2 research outputs found
Graphene Oxide: A Versatile Agent for Polyimide Foams with Improved Foaming Capability and Enhanced Flexibility
Close-celled aromatic polyimide (PI)/graphene
foams with low density
and improved flexibility were fabricated by thermal foaming of polyÂ(amic
ester)/graphene oxide (PAE/GO) precursor powders. The PAE/GO precursor
powders were prepared by grafting GO nanosheets with PAE chains, which
led to efficient dispersion of the GO nanosheets in PAE matrix. Incorporation
of GO resulted in an enhanced foaming capability of the precursor,
i.e., enlarged cell size and decreased foam density. Notably, a decrease
of 50% in the foam density was obtained via the addition of only 2
wt % GO in the precursor. In the foaming process, the GO nanosheets
functioned as a versatile agent that not only provided heterogeneous
nucleation sites but also produced gaseous molecules. By analyzing
the foaming mechanism, the excellent features of GO in heat transfer,
gas barrier, and strength reinforcement also facilitated to obtain
large and uniform cells in the foams. In addition, the PI/graphene
foams exhibited a prominent flexibility and enhanced flexural strength,
as an elastic-to-nonelastic conversion of the initial stage of the
compressive stress–strain curves was observed by increasing
the content of graphene in the PI matrix and an increase of 22.5%
in flexural strength was obtained by addition of 0.5 wt % GO in the
precursor
Conjunction of Conducting Polymer Nanostructures with Macroporous Structured Graphene Thin Films for High-Performance Flexible Supercapacitors
Fabrication
of hybridized structures is an effective strategy to promote the performances
of graphene-based composites for energy storage/conversion applications.
In this work, macroporous structured graphene thin films (MGTFs) are
fabricated on various substrates including flexible graphene papers
(GPs) through an ice-crystal-induced phase separation process. The
MGTFs prepared on GPs (MGTF@GPs) are recognized with remarkable features
such as interconnected macroporous configuration, sufficient exfoliation
of the conductive RGO sheets, and good mechanical flexibility. As
such, the flexible MGTF@GPs are demonstrated as a versatile conductive
platform for depositing conducting polymers (CPs), e.g., polyaniline
(PAn), polypyrrole, and polythiophene, through <i>in situ</i> electropolymerization. The contents of the CPs in the composite
films are readily controlled by varying the electropolymerization
time. Notably, electrodeposition of PAn leads to the formation of
nanostructures of PAn nanofibers on the walls of the macroporous structured
RGO framework (PAn@MGTF@GPs): thereafter, the PAn@MGTF@GPs display
a unique structural feature that combine the nanostructures of PAn
nanofibers and the macroporous structures of RGO sheets. Being used
as binder-free electrodes for flexible supercapacitors, the PAn@MGTF@GPs
exhibit excellent electrochemical performance, in particular a high
areal specific capacity (538 mF cm<sup>–2</sup>), high cycling
stability, and remarkable capacitive stability to deformation, due
to the unique electrode structures