氟掺杂对可逆固体氧化物电池性能的影响及相关动力学研究

Effect of Fluorine Doping on the Performance of Reversible Solid Oxide Cells and Related Kinetic Studies

可逆固体氧化物电池(RSOC)表现出优异的热力学和动力学性质,被认为是一种很有前途的能量转换装置.制备了两种RSOC电极材料La_(0.6)Sr_(0.4)Fe_(0.8)Co_(0.2)O_(3) (LSFC)和La_(0.6)Sr_(0.4)Fe_(0.8)Co_(0.2)F_(0.1)O_(2.9 )(F_(0.1)-LSFC),对比了F掺杂对电池放电和电解性能的影响并对电极表面动力学反应进行探究.研究表明F掺杂可降低B位元素价态、提高材料氧空位浓度,进而提高电池性能.700℃,30%H_(2)O/H_(2)燃料下,由F_(0.1)-LSFC组成的RSOC的最大功率密度为234.3 m W·cm^(-2),约为LSFC组成的RSOC的1.7倍.并且在1.3 V下,由LSFC和F_(0.1)-LSFC组成的RSOC的电流密度分别为-245.6和-417.9m A·cm^(-2).此外,通过电极表面动力学分析发现,对于氢氧化反应(HOR),F_(0.1)-LSFC电极反应的速度控制步骤(RDS)主要是电荷转移反应,而LSFC电极反应的RDS主要是氢气的吸附和解离反应;对于氧还原反应(ORR),RDS是吸附的氧原子还原成O^(-).

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_(0.6)Sr_(0.4)Fe_(0.8)Co_(0.2)O_(3) (LSFC)and La_(0.6)Sr_(0.4)Fe_(0.8)Co_(0.2)F_(0.1)O_(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,Sr F_(2) 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 Fe O_6octahedron,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%H_(2)O/H_(2) as the fuel is 234.3 m W·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 m A·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 O_(2).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 O_(2 )atmosphere is lower than that in H_(2) 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~-.