Supercritical CO₂-Assisted In-Situ Intercalation Polymerization of Polyaniline/Graphene Composites: Enhanced Electrochemical Performance for High-Performance Supercapacitor Electrodes

Supercritical CO₂-Assisted In-Situ Intercalation Polymerization of Polyaniline/Graphene Composites: Enhanced Electrochemical Performance for High-Performance Supercapacitor Electrodes | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Supercritical CO₂-Assisted In-Situ Intercalation Polymerization of Polyaniline/Graphene Composites: Enhanced Electrochemical Performance for High-Performance Supercapacitor Electrodes Jing Zhu, Huiqi Du, Chang Ma, Xia Wu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9404906/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Polyaniline/graphene (PANI/GR) composites are promising supercapacitor electrode candidates owing to its excellent electrochemical performance such as high theoretical specific capacity and good electrical conductivity. However, most reported ones suffer structural defects, leading to low specific energy and poor electrochemical stability. This work proposed a novel method to fabricate PANI/GR nanocomposite for supercapacitor. By synergizing supercritical fluid technology (SFT) and aniline cation (AN + ) intercalation, AN + realized effective intercalation and in-situ polymerization between graphite layers with assistance of supercritical carbon dioxide (scCO₂), enabling layer-by-layer assemble of PANI and GR (named SC). It is found that the layer structure of SC reduces PANI deformation, facilitates rapid ion diffusion, and extende interfacial interactions, therefore accelerating electron transfer throughout the electrode. The SC electrode achieves an exceptional specific capacitance of 669.0 F g⁻¹ at 1 A g⁻¹, with merely 7.5% capacitance loss after 5,000 cycles, demonstrating outstanding cycling stability. The corresponding SC//activated carbon asymmetric supercapacitor delivers an energy density of 29.2 Wh kg⁻¹ at a power density of 650 W kg⁻¹. This work provides an effective strategy for designing layered graphene-based energy storage composites to achieve superior electrochemical performances. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Supercapacitors are widely applied in flexible portable electronics, electric vehicles, and sensor systems [ 1 , 2 ]. They store energy through electric double-layer effect at electrode surface or pseudocapacitance effect generated by redox reactions within electrode [ 3 – 6 ]. Porous carbon-based materials, such as graphene (GR), activated carbon, carbon nanotubes, biomass derivatives, and so on, are mainly used for electric double-layer capacitor (EDLC) electrode. These materials are charactered of unique features such as rich mesoporous and microporous structures which enable rapid ion transport, resulting in fast response rates and outstanding cycling stability. Nevertheless, their lower specific capacitance remain a critical limitation for broader implementation [ 7 , 8 ]. For instance, the theoretical specific capacitance of GR is only 550 F/g. What’s worse, the van der Waals force between GR sheets leads to stacking and agglomeration between them, resulting in lower specific capacitance [ 9 ]. As commonly used EDLC materials, activated carbon and carbon nanotubes typically exhibit specific capacitances of only 100–300 F/g in aqueous electrolytes [ 10 ]. PC stores charge through fast and reversible redox reaction between electrode material and electrolyte. The most commonly used electrode materials include conductive polymers, transition metal oxides, transition metal chalcogenides, metal nitrides, and so on [ 11 – 14 ], owning high specific capacitance and energy density. Polyaniline (PANI) stands out with high theoretical specific capacitance of 2000 F/g, exceeding that of inorganic metal oxides (e.g., RuO₂, ~ 700 F/g) and other conductive polymers (e.g., polypyrrole, 300–500 F/g) [ 15 – 17 ]. Furthermore, its electrochemical performance can be optimized by tailoring molecular structure, morphology, and porosity through controlled polymerization or chemical modification reaction [ 18 , 19 ]. However, issues such as high self-discharge rates, low doping efficiency, and restricted ion transport result in weak cycling stability and capacity retention of PANI [ 20 ]. Based on the excellent properties of PANI and GR, composite PANI/GR have attracted significant research interest in recent years. PANI/GR combines both the advantages of PANI and GR, and shows synergistic effect when used as electrode material of supercapactior [ 21 – 25 ]. Mahato et al. [ 26 ] reported a nanoscale semi-crystalline composite PANI/GR, delivering specific capacitance of 525.5 F g⁻¹ at 0.1 A g⁻¹ when assembled into symmetric de vice. Although GR offers exceptional specific surface area, conductivity, and mechanical strength, reduced graphene oxide (rGO) is more widely used because of its high performance, low cost, and more feasibility [ 27 ]. Reduction treatment can partially restore GO's sp²-conjugated network while preserving its high specific surface area and structural defects that facilitate interfacial interactions with PANI, thereby enhancing electrical conductivity [ 28 ]. Umar et al. [ 29 ] developed an rGO@PANI nanocomposite, which exhibits specific capacitance of 314.2 F g⁻¹ at 1 A g⁻¹, 92% capacitance retention after 4,000 cycles. Upadhyay et al. [ 30 ] fabricated a flexible solid-state supercapacitor using PANI nanofiber-bridged rGO/RuO₂ nanoparticles, achieving a maximum areal capacitance of 677 mF cm⁻², a peak energy density of 60.18 µWh cm⁻² at 0.8023 mW cm⁻² power density. However, the oxidation and reduction processes of graphite to producing rGO causes structural defects, resulting in the decrease of conductivity and mechanical property. Therefore, the electrochemical performance of rGO still falls short of graphene. Graphite, which can be described as the three-dimensional crystalline form of GR or as a multi-layered stacked structure. It possesses a distinctive layered structure with a 3.35 Å interlayer spacing, enabling insertion of specific compound to form intercalation compound [ 31 – 33 ]. With graphite as raw material, Guo et al. [ 34 ] prepared the PANI/GR composite through intercalation and in-situ polymerization of aniline (AN) between graphite layers under ultrasonic condition. However, strong van der Waals forces and π-π interactions cause most GR layers remain tightly stacked, making difficult for AN molecule to penetrate into graphite layers [ 35 ]. As a green environmental protection technique, supercritical fluid technology (SFT) has attracted much more attention in recent years due to the specific character of supercritical fluid, such as small viscosity, high diffusivity, strong dissolving capacity, good selectivity, and so on [ 36 ]. In addition, the dissolving capacity of supercritical fluid can be adjusted through altering its temperature and pressure. Supercritical CO₂ (scCO₂) has gained significant attention due to its mild critical parameters ( T c = 304.2 K, P c = 7.38 MPa), exceptional solvation power, zero surface tension, chemical inertness, and low corrosiveness, finding wild applications in materials processing [ 37 ]. For instance, Wang et al. [ 38 ] developed an efficient GR exfoliation strategy through pressure modulation of scCO₂ to achieves graphite exfoliation into GR. The high density and low viscosity of scCO₂ dramatically enhance the graphite exfoliation efficiency. Herein, we present a novel approach, which integrating SFT with in-situ intercalative polymerization, to prepare PANI/GR composites. It is known that there is strong cation-π interaction between aniline cation (AN + ) and π electrons in GR sheet of graphite [ 39 ]. Considering that this interaction can further promote the separation of graphite layers, we adopt AN + as intercalating agent. The synthesis process is illustrated as Fig. 1 . Firstly, employes scCO₂ as intercalation medium to increase the layer spacing of graphite through decreasing pressure to increase the CO₂ molecular size. then, AN + and oxidizing agent are inserted between the graphite layers with assistant of scCO₂. Subsequent polymerization of AN + in supercritical condition enables well-ordered layer by layer assemble of PANI and GR, yielding PANI/GR composites (named SC). The novel approach avoids oxidation and reduction reaction of graphite, therefore voiding the damage of planar structure of GR. In addition, scCO₂ enhances the intercalation efficiency and Interfacial interactions between GR and PANI, thereby optimizing the structure and electrochemical performance of the composite. The composite SC achieves an exceptional specific capacitance of 669.0 F g⁻¹ at 1 A g⁻¹, with merely 7.5% capacitance loss after 5,000 cycles, outperforming PANI and PANI/GR (named PANI/G) prepared under normal pressure and temperature conditions, as well as many other reported PANI/GR composites. The corresponding SC//activated carbon (AC) asymmetric supercapacitor achieves an energy density of 29.2 Wh kg⁻¹ at a power density of 650 W kg⁻¹. The superior performance of this nanocomposite highlighting the significant potential of SFT for advanced energy storage composites manufacture. 2. Experimental section 2.1 Materials Aniline (Analytical pure), ammonium persulfate (Analytically pure), concentrated hydrochloric acid (37%), graphite powder (99.95%, > 100 mesh), polyvinyl pyrrolidone (Analytically pure), and N-methylpyrrolidone (Analytical pure) were purchased from Shanghai Aladdin Technology Co., Ltd. (China). Concentrated sulfuric acid (95%) and polyvinylidene fluoride (30,000-330,000 g mol − 1 ) were purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd. (China). Graphitized carbon black (Analytical pure) was purchased from Tianjin Umeng Chemical Technology Co., Ltd. (China). 2.2 Preparation of PANI, PANI/G, and SC PANI PANI was synthesized through chemical oxidative polymerization method. First, 0.28g aniline was mixed with 30 mL 1 M HCL solution to obtain the 0.1 M AN + /HCL solution (solution A). Subsequently, 0.68 g of (NH₄)₂S₂O₈ was dissolved in 30 mL hydrochloric acid solution under magnetic stirring at 3000 rpm until complete dissolution, yielding solution B. Solution B was then added dropwise to solution A over 0.5 hours under stirring at 3000 rpm in ice-water bath, following reaction for 6 hours. The product was washed three times with alternating anhydrous ethanol and deionized water, and then annealed in tube furnace under N₂ atmosphere at 200°C for 2 hours, yielding PANI. PANI/G 0.1 g graphite was ultrasonically dispersed in solution A for 30 minutes to form mixture. Then solution B was added dropwise to the mixture in ice-water bath, followed by continuous magnetic stirring at 3000 rpm for 6 hours. The product was washed three times with alternating anhydrous ethanol and deionized water, and annealed in tube furnace under N₂ atmosphere at 200°C for 2 hours, yielding PANI/G. SC 0.754 g aniline and 0.037 g graphite powder were dispersed in 60 mL of 1 M HCl solution via ultrasonication for 30 minutes. Then 0.5 g polyvinylpyrrolidone (PVP) was introduced to above mixture to realize complete dispersing by magnetic stirring at 3000 rpm to get solution C. Solution C was charged into the reactor (11) of 80 mL effective volume at the beginning of experiment. The schematic illustration of the experimental apparatus is shown in Fig. 2 . First, the valves (2, 3) were opened to pass CO 2 gas into the storage tank (4), and then the low-temperature circulating cooling pump (6) was turned on to cool the CO 2 liquid storage tank to 268 K to get liquid CO 2 . Then the stirrer (13) and temperature switches (14) were turned on. At the same time, the valves (8,10) were opened to allow the injection of CO 2 into the reactor (11) through the booster pump (9) until the experimental temperature and pressure. After