Stable Deep Doping of Vapor‐Phase Polymerized Poly(3,4‐ethylenedioxythiophene)/Ionic Liquid Supercapacitors

Abstract

Liquid-solution polymerization and vapor-phase polymerization (VPP) have been used to manufacture a series of chloride- and tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT) carbon paper electrodes. The electrochemistry, specific capacitance, and specific charge were determined for single electrodes in 1-ethyl-3-methylimidazolium dicyanamide (emim dca) ionic liquid electrolyte. VPP-PEDOT exhibits outstanding properties with a specific capacitance higher than 300 F g(-1) , the highest value reported for a PEDOT-based conducting polymer, and doping levels as high as 0.7 charges per monomer were achieved. Furthermore, symmetric PEDOT supercapacitor cells with the emim dca electrolyte exhibited a high specific capacitance (76.4 F g(-1) ) and high specific energy (19.8 Wh kg(-1) ). A Ragone plot shows that the VPP-PEDOT cells combine the high specific power of conventional ("pure") capacitors with the high specific energy of batteries, a highly sought-after target for energy storage.

Charge transport and structure in semimetallic polymers

“…In part this is due to the not doping to the same level as Tos – (1 anion in 2.4 EDOTs vs. 1 in 1.8), as shown in Figure (c) (determined from XPS, see Supporting Information Figure S2). It is important to note that the very high doping level herein compared with that generally reported as the theoretical limit for PEDOT (1 anion in 3 EDOTs) is hypothesised to be related to coordination of anions with the triblock copolymer within the VPP PEDOT . In direct comparison with , the insertion of Cl – yields a similar doping level to but a conductivity 2.5 times higher.…”

“…In more detailed studies by Bubnova et al, the differences from the use of PSS – or Tos – were shown to arise from a transition in the conducting polymer from a Fermi glass to a semimetal respectively. Despite the demonstration of PEDOT in electrical applications from thermoelectronics to spintronics to energy storage, no rationale has been provided to explain the role of the doping anion in achieving high electrical conductivity. Notably theoretical modelling, that is an essential and standard tool in many fields of material science, is to a large extend missing in conducting polymer research where the interpretation of experiments seldom relies on theoretical calculations.…”

“…In this study, we report the electronic properties of conducting polymer PEDOT with respect to the doping anions using various experimental techniques [Hall measurements, photoabsorption, grazing incidence wide‐angle X‐ray scattering, X‐ray Photoelectron Spectroscopy (XPS), and THz spectroscopy] combined with the theoretical modeling using atomistic MD simulations of material's morphology and the density functional theory (DFT) for calculations of electronic properties. Importantly this study focuses on high doping levels in excess of 50% (i.e., 1 anion for 2 EDOT monomers), where the conducting polymer (in this case PEDOT) is said to be semimetallic . This is in contrast to the majority of existing studies which are limited to the doping levels of 33% or less corresponding to pristine (i.e., as polymerized) PEDOT.…”

Flexible and Cellulose-based Organic Electronics

“…[6] Although PEDOT:PSS is the most researched form of PEDOT, many other counterions, such as chloride and p-toluenesulfonic acid (tosylate or Tos), have been investigated. [7] The choice of counter ion affects the doping level as well as the packing of the PEDOT chains and thus influences the conductivity. PEDOT:PSS can reach conductivities of ~1000 S/cm, while values of 2000-5000 S/cm have been reported with counterions such as tosylate [8] or trifluoromethanesulfonate [9] .…”

“…Typical reported values of capacitance based on conductive polymers is in the range 10-200 F/g. [7,39,102] Some metal oxides, like ruthenium oxide, have superior capacitance compared to both carbon and conductive polymers with a specific capacitance ~1000 F/g. [99] However, they often suffer from low conductivity and poor ion permeability.…”