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The development of electrically conductive and high surface area carbon is important for the improvement of supercapacitor energy densities. Yttrium hydroxide microspindles were prepared and shown ...

Two-dimensional mesoporous hexagonal carbon sheets (MHCSs) have been prepared via a chemical vapor deposition method employing mesoporous Mg(OH)

Hierarchical porous carbons (HPCs) hold great promise in energy-related applications owing to their excellent chemical stability and well-developed porous structures. Attention has been drawn toward developing new synthetic strategies and precursor materials that permit greater control over composition, size, morphology, and pore structure. There is a growing trend of employing metal-organic frameworks (MOFs) as HPC precursors as their highly customizable characteristics favor new HPC syntheses. In this article, we report a biomimetically grown bacterial-templated MOF synthesis where the bacteria not only facilitate the formation of MOF nanocrystals but also provide morphology and porosity control. The resultant HPCs show improved electrochemical capacity behavior compared to pristine MOF-derived HPCs. Considering the broad availability of bacteria and ease of their production, in addition to significantly improved MOF growth efficiency on bacterial templates, we believe that the bacterial-templated MOF is a promising strategy to produce a new generation of HPCs.

A series of aromatic polyimides derived from 4,4′-hexafluoroisopropylidine diphthalic anhydride (6FDA), with different ratios of 2,4,6-trimethyl-1,3-phenylenediamine (DAM), and 3,5-diaminobenzoic a...

Although propylene/propane separation remains a challenge for industrial processes, carbon molecular sieve membranes (CMSMs) have the potential to replace traditional separation methods. A high molecular weight crosslinkable polyimide was utilized to fabricate CMSMs, which showed pure gas permeabilities in excess of 400 barrers with propylene/propane selectivities as high as 25. Mixed gas (C3H8:C3H6 50:50) measurements yielded a propylene permeability of 257 barrers and a selectivity of 20. CMSMs from thermally precrosslinked polymer precursors demonstrated a 98% propylene permeability retention after aging for 20 days under vacuum. Active gas flow conditions resulted in slightly lower permeability retention (92.5%) after 15 days of testing.

For electrodes in electrochemical double-layer capacitors, carbon nanofibers (CNFs) were prepared by thermal treatment of precursor polymer nanofibers, fabricated by electrospinning. Poly(acrylonitrile-co-vinylimidazole) (PAV) was employed as a precursor polymer of carbon nanofibers due to the effective cyclization of PAV polymer chains during thermal treatment compared to a typical precursor, polyacrylonitrile (PAN). PAV solutions with different comonomer compositions were prepared and electrospun to produce precursor nanofibers. Surface images obtained from scanning electron microscopy showed that their nanofibrous structure was well preserved after carbonization. It was also confirmed that electrospun PAV nanofibers were successfully converted to carbon nanofibers after the carbonization step by Raman spectroscopy. Carbon nanofiber electrodes derived from PAV showed higher specific capacitances and energy/power densities than those from PAN, which was tested by coin-type cells. It was also shown that PAV with an acrylonitrile/vinylimidazole composition of 83:17 is most promising for the carbon nanofiber precursor exhibiting a specific capacitance of 114 F/g. Their energy and power density are 70.1 Wh/kg at 1 A/g and 9.5 W/kg at 6 A/g, respectively. In addition, pouch cells were assembled to load the higher amount of electrode materials in the cells, and a box-like cyclic voltammetry was obtained with high capacitances.

