Efficient overall water splitting in acid with anisotropic metal nanosheets

超高効率な水の電気分解を実現するナノシート状合金触媒を開発 --再生可能エネルギーによる水素社会実現へ大きく貢献--. 京都大学プレスリリース. 2021-02-17.Water is the only available fossil-free source of hydrogen. Splitting water electrochemically is among the most used techniques, however, it accounts for only 4% of global hydrogen production. One of the reasons is the high cost and low performance of catalysts promoting the oxygen evolution reaction (OER). Here, we report a highly efficient catalyst in acid, that is, solid-solution Ru‒Ir nanosized-coral (RuIr-NC) consisting of 3 nm-thick sheets with only 6 at.% Ir. Among OER catalysts, RuIr-NC shows the highest intrinsic activity and stability. A home-made overall water splitting cell using RuIr-NC as both electrodes can reach 10 mA cm−2geo at 1.485 V for 120 h without noticeable degradation, which outperforms known cells. Operando spectroscopy and atomic-resolution electron microscopy indicate that the high-performance results from the ability of the preferentially exposed {0001} facets to resist the formation of dissolvable metal oxides and to transform ephemeral Ru into a long-lived catalyst

Phase Control of Solid-Solution Nanoparticles beyond the Phase Diagram for Enhanced Catalytic Properties

The crystal structure, which intrinsically affects the properties of solids, is determined by the constituent elements and composition of solids. Therefore, it cannot be easily controlled beyond the phase diagram because of thermodynamic limitations. Here, we demonstrate the first example of controlling the crystal structures of a solid-solution nanoparticle (NP) entirely without changing its composition and size. We synthesized face-centered cubic (fcc) or hexagonal close-packed (hcp) structured PdxRu₁–x NPs (x = 0.4, 0.5, and 0.6), although they cannot be synthesized as bulk materials. Crystal-structure control greatly improves the catalytic properties; that is, the hcp-PdxRu₁–x NPs exceed their fcc counterparts toward the oxygen evolution reaction (OER) in corrosive acid. These NPs only require an overpotential (η) of 200 mV at 10 mA cm⁻², can maintain the activity for more than 20 h, greatly outperforming the fcc-Pd₀.₄Ru₀.₆ NPs (η = 280 mV, 9 min), and are among the most efficient OER catalysts reported. Synchrotron X-ray-based spectroscopy, atomic-resolution electron microscopy, and density functional theory (DFT) calculations suggest that the enhanced OER performance of hcp-PdRu originates from the high stability against oxidative dissolution

Clinical features of headache associated with mobile phone use: a cross-sectional study in university students

<p>Abstract</p> <p>Background</p> <p>Headache has been reported to be associated with mobile phone (MP) use in some individuals. The causal relationship between headache associated with MP use (HAMP) and MP use is currently undetermined. Identifying the clinical features of HAMP may help in clarifying the pathophysiology of HAMP and in managing symptoms of individuals with HAMP. The aim of the present study is to describe the clinical features of HAMP.</p> <p>Methods</p> <p>A 14-item questionnaire investigating MP use and headache was administered to 247 medical students at Hallym University, Korea. Individual telephone interviews were subsequently conducted with those participants who reported HAMP more than 10 times during the last 1 year on the clinical features of HAMP. We defined HAMP as a headache attack during MP use or within 1 hour after MP use.</p> <p>Results</p> <p>In total, 214 (86.6%) students completed and returned the questionnaire. Forty (18.9%) students experienced HAMP more than 10 times during the last 1 year in the questionnaire survey. In subsequent telephone interviews, 37 (97.4%) interviewed participants reported that HAMP was triggered by prolonged MP use. HAMP was usually dull or pressing in quality (30 of 38, 79.0%), localised ipsilateral to the side of MP use (32 of 38, 84.2%), and associated with a burning sensation (24 of 38, 63.2%).</p> <p>Conclusion</p> <p>We found that HAMP usually showed stereotyped clinical features including mild intensity, a dull or pressing quality, localisation ipsilateral to the side of MP use, provocation by prolonged MP use and often accompanied by a burning sensation.</p

