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Negative thermal expansion (NTE) is an abnormal thermophysical phenomenon. Although NTE has been discovered in a growing number of materials, it is difficult to achieve both strong NTE and a wide o...

High-entropy oxides based on transition metals, such as Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O (TM-HEO), have recently drawn special attention as potential anodes in lithium-ion batteries due to high specific capacity and cycling reversibility. However, the lithiation/delithiation mechanism of such systems is still controversial and not clearly addressed. Here, we report on an operando XAS investigation into TM-HEO-based anodes for lithium-ion cells during the first lithiation/delithiation cycle. This material showed a high specific capacity exceeding 600 mAh g-1 at 0.1 C and Coulombic efficiency very close to unity. The combination of functional and advanced spectroscopic studies revealed complex charging mechanisms, developing through the reduction of transition-metal (TM) cations, which triggers the conversion reaction below 1.0 V. The conversion is irreversible and incomplete, leading to the final collapse of the HEO rock-salt structure. Other redox processes are therefore discussed and called to account for the observed cycling behavior of the TM-HEO-based anode. Despite the irreversible phenomena, the HEO cubic structure remains intact for ∼60% of lithiation capacity, so proving the beneficial role of the configuration entropy in enhancing the stability of the HEO rock-salt structure during the redox phenomena.

Photoelectrochemical (PEC) water splitting devices using semiconductors and electrocatalysts rely on heterogeneous interfaces that drive charge separation, thus determining potential gradients that...

Negative thermal expansion (NTE) behaviors have been observed in various types of compounds. The achievement in the merits of promising low-cost and facile NTE oxides remains challenging. In the pr...

We have investigated the molecular and electronic structure of a TiO2-supported oxomolybdate phase upon reduction under methanol or dihydrogen atmosphere. In situ Mo K-edge X-ray absorption spectro...

International audience; The electronic and local structural properties of single crystals in the ground state (GS) of the photo-switchable compound Na2[Fe(CN)5NO]•2H2O (sodium nitroprussiate, SNP) have been investigated by X-ray Absorption Fine Structure Spectroscopy (XAFS) and FEFF simulations. In SNP, the XANES (X-ray Absorption Near Edge Structure) pre-edge region presents three distinct peaks with different intensities depending on the crystal axis orientation with respect to the polarization direction of the X-ray beam. The peaks correspond to a combination of 1s to 4p and 1s to 3d transitions with possibly mixed dipole and quadrupole character. The EXAFS fitting reveals, as expected, a biased structure according to the relative position of the crystal with respect to the beam polarization and the fittings are in accordance to theoretical values. The best fitted model has a large contribution from multi-scattering paths, which clarifies the interpretation of the actual peak contributions on the Fourier Transformed signal.

Gold nanoparticles (AuNP) exhibit particular plasmonic properties when stimulated by visible light, which makes them a promising tool to many applications in sensor technology and biomedical applications, especially when associated to sulfur-based compounds. Sulfur species form a great variety of self-assembled structures that cap AuNP and this interaction rules the optical and plasmonic properties of the system. Here, we report the behavior of citrate-stabilized gold nanospheres in two distinct sulfur colloidal solutions, namely, thiocyanate and sulfide ionic solutions. Citrate-capped gold nanospheres were characterized using ultraviolet–visible (UV-Vis) absorption, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM). In the presence of sulfur species, we have observed the formation of NP clusters and chain-like structures, giving rise to surface-enhanced effects. Surface-enhanced Raman spectroscopy (SERS) pointed to a modification in citrate vibrational modes, which suggests substitution of citrate by either thiocyanate or sulfide ions with distinct dynamics, as showed by in situ fluorescence. Moreover, we report the emergence of surface-enhanced infrared absorption (SEIRA) effect, which corroborates SERS conclusions. Further, SEIRA shows a great potential as a tool for specification of sulfur compounds in colloidal solutions, which is particularly useful when dealing with sensor technology.