Patent Application
20240150543
The present invention relates to iron oxide/hydroxide-containing conducting polymer composites and processes for their preparation by electrochemical methods using ferrate salts.
The use of composites comprising electrically conducting polymers with metal-containing (specifically, metal oxide-containing) nanoparticles is widespread in the fields of electrocatalysis, sensors (such as in electronic, electrochromic or optical sensors), and microelectronics.
Various methods are known for producing the above composites, of which electrochemical ones deserve special attention from a practical perspective, due to their low cost and efficiency. In these electrochemical processes, the conducting polymer layer can be prepared on the surface of the substrate directly from the solution containing its monomers.
Among conducting polymers, e.g., poly(3,4-ethylenedioxythiophene) (PEDOT) or poly(3,4-ethylenedioxypyrrole) (PEDOP) are suitable for the electrochemical production of composites containing MnO2 or WO3 [Liu R, Duay J, Lee S B (2010) Redox exchange induced MnO2 nanoparticle enrichment in poly (3,4-ethylenedioxythiophene) nanowires for electrochemical energy storage. ACS Nano 4 (2010) 4299-4307, D. V. Zhuzhelskii, E. G. Tolstopjatova, A. I. Volkov, S. N. Eliseeva, G. G. Lang, V. V. Kondratiev, Insights on the electrodeposition mechanism of tungsten oxide into conducting polymers: Potentiostatic vs. potentiodynamic deposition, Synthetic Metals 267 (2020) 116469, A. O. Nizhegorodova, S. N. Eliseeva, E. G. Tolstopjatova, G. G. Lang, D. Zalka, M. Ujvári, V. V. Kondratiev, EQCM study of redox properties of PEDOT/MnO2 composite films in aqueous electrolytes, Journal of Solid State Electrochemistry 22 (2018) 2357-2366]. In the above publications, the deposition was performed in acidic or neutral solutions since the electrochemical properties of PEDOT and PEDOP conducting polymers are more favorable in acidic media. Additionally, PEDOT and especially PEDOP films, deposited on substrates, are not sufficiently stable in alkaline medium.
Among metal oxide nanoparticles, iron oxide, especially magnetic magnetite (Fe3O4)-containing conducting polymers are of particular interest for practical applications. They can be used as contrast agents in magnetic resonance imaging (MRI), and in magnetic recording media, biomolecule separation, heterogeneous catalysis, environmental and food analyzes, as well as immunoassays. Hence, only a few methods are available in the literature for preparing composites. Shin et al. has disclosed a process (S. Shin, J. Jang, Chemical Communications 41 (2007) 4230; S. Shin, H. Yoon, J. Jang, Catalysis Communications 10 (2008) 178), in which the monomer (specifically, 3,4-ethylenedioxythiophene, EDOT) of the conducting polymer reacts with Fe3O4 in the presence of a strong acid (HCl). The resulting polymeric material (Fe3O4—PEDOT) is used for the adsorption of heavy metal ions and the photocatalytic decomposition of organic dyes. The disadvantages of this method are that the strong acid decomposes the nanostructured magnetic clusters, and the magnetic nanoparticles dissolve in HCl and form water-soluble Fe3+/Fe2+ ions, which leads to a decrease in the magnetite content. It is worth to note that no other iron oxide/hydroxide compounds form in strongly acidic medium; therefore, the solution contains solely the chloride salt of the above-mentioned iron ions.
In the process developed by Reddy et al. (K. R. Reddy, W. Park, B. C. Sin, J. Noh, and Y. Lee, Journal of Colloid and Interface Science, vol. 335, no. 1, pp. 34-39, 2009), a dispersed core-shell type composite is prepared by the in situ polymerization of an EDOT monomer in the presence of magnetic nanoparticles (Fe3O4) in the micellar solution of lignosulfonic acid. It is noted that the diffraction pattern of magnetite (Fe3O4) does not contain any indication of impurities, i.e., the material is considered to be pure.