stirring for 30 minutes, the decompression valve (19) of the reactor was open to gradually vent the CO₂ gas at a controlled flow rate until 5 MPa. Upon completion of depressurization, the decompression valve (19) was closed. Then solution B was injected into the reactor (11) with advection pump (18), and the reactor was pressurized to supercritical condition again to carry out the polymerization reaction with pump (9). Upon completion of reaction, the decompression valve (19) was opened and the product was collected through the sample valve (15). The product was sequentially washed three times with alternating anhydrous ethanol and deionized water, and annealed in a tube furnace under N₂ atmosphere at 200°C for 2 hours. The resulting composite was stored in desiccator and named as SC. 2.3 Electrochemical measurements The product, acetylene black, and polyvinylidene fluoride (PVDF) were mixed at 8:1:1 mass ratio and grounded in agate mortar for 30 minutes. During grinding, appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to minimize particle agglomeration. The resulting slurry was coated onto a stainless steel mesh current collector to form electrode sheets. Next, the electrode was dried under vacuum at 353 K for 12 h, tableted under 2 MPa for 3 min, and then immersed in 1 M H 2 SO 4 electrolyte for 12 h to serve as working electrode. The electrochemical performances were measured on an electrochemical workstation (CHI600C, Shanghai Chenhua Co., Ltd., China) using a three-electrode configuration in 1 M H 2 SO 4 electrolyte, with a platinum sheet and a standard calomel electrode used as the counter and reference electrodes, respectively. The specific capacitance (C m ) of individual electrodes and the specific capacitance ( C s ) of the whole device can be calculated from GCD curves via Eq. (1,2): C m = \(\:\frac{\text{I}\text{}\text{△}\text{t}}{\text{m}\text{△}\text{V}}\) (1) C s = \(\:\frac{\text{I}\text{}\text{△}\text{t}}{\text{M}\text{△}\text{V}}\) , (2) where I (A) is discharge current, m (g) is mass of electrode active material, M (g) is total mass of the anode and cathode, Δ t (s) is duration of a discharge cycle, and Δ V (V) is voltage fluctuation range during the discharge duration Δ t . The mass ratios of anode and cathode are calculated by Eq. (3– 5 ) to maintain charge balance between the anode and cathode: Q + = Q − (3) Q = M ∗ Δ V ∗ C (4) $$\:\frac{{\text{m}}^{\text{+}}}{{\text{m}}^{\text{-}}}\:=\:\frac{{\text{C}}^{\text{-}}\text{Δ}\text{V}}{{\text{C}}^{\text{+}}\text{Δ}\text{V}}$$ 5 where Δ V (V), C (F g − 1 ), Q + , and Q − are the potential window from GCD, specific capacitance, positive charge, and negative charge, respectively. The energy density E (Wh Kg − 1 ) and power density P (KW Kg − 1 ) can be estimated by Eq. (6, 7 ): E = \(\:\frac{\text{1}}{\text{2}}\) C s (Δ V ) 2 \(\:\frac{\text{1000}}{\text{3600}}\) (6) 3 Results and discussion 3.1 Morphology and structure characterization Figure 3 shows the SEM images of PANI, PANI/G, and SC, with TEM image of SC. The morphology of PANI nanofiber is relatively uniform with diameters ranging from 70 to 90 nm and length 1 µm (Fig. 3 a), similarly with the morphology of PANI for PANI/G (Fig. 3 b-c). It is seen that the PANI nanofiber for PANI/G aggregates into spherical clusters, with graphite sheets stacking together with almost no PANI attach on, indicating PANI and graphite merely physically mixed. In contrast, SC exhibits a GR-dominant lamellar morphology with uniformly anchored PANI nanofibers whose diameter is approximate 30 nm and length 1 µm (Fig. 3 d). TEM is also employed to further confirms the intercalated architecture of SC. It can be observed clearly that the diameters of PANI nanoparticles are about 80 nm, and the PANI nanofibers are uniformly embedded between GR sheets (Figs. 3 e-f). The SEM and TEM analysis demonstrate that scCO₂ effectively mediates the intercalating and in-situ polymerization of AN + between the graphite layers. Figure 4 a shows the XRD patterns of graphite, GR, PANI, and SC. For graphite, the strong and sharp diffraction peaks at 2 θ = 26.55° are attributed to (002) crystal planes, corresponding to interlayer spacing of 0.335 nm for graphite [ 40 , 41 ]. The XRD pattern of GR shows peak broadening and reduced intensity at 2 θ = 26.55° due to diminished interlayer ordering and structural regularity of GR sheets. The XRD pattern of PANI exhibits two broad peaks centered at 2 θ = 20.4° and 25.03°, corresponding to the (020) and (102) crystal planes of PANI in its emeraldine salt form. For SC nanocomposite, it can be observed that diffraction peaks assigned to the interlayer distance of graphite gradually moves from 26.55° to 26.05° with significant intensity reduction. This 0.50° shift corresponds to interlayer expansion of GR sheets (d-spacing increasing from 0.335 nm to 0.342 nm, calculated via Bragg's law: nλ = 2d sin θ , n = 1, λ = 0.15406 nm), which can be attributed to the intercalation of PANI between graphitic layers with assistance of scCO₂. The diffraction peak intensity of SC at 25.03° is significantly enhanced compared with PANI, indicating a more ordered arrangement of PANI molecular chains and increased crystallinity in the composite material. FTIR analysis (Fig. 4 b) is used to further examine the chemical composition of materials. For PANI, the peaks at 671, 810, and 1123 cm⁻¹ correspond to the C-H stretching vibration on the benzene ring, out of plane bending vibrations of C − H band in the aromatic ring, and -N = Q=N- stretching (Q represents quinone rings), respectively. The peaks at 1298 and 1400 cm − 1 are attributed to the C − N stretching vibration of the secondary aromatic amine and C-N stretching connecting the quinoid and the benzenoid. The peaks appeared at 1484, 1580, and 3450cm − 1 are ascribed to C = C stretching of the benzene and quinoid ring, and N-H stretching vibration, respectively [ 42 ]. PANI/G exhibits all characteristic peaks of PANI, and the strong peaks at 1620 and 3430cm − 1 originate from bending vibration of H-O-H and O-H stretching vibration in adsorbed free water. SC not only exhibits all characteristic peaks of PANI, but also appears a new peak at 1240 cm⁻¹, which can be attributed to the C-N·⁺ stretching vibration in protonic acid-doped PANI. Additionally, SC exhibits higher intensity than PANI and PANI/G at 1123 cm⁻¹ (C = N in quinoid ring), which can be interpreted as enhanced conjugation of the C = N bond in the quinoid structure due to the interaction between GR sheets and PANI. Raman spectroscopy is employed to further confirm the interaction between PANI and GR sheets [ 40 ]. As shown in Fig. 4 c, GR exhibit shows three characteristic peaks at 1342, 1580, and 2700cm − 1 , corresponding to D-band (C − C, the disordered graphite structure), G-band (C = C, sp 2 -hybridized carbon), and 2D-band [ 43 , 44 ]. For PANI/G and SC nanocomposite, the bands at 1175, 1392, and 1482 cm − 1 are assigned to in plane C − H bending of quinoid ring, C − C stretching of quinoid ring, and C = C stretching of quinoid ring, respectively. Additionally, the D and G peaks are difficult to distinguish for PANI/G due to their broad shapes, originating from the weak interfacial interaction between GR sheets and PANI under atmospheric pressure. For SC, the characteristic peaks of both GR and PANI are clearly distinguishable, confirming that scCO₂ promotes the uniform intercalation of AN + between the graphitic layers. Furthermore, the ID/IG ratio of SC is higher than that of GR, which can be attributed to minor structural defects caused during the supercritical CO₂-assisted AN + intercalation process, arising from interactions between PANI and GR sheets. XPS analysis further elucidates the composition and chemical states of SC nanocomposite. The full survey spectrum (Figure S1 ) confirms the presence of N, C, and O, proving the successful introduction of polyaniline between graphitic layers. Compared to PANI/G, the lower O1s peak intensity of SC indicates reduced oxygen-containing functional groups, which is consistent with the C/O atomic ratio of 7.42 for SC versus 1.02 for PANI/G. The higher C/O ratio in SC suggests fewer structural defects in GR sheets, ensuring enhanced electrical conductivity. The deconvolution C1s spectrum of SC nanocomposite (Fig. 4 d) shows three fitting peaks at 284.8, 287.6, and 290.9 eV, corresponding to sp 2 -hybridized C = C, C-O/C-N, and π-π band, respectively. The N1s spectrum (Fig. 4 e) deconvolutes into four peaks with quinonoid imine (= N-) at 398.9 eV, benzenoid amine (-NH-) at 399.8 eV, protonated nitrogen (-NH 3 ⁺) at 400.5 eV, and oxidized nitrogen at 401.6 eV. The presence of protonated nitrogen confirms the doped state of PANI, which is favorable for improving the electrochemical performance. O1s spectral analysis (Fig. 4 f) identifies oxygen defects in GR sheets with C = O (531.2 eV), C-OH (532.1 eV), adsorbed -OH (532.8 eV), and C-O-C (533.6 eV). Figure 5 presents N₂ adsorption-desorption isotherms and pore size distribution plots for PANI/G and SC. The adsorption-desorption isotherms of the PANI/G and SC exhibit type IV isotherms with pronounced hysteresis loops in the relative pressure range of 0.8-1.0, confirming the presence of mesoporous structures. The pore size distribution spans 0–41 nm, where mesopores (3–50 nm) facilitate electrolyte ion transport and active material utilization [ 45 ]. Notably, SC shows a significantly higher specific surface area (502.1 m 2 g − 1 ) and pore volume (0.195 cm 3 g − 1 ) than PANI/G (31.65 m 2 g − 1 and 0.098 cm 3 g − 1 ). It can be concluded that the AN + -GR interfacial bonding is enhances in scCO₂ and create a high-surface-area porous architecture. This synergistic effect provides more accessible active sites facilitating fast, reversible redox reactions that enhance electrochemical performance. 3.2 Optimization of experimental conditions The effects of reaction temperature, pressure, polymerization time, and pressure relief rate on the electrochemical properties of SC as electrode materials for supercapacitor are examined using a standard three-electrode system with 1 M H₂SO₄ as the electrolyte. 