•A membrane with a sandwiched structure has been prepared.•It exhibits high proton conductivity and low methanol permeability.•Its high performance arises from its sandwiched structure.•The cell with this membrane shows high power density and output voltage.Sulfonated poly(ether ether ketone) (SPEEK) membranes have been deposited on the both sides of a sulfonic acid functionalized graphene oxide (SGO) paper to form a proton exchange membrane (PEM) with a sandwiched structure. The obtained SPEEK/SGO/SPEEK membrane could exhibit proton conductivity close to Nafion® 112 and lower methanol permeability. The use of this SPEEK/SGO/SPEEK membrane greatly improves the performance of the semi-passive direct methanol fuel cell (DMFC). The semi-passive DMFC with the SPEEK/SGO/SPEEK membrane is found to be capable of delivering the peak power density 60% higher than that with the commercial Nafion® 112. This, along with its comparable durability to Nafion® 112, strongly suggests the great promise of using the SPEEK/SGO/SPEEK membrane as the PEM.The SPEEK/SGO/SPEEK membrane with a sandwiched structure has been used as proton exchange membrane and exhibits high performance when used in a direct methanol fuel cell.Download high-res image (298KB)Download full-size image

•The sandwiched SPEEK/SHGO/SPEEK membrane has been prepared.•The membrane exhibits high proton conductivity and low methanol permeability.•The holey structure of SHGO provides an additional path for the proton transport.•The sandwiched structure plays an important role in its high performance.•The cell with the sandwiched membrane show high performance and good stability.The sandwiched membrane which consists of the sulfonated holey graphene oxide paper with the deposition of the sulfonated poly(ether ether ketone) (SPEEK/SHGO/SPEEK) membrane on its both sides has been prepared. This membrane is reported to have higher proton conductivity (155.6 ± 1.6 mS cm−1), but lower methanol permeability (7.05 ± 0.21 × 10−6 cm2 s−1) than Nafion® 112 at 80 °C, whose respective values are 138.6 ± 1.4 mS cm−1 and 15.40 ± 0.46 × 10−6 cm2 s−1, respectively. The specific structure of the SHGO comprising the sulfonated and holey graphitic plane plays an important role in the high performance of the SPEEK/SHGO/SPEEK membrane. First, the sulfonated structure could increase the overall density of the sulfonic acid groups in the membranes, which increases the number of proton exchange groups participating in the proton transport. Second, the holey structure of the SHGO provides an additional path for the proton transport, which well avoids the blockage of the proton transport by the high aspect ratio graphitic planes. Third, the sulfonated and holey structure could also increase the interlayer spacing of the graphitic planes in the SHGO paper, which would promote the proton transport as well. Finally, the presence of the SHGO paper with the layer-by-layer stacked graphitic plane would effectively retard the diffusion of methanol through the membrane. When evaluated in the semi-passive direct methanol fuel cell (DMFC), the cell with the SPEEK/SHGO/SPEEK membrane shows higher stability and exhibits a maximum power density 61.1% higher than with Nafion® 112, which strongly suggests that the SPEEK/SHGO/SPEEK membrane could be used as the proton exchange membrane for DMFCs.A sandwiched SPEEK/SHGO/SPEEK membrane was synthesized and could exhibit high performance as a PEM for semi-passive direct methanol fuel cell.Download high-res image (244KB)Download full-size image

Herein, electrospinnability of perfluorosulfonic acid (PFSA)–polyvinylidene fluoride (PVDF) blends with different ratios of PVDF were investigated in detail. A well-formed nanofiber structure can be obtained only when the minimum ratio of PVDF in the blend reaches 9%. The reason was explained by the change in the properties, such as viscosity, conductivity, and surface tension, and interconnected aggregates in the blend solutions as revealed by dynamic light scattering (DLS) and the viscoelasticity behavior. After this, the property and morphology of the PFSA–PVDF nanofibers were investigated. SEM images showed that the average diameter of the nanofibers ranged from 75 to 170 nm. Small-angle X-ray scattering (SAXS) and DSC results showed that the microstructure of PFSA and the crystallization of PVDF in the nanofiber interfered with each other, which was attributed to the interaction between the backbone of PFSA and PVDF. CA and IEC revealed that the nanofibers were highly hydrophobic. Finally, the PFSA–PVDF nanofiber membranes were evaluated as a catalyst in the esterification reaction and as a separator in Li-ion battery. It was found that PFSA/PVDF nanofiber membrane with high PFSA ratio showed higher capacity and more stable cycle performance after 100 cycles as compared to the PVDF nanofiber, which could be used as a separator in Li-ion battery.

