Surface-Modified Ruthenium Nanorods for an Ampere-Level Bifunctional Hydrogen Evolution Reaction/Oxygen Evolution Reaction Electrocatalyst.

The practical applications of bifunctional ruthenium-based electrocatalysts with two active sites of Ru nanoparticles covered with RuO2 skins are limited. One reason is the presence of multiple equally distributed facets, some of which are inactive. In contrast, ruthenium nanorods with a high aspect ratio have multiple unequally distributed facets containing the dominance of active faces for efficient electrocatalysis. However, the synthesis of ruthenium nanorods has not been achieved due to difficulties in controlling the growth. Additionally, it is known that the adsorption capacity of intermediates can be impacted by the surface of the catalyst. Inspired by these backgrounds, the surface-modified (SM) ruthenium nanorods having a dominant active facet of hcp (100) through chemisorbed oxygen and OH groups (SMRu-NRs@NF) are rationally synthesized through the surfactant coordination method. SMRu-NRs@NF exhibits excellent hydrogen evolution in acid and alkaline solutions with an ultralow overpotential of 215 and 185 mV reaching 1000 mA cm-2, respectively. Moreover, it has also shown brilliant oxygen evolution electrocatalysis in alkaline solution with a low potential of 1.58 V to reach 1000 mA cm-2. It also exhibits high durability over 143 h for the evolution of oxygen and hydrogen at 1000 mA cm-2. Density functional theory studies confirmed that surface modification of a ruthenium nanorod with chemisorbed oxygen and OH groups can optimize the reaction energy barriers of hydrogen and oxygen intermediates. The surface-modified ruthenium nanorod strategy paves a path to develop the practical water splitting electrocatalyst.

Platinum Nanoparticles Bonded with Carbon Nanotubes for High-Performance Ampere-Level All-Water Splitting.

Platinum nanoparticles loaded on a nitrogen-doped carbon nanotubes exhibit a brilliant hydrogen evolution reaction (HER) in an alkaline solution, but their bifunctional hydrogen and oxygen evolution reaction (OER) has not been reported due to the lack of a strong Pt-C bond. In this work, platinum nanoparticles bonded in carbon nanotubes (Pt-NPs-bonded@CNT) with strong Pt-C bonds are designed toward ultralow overpotential water splitting ability in alkaline solution. Benefit from the strong interaction between platinum and high conductivity carbon nanotube substrates through the Pt-C bond also the platinum nanoparticles bonded in carbon nanotube can provide more stable active sites, as a result, the Pt-NPs-bonded@CNT exhibits excellent hydrogen evolution in acid and alkaline solution with ultralow overpotential of 0.19 and 0.23 V to reach 1000 mA cm-2, respectively. Besides, it shows superior oxygen evolution electrocatalysis in alkaline solution with a low overpotential of 1.69 V at 1000 mA cm-2. Furthermore, it also exhibits high stability over 110 h against the evolution of oxygen and hydrogen at 1000 mA cm-2. This strategy paves the way to the high performance of bifunctional electrocatalytic reaction with extraordinary stability originating from optimized electron density of metal active sites due to strong metal-substrate interaction.

Structure and complexation mechanism of aqueous Zn(II)-acetate complex studied by XAFS and Raman spectroscopies.

In this work, the structure of Zn acetate has been determined by a combination of X-ray absorption fine structure and Raman spectroscopy. We have analyzed the local atomic environment and the main vibrational bands of the acetate and Zn acetate at different pH. The results suggest that Zn acetate complex acquires a bidentate structure that modifies its first coordination shell. Meanwhile, the coordination shell of the hydrated Zn cation is formed by 6 hydroxides at a mean distance of 2.06 Å, the coordination shell of the Zn cation in the complex is formed by 2 hydroxides and 2 oxygens from the carboxyl group of the acetate, at a mean Zn-O distance of 1.96 Å. The structure of the Zn acetate complex is compared to those of Zn malonate and Zn citrate, none of which present a reduction in the coordination shell neither a shrinkage of the Zn-O shell distance.

Production of Noble-Metal Nanohelices Based on Nonlinear Dynamics in Electrodeposition of Binary Copper Alloys.

