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For efficient energy conversion and energy storage, developing highly efficient hydrogen permeable membranes is a crucial issue. Ceramic hydrogen permeable membranes, i.e., protonic electronic mixed conductors, work on bipolar transport of protons and electrons. Ceramic composite membranes meet this requirement with chemical and thermal stability, and they can be used not only as hydrogen permeable membranes but also as electrolytes in protonic ceramic fuel cells (PCFCs). Although improvement in protonic conductivity at heterointerfaces between constituting materials and/or space-charge relaxation around the resistive grain boundaries can be possible origins of the enhanced hydrogen permeability in the composite electrolyte membranes, its detailed mechanisms have not been clarified yet and the strategy of material design for composite membranes has not been established. In this study, the transport properties of composite electrolyte membranes consisting of protonic conductors and electronic conductors are investigated to realize highly efficient PCFC operating at low temperatures and to clarify the principles of carrier transport in the composite membranes. For the protonic conductor and the electronic conductor, we selected La2Ce2O7 (LDC) with a fluorite structure and La0.3Sr0.6TiO3 (LST) with a perovskite structure, respectively. The composite membrane composed of LDC and LST (LDC/LST) with various LDC to LST ratios was prepared by a solid-state reaction. Phase stability of LDC and LST were investigated by X-ray diffraction (XRD) measurements. Transport properties of hydrogen permeation cells using the LDC-LST composite membranes with Pt electrodes were assessed by electrochemical impedance spectroscopy (EIS) measurements and hydrogen permeation measurements. Hydrogen fluxes were measured by gas chromatography. The EIS measurements revealed that the grain-boundary resistance was reduced for the LDC/LST composite membrane in comparison with an LDC membrane. In particular, LDC/LST (weight ratio 1:2) showed the smallest grain-boundary resistance of 26 Ω cm at 600°C under 1%H2/Ar among the measured samples. Besides, the hydrogen permeation measurement showed that LDC/LST exhibited higher hydrogen permeability than the LDC membrane. In addition, the hydrogen flux of LDC/LST (1:2) was almost twice as high as that of LDC at 600°C. The low grain-boundary resistance and the high hydrogen permeability of LDC/LST composite membrane suggests that the introduction of LST accelerates the proton conduction in the membrane.

The mechanism of electrochemical promotion of ammonia formation was investigated by kinetic and deuterium isotope analyses using a cell with a Pt (anode)|BaCe0.9Y0.1O3 (BCY)|Fe (cathode) configuration on the introduction of a gaseous mixture of H2(D2)–N2 to the cathode at 550 °C. To clarify the mechanism of electrochemical ammonia synthesis, the reaction orders for hydrogen, α, and nitrogen, β, were investigated. The values of α and β did not change after applying a negative voltage, which indicates that the reaction mechanism at rest potential is the same as that with cathodic polarization. Furthermore, deuterium isotope analysis was conducted to investigate the mechanism of electrochemical promotion. The isotopic composition of ammonia (i.e., NH3−xDx) formed in the cathode was determined using Fourier-transform infrared spectroscopy (FTIR). The results show that the ammonia products with cathodic polarization correspond to the species of H2 (or D2) in the cathode, that is, NH3 (or ND3) was mainly formed when H2 (or D2) was introduced to the cathode. Isotopic analysis revealed that the ammonia formation rate via the electrochemical promotion of catalysis (EPOC) is faster than that via the charge-transfer reaction, suggesting that a significant increase in the ammonia formation rate will be caused by the EPOC.

The performance of an anode-supported proton-conducting solid oxide fuel cell (p-SOFC) was investigated by controlling transport properties of thin electrolyte membranes. Hole conductivity in electrolyte, which induces to degrade the cell performance, was sufficiently suppressed by using lanthanum tungstate La28-xW4+xO54+3x/2v2-3x/2 (LWO) with high proton conductivity and low hole conductivity. SrFe0.95Nb0.05O3-δ (SFN) and Ni-Ce0.9Gd0.1O2-δ (Ni-GDC10) cermet were used as the cathode and anode, respectively. GDC10 was also used as an interlayer to prevent chemical reactions between the electrolyte and electrodes. SEM images and electrochemical impedance spectroscopy showed that the boundaries between the electrolyte and electrodes were stable because GDC10 blocked chemical reactions and cation diffusion at the electrolyte-electrode interfaces. Fuel cell tests were also performed with SFN/GDC10/LWO/GDC10/Ni-GDC anode-supported single cells. The thickness of the LWO thin electrolyte was approximately 3 μm. The OCV values were measured to be 0.88 V and 0.94 V at 800 °C and 600 °C, respectively. Moreover, the evaluation of the leakage current indicated that thin LWO could achieve the low leakage current due to transport properties such as high proton conductivity and low hole and electron conductivities.

