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

氢作为一种可持续的能源载体，在可再生能源的转换和储存中起着决定性的作用，可再生能源随后可以在低温燃料电池中有效地转换回电能。主要问题是光伏发电和风力发电场的电力供应是间歇性的，这使得有必要开发出即使在负荷变化很大的情况下也能经济、稳定地运行的水电解槽。这需要在酸性环境中电解水分解，在酸性环境中，可以施加更高的过电压，而不会失去阳极材料的长期稳定性。在高过电压下，阳极腐蚀，导致电催化活性物质在长时间内的损失。在Hess教授（Berlin）和Over教授（Gießen）的联合项目中，我们展示了一种创新的方法来稳定电化学水分解中的活性电催化剂，即RuO2，而不会降低其极高的出氧活性（OER）。为此，将采用oer稳定氧化物（如TiO2和IrO2）对RuO2进行选择性局部钝化的方法。为了获得动态和稳态条件下阳极腐蚀的微观洞察，我们将使用基于方形RuO2（110）岛的专用单晶模型电极，具有明确的形态，并在原子尺度上以及实验和理论方法上跟踪阳极腐蚀及其局部钝化的结构和形态变化。在理论方面，将建立基于原子尺度的阶梯和台阶边缘腐蚀机理的从头算模型，并结合动力学蒙特卡罗方法，以确定对腐蚀和表面结构演变特别敏感的位置，并预测静止和动态条件下Ru的损失。在实验中，模型电极将使用成像（扫描隧道显微镜，扫描电子显微镜）和定量操作方法（x射线光电子能谱，质谱）和表面x射线衍射的组合进行检查。这些相应的实验和理论见解将提供对动态反应条件下腐蚀的全面理解，从而能够系统地提高材料的抗腐蚀稳定性。

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.