Rate-Dependent Nucleation and Growth of NaO2 in Na-O2 Batteries

Understanding the oxygen reduction reaction kinetics in the presence of Na ions and the formation mechanism of discharge product(s) is key to enhancing Na–O2 battery performance. Here we show NaO2 as the only discharge product from Na–O2 cells with carbon nanotubes in 1,2-dimethoxyethane from X-ray diffraction and Raman spectroscopy. Sodium peroxide dihydrate was not detected in the discharged electrode with up to 6000 ppm of H2O added to the electrolyte, but it was detected with ambient air exposure. In addition, we show that the sizes and distributions of NaO2 can be highly dependent on the discharge rate, and we discuss the formation mechanisms responsible for this rate dependence. Micron-sized (∼500 nm) and nanometer-scale (∼50 nm) cubes were found on the top and bottom of a carbon nanotube (CNT) carpet electrode and along CNT sidewalls at 10 mA/g, while only micron-scale cubes (∼2 μm) were found on the top and bottom of the CNT carpet at 1000 mA/g, respectively.Seventh Framework Programme (European Commission) (Marie Curie International Outgoing Fellowship, 2007-2013))National Science Foundation (U.S.) (MRSEC Program, award number DMR-0819762)Robert Bosch GmbH (Bosch Energy Research Network (BERN) Grant)China Clean Energy Research Center-Clean Vehicles Consortium (CERC-CVC) (award number DE-PI0000012)Skolkovo Institute of Science and Technology (Skoltech-MIT Center for Electochemical Energy Storage

Pilot Assessment of Soil-Transmitted Helminthiasis in the Context of Transmission Assessment Surveys for Lymphatic Filariasis in Benin and Tonga

<div><p>Background</p><p>Mass drug administration (MDA) for lymphatic filariasis (LF) programs has delivered more than 2 billion treatments of albendazole, in combination with either ivermectin or diethylcarbamazine, to communities co-endemic for soil-transmitted helminthiasis (STH), reducing the prevalence of both diseases. A transmission assessment survey (TAS) is recommended to determine if MDA for LF can be stopped within an evaluation unit (EU) after at least five rounds of annual treatment. The TAS also provides an opportunity to simultaneously assess the impact of these MDAs on STH and to determine the frequency of school-based MDA for STH after community-wide MDA is no longer needed for LF.</p><p>Methodology/Principal Findings</p><p>Pilot studies conducted in Benin and Tonga assessed the feasibility of a coordinated approach. Of the schools (clusters) selected for a TAS in each EU, a subset of 5 schools per STH ecological zone was randomly selected, according to World Health Organization (WHO) guidelines, for the coordinated survey. In Benin, 519 children were sampled in 5 schools and 22 (4.2%) had STH infection (<i>A. lumbricoides</i>, <i>T. trichiura</i>, or hookworm) detected using the Kato-Katz method. All infections were classified as light intensity under WHO criteria. In Tonga, 10 schools were chosen for the coordinated TAS and STH survey covering two ecological zones; 32 of 232 (13.8%) children were infected in Tongatapu and 82 of 320 (25.6%) in Vava'u and Ha'apai. All infections were light-intensity with the exception of one with moderate-intensity <i>T. trichiura</i>.</p><p>Conclusions</p><p>Synchronous assessment of STH with TAS is feasible and provides a well-timed evaluation of infection prevalence to guide ongoing treatment decisions at a time when MDA for LF may be stopped. The coordinated field experiences in both countries also suggest potential time and cost savings. Refinement of a coordinated TAS and STH sampling methodology should be pursued, along with further validation of alternative quantitative diagnostic tests for STH that can be used with preserved stool specimens.</p></div

Sampling strategy for coordinated TAS and STH surveys.

1<p>5 schools per ecological zone; all schools randomly selected from TAS sample except two schools in Tonga that were included in 2001–2002 STH survey.</p

Comparison of TAS and STH survey criteria.

1<p>World Health Organization (2011) Global Programme to Eliminate Lymphatic Filariasis: Monitoring and epidemiological assessment of mass drug administration: a manual for national elimination programs. Geneva.</p>2<p>World Health Organization (2011) Helminth control in school-age children: a guide for managers of control programmes – 2nd ed. Geneva.</p>3<p>Lot quality assurance sampling.</p>4<p>For <i>W. bancrofti</i>.</p

Benin TAS and STH survey results.

