Antimony substituted lanthanum orthoniobate proton conductor – structure and electronic properties.

X‐ray and neutron diffraction have been utilized to analyze the crystalline and electronic structure of lanthanum orthoniobate substituted by antimony. Using X‐ray absorption spectroscopy and photoelectron spectroscopy, changes in the electronic structure of the material upon substitution have been analyzed. The structural transition temperature between fergusonite and scheelite phases for 30 mol% antimony substitution was found to be 15 °C. Based on the neutron data, the oxygen nonstoichiometry was found to be relatively low. Moreover, no influence on the position of the valence band maximum was observed. The influence of the protonation on the electronic structure of constituent oxides has been studied. Absorption data show that the incorporation of protonic defects into the lanthanum orthoniobate structure leads to changes in lanthanum electronic structure and a decrease in the density of unoccupied electronic states.

Ceramic composites for single-layer fuel cells

Composite materials consisting of acceptor doped lanthanum orthoniobate electrolyte phase (La0.98Ca0.02NbO4) and Li2O:NiO:ZnO semiconducting phase were synthesized. The precursor powder of La0.98Ca0.02NbO4 was prepared in nanocrystalline (mechanosynthesis) and microcrystalline (solid-state synthesis) form. The composite can be applied in a single-layer fuel cell, because of the presence of two phases acting as an anode and a cathode simultaneously. X-ray diffraction data show that the materials consist of two expected phases. Scanning Electron Microscope images, with Energy Dispersive X-Ray analysis show that La0.98Ca0.02NbO4 as well as Li2O:NiO:ZnO are mixed together in the volume of the material. Open circuit voltage both for nano- and microcrystalline composite do not exceed 0.8 V. The single-layer fuel cell is degrading upon time and the voltage drop is observed. The processes of ZnO reduction and Zn diffusion and evaporation as responsible for cell degradation are discussed.

Conductivity, structure, and thermodynamics of Y2Ti2O7–Y3NbO7 solid solutions

P. Winiarz , A. Mielewczyk-Gryń , K. Lilova, S. Wachowski , T. Subramani, M. Abramchuk, E. Dzik , A. Navrotsky, M. Gazda DALTON TRANSACTIONS – 2020
The defect fluorite yttrium niobate Y3NbO7 and pyrochlore yttrium titanate Y2Ti2O7 solid solutions have been synthesized via a solid state synthesis route. The resulting stoichiometry of the oxides is Y2+xTi2−2xNbxO7, where x = 0 to x = 1. All of the samples were single-phase; however, for those with a predominant fluorite phase, a small amount of additional pyrochlore phase was detected. The volume of the solid solution unit cells linearly increases with increase in yttrium niobate content. The water uptake increases with (x) and the protonic defect concentration reaches almost 4.5 × 10−3 mol mol−1 at 300 °C. The calculated enthalpy of formation from oxides suggests strong stability for all of the compositions, with the values of enthalpy ranging from −84.6 to −114.3 kJ mol−1 . The total conductivity does not have a visible dependence on Y3NbO7 content. For each compound, the total conductivity is higher in wet air. Interestingly, for samples where x < 0.5, the ratio of conductivity in hydrogen to air increases with increasing temperature, while for x > 0.5, the trend is the opposite.

Evolution of magnetic and transport properties in (Cr1−xMnx)2AlC MAX-phase synthesized by arc melting technique

