Surface Extraction Process During Initial Oxidation of Pt(111): Effect of Hydrophilic/Hydrophobic Cations in Alkaline Media.

The surface oxidation states of the metal electrodes affect the activity, selectivity, and stability of the electrocatalysts. Oxide formation and reduction on such electrodes must be comprehensively understood to achieve next-generation electrocatalysts with outstanding performance and stability. Herein, the initial electrochemical oxidation of Pt(111) in alkaline media containing hydrophilic and hydrophobic cations is investigated by X-ray crystal truncation rod (CTR) scattering, infrared (IR) spectroscopy, and nanoparticle-based surface-enhanced Raman spectroscopy (SERS). Structural determination using X-ray CTR revealed surface buckling and Pt extraction at the initial stage of surface oxidation, depending on the cationic species. Vibrational spectroscopy is performed to identify the potential- and cation-dependent formation of three oxide species (IR-active OHad, Raman-active OHad/Oad(H2O), and Raman-active Oad). Hydrophilic alkali metal cations (Li+) inhibit surface roughening via irreversible oxide formation. Hydrophilic Li+ can strongly stabilize IR-active OHad, hindering the extraction of Pt surface atoms. Interestingly, bulky hydrophobic cations such as tetramethylammonium (TMA+) cation also reduce the extent of irreversible oxidation despite the absence of IR-active OHad. Hydrophobic TMA+ inhibits the formation of Raman-active OHad/Oad(H2O) associated with Pt extraction. In contrast, the moderate hydrophilicity of K+ has no protective effect against irreversible oxidation. Moderate hydrophilicity enables the coadsorption of Raman-active OHad/Oad(H2O) and Raman-active Oad. The electrostatic repulsion between Raman-active OHad/Oad(H2O) and neighboring Raman-active Oad promotes Pt extraction. These results provide insights into controlling the surface structures of electrocatalysts using cationic species during the oxide formation and reduction processes.

High-throughput and high-resolution powder X-ray diffractometer consisting of six sets of 2D CdTe detectors with variable sample-to-detector distance and innovative automation system.

The demand for powder X-ray diffraction analysis continues to increase in a variety of scientific fields, as the excellent beam quality of high-brightness synchrotron light sources enables the acquisition of high-quality measurement data with high intensity and angular resolution. Synchrotron powder diffraction has enabled the rapid measurement of many samples and various in situ/operando experiments in nonambient sample environments. To meet the demands for even higher throughput measurements using high-energy X-rays at SPring-8, a high-throughput and high-resolution powder diffraction system has been developed. This system is combined with six sets of two-dimensional (2D) CdTe detectors for high-energy X-rays, and various automation systems, including a system for automatic switching among large sample environmental equipment, have been developed in the third experimental hutch of the insertion device beamline BL13XU at SPring-8. In this diffractometer system, high-brilliance and high-energy X-rays ranging from 16 to 72 keV are available. The powder diffraction data measured under ambient and various nonambient conditions can be analysed using Rietveld refinement and the pair distribution function. Using the 2D CdTe detectors with variable sample-to-detector distance, three types of scan modes have been established: standard, single-step and high-resolution. A major feature is the ability to measure a whole powder pattern with millisecond resolution. Equally important, this system can measure powder diffraction data with high Q exceeding 30 Å-1 within several tens of seconds. This capability is expected to contribute significantly to new research avenues using machine learning and artificial intelligence by utilizing the large amount of data obtained from high-throughput measurements.

Novel Route for Enhancing Piezoelectricity of Ferroelectric Films: Controlling Nontrivial Polarization States in Pb(Zr, Ti)O3 Monodomain Superlattice Structure.

Artificial superlattice films made of Pb(Zr0.4Ti0.6)O3 and Pb(Zr0.6Ti0.4)O3 were investigated for their polarization states and piezoelectric properties theoretically and experimentally in this study. The developed theory predicts nontrivial polarization along neither [001] nor [111] directions in (111)-epitaxial monodomain superlattice films with uniform compressive strain. Such films were achieved via pulsed laser deposition. When the layer thickness is reduced to 3 nm, d33 becomes 128 ± 3.8 pm/V at 100 kV/cm and 71.3 ± 2.83 pm/V at 600 kV/cm, comparable to that of (111)-oriented Pb(Zr0.4Ti0.6)O3 or Pb(Zr0.6Ti0.4)O3 bulks and clearly exceeding that of the typical clamped films. The measurement agrees with the theoretical analysis, which reveals that the enhanced piezoelectricity is due to rotation of the nontrivial polarization. Furthermore, the theoretical study predicts an even larger d33 exceeding 300 pm/V for specific parameters in superlattice films with uniform tensile strain, which is promising for applications of microelectromechanical systems.

First synthesis of RuSn solid-solution alloy nanoparticles and their enhanced hydrogen evolution reaction activity.

Solid-solution alloys based on platinum group metals and p-block metals have attracted much attention due to their promising potential as materials with a continuously fine-tunable electronic structure. Here, we report on the first synthesis of novel solid-solution RuSn alloy nanoparticles (NPs) by electrochemical cyclic voltammetry sweeping of RuSn@SnOx NPs. High-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy maps confirmed the random and homogeneous distribution of Ru and Sn elements in the alloy NPs. Compared with monometallic Ru NPs, the RuSn alloy NPs showed improved hydrogen evolution reaction (HER) performance. The overpotentials of Ru0.94Sn0.06 NPs/C and Ru0.87Sn0.13 NPs/C to achieve a current density of 10 mA cm-2 were 43.41 and 33.19 mV, respectively, which are lower than those of monometallic Ru NPs/C (53.53 mV) and commercial Pt NPs/C (55.77 mV). The valence-band structures of the NPs investigated by hard X-ray photoelectron spectroscopy demonstrated that the d-band centre of RuSn NPs shifted downward compared with that of Ru NPs. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analyses indicated that in the RuSn alloy NPs, charge transfer occurs from Sn to Ru, which was considered to result in a downward shift of the d-band centre in RuSn NPs and to regulate the adsorption energy of intermediate Hads effectively, and thus enable the RuSn solid-solution alloy NPs to exhibit excellent HER catalytic properties.