Spatiotemporal pattern formation is dynamic self-organization widely observed in nature and drives various functions. Among these functions, chirality plays a central role. The relationship between dynamic self-organization and chirality has been an open question; therefore, the production of chiral nanomaterials by dynamic self-organization has not been achieved. Here, we show that the confinement of a two-dimensional spatiotemporal micropattern via the electrodeposition of a binary Cu alloy into a nanopore induces mirror symmetry breaking to produce a helical nanostructure of the noble-metal component although it is still not yet possible to control the handedness at this stage. This result suggests that spatiotemporal symmetry breaking functions as a mirror symmetry breaking if cylindrical pores are given as the boundary condition. This study can be a model system of how spatiotemporal symmetry breaking plays a role in mirror symmetry breaking, and it proposes a new approach to producing helical nanomaterials through dynamic self-organization.

Enhancement of Oxidation of Silicon Carbide Originating from Stacking Faults Formed by Mode-Selective Phonon Excitation Using a Mid-Infrared Free Electron Laser.

Silicon carbide (SiC) is a promising material for wide applications due to its excellent material properties including high physical and chemical stability as well as great electronic properties of a wide bandgap. The high stability, however, makes its surface processing difficult. Especially, electrochemical processing is not well-established because of low electrochemical reactivity. Here, we show that selective phonon excitation by a mid-infrared free electron laser (MIR-FEL) enhances the anodic reactions. The selective excitation of two different vibration modes of the Si-C bond induces two different stacking faults, which act as a current path. As an application, we discovered that MIR-FEL irradiation enables Pt electroless deposition. This work reveals the interactions among phonons, lattice defects, and electrochemical reactions, encouraging further development of not only electrochemical surface processing but also a new application of MIR-FEL.

Proton conduction in hydronium solvate ionic liquids affected by ligand shape.

We investigated the ligand dependence of the proton conduction of hydronium solvate ionic liquids (ILs), consisting of a hydronium ion (H3O+), polyether ligands, and a bis[(trifluoromethyl)sulfonyl]amide anion (Tf2N-; Tf = CF3SO2). The ligands were changed from previously reported 18-crown-6 (18C6) to other cyclic or acyclic polyethers, namely, dicyclohexano-18-crown-6 (Dh18C6), benzo-18-crown-6 (B18C6) and pentaethylene glycol dimethyl ether (G5). Pulsed-field gradient spin echo nuclear magnetic resonance results revealed that the protons of H3O+ move faster than those of cyclic 18C6-based ligands but as fast as those of acyclic G5 ligands. Based on these results and density functional theory calculations, we propose that the coordination of a cyclic ether ligand to the H3O+ ion is essential for fast proton conduction in hydronium solvate ILs. Our results attract special interest for many electro- and bio-chemical applications such as electrolyte systems for fuel cells and artificial ion channels for biological cells.

Reactivity of Zinc Cations under Spontaneous Accumulation of Hydrophobic Coexisting Cations in Hydrophobic Nanoporous Silicon.

The ion enrichment behavior due to surface-induced phase separation and the concomitant phase transition of electrolyte solutions between a liquid and a solid confined within nanopores of porous silicon is examined using concentrated aqueous solutions. We performed open-circuit potential measurements and differential scanning calorimetry (DSC) while varying the concentration of aqueous tetraethylammonium chloride (TEACl) solution. Open-circuit potential measurements revealed that the local OH- concentration within the nanopores increases as the bulk TEACl concentration increases. DSC measurements indicated that TEA+ cations are enriched within the nanopores and an extremely high concentration of TEA+ remarkably increases the local OH- concentration. This increase in the local pH should realize the selective precipitation of metal hydroxides within the nanopores. However, such precipitation was not observed in our investigations using aqueous solutions containing zinc cations. The experimental results suggest that ionic species within the nanopores of porous silicon are more stable than those in a bulk solution due to the formation of ion pairs with enhanced stability as well as kinetic factors that increase the activation energy for precipitation.

A Concentrated AlCl3-Diglyme Electrolyte for Hard and Corrosion-Resistant Aluminum Electrodeposits.

