Highly sulfonated polymer-grafted graphene oxide composite membranes for proton exchange membrane fuel cells

Study on the Application Performance of Polymer Electrolyte Membrane Functionalized with Triethyl Phosphite-Modified Graphene Oxide in Fuel Cells

In this paper, we successfully synthesize phosphoric acid functionalized graphene oxide (PGO) based on acid modification of graphene oxide. The composite membrane is further prepared by adding PGO into sulfonated poly(aryl ether ketone sulfone) containing carboxyl groups matrix (C-SPAEKS). The PGO as well as the composite membranes were characterized by a series of tests. The prepared composite proton exchange membranes (PEMs) have good mechanical and electrochemical properties. Compared to the C-SPAEKS membrane, the best composite membrane has a tensile strength of 40.7 MPa while exhibiting superior proton conductivity (110.17 mS cm-1 at 80 °C). In addition, the open-circuit voltage and power density of C-SPAEKS@1% PGO are 0.918 V and 792.17 mW cm-2, respectively. Compared with C-SPAEKS (0.867 V and 166 mW cm-2), it can be seen that our work has a certain effect on the improvement of the single cell performance. The above results demonstrate that the functionalized graphene oxide has greatly improved the electrochemical performance and even the overall performance of PEMs.

Recent Developments on Bioinspired Cellulose Containing Polymer Nanocomposite Cation and Anion Exchange Membranes for Fuel Cells (PEMFC and AFC)

Hydrogen fuel cell (FC) technologies are being worked on as a possible replacement for fossil fuels because they produce a lot of energy and do not pollute the air. In FC, ion-exchange membranes (IEMs) are the vital components for ion transport between two porous electrodes. However, the high production cost of commercialized membranes limits their benefits. Various research has focused on cellulose-based membranes such as IEM with high proton conductivity, and mechanical, chemical, and thermal stabilities to replace the high cost of synthetic polymer materials. In this review, we focus on and explain the recent progress (from 2018 to 2022) of cellulose-containing hybrid membranes as cation exchange membranes (CEM) and anion exchange membranes (AEM) for proton exchange membrane fuel cells (PEMFC) and alkaline fuel cells (AFC). In this account, we focused primarily on the effect of cellulose materials in various membranes on the functional properties of various polymer membranes. The development of hybrid membranes with cellulose for PEMFC and AFC has been classified based on the combination of other polymers and materials. For PEMFC, the sections are associated with cellulose with Nafion, polyaryletherketone, various polymeric materials, ionic liquid, inorganic fillers, and natural materials. Moreover, the cellulose-containing AEM for AFC has been summarized in detail. Furthermore, this review explains the significance of cellulose and cellulose derivative-modified membranes during fuel cell performance. Notably, this review shows the vital information needed to improve the ion exchange membrane in PEMFC and AFC technologies.

Composite Membranes Based on Functionalized Mesostructured Cellular Foam Particles and Sulfonated Poly(Ether Ether Sulfone) with Potential Application in Fuel Cells

Composite polymeric membranes were designed based on sulfonated poly(ether ether sulfone) (sPEES) and mesostructured cellular foam (MCF) silica nanoparticles functionalized with organic compounds. Parameters such as molecular weight (MW) of the polymer, nature of the functional group of the MCF silica, and percentage of silica charge were evaluated on the final properties of the membranes. Composite membrane characterization was carried out on their water retention capacity (high MW polymer between 20-46% and for the low MW between 20-60%), ion exchange capacity (IEC) (high MW polymer between 0.02 mmol/g-0.07 mmol/g and low MW between 0.03-0.09 mmol/g) and proton conductivity (high MW polymer molecular between 15-70 mS/cm and low MW between 0.1-150 mS/cm). Finally, the membrane prepared with the low molecular weight polymer and 3% wt. of functionalized silica with sulfonic groups exhibited results similar to Nafion^® 117.

Utilization of mesoporous phosphotungstic acid in nanocellulose membranes for direct methanol fuel cells

Nanocellulose (NC) composite membranes containing novel ternary materials including NC, imidazole (Im), and mesoporous phosphotungstic acid (m-PTA) were successfully fabricated by a phase inversion method. The single-particle size of NC was 88.79 nm with a spherical form. A m-PTA filler with a mesopore size of 4.89 nm was also successfully synthesized by a self-assembly method. Moreover, the fabricated membrane NC/Im/m-PTA-5 exhibited the best performances towards its proton conductivity and methanol permeability at 31.88 mS cm⁻¹ and 1.74 × 10⁻⁶ cm² s⁻¹, respectively. The membrane selectivity was 1.83 × 10⁴ S cm⁻³.

A NC/Im/m-PTA membrane was fabricated for direct methanol fuel cell applications.

