Polyvinylidenefluoride-co-hexafluoropropylene Research Articles

Polymer electrolytes based on Poly(VdF-co-HFP)/ionic liquid/carbonate membranes for high-performance lithium-ion batteries

In this study, we prepared the electrolytes by mixing the poly(vinylidene fluoride-co-hexafluoropropylene) (poly(VdF-co-HFP)) with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), ethylene carbonate (EC) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in several weight ratios. The as-prepared electrolytes reveal micropores with various morphologies depending on the added EC content. They also exhibit glass transition temperatures lower than 0 °C, decomposition temperatures higher than 200 °C and good limited oxygen index to about 34 wt%. Moreover, the addition of EC facilitates the improvement of ion transport without compromising the electrochemical stability, consequently resulting in high ionic conductivity around 2.3 × 10−3 S/cm at room temperature and a wide electrochemical window. In particular, the Li/LiFePO4 cells assembled with the electrolytes deliver remarkable discharge capacities of 143 mAh g−1, 120 mAh g−1 and 15 mAh g−1 at 0.2 C, 1 C and 5 C rates, respectively, with excellent capacity retention over 300 cycles at a rate of 0.2 C, as well as great interfacial stability after long-term cycling of charge-discharge. This study, in summary, provides a simple approach to prepare a quaternary electrolyte system and the findings indicate that the polymer electrolytes can be applied for high-performance LIBs.

Electrospun Nanofiber Membranes Incorporating PDMS-Aerogel Superhydrophobic Coating with Enhanced Flux and Improved Antiwettability in Membrane Distillation.

Electrospun nanofiber membranes (ENMs) have garnered increasing interest due to their controllable nanofiber structure and high void volume fraction properties in membrane distillation (MD). However, MD technology still faces limitations mainly due to low permeate flux and membrane wetting for feeds containing low surface tension compounds. Perfluorinated superhydrophobic membranes could be an alternative, but it has negative environmental impacts. Therefore, other low surface energy materials such as silica aerogel and polydimethylsiloxane (PDMS) have great relevancy in ENMs fabrication. Herein, we have reported the high flux and nonwettability of ENMs fabricated by electrospraying aerogel/polydimethylsiloxane (PDMS)/polyvinylidene fluoride (PVDF) over electrospinning polyvinylidene fluoride- co-hexafluoropropylene (PVDF-HFP) membrane (E-PH). Among various concentrations of aerogel, the 30% aerogel (E-M3-A30) dual layer membrane achieved highest superhydrophobicity (∼170° water contact angle), liquid entry pressure (LEP) of 129.5 ± 3.4 kPa, short water droplet bouncing performance (11.6 ms), low surface energy (4.18 ± 0.27 mN m-1) and high surface roughness ( Ra: 5.04 μm) with re-entrant structure. It also demonstrated nonwetting MD performance over a continuous 7 days operation of saline water (3.5% of NaCl), high antiwetting with harsh saline water containing 0.5 mM sodium dodecyl sulfate (SDS, 28.9 mN m-1), synthetic algal organic matter (AOM).

Enhancement of Na+ ion conduction in polymer blend electrolyte P(VdF-HFP) – PMMA- NaTf by the inclusion of EC

Polyvinylidenefluoride-co-hexafluoropropylene(PVdF-HFP) and polymethylmethacrylate (PMMA) and sodium triflate(NaTf) were used to prepare P(VdF-HFP)-PMMA-NaTf electrolytes using solution casting technique. The liquid plasticizer ethylene carbonate (EC) was added to the electrolytes in different concentrations say 10, 20, 30 and 40 wt% to achieve the enhancement of Na+ ion conduction at room temperature. Ionic conductivity of the samples was determined using AC impedance analysis and it was 7.86 × 10−8 S cm−1 for the polymer blend electrolyte at room temperature. Inclusion of EC was found to enhance the Na+ ion conduction and maximum value of ionic conductivity, 1.86 × 10−4 S cm−1, was obtained for the EC concentration of 30 wt%. This observation was explained on the basis of FTIR, XRD and AFM analysis of the samples which revealed the enhanced EC-polymer interaction and hence fast ion transport. Larger increase of dielectric constants and the reduced dielectric loss of EC added polymer blend electrolytes revealed the increase of the number of free Na+ ions. Thermal analysis of the samples was done through TGA-DTG technique and the thermal stability was found to decrease after the addition of EC.

