXene layers become evident, showcasing pronounced transparency and stacking that emphasize their 2D nature. The interfaces between MXene, Co₃O₄, and LaVO₄ are sharp and well-defined, suggesting strong interfacial bonding that enhances mechanical stability and charge transfer properties. At higher magnifications of 5 nm and 2 nm (Fig. 4H and J), the crystalline features of the Co–LaVO/Mx3 composite become clearly visible. Sharply defined lattice fringes confirm the well-ordered arrangement of atoms in the MXene, Co₃O₄, and LaVO₄ phases. The strong bonding at these interfaces and the uniform dispersion of Co₃O₄ and LaVO₄ ensure maximum exposure of active sites, enhancing the composite's functional properties. The SAED pattern (Fig. 4I) of Co–LaVO/Mx3 exhibits bright diffraction spots and rings, confirming its high crystallinity.⁴²Fig. 4J shows the HRTEM of Co–LaVO/Mx3 at 2 nm along with the corresponding Inverse Fourier Transform (IFT) images and line histograms of the selected lattice fringes. These analyses reveal lattice fringes with calculated d-spacings of 0.34 nm for the (200) planes of monoclinic LaVO₄,⁴³ 0.29 nm for the (220) planes of cubic Co₃O₄ (ref. 44) and 0.24 nm for the (002) planes of Ti-based MXene.⁴⁵

Fig. 4 HR-TEM of Co–LaVO at magnifications of (A) 50 nm, (B) 20 nm, (C) 10 nm, and (D) 2 nm and (E) SAED of Co–LaVO; HR-TEM of Co–LaVO/Mx3 at magnifications of (F) 20 nm, (G) 10 nm, and (H) 5 nm and (I) SAED of Co–LaVO/Mx3, (J) HR-TEM image of the Co–LaVO/Mx3 composite at a magnification of 2 nm, showing lattice fringes corresponding to distinct components of the composite. (i) LaVO₄ displays a lattice fringe spacing of 0.34 nm (ii) Co₃O₄ exhibits lattice fringes with a spacing of 0.29 nm, (iii) MXene shows a fringe spacing of 0.24 nm. Insets show the corresponding FFT patterns and intensity profiles for each region, confirming the high crystallinity and well-defined lattice structure of the composite.

Fig. 5 (A) Elemental mapping of the Co–LaVO composite showing uniform distribution of O, V, La, and Co elements over the composite, (B) EDX spectrum of Co–LaVO confirming the presence of the corresponding elements with no significant impurities. (C) Elemental mapping of Co–LaVO/Mx3, illustrating the uniform dispersion of additional elements, including C, Ti, and F introduced by the MXene incorporation alongside O, V, La, and Co, (D) EDX spectrum of Co–LaVO/Mx3 verifying the presence of all constituent elements and highlighting the contribution of MXene in the composite.

The EDAX spectra and elemental mapping further provide a comparative analysis of Co–LaVO and Co–LaVO/Mx3 composites, offering insights into their elemental compositions and distributions. For Co–LaVO (Fig. 5A), the elemental mapping reveals the uniform distribution of oxygen (O), vanadium (V), lanthanum (La), and cobalt (Co), confirming a homogeneous and well-structured material. The EDAX spectrum (Fig. 5B) supports this, showing the presence of these elements without significant impurities, validating the purity of the composite. In contrast, Co–LaVO/Mx3 includes additional elements such as carbon (C), titanium (Ti), and fluorine (F), alongside O, V, La, and Co, corroborating the effective integration of MXene into the composite (Fig. 5C). Elemental mapping illustrates the homogeneous dispersion of all elements, with carbon and titanium attributed to the MXene framework, cobalt and oxygen corresponding to Co₃O₄, and vanadium and lanthanum originating from LaVO₄. The fluorine content is uniformly distributed across the MXene surface, indicative of –F terminations that enhance the composite's stability and functionality. The EDX spectrum of Co–LaVO/Mx3 (Fig. 5D) further validates the presence of these elements, emphasizing the successful integration of MXene into the composite matrix. Additionally, peaks observed around ∼8.04 keV and ∼8.90 keV correspond to the Cu Kα and Kβ emission lines, respectively, which are attributed to the copper (Cu) grid used during TEM-EDS analysis. These peaks are well-known artifacts arising from the supporting substrate and do not originate from the sample itself. This comparative analysis underscores the structural integrity and uniform elemental distribution in both composites. While Co–LaVO displays a pure and homogeneous structure, the incorporation of MXene introduces additional functionalities, including improved electrochemical and catalytic properties. These findings validate the successful synthesis and integration of Co–LaVO and Co–LaVO/Mx3 composites, with MXene significantly contributing to enhanced material performance for advanced applications.

