Heterogeneous Oxidation Catalysis in the Liquid Phase

B09: Exploring the Role of Defects on the Active Site Evolution in Co-Based Spinels and Hydrous Oxides under OER Conditions by Correlative Microscopy

Prof. Dr. Tong Li • Prof. Dr. Kristina Tschulik

Co-based oxides and hydrous oxides have emerged as promising electrocatalysts for the oxygen evolution reaction (OER). Further improving these electrocatalysts requires detailed knowledge of structure-property relationships. However, the electrochemical performance of electrocatalysts may differ spatially due to the presence of surface defects, while standard electrochemical analysis probes the entire electrode surface, providing integral data. Moreover, electrocatalysts undergo dynamic changes in surface-near regions under OER conditions. Therefore, an approach that can reveal the local surface structure and correlate it with the local activity is urgently needed.

In this project, we will develop a correlative method to link the oxidation state, surface morphology and chemical compositions of Co-based oxides and hydrous oxides with their local activity. The new method will enable the correlation of scanning electrochemical cell microscopy (SECCM), electrochemical atomic force microscopy (EC-AFM), X-Ray photoelectron spectroscopy (XPS), and atom probe tomography (APT) measurements on the same local features that are pre-identified by the scanning electron microscopy (SEM)/electron backscatter diffraction (EBSD). We will focus on the Co-X (X: Fe, Mn) spinel oxides and hydrous oxides in the form of nanoparticles or thin films synthesized by electrochemical oxidation of Co. Specifically, SECCM will be employed to probe the local OER activity on the surface of oxides and hydrous oxides. APT in conjunction with EC-AFM and SEM/EBSD will be used to reveal the morphology, chemical composition, and local defects on the surface of oxides and hydrous oxides and their temporal evolutions during OER.

Overall, the project will improve the understanding of the structure-property relationships of Co-based oxides and hydrous oxides, with focus on the role of well-defined defects, such as grain boundaries. Since we will be able to identify and localize different crystal planes on the samples and link them to the local OER activity and associated morphological changes, jointly with the insights gained from theory and operando spectroscopy within the consortium, this project will give new insights into the active sites of Co-based spinels and hydrous oxides for OER. This new correlative electrochemical microscopy approach will be extended to other materials and reactions of interest in the CRC in the third funding period, including different reactions such as alcohol oxidation or catalysts, e.g., perovskites.

(Figure: Schematic diagram illustrating the material system in each WP and its key objectives (The Tschulik group will be responsible for SECCM, EC-AFM and EC testing. The Li group will perform SEM/EBSD, SEMM/FIB and APT measurements. XPS will be done by the S project)).