Proton-conducting Composite Membranes Research Articles

Robust and highly proton conductive COF composite membranes for fuel cell and electrochemical hydrogen compression

Robust and highly conductive proton exchange membrane (PEM) is the unremitting pursuit of numerous electrochemical energy technologies such as fuel cell and the emerging electrochemical hydrogen compression. Ionic covalent organic framework nanosheets (iCONs) with long-range ordered nanochannels and abundant ionic groups show substantial potential as next-generation PEM materials. However, it is challenging to assemble iCONs into membranes with both robustness and flexibility due to the electrostatic repulsion and rigid framework. Herein, we propose a hydrogen-bond binding strategy to fabricate sulfonic iCON (SCON) composite membranes by co-assembling tannic acid (TA) nanoaggregates and SCONs. The abundant and dynamically reversible hydrogen-bond interactions introduced by TA nanoaggregates establish effective linkage between SCONs and allow some restricted movements, endowing membranes with remarkably improved mechanical properties. The stacked SCONs construct long-range ordered nanochannels with well-arranged sulfonic groups in membranes, and the hydrogen-bond networks further facilitate the proton transport through Grotthuss mechanism. Consequently, TA/SCON composite membranes displays significantly enhanced tensile strength of 101.9 MPa, good flexibility and high proton conductivity of 490.1 mS cm−1 at 80 °C and 100 % RH simultaneously. This hydrogen-bond binding strategy offers a promising approach to fabricate robust and highly conductive PEMs for various proton-conducting applications.

Synthesis, Characterization and Proton Conducting Behavior of a Novel Composite Films Based on Phosphosilicate / Polypyrrole (PS/PPy)

Various phosphosilicate doped polypyrrole proton conductive thin films composite membranes were successfully prepared. Phosphosilicate obtained by sol-gel process by mixing tetraethoxy silane with phosphoric acid at a molar ratio 1:5. The proton conductivity increased with increasing both the content of phosphosilicate gel and relative humidity. Temperature dependence of conductivity showed a Vogel-Tamman-Fulcher type behavior, indicating that proton was transferred through a liquid like phase formed in micropores of phosphosilicate gel. The high conductivity of 0.065 S/cm with a membrane containing 60wt'% of the gel was obtained at 60°C at 90wt'% relative humidity. Key words: Membrane, conductivity, polypyrrole, composites, solid state.

SYNTHESIS AND CHARACTERIZATION OF PROTONCONDUCTING MEMBRANES BASED ON BACTERIAL CELLULOSE AND HUMAN HAIR KERATIN

Studies on composite proton-conducting membranes made of human hair keratin and bacterial cellulose have been done. Keratin from human hair is produced through hydrolysis using NaOH as a solvent. Composite membranes constructed of bacterial cellulose and human hair keratin had mass variations of 4.5/0.5, 4.7/0.3, and 4/1. At temperatures of 25 ºC, 40 ºC, 60 ºC, and 80 ºC, the proton-conducting composite membrane was evaluated for Fourier Transform InfraRed, X-Ray Diffraction, degree of swelling, and proton conductivity. The interaction of bacterial cellulose and human hair keratin appeared at the peak of 3000-3500 cm-1, as evidenced by functional group analysis of bacterial cellulose and human hair keratin composite membranes from Fourier Transform InfraRed. The produced composite membrane was semicrystalline in each mass variation, according to the results of the X-Ray Diffraction examination. The variant of bacterial cellulose and human hair keratin 4/1 showed the highest degree of swelling (34.09%). The composite membrane keratin made of bacterial cellulose and human hair had the maximum proton conductivity, with a variation of 4/1 and a value of 3.673 x 10-5 S/cm at a temperature of 25 ºC.