3.1 Three electrode system for supercapacitors

The cyclic voltammetry (CV) analysis of WCFs, LaVO, Co–LaVO, and their MXene composites (Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5) reveals significant insights into their electrochemical behaviours and performance as electrode materials in a three-electrode system using 1 M Na₂SO₄ as the aqueous electrolyte. The CV curves were obtained within a voltage range of 0 to 0.8 V vs. Ag/AgCl at a scan rate of 100 mV s⁻¹, aiming to assess the effect of MXene incorporation at various concentrations (Fig. 6A). The LaVO electrode, a single-phase material, shows typical pseudo-capacitive behavior with a semi-rectangular CV curve. However, it demonstrates limited specific capacitance and rate capability. The Co–LaVO electrode, which involves the incorporation of Co₃O₄ into LaVO₄, displays significantly enhanced electrochemical activity compared to LaVO alone. This enhancement can be attributed to the improved conductivity and electrochemical redox behaviour of Co₃O₄, which facilitates better charge storage and ion transport at the electrode interface. The Co–LaVO/Mx1 electrode shows a notable improvement in electrochemical performance. The CV curve shows increased current density compared to the Co–LaVO electrode, indicating better electrochemical activity. This improvement is likely due to the high surface area and excellent conductivity of MXene, which aids in ion diffusion and provides additional active sites for charge storage. The Co–LaVO/Mx3 electrode, demonstrates the highest electrochemical performance in terms of both capacitance and rate capability. The area under the CV curve is significantly larger than those for the other samples, indicating superior charge storage capacity. This improvement can be attributed to an optimal balance between the MXene content and the active material (Co–LaVO), which enhances the electrochemical response while preventing excessive MXene aggregation, thereby avoiding a reduction in ion transport pathways. In contrast, the Co–LaVO/Mx5 electrode shows a decrease in electrochemical performance. The CV curve exhibits a reduced current density compared to Co–LaVO/Mx3. This decrease in performance is likely due to the excessive amount of MXene, which leads to increased aggregation. As a result, the surface area of the active material decreases, reducing the number of available active sites for ion transport and subsequently lowering the overall capacitance. The Co–LaVO/Mx3 sample, shows the best balance between electrochemical activity and rate capability. The semi-rectangular shape of its CV curve, characteristic of pseudocapacitive behavior, suggests efficient charge storage with fast, reversible redox reactions. As seen in comparison with other electrode materials, the inclusion of MXene (especially Co–LaVO/Mx3) leads to superior electrochemical performance. MXene's high electrical conductivity and large surface area help improve ion transport and provide more active sites for charge storage, thus enhancing the overall electrochemical performance. However, excessive MXene content (as in Co–LaVO/Mx5) can result in aggregation that limits these benefits.

Fig. 6 (A and B) Relative assessment of CV curves of WCFs, LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 at 100 mV s⁻¹. (B) Comparison of specific capacitance of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 at 100 mV s⁻¹. (C–G) CV curves of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5, respectively at different scanning speeds. (H) Relative assessment of specific capacitance of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 at different scan rates (10 to 100 mV s⁻¹).

The specific capacitance comparison at a scan rate of 100 mV s⁻¹ for LaVO, Co–LaVO, and their MXene composites (Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5) revealed significant variations in electrochemical performance, with Co–LaVO/Mx3 demonstrating the maximum specific capacitance of 949.74 F g⁻¹ (Fig. 6B). The specific capacitance of the Co–LaVO/Mx3 electrode was notably superior compared to that of LaVO 190.64 F g⁻¹, Co–LaVO 312.72 F g⁻¹, Co–LaVO/Mx1 377.52 F g⁻¹, and Co–LaVO/Mx5 883.92 F g⁻¹, as shown in the CV analysis. The specific capacitance of the Co–LaVO/Mx3 composite reached a higher value, benefiting from the optimal concentration of MXene and the synergy between MXene and Co–LaVO leads to a robust structure that improves the specific capacitance and enhances the overall electrochemical activity of the electrode.

Fig. 6C–G presents CV graphs for LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 samples at scan rates varying from 10 to 100 mV s⁻¹. Moreover, Fig. S4† shows the CV graph of WCFs within a scan rate range of 10 to 100 mV s⁻¹. The pseudocapacitive behavior of the CV curves is evident across all samples, as indicated by their quasi-rectangular shapes, which persist even at high scan rates, reflecting excellent kinetic reversibility and rate capability. As the scan rate increases from 10 to 100 mV s⁻¹, the area under the CV curves expands for all samples, confirming enhanced charge storage with faster redox kinetics. Notably, the current density shows significant variation, with Co–LaVO/Mx3 consistently demonstrating superior performance due to the optimal integration of MXene, which enhances ion transport and charge storage. However, for Co–LaVO/Mx5, a slight decline in performance is observed at higher scan rates, likely due to increased resistance or agglomeration effects. The transformation of the CV curves from semi-rectangular shapes at lower scan rates to more rectangular profiles at higher scan rates further highlights the rapid and reversible surface-controlled charge storage processes.