Zheng et al. (M. Zheng, J. Huo, Y. Tu, J. Jia, J. Wu, and Z. Lan, RSC Advances, vol. 6, no. 2, pp. 1637-1643, 2016.) deposited a solution of EDOT precursor doped with Fe3O4 on fluorine-doped tin oxide (FTO) glass via spin-coating to form a PEDOT/Fe3O4 film with polymerization reaction. The technology requires many steps of preparation, moreover, it takes a long time, and less cost-effective. The produced film is used as a counter electrode in dye-sensitized solar cells (DSSC).
There are also reports in the literature for the preparation of core-shell composites containing γ-Fe2O3 and polyaniline or polypyrrole [R. Gangopadhyay A. De, Conducting Polymer Nanocomposites: A Brief Overview, Chemistry of Materials 12 (2000) 608-622.].
An important circumstance is that in the fabrication of core-shell systems, the polymer is deposited on the surface of the preformed magnetite or hematite nanoparticles. Thus, the “composite” actually consists of a set of tiny spherical units and the polymer does not form a coherent matrix. This attribution of the composite is disadvantageous in terms of mechanical stability, and such aggregate-like composites are obviously not suitable for applications, in which they might be subjected to severe mechanical deformation.
Qin et al., (Journal of Inorganic and Organometallic Polymers and Materials, published online: Jul. 14, 2020; https://doi.org/10.1007/s10904-020-01666-8; title: Acid—Assisted One—Step In—Situ Polymerization Synthesis of PANI/α-Fe2O3/β-FeOOH Composites and Its Formation Mechanism) presented polyaniline (PANI)-based composites, during preparation of which, iron oxide/hydroxide-containing composites form, where the polymerization is carried out in the presence of FeCl3, therefore, the final polymer contains FeCl3 among its chains. The final step of the process is the powder grinding of the resulting solid material. A similar procedure was applied by Prasanna et al. (Synthesis of polyaniline/alfa-Fe2O3 nanocomposite electrode material for supercapacitor applications; Materials Today Communications (2017), vol 12, 72-78) to prepare PANI/FeCl3 composite (in this case, a powdery material was obtained).
None of the methods described for the production of composites, containing iron oxide/hydroxide compounds embedded in a conducting polymer matrix, are electrochemical processes. Additionally, in the known methods, magnetite (Fe3O4) particles or in the case of PANI, Fe2O3/FeOOH particles are incorporated into the systems during the polymerization steps, not following the formation of the polymer films.
The present invention provides a simple, cost-effective, and reproducible electrochemical process for the preparation of iron oxide/hydroxide-containing conducting polymer composites. The conducting polymer can be e.g. poly(3,4-ethylenedioxythiophene) (PEDOT), polyaniline (PANI), poly(ortho-phenylenediamine) (PoPD), preferably poly(3,4-ethylenedioxythiophene) (PEDOT) or polyaniline (PANI) or other polymers of similar structure.
In an embodiment of the invention, the preferred conducting polymer is poly(3,4-ethylenedioxythiophene) that is PEDOT, which is a conducting polymer with good electrical conductivity, well-controllable optoelectronic and redox properties. The alkylenedioxy substituent on the polythiophene backbone serves to improve electrochemical, optical, and electrochromic properties. PEDOT is a widely employed conducting polymer because of its stability and reproducibility. It is found in TNT sensors, hydrogen chloride and ammonia vapor detectors, NO2 sensors, neural probes, uric acid and dopamine sensors, and other medical sensors. In case of PEDOT, the alkylenedioxy substituent on the polythiophene backbone is an ethylenedioxy group. In principle, it is also possible to use similar polymers with a β-polythiophene backbone, wherein the optionally substituted alkylenedioxy substituent contains greater number of carbon atoms, for example 3-12, preferably 3-8 carbon atoms. Such thiophene-based monomers are presented in the literate: a) J-H Kang et al.: A Dual-Polymer Electrochromic Device with High Coloration Efficiency and Fast Response Time: Poly(3,4-(1,4-butylene-(2-ene)dioxy)thiophene)—Polyaniline ECD, Chem. Asian J., 2011, 6, 2123-2129; and b) L. A. Estrada: “Direct (Hetero)arylation Polymerization: An Effective Route to 3,4-Propylenedioxythiophene-Based Polymers with Low Residual Metal Content”, dx.doi.org/10.102/mz4003886 I ACS Macro Lett. 2013, 2, 869-873). That is, starting materials can also be polymers with a polythiophene backbone, wherein thiophene monomers are substituted with 2-12 carbon atom-containing alkylenedioxy groups, which are optionally substituted. The preferred ones are those substituted with 2-8 carbon atom-containing alkylenedioxy groups, especially those substituted with 2 or 3 carbon atom-containing alkylenedioxy group, within PEDOT is considered to be the most preferred.
