Oxygen affinity: the missing link enabling prediction of proton conductivities in doped barium zirconates

Proton-conducting oxides, specifically doped barium zirconates, have garnered much attention as electrolytes for solid-state electrochemical devices operable at intermediate temperatures (400–600 °C). In chemical terms, hydration energy, E_(hyd), and proton–dopant association energy, E_(as), are two key parameters that determine whether an oxide exhibits fast proton conduction, but to date ab initio studies have for the most part studied each parameter separately, with no clear correlation with proton conductivity identified in either case. Here, we demonstrate that the oxygen affinity, E_(O.dopant), defined as the energy released when an oxide ion enters an oxygen vacancy close to a dopant atom, is the missing link between these two parameters and correlates well with experimental proton conductivities in doped barium zirconates. Ab initio calculations of point defects and their complexes in Sc-, In-, Lu-, Er-, Y-, Gd-, and Eu-doped barium zirconates are used to determine E_(hyd), E_(as), E_(O.dopant), and the hydrogen affinity, EH.host, of each system. These four energy terms are related by E_(hyd) = E_(O.dopant) + 2E_(H.host) + 2E_(as). Complementary impedance spectroscopy measurements reveal that the stronger the calculated oxygen affinity of a system, the higher the proton conductivity at 350 °C. Although the proton trapping site is also an important factor, the results show that oxygen affinity is an excellent predictor of proton conductivity in these materials

Oxygen affinity: the missing link enabling prediction of proton conductivities in doped barium zirconates

Proton-conducting oxides, specifically doped barium zirconates, have garnered much attention as electrolytes for solid-state electrochemical devices operable at intermediate temperatures (400–600 °C). In chemical terms, hydration energy, E_(hyd), and proton–dopant association energy, E_(as), are two key parameters that determine whether an oxide exhibits fast proton conduction, but to date ab initio studies have for the most part studied each parameter separately, with no clear correlation with proton conductivity identified in either case. Here, we demonstrate that the oxygen affinity, E_(O.dopant), defined as the energy released when an oxide ion enters an oxygen vacancy close to a dopant atom, is the missing link between these two parameters and correlates well with experimental proton conductivities in doped barium zirconates. Ab initio calculations of point defects and their complexes in Sc-, In-, Lu-, Er-, Y-, Gd-, and Eu-doped barium zirconates are used to determine E_(hyd), E_(as), E_(O.dopant), and the hydrogen affinity, EH.host, of each system. These four energy terms are related by E_(hyd) = E_(O.dopant) + 2E_(H.host) + 2E_(as). Complementary impedance spectroscopy measurements reveal that the stronger the calculated oxygen affinity of a system, the higher the proton conductivity at 350 °C. Although the proton trapping site is also an important factor, the results show that oxygen affinity is an excellent predictor of proton conductivity in these materials

Chromium deposition and poisoning of La0.8Sr0.2MnO3 oxygen electrodes of solid oxide electrolysis cells

The effect of the presence of an Fe–Cr alloy metallic interconnect on the performance and stability of La0.8Sr0.2MnO3 (LSM) oxygen electrodes is studied for the first time under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The presence of the Fe–Cr interconnect accelerates the degradation and delamination processes of the LSM oxygen electrodes. The disintegration of LSM particles and the formation of nanoparticles at the electrode/electrolyte interface are much faster as compared to that in the absence of the interconnect. Cr deposition occurs in the bulk of the LSM oxygen electrode with a high intensity on the YSZ electrolyte surface and on the LSM electrode inner surface close to the electrode/electrolyte interface. SIMS, GI-XRD, EDS and XPS analyses clearly identify the deposition and formation of chromium oxides and strontium chromate on both the electrolyte surface and electrode inner surface. The anodic polarization promotes the surface segregation of SrO and depresses the generation of manganese species such as Mn2+. This is evidently supported by the observation of the deposition of SrCrO4, rather than (Cr,Mn)3O4 spinels as in the case under the operating conditions of solid oxide fuel cells. The present results demonstrate that the Cr deposition is essentially a chemical process, initiated by the nucleation and grain growth reaction between the gaseous Cr species and segregated SrO on LSM oxygen electrodes under SOEC operating conditions

格子歪がPr2NiO4系酸化物の酸化物イオンおよび電子伝導に与える影響に関する研究

工学_材料物性工

格子歪がPr2NiO4系酸化物の酸化物イオンおよび電子伝導に与える影響に関する研究

工学_材料物性工

Overseas Support in the Field of Vascular Access

Since joining the Non-Governmental Organization Ubiquitous Blood Purification International in 2014, professionals who are mainly members of the Japanese Society for Dialysis Therapy (JSDT) have worked toward promoting dialysis therapy in several countries through help with organization of local nephrology societies and conducting educational activities. Since 2016, training at our hospital has been provided for doctors and dialysis staff from these countries as part of the activities of the JSDT. These activities also involve technical training for vascular access (VA) surgery and management. To date, lectures and practical teaching on VA procedures have been given in Cambodia and Vietnam, and a hands-on seminar on echo-guided puncture and VA management was held in Mongolia. In Mongolia and Myanmar, a plan to provide systemic VA surgery education has been developed, at the request of local nephrology societies. Doctors and medical staff from Vietnam, Laos, Cambodia, Nepal and Indonesia have visited our hospital and have observed operations as part of their training. To achieve sustainable medical support and academic activities, we have found it to be important to have a counterpart society in each country, and guidance has been provided when required on organization of a national nephrology society