As the scan speed increases from 10 to 100 mV s⁻¹, the specific capacitance for each sample shows a decreasing trend due to the limited diffusion of ions at higher scan rates (Fig. 6H). For LaVO, the specific capacitance values range from 587.41 F g⁻¹ at 10 mV s⁻¹ to 190.64 F g⁻¹ at 100 mV s⁻¹. Similarly, Co–LaVO shows an improvement, with values decreasing from 623.11 F g⁻¹ at 10 mV s⁻¹ to 312.71 F g⁻¹ at 100 mV s⁻¹. Among the MXene composites, Co–LaVO/Mx3 demonstrates the highest specific capacitance across all scan rates, ranging from 1314.08 F g⁻¹ at 10 mV s⁻¹ to 949.74 F g⁻¹ at 100 mV s⁻¹. This is attributed to the optimal integration of MXene, which provides enhanced charge transfer and surface accessibility for ion storage. The increasing trend from LaVO to Co–LaVO/Mx3 underscores the role of MXene in enhancing electrochemical performance, while the slight decline observed in Co–LaVO/Mx5 highlights the importance of optimizing MXene content.

Fig. 7A presents the comparison between GCD curves of WCFs, LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 at 1 A g⁻¹. The incorporation of MXene into the Co₃O₄–LaVO₄ system significantly enhances the electrochemical performance of the composites, as evidenced by their extended discharge times compared to pristine LaVO. Among these, Co–LaVO/Mx3 exhibits the longest discharge time, reflecting its superior charge storage capability. At a current density of 1 A g⁻¹, Co–LaVO/Mx3 achieves a remarkable specific capacitance of 1287.80 F g⁻¹, surpassing LaVO (575.67 F g⁻¹), Co–LaVO (610.66 F g⁻¹), Co–LaVO/Mx1 (783.56 F g⁻¹), and Co–LaVO/Mx5 (1196.45 F g⁻¹) (Fig. 7B). This trend demonstrates a consistent increase in discharge time and specific capacitance as the MXene content increases from Co–LaVO/Mx1 to Co–LaVO/Mx3, attributed to the synergistic interaction between MXene and Co₃O₄–LaVO₄, which enhances ion transport and charge storage. However, a minor decrease in performance is observed for Co–LaVO/Mx5, possibly resulting from an excessive amount of MXene, which obstructs reactive regions and limits ion accessibility. These outcomes underline the importance of optimizing MXene content to achieve the best electrochemical performance.

Fig. 7 (A) Relative assessment of GCD curves of WCFs, LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 at 1 A g⁻¹. (B) Comparative specific capacitance of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 at 1 A g⁻¹. (C–G) GCD curves of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5, respectively at various current densities. (H) Relative assessment of specific capacitance of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 at different current densities (1 to 12 A g⁻¹). (I) Comparative EIS analysis of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5.

The symmetrical GCD curves of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 at varying current densities validate the pseudocapacitive behaviour observed in the CV analysis (Fig. 7C–G). The potential response increases proportionally with current density, confirming efficient charge storage and discharge dynamics. At lower current densities, the GCD curves exhibit a quasi-triangular shape, characteristic of a reversible redox reaction mechanism. As the current density increases, the curves become more triangular, highlighting the dominance of surface-controlled charge storage mechanisms facilitated by MXene's high conductivity and interlayer ion diffusion. Fig. 7H shows the specific capacitance values derived from the GCD curves for all samples at different current densities. Co–LaVO/Mx3 achieves superior specific capacitance, with values of 1287.80, 1160.86, 1096.63, 1053.72, 1021.71, 995.89, 974.40, 956.42, 940.94, 930.75, 851.32, and 816.67 F g⁻¹ at current densities of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 A g⁻¹, respectively. These results outperform those of LaVO (ranging from 575.67 to 58.05 F g⁻¹) and Co–LaVO₄ (610.66 to 210.96 F g⁻¹), as well as the other MXene composites, Co–LaVO/Mx1 (783.56 to 243.97 F g⁻¹) and Co–LaVO/Mx5 (1196.45 to 760.98 F g⁻¹). The linear increase in specific capacitance from Co–LaVO/Mx1 to Co–LaVO/Mx3 reflects the optimal integration of MXene into the composite, resulting in enhanced ion transport, abundant electroactive sites, and efficient charge storage. However, the slight decline observed in Co–LaVO/Mx5 is likely due to the excessive MXene content, which reduces ion accessibility and active site utilization. Fig. 7H further demonstrates that Co–LaVO/Mx3 exhibits the highest specific capacitance, even at higher current densities. The superior performance of Co–LaVO/Mx3 is attributed to its optimal interlayer spacing and enhanced electrical conductivity, which facilitate fast ion intercalation/deintercalation and efficient charge transfer processes. These results highlight the Co–LaVO/Mx3 composite as a highly stable and efficient material, offering remarkable specific capacitance and excellent reversibility across a wide range of current densities.

