A free-standing, flexible PEDOT:PSS film and its nanocomposites with graphene nanoplatelets as electrodes for quasi-solid-state supercapacitors

Binder-free all-carbon composite supercapacitors

Carbon-based electrode materials have widely been used in supercapacitors. Unfortunately, the fabrication of the supercapacitors includes a polymeric binding material that leads to an undesirable addition of weight along with an increased charge transfer resistance. Herein, binder-free and lightweight electrodes were fabricated using powder processing of carbon nanofibers (CNFs) and graphene nanoplatelets (GNPs) resulting in a hybrid all-carbon composite material. The structural, morphological, and electrochemical properties of the composite electrodes were studied at different concentrations of GNPs. The specific capacitance (Cs) of the CNFs/GNPs composite was improved by increasing the concentration of GNPs. A maximum Cs of around 120 F g-1was achieved at 90 wt% GNPs which is around 5-fold higher in value than the pristine CNFs in 1 M potassium hydroxides (KOH), which then further increased to 189 F g-1in 6 M KOH electrolyte. The energy density of around 20 Wh kg-1with the corresponding power density of 340 W kg-1was achieved in the supercapacitor containing 90 wt% GNPs. The enhanced electrochemical performance of the composite is related to the presence of a synergistic effect and the CNFs establishing conductive/percolating networks. Such binder-free all-carbon electrodes can be a potential candidate for next-generation energy applications.

Performance of PEDOTOH/PEO-based Supercapacitors in Agarose Gel Electrolyte

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a prime example of conducting polymers materials for supercapacitors electrodes that offer ease of processability and sophisticated chemical stability during operation and storage in aqueous environments. Yet, continuous improvement on its electrochemical capacitance and stability upon long cycles remains a major interest in the field, such as the developing PEDOT-based composites. This work evaluates the electrochemical performances of hydroxymethyl PEDOT (PEDOTOH) coupled with hydrogel additives, namely poly(ethylene oxide) (PEO), poly(acrylic acid) (PAA), and polyethyleneimine (PEI), fabricated via a single-step electrochemical polymerization method in an aqueous solution. The PEDOTOH/PEO composite exhibits the highest capacitance (195.2 F g-1) compared to pristine PEDOTOH (153.9 F g-1), PEDOTOH/PAA (129.9 F g-1), and PEDOTOH/PEI (142.3 F g-1) at a scan rate of 10 mV s-1. The PEDOTOH/PEO electrodes were then assembled into a symmetrical supercapacitor in an agarose gel. The type of supporting electrolytes and salt concentrations were further examined to identify the optimal agarose-based gel electrolyte. The supercapacitors comprising 2 M agarose-LiClO4 achieved a specific capacitance of 27.6 F g-1 at a current density of 2 A g-1, a capacitance retention of ~94% after 10,000 charge/discharge cycles at 10.6 A g-1, delivering a maximum energy and power densities of 11.2 Wh kg-1 and 3.45 kW kg-1, respectively. The performance of the proposed supercapacitor outperformed several reported PEDOT-based supercapacitors, including PEDOT/carbon fiber, PEDOT/CNT, and PEDOT/graphene composites. This study provides insights into the effect of incorporated hydrogel in the PEDOTOH network and the optimal conditions of agarose-based gel electrolytes for high-performance PEDOT-based supercapacitor devices.

Novel Dispersion of 1D Nanofiber Fillers for Fast Ion-Conducting Nanocomposite Polymer Blend Quasi-Solid Electrolytes for Dye-Sensitized Solar Cells

Electrospun nanocomposite polymer blend poly(vinylidene difluoride-co-hexafluoropropylene) (PVDF-HFP)/poly(methyl methacrylate) (PMMA) membranes with a novel dispersion of x wt % of one-dimensional (1D) TiO₂ nanofiber fillers (x = 0.0-0.8 in steps of 0.2) were developed using the electrospinning technique. The developed nanocomposite polymer membranes were activated using various redox agents such as LiI, NaI, KI, and tetrabutyl ammonium iodide (TBAI). Introduction of the 1D TiO₂ nanofiber fillers improves the amorphous nature of the blended polymer membrane, as confirmed through X-ray diffraction (XRD) and Fourier transform infrared (FTIR), and yielded an electrolyte uptake of over 480% for a 6 wt % TiO₂ nanofiber filler-dispersed sample. PVDF-HFP/PMMA-1D 6 wt % TiO₂ nanofiber fillers with the LiI-based redox electrolyte provided a high conductivity of 2.80 × 10^-2 S cm^-1 and a power conversion efficiency (PCE) of 8.08% to their fabricated dye-sensitized solar cells (DSSCs). The observed better ionic conductivity and efficiency of the fabricated DSSCs could be due to the faster movement of the smaller-ionic-radius (Li) ions entrapped inside the amorphous polymer. This enhanced mobility of ions in the quasi-solid electrolyte leads to faster regeneration of the depleting electrons in the photoanode, resulting in improved efficiency. Further, the achieved high conductivity was analyzed in terms of the dynamics and relaxation mechanisms involved by the ionic charge carriers with complex impedance spectroscopy using a random barrier model and Havriliak-Negami formulation. It was observed that the high-conducting PVDF-HFP/PMMA-1D 6 wt % TiO₂ nanofiber fillers with LiI-based redox electrolyte show better ac conductivity parameters such as a σ of 5.82 × 10^-2 S cm^-1, ω_e (12685 rad s^-1), τ_e (0.909 × 10^-4 s), and n (0.578). Also, dielectric studies revealed that the high-conducting sample has a higher dielectric constant and subsequently high loss. The J-V characteristics were studied using the equivalent circuit of a single-diode model, and the parameters influencing the photovoltaic performance were determined by Symbiotic Organisms Search (SOS) algorithm. The results suggest that the high-efficient sample possesses a minimum series resistance of 1.33 Ω and a maximum shunt resistance of 997 Ω. Hence, the highest-conducting electrospun-blended polymeric nanocomposite (PVDF-HFP-PMMA-6 wt % TiO₂ nanofiber fillers) with LiI-based redox agent and tert-butyl pyridine (TBP) additive as the polymer quasi-solid electrolyte nanofibrous membrane can be a better electrolyte for high-performance dye-sensitized solar cell applications.

Synergistic effect of defects and porous structure in CoCCHH-CoSe heterogeneous-tube @PEDOT:PSS foam towards elastic supercapacitor with enhanced pseudocapacitances

It is still challenging to construct stable 3D energy storage materials at the nanoscale by precise pore structure control and reasonable surface modification. Herein, a novel interwoven porous Co(CO₃)_0.35Cl_0.20(OH)_1.10 (CoCCHH)-CoSe heterogeneous-tube @PEDOT:PSS 3D foam with abundant active sites is presented as supercapacitor electrodes. The electrochemical results indicated that the pore structure provides ample space for redox reaction, and increases the number of ion transport channels. Besides, rational surface modification brings about sufficient active sites for redox reaction. The stable, porous PEDOT:PSS foam with a 3D elastic frame exhibited excellent electrical conductivity. Thus, the CoCCHH-CoSe@PEDOT:PSS foam possessed excellent specific capacitance and energy density, due to the synergistic effect of the unique 3D structure and surface defects. The home-made supercapacitor with CoCCHH-CoSe@PEDOT:PSS foam as cathode materials showed high specific capacitance (440.6F g^-1 at 1 A g^-1) and excellent energy density (137.7 Wh kg^-1). This work provides a valuable strategy to develop potential materials for electrochemical energy storage.