Rapid Fabrication of Photoluminescent Electrospun Nanofibers without the Need of Chemical Polymeric Backbone Modifications

Photoluminescent electrospun nanofibers were fabricated by incorporating a cyclopentadiene derivative AIE-active luminogen within the polymeric matrices of polyvinylpyrrolidone (PVP), poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP), and poly(methylacrylate) (PMMA) under different solvents. Raman, infrared, and fluorescence spectroscopy showed the molecular integrity of the AIEgen is maintained during the electrospinning process while exhibiting a strong and uniformed phosphorescent radiative pathway of τaverage = 8.9 μs. This method allows for the rapid fabrication of photoluminescent nanofibers into a wide range of polymeric matrices without the need of chemical modifications. Taken together, the prepared electrospun phosphorescent nanofibers are a stepping stone for AIEgens to be applied in the digital manufacturing and design of smart textiles.

Fabrication and properties of PVDF and PVDF‐HFP microfiltration membranes

ABSTRACTPoly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) were used to fabricate porous microfiltration membranes via a thermally induced phase separation (TIPS) method, and dibutyl phthalate (DBP) was used as diluent. The effects of polymer concentration on structure and performance were studied in detail. In addition, the effect of incorporation of hexafluoropropylene (HFP) groups on the membrane was also investigated. The formation mechanism was proposed with the assistance of a phase diagram. The results showed that the incorporation of HFP groups resulted in a lower crystallization temperature (Tc) of the polymer/DBP system. In addition, the porosity, pure water flux, and ink solution flux decreased with increasing polymer concentration. In contrast, the water contact angle, ink rejection ratio, and mechanical properties had an increasing tendency. When the polymer concentration was 30 wt %, the obtained membrane was most suitable for microfiltration. Furthermore, the incorporation of HFP groups improved the properties of the obtained membrane, including better hydrophobicity, mechanical properties, antifouling property, and chemical resistance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46711.

Ion Transport Mechanisms in Single Ion Polymer Electrolytes for Application in Lithium Ion Batteries

In order to increase the energy density of lithium ion batteries, lithium metal is an attractive anode material based on its high specific capacity and low electrochemical potential. However, a major drawback of lithium metal anodes comprises dendrite growth due to unstable solid electrolyte interphase (SEI) resulting in severe safety hazards. Polymer electrolytes constitute a viable alternative to commonly utilized liquid electrolytes and are able to suppress or even avoid dendrite growth thereby providing increased safety. In particular, single ion conducting polymer electrolytes are promising for application in lithium ion or lithium metal batteries. In contrast to common dual ion conducting electrolytes, single ion conductors afford high transference numbers, hence significantly reducing polarization effects as only lithium ions are mobile whereas anions are bound at the polymer backbone. In this contribution we present various single ion conducting polymers composed of AB-type alternating block copolymers in which the lithium ions are bound to the backbone (e.g., bis(4-carboxyl benzene sulfonyl)imide moieties). Systematic variation of the constituents can control the achievable properties including the morphology, electrical and electrochemical properties of the resulting polymers. The electrolyte membranes fabricated for application in lithium meatal batteries are blends of single ion conducting aromatic polymers and a flexible linear polymer such as poly(vinylidene fluoride-co -hexafluoropropylene (PVDF-HFP). The appropriate ratio of the polymer blends is evaluated to yield membranes (swollen with thermally stable solvent solutions of ethylene carbonate and propylene carbonate (EC: PC, 1:1, v/v)), with increased ionic conductivity, reduced solvent uptake as well as sufficient flexibility and mechanical stability as well as reduced solvent uptake. We present optimized routes for the synthesis of single ion conducting polymers and suitable membrane compositions. Furthermore, feasible relations of both structural and physicochemical properties of the polymer membranes are discussed, particularly with respect to underlying ion transport properties or transport mechanisms, in this way potentially enabling controlled modification or adjustment of either the chemical structures or electrochemical properties of the polymer membranes. A morphology analysis is performed using small angle X-ray scattering (SAXS), while nuclear magnetic resonance spectroscopy (NMR) and electrochemical data including impedance as well as dielectric loss spectra are combined to unravel the major ion transport mechanisms and ion mobility in addition to ionic conductivity, complex permittivity, self-diffusion coefficients and transference numbers. Both the oxidative and reductive stability as well as cycling performance in NMC/ lithium metal cells are also presented. Profound understanding of the ion transport mechanisms and property relations in single ion conducting polymer electrolyte membranes is essential and will allow to design future electrolyte membranes having desired properties. Thereby, the requirement for different applications can be met and the application of safe and highly performing lithium metal batteries can be enabled.