Ruddlesden Popper oxides of LnSr(3)Fe(3)O(10-delta) (Ln = La, Pr, Nd, Sm, Eu, and Gd) as active cathodes for low temperature solid oxide fuel cells

Ruddlesden Popper type oxides of LnSr(3)Fe(3)O(10-delta) (Ln - La, Pr, Nd, Sm, Eu, and Gd) have been investigated as active cathodes for solid oxide fuel cells (SOFCs). Among the examined LnSr(3)Fe(3)O(10-delta), it was found that PrSr3Fe3O10-delta shows the highest activity for the cathode reaction. The prepared LnSr(3)Fe(3)O(10-delta) oxides have a tetragonal crystal structure with the space group I4/mmm. With decreasing the ionic size of Ln(3+), the unit cell volume and crystallite size decrease. The temperature and P-O2 dependences of electrical conductivities indicate the metal-like behaviour and the predominant hole conduction. The thermal expansion coefficient (TEC) values derived from the non-linear expansion curves of LnSr(3)Fe(3)O(10-delta) are reasonably compatible with those of La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte. The catalytic activity as cathodes for H-2-SOFCs depended on Ln ions. A high cathodic activity was achieved on LnSr(3)Fe(3)O(10-delta) (PSFO10) and a maximum power density of 0.51 W cm(-2) was achieved at 1073 K when 0.3 mm thick LSGM electrolyte was used. The surface exchange coefficient, k, also confirms the high activity for the dissociation of oxygen on PSFO10. Therefore, PrSr3Fe3O10-delta is highly promising as a cathode for low temperature SOFCsclose0

Probing Local Environments of Oxygen Vacancies Responsible for Hydration in Sc-doped Barium Zirconates at Elevated Temperatures: In Situ X-ray Absorption Spectroscopy, Thermogravimetry, and Active Learning Ab Initio Replica Exchange Monte Carlo Simulations

Proton-conducting oxides, specifically heavily Sc-doped barium zirconate perovskite, have attracted attention as electrolytes for intermediate-temperature protonic ceramic fuel cells because of their high proton conductivity and high chemical stability against carbon dioxide in that temperature regime. Hydration is a key reaction for incorporating protons by filling oxygen vacancies, VO, with hydroxyl groups and activating proton conduction in the perovskite. However, probing the local environment of oxygen vacancies responsible for hydration is challenging because the behavior depends on the temperature and water partial pressure, which necessitates in situ observations and calculations of the local environments at elevated temperatures. To obtain such information, we combined in situ X-ray absorption spectroscopy (XAS) for both the Sc and Zr K-edges, thermogravimetry, X-ray diffractometry, and active learning ab initio replica exchange Monte Carlo (RXMC) simulations in undoped and 20–40 at% Sc-doped barium zirconates at and below 800 °C. The presence of oxygen vacancies adjacent to Sc and Zr in the dehydrated samples and the hydration of these oxygen vacancies under a wet atmosphere were probed by in situ XAS for Sc and Zr pre-edges at elevated temperatures. Here, the microscopic hydration linearly responds to the macroscopic degree of hydration. RXMC sampling further supports the presence of Sc-VO-Zr and Sc-VO-Sc environments. An initial hydration occurs in the Sc-VO-Zr environment at and above 600 °C, but the Sc-VO-Sc environment contribution is greater at higher degrees of hydration. The Zr-Vo-Zr environment is the least abundant among them for the whole temperature range examined and thus has a negligible impact

Effects of Three-Dimensional Strain on Electric Conductivity in Au-Dispersed Pr_1.90Ni_0.71Cu_0.24Ga_0.05O_4+δ

The effects of tensile strain on the electronic properties of Cu- and Ga-doped Pr_1.9NiO₄ (PNCG) were investigated. The difference in the thermal expansion coefficient between PNCG (α = 13.5–13.9 × 10^–6 K^–1) and Au (α = 14.2 × 10^–6 K^–1) can induce tensile strain in PNCG, resulting in changes in electrical conductivity. Hall-effect measurements indicated that the tensile strain stabilized the oxidized state of PNCG, and the electrical conductivity increased because of the increased hole concentration. This suggests that the tensile strain affected the valence numbers of cations in PNCG, increasing the hole concentration and raising the conductivity. Furthermore, the BO₆ octahedral distance in the K₂NiF₄ structure was increased by the induced strain, decreasing the hole mobility

Correlation between fast oxygen kinetics and enhanced performance in Fe doped layered perovskite cathode for solid oxide fuel cells

Many researchers have recently focused on layered perovskite oxides as cathode materials for solid oxide fuel cells because of their much higher chemical diffusion and surface exchange coefficients relative to those of ABO(3)-type perovskite oxides. Herein, we study the catalytic effect of Fe doping into SmBa0.5Sr0.5Co2O5+delta on the oxygen reduction reaction (ORR) and investigate the optimal Fe substitution through an analysis of the structural characteristics, electrical properties, redox properties, oxygen kinetics, and electrochemical performance of SmBa0.5Sr0.5Co2-xFexO5+delta (x = 0, 0.25, 0.5, 0.75, and 1.0). The optimal Fe substitution, SmBa0.5Sr0.5Co1.5Fe0.5O5+delta, enhanced the performance and redox stability remarkably and also led to satisfactory electrical properties and electrochemical performance due to its fast oxygen bulk diffusion and high surface kinetics under typical fuel cell operating conditions. The results suggest that SmBa0.5Sr0.5Co1.5Fe0.5O5+delta is a promising cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs).close