Mesoporous hollow silica spheres as micro-water-tanks in proton exchange membranes

In order to decrease the swelling of Nafion^® and reduce the dependency of proton conductivity on high relative humidity (RH), mesoporous hollow silica spheres were synthesized and dispersed in Nafion matrix as micro-water-tanks in the proton exchange membranes (PEM). The morphologies of MHSi and Nafion/MHSi composite membranes are characterized by SEM and TEM. The effects of MHSi on water uptake, swelling, dehydration rate and proton conductivity of the composite membranes were investigated. The results show that, with a suitable portion of MHSi in the membrane, composite PEMs with enhanced water uptake, reduced swelling and improved proton conductivity are obtained.     

The Role of PANI/Nafion on the Performance of ORR in Gas Diffusion Electrodes of PEM Fuel Cell

In this work, gas diffusion electrodes were fabricated from Nafion and polyaniline (PANI) nanofibers. The goal of this work was to find the optimal combination of Nafion and polyaniline in gas diffusion electrodes. The electrodes were evaluated for oxygen reduction reaction effectiveness, and their electrochemical properties were investigated by using electrochemical techniques, and PEM single cell. The results revealed that electrodes containing both Nafion and polyaniline worked more efficiently than electrodes containing either Nafion or polyaniline only. The optimum combination is noted as 0.6 mg/cm² PANI and 0.4 mg/cm² Nafion.     

Novel sepiolite reinforced emerging composite polymer electrolyte membranes for high-performance direct methanol fuel cells

Methanol permeation is the main issue of Nafion membranes when they are used as a polymer electrolyte membrane (PEM) in direct methanol fuel cells (DMFCs). In the current study, novel nanocomposite polymer membranes are prepared by the integration of surface-modified sepiolite (MS) in polyvinylidene fluoride grafted polystyrene (PVDF-g-PS) copolymer as PEM in DMFCs. Sepiolite (SP) surface is chemically modified using vinyltriethoxysilane and analyzed by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Nanocomposite PVDF-g-PS/MS membranes are prepared by phase inversion technique and subsequently treated with chlorosulfonic acid to induce sulfonic acid (SO₃H) active sites at the membrane surface. The prepared nanocomposite membranes (S-PPMS) are analyzed for their physicochemical characteristics in terms of water uptake percentage, cation exchange capacity, proton conductivity (σ), and methanol permeability. MS dispersion in the copolymer matrix is proved through morphological SEM examination. The S-PPMS membranes exhibit increased proton conductivity due to the presence of well-dispersed MS and surface functional –SO₃H groups. A peak power density of 210 mWcm^?2 is recorded for S-PPMS10 at 110 °C, which is higher than the output obtained from Nafion-117. These promising results indicate the potential utilization of prepared nanocomposite PEMs for DMFC application.     

燃料电池用侧链型磺化聚砜质子交换膜的性能

在制备氯甲基化聚砜(CPS)的基础上,以1,2-二羟基苯-3,5-二磺酸钠为试剂,通过亲核取代反应制备一种侧链末端为磺酸基团的侧链型磺化聚砜(PS-BDS),并采用溶液浇注法制备相应的质子交换膜(PEM),研究温度对PEM性能的影响规律。 结果表明,由于亲水基团远离疏水聚合物主链,该PEM能够形成亲水微区远离疏水微区的相分离结构,亲水区域对主链的影响较小,该PEM在高磺化度下仍能保持较好的尺寸稳定性,随着温度的升高,PEM的吸水率(WU)、吸水溶胀率(SW)和质子传导率(PC)升高,其中PS-BDS-4(离子交换容量为1.57 mmol/g)在25和85 ℃时的SW仅为22.1%和55.0%,甲醇的渗透率(DK)仅为10.17×10^-7 cm²/s,低于商业化的Nafion115(16.8×10^-7 cm²/s)和Nafion117(23.8×10^-7 cm²/s),表现出很好的综合性能。     

Property improvement of nanocellulose‐reinforced proton exchange nanocomposite membrane coated with tetraethyl orthosilicate