A concentrated aluminum chloride (AlCl3)-diglyme (G2) electrolyte is used to prepare hard and corrosion-resistant aluminum (Al) electrodeposited films. The Al electrodeposits obtained from the electrolyte with an AlCl3/G2 molar ratio x = 0.4 showed a void-free microstructure composed of spherical particles, in stark contrast to flake-like morphologies with micro-voids for lower x. Neutral complexes rarely exist in the x = 0.4 electrolyte, resulting in a relatively high conductivity despite the high concentration and high viscosity. Nanoindentation measurements for the Al deposits with >99% purity revealed that the nanohardness was 2.86 GPa, three times higher than that for Al materials produced through electrodeposition from a well-known ionic liquid bath or through severe plastic deformation. Additionally, the void-free Al deposits had a <100> preferential crystal orientation, which accounted for better resistance to free corrosion and pitting corrosion. Discussions about the compact microstructure and <100> crystal orientation of deposits obtained only from the x = 0.4 concentrated electrolyte are also presented.

Hydro-nium bis-(tri-fluoro-methane-sulfon-yl)amide-18-crown-6 (1/1).

The structure of the title compound, H3O+·C2F6NO4S2 -·C12H24O6 or [H3O+·C12H24O6][N(SO2CF3)2 -], which is an ionic liquid with a melting point of 341-343 K, has been determined at 113 K. The asymmetric unit consists of two crystallographically independent 18-crown-6 mol-ecules, two hydro-nium ions and two bis-(tri-fluoro-methane-sulfon-yl)amide anions; each 18-crown-6 mol-ecule complexes with a hydro-nium ion. In one 18-crown-6 mol-ecule, a part of the ring exhibits conformational disorder over two sets of sites with an occupancy ratio of 0.533 (13):0.467 (13). One hydro-nium ion is complexed with the ordered 18-crown-6 mol-ecule via O-H⋯O hydrogen bonds with H2OH⋯OC distances of 1.90 (6)-2.19 (7) Å, and the other hydro-nium ion with the disordered crown mol-ecule with distances of 1.85 (6)-2.36 (6) Å. The hydro-nium ions are also linked to the anions via O-H⋯F hydrogen bonds. The crystal studied was found to be a racemic twin with a component ratio of 0.55 (13):0.45 (13).

Spontaneous Symmetry Breaking of Nanoscale Spatiotemporal Pattern as the Origin of Helical Nanopore Etching in Silicon.

Nanometric chiral objects such as twisted or helical nanoribbons represent a new class of objects having important potential in a large panel of applications, taking advantage, for example, of electromechanical or optical chirality, local chiral environment for catalysis, and chiral recognition. Supramolecular chemistry has played a central role in the production of such structures through either chiral macromolecules/foldamers or the self-assembly of chiral molecules; the latter can also be used as templates for the sol-gel transcription to silica materials, offering them polymorphisms with further structural stability. Here, we report a totally different and dynamic approach to produce helical mesostructures. This study focuses on helical nanopores that are spontaneously formed in the platinum-assisted chemical etching of silicon by dynamic self-organization under a nonequilibrium state. The symmetry breaking of a helical nanopore formation is achieved by the spatial symmetry breaking of a spatiotemporal pattern at the nanoscale and without incorporation of chiral molecules. Rotational motion of the platinum nanocatalyst, which is regarded as a spatiotemporal pattern at the etching frontier (the platinum/silicon interface), induces precession movement of the nanocatalyst, and movement of the catalyst during etching forms helical nanopores in the silicon. We consider that this study is an important milestone to understand the close relation between spatiotemporal pattern formation and the dynamic emergence of symmetry breaking in chemical reactions.

In situ semi-quantitative analysis of zinc dissolution within nanoporous silicon by X-ray absorption fine-structure spectroscopy employing an X-ray compatible cell.

The in situ study of the discharge process in a zinc-based half-cell employing a porous electrode as a structural scaffold is reported. The in situ characterization has been performed by synchrotron X-ray absorption fine-structure spectroscopy and, for this purpose, an inexpensive, simple and versatile electrochemical cell compatible with X-ray experiments has been designed and described. The experimental results reported here have been employed to semi-quantify the dissolved and undissolved zinc species during the discharge, allowing the cell feasibility to be tested and to better understand the functioning of the zinc half-cell based on porous electrodes.

Stratification of Colloidal Particles on a Surface: Study by a Colloidal Probe Atomic Force Microscopy Combined with a Transform Theory.

