PDF(Pubmed)
Abstract：
The oxygen exchange kinetics of epitaxial Pr0.1Ce0.9O2-δ electrodes was modified by decoration with submonolayer amounts of different basic (SrO, CaO) and acidic (SnO2, TiO2) binary oxides. The oxygen exchange reaction (OER) rate and the total conductivity were measured by in situ PLD impedance spectroscopy (i-PLD), which allows to directly track changes of electrochemical properties after each deposited pulse of surface decoration. The surface chemistry of the electrodes was investigated by near-ambient pressure XPS measurements (NAP-XPS) at elevated temperatures and by low-energy ion scattering (LEIS). While a significant alteration of the OER rate was observed after decoration with binary oxides, the pO2 dependence of the surface exchange resistance and its activation energy were not affected, suggesting that surface decorations do not alter the fundamental OER mechanism. Furthermore, the total conductivity of the thin films does not change upon decoration, indicating that defect concentration changes are limited to the surface layer. This is confirmed by NAP-XPS measurements which find only minor changes of the Pr-oxidation state upon decoration. NAP-XPS was further employed to investigate changes of the surface potential step on decorated surfaces. From a mechanistic point of view, our results indicate a correlation between the surface potential and the altered oxygen exchange activity. Oxidic decorations induce a surface charge which depends on their acidity (acidic oxides lead to a negative surface charge), affecting surface defect concentrations, any existing surface potential step, potentially adsorption dynamics, and consequently also the OER kinetics.
摘要：
外延Pr0.1Ce0.9O2-δ电极的氧交换动力学通过修饰亚单层量的不同碱性（SrO，CaO）和酸性（SnO2，TiO2）二元氧化物。通过原位PLD阻抗谱(i-PLD)测量氧交换反应(OER)速率和总电导率,这允许在每个沉积的表面装饰脉冲后直接跟踪电化学性能的变化。通过高温下的近环境压力XPS测量（NAP-XPS）和低能离子散射（LEIS）研究了电极的表面化学。虽然用二元氧化物装饰后观察到OER率的显著变化，表面交换电阻的pO2依赖性及其活化能不受影响，这表明表面装饰不会改变基本的OER机制。此外，薄膜的总电导率在装饰时不会改变，表明缺陷浓度变化仅限于表面层。这通过NAP-XPS测量得到证实,其在装饰时仅发现Pr-氧化态的微小变化。NAP-XPS进一步用于研究装饰表面上表面电势阶跃的变化。从机械的角度来看，我们的结果表明，表面电势和改变的氧交换活性之间存在相关性。氧化装饰诱导表面电荷，这取决于它们的酸度（酸性氧化物导致负表面电荷），影响表面缺陷浓度，任何现有的表面电位步骤，潜在的吸附动力学，因此也是OER动力学。