3.2.1 Reaction temperature The effects of reaction temperature on the electrochemical performance of composites SC are investigated under reaction pressure 15 MPa, polymerization time 2h, and pressure relief rate120 ml min⁻¹. The SC are synthesized at reaction temperature 313, 318, 323, 328, and 333 K, named SC-1, SC-2, SC-3, SC-4, and SC-5 as shown in Table 1 . The corresponding CV curves at scan rate of 5 mV s − 1 are shown in Figure S2a. Among them, composite SC-3, prepared at 323 K, exhibits the largest CV curve area, indicating the highest specific capacitance. The GCD curves at 1 A g − 1 are shown in Figure S2b. According to Eq. (1), the specific capacitances of materials SC-1, SC-2, SC-3, SC-4, and SC-5 are calculated as 272.2 F g⁻¹, 279.6 F g⁻¹, 527 F g⁻¹, 335.6 F g⁻¹, and 295.2 F g⁻¹. Consequently, 323 K is considered the optimal experimental temperature. The characters of scCO₂, such as dissolving capacity and dispersal ability, change with the variation of density responding to temperature. When temperature is lower than 323 K, the scCO₂’s dissolving capacity decreases and dispersal ability increases, resulting in weak molecular diffusion of AN + between graphite layers. When temperature is higher than 323 K, the scCO₂’s dissolving capacity increases and dispersal ability decreases, causing less AN + dissolved in scCO₂ and therefore less AN + intercalation between graphite layers. When the temperature is 323 K, the dissolving capacity and dispersal ability of scCO₂ achieves optimal balance that simultaneously enabling sufficient intercalation and homogeneous dispersion of AN + between graphite layers. Table 1 Composites synthesized at different reaction temperatures in scCO₂. No. T /K P /MPa t /h R /mL·min − 1 SC-1 313 15 2 120 SC-2 318 15 2 120 SC-3 323 15 2 120 SC-4 328 15 2 120 SC-5 333 15 2 120 3.2.2 Reaction pressure The effects of reaction pressure on the electrochemical performance of SC are investigated under reaction temperature 323 K, polymerization time 2h, and pressure relief rate 120 mL min⁻¹. The prepared materials are named SC-6, SC-3, and SC-7 corresponding to 10 MPa, 15 MPa, and 20 MPa as given in Table 2 . The corresponding CV and GCD curves are shown in Figure S2. According to Eq. (1), the specific capacitances of SC-6, SC-3, and SC-7 are 348.8 F g⁻¹, 527 F g⁻¹, and 372.4 F g⁻¹. It shows that the electrochemical performance of SC-3, prepared at 15 MPa, is the best. The dissolving capacity and dispersal ability of scCO₂ also very with the change of its pressure. When pressure increases, its density increases, folloing dissolving capacity increasing and dispersal ability decreasing. When pressure decreases, the variation tendency of dissolving capacity and dispersal ability for scCO₂ is opposite with that of pressure decreasing. In addition, excessive pressure (20 MPa) could induce GR sheet restacking, diminishing effective porosity and obstructing ion transport pathways. Therefore, 15MPa is the optimal experimental pressure. Table 2 Composites synthesized under different reaction pressures in scCO₂. No. T /K P /MPa t /h R /mL·min − 1 SC-6 323 10 2 120 SC-3 323 15 2 120 SC-7 323 20 2 120 3.2.3 Polymerization time The effect of aniline polymerization time is investigated under reaction temperature 323 K, reaction pressure 15 MPa, depressurization rate 120 mL·min − 1 . The prepared materials are named SC-8, SC-9, SC-3, and SC-10 corresponding to polymerization time 0.5 h, 1 h, 2h, and 3 h shown in Table 3 . The corresponding CV and GCD curves are shown in Figure S2. According to Eq. (1), the specific capacitances of SC-8, SC-9, SC-3 and SC-10 are 388.3 F g⁻¹, 429 F g⁻¹, 527 F g⁻¹, and 485 F g⁻¹, respectively. It is shown that the specific capacitance of composites progressively increases with longer polymerization time when polymerization time less than 2h, illustrating that AN + is still in the polymerization process. However, when polymerization time is more than 2h, the specific capacitance of composites decreases with polymerization time increasing. This phenomenon can be explained that excessive polymerization time may lead to excessive growth of PANI molecular chains, which is prone to form thick clusters or uneven coating layers, blocking the ion transport channels between GR sheets, reducing the effective specific surface area, thereby restricting the rapid diffusion of electrolyte ions, resulting in a decrease of electrochemical performance. Based on these findings, 2 h is identified as the optimal stirring time. Table 3 Composite materials synthesized under different polymerization time in scCO₂. No. T /K P /MPa t /h R /mL·min − 1 SC-8 323 15 0.5 120 SC-9 323 15 1 120 SC-3 323 15 2 120 Sc-10 323 15 3 120 3.2.4 Depressurization rate The effect of pressure relief rate on the electrochemical performance of SC is systematically examined. The prepared materials are denoted as SC-11, SC-3, SC-12, and SC-13 corresponding to 40, 120, 200, and 280 mL min⁻¹ as listed in Table 4 . The corresponding CV and GCD curves are shown in Figure S2. The CV curves reveal an inverse relationship between pressure relief rate and capacitive performance, with specific capacitances decreasing from 669 F g⁻¹ at 40 mL min⁻¹ to 485 F g⁻¹ at 280 mL min⁻¹. The experimental results show that rapid depressurization disrupts the self-assembly process of composite, leading to compromised polymer-GR interfacial bonding and consequently weak charge storage capacity. The depressurization rate of 40 mL min⁻¹ demonstrated optimal condition for maintaining structural integrity while allowing sufficient AN + chain alignment between graphite layers. Table 4 Composites synthesized under different depressurization rates in scCO₂. No. T /K P /MPa t /h R /mL min − 1 SC-11 323 15 2 40 SC-3 323 15 2 120 SC-12 323 15 2 200 SC-13 323 15 2 280 Thereby, the optimal experimental conditions for preparing SC composites in scCO₂ are reaction temperature 323 K, reaction pressure 15 MPa, polymerization time 2 h, and depressurization rate 40 mL min − 1 . In sum, nanocomposite SC-11 exhibits the best electrochemical performance. 3.3 The Electrochemical Performances The electrochemical performance of SC-11 as electrode materials for supercapacitor is further analyzed, and compared with that of PANI/G and PANI using a standard three-electrode system with 1 M H₂SO₄ as the electrolyte. Figure 6a presents the cyclic voltammetry (CV) curves of PANI, PANI/G, and SC-11 electrodes at a scan rate of 5 mV s - 1 . All three electrodes exhibit two pairs of redox peaks, which originate from the reversible transformation of benzenoid/amine and green/quinone forms in the PANI molecular structure, confirming a pseudocapacitive energy storage mechanism [46]. Notably, the SC-11 electrode exhibits the most intense redox peaks and the largest integrated area, indicating a higher specific capacity and enhanced redox kinetics compared to the other two electrodes. It can be explained that GR sheets and PANI presents coupled structured in SC, therefor realizing the charge transfer in continuous conductive network. Figure 6 b presents the CV curves of SC-11 electrode at scan rates ranging from 5 to 100 mV s − 1 . It is seen that with increasing of scan rate, a slight shift in the redox peak potentials is observed. This phenomenon can be attributed to the enhanced diffusion resistance and polarization within the electrode. Furthermore, even at the high scan rate of 100 mV s − 1 , SC-11 electrode retains well-defined redox peaks, demonstrating its excellent reversibility and rate capability. The charge storage process in SC-11electrode involves both surface capacitive and diffusion-controlled mechanisms. To elucidate the electrochemical kinetics of the, the relationship between oxidation peak currents ( i) and scan rates ( v ) was analyzed using the following equations: i = a v b (8) log i = log a + blog v (9) where, “a” and “b” are adjustable parameters. A b-value closes to 0.5 indicates diffusion-controlled behavior, while a value near 1 suggests dominant of surface capacitive process. The calculated b-values for SC-11electrode are 0.54, 0.79, 0.70, and 0.70 (Fig. 6 c). The first oxidation peak (b = 0.54) demonstrates diffusion-dominated behavior. The other peaks (b = 0.79, 0.70, and 0.70) indicate co-existing diffusion-controlled PC and surface capacitance. This hybrid behavior confirms a hybrid energy storage behavior of both electric double-layer and pseudocapacitance. Further quantitative analysis of capacitive and diffusion contributions was performed using: i = k 1 v + k 2 v 1/2 (10) where k 1 v and k 2 v 1/2 represent currents from capacitive processes and diffusion-controlled reactions, respectively. At the scan rate of 5 mV s − 1 , the diffusion-controlled contribution for SC electrode is 33.0% (Fig. 4 d), reflecting sufficient time for electrolyte ions to penetrate internal pores. As the scan rate increases from 5 to 100 mV s − 1 , diffusion-controlled contribution of SC decreases, while capacitive contributions increase, which is mainly caused by the insufficient time for ions to infiltrate into the internal pores of the electrodes at higher scan rates. Figure 6 e displays the GCD curves of PANI, PANI/G, and SC-11 electrodes at 1 A g − 1 . SC-11 electrode performs the longer discharge time than PANI and PANI/G electrodes, indicating a higher specific capacitance arising from the well-defined interface and synergetic effects between PANI and GR sheets. Furthermore, the GCD curves of SC-11 electrode at various current densities (Fig. 6 f) exhibit near-symmetrical profile. This characteristic further confirms the highly reversibility of the redox reactions occurring in the SC electrode, consistent with CV results. Specific capacitance calculated from GCD curves at 1 A g − 1 are 222.6, 270.6, and 669.0 F·g − 1 for PANI, PANI/G, and SC-11, respectively (Fig. 6 g). With increasing current density, specific capacities decrease due to SC-11 limited ion diffusion into electrode microstructures, reducing electroactive site utilization. Nevertheless, SC-11 retains 48.0% of its initial capacity at 20 A g − 1 , outperforming PANI (34.1%) and PANI/G (40.6%). Cycling stability is critical for electrode evaluation. Figure 6 h shows that PANI and PANI/G retain 77.6% and 85.2% of their initial capacitances after 5000 charge/discharge cycles, respectively. In contrast, SC-11 exhibits significantly superior stability, retaining 92.5% of its capacity. Overall, SC-11 exhibits outstanding supercapacitive properties with a high specific capacity, good rate capability and cycling stability, surpassing most previously reported PANI/GR materials [ 26 , 47 – 49 ]. EIS measurements were also conducted to assess internal resistance and ion diffusion kinetics of the as-prepared electrodes materials, and their Nyquist plots were fitted as shown in Fig. 6 i. Each Nyquist plot features a quasi-semicircle in the high-frequency region and an oblique line in the low-frequency region. The quasi-semicircle corresponds to the charge transfer resistance ( R ct), which is influenced by the electrical conductivity of the electrode material [ 50 ]. It is observed that R ct of SC-11 is less than 2 ohms, only 1/2 of that of PANI, suggesting the faster electron transfer within the lay-by-lay assembled structure. In addition, the slope in the high-frequency region for SC-11 is close to 90°, proving its good electrical conductivity. These improvements could be originated from the layered structure compose of graphene and polyaniline with assistant of scCO 2 , as well as its hierarchical porous, which synergistically enhance charge transport efficiency while maintaining structural stability. 3.4 Asymmetric Supercapacitor To further evaluate the application potential of the SC electrode, an asymmetric supercapacitor (SC-11//AC) was assembled using glass fiber filter membrane as the separator and 1 M H₂SO₄ aqueous solution as the electrolyte, with SC-11 as the positive electrode and activated carbon (AC) as the negative electrode. Figure 7 a presents CV curves of the SC-11//AC device at various potential windows. The CV curves maintain well-defined shapes with stable reversible redox peaks and no pronounced peak shift at the 0–1.3 V range, demonstrating excellent rate capability. Therefore, the 0–1.3 V window was selected for subsequent electrochemical performance evaluations. Figure 7 b displays the GCD profiles at various current densities. The symmetrical isosceles triangular shapes of all curves indicate that the device has a high Coulombic efficiency and good reversibility during rapid charge-discharge. The specific capacitances of the device are calculated to be 124.6, 114.1, 103.4, 73.8, and 50.7 F g − 1 at the current densities of 1, 2, 5, 10, 20 A g − 1 , respectively. In addition, SC-11//AC also shows impressive cycling performance, with 90.6% of capacitance retaining after 5,000 charge-discharge cycles at a current density of 10 A g − 1 . Figure 7 c demonstrates excellent cycling stability of the SC-11//AC device, with an inset showing two series-connected button supercapacitors powering a blue LED. Ragone plot analysis (Fig. 7 d) reveals that the device delivers a competitive energy density of 29.2 Wh kg⁻¹ at 650 W kg⁻¹, which compares favorably with many reported PANI/GR composite-based devices. [ 48 , 51 – 55 ]. 