Hybrid supercapacitors (SCs) made of carbon–metal oxide composites are devices which combine the advantages of electric double layer capacitors and pseudocapacitors viz high energy density, high power density and high cyclability. This is best achieved when the pseudocapacitive components are uniform in size and distribution on the conducting carbon support. Electrodes mats, fabricated from carbonized electrospun fibers generated from solutions of polyacrylonitrile (PAN) as the carbon source, cobalt (III) acetylacetonate as a metal oxide precursor, and polymethacrylic acid (PMAA) as a metal oxide precursor carrier were utilized in coin cell SCs. Fibers without the PMMA carrier were prepared for comparison. XRD and TGA showed conversion of the cobalt precursor to a mixture of cobalt and cobalt oxide (Co3O4). When the PMAA carrier was used, specific capacitance increased from 68 F g−1 in PAN-Co3O4 to 125 F g−1 in PAN-PMAA-Co3O4. The addition of PMAA to the system results in better uniformity, accessibility and dispersion of metal and metal oxide particles. Due to the relatively low surface area of carbonized samples, Co3O4 nanoparticles are the primary contributors to charge storage. The fabricated fibers show an energy density of 8.9 at 750 W kg−1, which is twice that of the fibers made without PMAA.

Lanthanum hydroxide nanorods were employed as both a template and catalyst for carbon synthesis by chemical vapor deposition. The resulting carbon possesses hollow nanorod shapes with graphitic walls. The hollow carbon nanorods were interconnected at some junctions forming a mazelike network, and the broken ends of the tubular carbon provide accessibility to the inner surface of the carbon, resulting in a surface area of 771 m2/g. The hollow carbon was tested as an electrode material for supercapacitors. A specific capacitance of 128 F/g, an energy density of 55 Wh/kg, and a power density of 1700 W/kg at 1 A/g were obtained using the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, as the electrolyte.

VTEC™ PI-1388 and 20 wt% (Al) NH2-MIL-53/VTEC™ PI-1388 mixed-matrix membranes (MMMs) with different thicknesses were tested for gas permeation of H2 and CO2 from 5 to 30 bar and from 35 to 300 °C. 50/50 H2/CO2 mixtures were also tested at 30 bar and 250 °C with stage cuts that ranged from 0.05 to 1. Gas permeation data show that the affinity of (Al) NH2-MIL-53 for VTEC™ PI-1388 is strong enough to perform gas separations under these conditions. At 30 bar and at temperatures above 200 °C, the performance of the MMMs for H2/CO2 separation improved significantly with increasing temperature. Specifically, the H2 permeability of the MMM at 300 °C increased by 70% with respect to that of VTEC™ PI-1388 (VTEC™ PI-1388: H2 = 85 Barrer, H2/CO2 = 4.0; MMM: H2 = 144 Barrer, H2/CO2 = 5.8). Gas mixture separations using VTEC™ PI-1388 and the MMM depended on the stage cut and reached a maximum H2/CO2 separation of 7.2 for VTEC™ PI-1388 and 7.5 for the MMM at a stage cut of 0.05.

Hierarchical porous carbons (HPCs) hold great promise in energy-related applications owing to their excellent chemical stability and well-developed porous structures. Attention has been drawn toward developing new synthetic strategies and precursor materials that permit greater control over composition, size, morphology, and pore structure. There is a growing trend of employing metal-organic frameworks (MOFs) as HPC precursors as their highly customizable characteristics favor new HPC syntheses. In this article, we report a biomimetically grown bacteria-templated MOF synthesis where the bacteria not only facilitate the formation of MOF nanocrystals, but also provides morphology and porosity control. The resultant HPCs show improved electrochemical capacity behavior compared to pristine MOF derived HPCs. Considering the broad availability of bacteria and ease of its production, in addition to significantly improved MOF growth efficiency on bacterial templates, we believe that bacteria-templated MOF is a promising strategy to produce a new generation of HPCs.

Hierarchical porous carbons (HPCs) hold great promise in energy-related applications owing to their excellent chemical stability and well-developed porous structures. Attention has been drawn toward developing new synthetic strategies and precursor materials that permit greater control over composition, size, morphology, and pore structure. There is a growing trend of employing metal-organic frameworks (MOFs) as HPC precursors as their highly customizable characteristics favor new HPC syntheses. In this article, we report a biomimetically grown bacteria-templated MOF synthesis where the bacteria not only facilitates the formation of MOF nanocrystals, but also provides morphology and porosity control. The resultant HPCs show improved electrochemical capacity behavior compared to pristine MOF derived HPCs. Considering the broad availability of bacteria and ease of its production, in addition to significantly improved MOF growth efficiency on bacterial templates, we believe that bacteria-templated MOF is a promising strategy to produce a new generation of HPCs.

