Ion-Driven Dynamics of Charge-Neutral Species in the Electrical Double Layer: Insights from Alternating and Constant Polarity Simulations

While most electrical double layer (EDL) theories focus on the distribution of ionic species near a charged surface, charge-neutral molecules, particularly in multicomponent electrolyte systems, can also redistribute and influence the selectivity and efficiency of electrochemical reactions. In this study, molecular dynamics (MD) simulations were used to investigate the behavior of charge-neutral molecules under both constant and rapid alternating polarity (rAP) electric fields. The dynamics of charge-neutral molecules in the EDL become tunable by the intricate interplay between electrode surface adsorption and electrostatic interactions with ions and charged surfaces. Our results indicate that under a constant polarity electric field, ion coordination governs the distribution of charge-neutral molecules as surface charge increases, leading to a pronounced deviation in their concentration within the EDL compared to the bulk solution. Under rAP conditions, rapid migration of ionic species further perturbs the EDL composition, resulting in a dynamic environment for charge-neutral species. We further examined the influence of rAP profiles on the residence times and diffusion behaviors of these molecules within the EDL, revealing that their response to alternating electric fields may suppress undesirable side reactions and enhance product selectivity.