The normal oxidation/reduction of PEDOT is as follows:
In an embodiment of the invention, it is preferred to reinforce the layers of the above polymers with non-conducting polymers (e.g., polyphenols [preferably poly(bisphenol-A)—PBPA], and polyalkenes). Films, reinforced with non-conducting polymers, are more resistant to degradation as a consequence of overoxidation that may occur during the process. That is, the reinforcement is “mechanical” in nature (thus referred to as “mechanical reinforcement”, as well) because the reinforcing polymer “fixes” the oxidized conducting polymer layers that tend to delaminate from the substrate. In addition, it protects the conducting polymer layer as a non-enclosed cover layer/cloud (e.g., essentially against UV radiation) but does not completely close it from the environment, allowing the conducting polymer to contact with the medium surrounding it.
Overoxidation is defined as the partial irreversible oxidation of the polymer at the applied positive potentials, which can lead to a considerable change in the structure or the degradation of the polymer film [G. G. Láng, M. Ujvári, S. Vesztergom, V. Kondratiev, J. Gubicza, K. J. Szekeres: The Electrochemical Degradation of Poly(3,4-ethylenedioxythiophene) Films Electrodeposited from Aqueous Solutions, Z. Phys. Chem. 2016 (230) 1281-1302.]. Causing this phenomenon by cyclic voltammetric method, we found that an oxidation peak appears at sufficiently positive potentials, where the polymer film is overoxidized, and there is no corresponding reduction peak at more negative potentials.
The moderate overoxidation can also be beneficial for the formation of the composite, as it increases the porosity of the film (which is also advantageous, for example, when used in sensors); while strong overoxidation leads to polymer degradation, separation of polymer chains, and delamination from the substrate. Reinforcement with non-conducting polymers also prevents the separation of the polymer chains and the delamination of the film. Irreversible deposition of PBPA on the surface of PEDOT films has been observed previously [E. Mazzotta, C. Malitesta, E. Margapoti, Direct electrochemical detection of bisphenol A at PEDOT-modified glassy carbon electrodes, Anal. Bioanal. Chem. 405 (2013) 3587-3592.], however, it was considered to be a detrimental phenomenon because of the passivation of electrodes, that is, its advantages of the process according to the invention were not recognized. Based on passivation, it is assumed that an even more closed (more “covering”) layer of PBPA was deposited in this study, than described in the present invention.
An essential feature of the process according to the invention is that the incorporation of iron oxides/iron hydroxides into the electrodeposited conducting polymer films on inert substrates (gold, platinum, graphite, glassy carbon, conducting carbon layers, and carbon fibers) is effected via reducing ferrate ions (FeO42−). That is, the production of conducting polymer layer and the incorporation of iron oxide and iron hydroxide compounds [including FeO(OH)] into it are spatially and temporarily separated processes. Thus, the conducting polymer layer can form under ideal conditions (i.e., only in the presence of the necessary reagents), which improves its quality.
As used herein, the term iron oxide means any of Fe(II) oxide (FeO), Fe(III) oxide (Fe2O3), and Fe3O4 (magnetite) containing both Fe(II) and Fe(III) atoms or a mixture of them in any ratio. The term iron hydroxide means any of Fe(II) hydroxide [Fe(OH)2] and Fe(III) hydroxide [Fe(OH)3] or a mixture of them in any ratio. The composite can contain a mixed oxide-hydroxide compound [FeO(OH)], too.