Solid oxide fuel cells (SOFCs) with proton-conducting solid electrolyte, instead of the oxide-ion conducting solid electrolyte have attracted attentions because of their high potential to reduce operating temperatures and to enhance the electrical efficiencies of SOFCs. In addition, the proton-conducting SOFCs with multistage electrochemical oxidation configuration will be promising technology for critically-high electric efficiencies. However, it is known that there are non-negligible charge -carriers other than protons in typical proton-conducting solid oxide electrolytes at relatively high temperatures. The existence of the partial conductivities of holes and/or electrons will cause the internal leakage current that consumes fuel but never generates any electrical power output. The higher ratio of the leakage current to external current will more deteriorate the electrical efficiency. In this study, the effects of blocking -layers formed on the air side surface of base electrolyte layer consisting of BaZr0.8Y0.2O3-δ (BZY82) for suppressing the leakage current have been investigated by using electrochemical parameters of the partial conduction of the materials. The chemical potential profile and leakage current showed large dependence on the material of the blocking -layer. Lanthanum tungstate was found to play a role as unique and strong blocking -layer against the leakage current.

Highly efficient carriers are developed for hydrogen production by methane cracking with carbon-dioxide activation in a chemical looping system. The carrier materials comprise BaZr0.9Y0.1O3−δ (BZY) with a high proton conductivity and Fe as a base metal, and they are prepared by doping Fe into BZY. Thermal gravimetric analysis (TGA) showed that Fe-doped BZY (BaZr0.9−xFexY0.1O3−δ, BZFY) with x = 0.4 (BZFY40) exhibited a high activity for carbon deposition with methane thermal decomposition. Surface observation and kinetic analysis suggested that the high activity for carbon deposition results from the promotion of tubular carbon growth with growth-mode transition from horizontal to vertical direction for the tubular carbon on reduced BZFY40. The rapid growth of carbon tubes proceeded with the base-growth mechanism, which can provide an advantage in the stable cycle reactions. The carbon removal reaction with carbon dioxide was also investigated. In BZFY, the removal reaction was completed in ~10 min. BZFY reacted with carbon dioxide under carbon dioxide flow to generate barium carbonate. From the BZFY surface observation before and after the reactions, the BZFY plate that was mechanically broken during the carbon deposition and removal cycles could be repaired by filling cracks with carbonate in the BZFY that was generated via the reduction reaction with methane. Therefore, carbon removal from the BZFY surface with carbon dioxide contributes to maintaining the BZFY particle shape during cycles with the self-healing scheme. The BZFY40 carrier has a high activity and durability for the carbon deposition and removal cycle and provides an effective system design for carbon dioxide-free hydrogen generation.

Controlling and manipulating defects in materials provides an extra degree of freedom not only for enhancing physical properties but also for introducing additional functionalities. In ferroelectric oxides, an accumulation of point defects at specific boundaries often deteriorates a polarization-switching capability, but on the one hand, delivers interface-driven phenomena. At present, it remains challenging to control oxygen vacancies at will to achieve a desirable defect structure. Here, we report a practical route to designing oxygen-vacancy distributions by exploiting the interaction with transition-metal dopants. Our thin-film experiments combined with ab-initio theoretical calculations for BiFeO3 demonstrate that isovalent dopants such as Mn3+ with a partly or fully electron-occupied eg state can trap oxygen vacancies, leading to a robust polarization switching. Our approach to controlling oxygen vacancy distributions by harnessing the vacancy-trapping capability of isovalent transition-metal cations will realize the full potential of switchable polarization in ferroelectric perovskite oxides.

