Conductivity spectroscopy on melt processed polypropylene-multiwalled carbon nanotube composites: Recovery after shear and crystallization

Frequency dependent investigations of conductivity and dielectric permittivity have been performed on composites of polypropylene (PP) containing different amounts of 2, 3.5, and 5 wt% of multiwalled carbon nanotubes (MWNTs) in the melt and during crystallization. The experiments were performed in a measurement slit die containing two dielectric sensors in plate-plate geometry, which was flanged to the outlet of a single screw laboratory extruder. AC conductivity and the related complex permittivity were measured in the frequency range from 20 Hz to 10⁶ Hz after stopping the extruder (recovery after shearing) and during cooling (non-isothermal crystallization). For a sample with a MWNT content of 2 wt% the AC conductivity shows a tremendous increase with time after shearing was stopped. This conductivity recovery is explained by the reorganization of the conducting network-like filler structure, which was partially destroyed by the shear. The reformation kinetics of filler clusters is assumed to be due to a cooperative aggregation. For conductive fillers in a thermoplastic matrix the kinetics of cooperative aggregation is coupled to the electrical percolation. The reorganization of the percolation network can be related to reformation of (i) the local contact regions between the nanotubes (separated by polymer chains) and (ii) to the reorientation of nanotubes oriented in the shear flow. The conductivity recovery is less pronounced for samples with MWNT concentrations well above the percolation threshold. During cooling of the melt to temperatures below crystallization a significant decrease in the conductivity and permittivity was detected. This is consistently expressed in the conductivity and permittivity spectra and can be explained by reduction of the amorphous phase (high ion mobility) on expense of the crystalline phase and/or by crystalline regions in the contact region between tubes.     

Dielectric spectroscopy on melt processed polycarbonate—multiwalled carbon nanotube composites

Complex permittivity and related AC conductivity measurements in the frequency range between 10⁻⁴ and 10⁷ Hz are presented for composites of polycarbonate (PC) filled with different amounts of multiwalled carbon nanotubes (MWNT) varying in the range between 0.5 and 5 wt%. The composites were obtained by diluting a PC based masterbatch containing 15 wt% MWNT by melt mixing using a Micro Compounder. From DC conductivity measurements it was found that for samples processed at a mixing screw speed of 150 rpm for 5 min, the percolation occurs at a threshold concentration (p_c) between 1.0 and 1.5 wt% MWNT. For concentrations of MWNT near the percolation threshold, the processing conditions (screw speed and mixing time) were varied. The differences in the dispersion of the MWNT in the PC matrix could be detected in the complex permittivity and AC conductivity spectra, and have been explained by changes in p_c. The AC conductivity and permittivity spectra are discussed in terms of charge carrier diffusion on percolation clusters and resistor-capacitor composites.     

Preparation, crystallization, electrical conductivity and thermal stability of syndiotactic polystyrene/carbon nanotube composites

A homogeneous dispersion of multi-walled carbon nanotubes (MWCNTs) in syndiotactic polystyrene (sPS) is obtained by a simple solution dispersion procedure. MWCNTs were dispersed in N-methyl-2-pyrrolidinone (NMP), and sPS/MWCNT composites are prepared by mixing sPS/NMP solution with MWCNT/NMP dispersion. The composite structure is characterized by scanning electron microscopy and transmission electron microscopy. The effect of MWCNTs on sPS crystallization and the composite properties are studied. The presence of MWCNTs increases the sPS crystallization temperature, broadens the crystallite size distribution and favors the formation of the thermodynamically stable β phase, whereas it has little effect on the sPS γ to α phase transition during heating. By adding only 1.0 wt.% pristine MWCNTs, the increase in the onset degradation temperature of the composite can reach 20 °C. The electrical conductivity is increased from 10^{−10∼−16} (neat sPS) to 0.135 S m⁻¹ (sPS/MWCNT composite with 3.0 wt.% MWCNT content). Our findings provide a simple and effective method for carbon nanotube dispersion in polymer matrix with dramatically increased electrical conductivity and thermal stability.     

