Principles of a Single-Molecule Rectifier in Electrolytic Environment

The idea of gating the electrical current across a single-chain molecule, confined between and linking two electrodes in electrolytic solution, in order to achieve an asymmetric current–voltage plot, was first put forward and substantiated with a detailed theory by Kornyshev and Kuznetsov (ChemPhysChem, 2006), and Kornyshev, Kuznetsov, and Ulstrup (PNAS, 2006). However, not all aspects of that effect have been studied in those papers. Its experimental confirmation, published by Capozzi et al. (Nature Nanotech., 2015), enthused us to revisit that theory, extending it and exploring all the regimes of system operation. In this article we present such comprehensive analysis, which reveals a set of new features. An important finding is that the introduction of more refined models of the electric double layer (beyond linear response) results in stronger rectification effects, already for relatively dilute electrolyte concentrations. The theory equally applies to electrode systems with and without full electrochemical potential control and highlights important differences for these two scenarios, for example, with regard to the effect of electrode surface area.