The electrochemical impedance spectroscopy (EIS) analysis of LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 was conducted to study their charge transport properties in the frequency range of 0.01 Hz to 100 kHz. The Nyquist plots for all samples, shown in Fig. 7I, reveal critical insights into their charge transfer resistance (R_ct) and solution resistance (R_s), which directly influence their electrochemical performance. The R_s values for LaVO, Co–LaVO, Co–LaVO/Mx1, Co–LaVO/Mx3, and Co–LaVO/Mx5 are 8.24 Ω, 7.41 Ω, 7.02 Ω, 5.45 Ω, and 6.28 Ω, respectively. Among these, Co–LaVO/Mx3 exhibits the lowest R_s, indicating superior electrical conductivity due to the optimized integration of MXene, which enhances electron transport pathways within the composite. Similarly, the R_ct values for the samples are 17.12 Ω, 15.98 Ω, 11.34 Ω, 7.05 Ω, and 9.34 Ω, respectively. The significantly lower R_ct for Co–LaVO/Mx3 reflects its improved electrode–electrolyte interface, facilitating efficient charge transfer. The incorporation of optimized MXene in Co–LaVO/Mx3 increases the active surface area and promotes better interaction between the electrolyte ions and the electrode material, enhancing its overall electrochemical performance. To further interpret these behaviors, the EIS spectra were fitted using an equivalent circuit model comprising R_s(CPE − (R − W))T, which accounts for the electrolyte resistance (R_s), non-ideal capacitive behavior (CPE), interfacial charge transfer resistance (R), Warburg diffusion (W), and low-frequency tangent capacitance (T) (Fig. S5†). The fitted model showed excellent agreement with the experimental data, especially for Co–LaVO/Mx3, which displayed the smallest semicircle and shortest diffusion tail in the Nyquist plot. This confirms its lowest R_s and R_ct values, corresponding to highly efficient electron and ion transport across the electrode–electrolyte interface. The optimized MXene loading in this sample creates a well-connected conductive framework, increasing charge mobility and active site accessibility. In contrast, the broader semicircles observed for LaVO and Co–LaVO indicate sluggish charge transfer due to their lower conductivity. Although Co–LaVO/Mx5 also benefits from MXene incorporation, a slight increase in R_ct compared to Co–LaVO/Mx3 suggests possible aggregation effects at higher MXene content, which may hinder ion diffusion. Overall, the EIS results and equivalent circuit fitting clearly establish that Co–LaVO/Mx3 demonstrates the most favorable charge transport kinetics among all samples, owing to its well-balanced electronic conductivity, interfacial architecture, and porous diffusion network. The conductivity of LaVO (0.00125 S cm⁻¹) improves with cobalt doping to 0.00164 S cm⁻¹ due to enhanced charge transport via Co²⁺/Co³⁺ states (Fig. S6†). Incorporating MXene further boosts conductivity: Co–LaVO/Mx1 reaches 0.00184 S cm⁻¹, while Co–LaVO/Mx3 peaks at 0.00343 S cm⁻¹—nearly three times that of LaVO—owing to the formation of efficient conductive networks. However, in Co–LaVO/Mx5 (0.00298 S cm⁻¹), excessive MXene slightly reduces conductivity, likely due to aggregation. Overall, Co–LaVO/Mx3 shows the most effective conductivity enhancement, making it ideal for electrochemical applications.

The electrochemical stability of Co–LaVO/Mx3 was evaluated through GCD measurements conducted over 10 000 cycles at a high current density of 12 A g⁻¹ within a voltage range of 0 to 0.8 V. As shown in Fig. S7,† the specific capacitance of Co–LaVO/Mx3 exhibited only a slight decline over extended cycling, retaining an impressive 90% of its initial value and a coulombic efficiency of 98% after 10 000 cycles. This high retention indicates exceptional long-term stability and durability, essential for practical energy storage applications. The minor loss in specific capacitance during cycling is attributed to the inherent stresses experienced during repeated charge–discharge processes. However, the strong structural integrity of the Co–LaVO/Mx3 composite ensures minimal degradation, maintaining stable performance even under high-stress conditions. The synergistic combination of Co₃O₄–LaVO₄ and MXene enhances both mechanical stability and electrochemical performance, enabling the material to withstand prolonged cycling with high efficiency. This remarkable cycling stability of Co–LaVO/Mx3, coupled with its high capacitance retention, positions it as a reliable and effective electrode material for advanced energy storage systems.

