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    Effect of supporting electrolyte on capacitance and morphology of electrodeposited poly(3,4-propylenedioxythiophene) derivatives bearing reactive functional groups
    (Royal Soc Chemistry, 2022) Sarac, Baran; Karazehir, Tolga; Gilsing, Hans-Detlev; Eckert, Juergen; Sarac, A. Sezai
    The interactions between the electrolyte and electroactive species in redox active PProDOT derivatives can be enhanced with better-performing electrodes for electrochemical energy conversion and storage. Differently functionalized 3,4-propylenedioxythiophenes (ProDOTs) are electropolymerized from acetonitrile using Et4NBF4, Et4NPF6, or NaClO4 as an electrolyte to evaluate the electrochemical performance of the considered polymer derivatives, as well as under monomer-free conditions. We propose a new equation to assess the kinetics of the diffusion-limited adsorption process with two independent solved parameters: diffusion slope k and power exponent b. Electron-donating groups attached to the monomer stabilize radical cation and dication formation during electrogrowth. The ProDOT-Br structure has a low oxidation potential owing to the electron-rich group in the heterocyclic structure, which grants access to a radical cation intermediate and interaction with the ions of the electrolyte. Surface roughness and morphology are assessed by atomic force microscopy and scanning electron microscopy, respectively. The changes in the Fourier transform infrared spectrum are more pronounced with the selection of electrolyte type than the type of derivatives. Except the -OBz derivative, the largest specific capacitance calculated from the area under the final cyclic voltammetry curves is obtained for Et4NBF4, followed by Et4NPF6 and NaClO4. In all systems, the -OPhCH2OH derivative exhibited the lowest electrolyte diffusion. More pronounced diffusion is observed for the PProDOT derivatives measured in Et4NPF6 and Et4NBF4 electrolytes, whereas the lowest diffusion is obtained for the NaClO4 electrolyte. Findings in this study provide new insights into the factors requiring attention upon tailoring assemblies for organic electronic applications.
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    Effective Methanol Oxidation with Platinum Nanoparticles-Decorated Poly(2-bromomethyl-2-methyl-3,4-propylenedioxythiophene)-Coated Glassy Carbon Electrode
    (Electrochemical Soc Inc, 2021) Karazehir, Tolga; Sarac, Baran; Gilsing, Hans-Detlev; Eckert, Juergen; Sarac, A. Sezai
    Here, we developed a porous network of bromomethyl-substituted 3,4-propylenedioxythiophene polymer using a simple and efficient technique of electrochemical deposition used as conductive support for methanol oxidation. Platinum nanoparticles (PtNPs) are well dispersed and decorated on a high surface area of electrochemically deposited Poly(2-bromomethyl-2-methyl-3,4-propylenedioxythiophene (PProDOT-Br) on a glassy carbon electrode (GCE). A thin film of PProDOT-Br acts as a supporting matrix for deposition of PtNPs and improves the interfacial properties between electrode and electrolyte. The PtNPs-decorated PProDOT-Br (Pt/PProDOT-Br) samples were characterized by X-ray diffraction, Fourier transform infrared attenuated total reflectance spectroscopy, atomic force microscopy, and scanning electron microscopy. Furthermore, the electrocatalytic performance of Pt/PProDOT-Br on GCE for methanol oxidation was assessed by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements. The findings suggest that the use of Pt/PProDOT-Br/GCE assemblies for efficient methanol oxidation in alkaline media with a small intermediate poisoning is promising for applications as anode material in DMFCs, which should be attributed to the PProDOT-Br support providing a larger surface area with porous nature and enabling the adsorption of more CH3OH for further oxidation. The developed porous network PProDOT-Br with high capacitance may also have large potential in supercapacitor applications.
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    Functionalized highly electron-rich redox-active electropolymerized 3,4-propylenedioxythiophenes as precursors and targets for bioelectronics and supercapacitors
    (Royal Soc Chemistry, 2021) Karazehir, Tolga; Sarac, Baran; Gilsing, Hans-Detlev; Gumrukcu, Selin; Eckert, Jurgen; Sarac, A. Sezai
    In order to combine capacitive properties with processability, e.g. solubility in organic solvents, poly(3,4-propylenedioxythiophene) derivatives containing different functional groups like oxyphenyl methanol (-OPhCH2OH), oxybenzyl (-OBz), bromide (-Br) and tosyl (-OTs) were synthesized and electropolymerized as thin films from acetonitrile (ACN) using Et4NBF4 as an electrolyte. Multifunctionality in the substitution pattern of the polymer exhibits a similar trend between monomer oxidation potentials and specific capacitance (C-sp) vs. crystal size. The presence of pi-pi stacking interactions in the polymer structures plays an important role in building the crystal structures. The same order of flat band potential and C-sp values are observed for -OBz < -Br < -OTs < -OPhCH2OH substitutions. The structures of PProDOT-OBz and PProDOT-OPhCH2OH resemble each other much more than those of PProDOT-Br and PProDOT-OTs. Impedance measurements were conducted at different applied biases in order to define a Mott-Schottky analysis revealing the dependence of the semiconducting properties on the type of substituent present in the PProDOT derivative.
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    Oligoether Ester-Functionalized ProDOT Copolymers on Si/Monolayer Graphene as Capacitive Thin Film Electrodes
    (Electrochemical Soc Inc, 2020) Karazehir, Tolga; Sarac, Baran; Gilsing, Hans-Detlev; Eckert, Juergen; Sarac, A. Sezai
    In this study, electrochemical polymerization of 3,4-propylenedioxythiophene (ProDOT 1), ProDOT bearing oligoether ester (ProDOT-EO-ester 2) and their copolymerization onto homogeneously CVD coated nano-graphene/Si support is realized to attain graphene/ProDOT based copolymer hybrid nanostructures. By introducing oligoether side chain to ProDOT backbone and using different [ProDOT]/[ProDOT-EO-ester] molar ratios ensures a considerable decrease in oxidation potential of polymer allowing tunable properties to copolymers revealing improvement electrochemical capacitance and electrochemical activity which are clearly reflected by the experimental results. Capacitive behavior of copolymers is determined by electrochemical impedance spectroscopy, cyclic voltammetry. Moreover, The structural, morphological and spectroscopic characterization of the copolymers is investigated by XRD, AFM, SEM, EDX, FTIR, and Raman, respectively. By the increase of ProDOT in the copolymer composition, the higher dopant concentration is attained suggesting an enhanced conductivity agree well with the impedance and CV results, where the copolymerization of ProDOT 1 and ProDOT-EO-ester 2 in equal molarity results in the highest specific capacitance and redox activity. The adopted equivalent circuit model for polymers is in good agreement with the experimental data of impedance. Due to the difference in conjugated structure between ProDOT and ProDOT-EO-ester by the presence of the EO-ester group leads to a decrease in charge transfer resistance with increasing mole fraction of ProDOT-EO-ester. The charge transfer resistance of [ProDOT](0)/[ProDOT-EO-ester](0) = 1:1 coated Si/graphene is nearly 51 and 24 times lower value compared to those of PProDOT and P(ProDOT-EO-ester) homopolymers coated Si/graphene, respectively, confirming that the copolymerization improves the electron conduction. By Mott-Schottky measurements, increasing mole fraction of ProDOT-EO-ester 2 in copolymer composition results in the alteration of semiconducting behavior. The developed graphene-polymer hybrid electrodes can be a potential candidate for energy storage devices. (C) 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.