Equivalent circuit analysis of a three-carrier electrolyte/electrode system

Perovskite type proton conductors are known to show non-monotonous transient responses due to non-ignorable contributions of holes and oxide ions as minor carriers. Efforts have been made to simulate the behavior of the three-carrier systems by numerical calculations1-4). In most cases, however, the calculation assumes reversible electrodes, and the results are not directly applicable for analyses of experimental results such as impedance spectra. The purpose of this study is to develop an equivalent circuit model of a three-carrier conductor as a simple but theoretically feasible tool to be used for practical analyses. In the modeling, charge carriers were assumed to be Hi•, VO••, and h•, for which the gradients of respective electrochemical potentials were taken as the driving forces in the following continuity equations, Please click Additional Files below to see the full abstract

Mechanism of oxygen release from Li-rich cathode material for lithium ion batteries

For further wide spread of high energy density batteries, one of the most important technological challenges is preventing thermal runaway. For that, a key phenomenon is the oxygen release from cathode active materials, because released oxygen may react with the organic solvent and generate heat. Therefore, it is important to understand the mechanism of oxygen release to ensure safe battery operation. While the reaction of charged cathode material and organic solvent was investigated well [1], the mechanism of oxygen release from cathode material is not understood so far [2]. In this study, oxygen release behavior of Li-rich cathode material Li1.2Mn0.6Ni0.2O2-d was investigated, and the mechanism of oxygen release was discussed based on defect chemistry and thermodynamics. Please click Additional Files below to see the full abstract

Evaluation of the Electronic and Local Structure of Mn in Proton-Conducting Oxide, Ca(Zr,Mn)O3-δ, To Elucidate a Direct Hydrogen-Dissolution Reaction

The protonation mechanism in Mn-doped CaZrO3 (CZM), which involves a direct hydrogen dissolution from the surrounding H2 gas, was investigated by thermogravimetry (TG) and X-ray absorption spectroscopy (XAS). The TG results implied the formation of oxygen vacancies in a H2 atmosphere. The Mn K-edge XAS spectra indicated a reduction of the Mn ions and local structure variations around the Mn ion, but the Zr K-edge spectra were independent of the surrounding atmosphere. The amount of oxygen vacancies was smaller with respect to the reduction of the Mn ions, suggesting direct dissolution of hydrogen. Unlike many typical perovskite-type proton conductors, protonation by direct dissolution of hydrogen and not hydration was the predominant reaction in Mn-doped CaZrO3. Our experimental results demonstrated that the hydration reaction was suppressed because the oxygen vacancy was stable in the distorted ZrO6 symmetry in the CaZrO3 crystal host, whereas protonation proceeded by the direct dissolution of hydrogen stabilizing near the Mn ions in the interstitial sites at the distorted MnO6 octahedron symmetry. The experimental results showed that the structural configurations around dopants play important roles in the stabilization of protons in perovskite-type CZM materials. We demonstrated a new group of proton conductors that can overcome issues with conventional proton conductors by utilizing the direct hydrogen dissolution reaction

Investigation of cathodic reaction in SOFCs and PCFCs by using patterned thin film model electrodes

In recent years, fuel cells operating at relatively high temperatures, such as solid oxide fuel cells (SOFCs) using an oxide ion conducting electrolyte and proton ceramics fuel cells (PCFCs) using an proton conducting electrolyte, attract attentions as high-efficient energy-conversion devices. For further enhancements of the performance and the durability of SCFCs and PCFCs, it is essential to understand the electrode reactions. In particular, the knowledge on the dominant reaction path in the electrodes would help us to optimize the material and the microstructure of the electrode. Please click Additional Files below to see the full abstract

電気化学システムに関する非平衡熱力学的研究

京都大学0048新制・論文博士博士(工学)乙第9927号論工博第3365号新制||工||1123(附属図書館)UT51-98-U200(主査)教授 伊藤 靖彦, 教授 小野 勝敏, 教授 粟倉 泰弘学位規則第4条第2項該当Doctor of EngineeringKyoto UniversityDFA

Thermoelectric Properties and Phase Transition of (ZnxCu2−x)V2O7

The phase stability and thermoelectric properties of the layered structure of (ZnxCu2-x)V2O7 solid solutions were studied for x ≥ 0.2. X-ray diffraction measurements, compositional studies, and thermal analysis verified that the low-temperature form of the (ZnxCu2-x)V2O7 solid solution (monoclinic structure, C2/c) was stable for 0.2 ≤ x ≤ 2 when heated below 863K in air. On heating, phase transformation occurred at least at 0.2 ≤ x ≤ 2 at a nearly constant temperature of approximately 873 K; above this temperature, a high-temperature form of the (ZnxCu2-x)V2O7 solid solution was formed. The Seebeck coefficients of the low-temperature (ZnxCu2-x)V2O7 solid solution exhibited large negative values in the range of approximately -520 to -700 μV/K, and the electrical resistivity increased with Zn addition. The maximum power factor of 1.99 x 10^[-7] W/mK2 was obtained at 823K for the low-temperature form of the (Zn0.2Cu1.8)V2O7 solid solution