Ionic currents exceeding the diffusion limitation in planar nano-cavities

Theory predicts that ionic currents through electrochemical cells at nanometer scale can exceed the diffusion limitation due to an expansion of the interfacial electrostatic double layer. Corresponding voltammetry experiments revealed a clear absence of a plateau for the current, which cannot be described by the classical Butler–Volmer approach using realistic values for the transfer coefficient. We show that extending the classical approach by considering the double layer structure using the Frumkin correction leads to an accurate description of the anomalous experimental data.

► Voltammograms of cells with nanometer electrode spacing can show anomalies. ► A model for nano-scale electrochemical cells with a reference electrode is given. ► An equation for voltammograms including the double layer structure is derived. ► We show that double layer expansion results in currents above the diffusion limit. ► The model results accurately resemble the experimental data for nano-scale cells.