Introduction Renewable and clean energies have attracted much interest in recent years due to environmental and economic concerns related to the use of fossil fuels. For this reason, solar and wind energies have become popular alternatives and are widely used in many countries as reliable energy sources. However, these technologies are intermittent by nature which makes it challenging to successfully integrate them into power grids. Reversible electrochemical cells provide an attractive way to store solar and wind energy surplus by operating as an electrolysis cell to produce hydrogen that can be later used to generate electricity by operating as a fuel cell. Reversible cells using proton conductive solid oxide electrolytes have some advantages over other technologies, for instance, they show higher ionic conductivity in the intermediate temperature range which lowers the need for heating. Nonetheless, previous studies show low faradaic efficiencies (FEs) that are usually between 20 and 70%, which means that less than 70% of the applied current is used to produce hydrogen. A state-of-the-art reversible cell by Choi et al [1]. in 2019 yielded a remarkable current density of -1.8 A cm-2 at 600°C and 1.3 V, but the reported faradaic efficiencies ranged from 40 to 75%. In a recent study BCZYYb+1.0wt% NiO electrolyte was used to obtain one of the highest reported faradaic efficiencies to date, between 90-98%. According to the authors, “low faradaic efficiencies can be almost entirely attributed to higher current leakage” [2]. Therefore, an electrolyte capable of considerably reducing leakage current is necessary. Lanthanum tungstate (LWO) is a promising electrolyte material since it has a good ionic conductivity, low electron conductivity and it is capable of suppressing hole conduction below 800°C [3]. In this study, we assess the performance of a solid oxide reversible cell using LWO and other common electrolyte materials like BCY10, BZY20 and BZCYYb1711. Methods The performances for LWO67 and other commonly used electrolyte materials were predicted based on their transport properties using Choudhury’s model [4] with the required conductivity parameters obtained by fitting to reported experimental data (Table 1). Power efficiencies (PEs) were computed for fuel cell operation and faradaic efficiencies for electrolysis cell operation. Additionally, the performances of LWO67/BCY10 electrolyte-supported-platinum (Pt)-symmetric cells were also evaluated using a fuel cell testing unit with an in-line gas chromatograph (GC) to measure the produced hydrogen. A potentiostat/galvanostat was used to measure the characteristic I-V curves and electrochemical impedance. Both the predictions and experiments were performed with a gas composition of 20% O2 in Ar (3% H2O) for the air electrode side and 1% H2 in Ar (3% H2O) for the hydrogen side. Pt was chosen as both the fuel and air electrode to be able to easily compare the efficiencies of LWO67 and BCY10 under the exact same conditions. This is because LWO can react with other electrodes and a thin protective layer would be necessary to prevent this from happening. Results and discussion According to the predictions, LWO67 exhibits the highest PE in fuel cell operation at typical operating conditions of current p-SOFC systems (Fig. 1). In the same way, LWO67 shows the highest faradaic efficiency in electrolysis operation (Fig. 2) exceeding that of BZCYYb by more than 10%. These results are due to LWO67’s low electron and hole conductivities and they suggest that it has great potential as an electrolyte for reversible cells. It was also found that the optimum electrolyte thickness is around 10 µm and lower values produce a decrease in the FE. This occurs because as ionic conductivity increases with decreasing thickness, so does the leakage current. Therefore, there is a trade-off relationship between the electrolyte thickness, the current density, and the efficiency. Moreover, the FEs measured experimentally were higher for LWO67. For example, at 650°C the FE was 26% for BCY10 while it was 37% for LWO67. Nevertheless, this difference is expected to be even higher in anode-supported cells with thinner electrolytes, indicating that LWO67 has potential as an electrolyte material. Additionally, it has been shown that poor electrode performance can affect the FE. Thus, a more active electrode should improve the performance. References [1] S. Choi, T.C. Davenport, S.M. Haile, Energy Environ. Sci. 12 (2019) 206–215. [2] C. Duan et al., Nat. Energy 4 (2019) 230–240. [3] G. Kojo, R. Tsukimura, J. Otomo, Solid State Ion. 306 (2017) 89–96. [4] N.S. Choudhury, J.W. Patterson, J. Electrochem. Soc. 118 (1971) 1398–1403. Figure 1

