Titanate nanotubes-embedded chitosan nanocomposite membranes with high isopropanol dehydration performance

Titanate nanotubes (TNTs) are prepared by a hydrothermal method, and then modified with poly(aspartic acid). Subsequently, they are incorporated into chitosan (CS) to fabricate the modified TNTs (MTNTs)-embedded chitosan hybrid membranes supported by the polyacrylonitrile (PAN) membrane (CS-MTNTs/PAN) and utilized for isopropanol dehydration. The physicochemical properties including physical morphology, chemical interaction, hydrophilicity, crystallinity, thermal stability and free-volume of CS-MTNTs hybrid separation layers are characterized by SEM, FTIR, water contact angle, XRD, TG and PALS analysis, respectively. It is found that the modification of poly(aspartic acid) can apparently improve the interfacial morphology and compatibility between TNTs and membrane matrix. Moreover, the superior isopropanol dehydration performance of CS-MTNTs/PAN composite membranes compared to pure CS membrane is verified via pervaporation experiments, which can be ascribed to the strong hydrophilicity and tubular structure of TNTs. For 90 wt% aqueous solution of isopropanol, the CS-MTNTs/PAN composite membrane containing 6 wt% MTNTs acquires the highest permeation flux and separation factor of 1498 g/m² h and 6237 at 80 °C, respectively. These results indicate the promising application potential of nanotube-filled membranes in the pervaporative dehydration of alcohols.     

Modified Sulfonated Poly(ether ether ketone) Based Mixed Matrix Membranes for Direct Methanol Fuel Cells

Mixed matrix membranes based on zeolite 4A‐methane sulfonic acid (MSA)‐sulfonated poly(ether ether ketone) (SPEEK) are evaluated as a potential polymer electrolyte membrane (PEM) for direct methanol fuel cells (DMFCs). Ion‐exchange capacity, sorption of water, and water–methanol mixture, proton conductivity, and methanol permeability for the mixed‐matrix membranes have been extensively investigated. The mixed‐matrix membranes are also characterized for their cross‐sectional morphology, mechanical, and thermal properties. DMFCs employing SPEEK‐MSA (20 wt.%) blend, zeolite 4A (4 wt.%)‐SPEEK‐MSA (20 wt.%) mixed matrix membranes deliver peak power densities of 130 and 159 mW cm^–2, respectively; while a peak power density of only 95 mW cm^–2 is obtained for the DMFC employing pristine SPEEK membrane at 70 °C. The results showed that these SPEEK based mixed matrix membranes exhibit higher DMFC performance and lower methanol permeability in comparison to Nafion‐117 membrane.     

The Construction and Application of Dual-Modified Carbon Nanotubes in Proton Exchange Membranes with Enhanced Performances

In this study, the carbon nanotubes (CNTs) are successively coated via sol-gel method with SiO₂ (SiO₂@CNTs), followed by grafting with 3-merraptnpropyltrimethnxysilane and oxidation with hydrogen peroxide to yield dual-modified CNTs (SSiO₂@CNTs). The SSiO₂@CNTs material is applied to prepared chitosan (CS) based composite proton exchange membranes by the incorporation of various content of SSiO₂@CNTs, the structure and properties of as-prepared composite membranes are fully investigated. Compared to pristine CS membrane, the SSiO₂@CNTs-filled composite membranes show improved thermal stability, mechanical stability, and methanol resistance, owing to the effective interface interaction and good compatibility between SSiO₂@CNTs and CS matrix. Additionally, the doping of SSiO₂@CNTs also generates a positive effect on the electrochemistry performance, due to the construction of abundant transport channel and providing more proton sources or proton sites. Particularly, the CS/SSiO₂@CNTs-7 membrane exhibits tensile strength of about 40.1 MPa and proton conductivity of 35.8 mS cm⁻¹ at 80 °C, which is almost 1.6 and 2.0 times higher than pure CS membrane, and lower methanol permeability of 0.9 × 10⁻⁶ cm² s⁻¹. The direct methanol fuel cell performance (DMFC) of CS/SSiO₂@CNTs-7 membrane is also improved with open circuit voltage of 0.67 V and maximum power density of 60.7 mW cm⁻² at 70 °C.     

