A phase-tuned layered 1T W-MoS₂/PEDOT:PSS hybrid: functional engineering towards self-binding supercapacitor cathodes

Abstract

A layered two-dimensional 1T-molybdenum disulfide (MoS₂), substitutionally doped with tungsten (W), and incorporated with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), was synthesized via a one-pot hydrothermal method to form W_xMo_1−xS₂/PEDOT:PSS hybrid composites as self-binding electrodes for supercapacitors. The optimal doping and hybrid construction of W_0.1Mo_0.9S₂/PEDOT:PSS (10W-MS/P) increase the interlayer spacing and stabilize the metallic 1T phase, which enhance the electrical conductivity and structural durability in an electrochemical analysis under a three-electrode configuration using 1 M H₂SO₄ electrolyte. 10W-MS/P exhibits a high specific capacitance (C_m) of 845.14 F g⁻¹ and an areal capacitance (C_a) of 4.73 F cm⁻² at 1 A g⁻¹ and the electrode also demonstrates excellent stability, retaining 89% of its capacitance after 10 000 cycles. The asymmetric coin cell supercapacitor (ASC-CC), fabricated using a self-binding cathode of 10W-MS/P, delivers an energy density of ≈6.53 Wh kg⁻¹ and a power density of ≈79.64 W kg⁻¹. After 20 000 continuous cycles, the device retains 75% of capacitance and it reveals that the hybrid material possesses significant potential as an efficient and durable electrode for next-generation energy storage applications.

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1. Introduction

The increase in global population, coupled with rapid advances in industry and technology, will drive worldwide energy demand up by nearly 50% over the coming decades.¹ As fossil fuel resources are swiftly depleted and environmental concerns intensify, there is a pressing need to develop innovative solutions focused on energy conservation and storage. In this context, the shift towards clean, renewable and highly efficient energy storage devices is essential.² Among several energy devices, supercapacitors have gained significant attention at the global level due to their outstanding power densities, long cycle lifespans, environmental friendliness, cost-effectiveness, and their broad range of electrode applications arising from distinctive physical and chemical characteristics.³ Various materials including metal–organic frameworks (MOFs), metal oxides, carbon-based materials, layered double hydroxides (LDHs) and transition metal dichalcogenides (TMDs) have been explored for supercapacitors.^4–7 TMDs stand out as promising electrode materials for supercapacitors because of their high specific surface area, hydrophilicity, exposed active edge sites, and multiple accessible oxidation states, all contributing to effective charge storage and fast ion transport.⁸ Within this material family, molybdenum disulfide (MoS₂) is especially notable, owing to its layered, sheet-like morphology and suitable band gap for energy storage applications. This morphology increases the accessible surface area for interlayer charge storage and provides ample space for ion intercalation during electrochemical cycling, facilitating improved charge kinetics and response.⁹ MoS₂ also features excellent chemical stability and high ionic conductivity. Its sandwich like S-M-S architecture, maintained by weak van der Waals forces, endows it with a theoretical storage capacity exceeding that of graphite.¹⁰ Two key crystallographic phases are observed in 2D MoS₂, the semiconducting 2H phase and the metallic 1T phase. The 1T-MoS₂ phase is particularly advantageous, offering a hydrophilic surface and electrical conductivity ≈10⁷ times higher than that of the 2H form.¹¹ These unique properties make 1T-MoS₂ a highly attractive material for next-generation supercapacitor electrodes.

The incorporation of transition metal elements via doping has been shown to significantly stabilize the 1T phase of MoS₂. Doping serves as a powerful approach to tuning the properties of 2D-MoS₂, particularly in modulating the relative properties of its crystal phases.¹² Various doping techniques have been employed, including electrostatic doping,¹³ substitutional doping,¹⁴ intercalation, and surface charge-transfer doping.¹⁵ Emerging methods such as reversible solid-state doping,¹⁶ remote modulation doping, and thickness modulation doping¹⁷ have also gained attention. Among these, substitutional doping is one of the most prevalent methods, involving the replacement of lattice atoms by different elements with varying valence electron counts, thereby altering the electronic carrier concentration.¹⁸ This doping not only influences electronic properties but can also induce morphological changes that lead to the preferential stabilization of octahedrally coordinated 1T phase sheets over hexagonal 2H sheets.¹⁹ Also, substitutional doping introduces significant strain within the MoS₂ nanosheet lattice, further modifying its electronic structure and enhancing its functional characteristics.²⁰ Moreover, integrating organic molecules such as conducting polymers (CPs) with 2D-MoS₂ results in the formation of organic–inorganic hybrid materials. CPs offer the advantages of low weight and excellent mechanical flexibility, making them highly attractive for supercapacitors.²¹ Among CPs, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) stands out due to its intrinsic conductivity and flexibility, acting as an efficient conductive binder to hold MoS₂ nanosheets together, facilitating the fabrication of self-binding organic–inorganic hybrid electrodes.²² Additionally, PEDOT:PSS enhances charge transport and mechanical stability of the electrodes, boosting their electrochemical performance. Its environmentally friendly water based processability, combined with tuneable conductivity, allows it to perform various functional roles within electronic devices, making it an ideal component for energy storage systems.²³

The first study on TMD-based supercapacitors reported a specific capacitance of around 100 F g⁻¹ for MoS₂ prepared by thermal evaporation.²⁴ Since then, multiple studies have focused on MoS₂ and MoS₂ based composites as electrode materials for supercapacitors. For example, Wang et al. demonstrated that reversible diffusion of electrolyte ions is enabled by a swollen lamellar structure with enlarged interlayer spacing, caused by the insertion of intercalants like NH₃ and NH₄⁺ hydrothermally in 1T/2H hybrid phase ammoniated MoS₂. This material exhibited a high pseudocapacitance of 346 F g⁻¹ and retained 95.4% of its capacitance after 2000 cycles.²⁵ In another study, Prakash et al. prepared vertically aligned Ni-doped MoS₂ with expanded interlayer spacing through a simple hydrothermal process.²⁶ The electrodes with 6% Ni doping showed a high specific capacitance of 528 F g⁻¹ at 1 A g⁻¹ and maintained 85% capacity retention after 10 000 cycles. More recently, Chao et al. reported a facile one-pot hydrothermal synthesis of solution-processable MoS₂/PEDOT:PSS hybrid electrodes that achieved a capacitance of 474 mF cm⁻² at 0.5 mA cm⁻² and excellent cycling stability with 224 mF cm⁻² retained after 5000 cycles at 4 mA cm⁻².²⁷ Collectively, these studies highlight the favourable electrochemical performance of MoS₂ and its hybrid electrodes, making them ideal candidates for supercapacitors.

