Solution blown biofunctionalized poly(vinylidene fluoride) nanofibers for application in proton exchange membrane fuel cells

Comparing solution blow spinning and electrospinning methods to produce collagen and gelatin ultrathin fibers: A review

Ultrathin fibers have been used to design functional nanostructured materials for technological and biomedical applications. Combining the use of renewable and compatible sources with the emerging alternative SBS (solution blow spinning) technique opens new opportunities for material applications. In this review, we introduce the benefits of SBS over the classical electrospinning technique by following studies that use collagen or gelatin. SBS offers distinct advantages over electrospinning in the preparation of ultrathin fibers based on natural proteins, including the absence of high-voltage sources and the possibility of using fewer toxic solvents. Notably, there is also the prospect of using SBS directly in injured tissues, opening new strategies for in situ structure assembly SBS is a suitable approach to produce fibers at the nanoscale that can be tailored to distinct diameters by blending or simply adjusting experimental conditions. The focus on producing collagen or gelatin fibers contributes to designing highly biocompatible mats with potential for promoting cellular growth and implantation, even though their applications can be found also in food packaging, energy, and the environment. Therefore, a comprehensive analysis of the topic is essential to evaluate the current strategies regarding these materials and allow for their expanded production and advanced applications.

A High-Proton Conductivity All-Biomass Proton Exchange Membrane Enabled by Adenine and Thymine Modified Cellulose Nanofibers

Nanocellulose fiber materials were considered promising biomaterials due to their excellent biodegradability, biocompatibility, high hydrophilicity, and cost-effectiveness. However, their low proton conductivity significantly limited their application as proton exchange membranes. The methods previously reported to increase their proton conductivity often introduced non-biodegradable groups and compounds, which resulted in the loss of the basic advantages of this natural polymer in terms of biodegradability. In this work, a green and sustainable strategy was developed to prepare cellulose-based proton exchange membranes that could simultaneously meet sustainability and high-performance criteria. Adenine and thymine were introduced onto the surface of tempo-oxidized nanocellulose fibers (TOCNF) to provide many transition sites for proton conduction. Once modified, the proton conductivity of the TOCNF membrane increased by 31.2 times compared to the original membrane, with a specific surface area that had risen from 6.1 m²/g to 86.5 m²/g. The wet strength also increased. This study paved a new path for the preparation of environmentally friendly membrane materials that could replace the commonly used non-degradable ones, highlighting the potential of nanocellulose fiber membrane materials in sustainable applications such as fuel cells, supercapacitors, and solid-state batteries.

Modified Cellulose Proton-Exchange Membranes for Direct Methanol Fuel Cells

A direct methanol fuel cell (DMFC) is an excellent energy device in which direct conversion of methanol to energy occurs, resulting in a high energy conversion rate. For DMFCs, fluoropolymer copolymers are considered excellent proton-exchange membranes (PEMs). However, the high cost and high methanol permeability of commercial membranes are major obstacles to overcome in achieving higher performance in DMFCs. Novel developments have focused on various reliable materials to decrease costs and enhance DMFC performance. From this perspective, cellulose-based materials have been effectively considered as polymers and additives with multiple concepts to develop PEMs for DMFCs. In this review, we have extensively discussed the advances and utilization of cost-effective cellulose materials (microcrystalline cellulose, nanocrystalline cellulose, cellulose whiskers, cellulose nanofibers, and cellulose acetate) as PEMs for DMFCs. By adding cellulose or cellulose derivatives alone or into the PEM matrix, the performance of DMFCs is attained progressively. To understand the impact of different structures and compositions of cellulose-containing PEMs, they have been classified as functionalized cellulose, grafted cellulose, acid-doped cellulose, cellulose blended with different polymers, and composites with inorganic additives.

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.

Performance enhancement of direct methanol fuel cells using a methanol barrier boron nitride–Nafion hybrid membrane

Sulfonated hexagonal boron nitride is explored as a potential filler to prepare Nafion hybrid membranes for direct methanol fuel cell (DMFC) applications.