Hybrid Network Sulfonated Polynorbornene/Silica Membranes with Enhanced Proton Conductivity by Doped Phosphotungstic Acid

A series of novel hybrid sulfonated polynorbornene‐silica (PBN–SiO₂) proton conducting membranes doped with different weight ratio of phosphotungstic acid (PWA) were prepared by the casting procedure. The proton conductivity of the composite membranes containing 40 wt.% PWA reached the maximum of 6.1 × 10^–2 S cm^–1 and increased gradually with PWA content and temperature elevating, while the methanol permeabilities (3.52–9.39 × 10^–7 cm² s^–1) of these membranes were much lower than that of Nafion 117 (2.36 × 10^–6 cm² s^–1). The membranes also exhibited excellent thermally stable and mechanical properties, which imply that the PBN–SiO₂–PWA membranes are promising materials in the direct methanol fuel cells (DMFC) applications.     

Poly(vinyl alcohol)–polyacrylamide blends with cesium salts of heteropolyacid as a polymer electrolyte for direct methanol fuel cell applications

A class of inorganic–organic hybrid membranes with low methanol permeability characteristics for possible direct methanol fuel cell (DMFC) applications was architected, formulated, and fabricated through the blending of poly(vinyl alcohol) (PVA) and polyacrylamide (PAM) followed by crosslinking with glutaraldehyde (Glu). Cesium salts of different heteropolyacids, including phosphomolybdic acid (PMA), phosphotungstic acid (PWA), and silicotungstic acid (SWA), were incorporated into the polymer network to form corresponding hybrid membrane materials, namely, PVA–PAM–CsPMA–Glu, PVA–PAM–CsPWA–Glu, and PVA–PAM–CsSWA–Glu, respectively (where “Cs” together with a heteropolyacid abbreviation indicates the cesium salt of that acid). All the three hybrid polymer membranes fabricated exhibited excellent swelling, thermal, oxidative, and additive stability properties with desired proton conductivities in the range 10^?2 S/cm at 50% relative humidity. A dense network formation was achieved through the blending of PVA and PAM and by crosslinking with Glu, which led to an order of magnitude decrease in the methanol permeability compared to the state‐of‐the‐art commercial Nafion 115 membrane. The hybrid membrane containing CsSWA exhibited a very low methanol permeability (1.4 × 10^?8 cm²/s) compared to other membranes containing cesium salt of heteropolyacids such as PMA and PWA. The feasibility of these hybrid membranes as proton‐conducting electrolytes in DMFC was investigated, and the preliminary results were compared with those of Nafion 115. The results illustrate the attractive features and suitability of the fabricated hybrid membranes as an electrolyte for DMFC applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Chitosan/CaCO3 solvent‐free nanofluid composite membranes for direct methanol fuel cells

Natural polyelectrolyte chitosan (CS) has been considered to be a promising proton‐exchange membrane material for direct methanol fuel cells due to its low cost and excellent methanol barrier ability. To further improve the ionic conductivity and mechanical property of CS, calcium‐carbonate solvent‐free nanofluids (CaCO₃‐SF) with unique flow behavior were prepared by an ion‐exchange method, and then used a novel nanofiller to modify CS to fabricate composite membranes. The surface‐grafted organic long chains on the surface of CaCO₃ nanoparticles could promote the homogeneous dispersion of CaCO₃ in the CS matrix, and thus improve the interfacial bonding and facilitate the load transfer from the matrix to stiff CaCO₃. When the content of CaCO₃‐SF was 6 wt%, the tensile strength and fracture elongation of the composite membrane were 28.25 MPa and 17.17%, respectively, which increased by 25% and 36% when compared with those of pure membrane. Moreover, the ? SO₃H groups in the structure of organic long chains could form new proton transport sites, and thus enhance the proton conductivity of the membranes. Consequently, when compared with pure CS membrane (0.0131 S cm^?1), incorporation of 6 wt% CaCO₃‐SF (0.0250 S cm^?1) exhibited about onefold increase of proton conductivity. POLYM. ENG. SCI., 59:2128–2135, 2019. © 2019 Society of Plastics Engineers     

Preparation and properties of chitosan/acidified attapulgite composite proton exchange membranes for fuel cell applications