4 Conclusions In this study, as supercapacitor electrode, the layer-by-layer assembled PANI/GR (named SC) composites have been prepared via a new method synergizing SFT and AN + intercalation. It is realized through effective intercalation and in-situ polymerization of AN + between graphitic layers with assistance of supercritical carbon dioxide (scCO₂), enabling layer-by-layer assembling of PANI and GR. The preparation process endows composite SC with unique nano morphology and coupled structured, which effectively mitigating deformation of PANI structural during discharge processes and realizing enhanced charge transfer. At experimental condition with reaction temperature 323 K, reaction pressure 15 MPa, polymerization time 2 h, and depressurization rate 40 mL·min⁻¹, SC presents an exceptional specific capacitance of 669.0 F g − 1 at 1 A g⁻¹, with merely 7.5% capacitance loss after 5000 cycles, which are significantly enhanced compared to PANI, PANI/G, and othe PANI/GR composites reported so far. The assembled SC-11//AC asymmetric supercapacitor achieved an energy density of 29.2 Wh kg⁻¹ at a power density of 650 W kg⁻¹, while retaining 90.6% capacitance after 5000 cycles. This study provides a rational strategy for designing layered graphene-based storage composites, offering promising prospects for advanced energy storage applications. Declarations CRediT authorship contribution statement Jing Zhu: Conceptualization, Funding acquisition, Project administration, Supervision, Writing-review & editing. Huiqi Du: Writing-original draft, Methodology, Investigation, Data curation. Chang Ma: Supervision, Conceptualization, Writing-original draft, Investigation, Data curation. Xia Wu: Writing-review & editing, Data curation. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding National Natural Science Foundation of China (Grant No. 22208132, 52004104, 22408131, 22508146). China Postdoctoral Science Foundation (Grant No. 2025M771812). Natural Science Research of Jiangsu Higher Education Institutions of China (Grant No. KK18530). 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9404906","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":630146627,"identity":"01bebda2-2d96-4170-b794-9d6cf01de45a","order_by":0,"name":"Jing Zhu","email":"","orcid":"","institution":"Jiangsu Ocean University","correspondingAuthor":false,"prefix":"","firstName":"Jing","middleName":"","lastName":"Zhu","suffix":""},{"id":630146628,"identity":"0d6a1598-c895-4e08-af85-f52b540a2d41","order_by":1,"name":"Huiqi Du","email":"","orcid":"","institution":"Jiangsu Ocean University","correspondingAuthor":false,"prefix":"","firstName":"Huiqi","middleName":"","lastName":"Du","suffix":""},{"id":630146629,"identity":"254a84b4-db19-41e8-b25a-36cf49a89427","order_by":2,"name":"Chang Ma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8klEQVRIie3RsYqDMBjA8U8+sEusa0RoXyEidCrcq3wi3NypdDuLEF9B38JHsGS4RdrV0VtutnS4jlU73RIdC81/CYT8CPkCYDK9YC7iqSXB2RqxEuNWNUG8TMaiO2xXQWbTPCLqeuPl9WcIF/YUkwQaEr4jVXRMWbe7SlgtG7JuO42wcqJwIBk6ZVBICL2G0M81BDlV8fMWp+wtRGVDNjINsXmUqIEkirUD+ZokjCnrOD5fMRgIiSnCFxJhHHJqiyA/86Cof1JfRz6U+3cfv9JVv6Lbb9fL7/h005F/7+o/hverlcwE/fTa2UdNJpPprXoAz+xN378ForoAAAAASUVORK5CYII=","orcid":"","institution":"Jiangsu Ocean University","correspondingAuthor":true,"prefix":"","firstName":"Chang","middleName":"","lastName":"Ma","suffix":""},{"id":630146630,"identity":"9c144356-05ff-4783-a694-6d298c385d44","order_by":3,"name":"Xia Wu","email":"","orcid":"","institution":"Jiangsu Ocean University","correspondingAuthor":false,"prefix":"","firstName":"Xia","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2026-04-13 13:40:01","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9404906/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9404906/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108007793,"identity":"ec509107-fadc-4585-9f19-bef5533db37a","added_by":"auto","created_at":"2026-04-28 13:02:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":300580,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the SC synthesis process.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/f073ac71540778fa6d1c0d59.png"},{"id":108001332,"identity":"4b2a75ba-7836-4dca-990c-7f055430dba6","added_by":"auto","created_at":"2026-04-28 12:00:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":172037,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the experimental apparatus: 1-CO\u003csub\u003e2\u003c/sub\u003e gas cylinder; 2-pressure regulating valve; 3,8,10,17-check valve; 4-storage tank; 5,12-pressure gauge; 6-low-temperature circulating cooling pump; 7,14-temperature controller; 9-pressure booster pump; 11- reactor; 13-stirring controller; 15-sample valve; 18-advection pump; 16,19-decompression valve.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/d408cd3f8c1d551e0c560f6f.png"},{"id":108007282,"identity":"70ddd820-dd54-4154-bd1c-2b54576e8e55","added_by":"auto","created_at":"2026-04-28 12:59:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1040168,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of (a) PANI, (b-c) PANI/G, (d) SC, and TEM image of (e-f) SC\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/6178a92efa58d9bb6af71105.png"},{"id":108001334,"identity":"a0b021f6-fbf2-41b8-b575-47546b5d6fd8","added_by":"auto","created_at":"2026-04-28 12:00:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":483043,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD patterns of Graphite, GR [40], PANI, and SC; (b) FT-IR spectra of PANI, PANI/G, and SC; (c) Raman spectra of GR[40], PANI/G, and SC; (d) C 1 s, (e) N 1 s, and (f) O 1 s XPS spectra of SC.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/50046506c4fea820dc35de9f.png"},{"id":108007590,"identity":"2f6f9cf9-e4d3-4e0c-ab9f-53a8f8c6f72e","added_by":"auto","created_at":"2026-04-28 13:00:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":297475,"visible":true,"origin":"","legend":"\u003cp\u003e(a) N₂ adsorption-desorption isotherms and (b) pore size distribution plots of PANI/G and SC.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/49a7fc7fbf28052447a13301.png"},{"id":108001336,"identity":"f9b91007-ae2e-426c-a80c-14a966d2b2b5","added_by":"auto","created_at":"2026-04-28 12:00:16","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":750555,"visible":true,"origin":"","legend":"\u003cp\u003e(a) CV curves of PANI, PANI/G, and SC-11 at a scan rate of 5 mV s\u003csup\u003e-1\u003c/sup\u003e; (b) CV curves of SC-11 at various scan rates; (c) Relationship between logarithmic current (log \u003cem\u003ei\u003c/em\u003e) and logarithmic scan rate (log \u003cem\u003ev\u003c/em\u003e); (d) Contribution of capacitive and diffusion-controlled currents of SC at various scan rates; (e) GCD curves of PANI, PANI/G, and SC-11 at 1 A g\u003csup\u003e-1\u003c/sup\u003e ; (f) GCD curves of SC-11 at various current densities; (g) Specific capacitance of PANI, PANI/G, and SC-11 at various current densities; (h) Cycling performance of PANI, PANI/G, and SC-11 at 10 A/g (inset in h shows the GCD curves of the first three and last three cycles of SC-11); (i) Impedance plots of PANI, PANI/G, and SC-11.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/dfe75f61ad458d69050a422d.png"},{"id":108001337,"identity":"b8aa1249-3b75-45bf-8bb7-70b75fec471a","added_by":"auto","created_at":"2026-04-28 12:00:16","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":440737,"visible":true,"origin":"","legend":"\u003cp\u003e(a) CV curves of SC-11//AC at various potential windows; (b) GCD curves of SC-11//AC at various current densities; (c) cycling performance of SC-11//AC (inset shows two tandem button supercapacitors powering a blue LED); Ragone plot of SC-11//AC compared with previously reported PANI/GR supercapacitors [48,51-55].\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/a1baa18587fa67c23295743b.png"},{"id":108086940,"identity":"b5d86e4b-1edd-48bb-bd59-2ec240d4a5e8","added_by":"auto","created_at":"2026-04-29 08:41:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3933463,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/d49635ad-28f7-4729-a932-9fdcade5018e.pdf"},{"id":108001330,"identity":"2b72e7a4-8d58-43b3-8749-010f448fa8e0","added_by":"auto","created_at":"2026-04-28 12:00:16","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":333740,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-9404906/v1/3eb3ad715d51cc36fea52d38.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Supercritical CO₂-Assisted In-Situ Intercalation Polymerization of Polyaniline/Graphene Composites: Enhanced Electrochemical Performance for High-Performance Supercapacitor Electrodes","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSupercapacitors are widely applied in flexible portable electronics, electric vehicles, and sensor systems [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. They store energy through electric double-layer effect at electrode surface or pseudocapacitance effect generated by redox reactions within electrode [\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Porous carbon-based materials, such as graphene (GR), activated carbon, carbon nanotubes, biomass derivatives, and so on, are mainly used for electric double-layer capacitor (EDLC) electrode. These materials are charactered of unique features such as rich mesoporous and microporous structures which enable rapid ion transport, resulting in fast response rates and outstanding cycling stability. Nevertheless, their lower specific capacitance remain a critical limitation for broader implementation [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. For instance, the theoretical specific capacitance of GR is only 550 F/g. What\u0026rsquo;s worse, the van der Waals force between GR sheets leads to stacking and agglomeration between them, resulting in lower specific capacitance [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. As commonly used EDLC materials, activated carbon and carbon nanotubes typically exhibit specific capacitances of only 100\u0026ndash;300 F/g in aqueous electrolytes [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePC stores charge through fast and reversible redox reaction between electrode material and electrolyte. The most commonly used electrode materials include conductive polymers, transition metal oxides, transition metal chalcogenides, metal nitrides, and so on [\u003cspan additionalcitationids=\"CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], owning high specific capacitance and energy density. Polyaniline (PANI) stands out with high theoretical specific capacitance of 2000 F/g, exceeding that of inorganic metal oxides (e.g., RuO₂, ~\u0026thinsp;700 F/g) and other conductive polymers (e.g., polypyrrole, 300\u0026ndash;500 F/g) [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Furthermore, its electrochemical performance can be optimized by tailoring molecular structure, morphology, and porosity through controlled polymerization or chemical modification reaction [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. However, issues such as high self-discharge rates, low doping efficiency, and restricted ion transport result in weak cycling stability and capacity retention of PANI [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBased on the excellent properties of PANI and GR, composite PANI/GR have attracted significant research interest in recent years. PANI/GR combines both the advantages of PANI and GR, and shows synergistic effect when used as electrode material of supercapactior [\u003cspan additionalcitationids=\"CR22 CR23 CR24\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Mahato et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] reported a nanoscale semi-crystalline composite PANI/GR, delivering specific capacitance of 525.5 F g⁻\u0026sup1; at 0.1 A g⁻\u0026sup1; when assembled into symmetric de vice.