Cationic polymer-grafted graphene oxide/CNT cathode-coating material for lithium-sulfur batteries

A cathode-coating material composed of cationic polymer-grafted graphene oxide (CPGO) and carbon nanotube (CNT) was prepared, where the CPGO was synthesized by grafting quaternized 2-(dimethylamino)ethyl methacrylate (QDMAEMA) onto graphene oxide (GO) via atom transfer radical polymerization (ATRP). GO has good compatibility with carbon black, the main component of the cathode in lithium–sulfur (Li–S) batteries. Here, the cationic polymer having the QDMAEMA unit was intentionally grafted onto GO to decrease the shuttle effect by increasing the chemical adsorption of polysulfide (PS). In addition, when CNT was mixed with CPGO, the compatibility with carbon black was found to be further increased. The lithium–sulfur (Li–S) battery with a sulfur-deposited Super P® carbon black (S/C) cathode coated with a mixture of CPGO and CNT was found to have much improved cell performance compared to those coated without any coating material, with only CPGO, with the mixture of GO and CNT, and with the mixture of PQDMAEMA and CNT. For example, the Li–S battery with the cathode coated using the mixture of CPGO and CNT retained a discharge capacity of 744 mA h g⁻¹ after 50 cycles at 0.2C-rate, while those of the Li–S batteries with bare S/C and CPGO-S/C cathodes were found to be much smaller, i.e., 488 mA h g⁻¹ and 641 mA h g⁻¹, respectively, under the same conditions. Therefore, the mixture of CPGO with CNT as the cathode-coating material showed a synergetic effect to enhance the cell performance of the Li–S battery system.

A cathode-coating material composed of cationic polymer-grafted graphene oxide (CPGO) and carbon nanotube (CNT) was prepared and used as a cathode-coating material for lithium sulfur batteries.

The Synthesis of Poly(Vinyl Alcohol) Grafted with Fluorinated Protic Ionic Liquids Containing Sulfo Functional Groups

There has been an ongoing need to develop polymer materials with increased performance as proton exchange membranes (PEMs) for middle- and high-temperature fuel cells. Poly(vinyl alcohol) (PVA) is a highly hydrophilic and chemically stable polymer bearing hydroxyl groups, which can be further altered. Protic ionic liquids (proticILs) have been found to be an effective modifying polymer agent used as a proton carrier providing PEMs' desirable proton conductivity at high temperatures and under anhydrous conditions. In this study, the novel synthesis route of PVA grafted with fluorinated protic ionic liquids bearing sulfo groups (-SO₃H) was elaborated. The polymer functionalization with fluorinated proticILs was achieved by the following approaches: (i) the PVA acylation and subsequent reaction with fluorinated sultones and (ii) free-radical polymerization reaction of vinyl acetate derivatives modified with 1-methylimidazole and sultones. These modifications resulted in the PVA being chemically modified with ionic liquids of protic character. The successfully grafted PVA has been characterized using ¹H, ¹⁹F, and ¹³C-NMR and FTIR-ATR. The presented synthesis route is a novel approach to PVA functionalization with imidazole-based fluorinated ionic liquids with sulfo groups.

Preparation of bottom-up graphene oxide using citric acid and tannic acid, and its application as a filler for polypropylene nanocomposites

The production of graphene oxide (GO) in large amounts for commercialization in the chemical industry has been limited because harsh and tedious process conditions are required. In this study, a novel carbon nanomaterial called 'bottom-up graphene oxide (BGO)' could be easily prepared for the first time by heat treatment of the mixture of citric acid (CA) and tannic acid (TA) with different weight ratios for the first time. BGO3 prepared using a 50/50 weight ratio of CA/TA was found to have an average lateral size of 250.0 nm and an average thickness of 7.2 nm, and it was further functionalized with cardanol to prepare cardanol functionalized BGO3 (CBGO3) to be used as a filler for the polypropylene (PP) nanocomposite, where cardanol was used to increase the compatibility between BGO3 and PP. The improved mechanical properties and thermal stability of PP nanocomposites containing CBGO3 could be ascribed to the intrinsic mechanical properties of the carbon nanomaterial and the increased compatibility by the attached cardanol on BGO3.

SO42-/SnO2 Solid Superacid Granular Stacked One-Dimensional Hollow Nanofiber for a Highly Conductive Proton-Exchange Membrane

A novel sulfated tin oxide solid superacid granular stacked one-dimensional (1D) hollow nanofiber (SO₄^2-/FSnO₂) is proposed as a nanofiller in sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) to manipulate a highly conductive proton nanochannel. It has unique microstructures with an open-end hollow nanofibric morphology and grain-stacked single-layer mesoporous fiber wall, which greatly enlarge the specific surface area and aspect ratio. The diverse acid sites, that is, SO₄^2-, Sn-OH Brönsted, and Sn⁴⁺ Lewis superacids, provide a high concentration of strong acidic proton carriers on the nanofiber surface and dynamically abundant hydrogen bonds for rapid proton transfer and interfacial interactions with -SO₃H groups in the SPPESK along the 1D hollow nanofiber. As a result, long-range orientated ionic clusters are observed in the SO₄^2-/FSnO₂ incorporated membrane, leading to simultaneous enhancement of proton conductivity (226.7 mS/cm at 80 °C), mechanical stability (31.4 MPa for the hydrated membrane), fuel permeation resistance, and single-cell performance (936.5 and 147.3 mW/cm² for H₂/O₂ and direct methanol fuel cells, respectively). The superior performance, as compared with that of the zero-dimensional nanoparticle-incorporated membrane, Nafion 115, and previously reported SPPESK-based membranes, suggests a great potential of elaborating superstructural 1D hollow nanofillers for highly conductive proton-exchange membranes.

