Probing Nanoconfined Ion Transport in Electrified 2D Laminate Membranes with Electrochemical Impedance Spectroscopy

The recent emergence of electrically conductive nanoporous membranes based on graphene and other 2D materials opens up new opportunities to revisit some longstanding nanoconfined ion transport problems under electrification. This work probes the ionic resistance in electrified multilayered graphene membranes with electrochemical impedance spectroscopy. This study demonstrates that the combination of additive-free feature and tunable slit pore sizes in the sub-10 nm range in graphene-based membranes has made it possible to deconvolute the different ionic processes from the impedance obtained and examine the exclusive influence of pore size on the ionic resistance in a quantitative manner. The trends revealed for the ionic resistance at the pore entrance and inside the pores under severe nanoconfinement (<2 nm) are found to be generally consistent with the microscale theoretical simulations previously reported. It also allows a quantitative analysis of the relative effects of the external polarization potential and ion identity under nanoconfinement. The results suggest that the classic electrochemical impedance spectroscopy technique, when applied to appropriate nanoporous electrode materials, can provide rich information about nanoconfined ion transport phenomena under electrification for fundamental understanding and application development.