An acrylonitrile based copolymer, poly(acrylonitrile-co-itaconic acid), P(AN-co-IA) was synthesized with different amounts of itaconic acid (IA) to study in situ porogen activity of IA to produce porous carbon nanofibers (CNFs) without any subsequent physical or chemical activation. The concept developed here avoids unnecessary and complex extra activation steps when fabricating CNFs which ultimately lead to lower char yields and uncontrollable pore sizes. The ability of COOH in P(AN-co-IA) to act as an in situ porogen by releasing CO2 during carbonization was verified by simultaneous thermogravimetric analysis-mass spectrometry compared to polyacrylonitrile (PAN). The specific surface area of PAN CNFs (27 m2 g-1) dramatically increases to 1427 m2 g-1 upon addition of ∼8 wt% IA without any ex situ activation. Furthermore, we confirmed that the porosity could be tuned by changing the IA content. The best electrochemical performance was obtained from the copolymer containing ∼8 wt% of IA, which gives a maximum specific capacitance of ∼93 F g-1 at a scan rate of 10 mV s-1 and energy density of ∼46 Wh kg-1 at 1 A g-1 without any subsequent physical or chemical activation.

Carbon nanofibers with high surface area have become promising electrode materials for supercapacitors because of their importance in increasing energy density. In this study, a high free volume polymer, 6FDA-DAM:DABA (6FDD) was blended with polybenzimidazole (PBI) in different ratios to obtain different compositions of PBI/6FDD immiscible polymer blends. Freestanding nanofiber mats were obtained via electrospinning using blend precursors dissolved in N,N-dimethylacetamide (DMAc). Subsequently, carbonization, followed by CO2 activation at 1000 °C was applied to convert the fiber mats into porous carbon nanofibers (CNFs). The addition of 6FDD shows significant effects on the microstructure and enhancement of the surface area of the CNFs. The obtained CNFs show specific surface area as high as 3010 m2 g−1 with pore sizes comparable to those of the electrolyte ions (PYR14TFSI). This provides good electrolyte accessibility to the pore of the carbon materials resulting in enhanced energy density compared to the CNFs obtained from pure PBI. Electrodes derived from PBI:6FDD (70 : 30) exhibited outstanding supercapacitor performance in coin cells with a specific capacitance of 142 F g−1 at the scan rate of 10 mV s−1 and energy density of 67.5 W h kg−1 at 1 A g−1 (58 W h kg−1 at 10 A g−1) thus demonstrating promising electrochemical performance for high performance energy storage system.

Thermally sensitive tetramethylammonium oxalate (TMAO) is incorporated as an in situ porogen into freestanding nonwoven nanofibers of polyacrylonitrile (PAN) produced by electrospinning. Supercapacitor electrode materials are prepared by a series of thermal treatments on these fibers, including stabilization followed by a single step carbonization and CO2 activation. The specific surface areas of the resultant carbon nanofibers (CNFs) are controlled by varying the amounts of TMAO in the precursor fibers. The electrochemical properties of the carbon nanofibers are characterized by cyclic voltammetry and galvanostatic charge–discharge tests. The highest surface area (2663 m2 g−1) and best electrochemical performance are obtained from PAN containing 0.1 wt% of TMAO (T10), which gives a maximum specific capacitance of 140 F g−1 at a scan rate of 10 mV s−1 in comparison to CNFs from PAN alone, which yielded only 90 F g−1. At a discharge current density of 1 A g−1, the obtained energy and power densities are 68 Wh kg−1 and 1.7 W kg−1, respectively, with capacitance retention of 80% after 1000 cycles.