In this work, we present W_xMo_1−xS₂/PEDOT:PSS hybrid electrode materials synthesized via a solution processable, one-pot hydrothermal reaction. Layered pristine 1T-MoS₂ was also prepared using the same hydrothermal method. Among the prepared hybrids, the W_0.1Mo_0.9S₂/PEDOT:PSS (10W-MS/P) electrode showed an increase in interlayer spacing, enhancing its capacitive properties and exhibiting superior performance. It achieved a maximum specific capacitance (C_m) of 845.14 F g⁻¹ and areal capacitance (C_a) of 4.73 F cm⁻² at 1 A g⁻¹. The self-binding hybrid electrodes retained their superior performance even at higher current densities (C_m and C_a of 119.71 F g⁻¹ and 0.67 F cm⁻², respectively, at 25 A g⁻¹). This electrode sustained an outstanding cycle life with 89% capacitance retention over 10 000 cycles under self-binding conditions in 1 M H₂SO₄ acidic electrolyte. Further, an asymmetric supercapacitor coin cell (ASC-CC) was fabricated using self-binding 10W-MS/P as the cathode and graphite powder (GP) as the negative electrode (10W-MS/P//GP). The cell delivers an energy density of ≈6.53 Wh kg⁻¹ and a power density of ≈79.64 W kg⁻¹, with a capacitance retention of 75% after 20 000 continuous cycles. This unique combination of properties suggests enhanced charge storage and transport capabilities. Our study presents an effective approach to stabilize the metallic 1T phase and achieve self-binding contact between the active material and substrate, highlighting its potential for portable energy storage devices.

2. Experimental methods

2.1. Materials

Ammonium molybdate tetrahydrate ((NH₄)₆Mo₇O₂₄·4H₂O), poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and tungsten(VI) chloride (WCl₆) were purchased from Tokyo Chemical Industry Pvt Ltd, India (TCI). Thiourea (CH₄N₂S), L-tartaric acid (C₄H₆O₆), ethanol and H₂SO₄ were obtained from Sisco Research Laboratories (SRL), Chennai.

2.2. Synthesis of IT-MoS₂ nanosheets

Pristine 1T-MoS₂ was synthesized by dissolving ammonium molybdate tetrahydrate (0.7 mM, 0.864 g) and L-tartaric acid (0.8 mM, 0.120 g) in 15 mL of deionised water. Thiourea (12.5 mM, 0.950 g) was then added, and the solution was stirred at room temperature for 1 hour. The resulting clear and homogeneous solution was transferred into a 25 mL Teflon lined stainless steel autoclave and heated at 180 °C for 24 hours. The product was collected by centrifugation and washed three times with deionised water and ethanol. Finally, the black product was dried under vacuum at 80 °C for 12 hours.

2.3. Synthesis of the MoS₂/PEDOT:PSS hybrid

The same procedure was followed for the synthesis of MoS₂/PEDOT:PSS hybrid. Ammonium molybdate tetrahydrate (0.7 mM, 0.864 g) and L-tartaric acid (0.8 mM, 0.120 g) were dissolved in 15 mL of deionised water. Thiourea (12.5 mM, 0.950 g) was added, and the solution was stirred at room temperature for 1 hour. Then, 192 µL of PEDOT:PSS (12 µL per mL) was added into the solution with the aid of sonication. The resulting polymer dispersed mixture was transferred to a 25 mL Teflon lined stainless steel autoclave and heated at 180 °C for 24 hours. The product was collected after centrifugation with deionised water and ethanol. Finally, the dark product was dried under vacuum at 80 °C for 12 hours.

2.4. Synthesis of W_xMo_1−xS₂/PEDOT:PSS hybrids

For the synthesis of W_xMo_1−xS₂/PEDOT:PSS hybrids, ammonium molybdate tetrahydrate (0.66, 0.63, and 0.59 mM corresponding to 0.821 g, 0.778 g, and 0.728 g, respectively), tungsten(VI) chloride (0.035, 0.07, and 0.105 mM corresponding to 0.013 g, 0.027 g, 0.039 g, respectively) and L-tartaric acid (0.8 mM, 0.120 g) were dissolved in 15 mL of deionised water. After addition of thiourea (12.5 mM), only tungsten was fully dissolved, and the solution was stirred at room temperature for 1 hour. Then, 192 µL of PEDOT:PSS (12 µL for 1 mL) was added to the solution with sonication. The polymer dispersed mixture was transferred to a 25 mL Teflon lined stainless steel autoclave and heated at 180 °C for 24 hours. The product was collected by centrifugation and washed three to four times with deionised water and ethanol. Finally, the dark product was dried under vacuum at 80 °C for 12 hours.

2.5. Self-binding electrode fabrication and asymmetric coin-cell assembly

The MoS₂/PEDOT:PSS and W_xMo_1−xS₂/PEDOT:PSS hybrid electrodes were fabricated using the doctor blade method. The slurry was prepared by mixing active hybrid material and carbon black in a weight ratio of 8 : 1, with a few drops of N-methyl-2-pyrrolidone (NMP), using a mortar and pestle, without the addition of an external binder. The resulting slurry was coated onto a graphite sheet (0.5 cm × 0.5 cm) and dried at 80 °C for 12 hours. A pristine MoS₂ electrode was prepared using the same method, but with the addition of polyvinylidene fluoride (PVDF) as a binder, in a weight ratio of 8 : 1 : 1 (active material : carbon black : PVDF).

The asymmetric CR2032 coin-cell supercapacitor was fabricated using 10W-MS/P as the cathode, graphite powder as the anode, and Whatman-40 filter paper soaked 1 M H₂SO₄ as the separator. The electrode mass ratio was optimized based on (eqn (3)) to ensure charge balance between the two electrodes. The cathode was prepared by coating 10W-MS/P onto a graphite sheet with a diameter of 16 mm using a self-binding strategy (8 : 1), as described for the W_xMo_1−xS₂/PEDOT:PSS hybrid electrode preparation. The anode was fabricated on a graphite sheet (16 mm) following the same method used for the MoS₂ electrode, with a binder-based composition (8 : 1 : 1). The CR2032 coin cell assembled by placing the cathode on the positive case, followed by the separator with two drops of 1 M H₂SO₄ electrolyte, then the anode, spacer, wave spring, and finally the negative case. After crimping, the coin cell was allowed to rest for 4 hours to ensure effective electrolyte diffusion into the electrodes. The fabricated cell was named ASC-CC (asymmetric supercapacitor-coin cell).

2.6. Electrochemical measurements

The electrochemical performance of the fabricated electrodes and CR2032 cell was analysed using cyclic voltammetry (CV), galvanic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS), conducted on an Origalys OGF500 electrochemical workstation.

The specific capacitance (C_m, F g⁻¹) and areal capacitance (C_a, F cm⁻²) were calculated from the non-linear GCD curves using the following (eqn (1) and (2)).²⁸

Here, i(A) represents the discharge current, ∫Vdt is the integrated area under the discharge curve, S(cm²) denotes the active electrode surface area, ΔV(V) is the potential window, and m(g) corresponds to the mass of active material coated on the graphite substrate.

