Li-S) batteries is seriously restricted by their low sulfur loading and utilization, sluggish reaction kinetics, and poor cycling stability. [4,5] So far, appropriate active adsorption [6,7] and catalytic centers, such as metal sulfides, [8][9][10] oxides, [11][12][13] nitrides, [14] and vanadium compounds, [15] have been introduced to enhance the sulfur utilization and accelerate the reversible conversion between lithium polysulfides (LiPSs) and Li 2 S. [16,17] However, high weight percentages of these additives sacrifice the overall energy density of Li-S batteries. Single-atom metal catalysts (SACs) comprising monodispersed metal atoms on appropriate substrates have a theoretical 100% atom utilization efficiency, and therefore have a much higher activity than conventional bulk metal and nanoparticle catalysts. [18,19] Various SACs have been introduced into Li-S batteries to improve their electrochemical performance. [20][21][22] Generally, the effects of SACs have been attributed to their good adsorption ability to LiPSs and their high catalytic activity. However, the lack of a fundamental understanding of the catalysis mechanism and the material properties that govern catalytic activity have hindered the selection and rational design of SACs for Li-S batteries. In previous studies, the SACs were usually Single-atom metal catalysts (SACs) are used as sulfur cathode additives to promote battery performance, although the material selection and mechanism that govern the catalytic activity remain unclear. It is shown that d-p orbital hybridization between the single-atom metal and the sulfur species can be used as a descriptor for understanding the catalytic activity of SACs in Li-S batteries. Transition metals with a lower atomic number are found, like Ti, to have fewer filled anti-bonding states, which effectively bind lithium polysulfides (LiPSs) and catalyze their electrochemical reaction. A series of single-atom metal catalysts (Me = Mn, Cu, Cr, Ti) embedded in threedimensional (3D) electrodes are prepared by a controllable nitrogen coordination approach. Among them, the single-atom Ti-embedded electrode has the lowest electrochemical barrier to LiPSs reduction/Li 2 S oxidation and the highest catalytic activity, matching well with the theoretical calculations. By virtue of the highly active catalytic center of single-atom Ti on the conductive transport network, high sulfur utilization is achieved with a low catalyst loading (1 wt.%) and a high area-sulfur loading (8 mg cm −2 ). With good mechanical stability for bending, these 3D electrodes are suitable for fabricating bendable/foldable Li-S batteries for wearable electronics.

Topological aspects of the geometry of DNA and similar chiral molecules have received a lot of attention, while the topology of their electronic structure is less explored. Previous experiments have revealed that DNA can efficiently filter spin-polarized electrons between metal contacts, a process called chiral-induced spin-selectivity (CISS). However, the underlying correlation between chiral structure and electronic spin remains elusive. In this work, we reveal an orbital texture in the band structure, a topological characteristic induced by the chirality. We find that this orbital texture enables the chiral molecule to polarize the quantum orbital. This orbital polarization effect (OPE) induces spin polarization assisted by the spin-orbit interaction from a metal contact and leads to magnetorestistance and chiral separation. The orbital angular momentum of photoelectrons also plays an essential role in related photoemission experiments. Beyond CISS, we predict that OPE can induce spin-selective phenomena even in achiral but inversion-breaking materials.

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We have performed Raman-scattering measurements on a high-quality single crystal of the recently discovered Fe-based superconductor K0.8Fe1.6Se2 (Tc = 32 K). At least thirteen phonon modes were observed in the wave number range 10−300 cm −1 . The spectra possess a four-fold symmetry indicative of bulk vacancy order in the Fe-deficient planes. We perform a vibration analysis based on first-principles calculations, which both confirms the ordered structure and allows a complete mode assignment. We observe an anomaly at Tc in the 180 cm −1 Ag mode, which indicates a rather specific type of electron-phonon coupling.

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