Synthesis and characterization of bisulfonated poly(vinyl alcohol)/graphene oxide composite membranes with improved proton exchange capabilities

Composite membranes based on poly(vinyl alcohol) (PVA) and graphene oxide (GO) were prepared by solution-casting method to be used as proton exchange membranes (PEMs) in fuel cell (FC) applications. Bisulfonation was employed as a strategy to enhance the proton conductivity of these membranes. First, a direct sulfonation of the polymer matrix was accomplished by intra-sulfonation of the polymer matrix with propane sultone, followed by the inter-sulfonation of the polymer chains using sulfosuccinic acid (SSA) as a crosslinking agent. Furthermore, the addition of graphene oxide (GO) as inorganic filler was also evaluated to enhance the proton-conducting of the composite membranes. These membranes were fully characterized by scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and tensile tests. Besides, the proton conductivity of these membranes in a fully hydrated state was also analyzed by electrochemical impedance spectroscopy (EIS). The effect of the intra- and inter-sulfonation of the polymer matrix on the structural, morphological, thermal and mechanical properties of the membranes were determined. Increasing the density of sulfonic acid groups in the membranes resulted in a trade-off between a better proton conductivity (improving from 0.26 to 1.00 mS/cm) and a decreased thermal and mechanical stability. In contrast, the incorporation of GO nanoparticles into the polymer matrix improved the thermal and mechanical stability of both bisulfonated composite membranes. The proton conductivity appreciably increased by the combination of bisulfonation and introduction of GO nanoparticles into the polymer matrix. The sPVA/30SSA/GO composite membrane exhibited a proton conductivity of 1.95 mS/cm at 25 °C. The combination of the GO nanoparticles with the chemical bisulfonation approach of PVA allows thus assembling promising proton exchange membrane candidates for fuel cell applications.     

Preparation of Nafion/sulfonated poly(phenylsilsesquioxane) nanocomposite as high temperature proton exchange membranes

Nafion/sulfonated poly(phenylmethyl silsesquioxane) (sPPSQ) composite membranes are fabricated using homogeneous dispersive mixing and a solvent casting method for direct dimethyl ether fuel cell (DDMEFC) applications operated above 100 °C. The inorganic conducting filler, sPPSQ significantly affects the characteristics in the nanocomposite membranes by functionalization with an organic sulfonic acid to PPSQ. Moreover, sPPSQ content plays an important role in membrane properties such as microstructure, proton conductivity, fuel crossover, and single cell performance test. With increasing sPPSQ content in the nanocomposite membrane, the proton conductivity increased and fuel crossover decreased. However, in a higher temperature range above 110 °C, Nafion/sPPSQ 5 wt.% composite membrane has the highest proton conductivity. Also, the DME permeability for the composite membrane with higher sPPSQ content increased sharply. The excessive sPPSQ content caused a large aggregation of inorganic fillers, leading to the deterioration of membrane properties. In this study, the optimal sPPSQ content for maximizing the DDMEFC performance was 5 wt.%. Our nanocomposite membranes demonstrated proton conductivities as high as 1.57 × 10⁻¹ S/cm at 120 °C, which is higher than that of Nafion. The cell performances were compared to Nafion/sPPSQ composite membrane with Nafion 115, and the composite membrane with sPPSQ yielded better cell performance than Nafion 115 at temperatures ranging from 100 to 120 °C and at pressures from 1 to 2 bar.     

Hybrid organic-inorganic nanostructured membranes for high temperature proton exchange membranes fuel cells (PEMFC)

Compared to internal combustion engines, proton-exchange membrane fuel cells (PEMFC) operate with zero emissions of environmental pollutants being this an adequate choice for transportation field. The increase of the operation temperature of PEMFC above 130°C is a great concern for the commercial application of the cells in electric vehicles. Hybrid organic-inorganic nanostructured membranes can combine the main properties to meet this objective: high proton conductivity along with thermal and chemical stability. The possibilities of synthesis of these hybrid structures grow exponentially with the combination of sol-gel chemistry and monomers. Three different approaches have been followed for obtaining hybrid membranes that present the properties needed for application in high temperature PEMFC: development of methacrylate and epoxy structures, and optimization of the inorganic component incorporating phosphorus. Proton conductivity has been endowed on the base of three strategies: a high concentration of hydroxyl groups from inorganic component, groups through sulfonation of phenyl rings, and incorporation of tungstophosphoric acid, H₃[P(W₃O₁₀)₄].     