For the asymmetric CR2032 coin-cell configuration, charge balance between the two electrodes was maintained according to the relationship q⁺ = q⁻, with the optimal mass ratio of the cathode and anode determined using (eqn (3)).

where C₊ and C₋ denote the specific capacitance of the positive and negative electrodes, m⁺/m⁻ are their respective masses, and ΔV corresponds to the potential windows. In this work, the total mass loading for the cathode and anode was 1.5 mg cm⁻² and 2.1 mg cm⁻², respectively.

The coulombic efficiency (η) of the device was evaluated from the GCD curve using (eqn (4)).

where t_c and t_d represent the charge and discharge times, respectively.

The energy density (E, Wh kg⁻¹) and power density (P, W kg⁻¹) were calculated using (eqn (5) and (6)).

where ΔV is the potential window obtained from the GCD curve, C_m is the specific capacitance, and Δt denotes the discharge time.

The electroactive surface area of the electrode materials was calculated using the Randles–Ševčík equation (eqn (7)).

where i_p is the peak current intensity, F is Faraday's constant, n is the number of electrons involved in the redox reaction, C is the electrolyte concentration, A is the electroactive surface area, D is the diffusion coefficient of the electrolyte in cm² s⁻¹, v is the scan rate, R is the universal gas constant, and T is the absolute temperature.

3. Results and discussion

The 1T MoS₂ nanosheets were synthesised via a hydrothermal method. In this process, phase formation is initiated through the thermal decomposition of thiourea under hydrothermal conditions, using ammonium molybdate tetrahydrate as the molybdenum (Mo) precursor. Thiourea plays a dual role, acting both as a reducing agent to convert Mo(VI) into Mo(IV) species and as a source of sulfide anions.²⁹ To control symmetry and promote homogeneous nanocrystal growth, tartaric acid was introduced.³⁰ During the hydrothermal reaction, tartaric acid decomposes into achiral products, which are subsequently removed during the washing step.^31,32 A similar mechanism was employed in the preparation of the hybrid materials. For tungsten (W) substitutional doping of MoS₂, tungsten chloride was used as the tungsten precursor, while poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was introduced as the conductive polymeric matrix to form the hybrid and self-binding material, as shown in Fig. 1a. The W doping ratio in MoS₂ (W_xMo_1−xS₂) was systematically varied at 5 : 95 (W_0.05Mo_0.95S₂), 10 : 90 (W_0.1Mo_0.9S₂), and 15 : 85 (W_0.15Mo_0.85S₂), whereas the PEDOT:PSS concentration was fixed at 12 µL mL⁻¹, following previous findings.^27,33 The hybrids were labelled as MS/P, 5W-MS/P, 10W-MS/P and 15W-MS/P, where W indicates tungsten, MS indicates MoS₂ and P indicates PEDOT:PSS. Exactly 192 µL of PEDOT:PSS dispersion (1.3 wt% solids, 1.0 g mL⁻¹ density) was added during synthesis (which is approximately equivalent to 2.5 mg of PEDOT:PSS solid). MoS₂ yield of 0.40 g (≈402.5 mg) corresponds to a PEDOT:PSS weight fraction of ≈0.6 wt%. Self-binding electrodes were fabricated using 100% hybrid powder without additional binder, thereby maintaining a PEDOT:PSS content of ≈0.6 wt%.

Fig. 1 (a) Schematic representation of the synthesis of pristine MoS₂ and W_xMo_1−xS₂/PEDOT:PSS hybrids, (b and c) XRD of pristine MoS₂ and MS/P, 5W-MS/P, 10W-MS/P, and 15W-MS/P hybrids, (d) crystallographic structure of 1T-MoS₂ according to ICSD 254956 adapted from the Cambridge Crystallographic Data Centre (CCDC), (e) Raman spectra of pristine and hybrid materials, (f) N2 adsorption–desorption curve of 10W-MS/P, and (g) pore size distribution curve of 10W-MS/P.

Powder X-ray diffraction (P-XRD) analysis was utilized to investigate the phase purity and crystal structure of materials. Detailed analysis of peaks at 9.14° and the second order peak at 18.34° corresponds to the crystallographic planes of (001) and (002), respectively, representing the 1T-phase formation of MoS₂. According to Bragg's law, the calculated d-spacings are 9.67 Å and 4.83 Å, respectively, which indicates that the d-spacing between the MoS₂ layer of ≈0.96 nm is attributed to the intercalation of ammonium ions and is characteristic of 1T-MoS₂ synthesised via the hydrothermal method.^34,35 The peaks at 32.64° and 57.37° correspond to the (101) and (110) planes, respectively (Fig. 1b). The observed diffraction matches well with that in the reference article by Branzi et al.³¹ and the ICSD 254956 file (Fig. 1d), confirming a hexagonal structure with the space group P3̄m1 and lattice parameters of a = b = 3.190 Å and c = 5.945 Å. Further, after W doping into MoS₂, no additional crystalline phase peaks were detected, which confirms successful substitutional doping of W and partial replacement of Mo in the lattice of MoS₂. Importantly, the (001) diffraction peaks of the doped samples exhibit a slight shift to lower diffraction angles compared to pure MoS₂, as shown in Fig. 1c, indicating a change in interlayer spacing and interlayer strain in the MS/P, 5W-MS/P, 10W-MS/P, and 15W-MS/P hybrid materials.³⁶ Additionally, the streaks and slight peak broadening observed around 24° to 30° correspond to PEDOT:PSS,³⁷ confirming successful formation of the hybrid material. The crystallite sizes were calculated using the Debye–Scherrer equation (eqn (8)), where λ denotes the X-ray wavelength of Cu Kα radiation and β and θ represent the full width at half maximum (FWHM) and the diffraction angle, respectively. Calculated values for the crystallite sizes were 32.29 nm, 32.29 nm, 25.06 nm, 21.97 nm, and 20.12 nm for pristine MoS₂, MS/P, 5W-MS/P, 10W-MS/P, and 15W-MS/P hybrids, respectively.

Raman spectra for MoS₂ and its hybrid materials were recorded over the wavenumber range of 120 cm⁻¹ to 450 cm⁻¹, as shown in Fig. 1e. The Raman spectrum for pristine MoS₂ displays vibrational modes, including the E_1g band at 282 cm⁻¹, which is associated with the octahedral coordination of Mo atoms in the 1T-MoS₂ structure.³⁸ Signals at 193 cm⁻¹ and 336 cm⁻¹ correspond to the J₂ and J₃ modes, in tandem with the 377 cm⁻¹ peak, which is assigned to the E²_1g mode of the 2H phase. A prominent Raman band at 149 cm⁻¹ corresponds to J₁ and can be attributed to the Mo–Mo stretching vibration characteristic of the 1T phase of MoS₂.³⁹ The hybrid materials exhibit similar spectral features, with peak shifts from their original positions indicative of defect formation and confirming successful W doping in the MoS₂ lattice. Additionally, peaks attributable to PEDOT:PSS are not observed due to the minimal presence of these polymer sources within the hybrids.