K. Sobolev, K. Kolincio , A. Emelyanov, A. Mielewczyk-Gryń , M. Gazda , M. Roman , A. Pazniak, V. Rodionova – JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS – 2020
Herein we initiate a comeback to the arc melting technique to produce MAX-phase solid solutions. Bulk samples of (Cr1−xMnx)2AlC MAX-phase with X = 0, 0.025, 0.05 and 0.1 were synthesized and studied by means of X-ray diffractometry, scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. Samples were established to be homogeneous with an incorporation of Cr7C3, AlCr2 and Al2O3 secondary phases which is slightly increasing with the raise of the dopant concentration. Manganese successfully intermixes in the MAX-phase structure due to the effect of the high-energetic plasma during the melting process. SQUID magnetometry identified the co-existence of ferro- and antiferromagnetic interactions with the latter prevailing in high temperatures and being attributed to the MAX-phase. Magnetic state transitions were observed at approximately 4 K and 5 K for doped samples which was associated with the presence of the marginal amount of ferromagnetic Mn-based secondary phases. The negative component of magnetoresistance was observed in highly doped samples at low temperatures that is likely due to the influence of ferromagnetic secondary phases as well. Transport properties measurement revealed the satisfactory quality of the produced samples.

Functional phase bistability in a nanocrystalline RbMn[Fe(CN)6] thin film fabricated by matrix-assisted laser evaporation

D. Maskowicz, M. Sawczak, R. Jendrzejewski, M. Gazda , H. Tokoro, S. Ohkoshi, Y. Garcia, G. Śliwiński – SCRIPTA MATERIALIA – 2020
One of the main barriers hindering applications of Prussian blue metal assemblies is their poor processability, which makes the fabrication of intact thin films very difficult. In this work, a nanocrystalline RbMn[Fe(CN)6]·xH2O film on silicon substrate was obtained for the first time via laser-stimulated deposition and investigated. Temperature-induced phase transition and bistability within broad hysteresis loop (120 K), along with transition temperatures up to 317 K, which is the highest in the RbMnFe series, were observed using variable-temperature Raman spectroscopy. This study thus proposes a reliable deposition approach for preparing a functional magnetic materials that operate at room temperature.

Investigation of praseodymium and samarium co-doped ceria as an anode catalyst for DIR-SOFC fueled by biogas

The Pr and Sm co-doped ceria (with up to 20 mol.% of dopants) compounds were examined as catalytic layers on the surface of SOFC anode directly fed by biogas to increase a lifetime and the efficiency of commercially available DIR-SOFC without the usage of an external reformer. The XRD, SEM and EDX methods were used to investigate the structural properties and the composition of fabricated materials. Furthermore, the electrical properties of SOFCs with catalytic layers deposited on the Ni-YSZ anode were examined by a current density-time and current density-voltage dependence measurements in hydrogen (24h) and biogas (90h). Composition of the outlet gasses was in situ analysed by the FTIR-based unit. It has been found out that Ce0.9Sm0.1O2-δ and Ce0.8Pr0.05Sm0.15O2-δ catalytic layers show the highest stability over time and thus are the most attractive candidates as catalytic materials, in comparison with other investigated lanthanide-doped ceria, enhancing direct internal reforming of biogas in SOFCs.

Nano Tin/Tin Oxide Attached onto Graphene Oxide Skeleton as a Fluorine Free Anode Material for Lithium-Ion Batteries

Herein, we show a composite formation method of tin/tin oxide nanoparticles with graphene oxide and CMC based on laser ablation technique as an electrode material for energy storage devices. The material exhibited a three-dimensional conducting graphene oxide network decorated with tin or tin oxide nanoparticles. The structure, homogeneous distribution of nanoparticles, and direct contact between inorganic and organic parts were confirmed by scanning electron microscopy and high-resolution transmission electron spectroscopy. Electrochemical performances of composite electrode material showed a reversible capacity of 644 mAh/g at a current density equal to 35 mA/g, and 424 mAh/g at 140 mA/g. The capacity retention of 90% after 250 cycles show that tested electrode material is suitable as a negative electrode for lithium-ion batteries.

