Crystal Structure Control of Binary and Ternary Solid-Solution Alloy Nanoparticles with a Face-Centered Cubic or Hexagonal Close-Packed Phase

The crystal structure significantly affects the physical and chemical properties of solids. However, the crystal structure-dependent properties of alloys are rarely studied because controlling the crystal structure of an alloy at the same composition is extremely difficult. Here, for the first time, we successfully demonstrate the synthesis of binary Ru–Pt (Ru/Pt = 7:3) and Ru–Ir (Ru/Ir = 7:3) and ternary Ru–Ir–Pt (Ru/Ir/Pt = 7:1.5:1.5) solid-solution alloy nanoparticles (NPs) with well-controlled hexagonal close-packed (hcp) and face-centered cubic (fcc) phases, through the chemical reduction method. The crystal structure control is realized by precisely tunning the reduction speeds of the metal precursors. The effect of the crystal structure on the catalytic performance of solid-solution alloy NPs is systematically investigated. Impressively, all the hcp alloy NPs show superior electrocatalytic activities for the hydrogen evolution reaction in alkaline solution compared with the fcc alloy NPs. In particular, hcp-RuIrPt exhibits extremely high intrinsic (mass) activity, which is 3.1 (3.2) and 6.7 (6.9) times enhanced compared to that of fcc-RuIrPt and commercial Pt/C

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

Association of Monosodium Glutamate Intake With Overweight in Chinese Adults: The INTERMAP Study

Animal studies indicate that monosodium glutamate (MSG) can induce hypothalamic lesions and leptin resistance, possibly influencing energy balance, leading to overweight. This study examines the association between MSG intake and overweight in the human species. We conducted a cross-sectional study of 752 healthy Chinese (48.7% women), ages 40 to 59 years, randomly sampled from three rural villages in north and south China. The great majority of participants prepared their foods at home, without use of commercially processed foods. Diet was assessed with four in-depth multi-pass 24-hour recalls. Participants were asked to demonstrate MSG amounts added in food preparation. Amounts shaken out were weighed by trained interviewers. Overweight was defined as body mass index ≥25.0 kg/m2 or ≥23.0 (based on World Health Organization recommendations for Asian populations). Eighty-two percent of participants used MSG. Average intake was 0.33 gram/day (standard deviation=0.40). With adjustment for potential confounders including physical activity and total energy intake, MSG intake was positively related to body mass index. Prevalence of overweight was significantly higher in MSG users than non-users. For users in the highest tertile of MSG intake compared to non-users, the multivariable-adjusted odds ratios of overweight (body mass index ≥23.0 and ≥25.0) were 2.10 (95% CI, 1.13–3.90, P for trend across four MSG categories=0.03) and 2.75 (95% CI, 1.28–5.95, P=0.04). This research provides human data that MSG intake may be associated with increased risk of overweight independent of physical activity and total energy intake

Recent progress in the structure control of Pd–Ru bimetallic nanomaterials

Pd and Ru are two key elements of the platinum-group metals that are invaluable to areas such as catalysis and energy storage/transfer. To maximize the potential of the Pd and Ru elements, significant effort has been devoted to synthesizing Pd–Ru bimetallic materials. However, most of the reports dealing with this subject describe phase-separated structures such as near-surface alloys and physical mixtures of monometallic nanoparticles (NPs). Pd–Ru alloys with homogenous structure and arbitrary metallic ratio are highly desired for basic scientific research and commercial material design. In the past several years, with the development of nanoscience, Pd–Ru bimetallic alloys with different architectures including heterostructure, core-shell structure and solid-solution alloy were successfully synthesized. In particular, we have now reached the stage of being able to obtain Pd–Ru solid-solution alloy NPs over the whole composition range. These Pd–Ru bimetallic alloys are better catalysts than their parent metal NPs in many catalytic reactions, because the electronic structures of Pd and Ru are modified by alloying. In this review, we describe the recent development in the structure control of Pd–Ru bimetallic nanomaterials. Aiming for a better understanding of the synthesis strategies, some fundamental details including fabrication methods and formation mechanisms are discussed. We stress that the modification of electronic structure, originating from different nanoscale geometry and chemical composition, profoundly affects material properties. Finally, we discuss open issues in this field

Chemical Synthesis, Characterization and Properties of Multi‐Element Nanoparticles

Multi-element nanoparticles (NPs) consisting of five or more elements have been increasingly studied in the past 5 years. Their emergence is taking materials science one step further because they exhibit superior properties to conventional NPs in a range of respects, including catalysis. This review focuses on the recent progress in multi-element NPs regarding synthesis, especially in regard to chemical synthesis, characterization, and properties. We begin with a brief introduction of the multi-element NPs and an overview of their synthesis methods. Then, we present representative examples of multi-element alloy NPs and ceramic NPs, including oxide NPs prepared by chemical syntheses. This review intends to provide useful insights into the chemical methods that are used to synthesize multi-element NPs, and includes a discussion on the possibilities arising from their use in new functional materials

Solid-solution alloy nanoparticles of a combination of immiscible Au and Ru with a large gap of reduction potential and their enhanced oxygen evolution reaction performance

Au and Ru are elements that are immiscible in the bulk state and have the largest gap in reduction potential among noble metals. Here, for the first time, AuxRu₁₋x solid-solution alloy nanoparticles (NPs) were successfully synthesized over the whole composition range through a chemical reduction method. Powder X-ray diffraction and scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed that Au and Ru atoms are homogeneously mixed at the atomic level. We investigated the catalytic performance of AuxRu₁₋x NPs for the oxygen evolution reaction, for which Ru is well known to be one of the best monometallic catalysts, and we found that even alloying with a small amount of Au could significantly enhance the catalytic performance

Selective control of fcc and hcp crystal structures in Au–Ru solid-solution alloy nanoparticles

ナノ合金の画期的な結晶構造制御法の開発に成功 --革新的材料の創製へ--. 京都大学プレスリリース. 2018-02-06.Binary solid-solution alloys generally adopt one of three principal crystal lattices—body-centred cubic (bcc), hexagonal close-packed (hcp) or face-centred cubic (fcc) structures—in which the structure is dominated by constituent elements and compositions. Therefore, it is a significant challenge to selectively control the crystal structure in alloys with a certain composition. Here, we propose an approach for the selective control of the crystal structure in solid-solution alloys by using a chemical reduction method. By precisely tuning the reduction speed of the metal precursors, we selectively control the crystal structure of alloy nanoparticles, and are able to selectively synthesize fcc and hcp AuRu3 alloy nanoparticles at ambient conditions. This approach enables us to design alloy nanomaterials with the desired crystal structures to create innovative chemical and physical properties