@article{7305, abstract = {When lithium–oxygen batteries discharge, O2 is reduced at the cathode to form solid Li2O2. Understanding the fundamental mechanism of O2 reduction in aprotic solvents is therefore essential to realizing their technological potential. Two different models have been proposed for Li2O2 formation, involving either solution or electrode surface routes. Here, we describe a single unified mechanism, which, unlike previous models, can explain O2 reduction across the whole range of solvents and for which the two previous models are limiting cases. We observe that the solvent influences O2 reduction through its effect on the solubility of LiO2, or, more precisely, the free energy of the reaction LiO2* ⇌ Li(sol)+ + O2−(sol) + ion pairs + higher aggregates (clusters). The unified mechanism shows that low-donor-number solvents are likely to lead to premature cell death, and that the future direction of research for lithium–oxygen batteries should focus on the search for new, stable, high-donor-number electrolytes, because they can support higher capacities and can better sustain discharge.}, author = {Johnson, Lee and Li, Chunmei and Liu, Zheng and Chen, Yuhui and Freunberger, Stefan Alexander and Ashok, Praveen C. and Praveen, Bavishna B. and Dholakia, Kishan and Tarascon, Jean-Marie and Bruce, Peter G.}, issn = {1755-4330}, journal = {Nature Chemistry}, number = {12}, pages = {1091--1099}, publisher = {Springer Nature}, title = {{The role of LiO2 solubility in O2 reduction in aprotic solvents and its consequences for Li–O2 batteries}}, doi = {10.1038/nchem.2101}, volume = {6}, year = {2014}, } @article{7304, abstract = {Lithium-air batteries have received extraordinary attention recently owing to their theoretical gravimetric energies being considerably higher than those of Li-ion batteries. There are, however, significant challenges to practical implementation, including low energy efficiency, cycle life, and power capability. These are due primarily to the lack of fundamental understanding of oxygen reduction and evolution reaction kinetics and parasitic reactions between oxygen redox intermediate species and nominally inactive battery components such as carbon in the oxygen electrode and electrolytes. In this article, we discuss recent advances in the mechanistic understanding of oxygen redox reactions in nonaqueous electrolytes and the search for electrolytes and electrode materials that are chemically stable in the oxygen electrode. In addition, methods to protect lithium metal against corrosion by water and dendrite formation in aqueous lithium-air batteries are discussed. Further materials innovations lie at the heart of research and development efforts that are needed to enable the development of lithium-oxygen batteries with enhanced round-trip efficiency and cycle life.}, author = {Kwabi, D.G. and Ortiz-Vitoriano, N. and Freunberger, Stefan Alexander and Chen, Y. and Imanishi, N. and Bruce, P.G. and Shao-Horn, Y.}, issn = {0883-7694}, journal = {MRS Bulletin}, number = {5}, pages = {443--452}, publisher = {CUP}, title = {{Materials challenges in rechargeable lithium-air batteries}}, doi = {10.1557/mrs.2014.87}, volume = {39}, year = {2014}, } @article{7301, abstract = {Several problems arise at the O2 (positive) electrode in the Li-air battery, including solvent/electrode decomposition and electrode passivation by insulating Li2O2. Progress partially depends on exploring the basic electrochemistry of O2 reduction. Here we describe the effect of complexing-cations on the electrochemical reduction of O2 in DMSO in the presence and absence of a Li salt. The solubility of alkaline peroxides in DMSO is enhanced by the complexing-cations, consistent with their strong interaction with reduced O2. The complexing-cations also increase the rate of the 1-electron O2 reduction to O2•– by up to six-fold (k° = 2.4 ×10–3 to 1.5 × 10–2 cm s–1) whether or not Li+ ions are present. In the absence of Li+, the complexing-cations also promote the reduction of O2•– to O22–. In the presence of Li+ and complexing-cations, and despite the interaction of the reduced O2 with the latter, SERS confirms that the product is still Li2O2.}, author = {Li, Chunmei and Fontaine, Olivier and Freunberger, Stefan Alexander and Johnson, Lee and Grugeon, Sylvie and Laruelle, Stéphane and Bruce, Peter G. and Armand, Michel}, issn = {1932-7447}, journal = {The Journal of Physical Chemistry C}, number = {7}, pages = {3393--3401}, publisher = {ACS}, title = {{Aprotic Li–O2 battery: Influence of complexing agents on oxygen reduction in an aprotic solvent}}, doi = {10.1021/jp4093805}, volume = {118}, year = {2014}, } @article{7300, abstract = {Photoinduced electron transfer (PET), which causes pH-dependent quenching of fluorescent dyes, is more effectively introduced by phenolic groups than by amino groups which have been much more commonly used so far. That is demonstrated by fluorescence measurements involving several classes of fluorophores. Electrochemical measurements show that PET in several amino-modified dyes is thermodynamically favorable, even though it was not experimentally found, underlining the importance of kinetic aspects to the process. Consequently, the attachment of phenolic groups allows for fast and simple preparation of a wide selection of fluorescent pH-probes with tailor-made spectral properties, sensitive ranges, and individual advantages, so that a large number of applications can be realized. Fluorophores carrying phenolic groups may also be used for sensing analytes other than pH or molecular switching and signaling.}, author = {Aigner, Daniel and Freunberger, Stefan Alexander and Wilkening, Martin and Saf, Robert and Borisov, Sergey M. and Klimant, Ingo}, issn = {0003-2700}, journal = {Analytical Chemistry}, number = {18}, pages = {9293--9300}, publisher = {ACS}, title = {{Enhancing photoinduced electron transfer efficiency of fluorescent pH-probes with halogenated phenols}}, doi = {10.1021/ac502513g}, volume = {86}, year = {2014}, } @article{7361, abstract = {Bistable switches are fundamental regulatory elements of complex systems, ranging from electronics to living cells. Designed genetic toggle switches have been constructed from pairs of natural transcriptional repressors wired to inhibit one another. The complexity of the engineered regulatory circuits can be increased using orthogonal transcriptional regulators based on designed DNA-binding domains. However, a mutual repressor-based toggle switch comprising DNA-binding domains of transcription-activator-like effectors (TALEs) did not support bistability in mammalian cells. Here, the challenge of engineering a bistable switch based on monomeric DNA-binding domains is solved via the introduction of a positive feedback loop composed of activators based on the same TALE domains as their opposing repressors and competition for the same DNA operator site. This design introduces nonlinearity and results in epigenetic bistability. This principle could be used to employ other monomeric DNA-binding domains such as CRISPR for applications ranging from reprogramming cells to building digital biological memory.}, author = {Lebar, Tina and Bezeljak, Urban and Golob, Anja and Jerala, Miha and Kadunc, Lucija and Pirš, Boštjan and Stražar, Martin and Vučko, Dušan and Zupančič, Uroš and Benčina, Mojca and Forstnerič, Vida and Gaber, Rok and Lonzarić, Jan and Majerle, Andreja and Oblak, Alja and Smole, Anže and Jerala, Roman}, issn = {2041-1723}, journal = {Nature Communications}, number = {1}, publisher = {Springer Nature}, title = {{A bistable genetic switch based on designable DNA-binding domains}}, doi = {10.1038/ncomms6007}, volume = {5}, year = {2014}, }