Water-air nanointerfaces are essential components of multiphase electrochemical processes in various energy-related applications, including water electrolysis, hydrogen fuel cells, and CO2 electrochemical reduction. Deep insights into the critical properties of the interfaces are much sought after but very challenging to obtain due to their highly dynamic, transparent, and nanoscopic nature. A new approach has been proposed for constructing stable water-air nanointerfaces using FIB-fabricated Janus nanopore electrodes. The curvature of the nanointerfaces can be controlled electrochemically, ranging from positive side (nanodroplets) to negative (nanoconcaves/ nanobubbles) ones. The morphologies of different nanointerfaces were fully characterized with AFM. Single-molecule collision events of charged dye molecules, recorded with fluorescence imaging, were used to probe the intrinsic properties of the nanointerfaces. A unique phenomenon of charged dye rejection was discovered for isoelectric nanointerface. The role of surface curvature on the collision frequency was also elucidated. We believe using the platform could greatly benefit deepening our understanding of the interfaces, thus guiding the rational design of various energy-related systems.