Zn rechargeable cell with a gel polymer electrolyte based on an ionic liquid

Lithium rechargeable cells based on liquid electrolytes have been used for numerous applications due to their high performance. At present, it has been identified the possible hazardous effects of those cells. As an alternative, much research is focused on non-lithium rechargeable cells based on Gel Polymer Electrolytes (GPEs). Basically, a GPE is consisted of a salt and solvent mixture entrapped inside a polymer network. However, these solvents are toxic and flammable. This imposes a limitation for the safety of GPEs. This paper, reported about a Zn rechargeable cell having a GPE based on an ionic liquid which eliminates the need of solvents. The polymer used was Poly-Vinylidene Fluoride co Hexa FluoroPropylene (PVdF-co-HFP). As the salt, Zinc Tri-Fluoromethanesulfonate (Zn(CF3SO3)2 – ZnTF) was used and 1 Butyl 3 Methyl Immidazolium Tri-Fluoromethanesulfonate (1B3MITF) was used as the Ionic Liquid (IL). It was observed that there is an optimum salt concentration that results the highest conductivity in IL. A Zn rechargeable cell was fabricated using the optimized composition of the GPE. It was observed that the cell is suitable for low power requirements.

An enhanced electrochemical and cycling properties of novel boronic Ionic liquid based ternary gel polymer electrolytes for rechargeable Li/LiCoO2 cells

A new generation of boronic ionic liquid namely 1-ethyl-3-methylimidazolium difluoro(oxalate)borate (EMImDFOB) was synthesized by metathesis reaction between 1-ethyl-3-methylimiazolium bromide and lithium difluoro(oxalate)borate (LiDFOB). Ternary gel polymer electrolyte membranes were prepared using electrolyte mixture EMImDFOB/LiDFOB with poly vinylidenefluoride-co-hexafluoropropylene (PVdF-co-HFP) as a host matrix by facile solvent-casting method and plausibly demonstrated its feasibility to use in lithium ion batteries. Amongst ternary gel electrolyte membrane, DFOB-GPE3, which contained 80 wt% of EMImDFOB/LiDFOB and 20 wt% PVdF-co-HFP, showed excellent electrochemical and cycling behaviors. The highest ionic conductivity was found to be 10−3 Scm−1 at 378 K. Charge-discharge profile of Li/DFOB-GPE3/LiCoO2 coin cell displayed a maximum discharge capacity of 148.4 mAhg−1 at C/10 rate with impressive capacity retention capability and columbic efficiency at 298 K.

Superhydrophobic dual layer functionalized titanium dioxide/polyvinylidene fluoride-co-hexafluoropropylene (TiO2/PH) nanofibrous membrane for high flux membrane distillation