The nitrogen adsorption–desorption isotherms of the pristine and hybrid materials, shown in Fig. 1f and S1a–d, exhibit a pronounced uptake at high relative pressures (P/P₀ ∼ 0.8–1.0) with clear hysteresis loops, characteristic of Type IV isotherms according to IUPAC classification and confirming the mesoporous nature of the materials.⁴⁰ The BET (Brunauer–Emmett–Teller) surface areas were determined to be ≈13.4 m² g⁻¹ for pristine MoS₂, ≈1.5 m² g⁻¹ for MS/P, ≈12.9 m² g⁻¹ for 5W-MS/P, ≈48.5 m² g⁻¹ for 10W-MS/P, and ≈15.5 m² g⁻¹ for 15W-MS/P. The corresponding BJH (Barrett–Joyner–Halenda) pore size distribution (Fig. 1g and S1e–h) reveals average pore diameters of ≈18.6 nm, ≈5.8 nm, ≈24.2 nm, ≈52.7 nm, and ≈19.9 nm, respectively, while pore volumes are ≈0.080 cc g⁻¹, ≈0.004 cc g⁻¹, ≈0.105 cc g⁻¹, ≈0.349 cc g⁻¹, and ≈0.102 cc g⁻¹. The decrease in surface area and pore volume upon adding PEDOT:PSS to MoS₂ is primarily due to polymer aggregation over the nanosheets, which blocks pores, fills interlayer spaces, and reduces N₂-accessible surface sites. W doping alters the surface area non-monotonically. At 10% W, the highest surface area, largest pore diameter and pore volume are achieved due to optimal defects, lattice strain, and 1T phase stabilization, which effectively overcome PEDOT:PSS-induced densification and maximize porosity. Lower (5%) and higher (15%) doping levels result in smaller values, caused by insufficient or excessive lattice distortion leading to limited exfoliation. The highly porous structure (≈52.7 nm) in the 10W-MS/P hybrid improves electrochemical performance by enabling efficient ion diffusion and electrolyte access.

X-ray photoelectron spectroscopy (XPS) was carried out to gain deeper insights into the surface elemental composition and chemical states of pristine MoS₂ and the hybrid 10W-MS/P material. The survey spectra (Fig. 2a) confirm the presence of Mo 3d, S 2p, S 2s, W 4f, O 1s, and C 1s signals in the hybrid 10W-MS/P, while pristine MoS₂ shows Mo 3d, S 2p, S 2s, C 1s, and O 1s signals. All the XPS spectra were calibrated using the C–C peak at 284.5 eV as the binding energy reference. The C 1s spectrum of pristine MoS₂ (Fig. 2b) exhibits peaks at 284.5, 285.1, 286.2, and 288.8 eV, attributed to C–C, C–O, C–S, and C=O bonds, respectively. These features originate from adventitious carbon, typical for an air exposed MoS₂ surface. In the hybrid, the C–O, C–S and C=O peaks are shifted from their original positions, indicating the incorporation of PEDOT:PSS moieties.⁴¹ The W 4f spectrum (Fig. 2c) displays two deconvoluted peaks at 38.6 and 36.2 eV, corresponding to W⁶⁺ 4f_5/2 and 4f_7/2 states, confirming successful W doping.³⁶ A detailed analysis of the Mo 3d core-level spectra (Fig. 2d) of pristine MoS₂ reveals the presence of Mo⁶⁺ peaks and S 2s orbital peaks at 235.9 and 225.6 eV, respectively. The same characteristic peaks observed for 10W-MS/P show a small blueshift of 0.21 eV for S 2s. In addition, pristine MoS₂ shows two distinct peaks at 231.5 and 228.6 eV corresponding to Mo 3d_3/2 and Mo 3d_5/2, which exhibit a small blueshift in 10W-MS/P. To understand these blueshifts in the Mo 3d_3/2 and Mo 3d_5/2 peaks, it was further deconvoluted. Upon deconvolution, it can be identified that the components can be attributed to the 1T (metallic) and 2H (semiconducting) phases of MoS₂.⁴² The phase ratios, calculated from the integrated area of the curves (Fig. 2e and f), indicate that the hybrid 10W-MS/P predominantly contains the 1T phase, contributing 65.8% and 76.3% for Mo 3d_3/2 and Mo 3d_5/2, respectively, compared to 34.2% and 23.7% for the 2H phase. In comparison, pristine MoS₂ displays a more balanced distribution, with the 1T : 2H ratio being 49.7% : 50.3% for Mo 3d_3/2 and 60.3% : 39.7% for Mo 3d_5/2. This marked increase in the 1T phase verifies phase engineering as a result of W substitutional doping. Further insights are obtained from the S 2p spectra (Fig. 2g), which reveal distinct S 2p_1/2 and S 2p_3/2 peaks.²⁷ In pristine MoS₂, these contribute around 60.3% and 57.3% at binding energies of 169.4 and 162.5 eV for S 2p_1/2 with complementary values of 39.7% and 42.7% at binding energies of 168.2 and 161.2 eV for 2p_3/2, characteristic of sulfur sites in the 1T/2H phases. In the hybrid 10W-MS/P, the same characteristic peaks appear with a small blueshift, with an increased contribution from S 2p_3/2 (PEDOT) and S 2p_3/2 (PSS), increasing to 55.9% and 59.7% (Fig. 2h and i), respectively, highlighting pronounced electronic interaction at the hybrid interface. The observed blueshifts in the Mo 3d, S 2p, and C 1s spectra of the 10W-MS/P hybrid arise from electronic structure modulation due to W substitutional doping and interfacial charge interaction with PEDOT:PSS. W possesses a higher electronegativity (χ = 2.36) than Mo (χ = 2.16). This induces partial electron transfer from Mo sites to W, decreasing electron density around Mo, causing blueshifts to higher binding energies in the Mo 3d peaks. Additionally, p-type PEDOT:PSS facilitates hole injection into the MoS₂ phase at the heterojunction, depleting electrons in the inorganic component via Fermi level alignment and interfacial dipole formation. This is evidenced by the blueshift in C 1s peaks from PEDOT:PSS carbon atoms, reflecting reduced electron shielding. These synergistic effects of W induced electron withdrawal and PEDOT:PSS hole doping collectively lower electron density, as further supported by increased S 2p_3/2 contributions from PEDOT (55.9%) and PSS (59.7%). This confirms strong interfacial coupling and successful organic–inorganic integration in the hybrid composite with tuned electronic properties.

Fig. 2 (a) XPS survey spectra of MoS₂ and the 10W-MS/P hybrid, high resolution spectra of (b) C 1s and (c) W 4f of 10W-MS/P, (d) Mo 3d, (e and f) bar graph of integrated areas of the 1T and 2H phases in MoS₂ and 10W-MS/P, (g) S 2p, and (h and i) bar graph of integrated areas of 2p_1/2 and 2p_3/2 in MoS₂ and the 10W-MS/P hybrid.

