Conductivity of de-doped poly(3,4-ethylenedioxythiophene)

The conductivity of chemically and electrochemically de-doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been investigated in situ. We observe a decrease in the conductivity by 4–5 orders of magnitude. The change of conductivity is correlated to the change of electronic structure. We obtain the dielectric function of the polymer by spectroscopic ellipsometry and note that anisotropy is observed in both doped and neutral states.     

Reflectance of conducting poly(3,4-ethylenedioxythiophene)

We present the reflectance spectrum of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with PF₆ with dc conductivity of 230 S/cm at room temperature, measured over a wide frequency range from 50 to 5×10⁴ cm⁻¹ (0.006–6 eV). The reflectance, R(ω), of PEDOT-PF₆ is characterized by metal-like signatures in the infrared (IR), including high R(ω) in the far-IR and a plasma frequency of approximately 1.2 eV. The optical conductivity, σ(ω), is dominated by intraband contributions below 1 eV, characteristic of a disordered metal near the metal–insulator (M–I) transition. The reflectance spectrum is in good quantitative agreement with the “localization-modified Drude (LMD) model”. Since the onset of the interband absorption (below 1.5 eV) is at lower energy than in other conducting polymers, PEDOT-PF₆ shows low absorption in the visible range between 2 and 3 eV. Our spectroscopic results demonstrate that this doped PEDOT system can be utilized as a transparent electrode for optoelectronic devices.     

Synthesis of highly conductive poly(3,4-ethylenedioxythiophene) fiber by simple chemical polymerization

Poly(3,4-ethylenedioxythiophene) (PEDOT) fiber was chemically synthesized by the polymerization of 2,5-dihalo-3,4-ethylenedioxythiophene in the presence of BF₃ without a template. The resulting conductive PEDOT fiber exhibited conductivity in the range of 150–250 S/cm (pressed powder pellet). The thermal stability of PEDOT was also improved and UV-spectroscopy analysis of a film exhibited a strong absorption band at 460 nm. The well-defined needle-shaped fibers of PEDOT were examined by SEM, and the average length and diameter of the fibers were 10 and 0.4 μm, respectively.     

Spectroelectrochemical studies of poly(3,4-ethylenedioxythiophene) in aqueous medium

The in situ electrochemical doping process of the poly(3,4-ethylenedioxythiophene) (PEDT) has been studied in an aqueous micellar medium by means of optical spectroscopies. The cyclic voltammetry (CV) and optical absorption results were compared with previous ones obtained either in acetonitrile or in water without surfactant. No significant effect of the medium, water or acetonitrile, was found, but the presence or absence of surfactant in water give rise to different doping CVs, especially in the reductive part. Resonant Raman scattering experiments show a behavior of PEDT different from the one in acetonitrile. The doping mechanism we deduced from these results should imply a variation between an “intermediate” electronic conformation of the polymer in the reduced state to a predominant benzenic one during doping. The comparison with our previous results obtained in acetonitrile leads us to think that the reduced PEDT is in fact slightly oxidized by the aqueous medium.     

Electro-assisted precipitation of electrolytes in poly(3,4-ethylenedioxythiophene) film

The electrolyte, NaBF₄, can be enriched into the matrix of poly(3,4-ethylenedioxythiophene) (PEDOT) film during the p-doping potential cycling between 0.6 and −0.9 V. It has been demonstrated that this enrichment is originated from the mixed ion transfer between doping and dedoping, i.e. BF₄⁻ anion migrate into the PEDOT film during the oxidation process, the Na⁺ cation insert into the film during the reduction process, and then, the electrolyte is accumulated into the film matrix after the multiple CV cycling. The quantitative analysis of energy-dispersive X-ray spectroscopy (EDX) confirmed the enrichment of NaBF₄ in the PEDOT film.     