New insights into the characteristics of early stage crystallization of a polyethylene

Small angle light scattering has been used to probe structure formation during isothermal crystallization of an ethylene-1-hexene copolymer (EH064, M_w = 70,000 g/mol, ρ = 0.900 g/cm³, M_w/M_n ∼ 2, 6.4 mol% hexene). It is shown that clear structural information on size scales ranging from hundreds of nanometers to several micrometers during early stage crystallization can be obtained by this method when crystallizing the polyethylenes at the high temperatures (above the peak melting temperature of a rapidly crystallized polymer sample) required for resolving early stage crystallization without the influence of the crystal growth. The results show that the early stage crystallization is characterized by large scale orientation fluctuations that precede the formation of local crystalline order manifest in X-ray scattering and the initial collapse of these large scale anisotropic/ordered domains. The scattering intensity increases exponentially with time initially, and the wave vector dependence of the growth rate of fluctuations is consistent with predictions for initial stages of a phase transformation process. However, the detailed mechanism cannot be described by existing models. The implications of our results are discussed within the context of proposed models for early stage crystallization.     

Thermal analysis and Raman spectroscopic studies of crystallization in poly(ethylene 2,6-naphthalate)

The combination of Fourier transform Raman spectroscopy and thermal analysis has been proved to be adequate for the study of the quantitative structural changes which take place in amorphous poly(ethylene 2,6-naphthalate) on annealing. Different conformer contents were found in the annealed samples depending on annealing conditions. In general, annealing of the amorphous poly(ethylene 2,6-naphthalate) from the glassy state induces a conformational transition of gauche to trans. The structure obtained during crystallization is characterized by a three-phase conformational model, including an amorphous phase, a rigid amorphous phase and a crystalline phase. The crystallization is further characterized by a three-zone process, firstly a primary crystallization process, secondly a variation of the rigid amorphous phase with a constant value of the crystalline phase and thirdly a secondary crystallization process. The bandwidth at half intensity at 1721 cm⁻¹ in the Raman spectrum varied between 32 cm⁻¹ for the complete amorphous phase and 7 cm⁻¹ for the total rigid phase, the sum of the rigid amorphous and crystalline phase. The bandwidth at half intensity at 1721 cm⁻¹ was directly related to the amount of the total rigid phase and confirmed by the variation of the heat capacity increase at the glass transition temperature. Two complementary bands in the Raman spectrum, at 1107 and 1098 cm⁻¹, were found to be related to the trans and gauche isomers. A difference was measured between the total trans content and the amount of rigid phase due to the presence of some trans conformations in the amorphous phase. The extrapolation of the bandwidth at half intensity at 1721 cm⁻¹ to the value of zero, corresponding to the complete crystalline phase, gave a melting enthalpy of 196 J/g and the corresponding density of the crystalline phase was 1.4390 g/cm³. A complete rigid phase structure was obtained by a melting enthalpy of 144 J/g and a density of 1.4070 g/cm³.     

Transient crystallization during drawing from ultra-high molecular weight polyethylene melts having different entanglement characteristics

The relationship between entanglement characteristics and transient crystallization during drawing from ultra-high molecular weight polyethylene (UHMW-PE) melts is discussed, based on a combination of in situ X-ray measurement and stress profile analysis. Films having different entanglement characteristics were prepared by solution blending of higher and lower MW samples having a viscosity average MW of 1.07 × 10⁷ (higher) and 1.73 × 10⁶ (lower), followed by compression molding at 180 °C. Stress profiles recorded at 155 °C above the melting temperature of 135 °C exhibited a plateau stress region, whose stress level was lower for the film prepared with more of the lower MW component. With drawing, an amorphous scattering gradually concentrated on the equator. Beyond the beginning point of the plateau stress region, such amorphous scattering abruptly disappeared and crystallization into a transient hexagonal phase occurred simultaneously. As soon as this hexagonal phase appeared, it rapidly transformed into an orthorhombic phase for the film exhibiting higher plateau stress. In contrast, the film exhibiting lower plateau stress exhibited a gentle transformation and a resurgence of the hexagonal phase in the later stage of drawing. These results demonstrate that “entanglement phase separation” proceeds during melt-drawing of UHMW-PE.     