1<p>Mean epg was only calculated for positive cases.</p

Benin STH infection by age group.

<p>Benin STH infection by age group.</p

Chemical Instability of Dimethyl Sulfoxide in Lithium–Air Batteries

Although dimethyl sulfoxide (DMSO) has emerged as a promising solvent for Li–air batteries, enabling reversible oxygen reduction and evolution (2Li + O₂ ⇔ Li₂O₂), DMSO is well known to react with superoxide-like species, which are intermediates in the Li–O₂ reaction, and LiOH has been detected upon discharge in addition to Li₂O₂. Here we show that toroidal Li₂O₂ particles formed upon discharge gradually convert into flake-like LiOH particles upon prolonged exposure to a DMSO-based electrolyte, and the amount of LiOH detectable increases with increasing rest time in the electrolyte. Such time-dependent electrode changes upon and after discharge are not typically monitored and can explain vastly different amounts of Li₂O₂ and LiOH reported in oxygen cathodes discharged in DMSO-based electrolytes. The formation of LiOH is attributable to the chemical reactivity of DMSO with Li₂O₂ and superoxide-like species, which is supported by our findings that commercial Li₂O₂ powder can decompose DMSO to DMSO₂, and that the presence of KO₂ accelerates both DMSO decomposition and conversion of Li₂O₂ into LiOH

Evaluation unit characteristics for LF and STH assessment.

1<p>Excludes children <5 years old and under 90 cm height.</p>2<p>Excludes children <2 years old.</p

Rate-Dependent Nucleation and Growth of NaO₂ in Na–O₂ Batteries

Understanding the oxygen reduction reaction kinetics in the presence of Na ions and the formation mechanism of discharge product(s) is key to enhancing Na–O₂ battery performance. Here we show NaO₂ as the only discharge product from Na–O₂ cells with carbon nanotubes in 1,2-dimethoxyethane from X-ray diffraction and Raman spectroscopy. Sodium peroxide dihydrate was not detected in the discharged electrode with up to 6000 ppm of H₂O added to the electrolyte, but it was detected with ambient air exposure. In addition, we show that the sizes and distributions of NaO₂ can be highly dependent on the discharge rate, and we discuss the formation mechanisms responsible for this rate dependence. Micron-sized (∼500 nm) and nanometer-scale (∼50 nm) cubes were found on the top and bottom of a carbon nanotube (CNT) carpet electrode and along CNT sidewalls at 10 mA/g, while only micron-scale cubes (∼2 μm) were found on the top and bottom of the CNT carpet at 1000 mA/g, respectively

Oxygen Reduction Reaction in Highly Concentrated Electrolyte Solutions of Lithium Bis(trifluoromethanesulfonyl)amide/Dimethyl Sulfoxide

The performance of current Li–air batteries is greatly limited by critical obstacles such as electrolyte decomposition, high charging overpotentials, and limited cycle life. Thus, much effort is devoted to fundamental studies to understand the mechanisms of discharge/charge processes and overcome the above-mentioned obstacles. In particular, the search for new stable electrolytes is vital for long-lasting and highly cyclable batteries. The highly reactive lithium superoxide intermediate (LiO₂) produced during discharge process can react with the electrolyte and produce a variety of byproducts that will shorten battery life span. To study this degradation mechanism, we investigated oxygen reduction reaction (ORR) in highly concentrated electrolyte solutions of lithium bis­(trifluoromethanesulfonyl)­amide (Li­[TFSA])/dimethyl sulfoxide (DMSO). On the basis of rotating ring disk electrode measurements, we showed that LiO₂ dissolution can be limited by increasing lithium salt concentration over 2.3 mol dm^–3. Our Raman results suggested that this phenomenon can be related to lack of free DMSO molecules and increasing DMSO–Li⁺ interactions with higher Li⁺ concentration. X-ray diffraction measurements for the products of ORR suggested that the side reaction of DMSO with Li₂O₂ and/or LiO₂ could be suppressed by decreasing the solubility of LiO₂ in highly concentrated electrolytes