\u003c/p\u003e \u003cp\u003eAlthough GR offers exceptional specific surface area, conductivity, and mechanical strength, reduced graphene oxide (rGO) is more widely used because of its high performance, low cost, and more feasibility [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Reduction treatment can partially restore GO's sp\u0026sup2;-conjugated network while preserving its high specific surface area and structural defects that facilitate interfacial interactions with PANI, thereby enhancing electrical conductivity [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Umar et al. [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] developed an rGO@PANI nanocomposite, which exhibits specific capacitance of 314.2 F g⁻\u0026sup1; at 1 A g⁻\u0026sup1;, 92% capacitance retention after 4,000 cycles. Upadhyay et al. [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] fabricated a flexible solid-state supercapacitor using PANI nanofiber-bridged rGO/RuO₂ nanoparticles, achieving a maximum areal capacitance of 677 mF cm⁻\u0026sup2;, a peak energy density of 60.18 \u0026micro;Wh cm⁻\u0026sup2; at 0.8023 mW cm⁻\u0026sup2; power density. However, the oxidation and reduction processes of graphite to producing rGO causes structural defects, resulting in the decrease of conductivity and mechanical property. Therefore, the electrochemical performance of rGO still falls short of graphene.\u003c/p\u003e \u003cp\u003eGraphite, which can be described as the three-dimensional crystalline form of GR or as a multi-layered stacked structure. It possesses a distinctive layered structure with a 3.35 \u0026Aring; interlayer spacing, enabling insertion of specific compound to form intercalation compound [\u003cspan additionalcitationids=\"CR32\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. With graphite as raw material, Guo et al. [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] prepared the PANI/GR composite through intercalation and in-situ polymerization of aniline (AN) between graphite layers under ultrasonic condition. However, strong van der Waals forces and π-π interactions cause most GR layers remain tightly stacked, making difficult for AN molecule to penetrate into graphite layers [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs a green environmental protection technique, supercritical fluid technology (SFT) has attracted much more attention in recent years due to the specific character of supercritical fluid, such as small viscosity, high diffusivity, strong dissolving capacity, good selectivity, and so on [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. In addition, the dissolving capacity of supercritical fluid can be adjusted through altering its temperature and pressure. Supercritical CO₂ (scCO₂) has gained significant attention due to its mild critical parameters (\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 304.2 K, \u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 7.38 MPa), exceptional solvation power, zero surface tension, chemical inertness, and low corrosiveness, finding wild applications in materials processing [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. For instance, Wang et al. [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] developed an efficient GR exfoliation strategy through pressure modulation of scCO₂ to achieves graphite exfoliation into GR. The high density and low viscosity of scCO₂ dramatically enhance the graphite exfoliation efficiency.\u003c/p\u003e \u003cp\u003eHerein, we present a novel approach, which integrating SFT with in-situ intercalative polymerization, to prepare PANI/GR composites. It is known that there is strong cation-π interaction between aniline cation (AN\u003csup\u003e+\u003c/sup\u003e) and π electrons in GR sheet of graphite [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Considering that this interaction can further promote the separation of graphite layers, we adopt AN\u003csup\u003e+\u003c/sup\u003e as intercalating agent. The synthesis process is illustrated as Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Firstly, employes scCO₂ as intercalation medium to increase the layer spacing of graphite through decreasing pressure to increase the CO₂ molecular size. then, AN\u003csup\u003e+\u003c/sup\u003e and oxidizing agent are inserted between the graphite layers with assistant of scCO₂. Subsequent polymerization of AN\u003csup\u003e+\u003c/sup\u003e in supercritical condition enables well-ordered layer by layer assemble of PANI and GR, yielding PANI/GR composites (named SC). The novel approach avoids oxidation and reduction reaction of graphite, therefore voiding the damage of planar structure of GR. In addition, scCO₂ enhances the intercalation efficiency and Interfacial interactions between GR and PANI, thereby optimizing the structure and electrochemical performance of the composite.\u003c/p\u003e \u003cp\u003eThe composite SC achieves an exceptional specific capacitance of 669.0 F g⁻\u0026sup1; at 1 A g⁻\u0026sup1;, with merely 7.5% capacitance loss after 5,000 cycles, outperforming PANI and PANI/GR (named PANI/G) prepared under normal pressure and temperature conditions, as well as many other reported PANI/GR composites. The corresponding SC//activated carbon (AC) asymmetric supercapacitor achieves an energy density of 29.2 Wh kg⁻\u0026sup1; at a power density of 650 W kg⁻\u0026sup1;. The superior performance of this nanocomposite highlighting the significant potential of SFT for advanced energy storage composites manufacture.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eAniline (Analytical pure), ammonium persulfate (Analytically pure), concentrated hydrochloric acid (37%), graphite powder (99.95%, \u0026gt;\u0026thinsp;100 mesh), polyvinyl pyrrolidone (Analytically pure), and N-methylpyrrolidone (Analytical pure) were purchased from Shanghai Aladdin Technology Co., Ltd. (China). Concentrated sulfuric acid (95%) and polyvinylidene fluoride (30,000-330,000 g mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) were purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd. (China). Graphitized carbon black (Analytical pure) was purchased from Tianjin Umeng Chemical Technology Co., Ltd. (China).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of PANI, PANI/G, and SC\u003c/h2\u003e \u003cp\u003e \u003cstrong\u003ePANI\u003c/strong\u003e \u003cp\u003ePANI was synthesized through chemical oxidative polymerization method. First, 0.28g aniline was mixed with 30 mL 1 M HCL solution to obtain the 0.1 M AN\u003csup\u003e+\u003c/sup\u003e/HCL solution (solution A). Subsequently, 0.68 g of (NH₄)₂S₂O₈ was dissolved in 30 mL hydrochloric acid solution under magnetic stirring at 3000 rpm until complete dissolution, yielding solution B. Solution B was then added dropwise to solution A over 0.5 hours under stirring at 3000 rpm in ice-water bath, following reaction for 6 hours. The product was washed three times with alternating anhydrous ethanol and deionized water, and then annealed in tube furnace under N₂ atmosphere at 200\u0026deg;C for 2 hours, yielding PANI.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003ePANI/G\u003c/strong\u003e \u003cp\u003e0.1 g graphite was ultrasonically dispersed in solution A for 30 minutes to form mixture. Then solution B was added dropwise to the mixture in ice-water bath, followed by continuous magnetic stirring at 3000 rpm for 6 hours. The product was washed three times with alternating anhydrous ethanol and deionized water, and annealed in tube furnace under N₂ atmosphere at 200\u0026deg;C for 2 hours, yielding PANI/G.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eSC\u003c/strong\u003e \u003cp\u003e0.754 g aniline and 0.037 g graphite powder were dispersed in 60 mL of 1 M HCl solution via ultrasonication for 30 minutes. Then 0.5 g polyvinylpyrrolidone (PVP) was introduced to above mixture to realize complete dispersing by magnetic stirring at 3000 rpm to get solution C. Solution C was charged into the reactor (11) of 80 mL effective volume at the beginning of experiment.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eThe schematic illustration of the experimental apparatus is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. First, the valves (2, 3) were opened to pass CO\u003csub\u003e2\u003c/sub\u003e gas into the storage tank (4), and then the low-temperature circulating cooling pump (6) was turned on to cool the CO\u003csub\u003e2\u003c/sub\u003e liquid storage tank to 268 K to get liquid CO\u003csub\u003e2\u003c/sub\u003e. Then the stirrer (13) and temperature switches (14) were turned on. At the same time, the valves (8,10) were opened to allow the injection of CO\u003csub\u003e2\u003c/sub\u003e into the reactor (11) through the booster pump (9) until the experimental temperature and pressure. After stirring for 30 minutes, the decompression valve (19) of the reactor was open to gradually vent the CO₂ gas at a controlled flow rate until 5 MPa. Upon completion of depressurization, the decompression valve (19) was closed. Then solution B was injected into the reactor (11) with advection pump (18), and the reactor was pressurized to supercritical condition again to carry out the polymerization reaction with pump (9). Upon completion of reaction, the decompression valve (19) was opened and the product was collected through the sample valve (15). The product was sequentially washed three times with alternating anhydrous ethanol and deionized water, and annealed in a tube furnace under N₂ atmosphere at 200\u0026deg;C for 2 hours. The resulting composite was stored in desiccator and named as SC.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Electrochemical measurements\u003c/h2\u003e \u003cp\u003eThe product, acetylene black, and polyvinylidene fluoride (PVDF) were mixed at 8:1:1 mass ratio and grounded in agate mortar for 30 minutes. During grinding, appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to minimize particle agglomeration. The resulting slurry was coated onto a stainless steel mesh current collector to form electrode sheets. Next, the electrode was dried under vacuum at 353 K for 12 h, tableted under 2 MPa for 3 min, and then immersed in 1 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte for 12 h to serve as working electrode. The electrochemical performances were measured on an electrochemical workstation (CHI600C, Shanghai Chenhua Co., Ltd., China) using a three-electrode configuration in 1 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte, with a platinum sheet and a standard calomel electrode used as the counter and reference electrodes, respectively.\u003c/p\u003e \u003cp\u003eThe specific capacitance \u003cem\u003e(C\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e) of individual electrodes and the specific capacitance (\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e) of the whole device can be calculated from GCD curves via Eq.\u0026nbsp;(1,2):\u003c/p\u003e \u003cp\u003e \u003cem\u003eC\u003c/em\u003e \u003csub\u003e \u003cem\u003em\u003c/em\u003e \u003c/sub\u003e= \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\text{I}\\text{}\\text{△}\\text{t}}{\\text{m}\\text{△}\\text{V}}\\)\u003c/span\u003e\u003c/span\u003e (1)\u003c/p\u003e \u003cp\u003e \u003cem\u003eC\u003c/em\u003e \u003csub\u003e \u003cem\u003es\u003c/em\u003e \u003c/sub\u003e= \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\text{I}\\text{}\\text{△}\\text{t}}{\\text{M}\\text{△}\\text{V}}\\)\u003c/span\u003e\u003c/span\u003e, (2)\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eI\u003c/em\u003e (A) is discharge current, \u003cem\u003em\u003c/em\u003e (g) is mass of electrode active material, \u003cem\u003eM\u003c/em\u003e (g) is total mass of the anode and cathode, Δ\u003cem\u003et\u003c/em\u003e (s) is duration of a discharge cycle, and Δ\u003cem\u003eV\u003c/em\u003e (V) is voltage fluctuation range during the discharge duration Δ\u003cem\u003et\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eThe mass ratios of anode and cathode are calculated by Eq.