Chemical composition of the discharge products as well as charging overpotential of the Na–air cell is correlated with the kinetic parameters.

We report the electronic structure of the iron-chalcogenide superconductor, Fe 1.04 ͑Te 0.66 Se 0.34 ͒, obtained with high-resolution angle-resolved photoemission spectroscopy and density-functional calculations. In photoemission measurements, various photon energies and polarizations are exploited to study the Fermi surface topology and symmetry properties of the bands. The measured band structure and their symmetry characters qualitatively agree with our density-functional theory calculations of Fe͑Te 0.66 Se 0.34 ͒, although the band structure is renormalized by about a factor of three. We find that the electronic structures of this iron chalcogenides and the iron pnictides have many aspects in common; however, significant differences exist near the ⌫ point. For Fe 1.04 Te 0.66 Se 0.34 , there are clearly separated three bands with distinct even or odd symmetry that cross the Fermi energy ͑E F ͒ near the zone center, which contribute to three holelike Fermi surfaces. Especially, both experiments and calculations show a holelike elliptical Fermi surface at the zone center. Moreover, no sign of spin density wave was observed in the electronic structure and susceptibility measurements of this compound.

The absorbing layer in state-of-the-art colloidal quantum-dot solar cells is fabricated using a tedious layer-by-layer process repeated ten times. It is now shown that methanol, a common exchange solvent, is the main culprit, as extended exposure leaches off the surface halide passivant, creating carrier trap states. Use of a high-dipole-moment aprotic solvent eliminates this problem and is shown to produce state-of-the-art devices in far fewer steps.

Ultrathin amorphous FePO4 coating derived by atomic layer deposition (ALD) is used to coat the 5 V LiNi0.5Mn1.5O4 cathode material powders, which dramatically increases the capacity retention of LiNi0.5Mn1.5O4. It is believed that the amorphous FePO4 layer could act as a lithium‐ions reservoir and electrochemically active buffer layer during the charge/discharge cycling, helping achieve high capacities in LiNi0.5Mn1.5O4, especially at high current densities.

A binder-free three-dimensional (3D) nanostructured air electrode composed of vertically grown nitrogen doped carbon nanotubes on carbon paper (NCNT-CP) is developed and applied to Na−O 2 cells. The 3D architecture of the air electrode results in increased discharge capacity by optimizing the utilized area of the electrode material. The chemical and electrochemical reaction mechanisms of the cell are also explored with the use of synchrotron-based X-ray absorption spectroscopy (XAS). Investigation of the discharge product of Na−O 2 cells during discharge and charge cycles using X-ray absorption near-edge structure (XANES) indicates that both sodium superoxide and peroxide are produced under various physicochemical conditions and can be subsequently decomposed with different overpotentials. Furthermore, formation of carbonate-based parasitic products is also shown to restrict the cyclability of the cell.