Amperometric alcohol biosensors based on conducting polymers: Polypyrrole,poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxypyrrole)

Alcohol biosensors based on conducting polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxypyrrole) (PEDOP) were constructed. Alcohol oxidase (AlcOx, from Pichia pastoris) was immobilized during electropolymerization of the monomers in sodium dodecylsulfate (SDS) and phosphate buffer electrolysis medium. Optimization of several parameters was carried out. The highest affinity was observed for the PEDOT/AlcOx sensor. Lowry protein determination method was also used to calculate the amount of immobilized enzyme in sensors. Before testing the biosensors on alcoholic beverages effects of interferents (glucose, acetic acid, citric acid, and l-ascorbic acid) were determined. The alcohol contents of the distilled beverages (vodka, dry cin, whisky, and rak?) were determined with the sensors constructed. A good match with the chromatography results was observed.     

Highly conducting free-standing poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) films with improved thermoelectric performances

Highly conducting free-standing poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films with room-temperature electrical conductivity of about 300 S cm^?1 were successfully prepared from PEDOT/PSS solution containing additives (DMSO or EG) on the smooth and flexible polypropylene (PP) film substrate with contact angle of 87°. As formed free-standing PEDOT/PSS films possess good flexibility and can be easily cut into various shapes with a knife. The contact angle of substrate has significant effect on the preparation of free-standing PEDOT/PSS films. Additionally, the process of adding DMSO or EG did not result in the change of carrier concentration but the increase of carrier mobility. The free-standing PEDOT/PSS film showed high electrical conductivity and stable Seebeck coefficient and its figure of merit (ZT) with high environment stability can be up to 10^?2, one order of magnitude higher than that of pressed PEDOT/PSS pellets (10^?3).     

Humidity-dependent characteristics of thin film poly(3,4-ethylenedioxythiophene) field-effect transistor

π-Conjugated poly(3,4-ethylenedioxythiophene) (PEDOT) based field-effect transistors (FETs) were fabricated in this study. A thin PEDOT layer (thickness ≈500 nm) with the desired pattern was formed as an active and a gate electrode by a vapor polymerization of 3,4-ethylenedioxythiophene (EDOT) on the photolithographically patterned ferric p-toluenesulfonate (FTS) oxidant layer. Crosslinked poly(vinyl cinnamate) (PVCN) insulating layer was formed by spin-coating and UV crosslinking. The currents (I_ds) of the PEDOT active channel decreased with increasing gate bias (V_g), implying p-type FET. The dc conductivities (σ_dc) and I_ds of the PEDOT active channel were measured as a function of V_g under various relative humidities (RHs) ranging from 0% to 55%. The σ_dc and the I_ds of the PEDOT channel rapidly decreased with increasing positive V_g under humid conditions, while those of the PEDOT channel showed no change with V_g in vacuum, i.e. 0% RH. The threshold gate bias, which is defined as the onset of the curve of I_ds versus V_g, rapidly decreased with increase of RH. The moisture absorbed in the PEDOT active channel may assist the dedoping of the system by the screening and/or the relative separation of constituent ions from PEDOT chain upon applying a positive V_g. When the positive V_g was removed (V_g = 0), the σ_dc of the channel recovered slowly and a relatively long relaxation time was observed, which implies that the PEDOT active layer was slowly redoped. For the PEDOT based FET, we observed the moisture assisted dedoping and the redoping processes of the PEDOT channel upon applying and removal of positive V_g under the humid conditions.     

Electrochromism of poly(3,4-ethylenedioxythiophene) films on Au nano-brush electrode

Au nano-brush membranes were prepared using a modified template method. Poly(3,4-ethylenedioxythiophene) (PEDOT) films were immobilized by an electropolymerization with the product membrane as the working electrode. The PEDOT film on the nano-brush electrode showed higher electrochromic (EC) coloration compared to the PEDOT film on an Au planar electrode.     