Current energy demands and technological advancements will require a wide array of energy storage devices such as supercapcitors that can deliver large quantities of energy quickly. Electrochemical double layer capacitors (EDLC) are capable of cycling thousands of times with minimal drop in total capacitance, and when used with an ionic liquid electrolyte they can deliver higher energy densities due to high operating voltages. Surface area, and pore size distribution play a critical role in the performance of EDLC devices due to their relationship to capacitance. Therefore, electrospun carbon nanofibers are a promising EDLC electrode material due to their high surface area, conductivity, and cyclability. Their surface area can be tailored with the inclusion of in-situ porogens in the polymer precursor and activation during carbonization. Polymer derived carbon fibers have been produced from polyacrylonitrile (PAN) using immiscible blends with sacrificial polymers like polystyrene (PS). The resulting carbons have high surface areas (>2,000 m2g-1), but a wide distribution of pore sizes. Altering the miscibility of the sacrificial polymer with the copolymer poly(styrene-co-acrylonitrile) (SAN) affords a unique fiber morphology with a high microporosity. Figure 1

Flexible, free standing and binder-free electrodes were fabricated by electrospinning from a series of lignin: polyvinyl alcohol (PVA) polymer blends, followed by heat treatment. PVA has the dual function of facilitating the electrospinning of lignin and acting as a sacrificial polymer. Upon stabilization, carbonization and CO2 activation, carbon nanofibers (ACNF) derived from the lignin:PVA 80:20 blend displayed a high surface area of 2170 m2 g-1 and a mesopore volume of 0.365 cm3 g-1. ACNFs derived from all the compositions show high degrees of graphitization based on Raman analysis. Pyr14TFSI ionic liquid (IL), modified by mixing with propylene carbonate and ethylene carbonate to reduce the viscosity and increase the ionic conductivity, was used as a high-performance electrolyte. The resulting IL mixture exhibited a four-fold increase in ionic conductivity compared to the neat IL Coin cell supercapacitors using electrodes derived from lignin:PVA 80:20 blends and this electrolyte displayed 87 F g-1 specific capacitance and 38 Wh kg-1 energy density which is the highest reported energy density for lignin:PVA blends to date.

Wrinkled mesoporous silica (WMS) has been shown to be a promising material for catalysis and drug delivery. The WMS possesses a unique wrinkled structure with conical shaped pores radiating from the center to the surface of each particle. Lanthanum oxide was supported on wrinkled mesoporous silica as a hard template for the synthesis of graphitic carbon. The resulting carbon material retains the unique wrinkled structure and has high surface area (∼879 m2/g) as well as graphitic walls which were observed by transmission electron microscopy. The amount of La loaded onto the silica support plays a key role in the formation of the mechanically and chemically stable carbon material.

For the first time, porous organic polymers (POPs) based on the smallest buckybowl, corannulene (BB-POPs) have been synthesized. Three POPs were synthesised via Sonogashira co-polymerization of 1,2,5,6-tetrabromocorannulene and alkyne linkers. BB-POP-3 exhibits the highest surface area (SABET = 560 m2 g−1) and CO2 adsorption of 11.7 wt%, while they retain the redox properties of corannulene.

An immiscible polymer blend comprised of high-performance copolyimide 6FDA-DAM:DABA(3:2) (6FDD) and polybenzimidazole (PBI) was compatibilized using 2-methylimidazole (2-MI), a commercially available small molecule. Membranes were fabricated from blends of 6FDD:PBI (50:50) with and without 2-MI for H2/CO2 separations. The membranes demonstrated a matrix-droplet type microstructure as evident with scanning electron microscopy (SEM) imaging where 6FDD is the dispersed phase and PBI is the continuous phase. In addition, membranes with 2-MI demonstrated a uniform microstructure as observed by smaller and more uniformly dispersed 6FDD domains in contrast to 6FDD:PBI (50:50) blend membranes without 2-MI. This compatibilization effect of 2-MI was attributed to interfacial localization of 2-MI that lowers the interfacial energy similar to a surfactant. Upon the incorporation of 2-MI, the H2/CO2 selectivity improved remarkably, compared to the pure blend, and surpassed the Robeson's upper bound. To our knowledge, this is the first report of the use of a small molecule to compatibilize a high-performance immiscible polymer blend. This approach could afford a novel class of membranes in which immiscible polymer blends can be compatibilized in an economical and convenient fashion.

