Skiba Emily J, Perry Nicola H
Department of Materials Science and Engineering, University of Illinois Urbana-Champaign, 1304 W Green St, Urbana, Illinois61801, United States.
Materials Research Laboratory, University of Illinois Urbana-Champaign, 104 S Goodwin Ave, Urbana, Illinois61801, United States.
ACS Appl Mater Interfaces. 2022 Oct 26;14(42):47659-47673. doi: 10.1021/acsami.2c12184. Epub 2022 Oct 13.
Solid-state heterointerfaces are of interest for emergent local behavior that is distinct from either bulk parent compound. One technologically relevant example is the case of mixed ionic/electronic conductor (MIEC)-metal interfaces, which play an important role in electrochemistry. Metal-MIEC composite electrodes can demonstrate improved catalytic activity vs single-phase MIECs, improving fuel cell efficiency. Similarly, MIEC surface reaction kinetics are often evaluated using techniques that place metal current collectors in contact with the surface under evaluation, potentially altering the response vs the native surface. Techniques enabling direct and local in situ observation of the behavior at and around such heterointerfaces are needed. Here, we develop a spatially resolved optical transmission relaxation (2D-OTR) method providing continuous evaluation of local, high-temperature, controlled atmosphere defect kinetics across a ∼1 cm sample area simultaneously in a contact-free manner. We apply it to observe the spatial variance of oxygen incorporation and evolution rates at ∼525-620 °C, in response to step changes in oxygen partial pressure, on MIEC SrTiFeO films as a function of distance from porous Pt and Au layers. Using this model geometry, we find significant enhancements in kinetics adjacent to the metals that decay over a few millimeter distance. To extract kinetic parameters, we fit the short-term optical data (initial portion of relaxations) with an exponential decay function appropriate for surface-exchange-limited kinetics, yielding apparent surface exchange coefficients () with spatial resolution, decreasing with distance from the metal. To understand the kinetic processes governing the complete (long-term) optical relaxations, we performed COMSOL simulations, which demonstrated that a combination of laterally varying and in-plane diffusion controls the observed kinetics over the full time range. Further support for spatially varying comes from demonstrations of changing surface and bulk chemistry vs distance from the metal-MIEC interface, by X-ray photoelectron and optical absorption spectroscopies, respectively. Although microporous Pt and Au are not excellent electrodes in isolation, both metals exert a synergistic effect on the oxygen surface exchange rate in the presence of the mixed conducting film.
固态异质界面因其展现出的与母体块体化合物不同的新兴局部行为而备受关注。一个与技术相关的例子是混合离子/电子导体（MIEC）-金属界面的情况，其在电化学中起着重要作用。金属-MIEC复合电极相对于单相MIEC可表现出更高的催化活性，从而提高燃料电池效率。同样，MIEC表面反应动力学通常使用将金属集流体与被评估表面接触的技术来评估，这可能会改变相对于原始表面的响应。因此，需要能够直接和局部原位观察此类异质界面及其周围行为的技术。在此，我们开发了一种空间分辨光传输弛豫（2D-OTR）方法，该方法能够以非接触方式同时对约1平方厘米的样品区域内的局部高温、可控气氛缺陷动力学进行连续评估。我们将其应用于观察在约525 - 620°C下，响应氧分压的阶跃变化，MIEC SrTiFeO薄膜上氧掺入和析出速率随距多孔Pt和Au层距离的空间变化。利用这种模型几何结构，我们发现在靠近金属处的动力学有显著增强，且这种增强在几毫米的距离内逐渐衰减。为了提取动力学参数，我们用适合表面交换受限动力学的指数衰减函数拟合短期光学数据（弛豫的初始部分），得到具有空间分辨率的表观表面交换系数（），其随距金属距离的增加而减小。为了理解控制完整（长期）光学弛豫的动力学过程，我们进行了COMSOL模拟，结果表明横向变化的和平面内扩散的组合在整个时间范围内控制了观察到的动力学。分别通过X射线光电子能谱和光吸收光谱证明了表面和体相化学随距金属-MIEC界面距离的变化，这进一步支持了的空间变化。尽管微孔Pt和Au单独作为电极并不理想，但在存在混合导电膜的情况下，这两种金属对氧表面交换速率都有协同作用。
