We report an in situ, temperature and H 2 pressuredependent, characterization of (2.6 ± 0.4) nm palladium nanoparticles supported on active carbon during the process of hydride phase formation. For the first time the core−shell structure is highlighted in the single-component particles on the basis of a different atomic structure and electronic configurations in the inner "core" and surface "shell" regions. The atomic structure of these particles is examined by combined X-ray powder diffraction (XRPD), which is sensitive to the crystalline core region of the nanoparticles, and by first shell analysis of extended Xray absorption fine structure (EXAFS) spectra, which reflects the averaged structure of both the core and the more disordered shell. In the whole temperature range (0−85 °C), XRPD analysis confirms the existence of two well-separated αand β-hydride phases with the characteristic flat plateau in the phase transition region of the pressure-lattice parameter isotherms. In contrast, first shell interatomic distances obtained from EXAFS exhibit a slope in the phase transition region, typical for nanostructured palladium. Such difference is explained by distinct properties of bulk "core" which has crystalline structure and sharp phase transition, and surface "shell" which is amorphous and absorbs hydrogen gradually without forming distinguishable αand β-phases. Combining EXAFS and XRPD we extract, for the first time, the Pd−Pd first-shell distance in the amorphous shell of the nanoparticles, that is significantly shorter than in the bulk core and relevant in catalysis. The core/shell model is supported by the EXAFS analysis of the higher shells, in the frame of the multiple scattering theory, showing that the evolution of the third shell distance (ΔR 3 /R 3 ) is comparable to the evolution of (Δa/a) obtained from XRPD since amorphous PdH x shell gives a negligible contribution in this range of distances. This operando structural information is relevant for the understanding of structure-sensitive reactions. Additionally, we demonstrate the differences in the evolution of the thermal parameters obtained from EXAFS and XRPD along the hydride phase formation.

Mixed-anion materials for Li-ion batteries have been attracting attention in view of their tunable electrochemical properties. Herein, we compare two isostructural (Fm3̅m) model intercalation materials Li2VO3 and Li2VO2F with O(2-) and mixed O(2-)/F(-) anions, respectively. Synchrotron X-ray diffraction and pair distribution function data confirm large structural similarity over long-range and at the atomic scale for these materials. However, they show distinct electrochemical properties and kinetic behaviour arising from the different anion environments and the consequent difference in cationic electrostatic repulsion. In comparison with Li2VO3 with an active V(4+/5+) redox reaction, the material Li2VO2F with oxofluoro anions and the partial activity of V(3+/5+) redox reaction favor higher theoretical capacity (460 mA h g(-1)vs. 230 mA h g(-1)), higher voltage (2.5 V vs. 2.2 V), lower polarization (0.1 V vs. 0.3 V) and faster Li(+) chemical diffusion (∼10(-9) cm(2) s(-1)vs. ∼10(-11) cm(2) s(-1)). This work not only provides insights into the understanding of anion chemistry, but also suggests the rational design of new mixed-anion battery materials.

New high‐capacity intercalation cathodes of Li2VxCr1−xO2F with a stable disordered rock salt host framework allow a high operating voltage up to 3.5 V, good rate performance (960 Wh kg−1 at ≈1 C), and cycling stability.

A facile water based synthesis method for HTB-FeF 3 /rGO and r-FeF 3 /rGO composites was developed using FeF 3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF 3 /rGO were cast in ambient air and the calendared electrode showed a stable specific energy of 470 Wh kg-1 (210 mAh g-1 , 12 mA g-1) after 100 cycles in the range 4.3-1.3 V with very little capacity fading. The good cycle stability is attributed to the intimate contact of FeF 3 nanoparticles with reduced graphene oxide carbon surrounding. We show using a combination of in situ XRD, XAS and ex situ Mössbauer spectroscopy that during discharge of HTB-FeF 3 /rGO composite Li is intercalated fast into the tunnels of the HTB-FeF 3 structure up to x = 0.95 Li followed by slow conversion to LiF and Fe nanoparticles below 2.0 V. During charge, the LiF and Fe phases are slowly transformed to amorphous FeF 2 and FeF 3 phases without reformation of the HTB-FeF 3 framework structure. At an elevated temperature of 55 °C a much higher specific energy of 780 Wh kg-1 was obtained.