A composite proton exchange membrane chitosan (CS)/attapulgite (ATP) was prepared with the organic–inorganic compounding of ATP and CS. The composite membranes were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). The mechanical properties, thermal stability, water uptake, and proton conductivity of the composite membranes were fully investigated. The composite membranes exhibited an enhanced mechanical property, dimensional and thermal stability compared to CS membrane, owing to the interface interaction between ATP and CS. The maximum tensile strength of 53.1 MPa and decomposition temperature of 223.4°C was obtained, respectively. More importantly, the proton conductivity of the composite membrane is also enhanced, the composite membrane with 4 wt% ATP content (CS/ATP-4) exhibited the highest proton conductivity of 26.2 mS cm⁻¹ at 80°C with 100% relative humidity, which is 25.1% higher than pure CS membrane. These results may explore a simple and green strategy to prepare CS-based PEMs, which have a great potential in the application of proton exchange membrane fuel cells.     

Novel sulfonated multi-walled carbon nanotubes filled chitosan composite membrane for fuel-cell applications

In the present study, multi-walled carbon nanotubes (MWCNTs) were sulfonated by 1,3-propane sultone and distillation–precipitation polymerization, respectively, and then incorporated into chitosan (CS) to prepare CS/MWCNTs composite membranes for fuel cell applications. CS/MWCNTs membranes show better thermal and mechanical stability than pure CS membrane due to the strong electrostatic interaction between the  SO₃H groups of MWCNTs and the  NH₂ groups of CS, which can restrict the mobility of CS chain. The sulfonated MWCNTs provide efficient proton hopping sites ( SO₃H,  SO₃⁻ …. ₃⁺HN ), thereby resulting in the formation of continuous proton conducting channels. The composite membranes with 5 wt % of MWCNTs modified by two different ways show a proton conductivity of 0.026 and 0.025 S·cm⁻¹, respectively. In conclusion, CS/MWCNTs membrane is a promising proton exchange membrane for fuel-cell applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47603.     

Synthesis and characterization of poly(vinyl alcohol)‐based membranes for direct methanol fuel cell

Membranes made of poly(vinyl alcohol) (PVA) and its ionic blends with sodium alginate (SA) and chitosan were synthesized and characterized for their ion-exchange capacity (IEC) and swelling index values to investigate their applicability in direct methanol fuel cells (DMFCs). These membranes were assessed for their intermolecular interactions, thermal stabilities, and mechanical strengths with Fourier transform infrared spectroscopy, X-ray diffraction methods, differential scanning calorimetry, thermogravimetric analysis, and tensile testing, respectively. Methanol permeability and proton conductivity were also estimated and compared to that of Nafion 117. In addition to being effective methanol barriers, the membranes had a considerably high IEC and thermal and mechanical stabilities. The addition of small amounts of anionic polymer was particularly instrumental in the significant reduction of methanol permeability from 8.1 × 10⁻⁸ cm²/s for PVA to 6.9 × 10⁻⁸ cm²/s for the PVA–SA blend, which rendered the blend more suitable for a DMFC. Low methanol permeability, excellent physicomechanical properties, and above all, cost effectiveness could make the use of these blends in DMFCs quite attractive. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1154–1163, 2005     

Chitosan membranes filled by GPTMS-modified zeolite beta particles with low methanol permeability for DMFC

Uniform zeolite beta particles about 800 nm in diameter were synthesized by a hydrothermal method, and functionalized by γ-glycidoxypropyltrimethoxysilane (GPTMS). Subsequently, chitosan (CS) membranes filled by GPTMS-modified zeolite beta particles were prepared, and characterized by SEM, FT-IR, XRD and TGA. Compared with the pure CS and Nafion^®117 membrane, these CS/zeolite beta hybrid membranes show apparently the lower methanol permeability, which could be assigned to the better interfacial morphology and compatibility between the GPTMS-modified zeolite beta particles and chitosan matrix. In all the prepared CS/zeolite beta hybrid membranes, the CS membrane filled by 10 wt.% GPTMS-modified zeolite beta particles exhibits the lowest methanol permeability, which is 4.4 × 10⁻⁷ and 2.2 × 10⁻⁷ cm² s⁻¹ at 2 and 12 M methanol concentration, respectively. The proton conductivity of this hybrid membrane is 1.31 × 10⁻² S cm⁻¹, which is slightly lower than that of the pure CS membrane. The selectivity of CS/GPTMS-zeolite beta membranes is comparable with Nafion^® 117 at 2 M methanol concentration, and much higher at 12 M methanol concentration.     

