Uncovering the Stabilization Mechanism in Bimetallic Ruthenium-Iridium Anodes for Proton Exchange Membrane Electrolyzers.

Proton exchange membrane (PEM) electrolyzers are attracting an increasing attention as a promising technology for the renewable electricity storage. In this work, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is applied for in situ monitoring of the surface state of membrane electrode assemblies with RuO2 and bimetallic Ir0.7Ru0.3O2 anodes during water splitting. We demonstrate that Ir protects Ru from the formation of an unstable hydrous Ru(IV) oxide thereby rendering bimetallic Ru-Ir oxide electrodes with higher corrosion resistance. We further show that the water splitting occurs through a surface Ru(VIII) intermediate, and, contrary to common opinion, the presence of Ir does not hinder its formation.

Effect of the nanometric scale thickness on the magnetization steps in Ca3Co2O6 thin films.

We report on the effect of the film thickness on the magnetic properties of Ca3Co2O6films with an emphasis on the magnetization steps usually observed in the M-H curves below 10 K. Films with thicknesses between 35 and 200 nm all present two magnetic transitions at about T(C1) = 22 K and T(C2) = 10 K, corresponding to a 3D long range ferrimagnetic order and the transition to the formation of a frozen spin state, respectively. The magnetization curves at 10 K exhibit the expected stepped variation. However, by decreasing the thickness below a critical value of about 60 nm, no magnetization plateau is observed when the M-H curve is recorded at 2 K. Moreover, an additional transition in the susceptibility curve is observed at 45 K. These changes can be attributed to the reduced coherence length of the propagation vector along and perpendicular to the chains, and are supported by the magnetization relaxation measurements which indicate a reduction of the relaxation time. These results are helpful for understanding the origin of the magnetization steps in the one-dimensional Ca3Co2O6 cobaltite and confront the theoretical models aimed at explaining the magnetic properties in this system.

Correlation of structural properties with energy transfer of Eu-doped ZnO thin films prepared by sol-gel process and magnetron reactive sputtering.

We investigated the structural and optical properties of Eu-doped ZnO thin films made by sol-gel technique and magnetron reactive sputtering on Si (100) substrate. The films elaborated by sol-gel process are polycrystalline while the films made by sputtering show a strongly textured growth along the c-axis. X-ray diffraction patterns and transmission electron microscopy analysis show that all samples are free of spurious phases. The presence of Eu(2+) and Eu(3+) into the ZnO matrix has been confirmed by x-ray photoemission spectroscopy. This means that a small fraction of Europium substitutes Zn(2+) as Eu(2+) into the ZnO matrix; the rest of Eu being in the trivalent state. This is probably due to the formation of Eu(2)O(3) oxide at the surface of ZnO particles. This is at the origin of the strong photoluminescence band observed at 2 eV, which is characteristic of the (5)D(0)-->(7)F(2) Eu(3+) transition. In addition the photoluminescence excitonic spectra showed efficient energy transfer from the ZnO matrix to the Eu(3+) ion, which is qualitatively similar for both films although the sputtered films have a better structural quality compared to the sol-gel process grown films.