Electrochemical synthesis of composite based on polyaniline and activated IR pyrolyzed polyacrylonitrile on graphite foil electrode for enhanced supercapacitor properties

Electrochemical copolymerization of 3,4-ethylenedioxythiophene and dithienothiophene: influence of feed ratio on electrical, optical and electrochromic properties

Designing a copolymer is an efficient and alternative method to generate new chemical and physical properties compared to parent homopolymers without complex synthesis and structural modification. We herein report the electrochemical deposition of copolymer using two monomers 3,4-ethylenedioxythiophene (EDOT) and dithieno[3,2-b:2',3'-d]thiophene (DTT). Three different copolymers P[EDOT-co-DTT] were synthesized by using different feed ratios of monomers (EDOT and DTT molar ratios in solution are 2 : 1, 1 : 1 and 1 : 2) in acetonitrile containing 0.1 M tetrabutylammonium perchlorate (TBAClO4) as a supporting electrolyte. Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and UV-vis-NIR spectroscopy were employed to characterize the obtained copolymers. Energy dispersive X-ray spectroscopy (EDX) analysis was used to estimate the composition of EDOT and DTT units in copolymers. The electrochemical and morphological properties were analyzed using cyclic voltammetry (CV) and field emission scanning electron microscopy (FESEM). In situ spectroelectrochemistry and electrochromic studies were performed to investigate the optical and switching properties of the resultant copolymers. The homopolymers poly(3,4-ethylenedioxythiophene) (PEDOT) and polydithieno[3,2-b:2',3'-d]thiophene (PDTT) were also prepared using similar electrochemical conditions and made comparisons where applicable. Computational calculations were done to understand the structure and energy levels of these polymers. It was found that these copolymers P[EDOT-co-DTT] show new properties as compared to homopolymers PEDOT and PDTT for organic electronic applications. Interesting to note that the resultant copolymers display the property of tunable electrochromism with improved transmittance and redox color change between the neutral and oxidized states.

Novel Hybrid Electrode Coatings Based on Conjugated Polyacid Ternary Nanocomposites for Supercapacitor Applications

Electrochemical behavior of novel electrode materials based on polydiphenylamine-2-carboxylic acid (PDPAC) binary and ternary nanocomposite coatings was studied for the first time. Nanocomposite materials were obtained in acidic or alkaline media using oxidative polymerization of diphenylamine-2-carboxylic acid (DPAC) in the presence of activated IR-pyrolyzed polyacrylonitrile (IR-PAN-a) only or IR-PAN-a and single-walled carbon nanotubes (SWCNT). Hybrid electrodes are electroactive layers of stable suspensions of IR-PAN-a/PDPAC and IR-PAN-a/SWCNT/PDPAC nanocomposites in formic acid (FA) formed on the flexible strips of anodized graphite foil (AGF). Specific capacitances of electrodes depend on the method for the production of electroactive coatings. Electrodes specific surface capacitances C_s reach 0.129 and 0.161 F∙cm^-2 for AGF/IR-PAN-a/PDPAC_ac and AGF/IR-PAN-a/SWCNT/PDPAC_ac, while for AGF/IR-PAN-a/PDPAC_alk and AGF/IR-PAN-a/SWCNT/PDPAC_alk C_s amount to 0.135 and 0.151 F∙cm^-2. Specific weight capacitances C_w of electrodes with ternary coatings reach 394, 283, 180 F∙g^-1 (AGF/IR-PAN-a/SWCNT/PDPAC_ac) and 361, 239, 142 F∙g^-1 (AGF/IR-PAN-a/SWCNT/PDPAC_alk) at 0.5, 1.5, 3.0 mA·cm^-2 in an aprotic electrolyte. Such hybrid electrodes with electroactive nanocomposite coatings are promising as a cathode material for SCs.

Molten salt electro-preparation of graphitic carbons

Graphite has been used in a wide range of applications since the discovery due to its great chemical stability, excellent electrical conductivity, availability, and ease of processing. However, the synthesis of graphite materials still remains energy-intensive as they are usually produced through a high-temperature treatment (>3000°C). Herein, we introduce a molten salt electrochemical approach utilizing carbon dioxide (CO₂) or amorphous carbons as raw precursors for graphite synthesis. With the assistance of molten salts, the processes can be conducted at moderate temperatures (700-850°C). The mechanisms of the electrochemical conversion of CO₂ and amorphous carbons into graphitic materials are presented. Furthermore, the factors that affect the graphitization degree of the prepared graphitic products, such as molten salt composition, working temperature, cell voltage, additives, and electrodes, are discussed. The energy storage applications of these graphitic carbons in batteries and supercapacitors are also summarized. Moreover, the energy consumption and cost estimation of the processes are reviewed, which provides perspectives on the large-scale synthesis of graphitic carbons using this molten salt electrochemical strategy.

Novel Hybrid Composites Based on Polymers of Diphenyl-Amine-2-Carboxylic Acid and Highly Porous Activated IR-Pyrolyzed Polyacrylonitrile

Hybrid composites based on electroactive polymers of diphenylamine-2-carboxylic acid (PDPAC) and highly porous carbon with a hierarchical pore structure were prepared for the first time. Activated IR-pyrolyzed polyacrylonitrile (IR-PAN-a), characterized by a highly developed surface, was chosen as a highly porous N-doped carbon component of the hybrid materials. IR-PAN-a was prepared using pyrolysis of polyacrylonitrile (PAN) in the presence of potassium hydroxide under IR radiation. Composite materials were obtained using oxidative polymerization of diphenylamine-2-carboxylic acid (DPAC) in the presence of IR-PAN-a both in an acidic and an alkaline medium. The composite materials were IR-heated to reduce the oxygen content and enhance their physical and chemical properties. The chemical structure, morphology, and electrical and thermal properties of the developed IR-PAN-a/PDPAC composites were investigated. The IR-PAN-a/PDPAC composites are thermally stable and electrically conductive. During the synthesis of the composites in an acidic medium, doping of the polymer component occurs, which makes the main contribution to the composite conductivity (1.3 × 10^-5 S/cm). A sharp drop in the electrical conductivity of the IR-PAN-a/PDPAC_ac-IR composites to 3.4 × 10^-10 S/cm is associated with the removal of the dopant during IR heating. The IR-PAN-a/PDPAC_alk composites prepared before and after IR heating show a gradual increase in electrical conductivity by five orders of magnitude to 1.6 × 10^-5 S/cm at 25-10⁶ Hz. IR heating of the obtained materials leads to a significant increase in their thermal properties. The IR-heated composites lose half of their initial weight in an inert atmosphere at temperatures above 1000 °C, whereas for IR-PAN-a/PDPAC, the temperature range is 840-849 °C.