A thorough understanding of nanoscale transport properties is vital for the development and optimization of nanopore sensors. The thickness of the electrical double layers (EDLs) at the internal walls of a nanopore, as well as the dimensions of the nanopore itself, plays a crucial role in determining transport properties. Herein, we demonstrate the effect of the electrolyte concentration, which is inversely proportional to the EDL thickness, and the effect of pore size, which controls the extent of the electrical double layer overlap, on the ion current rectification phenomenon observed for conical nanopores. Experimental and numerical results showed that as the electrolyte concentration is decreased, the rectification ratio reaches a maximum, then decreases, and eventually inverts below unity. We also show that as the pore size is decreased, the rectification maximum and the inversion take place at higher electrolyte concentrations. Numerical investigations revealed that both phenomena occur due to the shifting of ion enrichment distributions within the nanopore as the electrolyte concentration or the pore size is varied.

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Ion current rectification is highly reported in aqueous electrochemical systems and sensors but lacks exploration in organic systems due to the additional complexity introduced by non-aqueous solvents. Herein, a detailed study on ion current rectification with highly polar and mildly polar aprotic organic solvents as a function of tetraethylammonium tetrafluoroborate supporting electrolyte concentration is presented. To explain our experimental results, we introduce a previously unreported phenomenon: the formation of a double-junction diode within the nanopore that arises due to a complex interplay between ion and solvent enrichment effects. Finite element simulations are used to explore this phenomenon and the subsequent effect on the rectifying behavior of conical quartz nanopores.

Yi-Tao Long opened a general discussion of the paper by Paul W. Bohn: The electrochemical nanoconnement makes a major impact on controlling the mass transport. Could you please comment on the multi-phase effects on the mass transport under nanoconnement. What's the next breakthrough application we could expected in controlling the mass transport in nanoconnement.