Masashi Hattori

High energy density rechargeable magnesium battery using earth-abundant and non-toxic elements.

Rechargeable magnesium batteries are poised to be viable candidates for large-scale energy storage devices in smart grid communities and electric vehicles. However, the energy density of previously proposed rechargeable magnesium batteries is low, limited mainly by the cathode materials. Here, we present new design approaches for the cathode in order to realize a high-energy-density rechargeable magnesium battery system. Ion-exchanged MgFeSiO4 demonstrates a high reversible capacity exceeding 300 mAh·g−1 at a voltage of approximately 2.4 V vs. Mg. Further, the electronic and crystal structure of ion-exchanged MgFeSiO4 changes during the charging and discharging processes, which demonstrates the (de)insertion of magnesium in the host structure. The combination of ion-exchanged MgFeSiO4 with a magnesium bis(trifluoromethylsulfonyl)imide–triglyme electrolyte system proposed in this work provides a low-cost and practical rechargeable magnesium battery with high energy density, free from corrosion and safety problems.

Efficient hydrogen production from formic acid using TiO2-supported AgPd@Pd nanocatalysts

We report here the significant enhancement of catalytic activity of Ag–Pd bimetallic nanocatalysts with the formation of Ag–Pd catalysts having an average diameter of 4.2 ± 1.5 nm on TiO2 nanoparticles using a two-step microwave (MW)–polyol method. Data obtained using XRD and STEM-EDS indicated that Ag-Pd bimetallic nanocatalysts consisted of Ag82Pd18 alloy core and about 0.5 nm thick Pd shell, denoted as AgPd@Pd. The hydrogen production rate of AgPd@Pd/TiO2 from formic acid, 16.00 ± 0.89 L g−1 h−1, was 23 times higher than that of bare AgPd@Pd prepared under MW heating at 27 °C. It was even higher by 2–4 times than the best Ag@Pd and CoAuPd catalysts at 20–35 °C reported thus far. The apparent activation energy of the formic acid decomposition reaction using AgPd@Pd catalyst decreased from 22.8 to 7.2 kJ mol−1 in the presence of TiO2. Based on negative chemical shifts of the Pd peaks in the XPS data and the measured activation energies, the enhancement of catalytic activity in the presence of TiO2 was explained by the lowered energy barrier in the reaction pathways because of the strong electron-donating effects of TiO2 to Pd shells, which enhance the adsorption of formate to the catalyst and dehydrogenation from formate.

AgPd@Pd/TiO2 nanocatalyst synthesis by microwave heating in aqueous solution for efficient hydrogen production from formic acid

Ag100−xPdx/TiO2 (x = 7, 10, and 15) catalysts for hydrogen production from formic acid were synthesized in aqueous solution using MW heating. The hydrogen production rate of Ag100−xPdx@Pd/TiO2 increased concomitantly with decreasing x. The best catalytic activity ever reported was obtained for Ag93Pd7@Pd/TiO2 among all heterogeneous catalysts.

Investigation of electrical transport in anodized single TiO2 nanotubes

Electrical transport in anodized single titania nanotube (TNT) free from any structural effects of titania nanotube array (TNA) was investigated. An anodized TNA was disassembled into single TNTs with two-step anodization technique. Then, single TNT bridges between gold electrodes with a gap of 500 nm were prepared by dielectrophoretic alignment. Quantitative assessment of electron mobility inside single anatase and rutile TNT was carried out by 2-probe current-voltage measurement and analysis based on a metal-semiconductor-metal circuit model with Schottky barriers. Our approach to intrinsic electrical transport of single nanotube is quite effective for understanding the electronic and optical properties of TNA.

Synthesis of Ag–Au and Ag–Pd alloy triangular hollow nanoframes by galvanic replacement reactions without and with post-treatment using NaCl in an aqueous solution

Ag–Au and Ag–Pd alloy triangular hollow nanoframes were prepared using galvanic replacement (GR) reactions of Ag nanoprisms with HAuCl4 and Na2PdCl4 in an aqueous solution. Their growth mechanisms were studied by observing transmission electron microscopic (TEM) and TEM-energy dispersed X-ray spectroscopic (EDS), XRD, and ultraviolet (UV)-visible (Vis)-near infrared (NIR) extinction spectral data. Results show that Ag–Au alloy triangular frames start with formation of a truncated prism, followed by expansion of a hollow structure to the interior of the prism, reformation of the triangular shape, and finally formation of a triangular frame at ambient temperature within a few minutes. On the other hand, triangular Ag–Pd alloy plates are slowly formed by the addition of Na2PdCl4 and heating at 100 °C for 30–120 min. Results show that post-treatment using saturated NaCl solution is effective for the transformation of Ag–Pd alloy nanoplates to Ag–Pd nanoframes. The difference in the formation of nanoframes is explained by the difference in the dealloying rates between Ag–Au alloys by AuCl4− and Ag–Pd alloys by Pd2+. XRD data suggested that hexagonally closed packed (hcp) layers are involved as major components of the triangular Ag–Au and Ag–Pd alloy nanoframes.