Ionic conductivity in polyethylene-b-poly(ethylene oxide)/lithium perchlorate solid polymer electrolytes

The ionic conductivity and phase arrangement of solid polymeric electrolytes based on the block copolymer polyethylene-b-poly(ethylene oxide) (PE-b-PEO) and LiClO₄ have been investigated. One set of electrolytes was prepared from copolymers with 75% of PEO units and another set was based on a blend of copolymer with 50% PEO units and homopolymers. The differential scanning calorimetry (DSC) results, for electrolytes based on the copolymer with 75% of PEO units, were dominated by the PEO phase. The PEO block crystallinity dropped and the glass transition increased with salt addition due to the coordination of the cation by PEO oxygen. The conductivity for copolymers 75% PEO-based electrolyte with 15 wt% of salt was higher than 10⁻⁵ S/cm at room temperature and reached to 10⁻³ S/cm at 100 °C on a heating measurement. The blend of PE-b-PEO (50% PEO)/PEO/PE showed a complex thermal behavior with decoupled melting of the blocks and the homopolymers. Upon salt addition the endotherms associated with PEO domains disappeared and the PE crystals remained untouched. The conductivity results were limited at 100 °C to values close to 10⁻⁴ S/cm and at room temperature values close to 3 × 10⁻⁶ S/cm were obtained for the 15 wt% salt electrolyte. Raman study showed that the ionic association of the highly concentrated blend electrolytes at room temperature is not significant. Therefore, the lower values of conductivity in the case of the blend with 50% PEO can be assigned to the higher content of PE domains leading to a morphology with lower connectivity for ionic conduction both in the crystalline and melted state of the PE domains.     

Crystallization behavior of poly(l-lactic acid) affected by the addition of a small amount of poly(3-hydroxybutyrate)

The miscibility, crystallization and subsequent melting behavior in binary biodegradable polymer blends of poly(l-lactic acid) (PLLA) and low molecular weight poly(3-hydroxybutyrate) (PHB) have been investigated by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD). DSC analysis results indicted that PLLA showed no miscibility with high molecular weight PHB (M_w = 650,000 g mol⁻¹) in the 80/20, 60/40, 40/60, 20/80 composition range of the PHB/PLLA blends. On the other hand, it showed some limited miscibility with low molecular weight PHB (M_w = 5000 g mol⁻¹) when the PHB content was below 25%, as evidenced by small changes in the glass transition temperature of PLLA. The partial miscibility was further supported by changes of cold-crystallization behavior of PLLA in the blends. During the nonisothermal crystallization, it was found that the addition of a small amount of PHB up to 30% made the cold-crystallization of PLLA occur in the lower temperature. Meanwhile, the crystallization of PHB and PLLA was observed in the heating process by monitoring characteristic IR bands of each component for the low molecular weight PHB/PLLA 20/80 and 30/70 blends. The temperature-dependent IR and WAXD results also revealed that for PLLA component crystallization, the disorder (α′) phase of PLLA was produced, and that the α′ phase changed to the order (α) phase just prior to the melting point.     

Polycarbonate/liquid crystalline polymer blend: Crystallization of polycarbonate

The enhanced crystallization of polycarbonate in the blend of liquid crystalline polymer/polycarbonate/(ethylene-methyl acrylate-glycidyl methacrylate) copolymer (LCP/PC/E-MA-GMA) was studied by wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The LCP/PC/E-MA-GMA 5/95/5 blends annealed at 200 °C, for 2, 4, 6, and 10 h, present an obvious crystalline structure corresponding to PC crystallization. The PC crystal obtained shows two melting temperature, T_m1 of about 214 °C and T_m2 of about 231 °C, with a total heat of fusion of 29 J/g (annealing time = 10 h). The preliminary results indicate that amorphous PC can be induced to crystallization by the synergistic action of LCP dispersed phase and reactive compatibilizer.     

A highly conductive organic-inorganic hybrid electrolyte based on co-condensation of di-ureasil and ethylene glycol-containing alkoxysilane

