Degradation-control of perovskite oxide OER catalysts under dynamic operation conditions via advanced operando characterization and orbital-d-band engineering

分析和理解动态操作条件下的催化反应是DFG-SPP2080计划的主要目标。本文研究了碱性介质中析氧反应(OER)对水分解的催化作用。间歇可再生能源驱动的水裂(电解)制氢在未来的储能和转换装置中起着至关重要的作用，而所需催化剂的长期稳定性是该领域的主要障碍。我们建议的中心目标是了解OER-催化剂和电解液之间固/液界面的电化学过程，并揭示在外加动态负荷分布下的长期降解机理。我们的方法将钙钛矿作为有前途的OER催化剂，而轨道结构(即过渡金属3D-O 2p杂化轨道)是其催化活性的主要描述因素，可以通过阳离子取代进行系统的修饰。虽然在文献中讨论了轨道结构和活度之间的关系，但是轨道结构和长期稳定性之间的关系还没有被理解，将受到本提议的影响。在这项提议之前的工作中，我们证明了钙钛矿型催化剂的寿命关键取决于所施加的负荷分布的历史。当动态操作条件导致体相退化时，静态条件导致表面钝化。除了负载历史外，表面化学的动态变化增加了理解长期降解行为的复杂性：预计在动态OER条件下，钙钛矿表面会发生可逆(Oxy-)氢氧化物转化，从而增强降解。因此，为了改进OER催化剂，有必要了解动态(与静态)操作下轨道结构、表面化学和(电)化学降解之间的关系。因此，一种可重复、可控制和量身定制的催化剂合成，辅以(电)化学、电子和显微分辨率的动态操作下的活性表面的操纵性分析是必要的。在目前的方法中，我们将1)通过原子控制的催化剂外延，2)通过系统地表征轨道结构和电化学性能，3)通过使用相关扫描探针技术和基于同步辐射的X射线吸收光谱在动态操作条件下对表面化学、形貌和轨道结构进行操作研究，来实现这一点。我们联盟的全面方法和专业知识将使我们能够以原子精度揭示降解和应用负载历史之间的关系，得出对催化反应和涉及的表面转化的系统控制，并通过轨道工程的基于知识的材料设计最终改善OER催化剂的性能。

Analysis and understanding of catalytic reactions under dynamic operation conditions are the major goals of the DFG-SPP2080 program. The present proposal deals with the catalysis of the oxygen evolution reaction (OER) upon water splitting in alkaline media. Green hydrogen production from water splitting (electrolysis) powered by intermittent renewable energy sources plays a crucial role for future energy storage and conversion devices, whereas long-term stability of the required catalysts is the major obstacle in the field. The central aim of our proposal is to understand electrochemical processes at the solid/liquid interface between the OER-catalyst and the electrolyte and to unravel the mechanism of long-term degradation under the applied dynamic load profile.Our approach involves perovskites as promising OER catalysts whereas orbital structure (i.e. transition metal 3d- O 2p hybrid orbitals) is a major descriptor for their catalytic activity and can be systematically modified by cation substitution. While the relation between orbital structure and activity is discussed in literature, the relation of orbital structure and long-term stability is not yet understood and will be subject to the present proposal. In previous work to this proposal we demonstrated, that the lifetime of perovskite-catalysts crucially depends on the history of the applied load profile. While dynamic operation conditions lead to bulk degradation, static conditions lead to a surface passivation. Besides load history, dynamic changes of the surface chemistry add additional complexity to understanding the long-term degradation behavior: It is anticipated that under dynamic OER conditions reversible (Oxy-)Hydroxide transformations take place on the perovskite surface enhancing degradation. To improve the OER catalysts, it is thus essential to understand the relation between orbital structure, surface chemistry and (electro)chemical degradation under dynamic (vs. static) operation. Therefore, a reproducible, controllable and tailored catalyst synthesis complemented by operando analysis of the active surface under dynamic operation with (electro)chemical, electronic and microscopic resolution is mandatory. In the present approach we will achieve this 1) by atomically-controlled catalyst epitaxy, 2) by systematic characterization of orbital structure and electrochemical performance and 3) by operando investigations of surface chemistry, morphology and orbital structure under dynamic operation conditions using correlative scanning probe techniques and synchrotron-based x-ray absorption spectroscopy.The comprehensive methodology and expertise of our consortium will enable us to unravel the relation between degradation and applied load history with atomistic precision, to derive systematic control over catalytic reactions and involved surface transformations, and to ultimately improve OER-catalyst performance by knowledge-based materials design via orbital engineering.