An ideal separator of lithium-ion
battery (LIB) should have a zero
ionic resistance. Low ionic resistance (high ionic conductivity) will
greatly help to realize very fast ion diffusion and superhigh rate
capability of LIBs. The most effective technique to achieve low ionic
resistance of separator is to reduce its thickness or increase its
porosity. Paradoxically, the low thickness and high porosity will
inevitably decrease the mechanical strength of separators. Inspired
by the hierarchical structures of abalone shell, we demonstrate in
this work an ultrathin silica-anchored layered (PVdF/PE/PVdF) porous
fiber separator prepared via electrospinning. The separator displays
both ultrathin thickness (∼20 μm thick) and high mechanical
strength of ∼11.2 MPa, as well as high porosity, which results
in high electrolyte uptake (∼380%) and ionic conductivity (∼2.5
mS cm–1). When such thin separator was deployed
in a LiFePO4/Li cell, and the cell can deliver an initial
discharge capacity of 134.3 mA h g–1 at a high rate
of 10 C and maintain a capacity of 129.2 mA h g–1 after 300 charge–discharge cycles, showing excellent high-rate
performance. More interestingly, this study demonstrates a pathway
for the development of ultrathin and high-mechanical-strength electrospun
separators for high-rate Li-ion batteries.
One pot synthesis of 2,5‐dimethylfuran (2,5‐DMF) from saccharides under mild conditions is of importance for the production of biofuel and fine chemicals. However, the synthesis requires a multitude of active sites and suffers from slow kinetics due to poor diffusion in most composite catalysts. Herein, a metal‐acid functionalized 2D metal‐organic framework (MOF; Pd/NUS‐SO3H), as an ultrathin nanosheet of 3–4 nm with Lewis acid, Brønsted acid, and metal active sites, was prepared based on the diazo method for acid modification and subsequent metal loading. This new composite catalyst gives substantially higher yields of DMF than all reported catalysts for different saccharides (fructose, glucose, cellobiose, sucrose, and inulins). Characterization suggests that a cascade of reactions including polysaccharide hydrolysis, isomerization, dehydration, and hydrodeoxygenation takes place with rapid molecular interactions.
Developing
an efficient and selective catalyst for C–O hydrogenolysis
of biomass-derived aromatic aldehydes, such as 5-methylfurfural (MF),
5-hydroxymethylfurfural (HMF), and vanillin (VA), is highly significant
for the synthesis of biofuel and fine chemicals. Herein, metal–organic
framework (MOF)-encapsulating metal–acid interfaces (Pd@UiO–CH2SO3H, Pd@UiO–PhSO3H) were first
reported. Compared with traditionally supported catalysts (Pd/UiO–SO3H, Pd/UiO–NH2), Pd–acid-interface-encapsulated
MOFs show much higher activity and selectivity for MF to 2,5-dimethylfuran
(DMF), HMF to DMF, and VA to 2-methoxy-4-methylphenol (MMP) reactions.
In particular, Pd@UiO–SO3H shows the best catalytic
performance with 89.0 and 86.0% DMF yield from MF and HMF and a 99.4%
MMP yield from VA based on its suitable hydrophilicity, high hydrogen
activation ability, and abundant Pd–SO3H interface
active sites. According to the catalytic performance of Pd/UiO–NH2 and the results of an ATR-IR test, the acidic sites on the
Pd–acid interface can accelerate the activation of the hydroxyl
group for these hydrogenolysis reactions. This work provides an effective
design strategy for the preparation of MOF-encapsulating metal–acid
interfaces and shows the powerful synergistic effect of hydrogenation
and acid catalysis.
The integration of photochromic dithienylethenes (DTEs) with lipid vesicles as photoresponsive membrane disruptors for ion transport applications has been examined. We have synthesized three amphiphilic DTEs 1-3 that incorporate a terminally charged alkyl chain, and contain methyl or phenylethynyl substituents at the reactive carbons. Our photochromic reactivity studies suggest that the inclusion of a single alkyl chain favors the photoactive antiparallel conformation of DTEs, given the significant improvement in the cyclization quantum yield over previous phenylethynyl derivatives. Our ion permeation studies show that the open-ring isomers of these DTEs are more disruptive than the closed-ring isomers in the four lipid vesicle systems studied, regardless of their lamellar phase at room temperature. In addition, a steric effect was clearly observed as DTEs incorporating the comparatively smaller methyl group exhibited lower rates of ion permeation than the bulkier phenylethynyl group. In all cases, UV irradiation led to a reduction in ion permeability. In fact, the methyl analog exhibited a significant reduction in ion permeability in gel-phase lipid vesicles upon UV exposure. Also, the hexyl chain derivatives had a greater effect on membrane permeability than the dodecyl derivative owing to their relative position in the bilayer membrane of lipid vesicles.
Lithium–sulfur (Li–S) batteries are promising candidates for next‐generation energy storage devices owing to their advantages such as high theoretical specific capacity and energy density. However, the shuttle effect of polysulfide intermediates and the slow electrochemical kinetics have a severe passive effect on the cycling stability and rate performance. A Co3W3C@C composite was prepared through a simple one‐pot pyrolysis method and used as a modifying layer on a commercial separator. The obtained modified separator not only prevented the shuttle effect through both strong chemical interaction and a physical barrier toward polysulfides, but also acted as a catalytic membrane to catalyze the electrochemical redox of active sulfur species. By employing the coated separator, the cathode with 60 wt % sulfur delivered a high initial capacity of 1345 mAh g−1 at 0.1 A g−1, excellent rate performance with a high capacity of 670 mAh g−1 even at 7 A g−1, and outstanding cycle performance with a low decay rate of 0.06 % per cycle and an average Coulombic efficiency of 99.3 % within 500 cycles at 1 A g−1. Even at a sulfur loading of 3 mg cm−1, a high initial capacity of 869 mAh g−1 and 632 mAh g−1 after 200 cycles at 1 A g−1 were obtained. The results demonstrate the advantages of Co–W bimetallic carbide in preventing the shuttle effect and promoting the redox kinetics for high performance Li–S batteries.
The conversion of macromolecular saccharides (fructose, glucose, sucrose, and inulin) to 5‐hydroxymethylfurfural (HMF) is often limited by the mass transfer resistance of existing catalysts. Herein, a two‐dimensional metal–organic framework (NUS‐8‐PhSO3H) containing high densities of dual acidic sites (Lewis and Brønsted acid sites) was developed for the first time by diazo grafting. Characterization results and reaction kinetics showed that the rapid molecular diffusion leads to an unusual pseudozeroth reaction order and a considerably lower apparent activation energy for the fructose reaction over NUS‐8‐PhSO3H in contrast to the first order and higher activation energy over three‐dimensional counterpart (NUS‐16‐PhSO3H) and reported catalysts. In addition, NUS‐8‐PhSO3H can also produce substantially high HMF yields and has a low activation energy for other saccharides (glucose, sucrose, and inulin) by powerful tandem steps, including polysaccharide hydrolysis, glucose isomerization, and fructose dehydration. The preparation of hydrophobic acidic NUS‐8‐PhSO3H provides an efficient means of synthesizing HMF from various saccharides.
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