Colloidal probe atomic force microscopy (CP-AFM) can be used for measuring force curves between the colloidal probe and the substrate in a colloidal suspension. In the experiment, an oscillatory force curve reflecting the layer structure of the colloidal particles on the substrate is usually obtained. However, the force curve is not equivalent to the interfacial structure of the colloidal particles. In this paper, the force curve is transformed into the number density distribution of the colloidal particles as a function of the distance from the substrate surface using our newly developed transform theory. It is found by the transform theory that the interfacial stratification is enhanced by an increase in an absolute value of the surface potential of the colloidal particle, despite a simultaneous increase in a repulsive electrostatic interaction between the substrate and the colloidal particle. To elucidate the mechanism of the stratification, an integral equation theory is employed. It is found that crowding of the colloidal particles in the bulk due to the increase in the absolute value of the surface potential of the colloidal particle leads to pushing out some colloidal particles to the wall. The combined method of CP-AFM and the transform theory (the experimental-theoretical study of the interfacial stratification) is related to colloidal crystallization, glass transition, and aggregation on a surface. Thus, the combined method is important for developments of colloidal nanotechnologies.

Dynamic manipulation of the local pH within a nanopore triggered by surface-induced phase transition.

Manipulating the local pH within nanoconfinement is essential in nanofluidics technology and its applications. Since the conventional strategy utilizes the overlapping of an electric double layer formed for charge compensation by protons near a negatively charged pore-wall surface, pH variation within a pore is limited to the acidic side. To achieve the variation at the alkaline side, we developed a system comprising a hydrophobic pore-wall surface and aqueous solution containing hydrophobic cations. Beyond a threshold cation concentration, a nanopore is filled with the second phase where the cations are remarkably enriched due to surface-induced phase transition (SIFT) originating from the hydrophobic effect. It is accompanied by the enrichment of coexisting anions. We experimentally show that pH in the second phase is much higher than in the bulk solution. Electrochemical measurements strongly suggest that the pH value can be increased from 4.8 to 10.7 within a 10 nm nanopore in the most significant case. This is ascribed to the enrichment of hydroxide anions. We argue that the extent and rate of pH variation are controlled as desired.

Number Density Distribution of Small Particles around a Large Particle: Structural Analysis of a Colloidal Suspension.

Some colloidal suspensions contain two types of particles-small and large particles-to improve the lubricating ability, light absorptivity, and so forth. Structural and chemical analyses of such colloidal suspensions are often performed to understand their properties. In a structural analysis study, the observation of the number density distribution of small particles around a large particle (gLS) is difficult because these particles are randomly moving within the colloidal suspension by Brownian motion. We obtain gLS using the data from a line optical tweezer (LOT) that can measure the potential of mean force between two large colloidal particles (ΦLL). We propose a theory that transforms ΦLL into gLS. The transform theory is explained in detail and tested. We demonstrate for the first time that LOT can be used for the structural analysis of a colloidal suspension. LOT combined with the transform theory will facilitate structural analyses of the colloidal suspensions, which is important for both understanding colloidal properties and developing colloidal products.

Correction: Number density distribution of solvent molecules on a substrate: a transform theory for atomic force microscopy.

Correction for 'Number density distribution of solvent molecules on a substrate: a transform theory for atomic force microscopy' by Ken-ichi Amano et al., Phys. Chem. Chem. Phys., 2016, 18, 15534-15544.

Number density distribution of solvent molecules on a substrate: a transform theory for atomic force microscopy.

Atomic force microscopy (AFM) in liquids can measure a force curve between a probe and a buried substrate. The shape of the measured force curve is related to hydration structure on the substrate. However, until now, there has been no practical theory that can transform the force curve into the hydration structure, because treatment of the liquid confined between the probe and the substrate is a difficult problem. Here, we propose a robust and practical transform theory, which can generate the number density distribution of solvent molecules on a substrate from the force curve. As an example, we analyzed a force curve measured by using our high-resolution AFM with a newly fabricated ultrashort cantilever. It is demonstrated that the hydration structure on muscovite mica (001) surface can be reproduced from the force curve by using the transform theory. The transform theory will enhance AFM's ability and support structural analyses of solid/liquid interfaces. By using the transform theory, the effective diameter of a real probe apex is also obtained. This result will be important for designing a model probe of molecular scale simulations.

Spontaneous Formation of Microgroove Arrays on the Surface of p-Type Porous Silicon Induced by a Turing Instability in Electrochemical Dissolution.

