Cheng-Xin Li

Recent advancements in solid oxide electrochemical cells (SOCs) heavily depend on the development of active and stable oxygen electrodes that exhibit superior activity and stability for oxygen reduction and evolution reactions at low temperatures. Here, we report a new surface-constructed oxygen electrode, Sr(Mg,Ti,Fe)O3–δ coated with Co3O4 (SMTF–Co3O4), designed to operate below 500 °C for low-temperature SOCs. The electrode electrochemical performance is primarily improved by the in situ reaction of Co3O4 with surface-segregated SrO, forming SrCoO3 and Co3O4/SrCoO3/SMTF heterointerfaces, which significantly enhances the surface oxygen adsorption capacity. The SMTF–Co3O4 electrode demonstrates a remarkably low reaction activation energy of ∼0.56 eV, with electrode polarization resistance as low as 0.56 Ω cm2 at 450 °C. The full cell, incorporating a thin scandia-stabilized zirconia (ScSz) electrolyte (∼3 μm) and the SMTF–Co3O4 oxygen electrode, reaches maximum power density and electrolysis current density (at 1.3 V) of 0.6 W/cm2 and 0.44 A/cm2, respectively, at 500 °C. Especially, 5–8 times enhancement in the cell performance at 450 °C is achieved by SMTF with the surface construction compared to the pristine electrode. Furthermore, the SMTF–Co3O4 electrode maintains stable performance in both fuel cell and electrolysis modes.

To clarify the microstructural stability of heavily deformed tungsten thin sheets upon high temperature annealing, four tungsten based materials (pure W, W-1 wt% La₂O₃, W-5 wt% Re and W- 40 ppm K) were rolled to achieve an extreme thickness reduction of 97.5 %. Isochronal annealing from 1000 ℃ to 1550 ℃ and isothermal annealing at 1250 ℃ were carried out. Microstructural evolution, recrystallized fraction and hardness variation were characterized by OM, EBSD and Vickers hardness tests. Pure W shows the highest recrystallization susceptibility owing to high stored deformation energy. W-K undergoes rapid recrystallization within 1250~1350 ℃. Re solid solution effect postpones recrystallization nucleation and early stage grain boundary migration, so obvious recrystallization in W-Re only occurs above 1450 ℃. Benefiting from particle pinning, W-La₂O₃ exhibits sluggish recrystallization kinetics and superior high temperature microstructural stability. W-La₂O₃ retains relatively high hardness over the whole annealing range, while W-Re suffers severe softening after full recrystallization. The results indicate that solid solution strengthening mainly raises the onset temperature of recrystallization, whereas dispersion strengthening dominates in retarding recrystallization completion and suppressing grain growth.

CoAlNiCrFeHfY high entropy coatings containing 0, 0.5, 1, 2, and 3wt.% CeO2 were fabricated, and their oxidation at 1100℃ was systematically investigated. During coating deposition, CeO2 reacted in situ with Al in the molten pool to form Ce-Al-O compounds, which consumed Al and consequently led to the formation of minor Al-depleted phase. Long-term oxidation tests showed that α-Al2O3 was the predominant oxidation product in five coatings. The addition of a small amount of CeO2 (0.5wt.%) reduced the TGO growth rate to some extent and improved its spallation resistance, which was attributed to the REE induced by an appropriate amount of Ce4+ or Ce3+. In contrast, excessive CeO2 addition promoted the precipitation of Ce-rich oxides within the TGO. These precipitates not only increased the ionic diffusion rate by more than threefold, thereby accelerating TGO growth, but also generated high local compressive stresses (~30-40MPa), promoting rapid TGO spallation. These findings provide useful guidance for optimizing the composition of CoAlNiCrFeHfY high-entropy coatings to enhance their oxidation resistance in high-temperature applications.

Although the design of bilayer interconnects in solid oxide fuel cells (SOFCs) has attracted attention, the regulation mechanism of the bilayer interconnect system on the electrical transport properties remains unclear.

CoAlNiCrFeHfY high entropy coatings containing 0, 0.5, 1, 2, and 3wt.% CeO2 were fabricated, and their oxidation at 1100℃ was systematically investigated. During coating deposition, CeO2 reacted in situ with Al in the molten pool to form Ce-Al-O compounds, which consumed Al and consequently led to the formation of minor Al-depleted phase. Long-term oxidation tests showed that α-Al2O3 was the predominant oxidation product in five coatings. The addition of a small amount of CeO2 (0.5wt.%) reduced the TGO growth rate to some extent and improved its spallation resistance, which was attributed to the REE induced by an appropriate amount of Ce4+ or Ce3+. In contrast, excessive CeO2 addition promoted the precipitation of Ce-rich oxides within the TGO. These precipitates not only increased the ionic diffusion rate by more than threefold, thereby accelerating TGO growth, but also generated high local compressive stresses (~30-40MPa), promoting rapid TGO spallation. These findings provide useful guidance for optimizing the composition of CoAlNiCrFeHfY high-entropy coatings to enhance their oxidation resistance in high-temperature applications.

La₀.₆Sr₀.₄Co₀.₂Fe₀.₈O₃−δ (LSCF) has been widely employed as a cathode and current collector material for tubular segment in series solid oxide fuel cells (Tubular SIS-SOFCs), yet plasma-sprayed LSCF current collector layers (CCLs) often suffer from insufficient gas permeability and performance degradation caused by B-site element evaporation in high-temperature plasma jets, while conventional noble-metal current collectors increase cost and compromise long-term stability. In this work, a composite strategy was developed by incorporating transition-metal particles into LSCF feedstock via atmospheric plasma spraying (APS) to construct a noble-metal-free ceramic CCL. Due to poor wettability between overheated metal droplets and LSCF splats, metallic particles solidified in a dispersed morphology within the coating. During subsequent heat treatment, in situ oxidation-induced volumetric expansion of metal particles promoted controlled crack propagation, enhancing gas diffusion pathways, while thermally driven metal-ion diffusion partially compensated B-site depletion and restored lattice conductivity. Systematic investigation revealed that the LSCF–5Fe coating fabricated at 25 kW achieved an optimal balance between gas permeability, mechanical integrity, and electrical conductivity. Among different metals, LSCF–5Cu exhibited the highest post-treatment conductivity of 100.5 S cm⁻¹. Tubular SIS-SOFCs employing metal-particle-modified LSCF CCLs delivered over 50% higher maximum power output compared with pure LSCF counterparts, accompanied by significantly reduced polarization resistance and stable thermal cycling performance. These results demonstrate a scalable and cost-effective strategy for replacing noble-metal current collectors and enabling high-power tubular SIS-SOFCs.