Composite Polymers Development and Application for Polymer Electrolyte Membrane Technologies-A Review

Nafion membranes are still the dominating material used in the polymer electrolyte membrane (PEM) technologies. They are widely used in several applications thanks to their excellent properties: high proton conductivity and high chemical stability in both oxidation and reduction environment. However, they have several technical challenges: reactants permeability, which results in reduced performance, dependence on water content to perform preventing the operation at higher temperatures or low humidity levels, and chemical degradation. This paper reviews novel composite membranes that have been developed for PEM applications, including direct methanol fuel cells (DMFCs), hydrogen PEM fuel cells (PEMFCs), and water electrolysers (PEMWEs), aiming at overcoming the drawbacks of the commercial Nafion membranes. It provides a broad overview of the Nafion-based membranes, with organic and inorganic fillers, and non-fluorinated membranes available in the literature for which various main properties (proton conductivity, crossover, maximum power density, and thermal stability) are reported. The studies on composite membranes demonstrate that they are suitable for PEM applications and can potentially compete with Nafion membranes in terms of performance and lifetime.

Heterogeneous ion exchange membranes based on thermoplastic polyurethane (TPU): effect of PSS/DVB resin on morphology and electrodialysis

In this research, novel heterogeneous cation exchange membranes based on thermoplastic polyurethane (TPU) have been prepared by the solution casting technique. The effects of incorporation level of sulfonated polystyrene divinyl-benzene (PSS/DVB) resin on water uptake, ion exchange capacity, membrane potential and salt extraction have been elucidated. Morphological and water uptake studies suggested a two-phase heterogeneous membrane morphology owing to the presence of hard and soft segments in the TPU backbone and swelling of PSS/DVB particles. This morphology was shifted to a semi-gelled morphology throughout the membrane bulk when resin loading exceeded 50 wt%. The physically cross-linked hard segments in the TPU backbone ensured a compact membrane morphology and prevented the formation of water channels. The membrane potential showed that increasing the resin content increased the membrane transport number (max. 0.95) up to 50 wt% resin loading and beyond this, the transport number started decreasing showing a pronounced effect of voids and water flow channels developing on excessive swelling. The permselectivity reached a maximum (up to 0.92) and salt extraction values also increased (by varying voltage) up to 50 wt% loading and started decreasing beyond this optimum content. This study shows successful development of low-cost heterogeneous cation exchange membranes based on TPU with acceptable electrochemical properties.

Polymer-Brush-Decorated Graphene Oxide: Precision Synthesis and Liquid-Crystal Formation

Given the specificity of the structure and function of graphene oxide (GO), hybridization with a variety of compounds will further extend its applications. To that end, we examined a new method for introducing a polymer brush onto the GO surface. In this method, GO was surface-modified with 2-((3-((2-bromo-2-methylpropanoyl)oxy)propyl)thio)ethylamine hydrochloride, which is a newly synthesized compound that contains an initiating group for atom transfer radical polymerization (ATRP) and an amino group for reacting with the epoxy groups on the GO surface. The ATRP-initiator-functionalized GO was then used as a substrate for the surface-initiated ATRP of methyl methacrylate (MMA), which produced graft polymers of poly(MMA) (PMMA) with targeted molecular weights and narrow molecular weight distributions; the average graft density was ∼0.06 chains/nm². Because of their high dispersibilities and structural anisotropies, the PMMA-brush-decorated GOs formed lyotropic liquid crystals in their suspensions. In addition, similar suspensions with relatively high hybrid concentrations exhibited structural color that depended on the concentration.

Component Adjustment of Poly(arylene ether nitrile) with Sulfonic and Carboxylic Groups for Dielectric Films

Poly(arylene ether nitrile)s with sulfonic and carboxylic groups (SCPEN) were synthesized to investigate their electrical properties. This new series of copolymers were prepared by copolymerization of phenolphthalein, potassium hydroquinonesulfonate, and 2,6-difluorobenzonitrile, in different mole ratios. Their thermal, mechanical and dielectric properties were investigated in detail. By adjusting the composition of sulfonic and carboxylic groups, it can be concluded that the dielectric constant increases with the increase of sulfonic groups, and mechanical and thermal properties improve with the increase of carboxylic groups. The as-prepared SCPEN films show potential applications in electronic storage materials, which provide insights into the correlation of SCPEN electrical properties with its chemical structure. The structure–property relationship is established to broaden the application of functionalized PEN. Furthermore, SCPEN with rich polar groups may also be used as the polymer matrix to increase the interaction with the filler surface, ensuring a better dispersion of filler in the matrix. This provides a reference for the development of high dielectric materials.