Study on proton exchange membrane (PEM) with the aim toward excellent battery performance of PEM for fuel cells has attracted increasing attention. In this work, nanocellulose (CNC) aminated by KH792 noted as NN was prepared. CNC or NN/sulfophenylated poly(ether ether ketone ketone) (sPEEKK) nanocomposite membrane (SN) or (SNN) were produced by solution mixing. SNN was further coated with tetraethyl orthosilicate (TEOS) to obtain SNNT. The properties of sPEEKK, SN, SNN, and SNNT membranes were thoroughly investigated. The proton conductivity of SN4 was 0.22 S·cm^?1 at 90 °C, while a proton conductivity of 0.30 S·cm^?1 was obtained for SNN4, and an even higher value of 0.36 S·cm^?1 at 90 °C was obtained for the TEOS‐coated SNN4 (SNN4T). Meanwhile, SNN4T showed high thermal stability, and its T_d5 was as high as 318.2 °C. Furthermore, the composite membrane coated with TEOS also presented excellent oxidative stability. The mass of SNN2T after treated in Fenton agent for 1 h at 80 °C was still retained 96.2%, and it was not fully dissolved until 11 h. It was illustrated that aminated CNC/sPEEKK nanocomposite membranes coated with TEOS is a kind of promising materials as PEMs for fuel cells. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2190–2200     

Self-assembled tri-block terpolymer blend membranes reinforced with poly(methyl methacrylate)-coated gold nanoparticles obtained through phase inversion technique

The blend membranes of polystyrene-block-polyisoprene-block-polystyrene and polyethylene-block-poly(ethylene glycol)-block-polycaprolactone were designed using the phase inversion technique. The poly(methyl methacrylate)-coated gold nanoparticles are around 40–50 nm in size. The honeycomb-shaped nanopores were uniformly dispersed in polystyrene-block-polyisoprene-block-polystyrene/polyethylene-block-poly(ethylene glycol)-block-polycaprolactone/poly(methyl methacrylate)-coated gold nanoparticles blend membranes. There was a 16% increase in tensile strength and a 33% increase in tensile modulus of polystyrene-block-polyisoprene-block-polystyrene/polyethylene-block-poly(ethylene glycol)-block-polycaprolactone/poly(methyl methacrylate)-coated gold nanoparticles 1 relative to the neat membrane. With 1 wt% nanoparticles, the membrane showed a higher water flux of 59.2 mL cm^?2 min^?1 and a salt rejection ratio of 25.4%, while the polystyrene-block-polyisoprene-block-polystyrene/polyethylene-block-poly(ethylene glycol)-block-polycaprolactone membrane without poly(methyl methacrylate)-coated gold nanoparticles had lower flux (43.8 mL cm^?2 min^?1) and salt rejection (18.5%).     

燃料电池用聚合物质子交换膜的研究进展

质子交换膜（PEM）是质子交换膜燃料电池的核心组件之一,具有隔绝阴阳极、提供质子传递通道和阻止燃料渗透的作用. 商业化应用的全氟磺酸PEM存在燃料渗透严重、高温条件下导电性差和成本高的问题,开发性能优良的聚合物PEM显得很有必要. 本文讨论了近年来聚合物PEM的研究进展,分别从聚合物的主链、支链和交联结构角度介绍了分子结构对薄膜相分离、质子导电性、稳定性和电池性能等性能的影响,并讨论了聚合物分子结构设计方面存在的问题,最后对燃料电池用聚合物PEM在未来的发展方向进行了展望.     

Fluorophilic cobalt phthalocyanine‐containing Nafion membrane: high oxygen permeability and proton conductivity in the membrane

A multiply‐fluorinated cobalt phthalocyanine (CoFPC) was prepared, which could reversibly interact with oxygen. CoFPC was introduced into the hydrophobic perfluoroethylene‐backbone domain of the Nafion membrane. The localization of CoFPC did not reduce the high proton conductivity (10^?2–10^?3 S cm^?1) ascribed to the hydrophilic channel of Nafion. The oxygen permeability through the CoFPC/Nafion membrane was higher than the nitrogen permeability and that of the pristine Nafion membrane, and was significantly enhanced at the lower upstream pressure. The permselectivity of oxygen versus nitrogen increased beyond 20 with the CoFPC content in the membrane. The CoFPC/Nafion membrane was coated on a glassy carbon modified with a Pt/C catalyst. The high electrochemical reduction current of oxygen suggested that the CoFPC/Nafion membrane efficiently supplied oxygen to the Pt/C catalyst. Copyright © 2009 John Wiley & Sons, Ltd.     