Pulsed Laser Deposition of Bismuth Vanadate Thin Films—The Effect of Oxygen Pressure on the Morphology, Composition, and Photoelectrochemical Performance

K. Trzciński , M. Szkoda , M. Gazda , J. Karczewski , A. Cenian, G. Grigorian, M. Sawczak – Materials – 2020
Thin layers of bismuth vanadate were deposited using the pulsed laser deposition technique on commercially available FTO (fluorine-doped tin oxide) substrates. Films were sputtered from a sintered, monoclinic BiVO4 pellet, acting as the target, under various oxygen pressures (from 0.1 to 2 mbar), while the laser beam was perpendicular to the target surface and parallel to the FTO substrate. The oxygen pressure strongly affects the morphology and the composition of films observed as a Bi:V ratio gradient along the layer deposited on the substrate. Despite BiVO4, two other phases were detected using XRD (X-ray diffraction) and Raman spectroscopy—V2O5 and Bi4V2O11. The V-rich region of the samples deposited under low and intermediate oxygen pressures was covered by V2O5 longitudinal structures protruding from BiVO4 film. Higher oxygen pressure leads to the formation of Bi4V2O11@BiVO4 bulk heterojunction. The presented results suggest that the ablation of the target leads to the plasma formation, where Bi and V containing ions can be spatially separated due to the interactions with oxygen molecules. In order to study the phenomenon more thoroughly, laser-induced breakdown spectroscopy measurements were performed. Then, obtained electrodes were used as photoanodes for photoelectrochemical water splitting. The highest photocurrent was achieved for films deposited under 1 mbar O2 pressure and reached 1 mA cm−2 at about 0.8 V vs Ag/AgCl (3 M KCl). It was shown that V2O5 on the top of BiVO4 decreases its photoactivity, while the presence of a bulk Bi4V2O11@BiVO4 heterojunction is beneficial in water photooxidation.

Structural and catalytic properties of ceria layers doped with transition metals for SOFCs fueled by biogas

The aim of this paper was to investigate an influence of the nanocrystalline Ce0.8A0.2O2-δ (A = Mn, Fe, Co, Ni, Cu) materials on the direct internal reforming of biogas in SOFC. Structural analysis of fabricated compounds has been done. An in-situ analysis of a composition of outlet gases from operating SOFC was performed using FTIR spectroscopy with simultaneous electrical tests. It was found out, that type of dopant strongly affects biogas reforming process. The differences in absolute values of current density resulted mostly from a microstructure and probably phase composition of a deposited layers. Fuel cells with Ce0.8Co0.2O2-δ and Ce0.8Ni0.2O2-δ additional layers presented the highest drop of current density after switching from hydrogen to biogas, but simultaneously they were the most stable in time. Additional chemical analysis revealed that steam reforming and methane pyrolysis might be dominating reactions while working in biogas atmosphere.

Structural Properties and Water Uptake of SrTi1−xFexO3−x/2−δ

In this work, Fe-doped strontium titanate SrTi1−xFexO3−x/2−δ, for x = 0–1 (STFx), has been fabricated and studied. The structure and microstructure analysis showed that the Fe amount in SrTi1−xFexO3−x/2−δ has a great influence on the lattice parameter and microstructure, including the porosity and grain size. Oxygen nonstoichiometry studies performed by thermogravimetry at different atmospheres showed that the Fe-rich compositions (x > 0.3) exhibit higher oxygen vacancies concentration of the order of magnitude 1022–1023 cm−3. The proton uptake investigations have been done using thermogravimetry in wet conditions, and the results showed that the compositions with x < 0.5 exhibit hydrogenation redox reactions. Proton concentration at 400 °C depends on the Fe content and was estimated to be 1.0 × 10−2 mol/mol for SrTi0.9Fe0.1O2.95 and 1.8 × 10−5 mol/mol for SrTi0.5Fe0.5O2.75. Above 20 mol% of iron content, a significant drop of proton molar concentrations at 400 °C was observed. This is related to the stronger overlapping of Fe and O orbitals after reaching the percolation level of approximately 30 mol% of the iron in SrTi1−xFexO3−x/2−δ. The relation between the proton concentration and Fe dopant content has been discussed in relation to the B-site average electronegativity, oxygen nonstoichiometry, and electronic structure.