Reduced Ion Mobility in Asymmetric Graphene-SiN x Nanochannels

Two-dimensional nanochannels based on graphene membranes show great potential in applications such as ion separation, fast water transport, and green energy. So far, most studies have been focused on nanochannels using homogeneous wall materials, while the effect of vertically asymmetric wall materials on ion transport has long been overlooked. Here, we report on ion transport properties through asymmetric graphene-SiN x nanochannels. We propose a facile process that leverages simple operations of a convenient laser etching method for the fabrication of asymmetric graphene-SiN x nanochannels. Our experimental results indicate that the ion mobility within an asymmetric nanochannel is significantly reduced compared with the value in the bulk solution at high concentrations. Furthermore, molecular dynamics simulations show that the reduced ion mobility arises from the combined effects of the high surface charge density and the strong interfacial drag/friction associated with the SiN x wall, together with the redistributed ion/water structure in the asymmetric channel. Our study offers new insights in advancing the field of membrane science and smart nanofluidics.