The oxygen reduction reaction (ORR) activity of a Cu-doped Ba0.5Sr0.5FeO3−δ (Ba0.5Sr0.5Fe1−xCuxO3−δ, BSFCux, x = 0, 0.05, 0.10, 0.15) perovskite cathode was investigated in terms of oxygen vacancy formation and valence band structure. The BSFCux (x = 0, 0.05, 0.10, 0.15) crystallized in a cubic perovskite structure (Pm3¯m). By thermogravimetric analysis and surface chemical analysis, it was confirmed that the concentration of oxygen vacancies in the lattice increased with Cu doping. The average oxidation state of B-site ions decreased from 3.583 (x = 0) to 3.210 (x = 0.15), and the valence band maximum shifted from −0.133 eV (x = 0) to −0.222 eV (x = 0.15). The electrical conductivity of BSFCux increased with temperature because of the thermally activated small polaron hopping mechanism showing a maximum value of 64.12 S cm−1 (x = 0.15) at 500 °C. The ASR value as an indicator of ORR activity decreased by 72.6% from 0.135 Ω cm2 (x = 0) to 0.037 Ω cm2 (x = 0.15) at 700 °C. The Cu doping increased oxygen vacancy concentration and electron concentration in the valence band to promote electron exchange with adsorbed oxygen, thereby improving ORR activity.
The degradation behavior of PrBaCo2−xCuxO5+δ (x = 0, 0.2, 0.5) under thermal stress was investigated in terms of phase formation and polarization resistance. The tetragonal phase was indexed in all compositions of PBCCux, and the secondary phase, BaO, was identified after thermal degradation in the crystal structure analysis. BaO formation is induced by the nature of perovskite to terminate the surface with AO layer. For pristine specimens, the oxygen vacancy peak ratio was increased from 57% to 60% according to the decrease in the average oxidation number of the B-site ion with Cu doping. After thermal deterioration, the oxidation number of B-site ions was increased, and the M = O bonding peak increased due to the decrease in oxygen vacancies and BaO formation according to the thermal stress. In all compositions, the electrical conductivity decreased from 1000 S/cm to 17 S/cm, and the polarization resistance increased approximately 200 times. These results are considered to be related to the increase in the oxidation number of B-site ions along with the formation of secondary phases.
Cement mixture with calcite-ettringite seeds (CE seeds) was investigated in terms of early hydration and mechanical property. The ettringite crystals of ettringite seeds (E seeds) exhibited needle-like shapes with lengths of approximately 3 μm, and the ettringite crystals of CE seeds exhibited rodlike shapes with lengths less than 1 μm. A dense growth of network-structured ettringite and calcium silicate hydrate (C-S-H) was observed. The amount of cement hydrates was analysed by thermal analysis, and the weight loss of the hydrates was 1.62% (E seeds) and 1.79% (CE seeds) at approximately 104°C, indicating that the amount of hydrates was higher in the mixture with CE seeds. The average pore diameter and porosity of the mixtures decreased from 145 to 79 nm and from 14.88% to 13.89% with the addition of CE seeds. The initial and final setting times of the mixture with CE seeds were 20 and 21 min, which were 4.76% and 8.70% shorter than the setting times of mixture with E seeds. The compressive and flexural strengths of the mixture with CE seeds were 6% and 10% higher than those of the mixture with E seeds, respectively.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.