Vertically-Oriented Ti3C2Tx MXene Membranes for High Performance of Electrokinetic Energy Conversion.

The electrokinetic effect to convert the mechanical energy from ambient has gained sustained research attention because it is free of moving parts and easy to be miniaturized for microscale applications. The practical application is constrained by the limited electrokinetic energy conversion performance. Herein, we report vertically oriented MXene membranes (VMMs) with ultrafast permeation as well as high ion selectivity, in which the permeation is several thousand higher than the largely researched horizontally stacked MXene membranes (HMMs). The VMMs can achieve a high streaming current of 8.17 A m-2 driven by the hydraulic pressure, largely outperforming all existing materials. The theoretical analysis and numerical calculation reveal the underlying mechanism of the ultrafast transport in VMMs originates from the evident short migration paths, the low energy loss during the ionic migration, and the large effective inlet area on the membrane surface. The orientation of the 2D lamella in membranes, the long-overlooked element in the existing literatures, is identified to be an essential determinant in the performance of 2D porous membranes. These understandings can largely promote the development of electrokinetic energy conversion devices and bring advanced design strategy for high-performance 2D materials.