\u0026nbsp;(3\u0026ndash;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e5\u003c/span\u003e) to maintain charge balance between the anode and cathode:\u003c/p\u003e \u003cp\u003e \u003cem\u003eQ\u003c/em\u003e \u003csup\u003e+\u003c/sup\u003e = \u003cem\u003eQ\u003c/em\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (3)\u003c/p\u003e \u003cp\u003e \u003cem\u003eQ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eM\u003c/em\u003e \u0026lowast; Δ\u003cem\u003eV\u003c/em\u003e \u0026lowast; \u003cem\u003eC\u003c/em\u003e (4)\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\frac{{\\text{m}}^{\\text{+}}}{{\\text{m}}^{\\text{-}}}\\:=\\:\\frac{{\\text{C}}^{\\text{-}}\\text{\u0026Delta;}\\text{V}}{{\\text{C}}^{\\text{+}}\\text{\u0026Delta;}\\text{V}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere Δ\u003cem\u003eV\u003c/em\u003e(V), \u003cem\u003eC\u003c/em\u003e (F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), \u003cem\u003eQ\u003c/em\u003e\u003csup\u003e+\u003c/sup\u003e, and \u003cem\u003eQ\u003c/em\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e are the potential window from GCD, specific capacitance, positive charge, and negative charge, respectively.\u003c/p\u003e \u003cp\u003eThe energy density \u003cem\u003eE\u003c/em\u003e (Wh Kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and power density \u003cem\u003eP\u003c/em\u003e (KW Kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) can be estimated by Eq.\u0026nbsp;(6,\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e7\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e \u003cem\u003eE\u003c/em\u003e = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\text{1}}{\\text{2}}\\)\u003c/span\u003e\u003c/span\u003e \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e (Δ\u003cem\u003eV\u003c/em\u003e)\u003csup\u003e2\u003c/sup\u003e \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\text{1000}}{\\text{3600}}\\)\u003c/span\u003e\u003c/span\u003e (6)\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"582\" height=\"55\"\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Morphology and structure characterization\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the SEM images of PANI, PANI/G, and SC, with TEM image of SC. The morphology of PANI nanofiber is relatively uniform with diameters ranging from 70 to 90 nm and length 1 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea), similarly with the morphology of PANI for PANI/G (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb-c). It is seen that the PANI nanofiber for PANI/G aggregates into spherical clusters, with graphite sheets stacking together with almost no PANI attach on, indicating PANI and graphite merely physically mixed. In contrast, SC exhibits a GR-dominant lamellar morphology with uniformly anchored PANI nanofibers whose diameter is approximate 30 nm and length 1 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). TEM is also employed to further confirms the intercalated architecture of SC. It can be observed clearly that the diameters of PANI nanoparticles are about 80 nm, and the PANI nanofibers are uniformly embedded between GR sheets (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee-f). The SEM and TEM analysis demonstrate that scCO₂ effectively mediates the intercalating and in-situ polymerization of AN\u003csup\u003e+\u003c/sup\u003e between the graphite layers.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea shows the XRD patterns of graphite, GR, PANI, and SC. For graphite, the strong and sharp diffraction peaks at 2\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;26.55\u0026deg; are attributed to (002) crystal planes, corresponding to interlayer spacing of 0.335 nm for graphite [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. The XRD pattern of GR shows peak broadening and reduced intensity at 2\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;26.55\u0026deg; due to diminished interlayer ordering and structural regularity of GR sheets. The XRD pattern of PANI exhibits two broad peaks centered at 2\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;20.4\u0026deg; and 25.03\u0026deg;, corresponding to the (020) and (102) crystal planes of PANI in its emeraldine salt form. For SC nanocomposite, it can be observed that diffraction peaks assigned to the interlayer distance of graphite gradually moves from 26.55\u0026deg; to 26.05\u0026deg; with significant intensity reduction. This 0.50\u0026deg; shift corresponds to interlayer expansion of GR sheets (d-spacing increasing from 0.335 nm to 0.342 nm, calculated via Bragg's law: nλ\u0026thinsp;=\u0026thinsp;2d sin\u003cem\u003eθ\u003c/em\u003e, n\u0026thinsp;=\u0026thinsp;1, λ\u0026thinsp;=\u0026thinsp;0.15406 nm), which can be attributed to the intercalation of PANI between graphitic layers with assistance of scCO₂. The diffraction peak intensity of SC at 25.03\u0026deg; is significantly enhanced compared with PANI, indicating a more ordered arrangement of PANI molecular chains and increased crystallinity in the composite material.\u003c/p\u003e \u003cp\u003eFTIR analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) is used to further examine the chemical composition of materials. For PANI, the peaks at 671, 810, and 1123 cm⁻\u0026sup1; correspond to the C-H stretching vibration on the benzene ring, out of plane bending vibrations of C\u0026thinsp;\u0026minus;\u0026thinsp;H band in the aromatic ring, and -N\u0026thinsp;=\u0026thinsp;Q=N- stretching (Q represents quinone rings), respectively. The peaks at 1298 and 1400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are attributed to the C\u0026thinsp;\u0026minus;\u0026thinsp;N stretching vibration of the secondary aromatic amine and C-N stretching connecting the quinoid and the benzenoid. The peaks appeared at 1484, 1580, and 3450cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are ascribed to C\u0026thinsp;=\u0026thinsp;C stretching of the benzene and quinoid ring, and N-H stretching vibration, respectively [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. PANI/G exhibits all characteristic peaks of PANI, and the strong peaks at 1620 and 3430cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e originate from bending vibration of H-O-H and O-H stretching vibration in adsorbed free water. SC not only exhibits all characteristic peaks of PANI, but also appears a new peak at 1240 cm⁻\u0026sup1;, which can be attributed to the C-N\u0026middot;⁺ stretching vibration in protonic acid-doped PANI. Additionally, SC exhibits higher intensity than PANI and PANI/G at 1123 cm⁻\u0026sup1; (C\u0026thinsp;=\u0026thinsp;N in quinoid ring), which can be interpreted as enhanced conjugation of the C\u0026thinsp;=\u0026thinsp;N bond in the quinoid structure due to the interaction between GR sheets and PANI.\u003c/p\u003e \u003cp\u003eRaman spectroscopy is employed to further confirm the interaction between PANI and GR sheets [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, GR exhibit shows three characteristic peaks at 1342, 1580, and 2700cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to D-band (C\u0026thinsp;\u0026minus;\u0026thinsp;C, the disordered graphite structure), G-band (C\u0026thinsp;=\u0026thinsp;C, sp\u003csup\u003e2\u003c/sup\u003e-hybridized carbon), and 2D-band [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. For PANI/G and SC nanocomposite, the bands at 1175, 1392, and 1482 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are assigned to in plane C\u0026thinsp;\u0026minus;\u0026thinsp;H bending of quinoid ring, C\u0026thinsp;\u0026minus;\u0026thinsp;C stretching of quinoid ring, and C\u0026thinsp;=\u0026thinsp;C stretching of quinoid ring, respectively. Additionally, the D and G peaks are difficult to distinguish for PANI/G due to their broad shapes, originating from the weak interfacial interaction between GR sheets and PANI under atmospheric pressure. For SC, the characteristic peaks of both GR and PANI are clearly distinguishable, confirming that scCO₂ promotes the uniform intercalation of AN\u003csup\u003e+\u003c/sup\u003e between the graphitic layers. Furthermore, the ID/IG ratio of SC is higher than that of GR, which can be attributed to minor structural defects caused during the supercritical CO₂-assisted AN\u003csup\u003e+\u003c/sup\u003e intercalation process, arising from interactions between PANI and GR sheets.\u003c/p\u003e \u003cp\u003eXPS analysis further elucidates the composition and chemical states of SC nanocomposite. The full survey spectrum (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) confirms the presence of N, C, and O, proving the successful introduction of polyaniline between graphitic layers. Compared to PANI/G, the lower O1s peak intensity of SC indicates reduced oxygen-containing functional groups, which is consistent with the C/O atomic ratio of 7.42 for SC versus 1.02 for PANI/G. The higher C/O ratio in SC suggests fewer structural defects in GR sheets, ensuring enhanced electrical conductivity.\u003c/p\u003e \u003cp\u003eThe deconvolution C1s spectrum of SC nanocomposite (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) shows three fitting peaks at 284.8, 287.6, and 290.9 eV, corresponding to sp\u003csup\u003e2\u003c/sup\u003e-hybridized C\u0026thinsp;=\u0026thinsp;C, C-O/C-N, and π-π band, respectively. The N1s spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee) deconvolutes into four peaks with quinonoid imine (=\u0026thinsp;N-) at 398.9 eV, benzenoid amine (-NH-) at 399.8 eV, protonated nitrogen (-NH\u003csub\u003e3\u003c/sub\u003e⁺) at 400.5 eV, and oxidized nitrogen at 401.6 eV. The presence of protonated nitrogen confirms the doped state of PANI, which is favorable for improving the electrochemical performance. O1s spectral analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef) identifies oxygen defects in GR sheets with C\u0026thinsp;=\u0026thinsp;O (531.2 eV), C-OH (532.1 eV), adsorbed -OH (532.8 eV), and C-O-C (533.6 eV).\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents N₂ adsorption-desorption isotherms and pore size distribution plots for PANI/G and SC. The adsorption-desorption isotherms of the PANI/G and SC exhibit type IV isotherms with pronounced hysteresis loops in the relative pressure range of 0.8-1.0, confirming the presence of mesoporous structures. The pore size distribution spans 0\u0026ndash;41 nm, where mesopores (3\u0026ndash;50 nm) facilitate electrolyte ion transport and active material utilization [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. Notably, SC shows a significantly higher specific surface area (502.1 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and pore volume (0.195 cm\u003csup\u003e3\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) than PANI/G (31.65 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 0.098 cm\u003csup\u003e3\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). It can be concluded that the AN\u003csup\u003e+\u003c/sup\u003e-GR interfacial bonding is enhances in scCO₂ and create a high-surface-area porous architecture. This synergistic effect provides more accessible active sites facilitating fast, reversible redox reactions that enhance electrochemical performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Optimization of experimental conditions\u003c/h2\u003e \u003cp\u003eThe effects of reaction temperature, pressure, polymerization time, and pressure relief rate on the electrochemical properties of SC as electrode materials for supercapacitor are examined using a standard three-electrode system with 1 M H₂SO₄ as the electrolyte.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Reaction temperature\u003c/h2\u003e \u003cp\u003eThe effects of reaction temperature on the electrochemical performance of composites SC are investigated under reaction pressure 15 MPa, polymerization time 2h, and pressure relief rate120 ml min⁻\u0026sup1;. The SC are synthesized at reaction temperature 313, 318, 323, 328, and 333 K, named SC-1, SC-2, SC-3, SC-4, and SC-5 as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The corresponding CV curves at scan rate of 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are shown in Figure S2a. Among them, composite SC-3, prepared at 323 K, exhibits the largest CV curve area, indicating the highest specific capacitance. The GCD curves at 1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are shown in Figure S2b. According to Eq.