Electrochemical Materials, ETH Zurich , Zurich, 8093, Switzerland.
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
ACS Appl Mater Interfaces. 2016 Jun 15;8(23):14613-21. doi: 10.1021/acsami.6b03909. Epub 2016 Jun 6.
Samaria-doped ceria (SDC) thin films are particularly important for energy and electronic applications such as microsolid oxide fuel cells, electrolyzers, sensors, and memristors. In this paper, we report a comparative study investigating ionic conductivity and surface reactions for well-grown epitaxial SDC films varying the samaria doping concentration. With increasing doping above 20 mol % of samaria, an enhancement in the defect association is observed by Raman spectroscopy. The role of such associated defects on the films̀ oxygen ion transport and exchange is investigated by electrochemical impedance spectroscopy and electrochemical strain microscopy (ESM). The measurements reveal that the ionic transport has a sharp maximum in ionic conductivity and drops in its activation energy down to 0.6 eV for 20 mol % doping. Increasing the doping concentration further up to 40 mol %, it raises the activation energy substantially by a factor of 2. We ascribe the sluggish transport kinetics to the "bulk" ionic-near ordering in case of the heavily doped epitaxial films. Analysis of the ESM first-order reversal curve measurements indicates that these associated defects may have a beneficial role by lowering the activation of the oxygen exchange "surface" reaction for heavily doped 40 mol % of samaria. In a model experiment, through a solid solution series of samaria doped ceria epitaxial films, we reveal that the occurrence of associated defects in the bulk affects the surface charging state of the SDC films to increase the exchange rates. The implication of these findings is the design of coatings with tuned oxygen surface exchange by controlling the bulk associated clusters for future electrocatalytic applications.
掺杂氧化钐的氧化铈（SDC）薄膜在微固体氧化物燃料电池、电解槽、传感器和忆阻器等能源和电子应用中尤为重要。本文报道了一项比较研究，研究了不同掺杂浓度的外延 SDC 薄膜的离子电导率和表面反应。随着掺杂浓度的增加超过 20 摩尔%的氧化钐，拉曼光谱观察到缺陷缔合增强。电化学阻抗谱和电化学应变显微镜（ESM）研究了这种缔合缺陷对薄膜氧离子输运和交换的作用。测量结果表明，离子电导率的离子传输具有尖锐的最大值，并将其活化能降低至 20 摩尔%掺杂时的 0.6 eV。进一步将掺杂浓度提高到 40 摩尔%，会将活化能显著提高 2 倍。我们将缓慢的传输动力学归因于重掺杂外延薄膜中“体相”离子近有序。ESM 一阶反转曲线测量的分析表明，这些缔合缺陷可能通过降低氧交换“表面”反应的活化能，在重掺杂 40 摩尔%的氧化钐中发挥有益作用。在一个模型实验中，通过一系列掺杂氧化钐的氧化铈外延薄膜的固溶体，我们揭示了体相中缔合缺陷的存在会影响 SDC 薄膜的表面荷电状态，从而提高交换速率。这些发现的意义在于通过控制体相相关簇来设计具有可调氧表面交换的涂层，以用于未来的电催化应用。