As used herein, the term iron oxide/hydroxide refers to an iron-containing material comprising one or more compounds selected from: Fe2O3, Fe3O4, Fe(OH)2, Fe(OH)3, and FeO(OH). In preferred embodiments, the term iron oxide/hydroxide refers to an iron-containing material, which includes essentially one or more compounds selected from: Fe2O3, Fe3O4, Fe(OH)2, Fe(OH)3, and FeO(OH), and optionally, consists only of these listed.
The ratio of iron oxide to iron hydroxide compounds incorporated into the film (including FeO(OH) compound) can be modified by the electrochemical reduction and oxidation of the composite. Therefore, it is possible to achieve a composition, in which typically Fe(III) or typically Fe(II) compounds are present in the vast majority, or magnetite (Fe3O4)—a compound containing the mixture of Fe(II) and Fe(III) ions—dominate. In theory, the production process according to the invention is suitable for the synthesis of a composite comprising pure magnetite and a composite free of magnetite, as well. However, applying the electrochemical production method according to the invention in practice, however, other Fe(II) and Fe(III) compounds form in the composite in addition to magnetite. Such composites according to the invention differ from those known as prior art (i.e., they are considered novel), as in the known processes, pure magnetite is incorporated into the conducting polymer during the process of producing the polymer [or if other Fe(II) and Fe(III) compounds were incorporated into the polymer (by simple co-polymerization), PANI was the base polymer]. Magnetite is a rather stable compound, it is difficult to dissolve even in strong acids. Therefore, the products of the known processes starting from magnetite, contain other iron oxide/hydroxide compounds only as impurities (i.e., in amounts below 1 wt %, often only in trace amounts). In the composites according to the invention, the amount of iron oxide/hydroxide compounds other than magnetite is up to 100%, but typically at least 1-25 wt %, preferably it is 2-10 wt %, calculated from the total mass of the iron oxide/hydroxide compounds.
The possibility that iron oxide/hydroxide-containing nanoparticles can be introduced into the conducting polymer matrix starting from ferrate ions is unexpected based on previous knowledge, since ferrate ions are stable only in a strongly alkaline medium (pH>>13, typically 14-15) and they degrade rapidly in neutral or acidic medium. In contrast, electrochemical properties of conducting polymers are considerably worse in an alkaline medium, they are easily degraded (e.g., polymer films deposited on a support can easily delaminate). In addition, ferrate ions are quite strong oxidizing agents in neutral and mild alkaline media, therefore they can oxidize and degrade the polymer chains. It is assumed, that for these reasons, ferrate ions have not been used for the incorporation of iron oxide/hydroxide compounds into conducting polymers before. In our experiments, however, we have found that there is a pH range (7-13, preferably 9-12)—that is not obvious to a person skilled in the art—wherein the above negative phenomena has only a minor extent, which makes the use of ferrate ions possible for the incorporation of iron oxide/hydroxide compounds into the conducting polymer. That is, under these conditions, a part of conducting polymers (preferably PEDOT, polyaniline) is still sufficiently stable and electroactive, while the decomposition of ferrate ions occurs slowly enough to allow them to enter the polymer.
The non-obvious nature of the present invention is further confirmed by the fact that applying the known and widely used poly(3,4-ethylenedioxypyrrole) (PEDOP) conducting polymer, it was impossible to prepare iron oxide/hydroxide-containing composites by the methods described in this description, because, in contact with the medium (alkaline solution, containing ferrate ions) the polymer has become unusable (degraded).
Preparation of Iron Oxide/Hydroxide-Containing Conducting Polymer Composites
In a preferred embodiment of the invention, the conducting polymer layer was formed by galvanostatic polymerization (as described in Examples 1-7) or potentiodynamic deposition (as described in Example 8) on the surface of the substrate.
During galvanostatic deposition, the current between the working electrode and the counter electrode is kept constant, while the potential difference between the working electrode and the reference electrode is monitored in the cell as a function of time.