The alkaline pressure oxidation of gold-containing pyrite as a pretreatment prior to gold leaching : fundamentals and new approaches

Due to the depletion of gold ore easily processed, the demand for processing high carbonate refractory gold ore is increasing worldwide, and accordingly, the interest in alkaline pressure oxidation (POX) is also increasing. This study was conducted with the aim of investigating the fundamental kinetics of alkaline pressure oxidation and testing new concepts to improve the pre-existing alkaline POX process. Magnesium carbonate (MgCO₃) was proposed as an alternative alkaline reagent instead of sodium carbonate (Na₂CO₃). Formation of kieserite (MgSO₄·H₂O) at high temperatures has been confirmed. Addition of MgCO₃ may have a positive effect on cyanidation by replacing a part of the iron oxide - calcium sulfate based product layer with kieserite, which is expected to re-dissolve at low temperature and leave pores in the oxidized solid. However, the direct addition of MgCO₃ showed limitations in terms of extent of sulfide oxidation and gold recovery. A further attempt was made to affect the POX chemistry by addition of magnesium sulfate as a pre-treatment. This method showed potential regarding reduction of calcium carbonate (CaCO₃) reactivity as well as formation of desired magnesium hydroxide precipitate in the MgSO₄ pre-treatment stage. Two stage tests (MgSO₄ pre-treatment followed by alkaline POX) verified that the magnesium sulfate addition to POX had a beneficial effect on the gold recovery (8-10% increased) with a concurrent increase of sulfide oxidation. The kinetic study of pyrite oxidation showed the reaction rate can be modelled with the shrinking core model (SCM), and pyrite oxidation is under chemical reaction control in the initial stage regardless of key parameters (particle size, temperature, and Po2). However, rate control mechanism shifts to product layer diffusion with the effect of build-up of product layer. The activation energy for pyrite oxidation in the starting period was calculated at 36.1 kJ/mol which implied the reaction is controlled by chemical reaction, whereas the activation energy with a longer time span dramatically decreases to 15.9 kJ/mol (thought to be due to product layer diffusion rate control). In addition, it was found that excessive Na₂CO₃ addition to the POX system could have a detrimental effect on pyrite oxidation.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat

Origin of the catalytic activity of face-centered-cubic ruthenium nanoparticles determined from an atomic-scale structure.

Ruナノ粒子の構造と触媒活性との関連を見いだす : 局所構造, 平均構造の数値化で実現 機械学習用データを集積し新材料の創製に貢献. 京都大学プレスリリース. 2016-11-01.The 3-dimensional (3D) atomic-scale structure of newly discovered face-centered cubic (fcc) and conventional hexagonal close packed (hcp) type ruthenium (Ru) nanoparticles (NPs) of 2.2 to 5.4 nm diameter were studied using X-ray pair distribution function (PDF) analysis and reverse Monte Carlo (RMC) modeling. Atomic PDF based high-energy X-ray diffraction measurements show highly diffuse X-ray diffraction patterns for fcc- and hcp-type Ru NPs. We here report the atomic-scale structure of Ru NPs in terms of the total structure factor and Fourier-transformed PDF. It is found that the respective NPs have substantial structural disorder over short- to medium-range order atomic distances from the PDF analysis. The first-nearest-neighbor peak analyses show a significant size dependence for the fcc-type Ru NPs demonstrating the increase in the peak height due to an increase in the number density as a function of particle size. The bond angle and coordination number (CN) distribution for the RMC-simulated fcc- and hcp-type Ru NP models indicated inherited structural features from their bulk counterparts. The CN analysis of the whole NP and surface of each RMC model of Ru NPs show the low activation energy packing sites on the fcc-type Ru NP surface atoms. Finally, our newly defined order parameters for RMC simulated Ru NP models suggested that the enhancement of the CO oxidation activity of fcc-type NPs was due to a decrease in the close packing ordering that resulted from the increased NP size. These structural findings could be positively supported for synthesized low-cost and high performance nano-sized catalysts and have potential application in fuel-cell systems and organic synthesis