RESUMO
To improve performance of intermediate temperature solid oxide fuel cells (IT-SOFCs), the negative thermal expansion (NTE) material Sm0.85Zn0.15MnO3(SZM) is introduced in Ba0.5Sr0.5Fe0.8Cu0.1Ti0.1O3-δ(BSFCT) cathode. XRD results indicate that BSFCT, SZM and Ce0.8Sm0.2O2-δ(SDC) oxides have good chemical compatibility up to 1173 K. The average linear thermal expansion coefficient of BSFCT-xSZM (x= 0, 10, 20 and 30 wt.%) decreases markedly from 29.2 × 10-6 K-1forx= 0 wt.% to 15.6 × 10-6 K-1forx= 30 wt.%. The electrochemical performance of single cells with configuration of NiO-BZCY|SDC|BSFCT-xSZM is comparatively investigated in the 773-973 K. The best performance is observed forx= 20 wt.%, which should be caused by the balance between thermal matching of cathode/electrolyte layers and oxygen reduction reaction activity of composite cathodes. The corresponding peak power density in the 773-973 K is 136-918 mW cm-2, which is 249%-64% higher than that (39-559 mW cm-2) with single BSFCT cathode. Due to the existence of electron blocking layer at anode/electrolyte interface, the open circuit voltage of all cells is higher than 1.0 V. In short, the introduction of NTE oxide in conventional cathode materials may provide an effective strategy to enhance the performance of IT-SOFCs with electron blocking layer.
RESUMO
The resistivity, magnetization and ultrasonic properties of charge-ordered polycrystalline (Nd(0.75)Na(0.25))(x)(Nd(0.5)Ca(0.5))(1-x)MnO(3) have been investigated from 50 to 300 K. A considerable velocity softening accompanied by an attenuation peak was observed around the charge-ordering transition temperature (T(CO)) upon cooling. The simultaneous occurrence of the charge ordering (CO) and the ultrasonic anomaly implies strong electron-phonon coupling, which originates from the cooperative Jahn-Teller effect. At very low temperature, another broad attenuation peak was observed, which is attributed to the phase separation (PS) and gives a direct evidence of spin-phonon coupling in the compound. With increasing x, T(CO) shifts to lower temperature, the magnetization of the system is strengthened and the PS is enhanced. The temperature dependence of the longitudinal modulus shows that the Jahn-Teller coupling energy E(JT) decreases with increasing Na content. The analysis suggests that the charge mismatch effect may be the main reason for the suppression of the CO and enhancement of the PS.