Development of novel cellulose acetate-g-poly(sodium 4-styrenesulfonate) proton conducting polyelectrolyte polymer

The development of cheap and efficient proton conducting polymers attracts scientists' attention, resulting in its potential role in fuel cell applications. This work synthesized a novel cellulose acetate-g-poly(sodium 4-styrene sulfonate) via free radical polymerization using potassium persulfate (KPS) as an initiator. The effects of varying KPS concentration, cellulose acetate (CA), sodium 4-styrene sulfonate (Na-SSA) content, reaction time, and temperature on the grafting parameters were studied. Grafting parameters, including the grafting yield (GY %), Add-on (%) and grafting efficiency (GE %) of the grafting reaction, were evaluated. Additionally, FTIR, TGA, DSC, ¹HNMR and EDX analyses were studied. The developed graft copolymers membranes illustrated increased water uptake values and ion exchange capacity (IEC) with the add-on (%). Furthermore, the proton conductivity of the developed graft copolymers was found superior (4.77 × 10⁻³ S.cm⁻¹) to the pristine CA membrane (0.035 × 10⁻³ S.cm⁻¹).     

Preparation and characterization of fluorine-containing polybenzimidazole/imidazole hybrid membranes for proton exchange membrane fuel cells

Polybenzimidazole (PBI)/imidazole (Im) hybrid membranes were prepared from an organosoluble, fluorine-containing PBI with Im. The thermal decomposition of the PBI/Im hybrid membranes occurred at about 160 °C. The conductivities of the acid doped PBI/Im hybrid membranes increased with both the temperature and the Im content. The conductivity of acid doped PBI-40Im (molar ratio of Im/PBI = 40) reached 3.1 × 10⁻³ (S/cm) at 160 °C. The proton conductivities of PBI/Im hybrid membranes were over 2 × 10⁻³ (S/cm) at 90 °C and 90% relative humidity. The addition of Im could reduce the mechanical properties and methanol barrier ability of the PBI membranes.     

Synthesis and properties of water stable poly[bis(benzimidazobenzisoquinolinone)] ionomers for proton exchange membranes fuel cells

A novel sulfonated tetraamine, di(triethylammonium)-4,4′-bis(3,4-diaminophenoxy)biphenyl-3,3′-disulfonate (BAPBDS), was successfully synthesized by nucleophilic aromatic substitution of 4,4′-dihydroxybiphenyl with 5-chloro-2-nitroaniline, followed by sulfonation and reduction. A high-temperature polycondensation of sulfonated tetraamine, non-sulfonated tetraamine (4,4′-bis(3,4-aminophenoxy)biphenyl) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (a) or 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianydride (b) gave the poly[bis(benzimidazobenzisoquinolinones)] ionomers SPBIBI-a(x) or SPBIBI-b(x), where x refers to the molar percentage of the sulfonated tetraamine monomer. Flexible and tough membranes of high mechanical strength were obtained by solution casting and the electrolyte properties of the polymers were intensively investigated. The ionomer membranes displayed excellent dimensional and hydrolytic stabilities. Moreover, these novel membranes showed proton conductivities comparable to that of Nafion 117, especially at high temperature. In addition, the proton conductivities of the SPBIBI-a ionomer membranes were found to be higher than those of the SPBIBI-b ones due to the weakened acid–base interactions between the pyridinone ring and the sulfonic acid groups. The highest proton conductivity (0.174 S/cm) was obtained for the SPBIBI-a(100) membrane at 100 °C, with an IEC of 2.65 mequiv./g. A combination of excellent dimensional and hydrolytic stabilities indicated that the SPBIBI ionomers were good candidate materials for proton exchange membrane in fuel cell applications.     

Introduction of CdO nanoparticles into graphene and graphene oxide nanosheets for increasing adsorption capacity of Cr from wastewater collected from petroleum refinery

Graphene and graphene oxide nanocomposites are promising and fascinating types of nanocomposites because of their fast kinetics, unique affinity for heavy metals, and greater specific area. Initially, in this study, a green, cost-effective and facile method was utilized to prepare G, GO, CdO, G-CdO, and CdO-GO nanocomposites by Azadirachta indica and then analyzed using UV–vis spectroscopy, Fourier-transform spectroscopy, Raman, X-ray diffraction and scanning electron microscope. The synthesized nanocomposites were explored for chromium elimination from wastewater collected from a petroleum refinery. CdO-GO, G-CdO nanocomposites showed remarkable adsorption capability of 699 and 430 mg g^?1 which was higher than G (80 mg g^?1), GO (65 mg g^?1), and CdO (400 mg g^?1). Based on the R² (correlation coefficient) values, the kinetic statistics of Cr (VI) onto the G, GO, CdO, G-CdO, and CdO-GO were effectively obeyed by pseudo-second-order than by all other models. The R² values for the five nano-bioadsorbents were extraordinarily high (R² greater than 0.990) which ensured the chemisorption. This study ensured that the adsorptive removal rate of Cr (VI) is still greater than 85 % after repeated five cycles, suggesting that the produced nanomaterials are adsorbents with strong recyclability.     

