Continuous-Flow Chemical Synthesis for Sub-2 nm Ultra-Multielement Alloy Nanoparticles Consisting of Group IV to XV Elements.

Multielement alloy nanoparticles have attracted much attention due to their attractive catalytic properties derived from the multiple interactions of adjacent multielement atoms. However, mixing multiple elements in ultrasmall nanoparticles from a wide range of elements on the periodic table is still challenging because the elements have different properties and miscibility. Herein, we developed a benchtop 4-way flow reactor for chemical synthesis of ultra-multielement alloy (UMEA) nanoparticles composed of d-block and p-block elements. BiCoCuFeGaInIrNiPdPtRhRuSbSnTi 15-element alloy nanoparticles composed of group IV to XV elements were synthesized by sequential injection of metal precursors using the reactor. This methodology realized the formation of UMEA nanoparticles at low temperature (66 °C), resulting in a 1.9 nm ultrasmall average particle size. The UMEA nanoparticles have high durability and activity for electrochemical alcohol oxidation reactions and high tolerance to CO poisoning. These results suggest that the multiple interactions of UMEA efficiently promote the multistep alcohol oxidation reaction.

Ferrocene on Insulator: Silane Coupling to a SiO2 Surface and Influence on Electrical Transport at a Buried Interface with an Organic Semiconductor Layer.

A silane coupling-based procedure for decoration of an insulator surface containing abundant hydroxy groups by constructing redox-active self-assembled monolayers (SAMs) is described. A newly synthesized ferrocene (Fc) derivative containing a triethoxysilyl group designated FcSi was immobilized on SiO2/Si by a simple operation that involved immersing the substrate in a toluene solution of the Fc silane coupling reagent and then rinsing the resulting substrate. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the Fc group was immobilized on SiO2/Si in the Fe(II) state. Cyclic voltammetry measurements showed that the Fc groups were electrically insulated from the Si electrode by the SiO2 layer. The FcSi on SiO2/Si structures were found to serve as a good scaffold for formation of organic semiconductor thin films by vacuum thermal evaporation of C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), which is well-known as an organic field-effect transistor (OFET) material. The X-ray diffraction profile indicated that the conventional standing-up conformation of the C8-BTBT molecules perpendicular to the substrates was maintained in the thin films formed on FcSi@SiO2/Si. Further vacuum thermal evaporation of Au provided an FcSi-based OFET structure with good transfer characteristics. The FcSi-based OFET showed pronounced source-drain current hysteresis between the forward and backward scans. The degree of this hysteresis was varied reversibly via gate bias manipulation, which was presumably accompanied by trapping and detrapping of hole carriers at the Fc-decorated SiO2 surface. These findings provide new insights into application of redox-active SAMs to nonvolatile OFET memories while also creating new interfaces through junctions with functional thin films, in which the underlying redox-active SAMs play supporting roles.

Development of hard x-ray photoelectron spectroscopy using synchrotron radiation x-ray up to 30 keV.

Hard X-ray photoelectron spectroscopy (HAXPES) is a powerful tool for investigating the chemical and electronic states of bulk and buried interfaces non-destructively due to its large probing depth. To obtain a much larger probing depth and measure deeper regions than conventional HAXPES, we have developed a high-energy HAXPES (HE-HAXPES) system excited by photon energies up to 30 keV. This system is achieved by combining an applied bias voltage on the sample with a conventional hemispherical electron energy analyzer. By utilizing this system, we successfully observed a Si 1s peak from the bulk-Si substrate underneath the 110-nm-thick SiO2 film at a photon energy of 30 keV. Moreover, the system found that the asymmetrical spectral shape of the Si substrate signal originated from the electronic state, which is upward band bending formed at the interface between the SiO2 film and Si substrate. The HE-HAXPES system, excited by photon energy up to 30 keV, could be a very useful tool to yield genuine insights into the chemical and electronic states in deeply buried regions.

Superconcentrated NaFSA-KFSA Aqueous Electrolytes for 2 V-Class Dual-Ion Batteries.

Superconcentrated aqueous electrolytes containing NaN(SO2F)2 and KN(SO2F)2 (for which sodium and potassium bis(fluorosulfonyl)amides (FSA), respectively, are abbreviated) have been developed for 2 V-class aqueous batteries. Based on the eutectic composition of the NaFSA-KFSA (56:44 mol/mol) binary system, the superconcentrated solutions of 35 mol kg-1 Na0.55K0.45FSA/H2O and 33 mol kg-1 Na0.45K0.55FSA/H2O are found to form at 25 °C. As both electrolytes demonstrate a wider potential window of ∼3.5 V compared to that of either saturated 20 mol kg-1 NaFSA or 31 mol kg-1 KFSA solution, we applied the 33 mol kg-1 Na0.45K0.55FSA/H2O to two different battery configurations, carbon-coated Na2Ti2(PO4)3∥K2Mn[Fe(CN)6] and carbon-coated Na3V2(PO4)3∥K2Mn[Fe(CN)6]. The former cell shows highly reversible charge/discharge curves with a mean discharge voltage of 1.4 V. Although the latter cell exhibits capacity degradation, it demonstrates 2 V-class operations. Analysis data of the two cells confirmed that Na+ ions were mainly inserted into the negative electrodes passivated by a Na-rich solid electrolyte interphase, and both Na+ and K+ ions were inserted into the positive electrode. Based upon the observation, we propose new sodium-/potassium-ion batteries using the superconcentrated NaFSA-KFSA aqueous electrolytes.

