Vertically-Oriented Ti₃C₂T_x MXene Membranes for High Performance of Electrokinetic Energy Conversion

Abstract

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.

Angstrom-scale ion channels towards single-ion selectivity

“…However, the osmotic energy conversion properties of subnanometer 0D pores and 1D channels have not been studied. For 2D nanofluidic membranes including GO, 267 Mxene, [268][269][270] BN, 271 and hybrid 272 membranes, their osmotic power densities 253 are between 0.1 and 30 W m À2 , varying with the variations of materials, membrane thickness, and ion transport direction. For example, The vertical 269 and horizontal 270 osmotic power densities of 2D Mxene membranes are 21 and 25 W m À2 , respectively.…”

“…For 2D nanofluidic membranes including GO, 267 Mxene, [268][269][270] BN, 271 and hybrid 272 membranes, their osmotic power densities 253 are between 0.1 and 30 W m À2 , varying with the variations of materials, membrane thickness, and ion transport direction. For example, The vertical 269 and horizontal 270 osmotic power densities of 2D Mxene membranes are 21 and 25 W m À2 , respectively. In another instance, 3D, angstrom-sized membranes composed of a continuous UiO-66-NH 2 layer and ordered alumina nanochannels with highly selective and ultrafast ion transport were used for osmotic energy harvesting.…”

Nanofluidic osmotic power generators – advanced nanoporous membranes and nanochannels for blue energy harvesting

“…11,43 The possibility of this new generation of nanoporous membranes to operate as energy harvesters mostly comes from the presence of charged groups on the surface of nanometric pores (this property will be addressed in more detail below). So far, different methods to harvest energy using charged nanoporous membranes have been reported including streaming current, 44 diffusion current, 45 and diffusio-osmotic current. 46 In some cases, the differences reside not only in the experimental set-up but also in the basic principles.…”

Non-monotonic variation of flow strength in nanochannels grafted with end-charged polyelectrolyte layers

“…The early development of EKEC was pioneered by works from Kwok 12 and Daiguji 13 with an EKEC energy conversion efficiency of around 1%. With recent advances in nano-materials, 14 nano-manufacturing 2 and operation parameter optimization ( e.g. adjusting temperature 11 ), the EKEC systems have achieved significant progress.…”