Friction Force Microscopy as a tool to investigate (electro)catalytic processes at surfaces

Friction Force Microscopy as a tool to investigate (electro)catalyticprocesses at surfacesM.Maksumov1,2, A. Kaus2,3, Z. Teng4, K. Kleiner4, F. Gunkel3, F. Hausen1,21Forschungszentrum Jülich, IEK-9, 52428 Jülich, Germany2RWTH Aachen University, IPC, Landoltweg 2, 52065 Aachen, Germany3Forschungszentrum Jülich, PGI-7, 52428 Jülich, Germany4University of Münster, MEET, Correnstraße 46, 48149 Münster, [email protected]@fz-juelich.deA thorough understanding of (electro)catalytic surface transformations under dynamic reaction conditions is of utmost importance for a knowledge-based catalyst design. Friction Force Microscopy (FFM) as an atomic force microscopy based technique is capable to obtain materials specific information in addition to electrical and structural properties of catalysts in liquid media and under electrochemical conditions. This is especially relevant as surface transitions at early catalytic activity are subtle and might be easily overseen by pure topography mapping.It is the objective of this work to demonstrate the capabilities of FFM for investigating (electro)catalysts. It has been shown earlier that the frictional behavior of a bare metal differs significantly from its oxy/hydroxy-terminated surface under electrochemical conditions.The new results on combined electrochemical and frictional experiments on well-defined epitaxial perovskite oxide structures in aqueous liquids are illustrated. This approach represents the first application of these technique with respect to (electro)catalysis. Simultaneously recorded cyclic voltammograms and lateral forces, so-called frictograms, allow to correlate subtle and local surface transformations and the applied potential precisely.In conclusion, FFM represents a versatile new operando technique to investigate (electro)catalytic reactions under dynamic conditions on a local scale with high sensitivity to materials and structural changes

Friction Force Microscopy as a tool to investigate (electro)catalytic activities at surfaces

Production of green hydrogen energy based on water electrolysis, currently, have become one of the crucial topics in the framework of energy transition towards green energy technologies. In water splitting electrolysis catalysis or electrocatalysts play a critical role, where the development of active, stable and low-cost electrocatalysts is always on the agenda of the research works. [1] Designing of electrocatalysts with fundamental understanding of their surface transformations under dynamic reaction conditions still remains very challenging. This requires a fundamental understanding of all the processes involved on the atomic level, which is the main focus of my research work and part of the common goals of DFG Priority Programme 2080. The slow reaction kinetics at oxygen evolution reaction (OER) due to high overpotentials keep electrolysis from being of practical use and perovskites, as catalysts, could be used to minimize the overpotentials. However, perovskite electrocatalysts suffer from irreversible degradation reactions such as undesired surface transformations and morphology changes at grain boundaries and surfaces. [2-3] A comprehensive understanding of perovskite surface transformations under dynamic OER conditions at atomic level could be achieved by implementation of different electrochemical scanning probe microscopy techniques. Mainly, to investigate fundamental processes at the solid/liquid interface in electrocatalysis advanced atomic force microscopy (AFM) and scanning tunneling microscopy (STM) are employed in liquid environment under applied voltage bias. AFM enables the collection of data regarding the nanomechanical, electrical, and structural properties of sample in addition to the standard topography map that is captured. This is highly valuable considering sole topography mapping likely to miss the expected surface changes at the beginning of the OER. Previously, F. Hausen et al [4] applying a common tribology method based on AFM, operando electrochemical friction force microscopy (EC-AFM), reported that friction differences between a bare metal and and oxy/hydroxy-terminated surface in liquid environment clearly indicates direct fingerprint of chemical surface transformation. In our work, we investigate exclusively epitaxially grown perovskite oxide catalysts based on La1-xSrxCoO3 in alkali environment before and after electrocatalysis under dynamic and steady state operation conditions (as illustrated in Fig.1). Figure 1 clearly illustrates the difference of surface between as-grown perovskite oxide with the higher average friction of 18-20 nN than the post-catalaysis perovskite oxide with the average friction of 10-12 nN. The relevance of this research work and necessity to exchange the ideas with researchers around the world working on hydrogen energy technologies is highly encouraged from SPP2080 project as well as well aligned within the scope of H2Educate program from National Energy Education Development (NEED Project, US), which was designed to promote young researchers with educational materials, training and exchange programs. Figure 1. Friction maps of as-grown and post-catalysis of LaxSr1-xCoO3 in air, a and b respectively.1. Wang S., Lu A., Zhong CJ. Hydrogen production from water electrolysis: role of catalysts. Nano Convergence 8, 4 (2021). 2. Grimaud, A. et al. Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution. Nat. Commun. 4, 2439 (2013).3. Wan, G. et al. Amorphization mechanism of SrIO3 electrocatalyst: How oxygen redox initiates ionic diffusion and structural reorganization. 4. Hausen, F. et al. Anion adsorption and atomic friction on Au (111). Electrochimica Acta. 56, 28, 10694-10700 (2011)