Abstract:
Developing novel membranes marks a significant advancement in flexible energy storage systems. In this
work, a hybrid track-etched membrane (TeM) was synthesized through RAFT-mediated polymerization,
where poly(acrylic acid) (PAA) was grafted onto both the nanopore walls and surface of PET-based TeMs
(PET-g-PAA), creating a stable and functionalized matrix for further enhancements. The membrane was
then modified by incorporating electrospun composite nanofibers made from poly(vinylidene fluoridehexafluoropropylene) (PVDF-HFP) as the polymer matrix, ionic liquid (1-ethyl-3-methylimidazolium
tetrafluoroborate, EM-IMBF4) as the supporting electrolyte, and graphene oxide (GO) as the ionic
conductivity enhancer. The nanofibers (PVDF-HFP_GO) were deposited on either one or both surfaces
of the grafted membrane. These modifications substantially improved the membrane's active surface
area, porosity, and electrochemical performance, positioning it as a strong candidate for flexible energy
storage applications. Comprehensive characterizations verified the successful modification and
enhanced properties, including FTIR, SEM-EDX, XPS, TGA, porosity analysis, and contact angle
measurements. Electrochemical performance was evaluated through cyclic voltammetry (CV),
galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). Among the
tested membranes, the one modified with 0.5% GO-containing nanofibers demonstrated the highest
capacitance and coulombic efficiency. Although the membrane showed strong charge/discharge
efficiency and high initial performance, performance degradation was observed after extended cycling,
particularly at higher current densities. The ionic conductivity of the hybrid membranes (with a GO
concentration of 0.5%) reaches 14.83 × 10−3 mS cm−1 for single-sided nanofiber-covered membranes
and 39.08 × 10−3 mS cm−1 for double-sided nanofiber-covered membranes, while for similar samples
without addition of GO this values were found to be of 1.42 × 10−3 mS cm−1
, which is significantly
higher than conventional polymer-based electrolyte membranes (∼10−4 to 10−2 mS cm−1
), and
comparable to advanced ionic gel-based systems (∼10−2 to 10−1 mS cm−1
). The synergistic effects of
PAA grafting and PVDF-HFP_GO fibers delivered competitive charge/discharge efficiency when
compared to similar systems, though further optimization of current density and cycling stability is
required. This study highlights the potential of combining the RAFT-mediated grafting technique with
electrospun composite nanofibers in modifying TeMs to develop durable and flexible supercapacitor
membranes with promising electrochemical performance.