Enhancing proton conductivity of proton exchange membrane with SPES nanofibers containing porous organic cage

Effective proton conducting sites and establishing proton channels are two critical factors in developing high‐performance proton exchange membranes. This study first establishes a strategy in designing effective proton conducting channels for Nafion by using solution blowing of sulfonated polyethersulfone (SPES) nanofibers containing CC3, which is an emerging porous organic cage that possesses the advantages of dissolvable organic solvents and high proton conduction from its interconnected three‐dimensional pore structure. Our strategy results in SPES nanofiber networks with CC3 uniformly involved in and composite membranes with Nafion‐filled interfiber voids. Benefiting from such structural features, the composite membrane exhibits high proton conductivity (0.315 S cm^?1 at 80°C and 100% RH), low methanol permeability (0.69 × 10^?7 cm² S^?1), excellent water absorption, thermal and dimensional stability, and single‐cell performance. This study provides not only a valuable reference for the application of CC3 but also a new idea for establishment of proton transfer channels.     

Thermal stability of proton exchange fuel-cell membranes based on crosslinked-polytetrafluoroethylene for membrane-electrode assembly preparation

We investigated thermal properties of proton exchange membranes (PEMs) prepared by the radiation-induced grafting of styrene into crosslinked-polytetrafluoroethylene films and the subsequent sulfonation for fuel-cell applications. A conventional thermogravimetric analysis was found to be unreliable because the resulting curve varied greatly with the heating rate. Thus, in order to obtain accurate information, we performed an ex-situ heat-treatment analysis, which involved heating of the PEMs at fixed temperatures of 200-350 °C and measurement of their remaining weight, ion exchange capacity (IEC) and proton conductivity (σ) after washing in pure water. The IEC and σ did not change at any temperature up to 200 °C, indicating high thermal stability. At 250 °C, however, the PEM properties deteriorated probably via radical cleavage of the C-S bond between a sulfonic acid group and an aromatic ring, and condensation of two sulfonic acid groups. Finally, the PEM was hot-pressed with two electrodes at 200 °C to produce a good membrane-electrode assembly for a fuel cell.     

Water induced phase segregation in hydrocarbon proton exchange membranes

Proton exchange membranes(PEMs) are a key material for proton exchange membrane fuel cells(PEMFCs). Non-fluorinated hydrocarbon PEMs are low-cost alternatives to Nafion, but limited by the low proton conductivity, because of the weak phase segregation structure and narrow ion-transport channels.Various efforts have been taken to improve the performance of hydrocarbon PEMs, but mostly with complex methodologies. Here we demonstrate a simple, yet very efficient method to create phase segregation structure inside a typical hydrocarbon PEM, sulfonated poly(ether ether ketone)(SPEEK). By simply adding appropriate amounts of water into the DMF solvent, the resulting SPEEK membrane exhibits widened ion-transport channels, with the phase size of 2.7 nm, as indicated by both molecular dynamic(MD) simulations and transmission electron microscope(TEM) observations, and the proton conductivity is thus improved by 200%. These findings not only further our fundamental understanding of hydrocarbon PEMs, but are also valuable to the development of low-cost and practical fuel cell technologies.     

Preparation and characterization of sulfonated polyimide/TiO2 composite membrane for vanadium redox flow battery

A sulfonated polyimide (SPI)/TiO₂ composite membrane was fabricated by a blend way to improve its performance in vanadium redox flow battery (VRB). Both EDS and XRD results verify the successful preparation of the SPI/TiO₂ composite membrane. The surface SEM image shows its homogeneous structure. TG analysis identifies its thermal stability. The SPI/TiO₂ composite membrane possesses much lower permeability of VO²⁺ ions (2.02?×?10^?7 cm² min^?1) and favorable proton conductivity (3.12?×?10^?2 S cm^?1). The VRB single cell with SPI/TiO₂ composite membrane shows higher coulombic efficiency (93.80–98.00 %) and energy efficiency (83.20–67.61 %) at the current density ranged from 20 to 80 mA cm^?2 compared with that with Nafion 117 membrane. And the operational stability of the as-prepared composite membrane is good after 50 times of cycling tests. Therefore, the low-cost SPI/TiO₂ composite membrane with excellent battery performance exhibits a great potential for application in VRB.     