UV curable sulfonated hybrid materials and their performance as proton exchange membranes

In this study 2-acrylamido-2-methylpropanesulfonic acid (AMPS) containing UV curable nanocomposite membranes were prepared by using the sol–gel method. Tetraethylorthosilicate (TEOS), and 3-(methacryloyloxy)propyl trimethoxysilane (MAPTMS) were used, respectively as an inorganic precursor and coupling agent. Cross linking agents such as poly(ethylene glycol diacrylate) (PEGMA) and ethylene glycol dimethacrylate (EGDMA) were used to arrange the mechanical and physical properties of the resulting hybrid membrane. The hybrid formulation polymerized under UV irradiation and the gel percentage, water uptake of the membranes were calculated. The polymerization conversion of the organic part was investigated by using photo-differential scanning calorimetry (photo-DSC). The thermal and mechanical properties of the membranes indicated good stability. The morphological structure of membranes was investigated by scanning electron microscopy (SEM). In addition proton conductivity and methanol selectivity measurements were performed. The proton conductivity of the AMPS20–SOLGEL30 nanocomposite membrane is about 0.138 S cm^?1 at 50 °C. Selectivity toward methanol for the same membrane is very low with a selectivity factor of α = 0.032, which satisfies the requirements for DMFC applications.     

In situ sol–gel route to novel sulfonated polyimide?SiO2 hybrid proton‐exchange membranes for direct methanol fuel cells

Polyimides (PIs) as high‐performance organic matrices are used in the preparation of PI composites because of their excellent mechanical, thermal and dielectric properties. The sol–gel method is a promising technique for preparing these PI composites due to the mild reaction conditions and the process being controllable. Although sulfonated polyimide (SPI) proton‐exchange membranes have attracted much attention recently, studies on preparing SPI‐based hybrid proton‐exchange membranes for fuel cells have been rare. A series of SPI? SiO₂ hybrid proton‐exchange membranes were prepared from amino‐terminated SPI pre‐polymers, 3‐glycidoxypropyltrimethoxysilane (KH‐560) and tetraethylorthosilicate through a co‐hydrolysis and condensation process using an in situ sol–gel method. The reactive silane KH‐560 was used to react with amino‐terminated SPI to form silane‐capped SPI in order to improve the compatibility between the polymer matrix and the inorganic SiO₂ phase. The microstructure and mechanical, thermal and proton conduction properties were studied in detail. The hybrid membranes were highly uniform without phase separation up to 30 wt% SiO₂. The storage modulus and tensile strength of the hybrid membranes increased with increasing SiO₂ content. The introduction of SiO₂ improved the methanol resistance while retaining good proton conductivity. The hybrid membrane with 30 wt% SiO₂ exhibited a proton conductivity of 10.57 mS cm^?1 at 80 °C and methanol permeability of 2.3 × 10^?6 cm² s^?1 possibly because the crosslinking structure and SiO₂ phases formed in the hybrids could retain water and were helpful to proton transport. Copyright © 2010 Society of Chemical Industry     

Phthalonitrile end-capped sulfonated polyarylene ether nitriles for low-swelling proton exchange membranes

A series of phthalonitrile end-capped sulfonated polyarylene ether nitriles are synthesized via K₂CO₃ mediated nucleophilic aromatic substitution reaction at various molar ratios. The as-prepared polymer structures are confirmed by ¹H NMR and FTIR spectroscopy. The properties of membranes cast from the corresponding polymers are investigated with respect to their structures. The membranes exhibit good thermal and mechanical properties, low methanol permeability (0.01?×?10^?6–0.58?×?10^?6 cm²·s^?1 at 20 °C), and high proton conductivity (0.021–0.088 S·cm^?1 at 20 °C). The introduction of phthalonitrile is proved to increase intermolecular interaction, mainly contributing to the reduction in water uptake, swelling ratio, and methanol permeability. More importantly, its introduction does not decrease the proton conductivity, but there is a slight increase. Furthermore, the selectivity of SPEN-CN-50 can reach 4.11?×?10⁵ S·s·cm^?3, which is about nine times higher than that of Nafion 117. All the data show that the as-prepared membranes may be potential proton exchange membrane for DMFCs applications.     

