Meng Junling, Yuan Na, Liu Xiaojuan, Yao Chuangang, Liang Qingshuang, Zhou Defeng, Meng Fanzhi, Meng Jian
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun 130022, P. R. China.
Inorg Chem. 2015 Mar 16;54(6):2820-9. doi: 10.1021/ic502989c. Epub 2015 Mar 2.
The effects of intrinsic cation disorder and electron-deficient substitution for La1-xSrxCo0.5Mn0.5O3-δ (LSCM, x = 0, 0.5, and 0.75) on oxygen vacancy formation, and their influence on the electrochemical properties, were revealed through a combination of computer simulation and experimental study. First-principles calculations were first performed and found that the tendency of the oxygen vacancy formation energy was Mn(3+)-O*-Mn(4+) < Co(2+)-O*-Co(3+) < Co(2+)-O*-Mn(4+), meaning that antisite defects not only facilitate the formation of oxygen vacancy but introduce the mixed-valent transition-metal pairs for high electrical conductivity. Detailed partial density of states (PDOS) analysis for Mn on Co sites (MnCo) and Co on Mn sites (CoMn) indicate that Co(2+) is prone to being Co(3+) while Mn(4+) is prone to being Mn(3+) when they are on antisites, respectively. Also it was found that the holes introduced by Sr tend to enter the Co sublattice for x = 0.5 and then the O sublattice when x = 0.75, which further promotes oxygen vacancy formation, and these results are confirmed by both the calculated PDOS results and charge-density difference. On the basis of microscopic predictions, we intentionally synthesized a series of pure LSCM compounds and carried out comprehensive characterization. The crystal structures and their stability were characterized via powder X-ray Rietveld refinements and in situ high-temperature X-ray diffraction. X-ray photoelectron spectroscopy testified to the mixed oxidation states of Co(2+)/Co(3+) and Mn(3+)/Mn(4+). The thermal expansion coefficients were found to match the Ce0.8Sm0.2O2-δ electrolyte well. The electrical conductivities were about 41.4, 140.5, and 204.2 S cm(-1) at doping levels of x = 0, 0.5, and 0.75, and the corresponding impedances were 0.041, 0.027, and 0.022 Ω cm(2) at 850 °C, respectively. All of the measured results testify that Sr-doped LaCo0.5Mn0.5O3 compounds are promising cathode materials for intermediate-temperature solid oxide fuel cells.
通过计算机模拟和实验研究相结合的方式，揭示了La1-xSrxCo0.5Mn0.5O3-δ（LSCM，x = 0、0.5和0.75）的本征阳离子无序和缺电子取代对氧空位形成的影响及其对电化学性能的影响。首先进行了第一性原理计算，发现氧空位形成能的趋势为Mn(3+)-O*-Mn(4+) < Co(2+)-O*-Co(3+) < Co(2+)-O*-Mn(4+)，这意味着反位缺陷不仅促进了氧空位的形成，还引入了用于高电导率的混合价态过渡金属对。对Co位上的Mn（MnCo）和Mn位上的Co（CoMn）进行详细的态密度（PDOS）分析表明，当它们处于反位时，Co(2+)分别易于变为Co(3+)，而Mn(4+)易于变为Mn(3+)。还发现，当x = 0.5时，Sr引入的空穴倾向于进入Co亚晶格，而当x = 0.75时进入O亚晶格，这进一步促进了氧空位的形成，并且计算得到的PDOS结果和电荷密度差均证实了这些结果。基于微观预测，我们有意合成了一系列纯LSCM化合物并进行了全面表征。通过粉末X射线Rietveld精修和原位高温X射线衍射对晶体结构及其稳定性进行了表征。X射线光电子能谱证实了Co(2+)/Co(3+)和Mn(3+)/Mn(4+)的混合氧化态。发现热膨胀系数与Ce0.8Sm0.2O2-δ电解质匹配良好。在x = 0、0.5和0.75的掺杂水平下，电导率分别约为41.4、140.5和204.2 S cm(-1)，在850°C时相应的阻抗分别为0.041、0.027和0.022 Ω cm(2)。所有测量结果都证明，Sr掺杂的LaCo0.5Mn0.5O3化合物是中温固体氧化物燃料电池有前景的阴极材料。
