Synthesis and characterization of PrBa0.5Sr0·5Co2-xFexO5+δ (x=0.5, 1.0, 1.5, 2.0) as oxygen electrode for proton-conducting solid oxide cells
As clean energy conversion devices with the functions of power generation and hydrogen evolution , solid oxide cells (SOCs) are facing the obstacle of insufficient catalytic activity of traditional electrode materials under the trend of lower operation temperature . Here a double-perovskite material PrBa 0.5 Sr 0·5 Co 2-x Fe x O 5+δ (PBSCF, x = 0.5, 1.0, 1.5, 2.0) is reported and its application as oxygen electrode of symmetrical cells on the proton conductor BaZr 0·1 Ce 0·7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb1711) is investigated. The tests are carried out under atmospheres with different water content (0, 20% and 40%), showing the influence of Fe/Co molar ratio on the crystal structure, conductivity, electrochemical properties and micro morphology of PBSCF series materials. With the increasing of Fe substitution content, the polarization resistance of PBSCF series symmetrical cells decreases. PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (PBSCF05) symmetrical cell always shows the optimal performance and exhibits area-specific polarization resistance (ASR) of 0.08 Ω cm 2 at 700 °C under 20%H 2 O+80%air. Further experimental results and the distribution of relaxation times (DRT) analysis show that the presence of an appropriate amount of steam in atmosphere would optimize the conductive mechanism and promote proton migration, while the presence of excessive steam would hinder the diffusion of oxygen molecule. For the electrochemical reaction on the PBSCF electrode, the adsorption, dissociation and precipitation of oxygen are always the crucial rate-limiting steps, which is a direction worthy of further optimization.
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