The Preparation of Metal–Organic-Framework/Boron Phosphate Hybrid Materials for Improved Performances in Proton Exchange Membranes

New types of metal–organic framework based hybrid materials are designed and prepared, which involving the hybridization of various content of boron phosphate (BPO₄) with the precursor of HKUST-1. The structure of obtained HKUST-1/BPO₄ hybrid materials (HB) is fully investigated, and then applied to construct sulfonated poly (ether ether ketone) (SPEEK) based proton exchange membranes (SPEEK/HB). Owing to effective interactions between hybrid materials and SPEEK matrix, the achieved composite membranes reflect a considerable improvement in mechanical and thermal stability, oxidative stability, methanol permeation, and proton conductivity. In particular, the tensile strength of SPEEK/HB-20 composite membrane is 41.3 MPa, which is 1.5 times higher than pristine SPEEK, and the methanol permeability reduced to one-third of SPEEK at the same time. The SPEEK/HB-10 displays the highest proton conductivity of 37.4 mS cm⁻¹ at 80 °C, which is obviously higher than pristine SPEEK. These results reveal that the hybridization of HKUST-1 with BPO₄ provide a promising candidate in the modification of proton exchange membranes (PEMs), and this strategy also possess great application potential in other types of MOFs-based hybrid materials.     

Direct synthesis of sulfonated poly(ether ether ketone ketone)s (SPEEKKs) proton exchange membranes for fuel cell application

A series of sulfonated poly(ether ether ketone ketone)s (SPEEKK)s based membranes have been prepared and evaluated for proton exchange membranes (PEM). The membranes show very good thermal and mechanical stabilities. The structures of membranes were studied with AFM. The membranes show very good proton conductive ability (25 °C: 0.007-0.04 s/cm) and methanol resistance (25 °C: 7.68×10⁻⁸ to 5.75×10⁻⁷ cm²/s). The methanol diffusion coefficients of membranes are much lower than that of Nafion (2×10⁻⁶ cm²/s). The SPEEKKs membranes show very good respective in direct methanol fuel cells (DMFC) usages.     

Influence of Methanol Crossover on the Fuel Utilization of Passive Direct Methanol Fuel Cell

The effect of methanol crossover on the fuel utilization of a passive direct methanol fuel cell (DMFC) was reported. The results revealed that the Faradaic efficiency decreased from 46.9 to 17.4% when methanol concentration increased from 1.0 to 8.0 mol L^–1 at the lower current density 11.1 mA cm^–2. However, the Faradaic efficiency increased from 14.7 to 31.3% when methanol concentration increased from 1.0 to 8.0 mol L^–1 at a higher current density of 44.4 mA cm^–2. On the other hand, although the amount of methanol was increased, the Faradaic efficiency did not change, obviously due to the uniform methanol crossover and methanol diffusion at the same methanol concentration and constant current.     

Development of a Self‐Adaptive Direct Methanol Fuel Cell Fed with 20 M Methanol

A passive and self‐adaptive direct methanol fuel cell (DMFC) directly fed with 20 M of methanol is developed for a high energy density of the cell. By using a polypropylene based pervaporation film, methanol is supplied into the DMFC's anode in vapor form. The mass transport of methanol from the cartridge to the anodic catalyst layer can be controlled by varying the open ratio of the anodic bipolar plate and by tuning the hydrophobicity of anodic diffusion layer. An effective back diffusion of water from the cathode to the anode through Nafion film is carried out by using an additive microporous layer in the cathode that consists of 50 wt.% Teflon and KB‐600 carbon. Accordingly, the water back diffusion not only ensures the water requirement for the methanol oxidation reaction but also reduces water accumulation in the cathode and then avoids serious water flooding, thus improving the adaptability of the passive DMFC. Based on the optimized DMFC structure, a passive DMFC fed with 20 M methanol exhibits a peak power density of 42 mW cm^–2 at 25 °C, and no obvious performance degradation after over 90 h continuous operation at a constant current density of 40 mA cm^–2.     