Synthesis and growth mechanism of Au@Cu core–shell nanorods having excellent antioxidative properties

Au@Cu core–shell nanorods (NRs) were prepared using Au NRs as seeds. The resultant crystal structures were characterized using transmission electron microscopy (TEM), TEM-energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). When Cu shells were grown over Au NRs as seeds by reducing CuCl2·2H2O in an aqueous solution in the presence of hexadecylamine (HDA) and D-(+)-glucose (GLC) at 97 °C, Au@Cu NRs with {110} side facets were grown epitaxially as major side facets through a single island-growth mechanism. In this mechanism, crystal growth of Cu shells over Au core NRs starts from the formation of single semi-spherical nuclei on a wide side facet, followed by growth to neighbouring facets, with eventual full coverage by rectangular Cu shells with {110} side facets. When CuCl2·2H2O was replaced with Cu(OAc)2·H2O, layered growth of Cu shells was observed. Effects of the addition of NaCl to Cu(OAc)2·H2O show that Cl− ions play an important role in the single-island growth of Cu shells. The Au@Cu NRs exhibited much stronger antioxidative properties than spherical Cu particles.

Formation of Rh frame nanorods using Au nanorods as sacrificial templates

This report describes a new formation process of Rh frame structures using Au nanorods (NRs) as sacrificial templates. Initially, Au@Rh NRs were prepared by reducing Rh3+ in the presence of Au NRs, ascorbic acid, and cetyl trimethyl ammonium bromide (CTAB) in aqueous solution. After formation of Au@Rh NRs having an island-type of Rh shell, Rh NR frames, which consist of four side edges and top and bottom edges of NRs, were formed in one step through selective oxidative etching of an Au NR core and Rh shells over unstable facets such as {2 5 0} or {5 12 0} by X− (X = Br, Cl) + O2. An alternative method for the formation of Rh NR frames was the separation between the formation process of Au@Rh NRs and Rh NR frames by oxidative etching. In this two-step process, after formation of Au@Rh NRs, a similar shape of Rh NR frames having {100} facets as major planes was prepared by the addition of HCl. No Rh frame structure was formed from decahedral Au@Rh particles because smooth Rh shells without interspace were formed; Rh shells over low-index {111} facets were not etched by X− (X = Br, Cl) + O2. The results obtained from this study suggest a novel method for the formation of frame structures and constitute new information related to their formation mechanism.

Rapid spontaneous alloying between Pd nanocubes and Ag nanoparticles in aqueous solution at ambient temperature

Rapid spontaneous alloying between Pd nanocubes and spherical or triangular Ag nanoparticles was studied in an aqueous solution at ambient temperature using transmission electron microscopy (TEM), TEM-energy-dispersed X-ray spectroscopy (EDS), XRD, and UV-Vis spectroscopy of product particles. The results show that alloying occurs between Ag particles and Pd cubes and finishes within a few seconds, preserving the cubic shape with maximum Ag content of approximately 22%.

High-purity hydrogen generation by ultraviolet illumination with the membrane composed of titanium dioxide nanotube array and Pd layer

High-purity hydrogen generation was observed by using a membrane composed of a bilayer of an anodized titanium dioxide nanotube array (TNA) and a hydrogen permeable metal. This membrane was fabricated by transferring a TNA embedded in a titanium foil onto a sputtered 10-μm-thick palladium film. Alcohols are reformed photocatalytically and concurrently generated hydrogen is purified through the Pd layer. H2 with a purity of more than 99% was obtained from liquid alcohols under ultraviolet illumination onto the membrane. Thus, we demonstrated the integration of photocatalytic hydrogen production and purification within a single membrane.

Enhancement of catalytic activity of AgPd@Pd/TiO2 nanoparticles under UV and visible photoirradiation

The effects of photoirradiation for the production of hydrogen from the decomposition of formic acid (FA) were studied using Ag93Pd7@Pd/TiO2 (anatase (A) or P25 (P)) nanocatalysts. The catalytic activity was enhanced by a factor of 1.5–1.6 under UV and visible (vis) photoirradiation at room temperature for both TiO2 supports. It was explained by the formation of an electron-rich Pd shell because of the migration of photogenerated electrons from the TiO2 surface. The catalytic activity of Ag93Pd7@Pd/TiO2 (A) was 1.7–7.3 times higher than that of Ag93Pd7@Pd/TiO2 (P) without and under photoirradiation at 27–90 °C. The catalytic activity of Ag93Pd7@Pd/TiO2 (A) under photoirradiation at 27 °C with 468 mmol H2 g per catalyst per h, is the best value ever reported out of all of the heterogeneous catalysts using TiO2 (A) as a photocatalyst at room temperature.