A novel nanohybrid material composed of vanadium pentoxide nanofibres (VNFs) and exfoliated graphene were prepared by in-situ growth of VNFs onto graphene nanosheets, and explicated as electrode material for supercapacitor applications. The existence of non-covalent interactions between VNFs and graphene surfaces was confirmed by Raman and Fourier transform infrared (FTIR) spectroscopes. Morphological analysis of the nanohybrid revealed that the VNF layer uniformly grown on the graphene surfaces, producing high specific surface area and good electronic or ionic conducing path. High crystalline structure with small d-spacing of the VNFs on graphene was observed in X-ray diffraction (XRD) analysis. Compared to pristine VNF, the VNF/graphene nanohybrid exhibited higher specific capacitance of 218 F g −1 at current density of 1 A g −1 , higher energy density of 22 Wh kg −1 and power density of 3594 W kg −1 . Asymmetric supercapacitor devices were prepared using the Spectracarb 2225 activated carbon cloth and VNF/graphene nanohybrid as positive and negative electrode, respectively. The asymmetric device exhibited capacitance of 279 F g −1 at 1 A g −1 , energy density of 37.2 Wh kg −1 and power density of 3743 W kg −1 , which are comparable and or superior to reported asymmetric devices consisting of carbon material and metal oxide as electrode components.

Polymer blends yield carbon materials with superior performances for supercapacitor applications since blending can lead to controlled and fine pore architectures. In this study, a supercapacitor electrode material derived from an immiscible polymer blend comprising polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA) was investigated. PAN was used as the carbonizing polymer while PMMA was used as the sacrificial polymer. The polymer blend solutions in DMF were electrospun to obtain freestanding nanofiber mats. The resulting mat was carbonized and activated by CO2 at 1000 °C to obtain porous carbon nanofibers (CNFs), as PAN converts to carbon and the sacrificial polymer decomposes creating pores. We demonstrated that the pore sizes can be tuned by varying the amount of PMMA loading in the blend compositions. PAN : PMMA (95 : 5), was found to be the optimum blend composition, affording the highest surface area of 2419 m2 g−1, higher degree of graphitization, higher carbon yield and lower charge transfer resistance among the blend compositions studied. Furthermore, the PAN : PMMA (95 : 5) CNFs showed the highest capacitance of 140 F g−1 and energy densities of 67 W h kg−1 at 3.5 V and 101 W h kg−1 at 4 V in an ionic electrolyte (EMITFSI) and also showed good cycling stability with 85% capacitance retention after 1000 cycles.

This study reports the fabrication of a highly hydrogen selective cross-linked polymer skin on a highly permeable mixed matrix membrane. Selective polymer skins were prepared by spin coating a thin layer of 6FDA-durene polymer onto ZIF-8/6FDA-durene mixed matrix membranes followed by subsequent cross-linking of the 6FDA-durene layer with ethylene diamine (EDA) vapor. Resultant membrane yielded significantly high gas pair selectivities for the separation of H2/CO2, H2/N2 and H2/CH4 of 29, 341, and 278, respectively, while also maintaining a high hydrogen permeability of 500 Barrers. The superior separation performances of this system surpass the current permeability–selectivity tradeoff limits (Robeson 2008 upper bound) for H2/CO2, H2/N2, and H2/CH4 separations. The present work elucidates the potential of fabricating a highly selective layer (thin skin) on a highly permeable membrane to obtain high permeability and high selectivity simultaneously.