For efficient operation of proton ceramic fuel cell (PCFC), transport properties of hole and electron are important factors to be controlled as well as that of protons. Ba-based perovskite-type proton conductors have been used as typical electrolytes for the PCFCs because of their high proton conductivity. However, they also exhibit apparent hole conduction under oxidative atmospheres which causes leakage current through the electrolyte. The leakage current leads to not only a decrease in cell voltages but also a reduction of the energy efficiency since the leakage current cannot be utilized as electric power while hydrogen is consumed to generate protons and electrons. Therefore, a novel approach to suppress the leakage current has been required. Lanthanum tungstate (La28−x W4+x O54+3/2x ; LWO) with a high La/W ratio of 6.7 is one of the attractive proton conductors with a quite low hole conductivity. Though its proton conductivity is lower than the typical perovskite-type electrolytes, a high protonic transport number is attractive as a hole blocking layer for the PCFCs. An introduction of a thin LWO hole blocking layer on the Ba-based proton conductors with the high proton conductivity will suppress the leakage current by changing a profile of oxygen chemical potential in the electrolytes as we have proposed previously (Y. Matsuzaki et al., ECS Trans. 91, 1009-1018 (2019)). In this study, we explored the influence of the LWO hole blocking layer on the cell performances of PCFCs by theoretical calculations and experiments. In the theoretical calculations, a BZY|LWO bilayer cell model in which the LWO layer was located at the cathode side was employed. The calculations suggested that the bilayer structure not only improves efficiency but also gives flexibility to control the cell performance as required. Moreover, we experimentally investigated the performance of anode-supported cells with a BZY monolayer electrolyte and with a BZY|LWO bilayer electrolyte to elucidate the effect of the LWO layer. An LWO layer thickness (L LWO) dependence of the OCV in the BZY|LWO bilayer model was calculated based on the transport properties of BZY and LWO. Dependences of the energy efficiency and the power density with respect to a ratio of to a total electrolyte thickness (L total) of 10 μm were calculated for the model at a fixed external current density (I ext) of 250 mA/cm2 and at a fixed terminal voltage (V T) of 1.05 V, respectively. ε was defined by ε = V T I ext/V th I ion, where V th and I ion are a Nernst voltage and an ionic current density. We assumed the following operation conditions; operation temperature of 600 °C, 3% H2O + 97% H2 for anode gas, and 3% H2O + 19.4% O2 + 77.6 % Ar for cathode gas. In the experiments, a BZY monolayer electrolyte and a BZY|LWO bilayer electrolyte were prepared on NiO-BZY cermet substrates by the pulsed-laser deposition (PLD). La0.6Sr0.4Co0.2Fe0.8O3− d (LSCF) cathode was applied for both the cells. To suppress chemical reactions of LWO with BZY and LSCF, thin La-doped ceria (LDC) layers were introduced. The resulted structure of the monolayer cell and the bilayer cell were Ni-BZY|BZY(3.5 μm)|LSCF and Ni-BZY|BZY(3.5 μm)|LDC(40 nm)|LWO(1 μm)|LDC(40 nm)|LSCF, respectively. Cell performance tests were performed at 600 °C supplying 3% humidified H2 + Ar gas for the anode and 3% humidified 20% O2 + Ar gas for the cathode. The calculated OCV of the BZY monolayer model was 1.08 V and steeply increased up to 1.13 V by employing the thin LWO layer with L LWO/L total of 0.017 owing to suppression of the leakage current. Calculated dependences of ε and the power density for the model are shown in Fig.1. The efficiency and the power density showed a steep increase with increasing L LWO/L total. They showed the maximum values at certain L LWO/L total values, and then gradually decreased as L LWO/L total approached 1. This calculation result indicates that the cells exhibiting both the high ε and the high power density can be developed by employing the bilayer structure with the thin LWO hole blocking layer. Moreover, It is notable that, as the performance of the bilayer cell can be tuned by changing as presented in Fig. 1, the bilayer structure increases a degree of freedom for the design of the cells to satisfy various performance requirements. In the experiments, an enhancement of the OCV from 0.95 V for the BZY monolayer cell to 1.01 V for the bilayer cell was actually observed as suggested by the calculation. We consider that these theoretical calculations and experimental results present the effectiveness of the LWO hole blocking layer for the development of the high-performance PCFCs with high-design flexibility. Figure 1

We have investigated the local polarization switching behaviors of epitaxial (Bi1/2Na1/2)TiO3 (BNT) thin films obtained by a pulsed laser deposition (PLD). Using ozone gas as a deposition atmosphere of PLD, epitaxial growth of BNT films was achieved on SrRuO3/SrTiO3(100) electrode substrates. Piezoresponse force microscopy (PFM) revealed that BNT grains in the films have a single-domain structure without domain walls. These domain structures and the local polarization switching measured by PFM indicate that the oxidizing atmosphere of ozone gas is considered to suppress the generation of bismuth and oxygen vacancies in the deposited BNT layers. We propose that the PLD method using ozone is effective in obtaining high-quality single-phase BNT films with a less concentration of lattice vacancies.

