The
modulator 2-fluorobenzoic acid (2-fba) is widely used to prepare
RE clusters in metal–organic frameworks (MOFs). In contrast
to known RE MOF structures containing hydroxide bridging groups, we
report for the first time the possible presence of fluoro bridging
groups in RE MOFs. In this report we discuss the synthesis of a holmium-UiO-66
analogue as well as a novel holmium MOF, where evidence of fluorinated
clusters is observed. The mechanism of fluorine extraction from 2-fba
is discussed as well as the implications that these results have for
previously reported RE MOF structures.
The
development of electrically conductive and high surface area
carbon is important for the improvement of supercapacitor energy densities.
Yttrium hydroxide microspindles were prepared and shown to catalyze
carbon growth. The carbon exhibited a high surface area of 932 m2/g and high conductivity of 2.2 × 105 S/m.
The carbon/yttrium oxide interface was probed using XPS, Raman spectroscopy,
infrared spectroscopy, and solid-state fluorescence. Supercapacitor
cells were assembled using the yttrium-catalyzed carbon and EMI-TFSI
ionic liquid as the electrolyte. The symmetric supercapacitor cell
had a specific capacitance of 137.2 F/g, energy density of 57.4 Wh/kg,
and power density of 1724.3 W/kg, at 1 A/g.
Hierarchical porous carbon nanosheet (HPCN) materials of different thicknesses were fabricated on Mg(OH) 2 substrates utilizing a one-step chemical vapor deposition (CVD) approach. The templated carbon nanosheets are closely packed hierarchical nanostructures possessing high surface areas varying from 1323 to 1978 m 2 •g −1 . Symmetrical electrochemical doublelayer capacitors (EDLCs) were constructed using the HPCN and demonstrated a high specific capacitance of 205 F•g −1 at 5 mV/s using 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide (EMIM-TFSI) as an electrolyte. The energy density was 86 Wh•kg −1 , and a power density of up to 16.57 kW•kg −1 was observed. After 5000 charge−discharge cycles at 10 A•g −1 , the supercapacitor retained 90% of its initial capacity. This illustrates the great stability of the templated mesoporous carbon sheets for supercapacitors.
Despite
having an inherently low surface area upon carbonization,
polyacrylonitrile (PAN) remains one of the more widely studied precursor
polymers for making high-performance carbon fibers (CFs) for supercapacitors
because of its electrospinnability and high carbon yield. Copolymerization
with vinylimidazole (VIM) or acidic monomers such as itaconic acid
(IA) comprises an attractive approach to modify the properties of
PAN-based fibers to enhance their electrochemical performance. In
this study, a terpolymer, poly(acrylonitrile-co-1-vinylimidazole-co-itaconic acid) (P(AN-co-VIM-co-IA)), was synthesized with different ratios of AN with
VIM and/or IA monomers to develop CF precursors for supercapacitor
applications. Here, IA serves as an in situ porogen
that releases CO2 during the carbonization process to increase
the surface area and tailor the pore sizes. VIM moieties disrupt the
strong dipole–dipole interactions between nitrile groups in
pure PAN, thus facilitating the processability and thermal stabilization
of PAN. Benefiting from the above modifications, the resulting CFs
of terpolymers exhibited higher specific surface areas and superior
electrochemical performances and long-term stability compared to PAN
or corresponding copolymers of P(AN-co-VIM) or P(AN-co-IA). The terpolymer with 5 wt % of VIM and 23 wt % of
IA shows the highest capacitance of 97.0 F g–1 (10
mV s–1) with an energy density of 49 Wh kg–1 at 10 kW kg–1 upon carbonization, which was enhanced
to 136.7 F g–1 (10 mV s–1) and
79 Wh kg–1 at 10 kW kg–1 upon
activation with CO2.
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.