An in operando study of chemical expansion and oxygen surface exchange rates in epitaxial GdBaCo2O5.5 electrodes in a solid-state electrochemical cell by time-resolved X-ray diffraction
An in operando study of chemical expansion and oxygen surface exchange rates in epitaxial GdBaCo2O5.5 electrodes in a solid-state electrochemical cell by time-resolved X-ray diffraction
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通过时间分辨 X 射线衍射对固态电化学电池中外延 GdBaCo2O5.5 电极的化学膨胀和氧表面交换率进行实际研究
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
J. Santiso
中科院分区：
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作者：
Arindom Chatterjee;J. Caicedo;B. Ballesteros;J. Santiso
本报告探讨了具有层状钙钛矿结构的混合离子电子导电GdBaCo2O5.5±δ（GBCO）材料的外延薄膜的基本特性，其与用作电化学装置中的氧还原和析出反应的活性电极有关。在固态电化学电池中结合电压阶跃计时电流测量的时间分辨X射线衍射提供了对GBCO电极中的化学膨胀机制的更深入的了解。与具有无序氧空位的标准钙钛矿材料相反，在化合物氧化后，沿c轴沿着的化学膨胀系数αc显示负值。化学膨胀也显示出显著的不对称性，在δ 0处分别为αc = −0.037至−0.014。这种化学膨胀的变化表明与可变Co阳离子氧化态从Co2+ → Co3+ → Co4+相关的结构变化的不同机制。由于氧化还原反应由GBCO电极和气体气氛之间的氧表面交换主导，因此监测结构变化的时间响应允许直接确定氧还原和析出反应动力学。在δ 0区域中还原时，反应动力学逐渐减慢，这与穿过δ = 0时的结构变化和电子载流子离域一致。这项工作验证了时间分辨XRD技术的快速和可逆的测量电极活性在很宽的范围内的氧非化学计量在固态电化学电池在现实的工作条件下运行。
This report explores the fundamental characteristics of epitaxial thin films of a mixed ionic electronic conducting GdBaCo2O5.5±δ (GBCO) material with a layered perovskite structure, relevant for use as an active electrode for the oxygen reduction and evolution reactions in electrochemical devices. Time-resolved X-ray diffraction in combination with voltage step chrono-amperometric measurements in a solid state electrochemical cell provides a deeper insight into the chemical expansion mechanism in the GBCO electrode. The chemical expansion coefficient along the c-axis, αc, shows a negative value upon the compound oxidation contrary to standard perovskite materials with disordered oxygen vacancies. Chemical expansion also shows a remarkable asymmetry from αc = −0.037 to −0.014 at δ 0, respectively. This change in chemical expansion is an indication of a different mechanism of the structural changes associated with the variable Co cation oxidation state from Co2+ → Co3+ → Co4+. Since redox reactions are dominated by oxygen surface exchange between the GBCO electrode and gas atmosphere, monitoring the time response of the structural changes allows for direct determination of oxygen reduction and evolution reaction kinetics. The reaction kinetics are progressively slowed down upon reduction in the δ 0 region, in agreement with the structural changes and the electronic carrier delocalization when crossing δ = 0. This work validates the time-resolved XRD technique for fast and reversible measurements of electrode activity in a wide range of oxygen non-stoichiometry in a solid-state electrochemical cell operating under realistic working conditions.