The electrochemical performance of the Co–LaVO–Mx composite is significantly influenced by the concentration of MXene. At a low MXene concentration in Co–LaVO/Mx1, the composite exhibits improved conductivity due to the presence of MXene; however, the limited content does not fully utilize its conductive pathways, resulting in moderate electrochemical performance. With an optimal MXene concentration in Co–LaVO/Mx3, the composite demonstrates optimal performance, benefiting from a well-balanced structure that ensures superior electronic conductivity and efficient Na⁺ ion transport. The interconnected porous network enhances charge transfer kinetics and active material utilization, leading to the highest specific capacitance among the tested compositions and improved cycling stability. However, at a higher MXene concentration in Co–LaVO/Mx5, excessive MXene leads to aggregation, reducing the number of accessible active sites and impeding ion diffusion. This negatively impacts charge storage efficiency and electrochemical performance. Therefore, the optimal MXene loading in Co–LaVO/Mx3 provides the best balance between conductivity, ion diffusion, and structural stability, making Co–LaVO/Mx3 the most effective composition for high-performance energy storage applications (Fig. 8).

Fig. 8 Schematic illustration of the Co–LaVO/Mx electrode during the discharge/charge processes.

3.2 Charge storage mechanism

To thoroughly investigate the charge storage mechanism and reaction kinetics of the Co–LaVO/Mx3 composite, a detailed analysis was performed using CV to distinguish between capacitive and diffusion-controlled contributions. The CV measurements were performed within a potential range of 0 to 0.8 V at varying scan rates from 1 to 10 mV s⁻¹. The relationship between the current (i) and the scan rate (ν) was examined using the power-law equation, providing valuable insights into the contributions of different charge storage processes.⁴⁶

i = aν^b (1)

where a and b are adjustable parameters. The b-value is determined by analyzing the slope of the plot between the logarithm of current and the logarithm of scan rate. A b-value of 0.4 suggests a semi-infinite diffusion-controlled mechanism, whereas a b-value of 1.0 indicates a charge storage process dominated by capacitive behavior.⁴⁷ Values ranging from 0.5 to 1 typically indicate that both capacitive and diffusion-controlled mechanisms contribute to the overall charge storage process.⁴⁸ In this study, the b-value at 0.4 V was determined to be 0.96 (Fig. 9A), indicating rapid reaction kinetics with a substantial pseudocapacitive contribution. This suggests a charge storage mechanism primarily governed by surface processes with minimal diffusion constraints.⁴⁹ Similarly, b-values were determined at various potentials for Co–LaVO/Mx3, as shown in Fig. 9B and C. Within the potential range of 0.1 V to 0.7 V, the b-value for Co–LaVO/Mx3 exceeds 0.5, indicating a predominantly surface-mediated charge storage mechanism.²⁰

Fig. 9 (A) Plot of the logarithm of current vs. the logarithm of scan rate at 0.4 V; (B) plot of the logarithm of current versus the logarithm of scan rate at different voltages; (C) b-valuesat different voltages; (D) plot between 1/C (F g⁻¹) and v^1/2 (mV s⁻¹); (E) plot between C and ν^1/2; (F) plot between C_total and ν^1/2; (G) plot between C_outer and ν^1/2; (H) comparison of the contribution of outer and inner surface capacitance at different scan rates.

Additionally, the charge storage on the outer surface and within the inner bulk of the nanocomposite electrode was evaluated using the Trasatti equation.⁵⁰ The total charge (C_total) is typically determined as the sum of the charge stored on the electrode's outer surface (C_outer) and within its inner bulk (C_inner).

C_total = C_inner + C_outer (2)

As the scan rate increases, the diffusion of ions into the inner surfaces of the electrode becomes progressively limited, as there is insufficient time for the faradaic reactions, which are diffusion-controlled, to fully occur. Conversely, at lower scan rates, the ions have adequate time to access the inner surfaces, allowing the entire electrode to participate in the charge storage process. To determine the total capacitance (C_total), a plot of 1/C versus ν^1/2 is extrapolated to ν = 0 (Fig. 9D).²⁰ In contrast, the charge on the outer surface of the electrode remains unaffected by variations in the scan rate. The C_outer is determined from the intercept of the C(ν) vs. ν^−1/2 plot (Fig. 9E) i.e., when ν → ∞.⁵¹ Trasatti plots (Fig. 9F and G) offer valuable insights into the charge storage mechanism within the electrode, showing an internal surface charge storage capacity of 7711.15 F g⁻¹ and an external surface capacity of 1335.85 F g⁻¹. These results emphasize the dominant role of the outer surface in overall capacitance, driven by efficient ion transport and adsorption, particularly at higher scan rates. Fig. 9H illustrates the shift in charge storage behavior with increasing scan rates, highlighting the growing contribution of double-layer capacitance. At elevated scan rates, this mechanism becomes predominant as it relies on rapid ion adsorption on the electrode's outer surface. In contrast, diffusion-controlled faradaic reactions within the porous interior of the electrode become less significant, as the shorter time frame limits proton diffusion and interaction with deeper active sites.

