While lithium ion batteries (LIBs) are a ubiquitous commercial technology, [1,2] sodium ion batteries (NIBs) are receiving increasing scientific attention due to the much wider distributed reserves of Na precursors and the cost savings associated with an aluminum versus a copper anode current collector. [3][4][5][6][7] For both LIBs and NIBs, the gravimetric capacity of the cathode is lower than that of the anode. [8,9] On a volumetric basis, however, it is the graphite (LIBs) or the hard carbon (NIBs) anode that takes up the most room in a cell and is hence the "weakest link." Therefore, the general effort for both Li and Na technologies is to advance high capacity cathodes and simultaneously metal anodes. For instance lithium Energy density (energy per volume) is a key consideration for portable, automotive, and stationary battery applications. Selenium (Se) lithium and sodium metal cathodes are created that are monolithic and free-standing, and with record Se loading of 70 wt%. The carbon host is derived from nanocellulose, an abundant and sustainable forestry product. The composite is extremely dense (2.37 g cm −3 ), enabling theoretical volumetric capacity of 1120 mA h cm −3 . Such architecture is fully distinct from previous Se-carbon nano-or micropowders, intrinsically offering up to 2× higher energy density. For Li storage, the cathode delivers reversible capacity of 1028 mA h cm −3 (620 mA h g −1 ) and 82% retention over 300 cycles. For Na storage, 848 mA h cm −3 (511 mA h g −1 ) is obtained with 98% retention after 150 cycles. The electrodes yield superb volumetric energy densities, being 1727 W h L −1 for Li-Se and 980 W h L −1 for Na-Se normalized by total composite mass and volume. Despite the low surface area, over 60% capacity is maintained as the current density is increased from 0.1 to 2 C (30 min charge) with Li or Na. Remarkably, the electrochemical kinetics with Li and Na are comparable, including the transition from interfacial to diffusional control.

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Fluorescent conjugated polyelectrolytes represent an exciting area of research into new chemosensors. By virtue of their rapid electron and energy transfer paths, these highly correlated, one-dimensional systems have been depicted as "molecular wires" and show "million-fold" sensitivity compared to monomolecular sensor analogs. In this paper, a novel polyelectrolyte sensor, the ttp-PPESO, has been designed by incorporating terpyridine and sulfonate functional groups into the polyelectrolyte. This specifically tailored sensor has displayed remarkable quenching response toward copper(II) with a detection limit of 14.7 nM (0.93 ppb). It is capable of selectively screening copper without interference from 12 common cations. Molecular modeling suggests that binding occurs through a coordination interaction of the terpyridine and sulfonate. The additional multidentate nature from the sulfonate offers extraordinary chelating ability to the analyte. We anticipate that this unique binding mode will provide insight for the design of future more sensitive and selective systems.

TiO 2 polycrystalline sub-micron fibers can be used as photocatalysts for the degradation of a variety of organic molecules. Here we report on the optimization of these fibers for decontaminating pharmaceutical agents in aqueous medical waste streams. Mixed-phase TiO 2 fibers have been prepared via a sol-gel technique followed by electrospinning and calcination. By adjusting the calcination temperature, the rutile phase fraction in TiO 2 fibers can be tuned relative to the anatase phase from 0% to 100%. The effect of rutile phase fraction on grain size and specific surface area as well as their subsequent influences on the photocatalytic activity was investigated. An optimal grain size in post-calcined TiO 2 fibers was found to be critical to balance the e-/h + volume recombination, surface recombination rate, and charge diffusion rate. The photocatalytic activities of the post-calcined TiO 2 fibers with different rutile fractions were measured by monitoring the decreasing concentration of phenazopyridine in aqueous solution under UV illumination using UV-Vis absorption spectroscopy. Post-calcined TiO 2 fibers composing of 38 wt% rutile and 62 wt% anatase exhibited the highest initial degradation rate constant of 0.044 min-1. This optimal photocatalytic activity can be attributed to the combined influences of the fibers' phase composition, surface area and grain size.

Vapor-phase polymerized poly(3,4-ethylenedioxythiophene) (PEDOT)/TiO 2 composite fibers were fabricated and applied as the supercapacitor electrode materials. TiO 2 fibers were prepared as substrates for the vapor-phase polymerization process, by electrospinning and calcination in air. The symmetric supercapacitor cells assembled with the resulting composites were studied by a series of electrical measurements including cyclic voltammetry, charge-discharge characterization and electrochemical impedance spectroscopy. To further understand the capacitive behavior, the band gap energy of the composite fibers and the specific surface area of TiO 2 fibers calcined at varied temperatures were measured. The highest specific capacitance of PEDOT on TiO 2 fibers to date, 87.9 F g-1 , was achieved with the composite fibers prepared by vapor-phase polymerization at 50 °C on the TiO 2 fibers calcined at 550 °C. The pseudocapacitance and the reversibility of PEDOT were improved in comparison to other PEDOT/TiO 2 binary composites.