Proton Conductive Composite Membranes with Stable Anisotropic Though-Plane Conductivity: A New Preparation Approach

In common PEMFCs, a polymer electrolyte membrane selectively conducts protons but blocks passage of electrons and reactants. Nafion, current benchmark membrane material, offers a superior conductivity owing to unique morphology comprising randomly oriented elongated ionic nanochannels within a Teflon-like matrix. Nanochannel orientation is a promising approach to enhance Nafion conductivity, yet there has been no facile method to induce a strong and stable alignment within membranes in the most desired through-plane (TP) direction.Here we report a novel and facile preparation approach based on dual electrospun Nafion-PVDF nanofiber composite that yields a stable TP alignment. The preparation starts from electrospinning of a mixed fiber mat, which is subsequently converted to a solid membrane by plunging the mat into a thin slit. Due to extreme thinness, the electrospun nanofiber readily buckle into a folded structure, thereby a strong inherent microscopic channel orientation within nanofibers is readily converted to macroscopic TP channel alignment. Ultimately, the folded nanofibers fuse, consolidating the membrane.A pronounced TP alignment of ion channels in the membranes, sustaining fusion and annealing, is demonstrated using TEM and SAXS. The analysis also highlights the importance of PVDF fiber as a stabilizing and confining component. Electrospun PVDF fibers within consolidated Nafion-PVDF composite preserve channel orientation upon annealing both in TP and in-plane (IP) aligned membranes, while pure Nafion membranes, similarly prepared from electrospun Nafion fibers, rapidly lose structural anisotropicity. Finally, the impedance measurements demonstrate highly anisotropic conductivity of both TP- and IP-aligned membranes, consistent with their anisotropic structure. Thus, measured TP conductivity of TP-aligned 46% Nafion composite is nearly three times its IP conductivity and about 70% that of Nafion 212, thereby the conductivity normalized to Nafion content exceeds that of pure Nafion. The approach, still leaving much room for optimization, holds potential to advance PEMFC technology by overcoming current limitations and fully utilizing advantageous features of Nafion membranes. Figure 1

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Synthesis of (Si-PWA)-PVA/PTFE high-temperature proton-conducting composite membrane for DMFC

The inorganic silica immobilized PWA based (Si-PWA)-PVA/PTFE composite membrane was developed by an amalgamation of pore filling and layer by layer (LBL) casting. The composition of the top layer was optimized to be 0.3 M PWA: 0.2 M TEOS: 0.15PVA concerning to proton-conductivity and methanol permeability of the membrane. Surface morphological studies and elemental analysis were carried out by using SEM-EDX. The FT-IR and XRD analysis had confirmed the intercalation of sol with PTFE. Thermal deformation of the membrane was studied by TGA and it is stable up to 180 °C. Ion exchange capacity and water uptake were determined to be 2.38 meq per gram and 21.7%. The membrane has exhibited maximum proton conductivity of 41.2 mS cm−1 at 100 °C. The membrane has significantly lower methanol permeability of 3.2 × 10−7 cm2 S−1 compared to that of Nafion117 (7.9 × 10−7 cm2 S−1) at 28 °C and the same trend was observed at 40, 60, and 80 °C. The (Si-PWA)-PVA/PTFE composite membrane is showed enhanced proton conductivity and lower methanol permeability at elevated temperatures.

Fabrication and Characterization of Proton Conductive Membranes Based on Poly(methyl methacrylate-co-maleic anhydride)

In this study, proton conductive composite membranes were produced by using a poly(methylmethacrylate-co-maleic anhydride) (P(MMA-co-MAH)) copolymer and phosphotungstic Acid (PWA) as an additive of the proton conductive agent. P(MMA/MAH) 70/30, 50/50, and 30/70 were synthesized using a free radical polymerization reaction. PWA with a concentration of 2% was added to improve the performance of proton exchange membranes. Composite membranes of P(MMA30-co-MAH70)/PWA had the highest performance, and this improvement was attributed to the presence of MAH and PWA. By increasing the ratio of MMA:MAH from 30/70 to 70/30, thermal stability, ion exchange capacity and proton conductivity of membranes enhanced up to 310°C, 0.85 meq/g, and 5.77 mS/cm, respectively. Moreover, the addition of PWA into the membrane matrix improved the membrane characteristics so that thermal stability, ion exchange capacity, and proton conductivity increased to 317°C, 0.98 meq/g, and 14.42 mS/cm. The synthesized copolymer offered the required properties to be used for the fabrication of a proton conductive membrane.