One-step facile synthesis of poly(N-vinylcarbazole)-polypyrrole/graphene oxide nanocomposites: enhanced solubility,thermal stability and good electrical conductivity

Poly (N-vinylcarbazole)-polypyrrole/graphene oxide (PNVC-Ppy/GO) nanocomposites have been successfully prepared by one-step chemical oxidative polymerization using ferric chloride hexahydrate in the presence of dodecyl benzene sulfonic acid. The composite formation, morphology and the crystallinity of the composite have been characterized by FTIR spectroscopy, FESEM, and XRD, respectively. The incorporation of graphene oxide into the PNVC-Ppy matrix induces interaction between graphene oxide and PNVC-Ppy via hydrogen bonding and π–π* stacking. This π–π* stacking between the GO layers and PNVC-Ppy produces longer conjugation length leading to a higher solubility in organic solvents and enhanced electron mobility. The information of conjugation chain length and charge transfer capacity at the interface of the composite has been obtained from the Raman spectroscopy and photolumincience spectroscopy. The improved thermal stability and electrical d.c. conductivity (0.123?S/cm) of the resulting PNVC-Ppy/GO composite compared to the PNVC–Ppy copolymer (0.08?S/cm) is attributed to the incorporation of graphene oxide in the composite.     

Enhanced specific energy of silver-doped MnO2/graphene oxide electrodes as facile fabrication symmetric supercapacitor device

The present work is about the preparation of silver (Ag)-doped manganese oxide (MnO₂)/graphene oxide (GO) composite thin films are deposited by a facile and binder-free successive ionic layer adsorption and reaction (SILAR) method for the first time. The Brunauer-Emmett-Teller (BET) study revealed the nanosheets of MnO₂–Ag3/GO exhibit high specific surface area of 192 m² g^?1. The tailored flower-like morphology and interconnected nanosheets of MnO₂–Ag3/GO electrodes achieved high electrochemical performance. The maximum specific capacitance (Cs) of 877 F g^?1 at the scan rate of 5 mV s^?1 is obtained for MnO₂–Ag3/GO electrode tested in 1 M sodium sulfate (Na₂SO₄) electrolyte with capacity retention of 94.57% after 5000 cycling stability. The MnO₂–Ag3/GO composite-based flexible solid state symmetric supercapacitor (FSS-SSC) device delivered Cs as 164 F g^?1 with specific energy of 57 Wh kg^?1 at specific power of 1.6 kW kg^?1 and capacitive retention of 94% after 10,000 cycles.     

Sulfonated poly(arylene thioether phosphine oxide)s copolymers for proton exchange membrane fuel cells

High molecular weight sulfonated poly(arylene thioether phosphine oxide)s (sPATPO) with various sulfonation degrees were prepared directly by aromatic nucleophilic polycondensation of 4,4′-thiobisbenzenethiol with sulfonated bis(4-fluorophenyl) phenyl phosphine oxide and bis(4-fluorophenyl) phenyl phosphine oxide. sPATPO in the acid form with sulfonation degrees of 60–100% exhibits a glass transition temperature higher than 230 °C and a 5% weight loss temperature above 400 °C, indicating high thermal stability. sPATPO with a high sulfonation degree shows high proton conductivity and good resistance to swelling as well. For instance, sPATPO-70 displays the conductivity of 0.0783 S/cm and a swelling ratio of 11.6% at 90 °C. TEM micrographs showed that sPATPO membranes with a high sulfonation degree could form continuous ion channels, which are favorable for improving the proton conductivity but harmful to remaining the mechanical property. The membranes are expected to show good performances in fuel cell applications.     

Permeation of water as a tool for characterizing the effect of solvent, film thickness and water solubility in cellulose acetate membranes

Cellulose acetate membranes have been used in many applications; of particular interest are reverse osmosis systems, and as a neutral matrix for incorporation of different polymers (e.g., conducting polymers), inorganic ions (e.g., lanthanides) and organic (e.g., pharmaceutical) compounds. The properties of the new polymers derived from cellulose acetate or blends depend on those of cellulose acetate. This work presents an attempt to find links between thermodynamic and kinetic properties of cellulose acetate membranes in equilibrium with water. Water diffusion coefficients in cellulose acetate membranes are reported, measured with a simple water permeation technique. The comparison of these values with the percentage of water uptake and polymer thickness leads to interesting conclusions related with different polymer properties.     

