Composite membranes of Nafion and poly(styrene sulfonic acid)-grafted poly(vinylidene fluoride) electrospun nanofiber mats for fuel cells

Precise Control of the Preparation of Proton Exchange Membranes via Direct Electrostatic Deposition

In this work, we reported a novel preparation method for a proton exchange membrane (PEM) named, the direct electrostatic deposition method. In theory, any required thickness and size of PEM can be precisely controlled via this method. By direct electrostatic spraying of Nafion solution containing amino modified SiO2 nanoparticles onto a metal collector, a hybrid membrane of 30 μm thickness was fabricated. The DMFC assembled with a prepared ultrathin membrane showed a maximum power density of 124.01 mW/cm2 at 40 °C and 100% RH, which was 95.29% higher than that of Nafion. This membrane formation method provides potential benefits for the preparation of ultrathin PEMs.

De Novo Ion-Exchange Membranes Based on Nanofibers

The unique functions of nanofibers (NFs) are based on their nanoscale cross-section, high specific surface area, and high molecular orientation, and/or their confined polymer chains inside the fibers. The introduction of ion-exchange (IEX) groups on the surface and/or inside the NFs provides de novo ion-exchangers. In particular, the combination of large surface areas and ionizable groups in the IEX-NFs improves their performance through indices such as extremely rapid ion-exchange kinetics and high ion-exchange capacities. In reality, the membranes based on ion-exchange NFs exhibit superior properties such as high catalytic efficiency, high ion-exchange and adsorption capacities, and high ionic conductivities. The present review highlights the fundamental aspects of IEX-NFs (i.e., their unique size-dependent properties), scalable production methods, and the recent advancements in their applications in catalysis, separation/adsorption processes, and fuel cells, as well as the future perspectives and endeavors of NF-based IEMs.

A Robust Composite Proton Exchange Membrane of Sulfonated Poly (Fluorenyl Ether Ketone) with an Electrospun Polyimide Mat for Direct Methanol Fuel Cells Application

As a key component of direct methanol fuel cells, proton exchange membranes with suitable thickness and robust mechanical properties have attracted increasing attention. On the one hand, a thinner membrane gives a lower internal resistance, which contributes highly to the overall electrochemical performance of the cell, on the other hand, strong mechanical strength is required for the application of proton exchange membranes. In this work, a sulfonated poly (fluorenyl ether ketone) (SPFEK)-impregnated polyimide nanofiber mat composite membrane (PI@SPFEK) was fabricated. The new composite membrane with a thickness of about 55 μm exhibited a tensile strength of 35.1 MPa in a hydrated state, which is about 65.8% higher than that of the pristine SPFEK membrane. The antioxidant stability test in Fenton’s reagent shows that the reinforced membrane affords better oxidation stability than does the pristine SPFEK membrane. Furthermore, the morphology, proton conductivity, methanol permeability, and fuel cell performance were carefully evaluated and discussed.

Bi-Functional Composting the Sulfonic Acid Based Proton Exchange Membrane for High Temperature Fuel Cell Application

Although sulfonic acid (SA)-based proton-exchange membranes (PEMs) dominate fuel cell applications at low temperature, while sulfonation on polymers would strongly decay the mechanical stability limit the applicable at elevated temperatures due to the strong dependence of proton conduction of SA on water. For the purpose of bifunctionally improving mechanical property and high-temperature performance, Nafion membrane, which is a commercial SA-based PEM, is composited with fabricated silica nanofibers with a three-dimensional network structure via electrospinning by considering the excellent water retention capacity of silica. The proton conductivity of the silica nanofiber–Nafion composite membrane at 110 °C is therefore almost doubled compared with that of a pristine Nafion membrane, while the mechanical stability of the composite Nafion membrane is enhanced by 44%. As a result, the fuel cell performance of the silica nanofiber-Nafion composite membrane measured at high temperature and low humidity is improved by 38%.