A Novel SPEEK-PVA-TiO2 Proton Conducting Composite Membrane for PEMFC Operations at Elevated Temperature

A Novel SPEEK-PVA-TiO2 Proton Conducting Composite Membrane for PEMFC Operations at Elevated Temperature

A Proton Conducting Composite Membrane based on Polyvinyl Alcohol and Polyaniline-intercalated Graphene Oxide

A novel proton conducting membrane was synthesized based on a composite of polyvinyl alcohol (PVA) and sulfonated polyaniline-intercalated graphene oxide (SPANi-GO). The synthesized membranes were characterized by tensile strength measurement, thermo-gravimetric analysis, scanning electron microscopy, XRD and FTIR techniques. The effect of SPANi-GO on the proton conductivity of the PVA based membrane (PVA/SPANi-GO) was studied. The nanocomposite membrane exhibited an impressive ionic conductivity of 0.129 Scm−1 at 25°C. Further, the membranes showed excellent thermal and mechanical properties. The water content of the pristine as well as the nanocomposites membrane was found to be in the range of 42–52%. The results indicate that the simply prepared PVA/SPANi-GO is a promising proton conducting membrane for practical applications.

High performance proton-conducting composite based on vanadium-substituted Dawson-type heteropoly acid for proton exchange membranes

Proton exchange membranes (PEMs) are the key parts in proton exchange membrane fuel cells (PEMFCs). In this work, a proton-conducting composite membrane rGO-P2W16V2@SPEEK was synthesized from vanadium-substituted Dawson-type heteropoly acid (H8P2W16V2O62•20H2O, abbreviated as P2W16V2), sulfonated polyether ether ketone (SPEEK) and reduced graphene oxide (rGO). Characterizations proved the integrity of the Dawson-structure heteropoly acids (HPAs) in composites and the uniform inorganic-organic hybrid distribution. The membrane shows excellent proton conductivity of 7.90 × 10−2 S cm−1 at 50 °C and the proton conduction was proved to comply with the Grotthuss mechanism. Up to now, this is the first time that a Dawson-type HPA was reported for the application of PEMs and this work extended the application of polyoxometalate-based materials in the field of fuel cells.

Preparation and characterization of composite membranes with Brønsted acidic ionic liquid

Poly-(vinyl alcohol) (PVA) proton-conducting composite membranes were prepared using succinic acid (SA) as a cross-linking agent and Bronsted acidic ionic liquid (BAIL) as a proton source. The incorporated BAILs resulted in a relatively high proton conductivity compared with PVA/SA membrane without BAILs. The proton conductivities of PVA/SA/BAIL composite membranes increased versus the BAIL content. In addition, the optimal resultant proton conductivity of PVA/SA/BAIL composite membrane under dry condition could reach 0.4 mS/cm at 140 °C, which was higher than that of PVA/sulfosuccinic acid (SSA) composite membrane (0.032 mS/cm), PVA/SSA/5-aminotetrazole membrane (0.022 mS/cm at 130 °C), and PVA/chlorosulfonic acid/glutaraldehyde membrane (0.0585 mS/cm at 90 °C) measured at the same condition. It was notable that the PVA/SA/BAIL composite membranes could reach high thermal stability up to 150 °C, which was higher than that of traditional PVA membranes (below 80 °C).

Synthesis and Properties of Composite Membranes for Polymer Electrolyte Membrane Fuel Cells

The paper is devoted to the sol-gel synthesis of proton conductive organic-silicon composite membranes based on tetraethyl orthosilicate (TEOS) and copolymers of 2-methyl-5-vinylpyridine and vinyl chloride (MVP-VC), 2-methyl-5-vinylpyridine and vinyl acetate (MVP-VA), copolymers of ethylene glycol vinyl glycidyl ether and styrene (KS-1 and KS-2), and nitrogen-containing heteroaromatic derivatives of sulfonic acids: 2-phenyl-5-benzimidazolsulfonic acid (PBISA) and pyridine-3-sulfonic acid (PSA). Properties of synthesized membranes, such as proton conductivity, activation energy, ion exchange capacity, dimensional stability have been investigated.

