Solid-state ionics have attracted great interest in many fields of science and technology owing to their properties and applications. Some of these ionic conductors exhibit high ionic conductivity comparable to liquid electrolytes coupled with high stability against heat or mechanical damage. One of the most fruitful results of studying the solid-state ionics was the discovery of the superionic conductivity of silver iodide (AgI). AgI is a mixture of b and g phases at ambient temperature and it undergoes phase transition into the a phase at 146 8C. The a-AgI is known as a superionic conductor [1] and shows high silver ionic conductivity of over 1 S cm À1 . The conductivity of the a-AgI is comparable to that of liquid sulfuric acid, and is even higher than that of liquid AgI. In the a phase, the iodide ions solely form the crystal sublattice, and the silver ions diffuse over the numerous sites that exist inside the sublattice of iodide. [2] However, the highly ion-conductive phase appears only at high temperatures so far, and this makes it unsuitable for practical applications.Recently, nanomaterials have attracted a great deal of interest in scientific research and industrial applications. Their unique properties, based on their large surface-to-volume ratio and quantum size effect, are quite different from those of bulk materials. [3] In particular, a nanosized material has a characteristic phase behavior, [4] for example, the melting point of gold decreases with a decrease in the mean diameter. [4a, 5] Nanosized AgI, such as a nanoplate [6] or nanowire, [7] also shows a decrease in the phase transition temperature, which contributes to stabilizing the superionic phase at low temperature. [8] According to these results, it is expected that small AgI nanoparticles (NPs) could be used to achieve superionic conduction at ambient temperature. To date, methods for the preparation of AgI NPs with diameters above 10 nm have been reported < ; [8,9] however, to the best of our knowledge only one example of sub-10 nm AgI NPs has been described, in which the phase behavior is not clear. [10] Herein, we report on the successful synthesis of sub-10 nm AgI NPs, and the high stability of the a phase.The AgI NPs were synthesized by treating silver nitrate (AgNO 3 ) with potassium iodide (KI) in an aqueous solution in the presence of poly-N-vinyl-2-pyrrolidone (PVP) as a protective polymer (see the Supporting Information). Figure 1 shows a transmission electron microscope (TEM) image of the obtained AgI NPs and the size distribution. Their mean diameter was estimated to be 6.3 AE 4.2 nm. To date, the size of AgI NPs is reported to be controlled in the range of 11-40 nm by using sodium iodide. [8] We succeeded in preparing AgI NPs with a diameter of approximately 6 nm by using KI as an iodide source. Our results suggest that the potassium cation inhibits the growth of AgI nanocrystals, as PVP does. Similar cases have been reported for [a] S. COMMUNICATIONpreparing metal or semiconductor NPs, in which surface chemicals suppr...

Carbon materials, such as graphene nanoflakes, carbon nanotubes, and fullerene, can be widely used to store hydrogen, and doping these materials with lithium (Li) generally increases their H2-storage densities. Unfortunately, Li is expensive; therefore, alternative metals are required to realize a hydrogen-based society. Sodium (Na) is an inexpensive element with chemical properties that are similar to those of lithium. In this study, we used density functional theory to systematically investigate how hydrogen molecules interact with Na-doped graphene nanoflakes. A graphene nanoflake (GR) was modeled by a large polycyclic aromatic hydrocarbon composed of 37 benzene rings, with GR-Na-(H2)n and GR-Na+-(H2)n (n = 0–12) clusters used as hydrogen storage systems. Data obtained for the Na system were compared with those of the Li system. The single-H2 GR-Li and GR-Na systems (n = 1) exhibited binding energies (per H2 molecule) of 3.83 and 2.72 kcal/mol, respectively, revealing that the Li system has a high hydrogen-storage ability. This relationship is reversed from n = 4 onwards; the Na systems exhibited larger or similar binding energies for n = 4–12 than the Li-systems. The present study strongly suggests that Na can be used as an alternative metal to Li in H2-storage applications. The H2-storage mechanism in the Na system is also discussed based on the calculated results.

Hydrogen peroxide (H 2 O 2 ) is a unique molecule that is applied in various fields, including energy chemistry, astrophysics, and medicine. H 2 O 2 readily forms clusters with water molecules. In the present study, the reactions of ionized H 2 O 2 –water clusters, H 2 O 2 + (H 2 O) n , after vertical ionization of the parent neutral cluster were investigated using the direct ab initio molecular dynamics (AIMD) method to elucidate the reaction mechanism. Clusters with one to five water molecules, H 2 O 2 –(H 2 O) n ( n = 1–5), were examined, and the reaction of [H 2 O 2 + (H 2 O) n ] ver was tracked from the vertical ionization point to the product state, where [H 2 O 2 + (H 2 O) n ] ver is the vertical ionization state (hole is localized on H 2 O 2 ). After ionization, fast proton transfer (PT) from H 2 O 2 + to the water cluster (H 2 O) n was observed in all clusters. The HOO radical and H 3 O + (H 2 O) n −1 were formed as products. The PT reaction proceeds directly without an activation barrier. The PT times for n = 1–5 were calculated to be 36.0, 9.8, 8.3, 7.7, and 7.1 fs, respectively, at the MP2/6-311++G(d,p) level, indicating that PT in these clusters is a very fast process, and the PT time is not dependent on the cluster size ( n ), except in the case of n = 1, where the PT time was slightly longer because the bond distance and angle of the hydrogen bond in n = 1 were deformed from the standard structure. The reaction mechanism was discussed based on these results.