Multi-scale modeling of electrochemical interfaces: New methods and applications to RuO2 surfaces
Final Report Abstract
Computer simulations of electrochemical processes at electrocatalyst surfaces are crucial for understanding the limitations of modern energy conversion technologies. Already the structure of the electrochemical interface presents a complex problem due to the multifaceted interaction between surface and solvent which leads to the formation of an electrochemical double layer. Its intricate structure is dynamic and requires realistic model systems beyond the reach of ab initio electronic structure theory. In this project, we therefore developed new simulation protocols which combine simulation methods at multiple scales/level-of-coarse-graining to achieve computationally tractable, yet still predictive models of electrochemical catalyst surfaces. We specifically focused on the less studied transition metal oxide surfaces, using rutile IrO2 as a prototype and prominent material employed in water electrolysis. In a first step, we used density-functional theory to study the stability of oxidized low index surface orientations in idealized model systems and discovered that IrO2(111) becomes stable over IrO2(110) at reaction conditions. This change in dominating surface orientation would theoretically trigger catalyst particle shape reconstruction that could affect catalyst stability and activity. In a second step, we departed from the idealized model systems and trained a machine learning interatomic potential to study the IrO2(110)/water interface. This reactive potential is able to accurately describe large surface models in contact with water at the different surface oxidation states in our initial study, covering the relevant phase space. With this realistic model at hand, we primarily focused on the surface solvation. We found, that solvation is dominated by water adsorption on the bare metal sites along with the resulting hydrogen bonding network, while the dynamic IrO2(110)-water interaction only plays a marginal role. This finding is surprising, given that a strong water-oxide interaction was expected. We concluded, that routinely used idealized model systems which can incorporate water adsorption but neglect the explicit water interaction, already capture the dominating solvation effects at this surface. Our findings thus allow for a deep insight on the electrochemical interface of IrO2 and justify simplified models of electrochemical oxide/water interfaces.
Publications
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Ab Initio Thermodynamics Insight into the Structural Evolution of Working IrO2 Catalysts in Proton-Exchange Membrane Electrolyzers. ACS Catalysis, 9(6), 4944-4950.
Opalka, Daniel; Scheurer, Christoph & Reuter, Karsten