Characterization of sulfonated poly(arylene ether sulfone) (SPAES)/silica-phosphate sol-gel composite membrane: Effects of the sol-gel composition

Proton-conducting composite membranes were prepared from sulfonated poly(arylene ether sulfone) (SPAES) and silica-phosphate sol-gel by using a solution casting method. The silica and phosphate precursors of tetraethylorthosilicate (TEOS) and triethyl phosphate (TEP), and the sol-gel network formation of silica-phosphate, were confirmed using Fourier transform infrared (FTIR) spectroscopy. Increases in water affinity by incorporating silica-phosphate were observed in all composite membranes, which also resulted in higher ion-exchange capacity than with pure SPAES. The water desorption behavior of the SPAES composite membranes was determined by the weight loss at 80 °C using thermogravimetric analysis (TGA). The SPAES/7S3P (7 and 3 indicate the added molar ratio of silica and phosphate, respectively) composite membrane showed the strongest water retention capacity. As the temperature increased in fully hydrated conditions, all membranes exhibited increasing proton conductivity due to enhanced proton mobility. The proton conductivity at low humidity depended on the water retention capacity, indicating that the incorporation of silica-phosphate was effective in enhancing the proton conductivity through the hopping transfer. The best performance was obtained in the SPAES/7S3P composite membrane, showing a conductivity of 29.6 mS/cm at 120 °C with 40% relative humidity, which is twice to that of Nafion 112 (14.6 mS/cm).

Proton-conducting composite membranes based on polybenzimidazole and sulfonated mesoporous organosilicate

Sulfonated mesoporous organosilicate (s-MPOs) was synthesized by the one-step sol–gel method as a novel inorganic additive derived for use in the fuel cell. TEM observations revealed that the s-MPOs has well-ordered structure and many SO3H groups on the inner surface of the mesopores. The s-MPOs was added to the proton-conductive polymer matrix, polybenzimidazole (PBI) in the presence of H3PO4, and the proton conductivities were measured at 60–100 °C under controlled humidity. The PBI composites filled with only 1 wt% of s-MPOs gave proton conductivity more than 10-times higher than the original PBI/H3PO4 membrane. The s-MPOs possessing many SO3H groups were able to form effective proton conductive pathways via its periodic structure and to improve the conductivity. The greatest conductivity was estimated to be 0.21 S cm−1 at 80 °C and 98 %RH in case of a PBI/s-MPOs20 (incl. approx. 20 mol% of the SO3H units in MPS) composite.

Performance of a direct methanol fuel cell using flexible proton-conducting glass-based composite membrane

A direct methanol fuel cell (DMFC) with a proton-conducting composite membrane, which is synthesized from Nafion®/phosphosilicate (NPS) glass and sulfonated poly(ether ether ketone) (SPEEK) polymer, is prepared, and its performance is evaluated at different cell temperatures, methanol flow rates, and oxygen backpressures. The methanol permeability of the NPS/SPEEK composite membrane is determined to be 7.5 × 10−7 cm2 s−1. The developed DMFC releases a peak power density of 73.1 mW cm−2 at a cell temperature of 85 °C.

Proton-Conducting Composite Membranes Derived from Ferroxane-Polyvinyl Alcohol Complex

Abstract A composite membrane composed of iron oxide and polyvinyl alcohol (PVA) was investigated as an alternative electrolyte material for proton exchange membranes (PEMs) in fuel cells using hydrogen as a fuel. Acetic acid (AA)-stabilized lepidocrocite (γ-FeOOH) nanoparticles and goethite (α-FeOOH) nanoparticles (ferroxane) were mixed with dissolved PVA and air-dried to fabricate the PEMs. The ferroxane–PVA composite membrane showed higher proton conductivity than goethite–PVA composite membrane. However, the proton conductivities of the ferroxane–PVA composite membrane decreased as PVA content in the composite membranes increased. Fourier transform infrared spectroscopy analyses of the ferroxane–PVA composite membrane showed that a large portion of AA groups on the surface of ferroxane nanoparticles was lost when mixed with PVA. The tensile force resistance of the composite membrane was much higher compared with ferroxane-derived ceramic membranes.