Organic-inorganic hybrid electrolytes based on di-ureasil backbone structures by reacting poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (ED2000) with 3-(triethoxysilyl)propyl isocyanate (ICPTES), followed by co-condensation with methoxy(polyethylenoxy)propyl trimethoxysilane (MPEOP) in the presence of LiClO₄ were prepared and characterized by a variety of techniques. The hybrid electrolytes showed good resistance to crystallization and excellent conductivity for use in lithium-ion batteries, as determined by differential scanning calorimetry (DSC) and impedance measurements, respectively. The temperature dependence of the ionic conductivity exhibited a VTF (Vogel-Tamman-Fulcher)-like behavior for all the compositions studied and a maximum ionic conductivity value of 6.9 × 10⁻⁵ S cm⁻¹, a relatively high value for solid polymer electrolytes, was achieved at 30 °C for the hybrid electrolyte with a [O]/[Li] ratio of 16. A microscopic view of the dynamic behavior of the polymer chains (¹³C) and the ionic species (⁷Li) was provided by the ¹H and ⁷Li line widths measured from 2D ¹H-¹³C WISE (Wideline Separation) and variable temperature ⁷Li static NMR, respectively, to elucidate the influence of the mobility of the polymer chains and the charge carriers on the observed ionic conductivity. The present salt-free hybrid electrolyte after plasticization with 1 M LiClO₄ in EC/PC solution exhibited a swelling ratio of 275% and reached an ionic conductivity value up to 8.3 × 10⁻³ S cm⁻¹ at 30 °C, which make it a good candidate for the further development of advanced rechargeable lithium-ion batteries.     

Lamella reorientation in thin films of a symmetric poly(l-lactic acid)-block-polystyrene upon crystallization at different temperatures

The thin films of a symmetric crystalline-coil diblock copolymer of poly(l-lactic acid) and polystyrene (PLLA-b-PS) formed lamellae parallel to the substrate surface in melt. When annealed at temperatures well above the glass transition temperature of PLLA block (T_g^PLLA), the PLLA chains started to crystallize, leading to reorientation of lamellae. Such reorientation behavior exhibited dependence on the correlation between the crystallization temperature (T_c), the glass transition temperature of PS (T_g^PS), the peak melting point of PLLA crystals (T_m^PLLA), and the end melting point of PLLA crystals (T_m,end^PLLA). When annealed at (T_c=) 80 °C (T_c < T_g^PS < T_ODT, order-disorder transition temperature), 123 °C (T_g^PS < T_c < T_m^PLLA < T_ODT), 165 °C (T_g^PS < T_m^PLLA < T_c < T_m,end^PLLA < T_ODT), the parallel lamellae became perpendicular to the substrate surface, exclusively starting at the edge of surface relief patterns. Meanwhile, the corresponding lamellar spacing was significantly enhanced. The PLLA crystallization between PS layers was hypothesized to account for the lamella reorientation during annealing. The crystallization, chain conformation, and possible chain folding mechanisms were discussed, based on detailed analysis of the lamellar structure before and after crystallization.     

Super soft elastomers as ionic conductors

Melts of linear brush polymers with PEO side chains attached at each repeat unit of the backbones have been doped with CF₃SO₃⁻Li⁺. Mechanical properties and ionic conductivity of such systems have been analyzed using mechanical and dielectric spectroscopies. Mechanical spectra indicated a presence of super soft states for samples with long backbones or for systems which have been slightly cross-linked (G′<10⁴ Pa). In the case of the polymer with longer crystallizing PEO side chains (MW_av=1100 g/mol), the ionic conductivity reaching the 10⁻³ S/cm level at the optimum CF₃SO₃⁻Li⁺ concentration (EO/Li⁺=10:1) have been detected at temperatures not far above the room temperature. The presence of lithium ions suppresses completely the crystallization of PEO side chains.     

Poly(trimethylene terephthalate) copolyester containing ethylene glycol moieties. Part 1: Crystallization kinetics and melting behavior

A copolyester was characterized to have 91 mol% trimethylene terephthalate unit and 9 mol% ethylene terephthalate unit in a random sequence by using ¹³C NMR. Differential scanning calorimeter (DSC) was used to investigate the isothermal crystallization kinetics in the temperature range (T_c) from 180 to 207 °C. The melting behavior after isothermal crystallization was studied by using DSC and temperature modulated DSC (TMDSC). The exothermic behavior in the DSC and TMDSC curves gives a direct evidence of recrystallization. No exothermic flow and fused double melting peaks at T_c = 204 °C support the mechanism of different morphologies. The Hoffman-Weeks linear plot gave an equilibrium melting temperature of 236.3 °C. The kinetic analysis of the growth rates of spherulites and the morphology change from regular to banded spherulites indicated that there existed a regime II → III transition at 196 °C.     