\u0026nbsp;(1), the specific capacitances of materials SC-1, SC-2, SC-3, SC-4, and SC-5 are calculated as 272.2 F g⁻\u0026sup1;, 279.6 F g⁻\u0026sup1;, 527 F g⁻\u0026sup1;, 335.6 F g⁻\u0026sup1;, and 295.2 F g⁻\u0026sup1;. Consequently, 323 K is considered the optimal experimental temperature.\u003c/p\u003e \u003cp\u003eThe characters of scCO₂, such as dissolving capacity and dispersal ability, change with the variation of density responding to temperature. When temperature is lower than 323 K, the scCO₂\u0026rsquo;s dissolving capacity decreases and dispersal ability increases, resulting in weak molecular diffusion of AN\u003csup\u003e+\u003c/sup\u003e between graphite layers. When temperature is higher than 323 K, the scCO₂\u0026rsquo;s dissolving capacity increases and dispersal ability decreases, causing less AN\u003csup\u003e+\u003c/sup\u003e dissolved in scCO₂ and therefore less AN\u003csup\u003e+\u003c/sup\u003e intercalation between graphite layers. When the temperature is 323 K, the dissolving capacity and dispersal ability of scCO₂ achieves optimal balance that simultaneously enabling sufficient intercalation and homogeneous dispersion of AN\u003csup\u003e+\u003c/sup\u003e between graphite layers.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposites synthesized at different reaction temperatures in scCO₂.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eNo.\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eT\u003c/em\u003e/K\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e/h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e/mL\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e313\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e318\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e328\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-5\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e333\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 Reaction pressure\u003c/h2\u003e \u003cp\u003eThe effects of reaction pressure on the electrochemical performance of SC are investigated under reaction temperature 323 K, polymerization time 2h, and pressure relief rate 120 mL min⁻\u0026sup1;. The prepared materials are named SC-6, SC-3, and SC-7 corresponding to 10 MPa, 15 MPa, and 20 MPa as given in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The corresponding CV and GCD curves are shown in Figure S2. According to Eq.\u0026nbsp;(1), the specific capacitances of SC-6, SC-3, and SC-7 are 348.8 F g⁻\u0026sup1;, 527 F g⁻\u0026sup1;, and 372.4 F g⁻\u0026sup1;. It shows that the electrochemical performance of SC-3, prepared at 15 MPa, is the best.\u003c/p\u003e \u003cp\u003eThe dissolving capacity and dispersal ability of scCO₂ also very with the change of its pressure. When pressure increases, its density increases, folloing dissolving capacity increasing and dispersal ability decreasing. When pressure decreases, the variation tendency of dissolving capacity and dispersal ability for scCO₂ is opposite with that of pressure decreasing. In addition, excessive pressure (20 MPa) could induce GR sheet restacking, diminishing effective porosity and obstructing ion transport pathways. Therefore, 15MPa is the optimal experimental pressure.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposites synthesized under different reaction pressures in scCO₂.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eNo.\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eT\u003c/em\u003e/K\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e/h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e/mL\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-6\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e10\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-7\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e20\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3 Polymerization time\u003c/h2\u003e \u003cp\u003eThe effect of aniline polymerization time is investigated under reaction temperature 323 K, reaction pressure 15 MPa, depressurization rate 120 mL\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The prepared materials are named SC-8, SC-9, SC-3, and SC-10 corresponding to polymerization time 0.5 h, 1 h, 2h, and 3 h shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The corresponding CV and GCD curves are shown in Figure S2.\u003c/p\u003e \u003cp\u003eAccording to Eq.\u0026nbsp;(1), the specific capacitances of SC-8, SC-9, SC-3 and SC-10 are 388.3 F g⁻\u0026sup1;, 429 F g⁻\u0026sup1;, 527 F g⁻\u0026sup1;, and 485 F g⁻\u0026sup1;, respectively. It is shown that the specific capacitance of composites progressively increases with longer polymerization time when polymerization time less than 2h, illustrating that AN\u003csup\u003e+\u003c/sup\u003e is still in the polymerization process. However, when polymerization time is more than 2h, the specific capacitance of composites decreases with polymerization time increasing. This phenomenon can be explained that excessive polymerization time may lead to excessive growth of PANI molecular chains, which is prone to form thick clusters or uneven coating layers, blocking the ion transport channels between GR sheets, reducing the effective specific surface area, thereby restricting the rapid diffusion of electrolyte ions, resulting in a decrease of electrochemical performance. Based on these findings, 2 h is identified as the optimal stirring time.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposite materials synthesized under different polymerization time in scCO₂.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eNo.\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eT\u003c/em\u003e/K\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e/h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e/mL\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.5\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-9\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSc-10\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.4 Depressurization rate\u003c/h2\u003e \u003cp\u003eThe effect of pressure relief rate on the electrochemical performance of SC is systematically examined. The prepared materials are denoted as SC-11, SC-3, SC-12, and SC-13 corresponding to 40, 120, 200, and 280 mL min⁻\u0026sup1; as listed in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The corresponding CV and GCD curves are shown in Figure S2.\u003c/p\u003e \u003cp\u003eThe CV curves reveal an inverse relationship between pressure relief rate and capacitive performance, with specific capacitances decreasing from 669 F g⁻\u0026sup1; at 40 mL min⁻\u0026sup1; to 485 F g⁻\u0026sup1; at 280 mL min⁻\u0026sup1;. The experimental results show that rapid depressurization disrupts the self-assembly process of composite, leading to compromised polymer-GR interfacial bonding and consequently weak charge storage capacity. The depressurization rate of 40 mL min⁻\u0026sup1; demonstrated optimal condition for maintaining structural integrity while allowing sufficient AN\u003csup\u003e+\u003c/sup\u003e chain alignment between graphite layers.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposites synthesized under different depressurization rates in scCO₂.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eNo.\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eT\u003c/em\u003e/K\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e/h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e/mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-11\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e40\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-12\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e200\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSC-13\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e323\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e15\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e280\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThereby, the optimal experimental conditions for preparing SC composites in scCO₂ are reaction temperature 323 K, reaction pressure 15 MPa, polymerization time 2 h, and depressurization rate 40 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. In sum, nanocomposite SC-11 exhibits the best electrochemical performance.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.3 The Electrochemical Performances\u003c/h2\u003e \u003cp\u003eThe electrochemical performance of SC-11 as electrode materials for supercapacitor is further analyzed, and compared with that of PANI/G and PANI using a standard three-electrode system with 1 M H₂SO₄ as the electrolyte.\u003c/p\u003e\u003cp\u003eFigure 6a presents the cyclic voltammetry (CV) curves of PANI, PANI/G, and SC-11 electrodes at a scan rate of 5 mV s\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e. All three electrodes exhibit two pairs of redox peaks, which originate from the reversible transformation of benzenoid/amine and green/quinone forms in the PANI molecular structure, confirming a pseudocapacitive energy storage mechanism [46].\u0026nbsp;\u003c/p\u003e\u003cp\u003eNotably, the SC-11 electrode exhibits the most intense redox peaks and the largest integrated area, indicating a higher specific capacity and enhanced redox kinetics compared to the other two electrodes. It can be explained that GR sheets and PANI presents coupled structured in SC, therefor realizing the charge transfer in continuous conductive network.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb presents the CV curves of SC-11 electrode at scan rates ranging from 5 to 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. It is seen that with increasing of scan rate, a slight shift in the redox peak potentials is observed. This phenomenon can be attributed to the enhanced diffusion resistance and polarization within the electrode. Furthermore, even at the high scan rate of 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, SC-11 electrode retains well-defined redox peaks, demonstrating its excellent reversibility and rate capability.\u003c/p\u003e \u003cp\u003eThe charge storage process in SC-11electrode involves both surface capacitive and diffusion-controlled mechanisms. To elucidate the electrochemical kinetics of the, the relationship between oxidation peak currents (\u003cem\u003ei)\u003c/em\u003e and scan rates (\u003cem\u003ev\u003c/em\u003e) was analyzed using the following equations:\u003c/p\u003e \u003cp\u003e \u003cem\u003ei\u003c/em\u003e\u0026thinsp;=\u0026thinsp;a\u003cem\u003ev\u003c/em\u003e\u003csup\u003eb\u003c/sup\u003e (8)\u003c/p\u003e \u003cp\u003elog \u003cem\u003ei\u003c/em\u003e\u0026thinsp;=\u0026thinsp;log a\u0026thinsp;+\u0026thinsp;blog \u003cem\u003ev\u003c/em\u003e (9)\u003c/p\u003e \u003cp\u003ewhere, \u0026ldquo;a\u0026rdquo; and \u0026ldquo;b\u0026rdquo; are adjustable parameters. A b-value closes to 0.5 indicates diffusion-controlled behavior, while a value near 1 suggests dominant of surface capacitive process. The calculated b-values for SC-11electrode are 0.54, 0.79, 0.70, and 0.70 (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The first oxidation peak (b\u0026thinsp;=\u0026thinsp;0.54) demonstrates diffusion-dominated behavior. The other peaks (b\u0026thinsp;=\u0026thinsp;0.79, 0.70, and 0.70) indicate co-existing diffusion-controlled PC and surface capacitance. This hybrid behavior confirms a hybrid energy storage behavior of both electric double-layer and pseudocapacitance.