Stabilization of the RuO2 water splitting electrocatalyst under dynamic operating conditions by surface modification

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Hydrogen plays a decisive role as a sustainable energy carrier for the conversion and storage of renewable energies, which subsequently can be efficiently converted back into electricity in low-temperature fuel cells. The main problem is the intermittent supply of electrical energy by photovoltaics and wind farms, which makes it necessary to develop water electrolysers that still operate economically and, above all, stably even with large load changes. This requires electrolytic water splitting in acidic environments, where higher overvoltages can be applied without losing the long-term stability of the anode material. At high overvoltages, the anode corrodes, which results in the loss of electrocatalytically active material on long time scales. In this joint project of Prof. Hess (Berlin) and Prof. Over (Gießen), we demonstrate an innovative way to stabilize an active electrocatalyst in electrochemical water splitting, namely RuO2, without reducing its extraordinarily high activity in oxygen evolution (OER). For this purpose, the method of selective and local passivation of RuO2 by OER-stable oxides such as TiO2 and IrO2 will be applied. In order to gain microscopic insights into anodic corrosion under dynamic and steady-state conditions, we will use dedicated single-crystalline model electrodes based on square RuO2(110) islands with a well-defined morphology and follow the anodic corrosion and its local passivation with respect to structural and morphological changes on the atomic scale as well in experiments as with theoretical methods. In the area of theory, an ab initio-based model on the atomic scale for the mechanism of corrosion on terraces and step edges will be established and coupled with kinetic Monte Carlo methods in order to determine the sites that are particularly sensitive to corrosion and the structural evolution of the surface and predict the loss of Ru under stationary and dynamic conditions. In the experiments, the model electrodes will be examined using a combination of imaging (scanning tunneling microscopy, scanning electron microscopy) and quantitative operando methods (X-ray photoelectron spectroscopy, mass spectrometry) and surface X-ray diffraction. These corresponding experimental and theoretical insights will provide a comprehensive understanding of corrosion under dynamic reaction conditions, which enables a systematic improvement of the material stability against corrosion.