Furthermore, the diffusion and capacitive contributions in Co–LaVO/Mx3 were studied by utilizing by the following equation.

i(V) = k₁ν + k₂ν^1/2 (5)

where, i is the current, ν is the scan rate, k₂ν^1/2 signifies the diffusion-controlled contribution and k₁ν represents the capacitive contribution. With the linear fitting of the j(ν)/ν^1/2vs. ν^1/2 plot at different scan rates for the Co–LaVO/Mx3, k₁ and k₂ values were calculated from the slope and intercept, respectively (Fig. 10A). Fig. 10B and C illustrate the comparison between the capacitive (light green) and diffusion-controlled (red) contributions to charge storage in the Co–LaVO/Mx3 composite at scan rates of 1 mV s⁻¹ and 10 mV s⁻¹. At 1 mV s⁻¹, charge storage is diffusion-controlled, contributing 21.07% of the total charge storage, while the capacitive contribution is minimal at 78.92%. In contrast, at 10 mV s⁻¹, the diffusion-controlled contribution decreases to 15.73%, and the capacitive contribution increases significantly to 84.26%, indicating a shift toward surface-dominated charge storage with higher scan rates. This trend suggests that faster charge transfer kinetics at elevated scan rates favor capacitive processes, while diffusion constraints at the electrode surface are reduced. Further insights into the behavior at intermediate scan rates (2 to 9 mV s⁻¹) are provided in Fig. S8A–H,† reinforcing this observed transition from diffusion-dominated to capacitive-dominated storage as the scan rate increases. As depicted in Fig. 10D, the increase in capacitive contribution and the corresponding reduction in diffusion-controlled contribution with increasing scan rates are attributed to enhanced ion adsorption and desorption kinetics at the electrode surface. These processes become more prominent at higher scan rates, where faster kinetics limit the influence of bulk diffusion. These findings underscore the dynamic nature of charge storage mechanisms in the Co–LaVO/Mx3 composite, highlighting the material's adaptability across different operating conditions.

Fig. 10 (A) k₁ and k₂ are linearly fitted at various potentials. (B and C) CV curve at 1 and 10 mV s⁻¹ illustrating the contributions from both surface capacitance and diffusive capacitance, and (D) the proportion of charge storage arising from capacitive and diffusion-controlled mechanisms at varying scan rates.

4. VARTM assisted Co–LaVO/Mx3-based supercapacitor device

To assess the energy storage performance of the supercapacitor, a symmetric supercapacitor device (SS-device) was fabricated using the VARTM technique with Co–LaVO/Mx3 as the active material. As shown in Fig. S9,† the potential window of the device was carefully evaluated through CV measurements conducted over a range of voltages. The CV curves were examined to ensure electrochemical stability and to avoid any distortion or redox activity beyond the stable range. Based on this analysis, the optimal working potential was identified as 1.7 V. As illustrated in Fig. 11A, CV tests were performed across a voltage range of 0 to 1.7 V at varying scan rates to evaluate the electrochemical behavior of the SS-device. The CV curves exhibit an irregular rectangular shape with slight redox peaks, indicating the presence of both EDLC and faradaic redox reactions, both contributing to enhanced charge storage capability. At lower scan rates, the CV curves maintain their shape, demonstrating efficient charge storage and reversibility of the redox processes. As the scan rate increases, the current response proportionally rises, indicating good rate capability and rapid ion transport kinetics within the electrode material. The broad redox peaks suggest the contribution of multiple redox reactions from Co₃O₄ and LaVO₄, further enhancing the overall energy storage performance. Additionally, the absence of significant distortions in the CV curves even at higher scan rates suggests the structural integrity and stability of the Co₃O₄–LaVO₄–MXene composite.

Fig. 11 (A) CV of the Co–LaVO/Mx3 based SS-device at varying scan rates. (B) Galvanostatic charge/discharge profiles at different current densities. (C) Specific capacitance recorded across different current densities. (D) Ragone plots depicting the relationship between energy density and power density, referencing constituent materials reported in the existing literature. (E) Retention rates of capacitance recorded at a scan rate of 16 A g⁻¹ over 50 000 cycles, with the inset demonstrating the corresponding charge/discharge profiles (last 100 cycles) (F) electrochemical impedance spectroscopy data before and after 50 000 cycles. (G) Digital photograph showcasing the fabricated device powering a LED for 400 s, demonstrating its functionality.