Self-organization plays an imperative role in recent materials science. Highly tunable, periodic structures based on dynamic self-organization at micrometer scales have proven difficult to design, but are desired for the further development of micropatterning. In the present study, we report a microgroove array that spontaneously forms on a p-type silicon surface during its electrodissolution. Our detailed experimental results suggest that the instability can be classified as Turing instability. The characteristic scale of the Turing-type pattern is small compared to self-organized patterns caused by the Turing instabilities reported so far. The mechanism for the miniaturization of self-organized patterns is strongly related to the semiconducting property of silicon electrodes as well as the dynamics of their surface chemistry.

On-site quantitative elemental analysis of metal ions in aqueous solutions by underwater laser-induced breakdown spectroscopy combined with electrodeposition under controlled potential.

We propose a technique of on-site quantitative analysis of Zn(2+) in aqueous solution based on the combination of electrodeposition for preconcentration of Zn onto a Cu electrode and successive underwater laser-induced breakdown spectroscopy (underwater LIBS) of the electrode surface under electrochemically controlled potential. Zinc emission lines are observed with the present technique for a Zn(2+) concentration of 5 ppm. It is roughly estimated that the overall sensitivity over 10 000 times higher is achieved by the preconcentration. Although underwater LIBS suffers from the spectral deformation due to the dense plasma confined in water and also from serious shot-to-shot fluctuations, a linear calibration curve with a coefficient of determination R(2) of 0.974 is obtained in the range of 5-50 ppm.

Effect of cation species on surface-induced phase transition observed for platinum complex anions in platinum electrodeposition using nanoporous silicon.

In an earlier work [K. Fukami et al., J. Chem. Phys. 138, 094702 (2013)], we reported a transition phenomenon observed for platinum complex anions in our platinum electrodeposition experiment using nanoporous silicon. The pore wall surface of the silicon electrode was made hydrophobic by covering it with organic molecules. The anions are only weakly hydrated due to their large size and excluded from the bulk aqueous solution to the hydrophobic surface. When the anion concentration in the bulk was gradually increased, at a threshold the deposition behavior exhibited a sudden change, leading to drastic acceleration of the electrochemical deposition. It was shown that this change originates from a surface-induced phase transition: The space within a nanopore is abruptly filled with the second phase in which the anion concentration is orders of magnitude higher than that in the bulk. Here we examine how the platinum electrodeposition behavior is affected by the cation species coexisting with the anions. We compare the experimental results obtained using three different cation species: K(+), (CH3)4N(+), and (C2H5)4N(+). One of the cation species coexists with platinum complex anions [PtCl4](2-). It is shown that the threshold concentration, beyond which the electrochemical deposition within nanopores is drastically accelerated, is considerably dependent on the cation species. The threshold concentration becomes lower as the cation size increases. Our theoretical analysis suggests that not only the anions but also the cations are remarkably enriched in the second phase. The remarkable enrichment of the anions alone would give rise to the energetic instability due to electrostatic repulsive interactions among the anions. We argue that the result obtained cannot be elucidated by the prevailing view based on classical electrochemistry. It is necessitated to consult a statistical-mechanical theory of confined aqueous solutions using a molecular model for water.

Two-dimensional array of particles originating from dipole-dipole interaction as evidenced by potential curve measurements at vertical oil/water interfaces.

We propose a new method to evaluate the interaction potential energy between the particles adsorbed at an oil/water interface as a function of interparticle distance. The method is based on the measurement of the interparticle distance at a vertical oil/water interface, at which the gravitational force is naturally applied to compress the particle monolayer in the in-plane direction. We verified the method by examining whether we obtained the same potential curve upon varying the gravitational acceleration by tilting the interface. The present method is applicable in the force range from ∼0.1 to ∼100 pN, determined by the effective weight of the particles at the interface. The method gives a rather simple procedure to estimate a long range interaction among the particles adsorbed at oil/water interfaces. We applied this method to polystyrene particles at the decane/aqueous surfactant solution interface, and obtained the interparticle potential curves. All the potential curves obtained by the present method indicated that the interparticle repulsion is due to the electrical dipole-dipole interaction based on the negative charge of the particles. The mechanism of the dipole-dipole interaction is further discussed on the basis of the effects of surfactants.