Vapor phase polymerization (VPP) is used to fabricate
a series
of tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes
on carbon paper. The series of VPP PEDOT/tosylate coatings has varying
levels of crystallinity and electrical conductivity because of the
use (or not) of nonionic triblock copolymers in the oxidant solution
during synthesis. As a result, the impact of the structure on charge
storage capacity is investigated using tetra-n-butylammonium
hexafluorophosphate (0.1 M in acetonitrile). The ability to insert
anions, and hence store charge, of the VPP PEDOT/tosylate is inversely
related to its electrical conductivity. In the case of no nonionic
triblock copolymer employed, the VPP PEDOT/tosylate achieves electrochemical
doping levels of 1.0 charge per monomer or greater (≥100% doping
level). Such high doping levels are demonstrated to be plausible by
molecular dynamics simulations and density functional theory calculations.
Experiments show that this high doping level is attainable when the
PEDOT structure is weakly crystalline with (relatively) large crystallite
domains.
The
effect of thermal treatment on the structure and electrical/optical
properties of vapor phase-polymerized poly(3,4-ethylenedioxythiophene):tosylate
(PEDOT:Tos) and polypyrrole:tosylate (PPy:Tos) polymer films was investigated.
Thermal treatment was applied postpolymerization but prior to washing
the embedded oxidant layer out of the polymer film. Structural and
chemical changes arising from the treatment were studied in the context
of their conductive and electrochromic behavior. Spectroscopic analysis
indicated a rise in the doping levels of both conductive polymers
when exposed to thermal treatment. Additionally, an increase in the
film thickness was recorded after the oxidant and other unbound species
were removed from the polymer layer using an ethanol rinse. As such,
a strong indication that polymerization continued even in the absence
of (external) monomer vapor was present. This film thickness increase
was most pronounced for PPy:Tos but also present in the PEDOT:Tos
film. Heat-treated films exhibited enhanced cohesion, making them
more robust and therefore increasing the viability for the material
to be used in the optoelectronics area. This robustness, due to additional
(cross-linking) oligomer growth, came at the expense of lower conductivity
relative to their untreated counterparts.
Pyridinium
triflates are highly dissociated protic ionic liquids,
and nonstoichiometric compositions have been used in protic energy
devices such as the all-organic proton battery. Herein, we use a combination
of pulsed field gradient NMR spectroscopy and electrochemical impedance
spectroscopy to investigate the charge transport properties of the
nonstoichiometric protic ionic liquid 2-fluoropyridinium triflate
and the variation with the acid-doping level. While all diffusion
coefficients decreased with the level of acid doping, the room-temperature
conductivity increased because of the concurrent increase in charge
carrier concentration. The maximum room-temperature conductivity was
7.33 mS/cm, obtained when 14% of the pyridine was protonated with
triflic acid, while higher acid-doping levels lead to liquid/solid
mixtures with low conductivity. PEDOT supercapacitor cells with this
electrolyte demonstrated very high capacitance (83.9 F/g) and charge
storage capacity (23.3 mA h/g). In addition, we predict that using
an acid-doping level lower than before will result in superior electrolyte
performance in proton batteries because of improvements in conductivity,
processability, and electrochemical stability.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.