关键词: 可逆固体氧化物电池, 镧锶铁钙钛矿, 氢氧化反应, 氧还原反应, 电化学性能

Reversible solid oxide cell (RSOC) exhibits excellent thermodynamic and kinetic properties and is considered as a promising energy conversion device. In this work, two types of RSOC electrode materials, La_0.6Sr_0.4Fe_0.8Co_0.2O₃ (LSFC) and La_0.6Sr_0.4Fe_0.8Co_0.2F_0.1O_2.9(F_0.1-LSFC) are synthesized using the solid-state reaction method, the effects of fluorine doping on the cell discharge and electrolysis performance are discussed. Meanwhile, the electrode surface kinetic reactions are also explored through construction of equivalent symmetrical cells. After fluorine doping, SrF₂ precipitates in F_0.1-LSFC material, resulting in defects in perovskite La sites, which further leads to Coulomb cation exclusion and lattice disorder of FeO₆ octahedron, resulting in expansion of unit cell volume. Moreover, the results also show that fluorine doping can reduce the valence state of B-site elements, increase the concentration of oxygen vacancies, and thereby improve cell performance. The maximum power density of RSOC composed of F_0.1-LSFC at 700 ℃ with 30%H₂O/H₂ as the fuel is 234.3 mW•cm^-2, approximately 1.7 times higher than that of RSOC composed of LSFC. And at 1.3 V, the current densities of the RSOC composed of LSFC and F_0.1-LSFC are –245.6 and –417.9 mA•cm^-2, respectively. The effect of fluorine doping on the catalytic activity of perovskite materials for hydrogen oxidation reaction (HOR) is investigated. The results show that the catalytic activity of perovskite materials for HOR can be improved by fluorine doping. In addition, the electrochemical impedance spectra (EIS) under different hydrogen partial pressures were measured by adjusting the hydrogen partial pressure (p_H2) on both sides of the equivalent symmetrical cells, so as to explore the rate determining step (RDS) of electrode reaction. The results show that the RDS of electrode reaction changes after fluorine doping. For LSFC electrode, the RDS of reaction is mainly hydrogen adsorption and dissociation reaction, while for F_0.1-LSFC electrode, the RDS of reaction is mainly charge transfer reaction. Similarly, the test method of equivalent symmetrical cells is still used for oxygen reduction reaction (ORR) dynamics research. The difference is that the atmosphere on both sides of the cells becomes O₂. From EIS test results, it can be seen that with the increase of temperature, the polarization resistance (R_P) value of the equivalent symmetrical cell gradually decreases, and the R_P value of F_0.1-LSFC is lower than LSFC, indicating that fluorine doping and increasing the operating temperature can reduce the R_P value, thereby improving the catalytic activity of ORR. It is worth noting that the R_P value of the equivalent symmetrical cell composed of LSFC and F_0.1-LSFC in O₂atmosphere is lower than that in H₂ atmosphere, indicating that LSFC and F_0.1-LSFC electrode materials are more prone to ORR. On the other hand, the RDS of ORR process can be studied from the effect of oxygen partial pressure (p_O2) on EIS of equivalent symmetrical cells. The results show that the RDS of electrode for ORR process is the reduction of oxygen atoms to O^-.

Key words: reversible solid oxide cell, LaSrFeO₃ perovskite oxide, hydrogen oxidation reaction, oxygen reduction reaction, electrochemical performance