Electrochemical Adsorption on Pt Nanoparticles in Alkaline Solution Observed Using In Situ High Energy Resolution X-ray Absorption Spectroscopy

The oxygen reduction reaction (ORR) on Pt/C in alkaline solution was studied by in situ high energy resolution X-ray absorption spectroscopy. To discuss the X-ray absorption near-edge structure (XANES), this paper introduced the rate of change of the Δμ (RCD), which is an analysis method that is sensitive to surface adsorption. The surface adsorptions as hydrogen (below 0.34 V), superoxide anion (from 0.34 V to 0.74 V), hydroxyl species (from 0.44 V to 0.74 V), atomic oxygen (above 0.74 V), and α-PtO2 (above 0.94 V) were distinguished. It is clarified that the catalytic activity in an alkaline solution is enhanced by the stability of atomic oxygen and the low stability of superoxide anion/peroxide adsorption on the platinum surface

Charge Excitations in Nd2−xCexCuO4 Observed with Resonant Inelastic X-ray Scattering: Comparison of Cu K-edge with Cu L3-edge

We report a Cu K-edge resonant inelastic x-ray scattering (RIXS) study of momentum-dependent charge excitations in Nd2−xCexCuO4 (x = 0.075 and 0.18). The peak position and width of the excitations coincide excellently with those observed in Cu L3-edge RIXS. It demonstrates that the same charge excitations are observed at the two edges

Electronic and crystal structures of (Na1−xCax)Cr2O4 with anomalous colossal magnetoresistance

The electronic and crystal structures of (Na1−xCax)Cr2O4 have been studied in detail by combining photoelectron spectroscopy (PES), x-ray absorption spectroscopy (XAS), and x-ray diffraction (XRD). The PES results suggest a gap opening at the Fermi level with decreasing temperature and/or increasing the Ca concentration. The XAS spectra at the O K-absorption edge suggest a slight increase of the O 2p–Cr 3d hybridization at low temperatures in NaCr2O4 and Na0.8Ca0.2Cr2O4, which corresponds to the appearance of the antiferromagnetic order. However, XRD showed no corresponding structural transition. The experimental results were compared with spin-resolved density functional theory (DFT) calculations. In Na1−xCaxCr2O4 the pre-edge intensity of the XAS spectra at the O K-absorption edge is strongly suppressed with increasing x, in accordance with the gap opening by Ca doping. This observation is consistent with the DFT calculation, where the density of states just above and below the Fermi level diminishes as the electron is doped into NaCr2O4

In Situ Electrochemical, Electrochemical Quartz Crystal Microbalance, Scanning Tunneling Microscopy, and Surface X-ray Scattering Studies on Ag/AgCl Reaction at the Underpotentially Deposited Ag Bilayer on the Au(111) Electrode Surface

Ag/AgCl reaction at the Ag bilayer, which was underpotentially prepared on a Au(111) surface, was investigated using electrochemical quartz crystal microbalance (EQCM), scanning tunneling microscopy (STM), surface X-ray scattering (SXS), and electrochemical techniques. When the potential was scanned positively from -200 mV, the Cl^[-] ion was adsorbed on the Au(111) electrode surface around 0 mV, and then the phase transition of the adsorbed Cl^[-] ion layer from random orientation to (√3 x √3) structure took place at around +130 mV. The Ag bilayer and Cl^[-] ions were oxidatively reacted to form the AgCl monolayer with (√13 x √13)R13.9° structure around +200 mV, accompanied with the formation of AgCl monocrystalline clusters on the AgCl monolayer surface. The structure of the AgCl monolayer on the Au(111) surface was changed from (√13 x √13)R13.9° structure to (4 x 4) structure around +500 mV. When the potential was scanned back negatively, the AgCl monolayer was electrochemically reduced, and a Ag monolayer, not a bilayer, was formed on the Au(111) surface. In the subsequent potential cycles, the structural change between the Ag monolayer and the AgCl monolayer was reversibly observed. All oxidative structural changes were much slower than the reductive ones