Electronic transport in doped poly (3,4-ethylenedioxythiophene) near the metal-insulator transition

The temperature dependences of the conductivity and magnetoconductivity of poly(3,4-ethylenedioxythiophene) doped with PF₆, BF₄ and CF₃SO₃ in the metallic and critical regimes have been studied. Doped films exhibit a weak temperature dependence of the resistivity, ϱ(T), with the characteristic resistivity ratio ϱ_r = ϱ(1.4 K)/ϱ(291 K) = 1.5–20; i.e. close to the metal-insulator transition. For metallic samples (ϱ_r<2.1) prepared with each of the dopants, the sign of the temperature coefficient of resistivity (TCR) changes from negative to positive below 10 K; the temperature of the resistivity maximum, T_m, decreases with increasing ϱ_r. For samples with ϱ_r ~ 20, the power-law temperaturedependence characteristic of the critical regime of the metal-insulator transition is observed, with ϱ(T) ~ T^−0.6. High magnetic fields induce the transition from positive to negative TCR for all metallic samples with ϱ_r < 2.1 and decrease the low-temperature conductivity for samples with ϱ_r > 2.1. In both cases (negative and positive TCR), the low-temperature conductivity of metallic samples is well described by a T^1/2 dependence, both in the presence of a magnetic field and with the magnetic field equal to zero. The magnetoconductance of samples in metallic and critical regimes is negative, Isotropic, and, for metallic samples, exhibits H² and H^1/2 dependences at low and high magnetic fields, respectively. The results for metallic samples are explained as resulting from the influence of electron-electron interactions on the lowtemperature conductivity.     

One-step fabrication of conductive poly(3,4-ethylenedioxythiophene) hollow spheres in the presence of poly(vinylpyrrolidone)

Poly(3,4-ethylenedioxythiophene) (PEDOT) hollow spheres with the size ranged from 130 to 820 nm and a conductivity of 8 × 10^?2 S cm^?1 were prepared simply and directly via a one-step self-assembly approach in the presence of poly(vinylpyrrolidone) (PVP) as a soft template. It was found that the formation probability of PEDOT hollow spheres depended on the concentration of PVP. Bulk quantities of PEDOT hollow spheres can be obtained readily under the optimal conditions such as the concentration of PVP > 0.175 mM and PVP/EDOT molar ratio <1.4. The electron-rich oxygen atoms on the lactam groups in PVP were proposed to act as the chemically active sites to anchor EDOT cation radicals by virtue of electrostatic interaction and cause the self-assembly of PEDOT hollow spheres. Our investigation for the formation mechanism of PEDOT hollow spheres may shed some light on preparing of other hollow materials by proper molecular design and experimental condition optimization.     

Electrochemically controlled surface morphology and crystallinity in poly(3,4-ethylenedioxythiophene) films

The degree of crystallinity and surface morphology of poly(3,4-ethylenedioxythiophene) PEDOT, films was tuned by electrochemical synthesis. The films were produced by cyclic voltammetry in TBAPF₆–acetonitrile medium. The films were characterized by X-ray diffraction and by scanning electron microscope.     

Spectroscopic and conductivity studies of doping in chemically synthesized poly(3,4-ethylenedioxythiophene)

Spectroscopic methods (Raman (514.5 nm excitation), infrared (IR), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR)) and electrical conductivity measurements were used to characterize the electrically conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) prepared by persulfate oxidation under aqueous conditions. Elemental analysis was carried out on the resulting sulfate-doped PEDOT to determine the sulfate doping level. Due to the difficulty in dedoping highly stable p-doped PEDOT, the sulfate-pre-doped PEDOT was directly treated with iodine solution in order to investigate the secondary doping processes between PEDOT and iodine. Two processes were observed: (1) the further oxidation of the polymer by iodine to produce an increase in the doping level, with triiodide as the dopant and (2) the replacement of sulfate by triiodide in an ion-exchange process involving triiodide in equilibrium with iodine in the iodine solution. Conductivity studies, in conjunction with XPS and EPR experiments, were used to analyse the relationship between the doping level and conductivity that was explained by differences in the nature of SO₄²⁻ and I₃⁻ as dopant ions and a shift in the polaron/bipolaron equilibrium. The Raman spectra (785 nm excitation) of these PEDOT samples were also investigated and a significant change has been observed in the wavenumber of the symmetric C_α = C_β stretching bands with varying levels of dopants. A correlation was observed between the ratio of the integrated intensities of the symmetric C_α = C_β stretching bands and the doping level in PEDOT that can be useful for estimating the doping level of a PEDOT sample from its Raman spectrum.     