We investigated experimentally dependence of light fluence on treated depth with photosensitization reaction shortly after photosensitizer injection in rabbit myocardial tissue in vivo. In this particular photosensitization reaction scheme, the photosensitizer accumulation characteristics for target region are not available. Meanwhile, the photosensitizer dose and hospitalization period under restricted light circumstance might be reduced. Since both photosensitizer and oxygen supply are governed by blood flow, this photosensitization reaction is influenced significantly by blood flow variation in particular blood vessel occlusion. We employed the myocardial tissue to keep tissue blood flow during the photosensitization reaction because vessel blood flow speed in myocardial tissue is fast to resist vascular occlusion. Surgically exposed rabbits myocardial tissues were irradiated with the light fluence ranging 25-100 J/cm2 by a 663 nm diode laser 30 min after the injection of 2 mg/kg water soluble chlorin photosensitizer, Talaporfin sodium. Two weeks after the irradiation, the rabbits were sacrificed and the histological specimens of the irradiated area were made to measure scar layer thickness. The scar layer tissue thickness of 0.2-3.0 mm was observed microscopically by the light fluence ranging 25-100 J/cm2. The scarring threshold in the deposit light fluence was estimated to 15-25 J/cm3 based on the above mentioned relation assuming constant and uniform myocardial effective attenuation coefficient of 0.72 mm-1. The estimated scarring threshold in the deposit light fluence was lower than the threshold of conventional PDT. Large variation of the estimated threshold value might be attributed to unconsidered PDT parameter such as flow rate inhomogeneity in the myocardial tissue. These results suggested that the photosensitization reaction investigated in this study would be available to apply arrhythmia therapy such as atrial fibrillation.

We have proposed non-thermal electrical conduction block for atrial fibrillation treatment by the photosensitization reaction, in which the interval time between the photosensitizer injection and irradiation is less than tenth of that in conventional way. To study the mechanism of photosensitization reaction-induced electrical conduction block, intracellular Ca 2+ concentration change in rat myocardial cells was measured by fluorescent Ca 2+ indicator Fluo-4 AM with confocal laser microscopy. Measured rapid increase in the fluorescence intensity and a change in cell morphology indicated that cell membrane damage; that is Ca 2+ influx and eventually cell death caused by the photosensitization reaction. To demonstrate myocardial electrical conduction block induced by the photosensitization reaction, surgically exposed porcine heart under deep anesthesia was used. The myocardial tissue was paced with a stimulation electrode. The propagated electrical signals were measured by bipolar electrodes at two different positions. Thirty minutes after the injection of 5-10 mg/kg Porfimer sodium or Talaporfin sodium, the red laser light was irradiated to the tissue point by point crossing the measuring positions by the total energy density of less than 200 J/cm 2 . The electrical signal conduction between the measuring electrodes in the myocardial tissue was delayed by each irradiation procedure. The electrical conduction delay corresponded to the block line length was obtained. These results demonstrated the possibility of non-thermal electrical conduction block for atrial fibrillation treatment by the photosensitization reaction.

We demonstrated a possibility of electrical conduction block by ex vivo and in vivo experiments using rat models to establish a non-thermal treatment for atrial fibrillation by photosensitization reaction (PR). One hour after the injection of 2 mg/kg Talaporfin sodium to Wistar rat, the right ventricle (1.4 mmT) was extracted. Paced with a stimulation electrode, this tissue was placed in a tissue bath and immersed in irrigated Tyrode's solution of 37°C with 8 μg/ml Talaporfin sodium and the gas mixture bubbling of 95% CO2 and 5% O2. The propagated electrical signal was measured by two bipolar electrodes. Exciting light of 670 nm in wavelength was irradiated to the tissue between the bipolar electrodes by the power density of 1 W/cm2. After this irradiation, propagation signal blockade was obtained and continued up to three hours. Rat atrioventricular (AV) node was employed as a target region for chronic model. The heart of Wistar rat was surgically exposed. External four-lead electrocardiogram of this rat was measured. Thirty minutes after the injection of 10 mg/kg Talaporfin sodium to the rat, exciting light of 663 nm in wavelength was irradiated to the AV node by the power density of 500 mW/cm2 for ten minutes. Acute AV block was obtained during the irradiation. Two weeks after this procedure, complete AV block was confirmed. The rat was sacrificed to obtain the tissue specimen. We found that the AV node was replaced by scarring tissue under the microscopic observation of the specimen. We verified possibility of permanent electrical conduction block using PR.