A04: Surface Reactivity of Model Oxide Catalysts

Prof. Dr. Beatriz Roldán Cuenya

The goal of A04 is the fundamental understanding of the reactivity-, selectivity- and stability-determining properties of tailored model catalysts for oxidation reactions in the liquid phase. In particular, we aim to contribute to a better understanding of the role of frustrated phase transitions within liquid oxidation electrocatalysis by studying the kinetically determined transformations upon material exposure to catalytic conditions. The main objective is to identify the most important design principles of improved (electro)catalysts for liquid-phase oxidation reactions allowing a facile, sustainable active site formation under reaction conditions and being characterized by long activity periods. Additionally, we aim to improve the current knowledge of kinetically driven deactivation processes. Therefore, we will employ correlative (quasi-in situ, in situ and operando) spectro-microscopy investigations to identify material modifications as a response to changes in the local chemical potential during the reaction under steady-state operation. In addition, we will explore the additional influence of continuous and periodic changes in the temperature and electrical potential.

The structure, morphology, bulk and near-surface composition of well-defined pre-catalyst materials will be first studied quasi-in situ before and after electrocatalysis to unveil the main differences in the activity, selectivity and stability. Subsequently, the best performing materials will be subjected to an in depth in situ and operando characterization. We will study defect-engineered electrode materials to link the abundance and stability of distinct compositional and structural imperfections such as metal and oxygen vacancies with catalytic performance. Our target materials will be Co₃O₄-based nanoparticle (NP) and epitaxial thin film (e-TF) catalysts with Ni- and Cu-containing oxide overlayers of varying thicknesses to ensure relevant catalytic performance towards ethanol (electro)oxidation. To this end, a large set of (surface- and bulk-sensitive) operando methodologies including X-ray-based structural characterization, vibrational spectroscopy as well as electron and scanning probe microscopy will be applied. These studies will be complemented by quasi-in situ pre- and post-catalysis characterization using a variety of surface science methods. We will closely collaborate within the consortium to support and verify our findings with theoretical calculations and (operando) insights obtained by other groups on selected thin film oxide catalysts.

Following the success of our interactions within the CRC, we will continue to apply our methodology to selected thin films and nanoparticles of the CRC. We expect to extend the knowledge we obtained during the 2^nd funding period (FP2) regarding structure-activity relationships for the initial pre-catalyst state by a deepened insight into the working catalyst's operation mode and progress towards a deeper understanding of the solid-liquid interface during oxidation catalysis under extended operation, focusing on unveiling the origin of the materials’ deactivation leading to a better materials design through the active site stabilization.

Figure: In situ AFM during OER Micrographs of (A‑E) Co₃O₄(111) and (F-J) Co₃O₄(001) thin film sur­faces in air, at open circuit poten­tial and during OER, latter two con­ditions with lower and higher magni­fication. FFT images of the high-resolution AFM images shown as insets.