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

氢作为可再生能源转换和存储的可持续能源载体起着决定性的作用，这些可再生能源随后可以在低温燃料电池中高效地转化为电能。主要的问题是光伏和风电场断断续续地提供电能，这使得有必要开发出仍然经济地运行的电解水器，最重要的是，即使在负荷变化很大的情况下也能稳定地运行。这需要在酸性环境中分解电解水，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，阳极发生腐蚀，导致电催化活性物质在长时间尺度上的损失。在Hess教授(柏林)和Over教授(gieçen)的这个联合项目中，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，而不会降低其非常高的析氧活性(OER)。为此，将采用OER稳定的氧化物，如二氧化钛和二氧化IrO_2，选择性和局部钝化RuO_2的方法。为了对动态和稳态条件下的阳极腐蚀有微观的了解，我们将使用具有明确形貌的方形RuO2(110)岛为基础的专用单晶模型电极，并在原子尺度上跟踪阳极腐蚀及其局部钝化的结构和形态变化，以及实验和理论方法。在理论方面，将建立一个基于原子尺度的阶地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化特别敏感的位置，并预测静态和动态条件下Ru的损失。在实验中，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、质谱仪)和表面X射线衍射相结合的方法来检查模型电极。这些相应的实验和理论见解将使人们对动态反应条件下的腐蚀有一个全面的了解，从而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.