A new system based on dimethylacetamide, ethanolamine, and azobis(isobutyronitrile) (AIBN) was employed to synthesize porous Fe3O4 magnetic nanoparticles (MNPs) for the first time. The formation mechanism, morphology, and surface layer evolution of MNPs at the different AIBN ratios were revealed. The MNPs prepared without AIBN showed a randomly assembled morphology with a BET surface area of 174 m2/g, which is almost the highest reported until now. After AIBN was added, N2 gas and radical were produced by the thermal decomposition reaction. The high gas pressure enhanced the growth and self-assembly of nanounits, leading to a microsphere morphology. The radical caused a surface modification effect, which led to a decline in both the specific saturation magnetization and surface area of Fe3O4 MNPs. The surface of MNPs was fully modified when prepared at a high AIBN ratio. The methyl orange (MO) adsorption revealed that the modification coverage and surface composition of Fe3O4 MNPs are responsible for its adsorption capacity irrespective of the surface area. The naked Fe3O4 MNPs showed a limited adsorption capacity, which was saturated during the synthesis process. Moreover, the prepared MNPs(3) showed a maximum adsorption capacity of 46.7 mg/g. The surface coverage ratio revealed that its surface was almost fully covered with dye molecules. Moreover, it has shown good acidic stability and can be regenerated for dye adsorption applications.Keywords: Adsorption; Morphology evolution; Nanoparticles; Self-assembly; Surface modification;

The porous Polyvinylidene fluoride (PVDF) nanofibers were prepared by leaching method using polyethylene oxide (PEO) as porogen for the first time. The influences of the molecular weight (MW) and concentration of PEO, and the leaching solution on the morphology and the surface area of the porous PVDF nanofiber were systematically investigated. Polyethylene glycol 6000 (PEG6000) showed a better pore-forming effect. Optimized preparation parameters were obtained. With the ratio of PEG6000/PVDF reaching 1:1, the surface area of the resulting porous PVDF nanofiber was about three times higher than that of the pure PVDF nanofiber. Moreover, NaClO solution as leaching solution showed a very limited influence on the surface area of porous PVDF nanofiber. Afterwards, Ag NPs coated PVDF (Ag/PVDF) nanofiber was prepared by physical adsorption of Ag ions and in-situ reduction reaction using sodium borohydride as reductant. The photoactivity of Ag/PVDF nanofiber was evaluated by the photodegradation of methyl orange (MO) under visible light irradiation. Ag/PVDF nanofiber showed a better photoactivity than PVDF-Ag nanofiber prepared by the ex-situ blending method.

PAN/PAMAM blend nanofiber mats with different ratios were prepared by electrospinning process for the first time. Their structures were characterized by SEM, N2 adsorption/desorption and contact angle. It was found that PAN/PAMAM nanofiber with ratio of 12:3 has the highest surface area. The adsorption of methyl orange on blend nanofiber was investigated. With the ratio of PAMAM increasing in blend nanofiber, the adsorption capacity increased not very much. Overall the PAN/PAMAM nanofiber with ratio of 12:3 has the best property, its maximum adsorption capacity was found to be 120 mg/g although its surface area was only about 9.97 m2/g. It still maintained an efficient adsorption capacity even at 5th experiment, indicating an effective adsorbent for dye removal. The adsorption isotherm and adsorption kinetics were further investigated. The Freundlich isotherm provided the best fit for dye adsorption and the dynamical data fitted well with the second-order kinetic model. The possible mechanism was discussed.

Well-formed poly (vinyl alcohol) (PVA)–perfluorinated sulfonic acid (PFSA) nanofiber mats were fabricated via electrospinning process. Homogenous PFSA–PVA solutions were prepared by mixing PFSA-N, N-dimethylacetamide (DMAc) solution with PVA aqueous solution at different weight ratio. Increasing the weight ratio of PFSA in solution greatly increased the viscosity of the solution and slightly decreased the conductivity, which increased the diameter of the resulting PVA–PFSA nanofiber. The operating parameters such as tip to collector distance (TCD) and flow rate have a limited effect on the morphology of nanofibers, but high flow rate can improve the productivity. Ethyl acetate synthesis catalyzed by PVA–PFSA nanofiber mats was investigated, the results showed that all nanofibers have significantly catalytic activity, but the catalytic efficiency is related to the specific surface of PVA–PFSA nanofibers.