In this study, superhydrophobic dual layer membranes with highly porous structure were fabricated using electrospinning and electrospraying techniques. Electrospinning method was used to produce the support nanofibrous layer using polyvinylidene fluoride-co-hexafluoropropylene (PH) as the polymer and a mixed solvent system of N,N-Dimetylformamide (DMF) and acetone. Afterwards, hydrophobic, functionalized TiO2 nanoparticles were deposited on the surface of the support layer using the electrospraying technique. TiO2 chemical functionalization and their deposition on the support layer were investigated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. The effects of different concentrations of TiO2 nanoparticles (100 and 200wt%) and PH (7–9wt%) in the electrospraying solution on the dual layer membrane characteristics, such as surface morphology, pore size, porosity, water contact and sliding angle, mechanical properties, and liquid entry pressure (LEP) were thoroughly examined. The results show that porous superhydrophobic nanofibrous membranes with water contact angles higher than 150°, sliding angles lower than 10°, and low contact angle hysteresis were successfully fabricated. Consequently, the prepared membranes showed comparable LEP with the commercial polyvinylidene fluoride (PVDF) membrane, but at much higher porosity (>85%) and mean pore size (>0.70μm). Performance of the dual layer membranes, along with the single layer PH and commercial PVDF membranes, were carried out in a direct contact membrane distillation setup. The superhydrophobic nanofibrous membrane showed noticeably more stable operation compared with the neat PH membrane and consistently higher flux (38.71∓1.105Lm−2h−1) than the commercial PVDF membrane (26.64∓0.97Lm−2h−1) during 24h of operation.

Electrical studies on ionic liquid-based gel polymer electrolyte for its application in EDLCs

Ionic liquid-based gel polymer electrolyte (GPE) has been synthesized using standard solution cast technique. Different weight percent of ionic liquid, 1-Butyl-3-methylimidazolium chloride (BMIMCl) and liquid electrolyte, ethylene carbonate (EC)–propylene carbonate (PC)–tetra ethyl ammonium tetra fluoro borate (TEABF4) was incorporated in polymer, poly(vinylidene fluoride-co-hexafluoro propylene (PVdF-HFP) to obtain mechanically stable gel polymer electrolyte film (GPE) having maximum conductivity of ~10−3 S cm−1 at room temperature, which is acceptable from device fabrication point of view. Potential window and ionic transference number has been obtained to examine the potential limit and ionic characteristics of optimized GPE system. Temperature dependence behavior of electrical conductivity curve follows Arrhenius nature in the temperature range of 303–373 K. Pattern of dielectric constant and its loss as a function of frequency and temperature have been studied and is being explained on the basis of electrode interfacial polarization effect. Frequency-dependent conductivity spectra obey the Jonscher’s power law. Further, optimized composition of GPE has been tested successfully for its application in supercapacitor fabrication with activated charcoal as an electrode material. Maximum specific capacitance of 118.6 mF cm−2 equivalent to single electrode specific capacitance of 61.7 F g−1 have been observed for the optimized GPE film.

An efficient way to achieve high ionic conductivity and electrochemical stability of safer nonaflate anion-based ionic liquid gel polymer electrolytes (ILGPEs) for rechargeable lithium ion batteries

In the present study, we report a preparation of a new category of gel polymer electrolytes by immobilizing various compositions of lithium nonafluoro-1-butanesulfonate (LiNfO) salt and less viscous 1-ethyl-3-methylimidazolium nonafluoro-1-butanesulfonate (EMImNfO) ionic liquid in polyvinylidenefluoride-co-hexafluoropropylene (PVdF-co-HFP) matrix for their application in lithium ion batteries. Our study reveals that composition with 80% EMImNfO-LiNfO + 20% PVdF-co-HFP composition has the highest ionic conductivity of 10−2 S cm−1. The performance characteristics of highly conducting ionic liquid incorporated gel polymer electrolyte (ILGPE) is evaluated by using different electrochemical techniques such as chronoamperometry, cyclic voltammetry, and lithium compatibility test. ILGPEs exhibit excellent properties and will facilitate its use as a potential separator for lithium ion batteries.

