Realizing High Capacitance and Rate Capability in Polyaniline by Enhancing the Electrochemical Surface Area through Induction of Superhydrophilicity

Polyaniline (PANI) as a pseudocapacitive material has very high theoretical capacitance of 2000 F g^–1. However, its practical capacitance has been limited by low electrochemical surface area (ESA) and unfavorable wettability toward aqueous electrolytes. This work deals with a strategy wherein the high ESA of PANI has been achieved by the induction of superhydrophilicity together with the alignment of PANI exclusively on the surface of carbon fibers as a thin layer to form a hybrid assembly. Superhydrophilicity is induced by electrochemical functionalization of the Toray carbon paper, which further induces superhydrophilicity to the electrodeposited PANI layer on the paper, thereby ensuring a high electrode–electrolyte interface. The Toray paper is electrochemically functionalized by the anodization method, which generates a highly active electrochemical surface as well as greater wettability (superhydrophilic) of the carbon fibers. Because of the strong interaction of anilinium chloride with the hydrophilic carbon surface, PANI is polymerized exclusively over the surface of the fibers without any appreciable aggregation or agglomeration of the polymer. The PANI–Toray paper assembly in the solid-state prototype supercapacitor can provide a high gravimetric capacitance of 1335 F g^–1 as well as a high areal capacitance of 1.3 F cm^–2 at a current density of 10 A g^–1. The device also exhibits high rate capability, delivering 1217 F g^–1 at a current density of 50 A g^–1 and a high energy density of 30 W h kg^–1 at a power density of 2 kW kg^–1

Naphthalene Diimide Copolymers by Direct Arylation Polycondensation as Highly Stable Supercapacitor Electrode Materials

Conjugated donor–acceptor copolymers based on naphthalene diimide (NDI) as acceptor and thiophene-terminated oligophenylene­vinylene as donor moieties (P₁ and P₂, respectively) were synthesized using the direct (hetero) arylation (DHAP) polymerization route. Nitrile groups were introduced at the vinylene linkage in one copolymer (P₂) to fine-tune its electrochemical properties. Both polymers show π–π* transition in the 300–480 nm region and intramolecular charge transfer (ICT) from thiophene to NDI in the 500–800 nm region in the absorption spectra. P₂ exhibits a blue-shifted intramolecular charge transfer (ICT) band in the absorption spectrum as well as a lower reduction potential in the cyclic voltammogram compared to the analogous polymer without the nitrile substitution (P₁). The two polymers were evaluated as type III supercapacitor materials by preparing composite electrodes with carbon nanotubes (CNTs) and employing 0.5 M H₂SO₄ as the electrolyte. Their performance was compared with that of P­(NDI2OD-T2) as a reference polymer. The polymer P₂ based supercapacitor exhibits a specific capacitance of 124 F/g with excellent stability up to 5000 cycles with almost 100% retention of the initial capacitance in the potential window of −0.7 to 0.5 V. Compared to P₂, P₁ exhibits a specific capacitance of 84 F/g, while the corresponding value for the reference polymer P­(NDI2OD-T2) is 61 F/g under identical conditions

Naphthalene Diimide Copolymers by Direct Arylation Polycondensation as Highly Stable Supercapacitor Electrode Materials

Conjugated donor–acceptor copolymers based on naphthalene diimide (NDI) as acceptor and thiophene-terminated oligophenylene­vinylene as donor moieties (P₁ and P₂, respectively) were synthesized using the direct (hetero) arylation (DHAP) polymerization route. Nitrile groups were introduced at the vinylene linkage in one copolymer (P₂) to fine-tune its electrochemical properties. Both polymers show π–π* transition in the 300–480 nm region and intramolecular charge transfer (ICT) from thiophene to NDI in the 500–800 nm region in the absorption spectra. P₂ exhibits a blue-shifted intramolecular charge transfer (ICT) band in the absorption spectrum as well as a lower reduction potential in the cyclic voltammogram compared to the analogous polymer without the nitrile substitution (P₁). The two polymers were evaluated as type III supercapacitor materials by preparing composite electrodes with carbon nanotubes (CNTs) and employing 0.5 M H₂SO₄ as the electrolyte. Their performance was compared with that of P­(NDI2OD-T2) as a reference polymer. The polymer P₂ based supercapacitor exhibits a specific capacitance of 124 F/g with excellent stability up to 5000 cycles with almost 100% retention of the initial capacitance in the potential window of −0.7 to 0.5 V. Compared to P₂, P₁ exhibits a specific capacitance of 84 F/g, while the corresponding value for the reference polymer P­(NDI2OD-T2) is 61 F/g under identical conditions

Pt- and TCO-Free Flexible Cathode for DSSC from Highly Conducting and Flexible PEDOT Paper Prepared via in Situ Interfacial Polymerization

Here, we report the preparation of a flexible, free-standing, Pt- and TCO-free counter electrode in dye-sensitized solar cell (DSSC)-derived from polyethylenedioxythiophene (PEDOT)-impregnated cellulose paper. The synthetic strategy of making the thin flexible PEDOT paper is simple and scalable, which can be achieved via in situ polymerization all through a roll coating technique. The very low sheet resistance (4 Ω/□) obtained from a film of 40 μm thick PEDOT paper (PEDOT-p-5) is found to be superior to the conventional fluorine-doped tin oxide (FTO) substrate. The high conductivity (357 S/cm) displayed by PEDOT-p-5 is observed to be stable under ambient conditions as well as flexible and bending conditions. With all of these features in place, we could develop an efficient Pt- and TCO-free flexible counter electrode from PEDOT-p-5 for DSSC applications. The catalytic activity toward the tri-iodide reduction of the flexible electrode is analyzed by adopting various electrochemical methodologies. PEDOT-p-5 is found to display higher exchange current density (7.12 mA/cm²) and low charge transfer resistance (4.6 Ω) compared to the benchmark Pt-coated FTO glass (2.40 mA/cm² and 9.4 Ω, respectively). Further, a DSSC fabricated using PEDOT-p-5 as the counter electrode displays a comparable efficiency of 6.1% relative to 6.9% delivered by a system based on Pt/FTO as the counter electrode