LiCo 1Ày Fe y PO 4 solid solutions (0 # y # 1) were prepared by the mechanochemically assisted carbothermal reduction of Co 3 O 4 and Fe 2 O 3 . Mechanical activation was performed using a high-energy planetary mill AGO-2. The samples were characterized in detail by X-ray powder diffraction (XRD) using a Rietveld refinement, Fourier transform infrared spectroscopy (FTIR), M össbauer spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), galvanostatic cycling, and galvanostatic intermittent titration technique (GITT). According to XRD, all the samples are single-phase solid solutions, crystallized in an orthorhombic structure (S.G. Pnma). The cell volume of LiCo 1Ày Fe y PO 4 linearly increases vs. the Fe content. All the Fe ions are in the 2+ oxidation state and are octahedrally coordinated. The LiCo 1Ày Fe y PO 4 solid solutions show improved electrochemical performance, compared with LiCoPO 4 . Based on the data from XRD and GITT, the improvement is attributed to the enhanced Li + diffusion, due to the enlargement of the 1D diffusion channels in the polyanion structure of LiCoPO 4 and the reduced cell volume change in the material during the Li extraction/insertion process. Moreover, a systematic decrease in the average potential of the Co 2+ /Co 3+ redox pair is observed with the increased Fe content, leading to the reaction termination in the electrochemical window of conventionally available electrolytes. In situ synchrotron diffraction shows that upon charging LiCo 0.5 Fe 0.5 PO 4 , the twophase mechanism of Li (de)intercalation at the Fe 2+ /Fe 3+ and Co 2+ /Co 3+ redox stages changes to a solid solution-like mechanism, contrary to the pristine LiFePO 4 and LiCoPO 4 materials.

Alkali metal promoters have been widely employed for preparation of heterogeneous catalysts used in many industrially important reactions. However, the fundamentals of their effects are usually difficult to access. Herein, we unravel mechanistic and kinetic aspects of the role of alkali metals in CO2 hydrogenation over Fe‐based catalysts through state‐of‐the‐art characterization techniques, spatially resolved steady‐state and transient kinetic analyses. The promoters affect electronic properties of iron in iron carbides. These carbide characteristics determine catalyst ability to activate H2, CO and CO2. The Allen scale electronegativity of alkali metal promoter was successfully correlated with the rates of CO2 hydrogenation to higher hydrocarbons and CH4 as well as with the rate constants of individual steps of CO or CO2 activation. The derived knowledge can be valuable for designing and preparing catalysts applied in other reactions where such promoters are also used.

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Rietveld profiles, Mössbauer spectra and x-ray absorption fine structure (XAFS) were analyzed through the structural phase transition at T s = 355 K in HoBaCo 4 O 7 . Excess of the oxygen content over "O 7 " was avoided via annealing the samples in argon flow at 600 • C. Space groups (S.G.) P bn2 1 c and P 6 3 mc were used to refine the structure parameters in the low-and high-temperature phases, respectively. Additionally, the Cmc2 1 symmetry was considered as a concurrent model of structure of the low-temperature phase. In the high-temperature phase, severe anisotropy of thermal motion of the major part of the oxygen atoms was observed. This anisotropic motion turns to be quenched as the sample is cooled below T s . The variation of quadrupole splitting ε near T s is not similar to a steplike anomaly frequently seen at the charge-ordering transition. We observe instead a dip-like anomaly of the average ε near T s . Narrow distribution of the electric field gradient (EFG) over different cobalt sites is observed and explained on the basis of point-charge model. XAFS spectra show no evidence of significant difference between YBaCo 4 O 7 (T > T s ) and HoBaCo 4 O 7 (T < T s ). The origin of the transition at T s is ascribed to the condensation of the libration phonon mode associated with the rigid-body rotational movements of the starlike tetrahedral units, the building blocks of kagomé network. It is shown that the condensation of the libration mode is not compatible with translation symmetry for the hexagonal S.G., but compatible for the orthorhombic S.G. The orthorhombic lattice parameters and EFG components (V xx , V yy , V zz ) vary smoothly with temperature at approaching T s and closely follow each other.

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In this work, XRD, EDX, Mössbauer and NMR spectroscopy were used to study chemical and electrochemical Na + /Li + ion exchange in the sodium iron pyrophosphate Na 1.56 Fe 1.22 P 2 O 7 with a triclinic symmetry, S. G. P-1, and sodium vanadium fluorophosphate Na 3 V 2 (PO 4 ) 2 F 3 with a tetragonal symmetry, S. G. P4 2 /mnm, cathode materials. Electrochemical Na + /Li + ion exchange was performed in hybrid-ion cells with Li metal anode and LiPF 6 -based electrolyte, while chemical ion exchange was realized in the solution of LiBr in acetonitrile. A facile electrochemical and chemical Na + /Li + ion exchange was observed for both cathode materials, resulting in the formation of the mixed Na-Li compositions: ∼Na Sodium-ion batteries have been considered as potential candidates for stationary energy storage, because of the low cost and wide availability of sodium sources. Sodium is more abundant and less expensive than lithium. However, Na-ion based systems have a lower energy density compared to Li-ion systems since a reduction potential of sodium metal vs. SHE is 0.3 V higher than that of lithium. Sodium has a larger ionic radius and bigger molecular weight. Therefore, sodium-based insertion materials are of interest for low-cost and large-scale Na-ion batteries. Substantial research efforts have been invested during the previous years to produce electrode materials for sodium batteries allowing facile intercalation of the Na ions at suitable potentials. Amongst the cathode materials investigated, various layered oxides (e.g. Na 0.6 CoO 2 , Na 2/3 Fe 1/3 Mn 2/3 O 2 , Na 2/3 Ni 1/3 Mn 2/3 O 2 , NaNi 1/3 Co 1/3 Mn 1/3 O 2 , etc.) and polyanionic compounds (e.g. NaFePO 4 , Na 2 FePO 4 F, Na 3 V 2 (PO 4 ) 3 , NaFeSO 4 F, etc.) are the most favorite cathode materials.1 To enhance the electrochemical performance of sodium-based cathode materials, Barker et al. first proposed a concept of a hybrid-ion battery whereby a non-lithium containing cathode material is used in conjunction with metallic Li, graphite, Li 4 Ti 5 O 12 , etc., and Li-based or mixed Li/Na electrolytes.2-5 The Na + /Li + ion exchange is an effective way to produce new metastable mixed Na/Li phases for Li-ion batteries without causing many structural changes to the pristine sodium-based materials. A new design concept of the simultaneously energy storage of multi-metal ions may overcome respective disadvantages of singlemetal ions and bring to a synergy effect. 6,7 Since the operation of hybrid-ion batteries depends on the reactivity of the selected electrodes in respect of Li + and Na + ions, two Na-based cathode materials, differing by crystal structure, triclinic Na 1.56 Fe 1.22 P 2 O 7 and tetragonal Na 3 V 2 (PO 4 ) 2 F 3 , were selected in this work to study electrochemical and chemical Na + /Li + ion exchange and their performance in hybridion cells.Sodium iron pyrophosphates 8,9 with a triclinic symmetry (S.G. P-1) and sodium vanadium fluorophosphates with tetragonal symmetry (S.G. P4 2 /mnm) [10][11][12] were recently examined and showed good e...

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