Gel P (VdF/HFP) / PVAc / lithium hexafluorophosphate composite electrolyte containing nano ZnO filler for lithium ion batteries application: Effect of nano filler concentration on structure, thermal stability and transport properties

Nano ZnO filler incorporating gel co-polymer composites electrolytes membranes were prepared using a solution cast technique. All prepared membranes were characterized using different techniques such as X-ray diffraction (XRD), thermal analysis (TG, DSC), Fourier transform infra –red spectroscopy (FT-IR) and scanning electron microscopy (SEM). X-ray diffraction analysis showed the effect of lithium hexafluorophosphate (LiPF6), poly vinyl acetate (PVAc) and nano zinc oxide (ZnO) on the crystalline structure of the polyvinylidene fluoride –co– hexafluoro propylene (PVdF-co-HFP) matrix containing ethylene carbonate (EC) and diethyl carbonate (DEC) as plasticizers. FT-IR analysis confirmed the good dissolution of the LiPF6 salt and the good interaction of the nano ZnO filler with the co-polymer matrix. TG analysis showed the good thermal stability of the samples containing ZnO compared to the free one. Also, addition of nano ZnO filler enhanced the conductivity value of the co-polymer composites electrolytes. The sample containing 6 wt % of ZnO delivered the highest conductivity value of about 3.69 × 10−4 Ω−1 cm−1 at room temperature with a good thermal stability behavior (Td = 325 °C).

Nano lithium aluminate filler incorporating gel lithium triflate polymer composite: Preparation, characterization and application as an electrolyte in lithium ion batteries

Gel polymer composites electrolytes containing nano LiAlO2 as filler were prepared using a solution cast technique and characterized using different techniques such as X-ray diffraction (XRD), thermal analysis (TG, DSC), Fourier transform infra – red spectroscopy (FT-IR) and scanning electron microscope (SEM). X-ray diffraction analysis showed the effect of lithium tri fluoro methane sulphonate (LiCF3SO3), poly vinyl acetate (PVAc) and nano lithium aluminate (LiAlO2) on the crystalline structure of the poly vinylidene fluoride –co– hexa fluoro propylene (PVDF-co-HFP) matrix containing ethylene carbonate (EC) and diethyl carbonate (DEC) as plasticizers. FT-IR analysis confirmed both the good dissolution of the LiCF3SO3 salt and the good interaction of the nano LiAlO2 filler with the polymer matrix. TG analysis showed the good thermal stability of the LiAlO2 samples compared to the free one. Also, addition of nano LiAlO2 filler enhanced the conductivity value of the polymer composites electrolytes. The sample containing 2 wt% of LiAlO2 showed the highest conductivity value, 4.98 × 10−3 Ω −1 cm−1 at room temperature, with good thermal stability behavior (Td = 362 °C). This good conductive and thermally stable polymer nano composite electrolyte was evaluated as a promising membrane for lithium ion batteries application.

Water desalination using graphene-enhanced electrospun nanofiber membrane via air gap membrane distillation

This study demonstrates the preparation and desalination performance via air gap membrane distillation (AGMD) of a graphene-loaded electrospun nanofiber membrane. Different concentrations of graphene (0–10wt%) were incorporated in/on electrospun polyvinylidene fluoride-co-hexafluoropropylene (PH) membrane to obtain a robust, and superhydrophobic nanocomposite membrane. The results showed that graphene incorporation has significantly enhanced the membrane structure and properties with an optimal concentration of 5wt% (i.e., G5PH). Characterization of G5PH revealed membrane porosity of >88%, contact angle of >162° (superhydrophobic), and high liquid entry pressure (LEP) of >186kPa. These favourable properties led to a high and stable AGMD flux of 22.9L/m2h or LMH (compared with ~4.8 LMH for the commercial PVDF flat-sheet membrane) and excellent salt rejection (100%) for 60h of operation using 3.5wt% NaCl solution as feed (feed and coolant inlet temperatures of 60 and 20°C, respectively). A two-dimensional dynamic model to investigate the flux profile of the graphene/PH membrane is also introduced. The present study suggests that exploiting the interesting properties of nanofibers and graphene nanofillers through a facile electrospinning technique provides high potential towards the fabrication of a robust and high-performance AGMD membrane.