To further validate the suitable voltage window, GCD measurements were performed at different potential limits (Fig. S10†). The resulting GCD curves were analyzed for symmetry, linearity, and charge–discharge duration. The data confirmed that 1.7 V is the optimal operating potential, providing efficient charge storage with minimal polarization and stable performance over extended cycling. To further evaluate the electrochemical performance, GCD measurements were conducted at various current densities, as depicted in Fig. 11B. The GCD curves, recorded across a potential range of 0–1.7 V, exhibit quasi-triangular profiles, indicative of an efficient charge storage mechanism. Specific capacitance values were calculated to be 317.08, 273.47, 240.91, 207.78, 174.34, 130.43, 82.09, and 32.05 F g⁻¹ at current densities of 2, 4, 6, 8, 10, 12, 14 and 60 A g⁻¹, respectively (Fig. 11C). The observed decrease in specific capacitance with increasing current density is attributed to insufficient time for complete adsorption/desorption of electrolyte ions within the electrode pores, which hinders the faradaic redox reactions at the electrode–electrolyte interface. Furthermore, the rise in IR-drop with increasing current density highlights the inherent resistive losses within the device.⁵²

The Ragone plot in Fig. 11D offers a clear representation of the energy and power density performance of the Co–LaVO/Mx3 SS-device, emphasizing its excellent electrochemical properties. The device exhibits energy densities of 74.85, 64.46, 56.67, 48.88, 41.08, 30.69, 19.36, and 7.56 W h kg⁻¹ at a power density of 1000, 2000, 3000, 4000, 5000, 6000, 7000, and 8000 W kg⁻¹. This performance demonstrates the capability of the Co–LaVO/Mx3 to achieve a balanced trade-off between energy storage and power delivery. The observed values are competitive with, and in some cases, surpass those reported for other supercapacitor systems (Fig. 11D), showcasing the advanced design of the composite material (Table 1).

Table 1 A comparative analysis of the electrochemical properties of the Co–LaVO/Mx3 based device with previously developed supercapacitor materials

Device	Device fabrication method	Potential (V)	Electrolyte	Specific capacitance (F g^−1)	No. of cycles and capacitance retention	Energy density (W h kg^−1)	Power density (W kg^−1)	Ref.
Ti3C2Tx	—	1.5	1 M Na2SO4	64.2 at 0.17 A g^−1	3000 cycles, 82%	5.7	66.5	53
Te/Ti3C2Tx	—	1.8	1 M Na2SO4	150.6 at 0.17 A g^−1	3000 cycles, 92%	67.8	151	53
WO3/MXene//AC	Swagelok cell	1.5	1 M H2SO4	46 at 1 A g^−1	20 000 cycles, 72%	14	6000	20
Ti3C2Tx/CoS2/CuCo2S4	Pouch cell	1.8	1 M TEABF4/DMSO	93.7 at 1 A g^−1	10 000 cycles, 96%	42.2	60	54
NiCoP/MXene//AC	—	1.6	4 M KOH	140 at 1 A g^−1	5000 cycles, 86.57%	49.7	800.1	55
NiCo-LDH/Ti3C2Tx-5//AC	Swagelok cell	1.8	KOH	104.83 at 1 A g^−1	10 000 cycles, 85.71%	44.6	852.5	56
CuO@βCD/MXene	—	—	1 M KOH	1132.44 at 4.54 A g^−1	10 000 cycles, 86%	19.30	222.18	57
Co3O4–MXene	Swagelok cell	0 to −1	6 M KOH	95.71 at 1 A g^−1	8000 cycles, 83%	26.06	700	58
La doped Ni–Sn oxide/RGO	Coin cell	1.6	1 M Na2SO4	106 at 1 A g^−1	10 000 cycles, 75%	38	870	59
La2O3–NiO	Pouch cell	1.3	3 M KOH	48.75 at 1 A g^−1	2000 cycles, 77.2%	4.3	200	60
Co–LaVO/Mx3	VARTM	1.7	PVA–Na 2 SO 4 gel electrolyte	317.08 at 2 A g^− ^1	50 000 cycles, 71%	74.85	1000	Our study

---

The cycle stability of the Co–LaVO/Mx3 SS-device was rigorously evaluated at a high current density of 16 A g⁻¹, with the results depicted in Fig. 11E as capacitance retention over 50 000 charge–discharge cycles. Remarkably, the device retained approximately 71% of its initial capacitance, demonstrating outstanding long-term durability. The inset in Fig. 11E presents the GCD curves from the final 100 cycles, showing consistent performance and confirming the device's structural integrity with no noticeable degradation throughout the cycling process. In addition to its capacitance retention, the device exhibited a coulombic efficiency of 80% after 50 000 cycles. This high efficiency indicates negligible energy dissipation during the charge–discharge cycle, highlighting the device's exceptional energy management performance. These findings collectively highlight the superior stability, efficiency, and reliability of the Co–LaVO/Mx3 SS-device under high current and prolonged operational conditions.

The EIS analysis provided valuable insights into the electrochemical properties of the Co–LaVO/Mx3-based SS-device. Following 50 000 cycles, no significant variations were detected (Fig. 11F). The plot exhibited a small semicircle in the high-frequency region, corresponding to low charge transfer resistance and a nearly vertical line in the low-frequency region, signifying excellent capacitive behavior.

