Defect-mediated regulation of interfacial hydrophobic transport via cavitation thermodynamics.

The dynamical transport of reactants across the electric double layer is a pivotal yet poorly understood process in electrocatalysis, often overshadowed by the focus on surface adsorption energetics. In this work, we use ab initio molecular dynamics to elucidate the microscopic mechanism governing the hydrophobic solute penetration across the defect-mediated MoS2-water interface, based upon Lum-Chandler-Weeks theory. We show that the free-energy barriers associated with penetration into the Stern layer closely follow the local cavitation free-energy landscape, indicating that cavity formation constitutes the dominant thermodynamic contribution to hydrophobic transport across the EDL. Specifically, we identify that surface defects induce a rigid "O-down" water configuration that significantly amplifies the cavitation penalty, effectively gating the access of reactants to active sites and modulating the mass transport behavior of molecules with varying van der Waals radii. By combining artificial-cavity sampling with constrained AIMD free-energy calculations, we establish a direct connection between cavitation thermodynamics and the transport barriers of nonpolar probes, including H2, CH4, CF4, and CCl4, while identifying additional electrostatic contributions for the polar probe NH3. These results highlight interfacial solvent structure as a key descriptor of molecular transport and suggest that, beyond tuning electronic properties, surface engineering can influence catalytic performance through control of the solvent free-energy landscape.