In potentiodynamic deposition [cyclic voltammetry or (dynamic) cyclization of the electrode potential, or simply potentiodynamic cyclization], the potential of the working electrode is periodically varied according to a suitably selected triangular signal while measuring the current flowing through the cell. The advantage of this method is that the amplitude and frequency of the periodic potential perturbation can be chosen according to the properties of the system. This method can be applied to incorporate iron into the conducting polymer, as well, see further details below.
During the deposition process of conducting polymer, the current density (j) is typically 0.05-1.00 mA/cm2, preferably 0.1-0.3 mA/cm2, for example 0.2 mA/cm2. The reaction time is typically 500-15000 s, preferably 1000-8000 s, for example 1800 s or 3600 s. The pH of the solution is approx. neutral (e.g., pH=5-8), and the reaction was preferably carried out at room temperature (T=20-25° C.).
For the formation of iron oxide/hydroxide-containing conducting polymers—i.e., for the incorporation of iron into the film—two types of electrochemical processes were applied:
The reduction of ferrate ions takes place according to the following chemical reaction equations. In these equations, (P)− means the negatively charged section of the polymer chain, i.e., the “active site,” (P) is the active site in the neutral state, and (P)+ indicates the oxidized state of the active site. To stabilize ferrate ions, reduction is performed under alkaline conditions, preferably in the range of pH=10-14.
2FeO42−+10H3O++6(P)−=Fe2O3+15H2O+6(P)
3FeO42−+16H3O++10(P)−=Fe3O4+24H2O+10(P)
2FeO42−+10H3O++3(P)−=Fe2O3+15H2O+3(P)+
3FeO42−+16H3O++5(P)−=Fe3O4+24H2O+5(P)+
FeO42−+5H3O++3(P)−═Fe(OH)3+6H2O+3(P)
FeO42−+5H3O++3(P)−═FeO(OH)+7H2O+3(P)
Based on the above, redox reactions (electron transfer) occur among the active sites of the polymer chains and ferrate ions. The state of the polymer film can be controlled by adjusting the electrode potential to an appropriate range (which can preferably be modified with a potentiostat). The reduced state-film has to be removed from the cell used to perform the electrochemical reduction, and immersed in a solution containing ferrate ions (thus contacting the film with ferrate ions). This way, reactions can occur among active sites and ferrate ions. By repeating the reduction and immersion steps, the amount of iron oxide/hydroxide incorporated into the film can be gradually increased.
According to another production process, reduction takes place in a ferrate-containing solution, followed by soaking the formed material in the solution (relaxation) for 15-300 s, preferably 30-60 s (it is also a kind of implementation of the “contacting” discussed above). The iron content is increased by adding further ferrate solution and/or by repeating steps (i.e., by repeating the reduction and then the soaking step for several times).
Moreover, moderate overoxidation of the conducting polymer film can enhance the increase of the incorporating iron oxide/hydroxide content because cracks appear in the structure of the polymer (i.e., its porosity increases). Moderate overoxidation means that the conducting polymer is subjected to oxidation, which is strong enough to cause the conducting polymer to partially oxidize irreversibly. [In this case, the value of the electrode potential (positive potential limit in the case of cyclization) has to be (+0.8)-(+1.2) V vs. SSCE, preferably (+0.9)-(+1.1) V vs. SSCE in neutral medium (pH=5-7)].
2FeO42−+10H3O++6e−═Fe2O3+15H2O
3FeO42−+16H3O++10e−═Fe3O4+24H2O
FeO42−+5H3O++3e−═Fe(OH)3+6H2O
FeO42−+5H3O++3e−═FeO(OH)+7H2O
Thus, the iron oxide/hydroxide compounds form by the direct electrochemical reduction of ferrate ions.
By repeating the oxidation and reduction steps, the amount of iron oxide/hydroxide incorporated into the film can be gradually increased. The repetition of the oxidation and reduction steps can be performed by cyclic voltammetry (also known as potentiodynamic cyclization).