Novel sulfonated polyimide/ZrO2 composite membrane as a separator of vanadium redox flow battery

Sulfonated polyimide (SPI) and ZrO₂ are blended to prepare a series of novel SPI/ZrO₂ composite membranes for vanadium redox flow battery (VRFB) application. Results of atomic force microscopy and X‐ray diffraction reveal that ZrO₂ is successfully composited with SPI. All SPI/ZrO₂ membranes possess high proton conductivity (2.96–3.72 × 10^?2 S cm^?1) and low VO²⁺ permeability (2.18–4.04 × 10^?7 cm² min^?1). SPI/ZrO₂‐15% membrane is determined as the optimum one on account of its higher proton selectivity and improved chemical stability. The VRFB with SPI/ZrO₂‐15% membrane presents higher coulombic efficiency and energy efficiency than that with Nafion 117 membrane at the current density, which ranged from 20 to 80 mA cm^?2. Cycling tests indicate that the SPI/ZrO₂‐15% membrane has good operation stability in the VRFB system. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrogen‐Bonded Organic Frameworks (HOFs): A New Class of Porous Crystalline Proton‐Conducting Materials

Two porous hydrogen‐bonded organic frameworks (HOFs) based on arene sulfonates and guanidinium ions are reported. As a result of the presence of ionic backbones appended with protonic source, the compounds exhibit ultra‐high proton conduction values (σ) 0.75× 10^?2 S cm^?1 and 1.8×10^?2 S cm^?1 under humidified conditions. Also, they have very low activation energy values and the highest proton conductivity at ambient conditions (low humidity and at moderate temperature) among porous crystalline materials, such as metal–organic frameworks (MOFs) and covalent organic frameworks (COFs). These values are not only comparable to the conventionally used proton exchange membranes, such as Nafion used in fuel cell technologies, but is also the highest value reported in organic‐based porous architectures. Notably, this report inaugurates the usage of crystalline hydrogen‐bonded porous organic frameworks as solid‐state proton conducting materials.     

Active layer of fuel cell electrode with polymer electrolyte: Modeling of support grains, calculation of overall cathode characteristics

The active layer of the cathode of a fuel cell with polymer electrolyte (Nafion) is considered. The optimum carbon support structure is constructed using computer simulation: its carbon “skeleton” possesses the maximum outer surface area and provides electronic conductivity of the grains, support cubes, along the three coordinate axes. Nafion is absent in the support grain, so that the grain is capable of participating only in the transport of oxygen molecules, it possesses no proton conductivity. An estimate of all parameters of an optimum support grain is provided; in particular, the value of the effective Knudsen diffusion coefficient of oxygen is established. After this, effective proton conductivity and effective Knudsen diffusion coefficient are calculated already on the whole active layer scale, according to the model of equally sized cube grains of three types. In conclusion, the overall current in the active layer of a cathode with a polymer electrolyte was calculated for the percolation cluster consisting only of Nafion grains and the Knudsen diffusion of oxygen created only by a combined gas percolation cluster consisting of void grains and all support grains. The overall current value for t = 80°C and pressure of p* = 101 kPa proved to be low, hundreds of mA/cm². The current value can apparently be increased to several A/cm² if the support grains are developed that would simultaneously possess both proton conductivity and ability to sustain oxygen diffusion.     

Combined Intrinsic and Extrinsic Proton Conduction in Robust Covalent Organic Frameworks for Hydrogen Fuel Cell Applications

Developing new materials for the fabrication of proton exchange membranes (PEMs) for fuel cells is of great significance. Herein, a series of highly crystalline, porous, and stable new covalent organic frameworks (COFs) have been developed by a stepwise synthesis strategy. The synthesized COFs exhibit high hydrophilicity and excellent stability in strong acid or base (e.g., 12 m NaOH or HCl) and boiling water. These features make them ideal platforms for proton conduction applications. Upon loading with H₃PO₄, the COFs (H₃PO₄@COFs) realize an ultrahigh proton conductivity of 1.13×10^?1 S cm^?1, the highest among all COF materials, and maintain high proton conductivity across a wide relative humidity (40–100 %) and temperature range (20–80 °C). Furthermore, membrane electrode assemblies were fabricated using H₃PO₄@COFs as the solid electrolyte membrane for proton exchange resulting in a maximum power density of 81 mW cm^?2 and a maximum current density of 456 mA cm^?2, which exceeds all previously reported COF materials.     