A facile method for preparation of cardo poly(aryl ether sulfone) bearing pendent sulfoalkyl groups as proton exchange membranes

A series of cardo poly(aryl ether sulfone) copolymers bearing pendent sulfonic acid groups(SPES-X) have been prepared by a facile chemical graft method. The structure was confirmed by 1H-NMR spectra. The side-chain-type SPES-X membranes show significantly reduced swelling behavior and excellent mechanical properties as well as appropriate proton conductivity compared to the main-chain-type sulfonated polymers with similar ion exchange capacity(IEC) value. Moreover, they show methanol permeability in the range of 0.6 × 10-7-5.7 × 10-7 cm2/s which is lower than that of Nafion 117. All the results indicate that the SPES-X membranes are promising candidates for the direct methanol fuel cells.     

Surface modified multi‐walled carbon nanotubes and Nafion nanocomposite membranes for use in fuel cell applications

The preparation and characterization of the nanocomposite polyelectrolyte membranes, based on Nafion, sulfonated multi‐walled carbon nanotubes (MWCNT‐SO₃H) and imidazole modified multi‐walled carbon nanotubes (MWCNT‐Im), for direct methanol fuel cell applications is described. The results showed that the modification of multi‐walled carbon nanotubes (MWCNT) with proton‐conducting groups (sulfonic acid groups or imidazole groups) could enhance the proton conductivity of the nanocomposite membranes in comparison to Nafion 117. Regarding the interactions between the protonated imidazole groups, grafted on the surface of MWCNT, and the negatively charged sulfonic acid groups of Nafion, new electrostatic interactions can be formed in the interface of the Nafion and MWCNT‐Im, which result in both lower methanol permeability and higher proton conductivity. The physical characteristics of these manufactured nanocomposite membranes were investigated by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, water uptake, methanol permeability, and ion exchange capacity, as well as proton conductivity. The Nafion/MWCNT‐Im membranes showed the higher proton conductivity, lower methanol permeability, and, as a consequence, a higher selectivity parameter in comparison to the neat Nafion or Nafion membrane containing MWCNT‐SO₃H or ─OH functionalized multi‐walled carbon nanotubes (MWCNT‐OH) membranes. The obtained results indicated that the Nafion/MWCNT‐Im membranes could be used as efficient polyelectrolyte membranes for direct methanol fuel cell applications.     

质子交换膜燃料电池零下冷启动研究

在零下启动过程中,质子交换膜燃料电池阴极中氧气还原反应生成的水会在催化剂层内部结冰,因而阻碍氧气传输,覆盖催化剂层反应活性位点,降低电化学活性面积,影响燃料电池发电性能,甚至会导致零下启动失败;同时,结冰/融化循环还会破坏膜电极结构,影响燃料电池寿命。因此,质子交换膜燃料电池零下启动技术的研究对促进燃料电池汽车的推广应用有重要意义。本文针对质子交换膜燃料电池的零下启动过程,从实验研究、机理解释、模型分析及策略开发等角度对文献内容进行了梳理,并对涉及质子交换膜燃料电池零下启动过程的专利技术进行了总结。     

Recent progress in applications of graphene oxide for gas sensing: A review

This paper is a review of the recent progress on gas sensors using graphene oxide (GO). GO is not a new material but its unique features have recently been of interest for gas sensing applications, and not just as an intermediate for reduced graphene oxide (RGO). Graphene and RGO have been well known gas-sensing materials, but GO is also an attractive sensing material that has been well studied these last few years. The functional groups on GO nanosheets play important roles in adsorbing gas molecules, and the electric or optical properties of GO materials change with exposure to certain gases. Addition of metal nanoparticles and metal oxide nanocomposites is an effective way to make GO materials selective and sensitive to analyte gases. In this paper, several applications of GO based sensors are summarized for detection of water vapor, NO₂, H₂, NH₃, H₂S, and organic vapors. Also binding energies of gas molecules onto graphene and the oxygenous functional groups are summarized, and problems and possible solutions are discussed for the GO-based gas sensors.     