Electrospun nanofiber membranes incorporating fluorosilane-coated TiO2 nanocomposite for direct contact membrane distillation

The electrospinning technique as a method for fabricating hydrophobic membranes for membrane distillation (MD) has received much attention in recent times. In this study, TiO2 functionalized with 1H,1H,2H,2H-perfluorooctyltriethoxysilane was added directly to the dope solution for electrospinning in order to increase the hydrophobicity of the resulting MD membranes. Three concentrations (10%, 15% and 20%) of polyvinylidene fluoride-co-hexafluoropropylene (PH) dope solution were used for electrospinning with various amounts of TiO2 (1%, 5% and 10%) to generate nanofibers. The electrospun nanofiber membrane (ENM) of 20% PH with 10% TiO2 exhibited the highest surface hydrophobicity (contact angle=149°) resulting from good dispersion of the TiO2 particles, while the highest liquid entry pressure of 194.5kPa was observed for the ENM comprising 10% PH with 10% TiO2 due to its reduced pore sizes. Furthermore, the ENMs containing 10% TiO2 exhibited better flux and stable salt rejection than commercial and ENMs without TiO2. Notably, there was no severe wetting in the 20% PH ENM with 10% TiO2 over seven days of operation, despite the high salt concentration (7.0wt% NaCl) of the feed water.

Electrochemical and cycling performances of novel nonafluorobutanesulfonate (nonaflate) ionic liquid based ternary gel polymer electrolyte membranes for rechargeable lithium ion batteries

A new-fangled nonaflate anion based ionic liquid ternary gel polymer electrolytes was prepared and their function as an active separator for lithium ion battery applications has been characterized. The ionic liquid gel polymer electrolytes (IGPEs) were prepared using facile solution cast technique by incorporating electrolyte mixtures such as lithium nonafluorobutanesulfonate (LiNfO) and 1-butyl-3-methylimidazolium nonafluorobutanesulfonate (BMImNfO) in poly vinylidenefluoride-co-hexafluoropropylene (PVdF-co-HFP) matrix. The electrochemical performance and the interactions between PVdF-co-HFP, LiNfO and imidazolium-based ionic liquid BMImNfO are comparatively investigated. IGPEs obey Arrhenius relation and its ionic conductivity is found to be maximum of 10−2Scm−1 at 100°C. At low current rate, IGPE also exhibits good cycling performance with LiCoO2 and achieved a maximum discharge capacity of 138.1mAhg−1.

Flexible Supercapacitor Stackable with Solar Cells Based on PEDOT-Carbon Nanotube Nanocomposite Electrodes Using Ionic Liquid Gel Electrolytes for Solar Electricity Storage

