Effects of Hydration and Temperature on the Microstructure and Transport Properties of Nafion Polyelectrolyte Membrane: A Molecular Dynamics Simulation

Biocatalytic PEI-PSS membranes through aqueous phase separation: influence of casting solution pH and operational temperature

Biocatalytic membranes combine the separation properties of membranes and the catalytic abilities of enzymes, holding great promise for industries where both purification and conversion are required. In this work, polyelectrolyte complex membranes incorporated with lysozyme were prepared using polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS) through a one-step and mild pH shift aqueous phase separation (APS) approach. The effects of lysozyme addition and casting solution pH on the membrane properties were studied. All the membranes, both with and without added lysozyme, exhibited asymmetric structures with relatively dense top surfaces and porous cross-sections with finger-like macrovoids. The incorporation of lysozyme did not significantly influence the structure and permeability of the formed membranes. The PEI-PSS biocatalytic membranes exhibited temperature dependent enzymatic activity. The activity strongly increased with increased operational temperature, with the highest activity of 4.30 ± 0.15 U cm-2 at 45 °C. This indicates a responsive effect, where a higher temperature leads to some swelling of the polyelectrolyte complex membrane, making the enzyme more accessible to the used substrate. Moreover, the biocatalytic membranes demonstrate desirable enzymatic stability, maintaining 60% activity even after 60 days of storage. This study validates the potential of the water-based APS process as a straightforward approach for integrating enzymes into responsive biocatalytic membranes.

Measurement of Water Uptake and States in Nafion Membranes Using Humidity-Controlled Terahertz Time-Domain Spectroscopy

Perfluorinated sulfonic acid ionomers are well known for their unique water uptake properties and chemical/mechanical stability. Understanding their performance-stability trade-offs is key to realizing membranes with optimal properties. Terahertz time-domain spectroscopy has been demonstrated to resolve water states inside industrially relevant membranes, producing qualitatively agreeable results to conventional gravimetric analysis and prior demonstrations. Using the proposed humidity-controlled terahertz time-domain spectroscopy, here we quantify this detailed water information inside commercially available Nafion membranes at various humidities for direct comparison against literature values from dynamic vapor sorption, differential scanning calorimetry, and Fourier transform infrared spectroscopy on selected samples. Using this technique therefore opens up opportunities for rapid future parameter space investigation for membrane optimization.

Current Trends and Changes in Use of Membrane Molecular Dynamics Simulations within Academia and the Pharmaceutical Industry

There has been an almost exponential increase in the use of molecular dynamics simulations in basic research and industry over the last 5 years, with almost a doubling in the number of publications each year. Many of these are focused on neurological membranes, and biological membranes in general, applied to the medical industry. A smaller portion have utilized membrane simulations to answer more basic questions related to the function of specific proteins, chemicals or biological processes. This review covers some newer studies, alongside studies from the last two decades, to determine changes in the field. Some of these are basic, while others are more profound, such as multi-component embedded membrane machinery. It is clear that many facets of the discipline remain the same, while the focus on and uses of the technology are broadening in scope and utilization as a general research tool. Analysis of recent literature provides an overview of the current methodologies, covers some of the recent trends or advances and tries to make predictions of the overall path membrane molecular dynamics will follow in the coming years. In general, the overview presented is geared towards the general scientific community, who may wish to introduce the use of these methodologies in light of these changes, making molecular dynamic simulations more feasible for general scientific or medical research.

Experimental Investigation of Electro-Mechanical Behavior of Silver-Coated Teflon Fabric-Reinforced Nafion Ionic Polymer Metal Composite with Carbon Nanotubes and Graphene Nanoparticles

Ionic Polymer Metal Composites (IPMCs) are in high demand owing to the ongoing advancements in technology for various applications. New fabrication techniques and a quick retort towards the applied load are the significant reasons for considering IPMCs in smart devices. Here, a Teflon fabric-reinforced Nafion (TFRN) membrane is used to create an IPMC. The materials employed as electrodes are silver and nanofillers. The basement membrane, Nafion 438 (N-438), is sandwiched between the electrodes using a chemical decomposition technique. Subsequently, the electromechanical properties (actuation) of the membrane are tested. The micro and molecular structure of the IPMC membrane coated with Silver (Ag), Ag-Carbon nanotubes (CNTs), and Ag-Graphene nanoparticles samples are examined with the help of SEM and X-ray diffraction (XRD). The membrane scratch test is carried out to evaluate the abrasion and wear resistance of the membrane. The lowest coefficient of friction is shown by N438 + Ag + Graphene (0.05), which increased by 300% when compared to a pure N438 membrane. The hydration and tip deflection test were also performed to understand the water uptake percentage. At 90 °C, the highest water uptake was observed for N438 + Ag + Graphene (0.05), which decreased by 60, 42, 23, 14 and 26% when compared to N438, N438 + Ag, N438 + Ag + CNT (0.01), N438 + Ag + CNT (0.05) and N438 + Ag + Graphene (0.01), respectively. A proportional relationship between hydration level and tip deflection is observed and the highest bending performance is observed for the N438 + Ag + Graphene (0.05) membrane.

Effect of Nafion content and hydration level on the electrochemical area of a Pt nanocatalyst in the triple-phase boundary

Despite the great scientific effort, there are still some aspects of a polymeric membrane-based fuel cell (PEMFC) operation that are difficult to access experimentally. This is the case of the so-called triple-phase boundary (TPB), where the ionomer (commonly Nafion) interacts with the supported nanocatalyst (commonly Pt) and is key to the catalytic activity of the system. In this work, we use molecular dynamics simulations and electrochemical experiments on a Nafion/Pt/C system. We perform a systematic analysis, at an atomistic level, to evaluate the effect of several fundamental factors and their intercorrelation on the electrochemically active area (ECSA) of the catalysts. Our results reveal that at high Nafion contents, the catalyst utilization is affected due to the strong interaction between the sulfonic groups of the ionomer and the surface of the Pt nanoparticles (NPs). On the other hand, when the hydration level of the membrane decreases, the sulfonic groups have a greater occupation on the NP surface, covering the active area with hydrophobic Nafion chains and therefore increasing the inactive area. Voltammograms can corroborate our calculations. Overall, this investigation allows us to rationalize how the catalyst utilization is affected, which is an important step in establishing the relationship between the environment and the effectiveness and durability of the PEMFC system.