The morphology of pristine MoS₂ and hybrid materials was examined using high resolution-scanning electron microscopy (HR-SEM) and high resolution-transition electron microscopy (HR-TEM). The SEM images of pristine MoS₂ (Fig. 3a and b) reveal a stacked nanosheet structure. The formation of this hierarchical nanostructure is attributed to the role of tartaric acid in the hydrothermal growth of MoS₂ nanocrystals, which is consistent with previous observations reported by Branzi et al.³¹ TEM analysis provides further structural insights, notably, ultrathin nanosheets composed of 5 to 10 layers of S–Mo–S, as shown in Fig. 3c. The interlayer spacing, estimated from the diffraction fringes (Fig. 3e), is ≈0.96 nm, which correlates well with the d-spacing observed from the (001) diffraction peak in the XRD data. Additionally, the selected area electron diffraction (SAED) patterns of pristine MoS₂ (Fig. 3f) match perfectly with the ICSD 254956 crystallographic file. Scanning transmission electron microscopy (STEM) mapping images obtained from HR-TEM (Fig. 3g–j) further verify the homogeneous distribution of Mo and S without contamination from other elements. In contrast, the SEM images of the 10W-MS/P hybrid (Fig. 4a and b) illustrate the layer structures of W doped MoS₂ combined with PEDOT:PSS. TEM images (Fig. 4c and d) clearly show thinning of the nanosheets, along with agglomerations of PEDOT:PSS on W-MoS₂. This reduction in nanosheet thickness aligns with the average crystallite size calculated from XRD. Diffraction fringe analysis (Fig. 4e) indicates an average interlayer spacing of ≈0.98 nm in the hybrid, higher than that of pristine MoS₂, indicating interlayer strain within the hybrid material. The observed increase in interlayer spacing is primarily attributed to the steric hindrance of intercalated PEDOT:PSS molecular chains. The long, rigid conjugated backbone of PEDOT, together with the bulky sulfonate side groups of PSS, physically expands the MoS₂ layers, overcoming the weak van der Waals forces and resulting in ≈0.02 nm expansion. A secondary stabilizing contribution arises from van der Waals attraction between the π-conjugated PEDOT system and the MoS₂ basal planes, as well as possible hydrogen bonding between PSS sulfonate groups and edge sites on MoS₂. This interpretation is further supported by the slight shift in the C–S peak observed in the C 1s XPS spectrum (Fig. 2b), which reflects contributions from the thiophene C–S bonds in PEDOT and subtle charge delocalization at the PEDOT:PSS/MoS₂ interface. Furthermore, STEM mapping (Fig. 4g–l) confirms the elemental distribution of W, Mo, S, C, and O in the hybrid samples, consistent with respective compositions. Moreover, SEM images of other hybrids such as MS/P, 5W-MS/P, and 15W-MS/P along with their corresponding energy dispersive X-ray (EDX) spectra (Fig. S2a–i) further demonstrate the formation of well-integrated inorganic–organic hybrid materials.

Fig. 3 (a and b) HR-SEM images, (c and d) HR-TEM images, (e) interplanar spacing, (f) SAED, and (g–j) EDX elemental mapping images of pristine MoS₂.

Fig. 4 (a and b) HR-SEM images, (c and d) HR-TEM images, (e) interplanar spacing, (f) SAED, and (g–l) EDX elemental mapping images of the 10W-MS/P hybrid.

Thermogravimetric analysis (TGA) was employed to assess the thermal endurance of both pristine MoS₂ and the 10W-MS/P hybrid (Fig. S3). A primary mass loss occurring below 300 °C is mainly due to decomposition of sulfur in MoS₂ and the sulfonated groups present in the PSS component of the hybrid materials. Between 300 and 450 °C, notable weight loss corresponds to the oxidation of MoS₂ and W_0.1Mo_0.9S₂.⁴³ Above 450 °C, significant weight loss in the 10W-MS/P hybrid is associated with the degradation of the PEDOT:PSS polymer backbone.⁴⁴ The final residual mass after analysis was ≈45.21% for pristine MoS₂ and ≈21.13% for the 10W-MS/P hybrid. The reduced residual mass in the 10W-MS/P hybrid is due to the thermal degradation of the polymer component within the hybrid.

3.1. Electrochemical analysis in a three electrode cell

All the electrochemical measurements were performed in a three-electrode configuration using 1 M H₂SO₄ as the electrolyte. A platinum wire served as the counter electrode, an Ag/AgCl electrode functioned as the reference electrode, and the working electrode was a graphite sheet coated with the active material without external binders for all hybrid materials, with a mass loading of ≈1.4 mg. Fig. 5a presents the cyclic voltammetry (CV) responses of pristine MoS₂, MS/P, 5W-MS/P, 10W-MS-P, and 15W-MS/P hybrids at a constant scan rate at 100 mV s⁻¹. It is evident from the graph that the integrated area under the cyclic voltammogram of 10W-MS/P is higher in comparison to that of pristine and other hybrids. This observation suggests that the superior rate capability can be assigned to the presence of a layered structure with the PEDOT:PSS matrix, which effectively promotes rapid electron transfer and electrolyte ion diffusion. In Fig. 5b, the curve illustrates the surface redox pseudocapacitance characteristic of 10W-MS/P at various scan rates. This demonstration illustrates that the area of the CV curve expands within the voltage range of 0 to 0.55 V without any polarization. The configuration of the CV plots remains unaltered even at elevated scan rates, suggesting enhanced reversibility and favourable capacitive retention of the electrode material compared to pristine MoS₂. In Fig. 5c, the pristine MoS₂ CV curves exhibit no redox peaks, with the capacitance of the MoS₂ material being mainly ascribed to electrosorption.⁴⁵ The CV behavior of the other hybrids (Fig. S4a–c) shows the surface redox pseudocapacitance characteristic of the hybrids. According to the integrated area of the CV curves, the following order is revealed: MoS₂ < MS/P < 5W-MS/P < 10W-MS-P > 15W-MS/P. This arises from the substitutable doping of W and the incorporation of PEDOT:PSS. PEDOT:PSS acts as a protective matrix against W_xMo_1−xS₂ degradation. The electrochemical active surface area (ECSA) was determined using (eqn (7)). The ECSA values for pristine MoS₂, MS/P, 5W-MS/P, 10W-MS/P, and 15W-MS/P were found to be 0.55 × 10⁻⁴ cm², 0.72 × 10⁻⁴ cm², 0.92 × 10⁻⁴ cm², 1.03 × 10⁻⁴ cm², 0.53 × 10⁻⁴ cm², respectively. Notably, the 10W-MS/P hybrid exhibits a substantially higher ECSA compared to the other materials. This is related to the higher integrated area observed in the CV curves of 10W-MS/P.

Fig. 5 (a) comparison of CVs of the materials, (b) CV of 10W-MS/P, (c) CV of MoS₂, (d) GCD of 10W-MS/P, (e) GCD of MoS₂, (f) specific capacitance at different scan rates, (g) EIS of the materials, (h and i) contribution bar graph of MoS₂ and 10W-MS/P, and (j and k) cycling stability of MoS₂ and 10W-MS/P at 15 A g⁻¹ over 10 000 cycles.