Electrically conducting polymers (ECP) showing pseudo-capacitive property are actively researched as supercapacitor electrodes for energy storage. Nanocomposites with structured carbons contribute additional charge storage through electric double layer component enhancing the charge storage ability. The nanocomposites with CNTs hold additional promise to compensate for weak mechanical property of ECPs useful for flexible supercapacitor devices and enhance its electronic conductivity. Conventionally, the supercapacitor performance is evaluated using anion dopants in aqueous medium having voltage limitation and in organic electrolytes which are toxic. Ionic liquid gel electrolytes are promising but not widely studied for supercapacitor applications. Besides enabling stable high voltage operation, ionic liquid gel electrolyte makes supercapacitor assembly simple which can be configured as flat stackable layered device. These attributes are exploited in integration with the solar cells for the storage of solar electricity. We have investigated electrochemical and energy storage performance of poly(3,4-ethylenedioxy-thiophene) (PEDOT) and CNT nanocomposite electrodes based supercapacitors in the flexible solid-state format with ionic liquid gel electrolyte. In this work nanocomposite electrode was formed by co-deposition of PEDOT and CNT over the flexible graphite substrates using the galvanic pulsed electro-polymerization. The method involves ultrasonic dispersion of 1 wt% anionic CNT for 2 h in acetonitrile to which 0.1 M EDOT monomer and 0.2 M LiClO4 dopant was added. The PEDOT-CNT composite deposition is initiated as unipolar anodic current pulses of 4 mA.cm-2 amplitude with 10 ms ON time interspaced with 100 ms OFF time were sequentially applied for 20k cycles providing a unique way to control the electrode morphology. The symmetrical supercapacitor device was fabricated using ionic liquid 1-butyl-3-methylimidazolium tetrafluoro-borate ([BMIm]BF4) immobilized in poly(vinylidenefluoride -co-hexafluoropropylene (PVdF-HFP) forming a gel which was applied uniformly as ~50-70 μ layer sandwiched between the two PEDOT-CNT composite electrodes. With such stackable flat plate- supercapacitor device design, enhanced energy density is obtained and direct charge storage performance was realized when connected to solar cell module while mounted at the rear without affecting the form factor. The electrode morphology show randomly dispersed CNT of average diameter of 20-30 nm embedded within and encased by copolymerized PEDOT forming a 3-D network structure. The CNT is observed to enhance the PEDOT polymerization by facilitating charge transport at the substrate and also increase the electrode conductivity. Raman shifts in the 1425 cm−1 band assigned to symmetric Cα=Cβ (−O) stretching show in the formation of nanocomposite, the CNTs interact with the ethylenedioxy group of PEDOT resulting in high degree of conjugation and enhancrd charge transfer between CNTs and PEDOT molecular chains. Conjugated interaction is further confirmed by shift in disordered A1g mode of CNT. The cyclic voltammetry curves recorded over -1 to +1 V range showed fast and near vertical current switching at end potentials over wide 10-100 mV s-1 scan rates signifying highly capacitive property. Supercapacitor showed areal capacitance density of 357 mF.cm-2 yielding high single electrode specific capacitance of 297 F.g-1. The high areal specific capacitance in the PEDOT-CNT composite is due to dopant anion aggregation along the CNTs and enhanced conduction of dopant ions in ionic liquid through embedded CNT nanopores providing rapid pathways to delocalize the electrons from along the PEDOT molecular chain. Impedance data as Nyquist plots feature near vertical trend in the low frequency region and lower real impedance cutoff suggestive of highly capacitive property and low electrode-electrolyte resistance. Occurrence of high knee frequency of > 10 Hz suggests compared to PEDOT, the CNT nanocomposite has minimal diffusion limitation. Charge-discharge (CD) data at various currents cycled between 0.05-1.0V are triangular with low ESR of 20 Ohm.cm2 and Coulomb efficiency > 90%. Long-term CD cycling for 2000 cycles showed overall degradation of 21% with a nominal aggravation of merely 7% occurring in initial 400 cycles. These data show comparatively higher stability of CNT nanocomposite compared to PEDOT. The supercapacitor device functional properties were evaluated in terms of energy and power density parameters and presented as Ragone plots. Energy density of 18.3 Wh.kg-1 and corresponding power density of 5.1kW.kg-1 was recorded from CD data at 0.5 mA.cm-2 for 1V operation which is reasonably high for a gel electrolyte supercapacitor device. This paper would present detailed analysis of the pulse polymerization synthesis mechanism, microstructure and electrochemical properties of PEDOT-CNT nanocomposite. The supercapacitor device data on CV, CD, impedance and Ragone plots will be presented along with its efficacy in storing the solar electricity in combination with the solar cells.

Superhydrophobic nanofiber membrane containing carbon nanotubes for high-performance direct contact membrane distillation

Tailoring the membrane to have superhydrophobicity, coupled with high porosity, adequate pore sizes and narrow pore size distribution, and thin thickness could find potential application for high-performing direct contact membrane distillation (DCMD) process. Electrospinning is an excellent approach in fabricating nanofiber membranes with adequate properties required of an MD membrane. In this study, superhydrophobic, robust, mixed matrix polyvinylidene fluoride-co-hexafluoropropylene (PcH) nanofiber membranes were fabricated incorporating different concentrations (1–5wt%) of carbon nanotubes (CNTs) as nanofillers to impart additional mechanical and hydrophobic properties. The electrospun membrane has been designed to have two cohesive layers, a thin CNT/PcH top layer and a thick neat PcH bottom layer. Through different characterization techniques, CNTs were found to be widely distributed on/in the nanofibers, where more beads-on-string were formed at higher CNT content. However, the beads-on-string did not significantly affect the membrane porosity and pore size, as well as did not degrade the MD performance. Highly-porous structure was observed for all membranes and the nanofiber membrane showed comparable pore sizes with a commercial flat-sheet PVDF membrane but at a much higher porosity (>85%). The contact angle increased to superhydrophobic at 158.5° upon the incorporation of 5wt% CNTs in the nanofiber due to increased roughness and added effect of hydrophobic CNTs. The liquid entry pressure also increased when 5wt% CNT was added compared to the neat PcH nanofiber membrane. The resulting flux of the 5wt% CNT-incorporated nanofiber membrane (24–29.5L/m2h) was consistently higher than the commercial PVDF membrane (18–18.5L/m2h), with an average increase of 33–59% depending on the feed water type (35 or 70g/L NaCl solution) without compromising the salt rejection (>99.99%). The present nanofiber membranes containing CNTs with one-step electrospinning fabrication show high potential for DCMD desalination application.

