A high lithium conductive MoS /Celgard composite separator is reported as efficient polysulfides barrier in Li-S batteries. Significantly, thanks to the high density of lithium ions on MoS surface, this composite separator shows high lithium conductivity, fast lithium diffusion, and facile lithium transference. When used in Li-S batteries, the separator is proven to be highly efficient for depressing polysulfides shuttle, leading to high and long cycle stability. With 65% of sulfur loading, the device with MoS /Celgard separator delivers an initial capacity of 808 mAh g and a substantial capacity of 401 mAh g after 600 cycles, corresponding to only 0.083% of capacity decay per cycle that is comparable to the best reported result so far. In addition, the Coulombic efficiency remains more than 99.5% during all 600 cycles, disclosing an efficient ionic sieve preventing polysulfides migration to the anode while having negligible influence on Li ions transfer across the separator. The strategy demonstrated in this work will open the door toward developing efficient separators with flexible 2D materials beyond graphene for energy-storage devices.

A redox active pyridine based covalent organic framework was synthesized and used as an electrode in faradaic supercapacitors. The pyridine units in the DAP-COF undergo a reversible redox reaction, leading to an increase in specific capacitance relative to both its electroactive monomer and a COF lacking redox-active groups.

Mixed Ruddlesden-Popper (RP) perovskites are of great interest in light-emitting diodes (LEDs), due to the efficient energy transfer (funneling) from high-bandgap (donor) domains to low-bandgap (acceptor) domains, which leads to enhanced photoluminescence (PL) intensity, long PL lifetime, and high-efficiency LEDs. However, the influence of reduced effective emitter centers in the active emissive film, as well as the implications of electrical injection into the larger bandgap donor material, have not been addressed in the context of an active device. The electrical and optical signatures of the energy cascading mechanisms are critically assessed and modulated in a model RP perovskite series ((C H NH ) (CH(NH ) ) Pb Br ). Optimized devices demonstrate a current efficiency of 22.9 cd A and 5% external quantum efficiency, more than five times higher than systems where funneling is absent. The signature of nonideal funneling in RP perovskites is revealed by the appearance of donor electroluminescence from the device, followed by a reduction in the LED performance.

The prevalence of (1)pi sigma* states in the photochemistry of heteroaromatics is becoming increasingly clear from the recent literature. Photodissociation measurements have shown that following excitation of phenol molecules above the S(1)/S(2) conical intersection, H-atoms are eliminated with two distinct ranges of kinetic energy release. Those with high kinetic energy are attributed to direct dissociation while those with low kinetic energy are traditionally attributed to indirect dissociation or statistical unimolecular decay, both pathways giving electronic ground-state phenoxyl fragments. Using a combination of femtosecond pump/probe spectroscopy and velocity map ion imaging techniques, the time and energy resolved H-atom elimination in phenol-h(6) and phenol-d(5), following excitation at 200 nm has been measured. At the lowest kinetic energies, the H-atom elimination from phenol-d(5) occurs in <150 fs, in sharp contrast to what one expects from a statistical decay process. This implies that these H-atoms are formed through a direct dissociation process yielding electronically excited phenoxyl fragments.

The active role of the optically dark pi sigma* state, following UV absorption, has been implicated in the photochemistry of a number of biomolecules. This work focuses on the role of the pi sigma* state in the photochemistry of phenol upon excitation at 200 nm. By probing the neutral hydrogen following UV excitation, we show that hydrogen elimination along the dissociative pi sigma* potential energy surface occurs within 103 +/- 30 fs, indicating efficient coupling at the S1/S2 and S0/S2 conical intersections, with no identifiable role of statistical unimolecular decay of vibronically excited (S0) phenol in the timeframe of our measurements.

The ubiquitous nature of 1πσ* states in biological molecules has been a prime focus in recent years. Understanding the role of this dissociative state in the amino acids and their respective chromophores following UV excitation would enable a step change toward establishing a better understanding of the mechanisms of photostability of larger peptides in the gas-phase. This letter presents the first evidence of the active involvement of 1πσ* states in the H-atom elimination of the amino acid tyrosine and its subunit tyramine, following excitation at 200 nm.

High temperature processing thermoplastic polymers, polyetheretherketone (PEEK) and polyethersulphone (PES), were melt blended with carbon fibers (CFs) to make composites. These composites were investigated for their mechanical, thermal, and electrical properties. Mechanical properties that are expressed in terms of storage modulus, loss, and damping were enhanced with the addition of CFs. Thermal properties were determined by DSC and TGA. These methods help to understand the effects of fiber content and fiber-matrix adhesion in the composites. Composites were also tested for their electrical and thermal conductivity because CFs leave the composites thermally and electrically conductive. CFs enhanced the crystallinity of the PEEK appreciably that in turn influenced thermal conductivity, electrical resistivity, and the stiffness of PEEK/CF (composites of PEEK with CFs). PES/CF (composites of PES with CF) shows a different behavior due to the amorphous nature of PES. The work involves one filler and two different matrices, and so it provides an interesting comparison of how matrix morphology can influence the properties of composites. POLYM. COMPOS., 28: 785-796, 2007.FIG. 2. (a) Storage modulus of pure PEEK and the composites with CF. (b) Storage modulus of CF-reinforced PEEK composites after heating above T g .

Three dimensional iron oxide/graphene aerogel hybrid (Fe2O3/GA) was synthesized and used as electrode materials in flexible supercapacitor devices, which show high specific capacitance of 440 F g−1 with 89% capacitance retention after 2200 cycles.