The MIL-53 metal–organic framework (MOF) is known to change reversibly from an open-pore framework (MIL-53-ht) to a closed-pore framework (MIL-53-lt) depending on the temperature, pressure, or guest molecules absorbed. Three frameworks of the additive, MIL-53-as synthesized (MIL-53-as), MIL-53-ht, and MIL-53-lt, were prepared, characterized, and combined with Matrimid® to form mixed-matrix membranes (MMMs) for gas separations. The MIL-53-ht/Matrimid® MMMs exhibited higher values of permeability compared to Matrimid® as well as an increased CO 2 /CH 4 selectivity suggesting that the open-pore MIL-53 framework was maintained in the polymer matrix. In addition to higher permeability values, MIL-53-as/Matrimid® MMMs showed higher selectivity for gas pairs with kinetic diameters differing by ⩾0.5 A, including H 2 /O 2 , CO 2 /CH 4 , H 2 /CH 4 , and H 2 /N 2 , suggesting the presence of excess benzene dicarboxylic acid molecules within the pores that reduced its diameter enabling the material to discriminate between smaller and larger gases. MIL-53-lt did not retain its closed-pore form in the MMM. Rather, it irreversibly converted to the open-pore form (MIL-53-ht) due to the exchange of water present in the MIL-53 pores with chloroform solvent molecules during membrane casting and to pore penetration and confinement by Matrimid® polymer chains. This finding, that a polymer matrix stabilizes a MOF pore architecture within an MMM, is significant in that the desired selectivity of a MOF-MMM system may be achievable.

Crystals of highly soluble metal-organic polyhedra 18 (MOP-18) were synthesized and used as additives in Matrimid® 5218 to form mixed-matrix membranes. The MOP-18 linker was functionalized with long alkyl chains to help the crystals dissolve in common organic solvents. Scanning electron microscopy images revealed that the MOP-18 molecules do not aggregate into large particles even at loadings as high as 80 wt%, and the absence of polymer veins or polymer rigidification at the MOP-18/polymer interface was attributed to the improved dispersion of the MOP-18 molecules in the polymer matrix. The increase in the modulus of the membranes from 1.4 GPa for the pure polymer to 2.4 GPa upon incorporation of MOP-18 was attributed to the strong affinity of the polymer chains for the alkyl chains of MOP-18. Gas permeation results showed that the membranes became more permeable as the temperature was increased from 35 to 70 °C and that CO2 plasticization, which occurred at 35 °C and 8 bar, was minimized when the membranes were heated to 70 °C owing to an increase in the plasticization pressure to 21 bar. At 70 °C, the H2/CO2 selectivity remained constant when the transmembrane pressure was increased from 3 to 30 bar. The permeability and solubility data at high pressure and high temperature showed that the pore, core, and alkyl chains of MOP-18 introduced new sorption sites that significantly affected the gas transport properties of the membranes. The results also demonstrated that the MOP-18/polymer interface was mechanically stable at high pressure.

We have developed a novel approach for compatibilizing immiscible polymer blends using metal organic frameworks (MOFs). For the first time we demonstrated that the droplet diameter of the dispersed phase in a 1:1 immiscible polymer blend composed of 6FDA-DAM:DABA [copolymer of 4,4-hexafluoroisopropylidene diphthalic anhydride (6FDA), 2,4,6-trimethyl-1,3-phenylenediamine and 3,5-diaminobenzoic acid (DABA)], and polybenzimidazole (PBI), is dramatically reduced obtaining a uniform microstructure with the incorporation of as low as 5% (w/w) of the zeolitic imidazolate framework-8 (ZIF-8). This indicates a large improvement in the compatibility of the immiscible polymers with the inclusion of ZIF-8. As the ZIF-8 loading was further increased to 10% (w/w), the droplet diameter further decreased resulting in even higher compatibility. The compatibilizing effect can be attributed to a reduction in the interfacial energy of the immiscible polymers due to the interfacial localization of ZIF-8. This MOF based compatibilization of immiscible polymer blends can open up opportunities for the combination of different properties of polymers in membrane-based separations and in more applications.

