Development of Facile Nanofabrication Technique of 2D materials membrane for Electrocatalysis and Molecular Transport

Abstract

Preparing two-dimensional (2D) materials-based membranes in a is a prerequisite for their widespread application in electrocatalysis and molecular transport. An ultramicrotomy technique is used in this thesis to produce membranes of molybdenum disulfide (MoS2) with vertical orientations from mechanically exfoliated flakes, and also for producing pristine vermiculite, mica, laminate membranes, and slit-shaped channels. In the first half of the thesis, I introduced a facile way to fabricate edge exposed MoS2 for hydrogen evolution reaction (HER) where we used ultramicrotome to make vertically oriented MoS2. This is one of the most rapid methods reported for preparing vertically oriented transition metal dichalcogenides at room temperature. The membrane with the 2D materials is shown in a vertically aligned (exposed edges) form. As a result of this method, a simple route to the preparation of electrocatalysts can be provided, and further the morphology of MoS2 is engineered to maximize the HER catalytic performance. Additionally, these 2D membranes were spontaneously decorated with gold nanoparticles (5 nm) to enhance their activity for hydrogen evolution catalysis. Finally, these electrocatalysts were evaluated for reproducibility and stability over hundreds of voltage cycles. In the second part of the thesis the methodology was used to demonstrate a novel method of preparing nanochannels with well-defined geometries. The major bottleneck in the fabrication process of the sub-nanometer-sized fluidic channels was the low-throughput, expensive, and highly time-consuming channel fabrication techniques. In order to overcome these hurdles, we demonstrate an innovative approach using an ultramicrotome to fabricate a variety of confined 2D channels with highly precise dimensions in a facile methodology. Thin slices (thickness ~50 nm to about a um) were prepared with high accuracy in thickness, ± 2 %, with embedded 2D materials. These slices present atomically smooth cross-sections of the 2D materials. I have established the ultramicrotomy fabrication for preparing different types of 2D fluidic channels, pristine 2D channels, restacked laminate 2D channels, and slit-shaped channels made from van der Waals heterostructures. The fabrication process is versatile, and it is easy to integrate the resin membranes containing 2D channels into macroscopic devices. The ultramicrotomy can turn otherwise fragile laminate 2D channels into robust ones which sustain applied pressures and generate ionic streaming currents. The ultramicrotomed 2D channels offer a platform to investigate the ion-transport characteristics through the free space between the interlayers of layered materials, which is otherwise impossible to do while conserving the natural occurrence. The interstitial fluidic channels of the ultramicrotomed pristine vermiculite channels offer charge-selective ion transport. Our method enables in-plane fluidic transports in restacked laminate membranes which sustain pressures to produce ion streaming. Generally, fluidic devices of such restacked laminate membranes suffer from low mechanical stability and longer in-plane channel length. Importantly, we can produce multiple devices from single slit-shaped 2D channel stack with various channel lengths without compromising their functionality. The slit-shaped 2D channels are ideal candidates for exploring unexpected fluid-transport phenomena. However, fabricating a single device requires time-consuming and highly sophisticated fabrication techniques. The findings of our study provide a new means to prepare fluidic devices with an ability to tune the fluid path length and brings much needed easy and facile method to the 2D materials based fluidic device fabrication. In addition to representing a significant advance in nanofluidics, this work will also have a significant impact on multiple research domains involving nanoscale flows (batteries, supercapacitors, sensing, size-selective sieving, et

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ashok Keerthi (Supervisor) & Radha Boya (Supervisor)