Electrospun dual-layer nonwoven membrane for desalination by air gap membrane distillation

In the present study, dual-layer nanofiber nonwoven membranes were prepared by a facile electrospinning technique and applied for desalination by air gap membrane distillation (AGMD). Neat single and dual-layer nanofiber membranes composed of a hydrophobic polyvinylidene fluoride-co-hexafluoropropylene (PH) top layer with different supporting hydrophilic layer made of either polyvinyl alcohol (PVA), nylon-6 (N6), or polyacrylonitrile (PAN) nanofibers were fabricated with and without heat-press post-treatment. Surface characterization showed that the active layer (i.e., PH) of all electrospun nanofiber membranes (ENMs) exhibited a rough, highly porous (>80% porosity), and hydrophobic surface (CA>140°), while the other side was hydrophilic (CA<90°) with varying porosity. Heat-pressing the membrane resulted to thinner thickness (from >129μm to <100μm) and smaller pore sizes (<0.27μm). The AGMD experiments in a co-current flow set-up were carried out with constant inlet temperatures at the feed and permeate streams of 60±1.5 and 20±1.5°C, respectively. The AGMD module had a membrane area of 21cm2 and the thickness of the air gap was 3mm. The neat single and dual-layer ENMs showed a water permeate flux of about 10.9–15.5L/m2h (LMH) using 3.5wt.% NaCl solution as feed, which was much higher than that of a commercial PVDF membrane (~5LMH). The provision of a hydrophilic layer at the bottom layer enhanced the AGMD performance depending on the wettability and characteristics of the support layer. The PH/N6 dual-layer nanofiber membrane prepared under the optimum condition showed flux and salt rejection of 15.5LMH and 99.2%, respectively, which has good potential for AGMD application.

Formation of semi-IPN membrane composed of crosslinked SPS-[PVdF-co-HFP/Nafion] for application in DMFC: A fine tuning between crosslinker and initiator

The semi-interpenetrating (semi-IPN) membrane composed of crosslinked sulfonated polystyrene (SPS) within the host blend of PVdF-co-HFP (Polyvinylidenefluoride-co-hexafluoropropylene) and Nafion has already been tested as a promising polymer electrolyte membrane (PEM) in terms of improved water uptake, proton conductivity and electrical efficiency for application in the direct methanol fuel cell (DMFC). These desired results have generated further curiosity about a fine tuning between the contents of divinyl benzene (DVB) as a crosslinker and azobisisobutyronitrile (AIBN) as an initiator for the optimization of PEM characteristics. It has been observed that an increase in AIBN content leads to an acceptable degree of water uptake, swelling ratio and proton conductivity in PEM, while higher DVB content causes declined methanol crossover, leading to higher membrane selectivity. These two opposing effects are optimized in terms of proton conductivity, tensile strength and membrane selectivity for the membrane consisting of 0.4 wt% of AIBN and 1.2 wt% of DVB. Moreover, the maximum power density obtained for the membrane having optimum selectivity is 56 mW cm−2, when analyzed at 90 °C. These results indicate that one can achieve a high power density in comparison to Nafion by fine tuning the contents of initiator and cross-linker during the synthesis of the semi-IPN membrane.