Copper modified poly(3,4-ethylenedioxythiophene): Part II: Potentiostatic experiments

The electrochemical reduction of copper ions is investigated at poly(3,4-ethylenedioxythiophene) (PEDT) coated electrodes by means of potentiostatic experiments, cyclic voltammetry and ESR measurements. It is established that copper deposition at low overpotentials allows stabilization of a considerable amount (up to 10%) of copper species in the polymer layer and impeding the copper crystallization process. An additional redox couple is found to appear at the PEDT voltammogram showing two different valence states of the copper/polymer related species. ESR and electrochemical measurements allow concluding that the redox couple is related to the formation of a [Cu(I)PEDT]⁺ complex and corresponds to the [Cu(I)PEDT]⁺+e⁻↔Cu(0)PEDT reaction. ESR spectra show that Cu atoms specifically bonded to the polymer disturb the PEDT paramagnetic system.     

Electro-conductive properties of poly(3,4-ethylenedioxythiophene)/poly(ionic liquid) films with respect to its structure and morphology

Poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(1-vinyl-3-ethylimidazolium⁺ (trifluoromethane sulfonyl)imide^?) (PIL) complexes were prepared at various PEDOT/PIL molar ratios and dispersed in propylene carbonate at a concentration of 1 wt%. After casting, the maximum conductivity was measured to be 1.2 × 10^?1 S/cm, which could be explained by the 3D variable range hopping model. The optimum surface roughness of the PEDOT/PIL film was measured, showing S_a and S_q values of 5.92 and 11.0 nm, respectively. The conductivity of the polymerized PEDOT without a template process had low conductivity due to its poor surface roughness and large particle size. Therefore, the conductivity of PEDOT/PILs is determined by the particle size, crystallinity and surface morphology. These results were supported by surface mapping microscopy, X-ray photon spectroscopy, and X-ray diffraction.     

NaV_3O_8/poly(3,4-ethylenedioxythiophene) composites as high-rate and long-lifespan cathode materials for reversible sodium storage

Sodium-ion batteries have received a surge of interests for the alternatives to lithium-ion batteries due to their abundant reserves and low cost.The quest of reliable and high-performance cathode materials is crucial to future Na storage technologies.Herein,poly(3,4-ethylenedioxythiophene)(PEDOT) was successfully introduced to NaV_3O_8 via in situ oxidation polymerization,which can effectively enhance electron conductivity and ionic diffusion of NaV_3O_8 material.As a result,these NaV_3O_8@-PEDOT composites exhibit a significantly improved electrochemical performance including cycle stability and rate performance.In particular,NaV_3O_8@20 wt% PEDOT composite demonstrates better dispersibility and lower charge transfer resistance compared with bare NaV_3O_8,which delivers the first discharge capacity of 142 mAh-g~(-1)and holds about 128.7 mAh·g~(-1) after 300 cycles at a current density of 120 mA·g~(-1).Even at a high current density of 300 mA·g~(-1),a high reversible capacity of 99.6 mAh·g~(-1) is revealed.All these consequences suggest that NaV_3O_8@20 wt% PEDOT composite may be a promising candidate to serve as a high-rate and long-lifespan cathode material for sodium-ion batteries.     

Synthesis of discus-like Poly(3,4-ethylenedioxythiophene) nanoparticles using a bicellar template

Poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles with discus-like morphology were synthesized by chemical oxidation polymerization using bicelles as a soft template. The bicelles were assembled from the surfactant molecules of sodium perfluorooctanoate (FC7) and cetyltrimethylammonium bromide (CTAB). The PEDOT nanodiscuses have an average diameter around 200 nm and a central thickness of about 50 nm. The effects of synthetic parameters, such as surfactant concentration, molar ratio of oxidant and monomer, reaction temperature on PEDOT nanostructures have been investigated.