The development of cobalt-free mixed ionic-electronic conductors (MIECs) for protonic ceramic fuel cells and electrolysis cells (PCFCs/PCECs) requires electrode materials that combine high electrochemical activity with chemical compatibility towards barium-based proton-conducting electrolytes. While many studies have focused on avoiding barium-containing electrode systems due to stability concerns, such materials are in fact highly attractive for PCFCs and PCECs because they share the same cation sublattice as BaCeO3- and BaZrO3-based electrolytes that might minimize interfacial reactions and secondary phase formation. In this context, the perovskite ferrite Pr0.6Ba0.4FeO3–δ represents a promising matrix for electrode design. The present work investigates the effect of partial iron substitution by nickel in Pr0.6Ba0.4Fe1–xNixO3–δ (x = 0.1, 0.2, 0.3) on structural properties, electrical transport behavior, and electrochemical performance. The materials were characterized by X-ray diffraction, four-probe DC conductivity measurements, and electrochemical impedance spectroscopy on symmetrical cells with BaCe0.5Zr0.3Y0.1Yb0.1O3–δ electrolyte. The results establish clear composition–structure–property correlations: the nickel content systematically affects the lattice parameters, governs the conductivity behavior in oxidizing and reducing atmospheres, and influences the electrode polarization resistance and depends strongly on the operating conditions. Notably, the optimal nickel concentration differs between oxidizing and reducing environments, which has direct implications for selecting electrode compositions for specific applications. The findings demonstrate that nickel-doped Pr0.6Ba0.4FeO3–δ offers a flexible compositional platform for designing cobalt-free, barium-containing MIEC electrodes with enhanced compatibility and performance in protonic ceramic electrochemical devices.
The emf method was implied to measure the redox potentials of the molten LiF–BeF2–UF4/UF3 mixture at the temperatures of 923, 973 and 1023 K with a different ratio of uranium trifluoride and uranium tetrafluoride in the melt. Dependencies of the redox potentials of the studied systems have been obtained using a molybdenum indicator electrode. The redox potentials were found to change linearly as the temperature increased within the whole studied temperature range. Comparative analysis of the experimentally obtained data elucidated that measured redox potentials in the 0.73LiF–0.27BeF2 melts correspond to the definite UF4/UF3 ratio. The value of the media redox potential may be used to evaluate the molar fraction concentrations of trivalent and tetravalent uranium in the melt.
Neodymium tungstates and their composites with metal alloys, such as NiCu, have emerged as promising materials for hydrogen separation membranes due to their high proton conductivity and stability in CO2-containing atmospheres. The fabrication of gas-tight ceramics based on these materials constitutes a distinct challenge. A promising approach to address this issue is the utilization of advanced sintering techniques, such as radiation-thermal sintering using an electron beam. The present study investigates the impact of radiation-thermal sintering temperature on the structural, textural properties, hydration ability, and oxygen mobility of Nd5.5WO11.25−δ oxides and NiO–CuO–Nd5.5WO11.25−δ composites, the precursors of NiCu alloy – Nd5.5WO11.25−δ materials for hydrogen separation membranes. The main phase of the Nd5.5WO11.25−δ samples is defective double fluorite, while their composites contain various nickel and copper oxides along with the neodymium tungstate phase. The attainment of gas-tightness in Nd5.5WO11.25−δ samples is achieved even at relatively low sintering temperatures (1200–1300 °C), which is unattainable through sintering in a furnace. Conversely, the composite samples exhibit high porosity. Hence, the procedure of preparing the NiO–CuO–Nd5.5WO11.25−δ composites required further optimization. Nd5.5WO11.25−δ sintered by e-beam at 1100–1300 °C exhibit optimal hydration properties. The highest oxygen mobility is demonstrated for the samples sintered at 1100 and 1200 °C (D* up to ~ 10−8 cm2/s), which is promising in the context of the incorporation and transport of protons in hydrogen separation membranes. Consequently, e-beam sintering emerges as a promising method for producing proton conductive ceramics based on Nd tungstate.
Solid oxide cells require highly active, stable air electrodes for intermediate-temperature operation. Owing to dual-doping synergetic effects, Pr1.6Ca0.4Ni0.6Cu0.4O4+δ material exhibits enhanced phase stability under operational conditions compared to Pr2NiO4+δ along with a low polarization resistance of 0.40–0.65 Ohm · cm² at 700 °C. However, its low-temperature electrochemical activity significantly deteriorates due to a reduction in the highly mobile interstitial oxygen content resulting from doping. To extend the operational range of this electrode, this study aims to enhance its performance using the infiltration technique. The investigation includes optimization of the electrode backbone structure and evaluation of the effects of precursor concentration and the number of infiltration cycles on microstructure and electrochemical properties. The results demonstrate that a 1 M solution prevents surface blocking, yielding uniform catalyst distribution. The optimized electrode exhibits a remarkably low polarization resistance of 0.25 Ohm · cm2 at 600 °C. Furthermore, direct infiltration into the functional layer ensures superior long-term stability and provides a scalable strategy for advanced electrochemical devices.
This study presents a comparative characterisation of 16 mm Brazilian imported and locally produced Land craft industrial (LCI) reinforcement steel rebars through chemical analysis, ImageJ microstructural evaluation, sliding wear testing, and electrochemical corrosion assessment in 1 M H2SO4. Chemical analysis showed that Brazilian steel exhibited lower levels of detrimental impurities – sulphur (0.014 %), phosphorus (0.0097 %), and copper (0.013 %) – relative to LCI steel (0.056 %, 0.106 %, and 0.253 %, respectively), indicating superior compositional purity. Microstructural analysis revealed a significantly finer grain structure in Brazilian steel (average grain size: 201.94 µm2; Feret diameter: 11.61 µm) compared to coarser-grained LCI steel (1776.30 µm2; 20.71 µm). Sliding wear tests demonstrated that LCI steel lost less mass (0.029 g) than Brazilian steel (0.038 g) under identical sliding conditions, indicating better wear resistance attributed to its coarser, carbide-rich microstructure. Electrochemical evaluation, supported by open-circuit potential measurements, potentiodynamic polarisation curves, and scanning electron microscopy/energy dispersive spectrum (SEM/EDS) post-exposure compositional analysis, revealed distinct corrosion susceptibilities between the two steels in acidic medium: LCI steel showed a higher polarisation resistance (Rp = 23.8 Ohm vs. 6.0 Ohm), a lower corrosion current density (icorr ≈ 128 vs. ≈ 1267 µA/cm2), and a lower corrosion rate (CR ≈ 1.49 vs. ≈ 14.7 mm/y) than Brazilian steel, with compositional and microstructural differences playing a significant role. These results provide a quantitative basis for assessing the corrosion and wear behaviour of both imported and domestically manufactured reinforcement steels under the tested conditions.