Synthesis and peculiarities of electric properties of Li1.3Zr1.4Ti0.3Al0.3(PO4)3 solid electrolyte ceramics

The solid electrolyte Li_1.3Zr_1.4Ti_0.3Al_0.3(PO₄)₃ compound was synthesized by a solid-state reaction. The ceramic samples were sintered 1, 2 and 3 h and studied by X-ray and complex impedance spectroscopy in the frequency range from 10⁶ to 1.2 × 10⁹ Hz in temperature range from 300 to 600 K. The investigated compound at room temperature belongs to rhombohedral symmetry (s.g. ) with six formula units in the lattice. Two regions of relaxation dispersion were found. The dispersions are related to the fast Li⁺ ion transport in the grain and grain boundaries of ceramics. Varying of the sintering time affects the density of the ceramics, the values of total conductivity and its activation energy. The values of grain conductivity, its activation energy, and relaxation frequency in grain, dielectric permittivity and dielectric losses are independent from sintering duration of the ceramics. The value of activation energy of grain conductivity and activation energy of relaxation frequency is the same. That can be attributed to the fact that the temperature dependence of the grain conductivity is caused only by the mobility of Li⁺ ions, while a number of charge carriers remains constant with temperature.     

The effect of molecular weight on the lamellar structure, thermal and mechanical properties of poly(hydroxybutyrate-co-hydroxyvalerates)

A poly(hydroxybutyrate-co-hydroxyvalerate) with 9% hydroxyvalerate content has been thermally degraded to give a set of materials of different molecular weights. The effect of molecular weight on the lamellar structure, thermal and mechanical properties was investigated. The long period, lamellar and amorphous thickness all increase as molecular weight increases; their values vary linearly with 1/(molecular weight). Observed melting temperatures increase with molecular weight, following the same functional form, while melting enthalpy and non-isothermal crystallization temperature decrease. Young's modulus varies by 13% with molecular weight; changes in crystallinity cannot explain this effect in detail. Ultimate tensile strength increases rapidly with molecular weight and then levels off at 28.5 MPa above 10⁵ g/mol. This can also be seen as a linear variation with 1/(molecular weight). The strain at the point of ultimate tensile strength also increases rapidly up to 10⁵ g/mol but then continues to increase at a slower rate.     

Melting behavior of poly(l-lactic acid): Effects of crystallization temperature and time

Effects of crystallization temperature and time on the melting behavior of poly(l-lactic acid) were studied with differential scanning calorimetry (DSC). The isothermal crystallization was performed at various temperatures (T_cs), and DSC melting curves for the isothermally crystallized samples were obtained at 10 K min⁻¹. When T_c was lower than T_d (∼135 °C), the double melting peaks appeared. The melting behavior, especially T_c dependence of the melting temperature (T_m), discretely changed at T_b (=113 °C), in accordance with the discrete change of the crystallization behavior at T_b, which was previously reported. When T_c was higher than T_d, a single melting peak appeared. In addition, T_c dependence of dT_m/dT_c discretely changed at T_d. That is, the melting behavior, especially T_c dependence of T_m and dT_m/dT_c, are different in three temperature regions of T_c divided by T_b and T_d: Regions I (T_c ≤ T_b), II (T_b ≤ T_c ≤ T_d), and III (T_d ≤ T_c). The effect of crystallization time on the melting behavior, melting temperature and heat of fusion in each temperature region of T_c is also discussed.     

Effects of molecular weight on poly(ω-pentadecalactone) mechanical and thermal properties

A series of poly(ω-pentadecalactone) (PPDL) samples, synthesized by lipase catalysis, were prepared by systematic variation of reaction time and water content. These samples possessed weight-average molecular weights (M_w), determined by multi-angle laser light scattering (MALLS), from 2.5 × 10⁴ to 48.1 × 10⁴. Cold-drawing tensile tests at room temperature of PPDL samples with M_w between 4.5 × 10⁴ and 8.1 × 10⁴ showed a brittle-to-ductile transition. For PPDL with M_w of 8.1 × 10⁴, inter-fibrillar slippage dominates during deformation until fracture. Increasing M_w above 18.9 × 10⁴ resulted in enhanced entanglement network strength and strain-hardening. The high M_w samples also exhibited tough properties with elongation at break about 650% and tensile strength about 60.8 MPa, comparable to linear high density polyethylene (HDPE). Relationships among molecular weight, Young's modulus, stress, strain at yield, melting and crystallization enthalpy (by differential scanning calorimetry, DSC) and crystallinity (from wide-angle X-ray diffraction, WAXD) were correlated for PPDL samples. Similarities and differences of linear HDPE and PPDL molecular weight dependence on their mechanical and thermal properties were also compared.     