Progress of electrospray and electrospinning in energy applications

In the promotion of energy strategies to address the global energy crisis, nanotechnology has been successfully used to generate novel energy materials with excellent characteristics, such as high specific surface area, good flexibility and large porosity. Among the various methods for fabricating nanoscale materials, electrospray and electrospinning technologies have unlocked low-cost, facile and industrial routes to nanotechnology over the past ten years. This review highlights research into the key parts and primary theory of these techniques and their application in preparing energy-related materials and devices: especially fuel cells, solar cells, lithium ion batteries, supercapacitors as well as hydrogen storage systems. The challenges and future prospects of the manufacturing technologies are also covered in this paper.

High-performance membranes with full pH-stability

Following current strong demands from, among others, paper, food and mining industries, a novel type of nanofiltration membrane was developed, which displays excellent performance in terms of selectivity/flux with a unique combination of chemical stability over the full (0-14) pH-range and thermal stability up to 120 °C. The membrane consists of polyvinylidene fluoride grafted with polystyrene sulfonic acid. The optimum membrane showed water permeances of 2.4 L h-1 m-2 bar-1 while retaining NaCl, MgSO4 and Rhodamine B (479 Da) for respectively ≈60%, ≈80% and >96%.

Understanding methods of preparation and characterization of pore-filling polymer composites for proton exchange membranes: a beginner’s guide

Composite membranes based on porous support membranes filled with a proton-conducting polymer appear to be a promising approach to develop novel proton exchange membranes (PEMs). It allows optimization of the properties of the filler and the matrix separately, e.g. for maximal conductivity of the former and maximal physical strength of the latter. In addition, the confinement itself can alter the properties of the filling ionomer, e.g. toward higher conductivity and selectivity due to alignment and restricted swelling. This article reviews the literature on PEMs prepared by filling of submicron and nanometric size pores with Nafion and other proton-conductive polymers. PEMs based on alternating perfluorinated and non-perfluorinated polymer systems and incorporation of fillers are briefly discussed too, as they share some structure/transport relationships with the pore-filling PEMs. We also review here the background knowledge on structural and transport properties of Nafion and proton-conducting polymers in general, as well as experimental methods concerned with preparation and characterization of pore-filling membranes. Such information will be useful for preparing next-generation composite membranes, which will allow maximal utilization of beneficial characteristics of polymeric proton conductors and understanding the complicated structure/transport relationships in the pore-filling composite PEMs.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Sulfonic acid-grafted polyvinylidene fluoride electrospun mats as electro-Fenton reactor membrane components

Illustration of reaction mechanism of the EF process.

Nafion-Initiated ATRP of 1-Vinylimidazole for Preparation of Proton Exchange Membranes

Nafion is one of the most widely investigated materials applied in proton exchange membranes. Interestingly, it was found that Nafion could serve as a macroinitiator to induce atom transfer radical polymerization (ATRP) on its C-F sites. In this study, poly(1-vinylimidazole) was selectively bonded on the side chains of Nafion via the Nafion-initiated ATRP process, which was confirmed by the measurements of (1)H/(19)F nuclear magnetic resonance spectra, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, differential scanning calorimeter and matrix-assisted laser desorption ionization-time-of-flight/time-of-flight mass spectrometry. The as-prepared Nafion-co-poly(1-vinylimidazole) (Nafion-PVIm) membranes, with tunable loading amount of imidazole rings, presented greatly enhanced proton conductivity and methanol resistivity due to their well-controlled chemical structures. Especially, chemically bonding PVIm with Nafion chains endowed the Nafion-PVIm membranes with high stability in proton conductivity. For the first time, we revealed the great potentials of the Nafion-initiated ATRP process in developing high-performance proton exchange membranes.

Electrospun nanofiber enhanced imidazolium-functionalized polysulfone composite anion exchange membranes

A novel method of improving interfacial compatibility in electrospun anion exchange membranes is developed by using imidazolium-functionalized polysulfone as both fiber mats and interfiber voids filler.

Redox reaction mediated direct synthesis of hierarchical flower-like CuO spheres anchored on electrospun poly(vinylidene difluoride) fiber surfaces at low temperatures

Flower-like CuO spheres anchored on electrospun PVDF fiber surfaces as catalytic membranes for the photodegradation of rhodamine B aqueous solutions.