Novel sulfonated poly (ether ether ketone)/silica coated carbon nanotubes high‐performance composite membranes for direct methanol fuel cell

The major risk of using carbon nanotubes (CNTs) to modify proton exchange membranes (PEMs) in fuel cells is possible short‐circuiting due to the excellent electrical conductivity of CNTs. In this article, silica‐coated CNTs (SiO₂@CNTs) were successfully prepared by a simple sol–gel process and then used as a new additive in the preparation of sulfonated poly (ether ether ketone) (SPEEK)‐based composite membranes. The insulated and hydrophilic silica coated on the surface of CNTs not only eliminated the risk of short‐circuiting, but also enhanced the interfacial interaction between CNTs and SPEEK, and hence promoted the homogeneous dispersion of CNTs in the SPEEK matrix. Moreover, compared to the methanol permeability of the pure SPEEK membrane (3.42 × 10^?7 cm² s^?1), the SPEEK/SiO₂@CNT composite membrane with a SiO₂@CNT loading of 5 wt% exhibits almost one order of magnitude decrease of methanol crossover, while the proton conductivity still remained above 10^?2 S cm^?1 at room temperature. The obtained results expose the possibility of SPEEK/SiO₂@CNT membranes to be served as high‐performance PEMs in direct methanol fuel cells. Copyright © 2015 John Wiley & Sons, Ltd.     

Novel sulfonated block copolymer containing pendant alkylsulfonic acids: Syntheses,unique morphologies,and applications in proton exchange membrane

In this article, we report the syntheses and characterizations of a series of novel block polyelectrolytes, poly(styrene‐block‐sulfonated hydroxystyrene) (PS‐b‐sPHS), containing pendant sulfonic acid groups attached to the backbone via propyl spacers in the sPHS domain. PS‐b‐sPHS with various compositions were synthesized via anionic polymerization and the following analogous chemistry to achieve accurate control of molecular weight (M_w), narrow polydispersity and high degree of sulfonation. Proton exchange membranes (PEMs) were prepared from PS‐b‐sPHS with sulfonic acids in either potassium salts or tetra‐alkylammonium salts via solvent casting and following treatments. Some unique morphologies, such as hallow channels and lamellar arrangement of strings of beads, were observed as a consequence of equilibrium between microphase separation and columbic interactions between polyelectrolytes. The transportation properties were found to closely relate to the morphologies of the PEMs. The combination of microphase separation of block polyelectrolytes and freedom of movement of pendent alkylsulfonic acids was demonstrated to effectively enhance the proton transport and suppress the methanol crossover for the PEMs, leading to the selectivity higher than Nafion 117 by five times at most. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polymeric proton conducting membranes for medium temperature fuel cells (110–160°C)

The availability of stable polymeric membranes with good proton conductivity at medium temperatures is very important for the development of methanol PEM fuel cells. In view of this application, a systematic investigation of the conductivity of Nafion 117 and sulfonated polyether ether ketone (S-PEEK) membranes was performed as a function of relative humidity (r.h.) in a wide range of temperature (80–160°C). The occurrence of swelling/softening phenomena at high r.h. values prevented conductivity determinations above certain temperatures. Nevertheless, when r.h. was maintained at values lower than 80%, measurements were possible up to 160°C. The results showed that Nafion is a better proton conductor than S-PEEK at low r.h. values, especially at temperatures lower than 120°C. The differences in conductivity were, however, leveled out with the increasing r.h. and temperature. While at 100°C and 35% r.h. the conductivity of S-PEEK 2.48 was about 30 times lower than the conductivity of Nafion, both membranes reached a comparable conductivity (4×10⁻² S cm⁻¹) at 160°C and 75% r.h. The effect of superacidity and crystallization of the polymers on the conductivity, as well as the possibility of using Nafion and S-PEEK membranes in medium temperature fuel cells, are discussed.     

Non-Fluorinated Polymer Composite Proton Exchange Membranes for Fuel Cell Applications – A Review

The critical component of a proton exchange membrane fuel cell (PEMFC) system is the proton exchange membrane (PEM). Perfluorosulfonic acid membranes such as Nafion are currently used for PEMFCs in industry, despite suffering from reduced proton conductivity due to dehydration at higher temperatures. However, operating at temperatures below 100 °C leads to cathode flooding, catalyst poisoning by CO, and complex system design with higher cost. Research has concentrated on the membrane material and on preparation methods to achieve high proton conductivity, thermal, mechanical and chemical stability, low fuel crossover and lower cost at high temperatures. Non-fluorinated polymers are a promising alternative. However, improving the efficiency at higher temperatures has necessitated modifications and the inclusion of inorganic materials in a polymer matrix to form a composite membrane can be an approach to reach the target performance, while still reducing costs. This review focuses on recent research in composite PEMs based on non-fluorinated polymers. Various inorganic fillers incorporated in the PEM structure are reviewed in terms of their properties and the effect on PEM fuel cell performance. The most reliable polymers and fillers with potential for high temperature proton exchange membranes (HTPEMs) are also discussed.