High-pressure solution blending of poly(?-caprolactone) with poly(methyl methacrylate) in acetone + carbon dioxide

The miscibility of blends of poly(?-caprolactone) (PCL, M_w = 14,300) with poly(methyl methacrylate) (PMMA, M_w = 15K or 540K) in acetone + CO₂ mixed solvent has been explored. The liquid-liquid phase boundaries at different temperatures have been determined for mixtures containing 10 wt% total polymer blend, 50 wt% acetone and 40 wt% CO₂. The PCL and PMMA contents of the blends were varied while holding the total polymer concentration at 10 wt%. The polymer blend solutions all displayed LCST-type behavior and required higher pressures than individual polymer components for complete miscibility. Complete miscibilities were achieved at pressures within 40 MPa. The DSC scans show that the blends are microphase-separated. The blends display the melting transition of PCL and the glass transition temperature of the PMMA phases. The presence of PMMA is found to influence the crystallization and melting behavior of PCL in the blends. The DSC results on heat of melting and the FTIR spectra, specifically the changes at 1295 cm⁻¹ band show the changes (decrease) in overall crystallinity of the blend upon addition of PMMA.     

Measurement of through-plane effective thermal conductivity and contact resistance in PEM fuel cell diffusion media

An experimental study was performed to determine the through-plane thermal conductivity of various gas diffusion layer materials and thermal contact resistance between the gas diffusion layer (GDL) materials and an electrolytic iron surface as a function of compression load and PTFE content at 70 °C. The effective thermal conductivity of commercially available SpectraCarb untreated GDL was found to vary from 0.26 to 0.7 W/(m °C) as the compression load was increased from 0.7 to 13.8 bar. The contact resistance was reduced from 2.4×10⁻⁴ m²°C/W at 0.7 bar to 0.6×10⁻⁴ m²°C/W at 13.8 bar. The PTFE coating seemed to enhance the effective thermal conductivity at low compression loads and degrade effective thermal conductivity at higher compression loads. The presence of microporous layer and PTFE on SolviCore diffusion material reduced the effective thermal conductivity and increased thermal contact resistance as compared with the pure carbon fibers. The effective thermal conductivity was measured to be 0.25 W/(m °C) and 0.52 W/(m °C) at 70 °C, respectively at 0.7 and 13.8 bar for 30%-coated SolviCore GDL with microporous layer. The corresponding thermal contact resistance reduced from 3.6×10⁻⁴ m²°C/W at 0.7 bar to 0.9×10⁻⁴ m²°C/W at 13.8 bar. All GDL materials studied showed non-linear deformation under compression loads. The thermal properties characterized should be useful to help modelers accurately predict the temperature distribution in a fuel cell.     

Electrophoretic deposition (EPD) of hydrous ruthenium oxides with PTFE and their supercapacitor performances

The effect of PTFE addition was investigated for the electrophoretic deposition (EPD) of hydrous ruthenium oxide electrodes. Mechanical stability of electrode layers, together with deposition yield, was enhanced by using hydrous ruthenium oxide/PTFE dispersions. High supercapacitor performance was obtained for the electrodes prepared with 2% PTFE and 10% water. When PTFE content was higher, the rate capability became poor with low electronic conductivity; higher water content than 10% resulted in non-uniform depositions with poor cycleability and power capability. When electrodes were heat treated at 200 °C for 10 h, the specific energy was as high as 17.6 Wh/kg based on single electrode (at 200 W/kg); while utilizable energy was lower with heat treatment time of 1 and 50 h, due to the high resistance and gradual crystallization, respectively. With PTFE addition and heat treatment at 200 °C for 10 h, the specific capacitance was increased by 31% (460 → 599 F/g at ca. 0.6 mg/cm²) at 10 mV/s, and the deposition weight was increased up to 1.7 mg/cm² with initial capacitance of 350 F/g.