Constructing Amino-Functionalized Flower-like Metal-Organic Framework Nanofibers in Sulfonated Poly(ether sulfone) Proton Exchange Membrane for Simultaneously Enhancing Interface Compatibility and Proton Conduction

A novel flower-like MIL-53(Al)-NH₂ nanofiber (MNF) was successfully constructed, in which the electro-blown spinning Al₂O₃ nanofibers were introduced as Al precursors to coordinate with ligand in hydrothermal reaction for the formation of MOFs nanofibers. By incorporating the functional and consecutive MNFs fillers in sulfonated poly(ether sulfone) (SPES) matrix, high-performance MNFs@SPES hybrid membranes were obtained. Specifically, the peak stress strength could be strengthened to 33.42 MPa and the proton conductivity was remarkably improved to 0.201 S cm^-1 as MNFs content increased to 5 wt %, achieving a simultaneous improvement on proton conduction and membrane stability. The highly promoted performance could be ascribed to the synergy advantages of unique structure and amino modification of MNFs: (1) The flower-like nanofiber structure of MNFs with high surface area could be beneficial to construct long-range and compatible interfaces between MNFs and SPES matrix, leading to sufficient continuous proton pathways as well as strengthened stability for the hybrid membrane. (2) The hydrophilic MNFs rendered the hybrid membrane with sufficient water retention for proton transfer via Vehicle mechanism. (3) Functional -NH₂ groups of MNFs and -SO₃H groups of SPES were consecutively and tightly bonded via acid-base electrostatic interactions, which further accelerated the proton conduction via Grotthuss hopping mechanism and effectively suppressed the methanol penetration in the meanwhile for the MNFs@SPES hybrid membranes.

Proton-Conducting Poly-γ-glutamic Acid Nanofiber Embedded Sulfonated Poly(ether sulfone) for Proton Exchange Membranes

Development and fabrication of novel proton exchange membranes (PEMs) with excellent performance have a great significance to the commercial application of PEM fuel cell. Inspired from the proton-conducting mechanism, γ-poly(glutamic acid) (γ-PGA) nanofibers (NFs) are first fabricated by solution blowing with the help of polylactic acid (PLA) and designed to form amino acid arrays as efficient proton channels for PEMs. The NFs with 50% γ-PGA exhibit a high proton conductivity of 0.572 S cm^-1 at 80 °C/50% relative humidity (RH), and 1.28 S cm^-1 at 40 °C/90% RH. Density functional theory is carried out to explain the mechanisms of proton hopping in γ-PGA, and the activation energy barriers from NH to COO^- for trans and cis conformations under anhydrous conditions are only 0.64 and 0.62 eV, respectively. Then the γ-PGA/PLA NFs are incorporated into sulfonated poly(ether sulfone) to prepare PEMs, which show remarkable performance compared with the Nafion membrane. The composite membrane with 30 wt % NFs exhibits the highest proton conductivity (0.261 S cm^-1 at 80 °C/100% RH). The direct methanol fuel cells with this membrane show a maximum power density (202.3 mW cm^-2) among all of the PEMs, showing great application potential in the field of PEMs.

Self-Assembly DBS Nanofibrils on Solution-Blown Nanofibers as Hierarchical Ion-Conducting Pathway for Direct Methanol Fuel Cells

In this work, we reported a novel proton exchange membrane (PEM) with an ion-conducting pathway. The hierarchical nanofiber structure was prepared via in situ self-assembling 1,3:2,4-dibenzylidene-d-sorbitol (DBS) supramolecular fibrils on solution-blown, sulfonated poly (ether sulfone) (SPES) nanofiber, after which the composite PEM was prepared by incorporating hierarchical nanofiber into the chitosan polymer matrix. Then, the effects of incorporating the hierarchical nanofiber structure on the thermal stability, water uptake, dimensional stability, proton conductivity, and methanol permeability of the composite membranes were investigated. The results show that incorporation of hierarchical nanofiber improves the water uptake, proton conductivity, and methanol permeability of the membranes. Furthermore, the composite membrane with 50% hierarchical nanofibers exhibited the highest proton conductivity of 0.115 S cm-1 (80 °C), which was 69.12% higher than the values of pure chitosan membrane. The self-assembly allows us to generate hierarchical nanofiber among the interfiber voids, and this structure can provide potential benefits for the preparation of high-performance PEMs.