The Co–LaVO/MX-3 composite exhibits exceptional stability and performance due to the synchronized interaction of its components. The MXene layer, with its superior conductivity and mechanical strength, plays a crucial role in mitigating structural degradation of the composite during prolonged electrochemical cycles. This property ensures the mechanical resilience of the overall material, preserving the integrity of Co₃O₄ and LaVO₄ during repeated charge and discharge processes. Furthermore, MXene serves as a flexible and robust protective layer, accommodating the volume changes of Co₃O₄ and LaVO₄ during redox reactions. This buffering action reduces the likelihood of cracking or fracturing, enhancing the cycle stability and maintaining the structural cohesion of the composite. Additionally, the high conductivity of MXene accelerates electron transport, while the redox-active properties of Co₃O₄ and LaVO₄ synergistically contribute to the superior electrochemical performance, ensuring long-term durability and efficiency of the composite electrode.²⁰ To demonstrate its practical potential, the VARTM assisted Co–LaVO/Mx3-based SS-device was tested to illuminate LEDs (Fig. 11G). The device successfully illuminated seven LEDs for 400 s, underscoring its capability as a reliable energy storage solution. These results highlight the potential of Co–LaVO/Mx3 composites as advanced materials for high-performance supercapacitors, paving the way for their integration into next-generation energy storage technologies.

5. Conclusion

The electrochemical behaviour of LaVO, Co–LaVO, and Co–LaVO/MXene composites, with different concentrations of MXene was comprehensively analysed to identify the optimal electrode material for supercapacitors. Among these, the Co–LaVO/Mx3 composite demonstrated the highest performance, attaining a specific capacitance of 1287.80 F g⁻¹ at 1 A g⁻¹. This performance significantly surpassed that of pristine LaVO (575.67 F g⁻¹), Co–LaVO (610.66 F g⁻¹), Co–LaVO/Mx1 (783.56 F g⁻¹), and Co–LaVO/Mx5 (1196.45 F g⁻¹). The exceptional performance of the Co–LaVO–Mx3 composite stems from its optimized MXene content, which ensures a balanced combination of conductivity, efficient ion transport, and abundant redox-active sites. MXene's layered structure enables rapid ion diffusion, enhances charge transfer kinetics, and increases the operational voltage window. The strong van der Waals interactions within MXene prevent self-restacking and aggregation of Co₃O₄ and LaVO₄ particles, thereby enhancing the structural stability and ensuring uniform dispersion. Lower MXene content in Co–LaVO/Mx1 was insufficient to achieve significant conductivity enhancement, while higher MXene content in Co–LaVO/Mx5 led to aggregation, reducing ion accessibility and active surface area. The Co–LaVO/Mx3 composite benefits from the synergistic combination of its components. Co₃O₄ contributes high redox activity through the Co²⁺/Co³⁺ couple, while LaVO₄ enhances stability and introduces additional redox functionality via the V⁵⁺/V⁴⁺ couple. MXene's outstanding conductivity and abundant active sites enhance charge transfer and promote efficient ion transport. The synergistic interactions among these components result in improved specific capacitance, excellent cycling stability, and efficient energy storage performance. The Co–LaVO/Mx3 composite also demonstrated remarkable cycling stability, retaining approximately 90% of its initial capacitance after 10 000 charge–discharge cycles. For practical applications, a SS-device was fabricated by employing the VARTM technique, with Co–LaVO/Mx3 hydrothermally deposited on WCF. The SS-device achieved a specific capacitance of 317.57 F g⁻¹ at 2 A g⁻¹ and a maximum energy density of 74.85 W h kg⁻¹ at a power density of 1000 W kg⁻¹. It maintained excellent cycling stability, retaining 71% of its initial capacitance over 50 000 cycles. These findings showcase the transformative impact of MXene in enhancing the electrochemical performance of Co₃O₄–LaVO₄ composites, particularly through improved conductivity, efficient ion transport, and elevated redox activity. The Co–LaVO/Mx3 composite stands out as a breakthrough material for energy storage, combining exceptional specific capacitance and long-term cycling stability with robust practical applicability. Its performance highlights its potential to drive advancements in next-generation supercapacitors, addressing the growing demand for high-efficiency, durable, and compact energy storage solutions in cutting-edge technologies.

Data availability

The data supporting the findings of this study, titled “Effect of MXene on Co₃O₄–LaVO₄ nanocomposites for synergistic charge transport enhancement and high-performance VARTM assisted solid-state supercapacitor devices using woven carbon fiber” are available within the article and its ESI† files.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This work was financially supported by the Korea Ministry of Environment (MOE) as a Graduate School specialized in Integrated Water Resources Management. Additionally, this work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIT) (No. RS-2019-NR040065). Technical assistance for HR-TEM was provided by the Core Research Support Center for Natural Products and Medical Materials (CRCNM).

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5ta02046h

‡ These authors contributed equally.

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