2 research outputs found
Supercapacitors Based on Polymeric Dioxypyrroles and Single Walled Carbon Nanotubes
This paper reports a novel supercapacitor electrode design
based on polyÂ(3,4-propylenedioxypyrrole) (PProDOP) electropolymerized
onto thin films of single walled carbon nanotubes (SWNTs) on glass
substrates. This permits the electropolymerization of thicker PProDOP
films than can be deposited onto flat gold-coated Kapton electrodes
and a correspondingly greater capacitance per unit area. A pyrene
functionalized polyfluorene, designated Sticky-PF, was designed and
used as an effective monolayer interfacial adhesion modifier between
the SWNT films and PProDOP via noncovalent self-assembly onto the
SWNT film surfaces before polymer electrodeposition. The thickness
of the electrodeposited PProDOP was found to be self-limiting at thicknesses characteristic of each substrate electrode.
Optimized areal capacitance values for PProDOP on flat gold and Sticky-PF
coated SWNT films were measured to be 8.1 mF/cm<sup>2</sup> and 16.4
mF/cm<sup>2</sup>, respectively, with the twofold enhancement due
to the thicker films possible on the SWNT electrode. The specific
capacitance of PProDOP on gold and Sticky-PF|SWNT film substrates
were found to be similar at 141 F/g and 122 F/g, respectively, indicating
the capacitance to be due to the electroactive polymer. The areal
capacitance values of the corresponding supercapacitor devices constructed
with Au/Kapton substrates was 3.2 mF/cm<sup>2</sup>, whereas a significantly
greater value of 8.8 mF/cm<sup>2</sup> was measured for the Sticky-PF|SWNT
film substrates. The supercapacitors prepared using the Au/Kapton
substrates were highly stable, retaining 80% of their electroactivity
after 32 700 nonstop charge/discharge cycles (100% depth of
discharge). Supercapacitors made using the Sticky-PF|SWNT substrates
showed a steady loss of capacitance to about 57% of the original value
(to 5.0 mF/cm<sup>2</sup>) after 32 700 charge/discharge cycles,
which was still 38% larger than the initial capacitance of the gold
electrode devices
Competition between Ultrafast Energy Flow and Electron Transfer in a Ru(II)-Loaded Polyfluorene Light-Harvesting Polymer
This Letter describes the synthesis and photophysical
characterization
of a RuÂ(II) assembly consisting of metal polypyridyl complexes linked
together by a polyfluorene scaffold. Unlike many scaffolds incorporating
saturated linkages, the conjugated polymer in this system acts as
a functional light-harvesting component. Conformational disorder breaks
the conjugation in the polymer backbone, resulting in a chain composed
of many chromophore units, whose relative energies depend on the segment
lengths. Photoexcitation of the polyfluorene by a femtosecond laser
pulse results in the excitation of polyfluorene, which then undergoes
direct energy transfer to the pendant RuÂ(II) complexes, producing
RuÂ(II)* excited states within 500 fs after photoexcitation. Femtosecond
transient absorption data show the presence of electron transfer from
PF* to RuÂ(II) to form charge-separated (CS) products within 1–2
ps. The decay of the oxidized and reduced products, PF<sup>+•</sup> and RuÂ(I), through back electron transfer are followed using picosecond
transient absorption methods