TY - JOUR AB - Non-aqueous lithium-oxygen batteries cycle by forming lithium peroxide during discharge and oxidizing it during recharge. The significant problem of oxidizing the solid insulating lithium peroxide can greatly be facilitated by incorporating redox mediators that shuttle electron-holes between the porous substrate and lithium peroxide. Redox mediator stability is thus key for energy efficiency, reversibility, and cycle life. However, the gradual deactivation of redox mediators during repeated cycling has not conclusively been explained. Here, we show that organic redox mediators are predominantly decomposed by singlet oxygen that forms during cycling. Their reaction with superoxide, previously assumed to mainly trigger their degradation, peroxide, and dioxygen, is orders of magnitude slower in comparison. The reduced form of the mediator is markedly more reactive towards singlet oxygen than the oxidized form, from which we derive reaction mechanisms supported by density functional theory calculations. Redox mediators must thus be designed for stability against singlet oxygen. AU - Kwak, Won-Jin AU - Kim, Hun AU - Petit, Yann K. AU - Leypold, Christian AU - Nguyen, Trung Thien AU - Mahne, Nika AU - Redfern, Paul AU - Curtiss, Larry A. AU - Jung, Hun-Gi AU - Borisov, Sergey M. AU - Freunberger, Stefan Alexander AU - Sun, Yang-Kook ID - 7280 JF - Nature Communications SN - 2041-1723 TI - Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen VL - 10 ER - TY - JOUR AB - Singlet oxygen (1O2) causes a major fraction of the parasitic chemistry during the cycling of non‐aqueous alkali metal‐O2 batteries and also contributes to interfacial reactivity of transition‐metal oxide intercalation compounds. We introduce DABCOnium, the mono alkylated form of 1,4‐diazabicyclo[2.2.2]octane (DABCO), as an efficient 1O2 quencher with an unusually high oxidative stability of ca. 4.2 V vs. Li/Li+. Previous quenchers are strongly Lewis basic amines with too low oxidative stability. DABCOnium is an ionic liquid, non‐volatile, highly soluble in the electrolyte, stable against superoxide and peroxide, and compatible with lithium metal. The electrochemical stability covers the required range for metal–O2 batteries and greatly reduces 1O2 related parasitic chemistry as demonstrated for the Li–O2 cell. AU - Petit, Yann K. AU - Leypold, Christian AU - Mahne, Nika AU - Mourad, Eléonore AU - Schafzahl, Lukas AU - Slugovc, Christian AU - Borisov, Sergey M. AU - Freunberger, Stefan Alexander ID - 7276 IS - 20 JF - Angewandte Chemie International Edition SN - 1433-7851 TI - DABCOnium: An efficient and high-voltage stable singlet oxygen quencher for metal-O2 cells VL - 58 ER - TY - JOUR AB - Li–O2 batteries are plagued by side reactions that cause poor rechargeability and efficiency. These reactions were recently revealed to be predominantly caused by singlet oxygen, which can be neutralized by chemical traps or physical quenchers. However, traps are irreversibly consumed and thus only active for a limited time, and so far identified quenchers lack oxidative stability to be suitable for typically required recharge potentials. Thus, reducing the charge potential within the stability limit of the quencher and/or finding more stable quenchers is required. Here, we show that dimethylphenazine as a redox mediator decreases the charge potential well within the stability limit of the quencher 1,4-diazabicyclo[2.2.2]octane. The quencher can thus mitigate the parasitic reactions without being oxidatively decomposed. At the same time the quencher protects the redox mediator from singlet oxygen attack. The mutual conservation of the redox mediator and the quencher is rational for stable and effective Li–O2 batteries. AU - Kwak, Won-Jin AU - Freunberger, Stefan Alexander AU - Kim, Hun AU - Park, Jiwon AU - Nguyen, Trung Thien AU - Jung, Hun-Gi AU - Byon, Hye Ryung AU - Sun, Yang-Kook ID - 7281 IS - 11 JF - ACS Catalysis SN - 2155-5435 TI - Mutual conservation of redox mediator and singlet oxygen quencher in Lithium–Oxygen batteries VL - 9 ER - TY - JOUR AB - Interphases that form on the anode surface of lithium-ion batteries are critical for performance and lifetime, but are poorly understood. Now, a decade-old misconception regarding a main component of the interphase has been revealed, which could potentially lead to improved devices. AU - Freunberger, Stefan Alexander ID - 7282 IS - 9 JF - Nature Chemistry SN - 1755-4330 TI - Interphase identity crisis VL - 11 ER - TY - JOUR AB - Potassium–air batteries, which suffer from oxygen cathode and potassium metal anode degradation, can be cycled thousands of times when an organic anode replaces the metal. AU - Petit, Yann K. AU - Freunberger, Stefan Alexander ID - 7283 IS - 4 JF - Nature Materials SN - 1476-1122 TI - Thousands of cycles VL - 18 ER - TY - JOUR AB - In this issue of Joule, Dongmin Im and coworkers from Samsung in South Korea describe a prototype lithium-O2 battery that reaches ∼700 Wh kg–1 and ∼600 Wh L–1 on the cell level. They cut all components to the minimum to reach this value. Difficulties filling the pores with discharge product and inhomogeneous cell utilization turn out to limit the achievable energy. Their work underlines the importance of reporting performance with respect to full cell weight and volume. AU - Prehal, Christian AU - Freunberger, Stefan Alexander ID - 7284 IS - 2 JF - Joule SN - 2542-4351 TI - Li-O2 cell-scale energy densities VL - 3 ER - TY - GEN AB - Telencephalic organoids generated from human pluripotent stem cells (hPSCs) are emerging as an effective system to study the distinct features of the developing human brain and the underlying causes of many neurological disorders. While progress in organoid technology has been steadily advancing, many challenges remain including rampant batch-to-batch and cell line-to-cell line variability and irreproducibility. Here, we demonstrate that a major contributor to successful cortical organoid production is the manner in which hPSCs are maintained prior to differentiation. Optimal results were achieved using fibroblast-feeder-supported hPSCs compared to feeder-independent cells, related to differences in their transcriptomic states. Feeder-supported hPSCs display elevated activation of diverse TGFβ superfamily signaling pathways and increased expression of genes associated with naïve pluripotency. We further identify combinations of TGFβ-related growth factors that are necessary and together sufficient to impart broad telencephalic organoid competency to feeder-free hPSCs and enable reproducible formation of brain structures suitable for disease modeling. AU - Watanabe, Momoko AU - Haney, Jillian R. AU - Vishlaghi, Neda AU - Turcios, Felix AU - Buth, Jessie E. AU - Gu, Wen AU - Collier, Amanda J. AU - Miranda, Osvaldo AU - Chen, Di AU - Sabri, Shan AU - Clark, Amander T. AU - Plath, Kathrin AU - Christofk, Heather R. AU - Gandal, Michael J. AU - Novitch, Bennett G. ID - 7358 T2 - bioRxiv TI - TGFβ superfamily signaling regulates the state of human stem cell pluripotency and competency to create telencephalic organoids ER - TY - CONF AB - The genus g(G) of a graph G is the minimum g such that G has an embedding on the orientable surface M_g of genus g. A drawing of a graph on a surface is independently even if every pair of nonadjacent edges in the drawing crosses an even number of times. The Z_2-genus of a graph G, denoted by g_0(G), is the minimum g such that G has an independently even drawing on M_g. By a result of Battle, Harary, Kodama and Youngs from 1962, the graph genus is additive over 2-connected blocks. In 2013, Schaefer and Stefankovic proved that the Z_2-genus of a graph is additive over 2-connected blocks as well, and asked whether this result can be extended to so-called 2-amalgamations, as an analogue of results by Decker, Glover, Huneke, and Stahl for the genus. We give the following partial answer. If G=G_1 cup G_2, G_1 and G_2 intersect in two vertices u and v, and G-u-v has k connected components (among which we count the edge uv if present), then |g_0(G)-(g_0(G_1)+g_0(G_2))|<=k+1. For complete bipartite graphs K_{m,n}, with n >= m >= 3, we prove that g_0(K_{m,n})/g(K_{m,n})=1-O(1/n). Similar results are proved also for the Euler Z_2-genus. We express the Z_2-genus of a graph using the minimum rank of partial symmetric matrices over Z_2; a problem that might be of independent interest. AU - Fulek, Radoslav AU - Kyncl, Jan ID - 7401 SN - 1868-8969 T2 - 35th International Symposium on Computational Geometry (SoCG 2019) TI - Z_2-Genus of graphs and minimum rank of partial symmetric matrices VL - 129 ER - TY - CHAP AB - We illustrate the ingredients of the state-of-the-art of model-based approach for the formal design and verification of cyber-physical systems. To capture the interaction between a discrete controller and its continuously evolving environment, we use the formal models of timed and hybrid automata. We explain the steps of modeling and verification in the tools Uppaal and SpaceEx using a case study based on a dual-chamber implantable pacemaker monitoring a human heart. We show how to design a model as a composition of components, how to construct models at varying levels of detail, how to establish that one model is an abstraction of another, how to specify correctness requirements using temporal logic, and how to verify that a model satisfies a logical requirement. AU - Alur, Rajeev AU - Giacobbe, Mirco AU - Henzinger, Thomas A AU - Larsen, Kim G. AU - Mikučionis, Marius ED - Steffen, Bernhard ED - Woeginger, Gerhard ID - 7453 SN - 1611-3349 T2 - Computing and Software Science TI - Continuous-time models for system design and analysis VL - 10000 ER - TY - JOUR AB - We report the fabrication of BaTiO3-Ni magnetoelectric nanocomposites comprising of BaTiO3 nanotubes surrounded by Ni matrix. BaTiO3 nanotubes obtained from the hydrothermal transformation of TiO2 have both inner and outer surfaces, which facilitates greater magnetoelectric coupling with the surrounding Ni matrix. The magnetoelectric coupling was studied by measuring the piezoelectric behavior in the presence of an in-plane direct magnetic field. A higher magnetoelectric voltage coefficient of 110 mV/cm·Oe was obtained, because of better coupling between Ni and BaTiO3 through the walls of the nanotubes. Such nanocomposite developed directly on Ti substrate may lead to efficient fabrication of magnetoelectric devices. AU - Vadla, Samba Siva AU - Costanzo, Tommaso AU - John, Subish AU - Caruntu, Gabriel AU - Roy, Somnath C. ID - 7459 JF - Scripta Materialia SN - 1359-6462 TI - Local probing of magnetoelectric coupling in BaTiO3-Ni 1–3 composites VL - 159 ER -