James F. Ponder

Solution Processed PEDOT Analogues in Electrochemical Supercapacitors

We have designed fully soluble ProDOTx-EDOTy copolymers that are electrochemically equivalent to electropolymerized PEDOT without using any surfactants or dispersants. We show that these copolymers can be incorporated as active layers in solution processed thin film supercapacitors to demonstrate capacitance, stability, and voltage similar to the values of those that use electrodeposited PEDOT as the active material with the added advantage of the possibility for large scale, high-throughput processing. These Type I supercapacitors provide exceptional cell voltages (up to 1.6 V), highly symmetrical charge/discharge behavior, promising long-term stability exceeding 50 000 charge/discharge cycles, as well as energy (4-18 Wh/kg) and power densities (0.8-3.3 kW/kg) that are comparable to those of electrochemically synthesized analogues.

Design of Hybrid Electrochromic Materials with Large Electrical Modulation of Plasmonic Resonances

We present a rational approach to fabricating plasmonically active hybrid polymer-metal nanomaterials with electrochemical tunability of the localized surface plasmon resonances (LSPRs) of noble metal nanostructures embedded in an electroactive polymer matrix. The key requirement for being able to significantly modulate the LSPR band position is a close overlap between the refractive index change [Δn(λ)] of a stimuli-responsive polymeric matrix and the intrinsic LSPR bands. For this purpose, gold nanorods with a controlled aspect ratio, synthesized to provide high refractive index sensitivity while maintaining good oxidative stability, were combined with a solution-processable electroactive and electrochromic polymer (ECP): alkoxy-substituted poly(3,4-propylenedioxythiophene) [PProDOT(CH2OEtHx)2]. Spectral characteristics of the ECP, in particular the Δn(λ) variation, were evaluated as the material was switched between oxidized and reduced states. We fabricated ultrathin plasmonic electrochromic hybrid films consisting of gold nanorods and ECP that exhibited a large, stable, and reversible LSPR modulation of up to 25-30 nm with an applied electrical potential. Finite-difference time-domain (FDTD) simulations confirm a good match between the experimentally measured refractive index change in the ECP and the plasmonic response during electrochemical modulations.

Electrochromic tuning of transparent gold nanorods with poly[(3,4-propylenedioxy)pyrrole] shells in the near-infrared region

We report on electrochemically tunable hybrid nanostructures composed of gold nanorods encapsulated within directly polymerized poly[(3,4-propylenedioxy)pyrrole] (PProDOP) nanoshells with controlled nanoscale thicknesses. This system displays narrow visible-near infrared absorption bands upon applying a variable electric potential due to the remarkable transmissivity of PProDOP at various oxidation states. The PProDOP shells were synthesized by in situ chemical oxidative polymerization using a mild oxidizing agent. The PProDOP demonstrated outstanding electrochemical performance, such as reversible electroactivity, high transmissivity in the visible range at various oxidation states, as well as a low oxidation potential (−1.06 V vs. Fc/Fc+). We suggest that the stable reversible modulation of the observed plasmonic response of the gold nanorods was caused by the variation of the refractive index of PProDOP shells at different oxidation states as shown by spectroscopic ellipsometry and confirmed by finite-difference time-domain (FDTD) simulations. A surface plasmon resonance (LSPR) band of gold nanorods at 800 nm was shifted reversibly by 24 nm by multiple cycling of the electric potential. Overall, these core–shell structures with electrochemical plasmonic tunability in the near-infrared region allow for tailoring of the optical and electrochemical properties of pre-programmed plasmon responses for active control of colorimetric appearance not just across the visible range but also toward the near-infrared.

Soluble phenylenedioxythiophene copolymers via direct (hetero)arylation polymerization: a revived monomer for organic electronics

Dioxyheterocycles, particularly 3,4-ethylenedioxythiophene (EDOT), have proven to be useful building blocks for conjugated materials targeting various applications. The 3,4-phenylenedioxythiophene (PheDOT) unit is similar to the EDOT unit in terms of planarity and steric interactions, but has different electronic properties because of the attached phenyl ring. This unit has been incorporated into soluble alternating copolymers for the first time via direct (hetero) arylation polymerization (DHAP). These polymers are effective electrochromes with vibrantly colored charge neutral states and colorless, transmissive oxidized states. Spray cast films are highly stable to redox switching, showing only a 1% decrease in contrast after 2000 switches without film encapsulation.

Flexible, aqueous-electrolyte supercapacitors based on water-processable dioxythiophene polymer/carbon nanotube textile electrodes

Water-processed, aqueous electrolyte supercapacitors are demonstrated incorporating an alternating copolymer of a functionalized 3,4-propylenedioxythiophene unit with a 2,2′-bis(3,4-ethylenedioxythiophene) unit (PE2) into carbon nanotube textiles. The side chains functionalizing PE2 allow the solubility to be tuned from the organic soluble precursor polymer, to a water-soluble polyelectrolyte, and finally to a solvent resistant form by a dilute acid wash (SR-PE2). Thin SR-PE2 films (60 μg cm−2) are electroactive over a wide potential window with a mass capacitance of 54 F g−1 at a discharge rate of 1.6 s (38 A g−1). These films exhibit a 65% capacitance retention at an 80 millisecond discharge time (560 A g−1). Flexible, free-standing electrodes were fabricated by depositing SR-PE2 onto a nonwoven carbon nanotube textile (CNT-T) and were assembled into symmetrical, flexible supercapacitors where the addition of polymer resulted in a boost in volumetric capacitance by 400 percent compared to the bare CNT-T electrode. Independent of whether the SR-PE2 films are cast from an organic solvent or water, device electrodes exhibit 11.4 F cm−3 (45 mF cm−2, 15.9 F g−1) which leads to an energy density of 0.10 mW h cm−3 at 7.5 mW cm−3 considering the total device volume. The CNT-T imparts a high degree of flexibility allowing the supercapacitors to retain 88% of their charge storage capacity when bent to a 0.8 mm radius as well as complete capacitance retention after 2000 bending cycles to a 3.5 mm radius. The devices assembled in air with a benign KCl electrolyte maintained 83% capacitance retention after 10 000 charge/discharge cycles highlighting the stability of these materials and utility for this processing approach for high throughput energy storage devices.