The electrochemically active iron oxide/hydroxide compounds—incorporated as nanoparticles into the composite electrode—can be converted into each other by varying the electrode potential, according to the following reaction equations (this is of course true for the final product of both of the above processes), for instance:
3Fe2O3+2H3O++2e−=2Fe3O4+3H2O
3Fe(OH)3+H3O++e−═Fe3O4+6H2O
3FeO(OH)+H3O++e−═Fe3O4+3H2O
Using both types of processes, it was observed that ferrate treatment—i.e., the incorporation of iron oxide/hydroxide particles into the polymer films—considerably improved the electrochemical properties of the polymer films. From a practical point of view, it might be especially interesting that the frequency-dependent capacity of the films has increased in the range of medium frequencies (see
a) shows cyclic voltammograms (curves are recorded during the third cycle, E=(−0.3)-(+0.6) V vs. SSCE, v=100 mV/s);
a) and b) shows SEM images of a PEDOT|iron oxide/hydroxide composite layer deposited on a gold substrate according to Example 1 (Table 1 #1) with a) secondary electrons b) backscattered electrons. The scales at the bottom of the images correspond to 50 μm.
All electrochemical measurements were performed at room temperature (22.0±0.5) ° C. Solutions were saturated with oxygen free argon gas (Linde 5.0) before use, and the inert gas atmosphere was maintained during the experiments. Electrochemical measurements were performed with a Zahner IM6 electrochemical workstation controlled by a Thales software. Scanning electron microscopic (SEM) images were taken with a Quanta™ 3D FEG high-resolution dual-beam scanning electron microscope (SEM/FIB). Both secondary and scattered electrons were detected during scanning.
Investigation of the PEDOT Layer
The electrochemical investigation of the PEDOT layer was carried out in a three-electrode cell, which has a volume of 150 cm3, and the working electrode was a PEDOT layer, deposited on a gold disk (A=0.196 cm2), the reference electrode was a sodium chloride saturated calomel electrode (SSCE), and the counter electrode was a ring-shaped platinum plate. These electrodes were immersed in a 0.1 mol/dm3 H2SO4 solution. The potential window used in cyclic voltammetric studies was E=(−0.1)-(+0.8) V vs. SSCE, scan rates were v=100 and 50 mV/s. Electrochemical impedance spectroscopic (EIS) measurements were performed in the frequency range of 50 kHz to 96.1 mHz, the perturbation signal amplitude was 5 mV, and the electrode potential was E=(+0.4) V or (+0.2) V vs. SSCE.
I. Synthesis of PEDOT Layer-Containing Composites
*: The pH is decreasing during the process.
The following examples were carried out basically as described in Example 1, therefore, only the main characteristics will be given of the processes.
*: The pH is decreasing during the process.
*: The pH is decreasing during the process.
Immersion of the reduced PEDOT layer in the solution of step (2) (t=300 s).
*: The pH is decreasing during the process.
*: The pH is decreasing during the process.
*: The pH is decreasing during the process.
*: The pH is decreasing during the process.
*: The pH is decreasing during the process.
Table 1 summarizes the parameters of the production of various PEDOT/FexOy composites and their iron content in atomic percent (atom %).
The content of
The content of
The presence of iron oxides in layers can also be detected by Mossbauer spectroscopy. The composition cannot be given due to the small size of the iron-containing crystals.
II. Production of a Conducting Polymer Layer Reinforced with PBPA Layer
Preparation of PEDOT Film Reinforced with Poly(Bisphenol A) [PBPA]
Step 1: Deposition of Poly(3,4-Ethylenedioxythiophene) Layer
The electrochemical deposition of the PEDOT layer was carried out in a three-electrode cell, which has a volume of 150 cm3, in which the working electrode was a gold disk (A=0.196 cm2), the reference electrode was the potassium chloride saturated calomel electrode (SCE), and the counter electrode was a ring-shaped platinum disk. These electrodes were immersed in a 0.01 mol/dm3 EDOT/0.1 mol/dm3 Na2SO4 (pH=5) as-prepared solution. We applied j=0.2 mA/cm2 current density during the galvanostatic deposition. The deposition time was t=1800 s.
The prepared polymer layer was soaked in Milli-Q water for relaxation for one day (thus ensuring the removal of the oligomers).
