Tatsumi Ishihara

Solid oxide fuel cells (SOFCs) require electrolytes with high oxide-ion conductivity at low temperatures (200–400 °C) to reduce costs. Here, we report that Bi _1.9 Te _0.1 LaO _4.05 Br exhibits oxide-ion conductivity of 0.01 S cm⁻¹ at 233 °C within the “Norby gap” in dry atmospheres. This performance exceeds that of leading proton conductors, such as BaZr _0.8 Y _0.2 O _2.9 and BaZr _0.4 Ce _0.4 Y _0.1 Yb _0.1 O _2.9 , as well as representative oxide-ion conductors, including yttria-stabilized zirconia (YSZ), LaGaO ₃ -based phases (LSGM), and Bi ₂ V _0.7 Sb _0.3 O _5.5 . Bi _1.9 Te _0.1 LaO _4.05 Br also exhibits negligible chemical expansion and high chemical stability under oxidizing, reducing, and CO ₂ -containing atmospheres. The high conductivity is associated with a layered Sillén structure composed of Bi-containing triple fluorite-like slabs and Br layers, together with oxygen vacancies that enable vacancy-mediated oxide-ion migration. Despite the presence of excess oxide ions, oxide-ion transport predominantly occurs via a vacancy mechanism, as revealed by ab initio molecular dynamics simulations, static density functional theory calculations, and neutron diffraction analyses. These findings establish a design principle for high-performance oxide-ion conductors based on vacancy-mediated oxide-ion transport in excess-oxygen Bi-containing Sillén oxyhalides.

Cu exsoultion and the formation of a Zn-rich surface on CZFO promote efficient CO ₂ –H ₂ O co-electrolysis, enhancing CO production with high faradaic efficiency and excellent durability.

Energy conversion and storage with high efficiency are among the most important subjects for achieving a carbon-neutral society from the perspectives of environmental protection and energy security. In this review, solid oxide cells using LaGaO3-based perovskite oxides as electrolytes are described, together with their reversible operation in electrolysis and fuel-cell modes. Since tight gas sealing is essential for achieving high efficiency, a tubular cell design was adopted, in which a LaGaO3-based oxide film prepared by dip coating and co-sintering was used as the electrolyte. Despite the tubular design, the prepared cell exhibited high performance in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes, with high reversibility between the two operating modes. The CO2 electrolysis performance of this tubular-type cell is also described. In addition, the application of a highly concentrated ion-conducting aqueous electrolyte combined with tetraglyme, referred to as a hybrid aqueous electrolyte, is introduced, together with its application to a dual-ion battery.

Defect states in semiconductor photocatalysts can influence interfacial electron transfer and charge-carrier recombination, depending on their electronic properties and spatial distribution relative to reactive interfaces. Accordingly, a hexadecyltrimethylammonium bromide (CTAB)-assisted sol-gel method is employed to regulate oxygen-related defect environments in a single-phase cubic fluorite (Ce0.2Zr0.2Pr0.2Eu0.2Y0.2)O2-δ high-entropy oxide (HEO). Adjusting the CTAB amount during synthesis modifies lattice microstrain, nanocrystallite aggregation, specific surface area, surface cation oxidation-state distributions, and defect-associated oxygen environments. An intermediate CTAB amount yields the highest H2 evolution rate, coinciding with the highest relative contribution of the defect-associated species to the O 1s spectrum and comparatively low electron paramagnetic resonance (EPR) signal intensity. The optimized single-phase, cocatalyst-free fluorite HEO achieves H2 evolution rates of 483 and 1429 μmol g-1 h-1 at incident irradiances of 100 and 250 mW cm-2, respectively, and outperforms TiO2 P25 under identical conditions. These results identify CTAB-mediated modulation of oxygen-related defect environments as a viable strategy for enhancing photocatalytic H2 evolution in fluorite HEOs.

SrO/Co ₃ O ₄ perimeter interfaces promote oxygen dissociation by lowering the Co ₃ O ₄ work function and improving oxygen reduction kinetics.

A single cell with the configuration of LSCF/GDC/LSGM/Ni-SDC was fabricated and kinetic analysis of the electrochemical performance of electrodes under steam electrolysis and fuel cell operation was performed at 550-800 °C. Electrochemical impedance spectroscopy revealed that the polarization resistance of the LSCF/GDC air electrode (0.12 Ω cm²) was lower than that of the Ni-SDC fuel electrode (0.25 Ω cm²) at 800 °C, while both values became comparable at lower temperatures, indicating temperature dependence changes in electrode polarization behaviour. Tafel analysis based on the Butler-Volmer equation was performed separately for each electrode by using two reference electrodes. The Ni-SDC fuel electrode showed asymmetric kinetic behaviour, with activation energies of 0.94 and 1.25 eV in SOFC and SOEC modes, respectively, suggesting different reaction pathways under anodic and cathodic polarization. In contrast, the LSCF/GDC air electrode exhibited nearly identical exchange current density values at 800 °C in both modes, indicating highly reversible kinetic. The reconstructed Butler-Volmer curves showed good agreement with experimental data, confirming the reasonable values of the kinetic parameters of electrodes.

Metal-support solid oxide cells are attracting much interest as advanced fuel cells from high reliability and thermal management. However, there is limited number of metal support proton conducting fuel cells reported, In this study, metal support BaZr0.44Ce0.36Y0.2O3-δ (BZCY) electrolytes was studied and for solving the decreased open circuit voltage due to insufficient proton transport number in the high PO2 range, Ba-doped LaScO3 (LBS) thin films on air side of BZCY cells were applied. Doped LaScO3-based oxides are known for their excellent chemical and structural stability. However, the doped LaScO3 proton conductor typically requires a high sintering temperature (>1300 °C) when prepared using the conventional PCFC fabrication process. In this study, Ba2+ was substituted at the La3+ site to induce further lattice expansion and oxygen vacancy formation, thereby promoting hydration and proton incorporation. The LBS layer, deposited by the pulsed laser deposition (PLD) technique at 800 °C to obtain a dense and thin proton-conducting layer including BZCY electrolyte. On the surface of the electrolyte of PCFCs, this LBS layer effectively enhances water uptake and proton conduction during cell operation. It was found that OCV of 1.03V close to the theoretical one and the highest power density of 903 mW/cm2 were achieved.

Understanding and controlling dopant–vacancy interactions is central to the design of high-performance oxide-ion conductors.

A double-decker cell is fabricated by stacking an oxide-conducting half-cell onto a proton-conducting half-cell, interconnected by a porous interlayer. This double-decker cell is considered an ideal solid oxide cell for steam electrolysis.