The diffusion rate of oxygen has a significant impact on the power density, rate capacity, discharge capacity, and electrolyte stability of lithium-air batteries (H. 2012,5,[7893][7894][7895][7896][7897]. Oxygen diffusivity in the solid porous cathodes of gas-based batteries is typically obtained by employing a few electrochemical models. In addition to the indirect computing characteristic, previous methods of evaluating oxygen diffusivity require multiple voltage-current experiments over intact lithium-air batteries, and can cause unnecessary costs resulting from the waste of materials from other battery components (J. Read, J. Electrochem. Soc. 2006, 153, A96-A100). In this report, through derivation and analytical design, a methodology is proposed for the direct out-of-cell oxygen diffusivity measurement in lithium-air batteries. The proposed electrochemical devices allow for efficient diffusivity measurements in porous solid cathodes, as well as subsequent quantitative pre-evaluation of important battery parameters including electrode porosity, thickness, and tortuosity. The proposed methodology is expected to facilitate the development of lowcost battery systems for a variety of applications, such as largecapacity automobile batteries and electronics.-With a high energy density and simple operation, the lithiumair battery has evolved to be an exceptionally promising candidate for mitigating the increasing unsustainability from the aggravated consumption of fossil resources. [1][2][3] Despite tremendous interest drawn to the lithium-air battery, it still suffers from a number of issues associated with the performance of its electrolyte and electrode materials. [2,4] High-performance electrolyte/electrode materials not only provide large energy densities, but also endure a number of operation cycles. Both aspects largely rely on efficient mass transport, that is, lithiumion conduction and oxygen diffusion in the operation of the lithium-air battery. [5,6] Unlike electrode-supported solid-oxide fuel cells, the maximum attainable current density is limited by polarization losses at the electrodes; in the case of bulk lithium-air batteries, the Li-ion diffusion coefficient in the electrolyte is lower than the fuel gas diffusion at the cathode. However, for lithium-air batteries with nanostructured cathodes, the cathode gas diffusion is governed by Knudsen diffusion, and thus the total mass transport associated with the batteries can be limited by cathode gas diffusion. Conductivity of lithium ions has been measured through electrochemical impedance spectroscopy and the galvanostatic intermittent titration technique, among others. [7,8] Except for indirect methods through computations based on multiple voltage-current measurements, an efficient methodology for the direct measurement of oxygen diffusivity in lithium-air batteries is still lacking. In this report, we show that direct oxygen diffusivity measurements can be realized by using a series of electrochemical devices, upon analytical derivation based on c...

Identifying key toxicants in sediment is a great challenge, particularly if nontarget toxicants are involved. To identify the contaminants responsible for sediment toxicity to Chironomus dilutus in Guangzhou reach of the Pearl River in South China, passive dosing and in vivo toxicity testing were incorporated into effect-directed analysis (EDA) to account for bioavailability. Fractionation of sediment extracts was performed with gel permeation chromatography and reverse phase liquid chromatography sequentially. Polydimethylsiloxane served as passive dosing matrix for midge bioassays. The fractions showing abnormal enzymatic response were subject to a nontarget analysis, which screened out 15 candidate toxicants. The concentrations of the screened contaminants (log-based organic carbon normalized) in sediments of 10 sites were compared to sediment toxicity (10 and 20 day mortality and 10 day enzymatic response) to C. dilutus using correlation analyses. The results suggested that oxidative stress induced by cypermethrin, dimethomorph, pebulate and thenylchlor may have in part caused the observed toxicity to C. dilutus. The present study shows that EDA procedures coupled with passive dosing and in vivo toxicity testing can be effective in identifying sediment-bound toxicants, which may pose high risk to benthic organisms but are not routinely monitored and/or regulated. The findings of the present study highlight the importance of incorporating environmentally relevant approaches in assessing sediment heavily impacted by a multitude of contaminants, which is often the case in many developing countries.

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Whole life-cycle bioassays with Chironomus dilutus were performed to evaluate sediment toxicity in Tai Lake, a typical freshwater lake in China. Meanwhile, contaminants of concern were analyzed in sediment. The sediments in Tai Lake showed no acute mortality in 10-day testing to C. dilutus. After chronic exposure to the sediments, however, adverse effects-including decreased survival and sublethal impairments of growth, emergence, and fecundity-were observed at most sites in Tai Lake. A variety of contaminants were detected in sediment with the total concentrations in the range of 504-889 ng/g dry weight (dw) for polycyclic aromatic hydrocarbons, 0.56-1.81 ng/g dw for polychlorinated biphenyls, 38.6-87.8 ng/g dw for polybrominated diphenyl ethers, 8.34-14.2 ng/g dw for organochlorine pesticides, 1.27-2.95 ng/g dw for organophosphate pesticides, 0.11-0.21 ng/g dw for pyrethroid pesticides, and 332-609 µg/g dw for metals. Finally, a canonical correlation analysis was applied to link chronic sediment toxicity to the toxic units of individual contaminants. Results suggested that two pesticides (hexachlorocyclohexane and chlorpyrifos) and two metals (chromium and nickel) in sediments from Tai Lake were the potential contributors to the noted toxicity in C. dilutus in the life-cycle toxicity testing. In conclusion, acute bioassays with the benthos were not sensitive enough to assess sediment toxicity in freshwater lakes in China, and it is desirable to integrate chronic toxicity testing with chemical analysis to better understand sediment risk.

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