A quaternized poly(vinyl alcohol)/chitosan composite alkaline polymer electrolyte: preparation and characterization of the membrane

Quaternized poly(vinyl alcohol)/chitosan (QPVA/CS) composite membranes were prepared by solution casting method with AlCl₃·6H₂O aqueous solution as solvent for CS and glutaraldehyde as a crosslinker. The crystalline, thermal and mechanical properties of the QPVA/CS composite membranes were studied by Fourier transform infrared spectroscopy, X-ray diffractometry, differential scanning calorimetry, thermogravimetry and tensile test measurements, respectively. The composite membranes were immersed in potassium hydroxide aqueous solution to form polymer electrolyte membranes. The alkaline uptake, swelling ratio, ion conductivity and methanol permeability of the electrolyte membranes were studied. The experimental results indicated that aluminum chloride hexahydrate (AlCl₃·6H₂O) had a positive effect on the mechanical properties of the QPVA/CS composite membrane. The elongation-at-break of this membrane reached the maximum of 401.0%. The alkaline uptake and swelling ratio of the composite membranes decreased. With the addition of 30 wt% AlCl₃·6H₂O, the composite membrane showed the ion conductivity and methanol permeability of 1.82 × 10^?2 S cm^?1 and 2.17 × 10^?6 cm² s^?1, respectively. These values were higher than those of the membrane with acetic acid as the solvent for CS. The selectivity of the QPVA/CS membrane could reach 8.39 × 10³ S s cm^?3. This study showed that with AlCl₃·6H₂O as the solution for CS, the high performance QPVA/CS composite alkaline polymer electrolyte membrane could be prepared.     

Proton-conducting membranes from phosphotungstic acid-doped sulfonated polyimide for direct methanol fuel cell applications

A series of novel hybrid proton conducting membranes based on sulfonated naphthalimides and phosphotungstic acid (PTA) were prepared from N-Methyl Pyrrolidone (NMP) solutions. These hybrid organic-inorganic materials, composed of two proton-conducting components, have high ionic conductivities (9.3 × 10^?2 S cm^?1 at 60 °C, 15% PTA), and show good performance in H₂|O₂ polymer electrolyte membrane fuel cells (PEMFC), previously reported by us. Moreover, they have low methanol permeability compared to Nafion^®112. In this paper we describe, for the first time, the behaviour of these hybrid membranes as electrolyte in a direct methanol fuel cell (DMFC). The maximum power densities achieved with PTA doped sulfonated naphthalimide membrane, operating with oxygen and air, were 34.0 and 12.2 mW cm^?2, respectively; about the double and triple higher than those showed by the non-doped membrane at 60 °C.     

Sulfonated polyether ether ketone composite proton exchange membranes incorporated with a novel hierarchical-structure hybrid nanofiller consisting solid superacid zirconium phosphate and CNTs

How to simultaneously improved the proton conductivity and mechanical strength is a key problem facing currently used proton exchange membranes (PEMs). Herein, a solid inorganic superacid-zirconium phosphate (ZrP) with a two-dimensional layer structure was combined with one-dimensional carbon nanotubes (CNTs) to prepare hybrid nanofiller ZrP-CNTs by an in situ chemical deposition method. The new hybrid nanofiller was then applied to modify sulfonated polyether ether ketone (SPEEK), a widely used PEM matrix, to obtain a series of composite membranes. The structure and properties of the membranes were fully characterized by SEM, XRD, FTIR, TG, tensile properties, and proton conductivity. The results showed that the proton conductivities of the membranes were significantly improved due to the addition of super solid acid-ZrP that has abundant proton sources or proton sites. Moreover, the composite membranes exhibited better mechanical properties and thermal stability than those of pure SPEEK membrane, owing to the great interface interaction and good compatibility between ZrP-CNTs and SPEEK. The composite membrane (2 wt% ZrP-CNTs) demonstrated the optimal comprehensive performance. Its proton conductivity was 36.63 mS cm⁻¹ and its tensile strength was 37.56 MPa, which was 70% and 10%, respectively, higher than those of the pure SPEEK membrane under the same condition.