ABSTRACT
Highly active triple (proton, oxygen-ion, and electron) conducting materials BaxCo0.4Fe0.4Zr0.1Y0.1O3-δ (BxCFZY, x = 0.9-1.1) were prepared and characterized as potential cathodes for protonic ceramic fuel cells (PCFCs) in this work. The crystal structure, oxygen vacancy concentration, electrical conductivity, oxygen ion transfer properties, and electrochemical performance of BxCFZY oxides were systematically evaluated. The electrical conductivity of BxCFZY decreases but oxygen vacancies increase with increasing Ba content, indicating that the charge compensation was mainly achieved by the production of oxygen vacancy rather than the increase in the valence of transition metal cations. The power density of 1170 mW cm-2 and the polarization resistance of 0.05 Ω cm2 were achieved at 700 °C for the anode-supported single cells with B1.1CFZY cathode, suggesting that the excess A site on the BxCFZY had a positive effect on the catalytic activity for the oxygen reduction reaction. Furthermore, the distribution of relaxation time (DRT) analysis method was adopted to determine the electrochemical processes of the cells with BxCFZY cathodes. The calculated results confirmed that the cell with B1.1CFZY cathode exhibited the optimum performance due to the best oxygen ion transfer properties in BxCFZY cathodes.
ABSTRACT
A type of carbon molecular sieve (CMS-3KT) was used as the adsorbent for the CH4 enrichment of a methane/oxygen/nitrogen (CH4/O2/N2) mixture using micro-positive pressure vacuum pressure swing adsorption (â¼120 kPa). The adsorption isotherms of individual CH4, O2, and N2 on CMS-3KT were studied and fitted. The results indicated the important influence of the adsorbent surface heterogeneity on the adsorption equilibrium process. In addition, the interaction of adsorbent-adsorbate in this process was studied from the measured adsorption heat. The adsorption uptake curves were fitted linearly with a classical micropore model for evaluating the kinetics-based separation possibility of CH4/O2/N2, and the corresponding diffusion time constants of CH4, O2, and N2 were calculated. Based on the results of adsorption equilibrium and kinetics, breakthrough experiments were employed to explore the upper limit value of methane concentration in feed gas such that methane can be enriched feasibly but difficultly. The breakthrough experiments were performed on the CH4/O2/N2 mixture with CH4 concentration ranging from 1 to 30%. Regarding industrial application, the O2 removal and CH4 enrichment performance of ultra-low-concentration methane (CH4 < 5%) were evaluated according to the results of the breakthrough experiment. The results indicated that the proposed method was promising for enriching O2-containing ultra-low-concentration CBM.
