2 research outputs found
Electrochemical Characterization and Catalytic Application of Gold-Supported Ferrocene-Containing Diblock Copolymer Thin Films in Ethanol Solution
This
paper reports the electrochemical behavior and catalytic property
of electrode-supported thin films of polystyrene-<i>block</i>-polyÂ(2-(acryloyloxy)Âethyl ferrocenecarboxylate) (PS-<i>b</i>-PAEFc) in an ethanol (EtOH) solution. The electrochemical properties
of PS-<i>b</i>-PAEFc films with different PAEFc volume fractions
(<i>f</i><sub>PAEFc</sub> = 0.47, 0.30, and 0.17) in 0.1
M ethanolic sodium hexafluorophosphate (NaPF<sub>6</sub>) were compared with those in an acetonitrile
(MeCN) solution of 0.1 M tetrabutylammonium hexafluorophosphate. Pristine
PS-<i>b</i>-PAEFc films did not afford significant faradaic
currents in the EtOH solution because EtOH is a nonsolvent for both
PS and PAEFc. However, the films could be rendered redox-active in
the EtOH solution by applying potentials in the MeCN solution to induce
the redox-associated incorporation of the supporting electrolytes
into the films. Atomic force microscopy images verified the stability
of PAEFc microdomains upon electrochemical measurements in these solutions.
Cyclic voltammograms measured in the EtOH solution for PS-<i>b</i>-PAEFc with the larger <i>f</i><sub>PAEFc</sub> were diffusion-controlled regardless of ellipsometric film thickness
(23–152 nm) at relatively slow scan rates, in contrast to those
in the MeCN solution that were controlled by surface-confined redox
species. The electron propagation efficiency in the EtOH solution
was significantly lower than that in the MeCN solution because of
the poorer swelling of the films, which limited the migration of counterions
and the collisional motions of the ferrocene moieties. PS-<i>b</i>-PAEFc films were applied as electrochemically responsive
heterogeneous catalysts based on the ferrocenium moieties for Michael
addition reaction between methyl vinyl ketone and ethyl 2-oxocyclopentanecarboxylate
(E2OC) in 0.1 M NaPF<sub>6</sub>/EtOH. The catalytic activities of
thin films were similar regardless of <i>f</i><sub>PAEFc</sub>, suggesting that the catalytic reaction took place for the reactants
that could penetrate through the film and reach PAEFc microdomains
communicable with the underlying electrode. Interestingly, the permeability
of PS-<i>b</i>-PAEFc films provided a means to control the
reaction selectivity, as suggested by negligible reaction of E2OC
with <i>trans</i>-4-phenyl-3-buten-2-one
Electron Propagation within Redox-Active Microdomains in Thin Films of Ferrocene-Containing Diblock Copolymers
This paper reports the electrochemical
behavior of redox-active
microdomains in thin films of ferrocene-containing diblock copolymers,
polystyrene-<i>block</i>-polyÂ(2-(acrylÂoyloxy)Âethyl
ferroceneÂcarboxylate) (PS-<i>b</i>-PAEFc). PS-<i>b</i>-PAEFc with different PAEFc volume fractions (PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub>, PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub>, and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>12</sub>, where the subscripts represent the polymerization
degree of each block; <i>f</i><sub>PAEFc</sub> = 0.47, 0.30,
and 0.17, respectively) was synthesized by sequential atom transfer
radical polymerization. PS-<i>b</i>-PAEFc films of controlled
thicknesses (20–160 nm) were prepared on gold substrates via
spin-coating and characterized by ellipsometry. Microdomains were
observed via atomic force microscopy on the surfaces of PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub> and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub> thin films but not on the surfaces
of PS<sub>154</sub>-<i>b</i>-PAEFc<sub>12</sub> thin films.
Electrochemical behavior of films was assessed by cyclic voltammetry
and chronocoulometry in acetonitrile solution. The redox potential
of ferrocene moieties was similar (ca. + 0.29 V vs Fc<sup>+</sup>/Fc)
regardless of <i>f</i><sub>PAEFc</sub> and film thickness.
For PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub> and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub>, thicker films afforded
larger faradaic peak currents and exhibited diffusion-controlled voltammograms
at faster sweep rates. PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub> produced voltammograms less influenced by solvent-induced
swelling than PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub>, reflecting the improved morphological stability of PAEFc microdomains
by redox-inert PS frameworks. In contrast, PS<sub>154</sub>-<i>b</i>-PAEFc<sub>12</sub> films yielded similar faradaic peak
currents regardless of film thickness and exhibited voltammograms
indicative of surface-confined species. These observations suggest
that PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub> and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub> films contain continuous
PAEFc microdomains extending from the electrode to the surface, in
contrast to the PS<sub>154</sub>-<i>b</i>-PAEFc<sub>12</sub> films which contain isolated PAEFc microdomains buried within the
PS matrix. Electron propagation took place only through PAEFc microdomains
that could electrically communicate with the underlying electrode.
Apparent diffusion coefficients within PAEFc microdomains were similar
(≈ 2 × 10<sup>–11</sup> cm<sup>2</sup>/s) for PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub> and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub>. The relatively low efficiency
in electron propagation was attributable to ineffective electron self-exchange
reaction within the PAEFc microdomains and/or limited counterion migration
through the acetonitrile-swollen microdomains. These results provide
guidance in design of redox-active metalloblock copolymers for various
applications, which include electrocatalysis, electrochemical mediation
in enzyme sensors, and redox-controlled molecular deposition