The electrochemical behaviour of galvanic charge–discharge (GCD) for 10W-MS/P is illustrated in Fig. 5d. It shows the GCD curves at various current densities. A small deviation from the triangular behaviour typical of electric double layer capacitors (EDLCs) reveals charge storage through a pseudocapacitive mechanism, which is consistent with the findings from the cyclic voltammetry (CV) test. The 10W-MS/P hybrid achieves an extended discharge time of 870.2 s, which is higher than the individual discharge times of pristine MoS₂ and the other hybrids MS/P, 5W-MS/P, and 15W-MS/P, which are 366.9 s, 517 s, 761.2 s and 404.9 s, respectively. The 10W-MS/P hybrid offers the highest specific capacitance (C_m) of 845.14 F g⁻¹ and areal capacitance (C_a) of 4.73 F cm⁻² at 1 A g⁻¹, as calculated using (eqn (1) and (2)). In contrast, the MS/P, 5W-MS/P and 15W-MS/P hybrids display lower efficiencies compared to 10W-MS/P, with C_m and C_a values of 560.18 F g⁻¹, 778.84 F g⁻¹, and 440.56 F g⁻¹ and 3.13 F cm⁻², 4.36 F cm⁻², and 2.46 F cm⁻² at 1 A g⁻¹, respectively, as shown in Fig. S4d–f. Pristine MoS₂ exhibits even lower GCD performance, with smaller C_m and C_a values of 414.45 F g⁻¹ and 2.32 F cm⁻² at 1 A g⁻¹, respectively, compared to the hybrids shown in Fig. 5e. The superior capacitance of 10W-MS/P over the fabricated electrodes is attributed to the synergistic effect of W doping and PEDOT:PSS incorporation in MoS₂, which enhances electrical conductivity, provides more active sites, and increases both ionic mobility and the molar conductivity of H₃O⁺ in H₂SO₄ electrolyte solutions. When the tungsten doping concentration in MoS₂/PEDOT:PSS reaches 15% (15W-MS/P), electrochemical performance decreases, likely due to the structural distortion and electron traps, which limit the surface area and suppress redox activity, thereby decreasing the overall C_m and C_a, as reflected in the ECSA calculated from CV curves. The GCD curves for the 10W-MS/P electrode show a decrease in discharge time with increasing current density, suggesting enhanced rate capability for the electrodes as depicted in Fig. 5d. This behaviour also reveals a slight decrease in C_m for all materials as the current density increases, as shown in Fig. 5f. However, the electrodes maintained superior performance even at 25 A g⁻¹, as shown in Fig. S5a–e. This demonstrates the excellent rate capability of the hybrid materials, retaining high specific capacitance. The calculated (Fig. S5f) C_m values of 7.08 F g⁻¹, 37.78 F g⁻¹, 103.89 F g⁻¹, 119.71 F g⁻¹ and 77.92 F g⁻¹ and C_a values of 0.03 F cm⁻², 0.21 F cm⁻², 0.58 F cm⁻², 0.67 F cm⁻², and 0.43 F cm⁻² were obtained for MoS₂, MS/P, 5W-MS/P, 10W-MS/P, and 15W-MS/P, respectively.

Electrochemical impedance spectroscopy (EIS) was performed to investigate the reaction kinetics of the materials over a frequency range from 1 kHz to 100 mHz. The resulting Nyquist plots are presented in Fig. 5g. Distribution of relaxation time (DRT) analysis was conducted using the ‘DRTtools’ web interface to resolve overlapping electrochemical processes and quantify individual contributions such as electrolyte resistance (R_s), charge-transfer resistance (R_ct), interfacial polarization/electric double layer capacitance (C_dl), and diffusion related contributions.⁴⁶ This method transforms impedance data into a distribution function γ(log τ) vs. log τ, where each peak's position (τ₁–τ₄) corresponds to the characteristic time constant of distinct relaxation processes at different timescales. The DRT spectra reveal four characteristic peaks: high frequency (τ₁ ≈ 10⁻³ s) for R_s, mid-high frequency (τ₂ ≈ 10⁻² s) for R_ct, mid frequency (τ₃ ≈ 10⁻¹ s) for interfacial polarization/C_dl, and low frequency (τ₄ ≈ 10° s) for diffusion. Notably, no distinct high-frequency τ₁ peak (Fig. S6a) appears for pristine and hybrid materials, indicating negligible solution resistance due to excellent electrode/electrolyte contact. The τ₂ (Fig. S6b) values were 0.32, 0.50, 0.50, 0.29, and 0.54 Ω for MoS₂, MS/P, 5W-MS/P, 10W-MS/P, and 15W-MS/P, respectively. The τ₃ (Fig. S6c) values were 1.39, 2.08, 1.87, 0.77, and 2.25 Ω, respectively. The τ₄ (Fig. S6d) values were 99.13, 105.50, 69.25, 80.03, and 83.59 Ω, respectively. These results demonstrate that 10W-MS/P exhibits the lowest R_ct (0.29 Ω) and C_dl (0.77 Ω) resistance, confirming optimal charge-transfer kinetics and double layer capacitance formation, while maintaining competitive diffusion performance.

To investigate the charge storage behaviour of pristine MoS₂ and its hybrid materials, the total capacitance of an electrode is typically separated into two main components: capacitive capacitance and diffusion capacitance. The capacitive capacitance part originates from fast electrochemical processes at the electrode–electrolyte interface, such as rapid ion adsorption/desorption and faradaic redox reactions. Conversely, diffusion capacitance is associated with the movement of ions within the bulk of the electrode and electrolyte. To comprehensively evaluate the capacitance performance of electrode materials, it is essential to quantify the contribution from both these processes. The current response at a specific scan rate, generally derived from cyclic voltammetry analysis, can be described by eqn (9).

i = av^b (9)

where i is the current at scan rate v, and a and b are fitting parameters. Here, a b-value close to 0.5 indicates a diffusion-dominated process, while a value closer to 1 points to a surface-controlled capacitive mechanism. This relationship can be rewritten as

i(v) = k₁v + k₂v^0.5 (10)

where i represents the current at a fixed voltage (v), with k₁ and k₂ denoting the capacitive and diffusion-controlled contributions, respectively. By analysing these constants, the relative proportions of each charge storage mechanism can be quantified, allowing for a more precise understanding of the electrochemical behaviour of the electrode material. Fig. 5h shows that pristine MoS₂ displays a predominant diffusion-controlled contribution across various scan rates. On the other hand, the 10W-MS/P hybrid (Fig. 5i) exhibits an increasing capacitive contribution as the scan rate rises, whereas the diffusion-controlled contribution decreases. This behaviour results from reduced interaction time between electrolyte ions and the electrode surface at a higher scan rate, thus limiting the oxidation process. Specifically, the capacitive contribution increases from 19.54% at 10 mV s⁻¹ to 35.20% at 50 mV s⁻¹, while the diffusion contribution decreases from 80.46% to 64.80% over the same range. The enhanced capacitive capacitance of 10W-MS/P composed of pristine MoS₂ is attributed to W doping and incorporation of PEDOT:PSS. Furthermore, the contribution percentages of the other hybrids (Fig. S7a–c) reveal that in MS/P, PEDOT:PSS incorporation enhances the capacitive contribution due to its redox nature. Introduction of W into the MoS₂ lattice increases the diffusion-controlled capacitance, but at higher doping (15%), capacitive capacitance increases compared to the other hybrids. The W_xMo_1−xS₂ nanosheets coupled with PEDOT:PSS provide an adequate surface area facilitating electron diffusion and active pathways for SO₄²⁻ ion migration within the surface of the material.