\u003c/p\u003e \u003cp\u003eFurther quantitative analysis of capacitive and diffusion contributions was performed using:\u003c/p\u003e \u003cp\u003e \u003cem\u003ei\u003c/em\u003e\u0026thinsp;=\u0026thinsp;k\u003csub\u003e1\u003c/sub\u003e\u003cem\u003ev\u003c/em\u003e + k\u003csub\u003e2\u003c/sub\u003e\u003cem\u003ev\u003c/em\u003e\u003csup\u003e1/2\u003c/sup\u003e (10)\u003c/p\u003e \u003cp\u003ewhere k\u003csub\u003e1\u003c/sub\u003e\u003cem\u003ev\u003c/em\u003e and k\u003csub\u003e2\u003c/sub\u003e\u003cem\u003ev\u003c/em\u003e\u003csup\u003e1/2\u003c/sup\u003e represent currents from capacitive processes and diffusion-controlled reactions, respectively.\u003c/p\u003e \u003cp\u003eAt the scan rate of 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the diffusion-controlled contribution for SC electrode is 33.0% (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed), reflecting sufficient time for electrolyte ions to penetrate internal pores. As the scan rate increases from 5 to 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, diffusion-controlled contribution of SC decreases, while capacitive contributions increase, which is mainly caused by the insufficient time for ions to infiltrate into the internal pores of the electrodes at higher scan rates.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee displays the GCD curves of PANI, PANI/G, and SC-11 electrodes at 1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. SC-11 electrode performs the longer discharge time than PANI and PANI/G electrodes, indicating a higher specific capacitance arising from the well-defined interface and synergetic effects between PANI and GR sheets. Furthermore, the GCD curves of SC-11 electrode at various current densities (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef) exhibit near-symmetrical profile. This characteristic further confirms the highly reversibility of the redox reactions occurring in the SC electrode, consistent with CV results.\u003c/p\u003e \u003cp\u003eSpecific capacitance calculated from GCD curves at 1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are 222.6, 270.6, and 669.0 F\u0026middot;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for PANI, PANI/G, and SC-11, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eg). With increasing current density, specific capacities decrease due to SC-11 limited ion diffusion into electrode microstructures, reducing electroactive site utilization. Nevertheless, SC-11 retains 48.0% of its initial capacity at 20 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, outperforming PANI (34.1%) and PANI/G (40.6%).\u003c/p\u003e \u003cp\u003eCycling stability is critical for electrode evaluation. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eh shows that PANI and PANI/G retain 77.6% and 85.2% of their initial capacitances after 5000 charge/discharge cycles, respectively. In contrast, SC-11 exhibits significantly superior stability, retaining 92.5% of its capacity. Overall, SC-11 exhibits outstanding supercapacitive properties with a high specific capacity, good rate capability and cycling stability, surpassing most previously reported PANI/GR materials [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan additionalcitationids=\"CR48\" citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eEIS measurements were also conducted to assess internal resistance and ion diffusion kinetics of the as-prepared electrodes materials, and their Nyquist plots were fitted as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ei. Each Nyquist plot features a quasi-semicircle in the high-frequency region and an oblique line in the low-frequency region. The quasi-semicircle corresponds to the charge transfer resistance (\u003cem\u003eR\u003c/em\u003ect), which is influenced by the electrical conductivity of the electrode material [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. It is observed that \u003cem\u003eR\u003c/em\u003ect of SC-11 is less than 2 ohms, only 1/2 of that of PANI, suggesting the faster electron transfer within the lay-by-lay assembled structure. In addition, the slope in the high-frequency region for SC-11 is close to 90\u0026deg;, proving its good electrical conductivity. These improvements could be originated from the layered structure compose of graphene and polyaniline with assistant of scCO\u003csub\u003e2\u003c/sub\u003e, as well as its hierarchical porous, which synergistically enhance charge transport efficiency while maintaining structural stability.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Asymmetric Supercapacitor\u003c/h2\u003e \u003cp\u003eTo further evaluate the application potential of the SC electrode, an asymmetric supercapacitor (SC-11//AC) was assembled using glass fiber filter membrane as the separator and 1 M H₂SO₄ aqueous solution as the electrolyte, with SC-11 as the positive electrode and activated carbon (AC) as the negative electrode. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea presents CV curves of the SC-11//AC device at various potential windows. The CV curves maintain well-defined shapes with stable reversible redox peaks and no pronounced peak shift at the 0\u0026ndash;1.3 V range, demonstrating excellent rate capability. Therefore, the 0\u0026ndash;1.3 V window was selected for subsequent electrochemical performance evaluations. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb displays the GCD profiles at various current densities. The symmetrical isosceles triangular shapes of all curves indicate that the device has a high Coulombic efficiency and good reversibility during rapid charge-discharge. The specific capacitances of the device are calculated to be 124.6, 114.1, 103.4, 73.8, and 50.7 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at the current densities of 1, 2, 5, 10, 20 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. In addition, SC-11//AC also shows impressive cycling performance, with 90.6% of capacitance retaining after 5,000 charge-discharge cycles at a current density of 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec demonstrates excellent cycling stability of the SC-11//AC device, with an inset showing two series-connected button supercapacitors powering a blue LED. Ragone plot analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed) reveals that the device delivers a competitive energy density of 29.2 Wh kg⁻\u0026sup1; at 650 W kg⁻\u0026sup1;, which compares favorably with many reported PANI/GR composite-based devices. [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan additionalcitationids=\"CR52 CR53 CR54\" citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eIn this study, as supercapacitor electrode, the layer-by-layer assembled PANI/GR (named SC) composites have been prepared via a new method synergizing SFT and AN\u003csup\u003e+\u003c/sup\u003e intercalation. It is realized through effective intercalation and in-situ polymerization of AN\u003csup\u003e+\u003c/sup\u003e between graphitic layers with assistance of supercritical carbon dioxide (scCO₂), enabling layer-by-layer assembling of PANI and GR. The preparation process endows composite SC with unique nano morphology and coupled structured, which effectively mitigating deformation of PANI structural during discharge processes and realizing enhanced charge transfer. At experimental condition with reaction temperature 323 K, reaction pressure 15 MPa, polymerization time 2 h, and depressurization rate 40 mL\u0026middot;min⁻\u0026sup1;, SC presents an exceptional specific capacitance of 669.0 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 1 A g⁻\u0026sup1;, with merely 7.5% capacitance loss after 5000 cycles, which are significantly enhanced compared to PANI, PANI/G, and othe PANI/GR composites reported so far. The assembled SC-11//AC asymmetric supercapacitor achieved an energy density of 29.2 Wh kg⁻\u0026sup1; at a power density of 650 W kg⁻\u0026sup1;, while retaining 90.6% capacitance after 5000 cycles. This study provides a rational strategy for designing layered graphene-based storage composites, offering promising prospects for advanced energy storage applications.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eJing Zhu:\u003c/strong\u003e Conceptualization, Funding acquisition, Project administration, Supervision, Writing-review \u0026amp; editing. \u003cstrong\u003eHuiqi Du:\u003c/strong\u003e Writing-original draft, Methodology, Investigation, Data curation. \u003cstrong\u003eChang Ma:\u0026nbsp;\u003c/strong\u003eSupervision, Conceptualization, Writing-original draft, Investigation, Data curation. \u003cstrong\u003eXia Wu:\u0026nbsp;\u003c/strong\u003eWriting-review \u0026amp; editing, Data curation.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; National Natural Science Foundation of China (Grant No. 22208132, 52004104, 22408131, 22508146). China Postdoctoral Science Foundation (Grant No. 2025M771812). Natural Science Research of Jiangsu Higher Education Institutions of China (Grant No. KK18530). Open-end Funds of Jiangsu Key Laboratory of Function Control Technology for Advanced Materials, Jiangsu Ocean University (Grant No. jsklfctam201810).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKumar P, Sephra P, Gupta M, Jeoti V, Tharini C, Stojanović GM. Flexible and sustainable energy storage: Recent progress and prospects in wearable supercapacitors. 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Eur Polym J. 2024;218:113366. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.eurpolymj.2024.113366\u003c/span\u003e\u003cspan address=\"10.1016/j.eurpolymj.2024.113366\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9404906/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9404906/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePolyaniline/graphene (PANI/GR) composites are promising supercapacitor electrode candidates owing to its excellent electrochemical performance such as high theoretical specific capacity and good electrical conductivity. However, most reported ones suffer structural defects, leading to low specific energy and poor electrochemical stability. This work proposed a novel method to fabricate PANI/GR nanocomposite for supercapacitor. By synergizing supercritical fluid technology (SFT) and aniline cation (AN\u003csup\u003e+\u003c/sup\u003e) intercalation, AN\u003csup\u003e+\u003c/sup\u003e realized effective intercalation and in-situ polymerization between graphite layers with assistance of supercritical carbon dioxide (scCO₂), enabling layer-by-layer assemble of PANI and GR (named SC). It is found that the layer structure of SC reduces PANI deformation, facilitates rapid ion diffusion, and extende interfacial interactions, therefore accelerating electron transfer throughout the electrode. The SC electrode achieves an exceptional specific capacitance of 669.0 F g⁻\u0026sup1; at 1 A g⁻\u0026sup1;, with merely 7.5% capacitance loss after 5,000 cycles, demonstrating outstanding cycling stability. The corresponding SC//activated carbon asymmetric supercapacitor delivers an energy density of 29.2 Wh kg⁻\u0026sup1; at a power density of 650 W kg⁻\u0026sup1;. This work provides an effective strategy for designing layered graphene-based energy storage composites to achieve superior electrochemical performances.\u003c/p\u003e","manuscriptTitle":"Supercritical CO₂-Assisted In-Situ Intercalation Polymerization of Polyaniline/Graphene Composites: Enhanced Electrochemical Performance for High-Performance Supercapacitor Electrodes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-28 12:00:12","doi":"10.21203/rs.3.rs-9404906/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c26d1cfa-0f32-4233-8340-c8053f4932ab","owner":[],"postedDate":"April 28th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-29T08:41:04+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-28 12:00:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9404906","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9404906","identity":"rs-9404906","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}