Step 2: Deposition of Poly(Bisphenol A) [PBPA] Layer
The electrochemical deposition of the PBPA layer on the PEDOT layer was performed with a potentiodynamic method, in a 30 cm 3 three-electrode cell, in which the working electrode was the PEDOT layer, deposited on a gold plate (A=0.196 cm2), immersed in a 100 ppm BPA/0.5 mol/dm3 H2SO4 (pH=0.6) solution; reference electrode was a saturated sodium chloride filled calomel electrode (SSCE); and the counter electrode was a platinum wire. During potentiodynamic deposition, the potential window was E=−0.1-(+1.0) V vs. SSCE, scanning speed was v=100 mV/s, and the number of cycles was 10.
Step 3: Investigation of the PEDOT/PBPA Layer
The electrochemical deposition of the PEDOT layer was carried out in a three-electrode cell, which has a volume of 150 cm3, in which the working electrode was a gold disk (A=0.196 cm2), the reference electrode was potassium chloride saturated calomel electrode (SCE), the counter electrode was a ring-shaped platinum plate. These electrodes were immersed in a 0.1 mol/dm3 EDOT/0.1 mol/dm3 Na2SO4 (pH=1.3) as-prepared solution. The potential window during the cyclic voltammetric investigations was E=(−0.1)-(+0.8) V vs. SSCE, scanning speed was v=100, and 50 mV/s. Electrochemical impedance spectroscopic (EIS) measurements were performed in the frequency range of 50 kHz-96.1 mHz, the perturbation signal amplitude was 5 mV, and the electrode potential was E=0.4 V or 0.2 V vs. SSCE.
Step 4: Overoxidation of the PEDOT/PBPA Layer
The overoxidation of the PEDOT layer, prepared in step 2, was carried out in a three-electrode cell, its volume was 150 cm3, and the working electrode is a PBPA reinforced PEDOT layer deposited on a gold disk (A=0.196 cm2), the reference electrode was sodium chloride saturated calomel electrode (SSCE), the counter electrode was a ring-shaped platinum plate. These electrodes were immersed in a 0.1 mol/dm3 H2SO4 solution. During overoxidation, the potential window was E=0.4-1.5 V vs. SSCE, scanning speed was v=50 mV/s, and the number of cycles was 3.
Step 5: Investigation of the Overoxidized PEDOT Layer
The electrochemical investigation of the overoxidized PEDOT layer, prepared in step 4, was carried out in a three-electrode cell, its volume was 150 cm3, in which the working electrode is a PBPA-reinforced PEDOT layer deposited on a gold disk (A=0.196 cm2), the reference electrode was sodium chloride saturated calomel electrode (SSCE), and the counter electrode was a ring-shaped platinum plate. These electrodes were immersed in a 0.1 mol/dm3 H2SO4 solution. The potential window during the cyclic voltammetric investigations was E=(−0.1)-(+0.8) V vs. SSCE, scanning speed was v=100 and 50 mV/s. Electrochemical impedance spectroscopic (EIS) measurements were performed in the frequency range of 50 kHz-96.1 mHz, the perturbation signal amplitude was 5 mV, and the electrode potential was E=0.4 V or 0.2 V vs. SSCE.
The content of
Deposition of the Bisphenol A Layer after the Ferrate Treatment
*: The pH is decreasing during the process.
Fe content of the material formed: 13.3% (atom %).
Deposition of the Bisphenol a Layer Before the Ferrate Treatment
*: The pH is decreasing during the process.
Fe content of the material: 0.5 atom %.
III. Synthesis of PANI Film-Containing Composites
Instead of applying galvanostatic polymerization—as in the synthesis of PEDOT films—in case of certain polymers, e.g., polyaniline, potentiodynamic deposition is recommended, as galvanostatic deposition is less efficient. Further steps of preparation are the same as those discussed for PEDOT.
*: The pH is decreasing during the process.
The incorporation of iron into the polymer film is observable as the initially bright green polymer layer turns into purple-bluish after the treatment.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2100074 | Feb 2021 | HU | national |
| P2200046 | Feb 2022 | HU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/HU2022/050014 | 2/23/2022 | WO |
