The frequency dependences of dielectric constant (εr′) for 8 mol% Y2O3 stabilized ZrO2 (8YSZ) with two kinds of electrodes, Pt and La0.6Ca0.4MnO3 (LCM), were successfully explained by the superposition of both electrolyte-electrode interfacial polarizations and Debye-type polarizations due to dopant-vacancy associates. The different behaviors in the frequency dependence of εr′ for 8YSZ having the different electrodes were ascribed to the dopant-vacancy associates, (YZr′–VO••) and (YZr′–VO••–YZr′), which were very large for 8YSZ with Pt electrode, but almost disappeared for 8YSZ with LCM electrode. The frequency dependences of the ac conductivity (σac) were also explained by the relaxation phenomena of the dopant-vacancy associates, suggesting that the dispersion of σac can not be ascribed to grain boundary effect of electrolyte.
This work focuses on the effect of sputter-deposited Pt alloys upon 2-propanol oxidation. Platinum based bimetallic, i.e., Pt–Ru, Pt–W, Pt–Sn, and Pt–Mo, and trimetallic, i.e., Pt–Ru–W, Pt–Ru–Sn, Pt–Ru–Au, and Pt–W–Au, electrodes were deposited on Si, Au, and Pt substrates. The activity was evaluated with linear voltammetry and potential step methods at room temperature and atmospheric conditions. Among the bimetallic compositions, the maximum current density of Pt–W was about twice that of Pt–Ru. Other bimetallic composition was inferior to Pt–Ru at the investigated conditions. Among the tested materials, the trimetallic composition of Pt–Ru–W showed the highest current density and lowest onset potential for 2-propanol oxidation. The Au species also showed catalytic activity for 2-propanol oxidation.
We examined the carbon deposition behavior on a nickel-based anode for solid oxide fuel cells (SOFCs) operated at 1073 K under dry or humidified methane (CH4) stream conditions, by observing the anode microstructures, open circuit voltages (OCVs) and anode/electrolyte interfacial resistance. When the measurement was made in the dry methane stream, the OCV gradually decreased and the interfacial resistance increased, with carbon deposition on the whole anode. In a humidified methane stream with a steam/carbon ratio (S/C) of 0.25 or 0.50, the OCV gradually decreased while the interfacial resistance was nearly constant and there was no carbon deposition near the anode/electrolyte interface. It is shown that the OCV decrease under the humidified methane conditions is associated with the decrease in the reaction sites for steam reforming. It is expected that the OCV decrease is an indication of carbon deposition.
Using first-principles band calculations, we investigate various bulk properties, such as redox potentials, crystal and electronic structure, diffusion properties of Li, defect formation of Li/M site exchange, solubility limits for dilute Li/vacancy composition, and elastic properties of LixMPO4 (M=Mn, Fe, Co, Ni) in the Olivine-type structure. The calculated redox potentials showed in a better accordance with experiments by the using GGA+U method for Ueff (=U−J)=4.0 eV than the GGA method. These obtained computational results revealed the relationship between bulk properties and crystal/electronic structure. For examples, (1) volumetric change by electrochemical Li removal/uptake reaction related to the repulsive interaction between O 2p electrons and octahedrally coordinated transition metal (TM) eg electrons, (2) electronic defect (polaron) localization caused an increase of activation energies of Li ion hopping, and so on. Using these fundamental bulk properties, comprehensive discussion was made from the view point of electrochemical performance.