The electrodes were subjected to continuous and repetitive charge–discharge cycles at a current density of 15 A g⁻¹ to evaluate the cycling durability. The electrode consisting of MoS₂ exhibits poor stability, retaining 56% of its capacitance after 10 000 cycles (Fig. 5j) and maintaining 97% coulombic efficiency. The hybrids MS/P (Fig. S8a), 5W-MS/P (Fig. S8b), 10W-MS/P (Fig. 5k) and 15W-MS/P (Fig. S8c) exhibit 55%, 70%, 89%, and 25%, respectively, and coulombic efficiencies of 98%, 98%, 98%, and 99%, respectively. It is evident that the 10W-MS/P hybrid possesses superior cycling stability compared to the pristine and other hybrid compositions, even under acidic electrolyte conditions. The results also indicate that increasing the W content enhances stability, but doping beyond 10% leads to lattice distortion, which decreases cycling stability. This relates well with the CV, GCD, and EIS studies. The enhanced cycling stability of 10W-MS/P is primarily attributed to the optimized W doping configuration in MoS₂ (W_0.1Mo_0.9S₂), which promotes rapid ion transfer and electrolyte diffusion and mitigates volume changes during prolonged charge–discharge cycles.

To confirm the superior performance of self-binding hybrid materials, PVDF-bound electrodes (MS/P-PVDF, 5W-MS/P-PVDF, 10W-MS/P-PVDF, and 15W-MS/P-PVDF) were fabricated. Fig. S9a-i show their CV and GCD performance, with 10W-MS/P-PVDF achieving the highest C_m of 700.96 F g⁻¹ and C_a of 3.92 F cm⁻² at 1 A g⁻¹. In contrast, MS/P-PVDF, 5W-MS/P-PVDF, and 15W-MS/P-PVDF exhibited lower C_m and C_a values of 411.80 F g⁻¹, 674.38 F g⁻¹, and 603.35 F g⁻¹ and 2.30 F cm⁻², 3.77 F cm⁻², and 3.37 F cm⁻² at 1 A g⁻¹, respectively, demonstrating binder effects on capacitance. EIS-DRT analysis (Fig. S10a and b) reveals that PVDF binding increases all resistance components compared to self-binding electrodes, and no high-frequency τ₁ peaks (R_s) appear, but τ₂ (R_ct) (Fig. S10c) values were 0.76, 0.45, 0.70, and 0.42 Ω; τ₃ (C_dl) (Fig. S10d) values were 3.57, 1.49, 2.01, and 1.62 Ω; and τ₄ (diffusion) (Fig. S10e) values were 77.78, 46.75, 160.47, and 30.91 Ω for MS/P-PVDF, 5W-MS/P-PVDF, 10W-MS/P-PVDF, and 15W-MS/P-PVDF, respectively, all higher than those of self-binding 10W-MSP. Cycling stability (Fig. S11a–d) shows that PVDF electrodes retain only 47%, 40%, 34%, and 38% of capacitance and 97%, 99%, 98%, and 98% of coulombic efficiency, respectively, confirming that PVDF decreases stability. The electrically insulating PVDF disrupts electron transport pathways, coats the active material surfaces, increases internal resistance and blocks ion accessible sites/pores, leading to reduced specific capacitance and faster capacity fading during cycling, validating self-binding superiority.

3.2. Possible charge storage mechanism

The 1 M H₂SO₄ electrolyte produces hydronium ions (H₃O⁺) and sulfate ions (SO₄²⁻) in aqueous solution,^47,48 as shown in the reaction equation below.

H₂SO₄ + 2H₂O ⇌ 2H₃O⁺ + SO₄²⁻

A possible charge storage mechanism of pristine MoS₂ and its W_xMo_1−xS₂/PEDOT:PSS hybrids has been provided. Primarily, hydronium ions generated from the sulfuric acid electrolyte diffuse between the van der Waals layers of MoS₂ and W_xMo_1−xS₂. Because the ionic radius of hydronium ions is ≈0.28 nm, which is smaller than the interlayer spacing of MoS₂ (0.96 nm) and W_0.1Mo_0.9S₂ (0.98 nm), hydronium ions can easily intercalate and deintercalate in these layers. This process leads to rapid and reversible pseudocapacitive charge storage. Additionally, an electrical double layer forms at the electrode–electrolyte interface due to the adsorption of SO₄²⁻ ions onto the surface of MoS₂ and W_xMo_1−xS₂, contributing further non-faradaic capacitance. Simultaneously, the PEDOT:PSS matrix undergoes reversible oxidation and reduction of its PEDOT chains, balanced by the negatively charged PSS polyanions. In this context, hydronium ions act as proton donors, facilitating the redox activity of PEDOT:PSS. This highlights the crucial role of hydronium ions in the charge storage mechanism of these hybrid materials, as schematically illustrated in Fig. 6. The respective redox reaction equation of the inorganic–organic hybrid can be written as

W_xMo_(1−x)S₂ + xH₃O⁺ + xe⁻ ⇌ W_xMo_(1−x)S₂(H_x) + xH₂O

PEDOT⁺PSS⁻ + xe⁻ + xH₃O⁺ ⇌ PEDOT⁰PSS⁻ + xH₂O

Fig. 6 Schematic illustration of the charge storage mechanism.

Additionally, the overall results show that the hybrid electrodes demonstrate higher performance in a self-binding environment compared to binder-included electrodes. W doping enhances the density of active sites and the increase in the metallic 1T phase fraction of MoS₂ upon W doping is well supported by XPS analysis. PEDOT:PSS serves a dual role in these electrodes: (i) providing a conductive network during charge–discharge processes and (ii) acting as a self-binder to ensure proper contact between the electrode material and substrate (graphite sheet).