Sulfated Alginate as an Effective Polymer Binder for High-Voltage LiNi0.5Mn1.5O4 Electrodes in Lithium-Ion Batteries.

Although the increasing demand for high-energy-density lithium-ion batteries (LIBs) has inspired extensive research on high-voltage cathode materials, such as LiNi0.5Mn1.5O4 (LNMO), their commercialization is hindered by problems associated with the decomposition of common carbonate solvent-based electrolytes at elevated voltages. To address these problems, we prepared high-voltage LNMO composite electrodes using five polymer binders (two sulfated and two nonsulfated alginate binders and a poly(vinylidene fluoride) conventional binder) and compared their electrochemical performances at ∼5 V vs Li/Li+. The effects of binder type on electrode performance were probed by analyzing cycled electrodes using soft/hard X-ray photoelectron spectroscopy and scanning transmission electron microscopy. The best-performing sulfated binder, sulfated alginate, uniformly covers the surface of LNMO and increased its affinity for the electrolyte. The electrolyte decomposition products generated in the initial charge-discharge cycle on the alginate-covered electrode participated in the formation of a protective passivation layer that suppressed further decomposition during subsequent cycles, resulting in enhanced cycling and rate performances. The results of this study provide a basis for the cost-effective and technically undemanding fabrication of high-energy-density LIBs.

Destruction of mesoscopic chemically modulated domains in single phase high entropy alloy via plastic deformation.

Chemically modulated mesoscopic domains in a fcc single phase CrMnFeCoNi equi-atomic high entropy alloy (HEA) are detected by small angle diffraction performed at a synchrotron radiation facility, whereas the mesoscopic domains cannot be detected by conventional X-ray diffraction and 2D mappings of energy dispersive X-ray spectroscopy by scanning electron microscopy and scanning transmission electron microscopy. The mesoscopic domains are deformed and shrieked, and finally destructed by plastic deformation, which is supported by the comprehensive observations/measurements, such as electrical resistivity, Vickers hardness, electron backscattering diffraction, and hard X-ray photoemission spectroscopy. The destruction of the mesoscopic domains causes the decrease in electrical resistivity via plastic deformation, so called K-effect, which is completely opposite to the normal trend of metals. We confirmed that the presence and the size of local chemical ordering or short-range order domains in the single phased HEA, and furthermore, Cr and Mn are related to form the domains.

Compositional dependence of structures and hydrogen evolution reaction activity of platinum-group-metal quinary RuRhPdIrPt alloy nanoparticles.

Platinum-group-metal quinary RuRhPdIrPt alloy nanoparticles were synthesised with compositions slightly away from equimolar, and their crystal and electronic structures were investigated. Their lattice constant changed linearly with composition, while the d-band centre changed nonlinearly. Their catalytic activities for the hydrogen evolution reaction were not correlated with their d-band centre.

Development of KPF6/KFSA Binary-Salt Solutions for Long-Life and High-Voltage K-Ion Batteries.

A series of binary-salt electrolytes of KPF6/KN(SO2F)2 (KFSA) in carbonate ester solvents have been developed for high-voltage K-ion batteries by clarifying the effect of salt ratio and different solvents on the physical properties of the electrolyte solutions and electrochemical performance of K-ion batteries. The KPF6/KFSA carbonate ester solutions, such as KPF6/KFSA ethylene carbonate (EC)/diethyl carbonate (DEC), exhibit higher ionic conductivity than single-salt KPF6 one, and higher KFSA content results in higher ionic conductivity. The KPF6-rich binary-salt electrolytes with KPF6/KFSA ratios of ≥3 (mol/mol) provide enough oxidation stability and passivation against Al corrosion at 4.6 V over 100 h, ensuring reversible operation of a 4 V class positive electrode, K2Mn[Fe(CN)6] in half-cell. Graphite negative electrodes exhibit higher Coulombic efficiency and better rate performance in 0.75 mol kg-1 K(PF6)0.9(FSA)0.1/EC/DEC and 1 mol kg-1 K(PF6)0.75(FSA)0.25/EC/DEC electrolytes than those in the KPF6 one. Surface analysis by hard X-ray photoelectron spectroscopy reveals that the decomposition product of N(SO2F)2- anion contributes to stabilizing solid electrolyte interphase on a graphite electrode. From comparing different solvents of EC/DEC, EC/ethyl methyl carbonate, and EC/propylene carbonate (PC), the K2Mn[Fe(CN)6] electrode demonstrates the highest Coulombic efficiency in the EC/PC binary electrolyte, while graphite electrodes exhibit no significant difference. Based on the half-cell tests, we successfully achieve the 3.6 V class full cell of graphite|K(PF6)0.75(FSA)0.25/EC/PC|K2Mn[Fe(CN)6] showing excellent cyclability over 500 cycles, which is far superior to that of the conventional KPF6/EC/DEC electrolyte cell.

Characterization of interface of Al-Ni/a-Si for thin film transistor using high-resolution Rutherford backscattering spectrometry.

High-resolution Rutherford backscattering spectrometry (HRBS) in combination with grazing angle argon sputtering was carried out to characterize the interface of aluminum-nickel (Al-Ni) alloy and amorphous-silicon films in a thin film transistor (TFT) for liquid crystal display (LCD). After thinning the top Al-Ni layer by a 1-keV Ar sputtering, the sensitivity of the interface oxygen was improved to be twice higher than that before sputtering. The results revealed that the oxygen at the interface relates to the contact characteristics.