Lignin was blended with polyacrylonitrile (PAN) in different ratios and fabricated into carbon nanofiber electrodes by electrospinning followed by thermal stabilization, carbonization and subsequent activation by CO2 of the carbonized mats. These carbon fiber electrodes exhibit high surface area, high mesoporosity, high graphitic content and high electrical conductivity. Activated carbon nanofiber mats derived from PAN:Lignin 70:30 blends display a surface area of 2370 m2 g-1 with 0.635 cm3 g-1 mesopore volume. These results are due to the selective partial removal of carbonized lignin during the activation step. Coin cell supercapacitors employing these electrodes exhibit 128 Fg-1 specific capacitance, 59 Wh kg-1 energy density and a 15 kW kg-1 power density when operated at 3.5 V using an ionic liquid electrolyte. Since lignin is an inexpensive, abundant, and green polymer, incorporating it into carbon blends enhances the scalability of such materials in energy storage applications.

Composite electrodes composed of vanadium pentoxide nanoflowers (VNFs) and carbon nanofibers (CNFs) were prepared by co-electrospinning method. Co-polymer poly(acrylonitrile-co-itaconic acid) was used to provide the carbon backbone. Presence of the itaconic acid allows for in situ activation. Morphological analysis shows that upon carbonization the resulting composite fibers have a fiber diameter of 60nm ±15nm at a 15wt% V2O5 concentration in the electrospinning solution. This composite was applied towards a two-electrode asymmetric supercapacitor device. Presence of redox active vanadium oxide composited with high surface area CNFs can help to enhance the electrochemical performance of the device. Different loadings of V2O5 were tested in order to observe how increasing loading effects the performance of the device. Results have shown specific capacitance of 150 Fg-1 at a 15wt% V2O5 loading using ionic liquid electrolyte. Ionic liquid electrolyte allows for the voltage window to be expanded, which can help to enhance the energy density. These composite electrodes have shown results comparable to ones reported using aqueous electrolytes. Figure 1

Carbon nanofibers (CNFs) were fabricated by blending PBI (Polybenzimidazole) and 6FDD (6FDA-DAM-DABA, a copolymer of 4,4-hexafluoroisopropylidene diphthalic anhydride (6FDA), 2,4,6-trimethyl-1,3-phenylenediamine (DAM) and 3,5-diaminobenzoic acid (DABA)). PBI and 6FDD are immiscible polymers comprising PBI as continuous phase and 6FDD as dispersed phase. PBI:6FDD polymer blend was compatibilized with 2-methylimidazole (2-MI). Pure polymers, immiscible blend (PBI:6FDD 50:50), and compatibilized polymer blends (PBI:6FDD 50:50 blend with 9% 2-MI and 20% 2-MI) were electrospun. As spun fiber mats were subjected to thermal stabilization at 450 °C and carbonize and 1000 °C under nitrogen gas flow. Carbonized CNFs were exposed to react with CO2 at 1000 °C. The kinetic equation f = 1-exp(-atb) was applied to evaluate constants a and b, in order to get a better understanding of the oxidation reaction of different carbon materials. The specific surface area (SSA) was calculated using QSDFT (quenched solid density functional theory) method.

Global demand for alternative energy storage and improved energy infrastructure will require energy storage devices that can store large quantities of energy and deliver them quickly. These devices should do so for thousands upon thousands of cycles. Supercapacitor devices are an attractive method for future energy storage due to their highpower densities and cyclability compared to other battery devices. For supercapacitor devices to be a more viable choice energy density needs to be improved. One technique to do so is to create hybrid electrodes which combine the fast charging/discharging and cyclability of electrochemical double layer capacitor (EDLC) materials with high energy redox active metal oxides. A common technique is to decorate carbonaceous materials with nanostructured metal oxides (e.g., Ru, Mn, V, Mo, W), which can increase the energy but can limit accessibility to a high surface area conducting carbon. Several of these metal oxides have phases that will inhibit conductivity and limit the power of the device. Polyacrylonitrile derivatives and phase separated blends can be used to tailor a variety of pore sizes (micro & meso) to both increase energy and power of a device. The research to be presented uses coaxial electrospinning to form conductive porous carbon sheath with a multitude of pores calculated by QSDFT. This porous carbon encases a core of tungsten oxide derived from the heteropoly acid, phosphotungstic acid. The graded porous nature of the carbon sheath provides a high surface area EDLC material while simultaneously providing access of the electrolyte to the metal oxide. Figure 1

