火焰法与喷雾干燥法共合成固体氧化物燃料电池阴极La_(0.6)Sr_(0.4)CoO_(3–δ)–Ce_(0.8)Gd_(0.2)O_(2–δ)的微观结构与性能分析

Microstructure and Performance Analysis of Solid Oxide Fuel Cell La_(0.6)Sr_(0.4)CoO_(3-δ)-Ce_(0.8)Gd_(0.2)O_(2-δ)Cathode Synthesized by Flame Spray Pyrolysis and Spray Drying

实现阴极结构的纳米化以提升电极三相界面长度,是提升固体氧化物燃料电池(SOFC)性能的有效途径。基于火焰喷雾热解法和喷雾干燥法,分别一步法合成纳米级和亚微米级的La_(0.6)Sr_(0.4)CoO_(3-δ)-Ce_(0.8)Gd_(0.2)O_(2-δ)复相材料。将2种粒径范围材料按照不同质量比混合,制成氧化钇部分稳定氧化锆电解质支撑的固体氧化物燃料电池的阴极,并系统分析电池性能与结构特征。结果表明,喷雾干燥合成材料与火焰喷雾热解合成材料的质量比为70:30时,SOFC电化学性能最优,850℃时最大功率密度为0.47 W/cm^(2),面电阻为0.62Ω·cm^(2),相应的欧姆阻抗和极化阻抗为0.36Ω·cm^(2)和0.26Ω·cm^(2)。实验证明,混合不同粒径颗粒制成的SOFC阴极,可有效构建电子–离子导通网络,并形成更多的三相界面和反应活性位点,从而获得较好的电化学性能。本研究为固体氧化物燃料电池阴极材料微观结构和性能优化提供了新的思路。

Introduction Optimizing the nanostructure of the cathode is an effective approach to enhance the performance of solid oxide fuel cells at a triple-phase boundary(TPB).The most commonly used method is an impregnation method,which can produce nano-sized particles on the cathode framework structure.However,it is not able to achieve the related large-scale application due to its laborious preparation process and unstable performance.In this paper,nano-sized and submicron-sized composite powders of La_(0.6)Sr_(0.4)CoO_(3-δ)-Ce_(0.8)Gd_(0.2)O_(2-δ)(LSC−GDC)were synthesized by flame spray pyrolysis(FSP)and spray drying(SD)methods for the preparation of cathode,respectively.Methods A uniform submicron-sized LSC−GDC composite powder was prepared by SD with a solution of metal nitrates as a precursor solution.Also,a uniform nano-sized LSC−GDC composite powder was directly synthesized by FSP with a solution of metal acetates as a precursor solution.The submicron-sized and nano-sized powders were blended in different mass ratios(i.e.,100:0,90:10,80:20,70:30,60:40,50:50,and 40:60)to produce cathode slurries.These slurries were then screen-printed onto the button cells of NiO−GDC|GDC|3YSZ|GDC|LSC−GDC|LSC structure with an effective electrode area of approximately 0.5 cm^(2).The voltammetric characteristics of the cells were tested by an electrochemical workstation.The electrochemical characterization was performed by electrochemical impedance spectroscopy(EIS)at open circuit voltage(OCV),and the impedance spectra were analyzed via distribution of relaxation time(DRT)analysis.Results and discussion Nano-sized particles synthesized by FSP and submicron-sized particles synthesized by SD can be distinguished via microscopic analysis.In addition,the fine particles are evenly distributed around the coarse particles,having a porous structure that meets an expected cathode microstructure.Under the experimental conditions,the overall ohmic impedance and polarization impedance both increase and then decrease as the proportion of nano-sized particles increases.The cathode performance is optimal when a mass ratio of SD powder:flame FSP powder is 70:30.Under SOFC mode at 850℃,the maximum power density of the button cell is 0.47 W/cm^(2),with an area specific resistance of 0.62Ω·cm^(2).The corresponding ohmic impedance and polarization impedance values are 0.36Ω·cm^(2) and 0.26Ω·cm^(2),respectively.Combined with the results by DRT analysis,the doping of an appropriate amount of nano-sized powder significantly enhances the cathode O_(2) reduction reaction(ORR)process and cathode oxygen diffusion process.Conclusions Nano-sized and submicron-sized LSC−GDC composite materials were prepared by FSP and SD as one-pot methods,respectively.The feasibility of these two approaches for the large-scale preparation of SOFC cathode powders was investigated.The results showed that incorporating an appropriate amount of nano-sized powder into the submicron-sized powder for the preparation of the cathode could effectively enhance the cell performance.