SiO 2 nanoparticles-coated poly(paraphenylene terephthalamide) nonwovens as reinforcing porous substrates for proton-conducting, sulfonated poly(arylene ether sulfone)-impregnated composite membranes

We demonstrate a new reinforcing porous substrate for a proton-conducting composite membrane targeting proton exchange membrane fuel cells (PEMFC) applications. This porous substrate is based on hygroscopic SiO 2 nanoparticles-coated poly(paraphenylene terephthalamide) (PPTA) nonwovens. The SiO 2 nanoparticles (530 nm), which are interconnected by tetraethoxy silane (TEOS)-based silicate binders, play a crucial role in improving mechanical properties, hydrophilicity, and water retention capability of the substrate. The PPTA nonwoven serves as a support layer offering flexibility and toughness to the substrate. The SiO 2 nanoparticles-coated PPTA nonwoven substrate is subsequently impregnated with sulfonated poly(arylene ether sulfone) (SPAES, degree of sulfonation = 49.3%) that acts as a proton-conducting electrolyte. In comparison to a pristine SPAES membrane, the porous substrate-reinforced SPAES composite membrane presents the substantially improved dimensional change, and more intriguingly, is effective in suppressing the steep decline of proton conductivity at a low humidity condition of 30 °C/50% RH.

Fabrication and characterization of poly(vinyl alcohol)/montmorillonite/poly(styrene sulfonic acid) proton-conducting composite membranes for direct methanol fuel cells

A high performance poly(vinyl alcohol)/montmorillonite/poly(styrene sulfonic acid) (PVA/MMT/PSSA) proton-conducting composite membrane was fabricated by a solution casting method. The characteristic properties of these blend composite membranes were investigated by using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, methanol permeability measurement, and the AC impedance method. The ionic conductivities for the composite membranes are in the order of 10 −3 S cm −1 at ambient temperature. There are two proton sources used on this novel composite membrane: the modified MMT fillers and PSSA polymer, both materials all contain the –SO 3H group. Therefore, the ionic conductivity was greatly enhanced. The methanol permeabilities of PVA/MMT/PSSA composite membranes is of the order of 10 −7 cm 2 s −1. It is due to the excellent methanol barrier properties of the PVA polymer. The peak power densities of the air-breathing direct methanol fuel cells (DMFCs) with 1M, 2M, 4M CH 3OH fuels were 14.22, 20.00, and 13.09 mW cm −2, respectively, at ambient conditions. The direct methanol fuel cell with this composite polymer membrane exhibited good electrochemical performance. The proposed PVA/MMT/PSSA composite membrane is therefore a potential candidate for future applications in DMFC.

Direct methanol fuel cell based on poly(vinyl alcohol)/titanium oxide nanotubes/poly(styrene sulfonic acid) (PVA/nt-TiO 2/PSSA) composite polymer membrane

The high performance poly(vinyl alcohol)/titanium oxide nanotubes/poly(styrene sulfonic acid) (PVA/nt-TiO 2/PSSA) proton-conducting composite membrane is prepared by a solution casting method. The characteristic properties of these blend composite membranes are investigated by thermal gravimetric analysis (TGA), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), micro-Raman spectroscopy, dynamic mechanical analysis (DMA), methanol permeability measurement and AC impedance method. It is found that the peak power densities of the DMFC with 1, 2, and 4 M CH 3OH fuels are 12.85, 23.72, and 10.99 mW cm −2, respectively, at room temperature and ambient air. Especially, among three methanol concentrations, the 2 M methanol shows the highest peak power density among three methanol concentrations. The results indicate that the air-breathing direct methanol fuel cell comprised of a novel PVA/nt-TiO 2/PSSA composite polymer membrane has excellent electrochemical performance and stands out as a viable candidate for applications in DMFC.

Implantation of Nafion® ionomer into polyvinyl alcohol/chitosan composites to form novel proton-conducting membranes for direct methanol fuel cells

Abstract A series of cost-effective, proton-conducting composite membranes, comprising of Nafion® ionomer, chitosan (CS), and polyvinyl alcohol (PVA), is successfully prepared. By taking advantage of the strong electrostatic interactions between Nafion® ionomer and CS component, Nafion ionomer is effectively implanted into the PVA/CS composite membranes, and improves proton conductivity of the PVA/CS composite membranes. Furthermore, this effect dramatically depends on the composition ratio of PVA/CS, and the optimum conductivity is obtained at the PVA/CS ratio of 1:1. The developed composite membranes exhibit much lower methanol permeability compared with the widely used Nafion® membrane, indicating that these novel membranes have great potential for direct methanol fuel cells (DMFCs).