Sulfonated poly(phenylene oxide) membranes as promising materials for new proton exchange membranes

Poly(phenylene oxide) (PPO) was sulfonated to different ion exchange capacities (IECs) using chlorosulfonic acid as the sulfonating agent. Tough, ductile films were successfully cast from sulfonated PPO (SPPO) solutions in N‐methyl‐2‐pyrrolidone or N,N‐dimethylformamide. The obtained membranes had good thermal stability revealed by thermogravimetric analysis (TGA). Compared with an unsulfonated PPO membrane, the hydrophilicity and water uptake of the SPPO membranes were enhanced, as shown by reduced contact angles with water. The tensile test indicated that the SPPO membranes with IEC ranging from 0.77 to 2.63 meq/g were tough and strong at ambient conditions and still maintained adequate mechanical strength after immersion in water at room temperature for 24 hr. The results of wide‐angle X‐ray diffraction (WAXD) showed amorphous structures for PPO and SPPO while the peak intensity decreased after sulfonation. The proton conductivity of these SPPO membranes was measured as 1.16 × 10^?2 S/cm at ambient temperature, which is comparable to that of Nafion 112 at similar conditions and in the range needed for high‐performance fuel cell proton exchange membranes. Copyright © 2006 John Wiley & Sons, Ltd.     

Sulfonated poly(ether sulfone)s with binaphthyl units as proton exchange membranes for fuel cell application

Sulfonated poly(ether sulfone)s containing binaphthyl units (BNSHs) were successfully prepared for fuel cell application. BNSHs, which have very simple structures, were easily synthesized by postsulfonation of poly(1,1′‐dinaphthyl ether phenyl sulfone)s and gave tough, flexible, and transparent membranes by solvent casting. The BNSH membranes showed low water uptake compared to a typical sulfonated poly(ether ether sulfone) (BPSH‐40) membrane with a similar ion exchange capacity (IEC) value and water insolubility, even with a high IEC values of 3.19 mequiv/g because of their rigid and bulky structures. The BNSH‐100 membrane (IEC = 3.19 mequiv/g) exhibited excellent proton conductivity, which was comparable to or even higher than that of Nafion 117, over a range of 30–95% relative humidity (RH). The excellent proton conductivity, especially under low RH conditions, suggests that the BNSH‐100 membrane has excellent proton paths because of its high IEC value, and water insolubility due to the high hydrophobicity of the binaphthyl structure. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5827–5834, 2009     

Facile synthesis of cobalt oxide/reduced graphene oxide composites for electrochemical capacitor and sensor applications

Reduced graphene oxide sheets decorated with cobalt oxide nanoparticles (Co₃O₄/rGO) were produced using a hydrothermal method without surfactants. Both the reduction of GO and the formation of Co₃O₄ nanoparticles occurred simultaneously under this condition. At the same current density of 0.5 A g⁻¹, the Co₃O₄/rGO nanocomposites exhibited much a higher specific capacitance (545 F g⁻¹) than that of bare Co₃O₄ (100 F g⁻¹). On the other hand, for the detection of H₂O₂, the peak current of Co₃O₄/rGO was 4 times higher than that of Co₃O₄. Moreover, the resulting composite displayed a low detection limit of 0.62 μM and a high sensitivity of 28,500 μA mM⁻¹cm⁻² for the H₂O₂ sensor. These results suggest that the Co₃O₄/rGO nanocomposite is a promising material for both supercapacitor and non-enzymatic H₂O₂ sensor applications.     

End-group cross-linked membranes based on highly sulfonated poly(arylene ether sulfone) with vinyl functionalized graphene oxide as a cross-linker and a filler for proton exchange membrane fuel cell application

High-performance end-group cross-linked sulfonated poly(arylene ether sulfone) (SPAES) membranes are developed using thiolate-terminated SPAES with very high degree of sulfonation (DS) such as 90 mol% (SK-SPAES90) and vinyl functionalized graphene oxide (VGO) as a cross-linker and a filler through the thiol-Michael addition reaction. Since free-standing membranes for fuel cell application could not be prepared using the water soluble and highly proton conductive SPAES with high DS of 90 mol%, cross-linked SPAES90 membranes are intentionally prepared. The cross-linked membranes are found to have good physicochemical properties with excellent proton conductivity that can be applied for the proton exchange membrane. In particular, the cross-linked SPAES90 membrane prepared using 1.0 wt% of VGO exhibits better dimensional stability than a SPAES70 membrane from the linear SPAES with DS of 70 mol% and the proton conductivities of this membrane are larger than those of Nafion 211 at 80 °C under different relative humidity conditions (40%-95%).     

Evaluation of the permeability of modified cellulose acetate propionate membranes for use in biosensors based on hydrogen peroxide detection

Phase inversion cellulose acetate propionate membranes showed lowpermeability to hydrogen peroxide aqueous solutions. Their permeability wasincreased by alkaline hydrolysis of the ester linking units. However, thepermeability remained lower than that of an unsubstituted cellulose membrane.The inclusion of hydroxypropyl cellulose in the membrane formulation, followedby an alkaline hydrolysis step, increased permeability to hydrogen peroxideaqueous solutions to 29% of that of an unsubstituted cellulose membrane.