Molecular Dynamics Study on Swelling and Exfoliation Properties of Montmorillonite Nanosheets for Application as Proton Exchange Membranes

Abstract

Existing proton exchange membranes have the disadvantages of low proton conductivity at high temperature, high cost, and poor barrier properties. Montmorillonite (MMT) materials have excellent thermal and chemical stability, and two-dimensional nanostructures formed by exfoliated MMT show excellent proton conductivity. Therefore, they are expected to become new proton exchange membrane materials. However, the existing exfoliation methods still lack a unified theoretical guidance. In this work, we systematically investigate the detailed swelling and exfoliation properties of MMT with different intercalation cations via extensive molecular dynamics simulations. We find that the swelling properties are determined by the hydration capacity of interlayer cations, and the exfoliation mainly occurs via a lateral sliding process between adjacent layers. The exfoliation energy barrier strongly depends on the interaction strength between interlayer cations and MMT nanosheets, swelling degree, and surface charge density. Lower interaction strength and a higher swelling degree together with larger surface charge density can result in an easy exfoliation process. Our work unveiled the detailed mechanism of the exfoliation process of MMT nanosheets and may contribute to the search for efficient MMT exfoliation methods.

Thermal-Tolerant CdPS3-Polybenzimidazole Membranes with High Proton Conductivity

“…For treatment time, the solution with 10 mol L −1 K ions was stirred at 90 °C for 3, 6, 18, and 24 h, separately. Similarly, the optimization of the conditions for Li-ion treatment was conducted with different temperatures (30,50,70, and 90 °C), Li concentrations (1, 1.5, and 2 mol L −1 ), and treatment times (2, 4, 6, and 8 h), respectively.…”

“…To enhance membrane performance, some proton-conductive membranes were developed by using quantum dots or frameworks . Alternatively, two-dimensional (2D) inorganic materials, such as mica and graphene, emerge with promising potential for proton transport at elevated temperatures owing to their thermal stability. − Among them, the transition-metal phosphorus trichalcogenides, which are a large family of layer-structured materials with a formula of MPX 3 (M = Cd, Mn, Fe, Co, Ni, Zn, or Cr; X = S or Se), are newly investigated for efficient proton exchange . As lacking proton-transport paths, the bulk MPX 3 crystal is actually proton-insulative.…”

Graphene Oxide-Intercalated Montmorillonite Layered Stack Incorporated into Poly(2,5-Benzimidazole) for Preparing Wide-Temperature Proton Exchange Membranes

“…Clay minerals can be introduced to prepare organic–inorganic composite membranes due to their low price, easy access, and environmental friendliness. − Montmorillonite (MMT) is a representative two-dimensional nanomineral that consists of tetrahedral silica and octahedral alumina sheets in a physical silicate ratio of 2:1. , After intercalation, MMT shows greatly improved water retention and immobilizes acidic media, which improves the performance of the PEMFC and can potentially be used over a wide temperature range. , Besides, due to the amphiphilic nature of GO, mineral materials can combine with it easily, in addition to being incorporated into polymeric matrices. This property enables GO and MMT to combine in a way that greatly reduces the level of agglomeration of MMT or restacking of GO.…”

“…31−33 Montmorillonite (MMT) is a representative two-dimensional nanomineral that consists of tetrahedral silica and octahedral alumina sheets in a physical silicate ratio of 2:1. 34, 35 After intercalation, MMT shows greatly improved water retention and immobilizes acidic media, which improves the performance of the PEMFC and can potentially be used over a wide temperature range. 36,37 Besides, due to the amphiphilic nature of GO, mineral materials can combine with it easily, in addition to being incorporated into polymeric matrices.…”