Novel cross-linked poly(vinyl alcohol)-based electrolyte membranes for fuel cell applications

Advances in Polyvinyl Alcohol-Based Membranes for Fuel Cells: A Comprehensive Review on Types, Synthesis, Modifications, and Performance Optimization

Fuel cell technology is at the forefront of sustainable energy solutions, and polyvinyl alcohol (PVA) membranes play an important role in improving performance. This article thoroughly investigates the various varieties of PVA membranes, their production processes, and the numerous modification tactics used to solve inherent problems. Various methods were investigated, including chemical changes, composite blending, and the introduction of nanocomposites. The factors impacting PVA membranes, such as proton conductivity, thermal stability, and selectivity, were investigated to provide comprehensive knowledge. By combining various research threads, this review aims to completely investigate the current state of PVA membranes in fuel cell applications, providing significant insights for both academic researchers and industry practitioners interested in efficient and sustainable energy conversion technologies. The transition from traditional materials such as Nafion to PVA membranes has been prompted by limitations associated with the former, such as complex synthesis procedures, reduced ionic conductivity at elevated temperatures, and prohibitively high costs, which have hampered their widespread adoption. As a result, modern research efforts are increasingly focused on the creation of alternative membranes that can compete with conventional technical efficacy and economic viability in the context of fuel cell technologies.

Polyvinyl Alcohol/Nafion®-Zirconia Phosphate Nanocomposite Membranes for Polymer Electrolyte Membrane Fuel Cell Applications: Synthesis and Characterisation

PVA (polyvinyl alcohol)-ZrP (PVA/ZrP) and Nafion®/PVA-ZrP nanocomposite membranes were synthesised using the recasting method with glutaraldehyde (GA) as a crosslinking agent. The resulting nanocomposite membranes were characterised using a variety of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results of SEM revealed well-distributed zirconia phosphate (ZrP) within the membrane matrix, and the SEM images showed a uniform and dense membrane structure. Because ZrP nanoparticles are hydrophilic, the Nafion®/PVA-ZrP nanocomposite membrane had a higher water uptake of 53% at 80 °C and higher 0.19 S/cm proton conductivity at room temperature than the commercial Nafion® 117 membrane, which had only 34% and 0.113 S/cm, respectively. In comparison to commercial Nafion® 117 membranes, PVA-ZrP and Nafion®/PVA-ZrP nanocomposite membranes had a higher thermal stability and mechanical strength and lower methanol crossover due to the hydrophilic effect of PVA crosslinked with GA, which can make strong hydrogen bonds and cause an intense intramolecular interaction.

Vanadium Oxide Nanosheet-Infused Functionalized Polysulfone Bipolar Membrane for an Efficient Water Dissociation Reaction

A high-performing bipolar membrane (BPM) was fabricated using functionalized polysulfones as the ion-exchange layers (IELs) and two-dimensional (2D) V₂O₅-nanosheets blended with polyvinyl alcohol (PVA) as the water dissociation catalyst (WDC) at the interfacial layer. The composite BPM showed a low resistance of 0.79 Ω cm², confirming the good contact between the IEL and WDC, much needed for the ionic conductivity. It also demonstrated high water dissociation performance with a water dissociation voltage of 1.11 V corresponding to a current density of 1.02 mA/cm² in the presence of a 1 M NaCl electrolytic solution. The functionalization of the polysulfone with -SO₃^- and R₄N⁺ groups successfully resulted in the increase of hydrophilicity of the polymer, thereby increasing the water uptake capacity of the membranes. The blending of 2D V₂O₅ nanosheets with PVA proved to be an effective WDC, as confirmed by the increased conductivity and efficiency of the water dissociation (WD) reaction. The 2D V₂O₅-ns have great potential toward water adsorption onto its surface, thereby interacting with the water molecules, weakening the bonding force of water, and dissociating it into H⁺ and OH^-. The transportation of coions across the membranes and generation of protons and hydroxyl ions at the interfacial layer are correlated with the change in the pH of the catholyte and anolyte as a function of current density during the WD reaction. The high performance of the composite BPM (BPM_VO-ns) was demonstrated at a higher current density of 100 mA/cm² with a WD resistance of 0.027 Ω cm². The durability was tested by subjecting it to 45 h of run at lower (1.02 mA/cm²) and higher (100 mA/cm²) current densities which display a negligible change in the interlayer voltage. Thus, the fabricated composite BPMs pave the way to be utilized for efficient and durable WD reactions under neutral electrolytic conditions.

Sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene/sulfonated poly(ether sulfone) and hexagonal boron nitride electrolyte membrane for fuel cell applications

Novel proton exchange membranes consisting of sulfonated polystyrene ethylene butylene polystyrene (sPSEBPS), sulfonated poly ether sulfone (SPES) and hexagonal boron nitride (hBN) were fabricated using a facile solution casting technique. The PSEBPS polymer was functionalized using chlorosulfonic acid as the sulfonating agent. Polymerization was typically conducted by taking three different monomers, namely 3,6-dihydroxy naphthalene-2,7-disulfonic acid disodium salt, 4,4'-dichlorodiphenyl sulfone, and bisphenol-A, to yield sulfonated poly ether sulfone (SPES). The resultant SPES polymer was blended with sPSEBPS followed by incorporation with an appropriate quantity of hBN. The physicochemical and structural properties of the membranes were studied in order to evaluate their compatibility with fuel cell applications. X-Ray photoelectron spectroscopy data validated the successful incorporation of the filler into the polymer matrix. Water absorption of the membranes was found in the range between 19.5 and 29.8%. The membrane loaded with 4.0 wt% of hBN showed the maximum ion-exchange capacity of 1.21 meq g^-1, whereas the control sPSEBPS/SPES membrane was restricted to 0.48 meq g^-1. The composite membrane loaded with hBN displayed higher thermal stability than that of the control sample. The sPSEBPS/SPES/hBN-4 composite membrane exhibited an ionic conductivity of 0.0329 S cm^-1 at 30 °C. Overall, the experimental data of the prepared composite membranes revealed that the materials are potential candidates for fuel cells.

Enhancement of Electrochemical Stability Window and Electrical Properties of CNT-Based PVA-PEG Polymer Blend Composites

New polymer blend composite electrolytes (PBCEs) were prepared by the solution casting technique using poly(vinyl alcohol) (PVA)-polyethylene glycol (PEG), sodium nitrate (NaNO₃) as a doping salt and multiwalled carbon nanotubes (MWCNTs) as fillers. The X-ray diffraction pattern confirms the structural properties of the polymer blend composite films. FTIR investigations were carried out to understand the chemical properties and their band assignments. The ionic conductivity of the 10 wt % MWCNTs incorporated PVA-PEG polymer blend was measured as 4.32 × 10^-6 S cm^-1 at 20 °C and increased to 2.253 × 10^-4 S/cm at 100 °C. The dependence of its conductivity on temperature suggests Arrhenius behavior. The equivalent circuit models that represent the R _s(Q₁(R₁(Q₂(R₂(CR₃))))) were used to interpret EIS data. The dielectric behavior of the samples was investigated by utilizing their AC conductance spectra, dielectric permittivity, dielectric constant (εⁱ and ε^r), electric modulus (Mⁱ and M^r), and loss tangent tan δ. The dielectric permittivity of the samples increases due to electrode polarization effects in low frequency region. The loss tangent's maxima shift with increasing temperature; hence, the peak height rises in the high frequency region. MWCNTs-based polymer blend composite electrolytes show an enhanced electrochemical stability window (4.0 V), better transference number (0.968), and improved ionic conductivity for use in energy storage device applications.

Sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene based membranes containing CuO@g-C3N4 embedded with 2,4,6-triphenylpyrylium tetrafluoroborate for fuel cell applications

New series of polymer composite membranes were prepared from sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (S-PSEBS) and copper oxide loaded in graphitic carbon nitride (CuO@N-C) embedded with an ionic liquid, 2,4,6-triphenylpyrylium tetrafluoroborate. The structural and physicochemical properties of the composite membranes were studied in detail. Electrolyte membrane loaded with 8.0 wt% of CuO@N-C exhibited the maximum ion-exchange capacity of 3.1 meq. g^-1, whereas that of the pristine membrane was restricted to 1.8 meq. g^-1. From the TGA profile of the composite membrane, it was found to exhibit adequate thermal stability to be employed as electrolyte in fuel cells. Proton conductivity of the composite membranes was found to be in the range between 0.0179 S cm^-1 and 0.0229 S cm^-1. Indeed, the substantial results achieved with the S-PSEBS/CuO@N-C composite membranes were indicative of the notable features of the membranes for use in fuel cells.

Engineering polymer film porosity for solvent triggered actuation

We report a novel approach for the fabrication of porous polymer films and their self-folding behavior in response to water. In this approach, the poly(vinyl alcohol) (PVA) films of tunable porosity are prepared by direct casting of aqueous PVA solution into a nonsolvent, isopropyl alcohol (IPA). The method developed is simple, efficient and low-cost. The results presented provide a modular route to tune the distribution of pores across the film thickness by varying the volume of nonsolvent and the polymer solution. We show that asymmetric porous polymer films (which consist of pores across a certain thickness of the film in the plane perpendicular to its surface) as well as symmetric porous polymer films (which have pores across the entire film) can be fabricated by this versatile method. The percentage of pores in the polymer film calculated as , where tp is the thickness of the film across which the pores exist and ttotal is the total thickness of the film, can be tuned over a wide range. The emanated porous PVA films are found to show self-folding behaviour in response to water. Our results indicate that the pore architecture in the films significantly enhances the actuation speed. The self-folding originating due to the diffusion of water molecules across the film is observed to occur in a controlled and predictable manner for the films with 60% pores and above. A detailed study of the folding characteristics and actuation speed in relation to folding time is substantiated.