3.3. Electrochemical analysis of the self-binding cathode in an asymmetric coin cell

To further explore practical implementation, the electrochemical performance of the high performance 10W-MS/P hybrid was examined in an asymmetric supercapacitor-coin cell (ASC-CC). In this device, graphite powder (GP) was used as the anode and 10W-MS/P functioned as the cathode, with 1 M H₂SO₄ as the electrolyte and Whatman-40 filter paper utilized as the separator membrane, as shown in Fig. 7a, which depicts all the necessary components for the coin cell assembly. The CV curves of the anode and cathode at a scan rate of 100 mV s⁻¹ demonstrate that both electrodes have a potential window of 0.55 V (Fig. 7b). The CV curves of the ASC-CC are shown in Fig. 7d at a different scan rate in the potential range of 0 to 1.3 V. All the CV curves exhibit distinct redox peaks, characteristic of pseudocapacitive behaviour. As the scan rate increases, the area under the curve also increases. Fig. 7e illustrates the non-triangular shape of the charge–discharge GCD curve, which results from the redox reaction occurring at the interface between the electrolyte and the electrode within the device. The GCD curve for the ASC-CC electrodes exhibits a maximum specific capacitance (C_m) and areal capacitance (C_a) of 7.73 F g⁻¹ and 1.19 × 10⁻² F cm⁻² at a current density of 0.2 A g⁻¹, as well as a minimum C_m and C_a of 1.13 F g⁻¹ and 0.1 × 10⁻² F cm⁻² at a current density of 1 A g⁻¹. As the current density increases, there is a notable decrease in C_m, as shown in Fig. S12. This phenomenon is likely attributed to significant adsorption of electrolyte ions by the interfacial region, which leads to a rapid reduction in ion concentration at the electrode interface and subsequently increases polarization. The energy and power densities, which indicate the energy storage capacity of the device, were calculated using (eqn (5) and (6)), respectively. The Ragone plot demonstrates that the ASC-CC achieves a high energy density of ≈6.53 Wh kg⁻¹ and power density of ≈79.64 W kg⁻¹ at a current density of 0.2 A g⁻¹, as shown in Fig. 7f.^49–52

Fig. 7 (a) Schematic illustration of the asymmetric coin cell 10W-MS/P//GP, (b) CV curves of 10W-MS/P and GP at 100 mV s⁻¹, (c) fabricated coin cell, (d) CV curves at different scan rates, (e) GCD curves at various current densities, (f) Ragone plot, (g) EIS of the device, (h) distribution of relaxation time (DRT) analysis of the device, and (i) cycling stability of ASC-CC at 2 A g⁻¹ over 20 000 cycles.

In addition, EIS was performed to investigate the internal charge transfer kinetics of the ASC-CC device. Fig. 7g shows only Warburg impedance in the Nyquist plot, indicating diffusion dominated behavior at low frequencies. The electrolyte resistance (R_s), charge-transfer resistance (R_ct), interfacial polarization/electric double layer capacitance (C_dl), and diffusion contribution were calculated using distribution of relaxation time (DRT) analysis (Fig. 7h).⁴⁶ The calculated values were 6.09, 6.72, 86.41, and 302.35 Ω for R_s (τ₁), R_ct (τ₂), interfacial polarization/C_dl (τ₃), and diffusion resistance (τ₄), respectively. The Bode plot of the device, displayed in Fig. S13a, consists of two key components: the Bode impedance, which shows the relationship between frequency and the magnitude (|Z|), and the Bode phase plot, which presents frequency versus phase angle with the phase near 0° at high frequencies. This plateau near 0° indicates that at elevated frequencies, the device maintains phase consistency between input and output, an important feature for supercapacitor behaviour. At lower frequencies, the system demonstrates notable capacitive properties, while at higher frequencies, its response becomes increasingly resistive. Such characteristics confirm the coin cell's excellent capability for practical energy storage applications. Analysis of the complex permittivity (ε(ω)) of the device provides crucial insights into the electrode–electrolyte interface, particularly regarding the effect of a thin layer when an electric field is applied. The value of ε(ω) depends on the frequency of the applied electric field, reflecting the dynamic polarization of the materials across varying frequencies. Complex permittivity is described by two components: the real part or dielectric constant (ε′) and the imaginary part or dielectric loss (ε″). These quantities for the coin cell were calculated using standard (eqn (11) and (12)).

The trends in ε′ and ε″, as illustrated in Fig. S13b, are influenced by both operating voltage and frequency, each revealing distinct aspects of the material performance. The dielectric constant (ε′) relates to the energy storage ability of the material under an applied electric field, while the dielectric loss (ε″) quantifies the energy dissipated as heat. Both ε′ and ε″ decrease at higher frequencies, which is attributed to relaxation phenomena that limit ion responses at these frequencies. This behaviour further reinforces the presence of pseudocapacitive charge storage in the devices, as relaxation effects are typically associated with ion dissociation processes at high frequencies.

To further evaluate the device efficiency, cycling stability was assessed through GCD testing at 2 A g⁻¹, with the results presented in Fig. 7i. Over 20 000 continuous cycles, the 10W-MS/P//GP electrodes in the ACS-CC retained 75% of their initial specific capacitance, accompanied by an excellent coulombic efficiency of 98%. Furthermore, a coin cell cathode (10W-MS/P) was fabricated without an external binder, underscoring the exceptional efficiency of the hybrid material and supporting the practical applicability of the ASC-CC device.

4. Conclusion

In summary, a one-pot hydrothermal strategy was developed to synthesize W_xMo_1−xS₂/PEDOT:PSS (W-MS/P) hybrids, resulting in a series of high-performance electrode materials. Notably, the optimized 10W-MS/P (W_0.1Mo_0.9S₂/PEDOT:PSS) hybrid exhibited superior electrochemical performance compared to pristine MoS₂, along with enhanced cycling stability and rate capability. Substitutional W doping effectively modulated the crystal structure of MoS₂ by increasing the metallic 1T phase content and compacting interlayer spacing, thereby boosting electrochemical activity. The incorporation of PEDOT:PSS further improved conductivity and served as a robust binder, ensuring strong interaction between the active material and the graphite substrate. Importantly, the ASC-CC delivers notable energy and power densities with outstanding capacitance retention over 20 000 cycles. These results highlighting its potential for remarkable pseudocapacitive behaviour as well as its outstanding structural durability firmly establish the hybrid as a highly promising electrode material for next generation energy storage devices.

Conflicts of interest

The authors declare no conflicts of interest.

Data availability

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information: comprehensive characterization data including BET analysis of pristine MoS₂ and hybrids, TGA plots of pristine MoS₂ and 10W-MS/P, SEM-EDX analysis, CV and GCD curves, capacitive contribution bar graphs, and cycling stability data for MS/P, 5W-MS/P, and 15W-MS/P hybrids, along with high current density GCD measurements (10–25 A g⁻¹). Additionally, it includes DRT analysis for pristine MoS₂ and all hybrids, PVDF-bound control electrodes (CV, GCD, EIS-DRT, and cycling stability), device-level performance (specific capacitance vs. current density and Bode plots), dielectric properties (dielectric constant and loss), and a comprehensive comparison table benchmarking MoS₂-based supercapacitor materials from recent literature. See DOI: https://doi.org/10.1039/d5ta09598k.

Acknowledgements

The authors sincerely thank the ANRF-SERB-CRG (CRG/2022/000049), New Delhi. The authors also thank the SRM Institute of Science and Technology (SRMIST) for offering research facilities.

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