Probing Solvent Dynamics at the Single-Molecule Limit

The Electric Double Layer (EDL) that self-organizes at electrode-electrolyte interfaces plays a fundamental role in electrochemistry. While its structure has been extensively studied over the last 150 years, its dynamic behavior is still not completely understood. Here, we present a novel experimental approach to probe the EDL using single-molecule junctions as ultrasensitive probes, validated by a preliminary study of the Inner Helmholtz Plane (IHP). We measured the current response of single-molecule devices under square-wave bias in various solvent environments, and we found remarkable differences falling into three categories: large nonlinear transients in highly polar solvents, capacitor-like responses in solvents of intermediate polarity, and no significant transients (within our frequency limits) in nonpolar solvents. By fitting the solvent behavior to a molecular-level equivalent circuit, our data reveal trends in how the nature of the solvent influences IHP dynamics and provide insights into the origin of nonlinearity.