Investigating the Impact of Pt(hkl) Surface Structure on Electrochemical Double Layer Capacitance: Aimd Simulations and Experimental Insights

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A comprehensive understanding of the electrical double layer (EDL) properties is essential to engineer electrochemical systems. The classical theory of EDL can reasonably explain experimental observations for only a few ideal systems like the liquid metal mercury electrodes, which are not suitable for practical applications. The EDL at solid electrodes, which are often used in electrochemical energy systems, have non-trivial dependences from several factors such as the electrode structure, its chemical composition, and complex interactions between the electrode surface and electrolyte species. Taking these factors into account requires a more detailed description of the EDL than that provided by the classical EDL theory.In this study, we focus on the double layer capacitance as a key property of the EDL to rationalize experimental measurements of the capacitance as a function of the electrode surface structure. We employ ab initio molecular dynamics simulations to explicitly model several Pt(hkl)/water interfaces considering a series of flat and stepped surfaces at the potential of zero charge. We find that the orientation of water dipole moments at the interface depends strongly on the surface atomic structure, which can then influence the EDL capacitance. Our results suggest that simply by introducing surface defects such as steps on the Pt surface, the EDL capacitance can be varied significantly. We discuss our computational results in light of recent experimental data reported in J. Am. Chem. Soc. 2024, 146, 6, 3883–3889 and prior studies. We believe that the obtained insights are essential in advancing the fundamental understanding of the effect of electrode atomic structure on the basic electrochemical properties of electrocatalytic systems.