Immiscible polymer blends yield carbon materials with fine and controlled pore architectures for supercapacitor applications. Aromatic polyimides derived from 4,4’-hexafluoroisopropylidine diphthalic anhydride (6FDA) have attracted attention as high performance polymers due to their high free volume and thermal stability. In this study, 6FDA and DABA (3,5-diamino benzoic acid) were used as monomers to synthesize 6FDA-DABA polymer. The synthesized polymer was blended with polyacrylonitrile to prepare a series of immiscible polymer blend compositions which were electrospun, subsequently carbonized and tested for electrochemical performance. Both polymers afford carbons upon thermal treatment up to 1000 °C under an inert environment. 6FDA-DABA has a carboxylic moiety which acts as an in-situ porogen upon decarboxylation, creating pores in electrospun fibers which are accessible to electrolyte ions. Preliminary studies show promising results upon only carbonization as an electrode material for supercapacitors. Results obtained from further activation by CO2 at 1000 °C were: specific capacitance of 137 F/g, with an energy density 66 Wh/kg, and a power density of 1.7 kW/kg with an excellent capacitance retention of 99% after 1500 cycles.

Electrochemical double layer capacitors (EDLCs) utilize electrodes with high surface area to achieve high-energy storage capability. In this study, flexible and freestanding carbon nanofibers derived from PIM-1, a microporous polymer with high free volume, were prepared by pyrolysis of the electrospun polymer. A BET surface area of 546 m2 g−1 was obtained upon carbonization of the electrospun PIM-1 fibers. After further heat treatments such as steam-activation and annealing, the surface area increased to 1162 m2 g−1. These carbon fibers were directly used as electrodes without the use of binders in a coin cell (CR2032) configuration and were characterized by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The activated and annealed fibers gave a specific capacitance of 120 F g−1 at a scan rate of 10 mV s−1 using 1,3-ethylmethylimidizaolium bis(trifluoromethanesulfonyl)imide as the ionic liquid electrolyte. From the galvanostatic charge–discharge test, the supercapacitor exhibited energy and power densities of 60 W h kg−1 (active material) and 1.7 kW kg−1, respectively, at a current density of 1 A g−1. High power application of this device was demonstrated by its 77% retention of the energy density (47 W h kg−1) at a higher discharge current density of 5 A g−1.

In this study MnO 2 nanorodes (MNR) were fabricated on reduced graphene oxide (rGO) sheets using a facile hydrothermal synthesis route. As prepared binder free MNR-rGO electrodes exhibited promising electrochemical performance. A similar approach was employed to prepare V 2 O 5 nanowire (VNW) on rGO electrodes as anodes for supercapacitor applications. The VNW-rGO anode and MNR-rGO cathode were combined to form a novel hybrid supercapacitor. The hybrid supercapacitor exhibited excellent electrochemical performance reflecting the synergistic effect of combining the MNR-rGO electrode and VNW-rGO electrode. This novel hybrid supercapacitor delivered an energy density of ~15 W h/kg with a specific capacitance of 36.9 F/g. These results suggest that the binder free flexible MNR-rGO electrode is a promising cathode material for asymmetric supercapacitors and also for hybrid devices, which incorporate metal oxide anodes.

The demand for cost-efficient separations requires membranes with high gas flux and high selectivity which opens the path for further improvements. Mixed matrix membranes (MMMs) made from 33.3 wt % ZIF-8 in 6FDA-durene were tested at 35 °C and 3.5 atm. At 33.3 wt % loading of ZIF-8, H2, N2, O2, and CH4 gas permeabilities increased approximately 400%. Cross-linking the surface of this MMM, by reacting with ethylenediamine vapor, yielded a 10-fold increase in H2/CO2, H2/N2, and H2/CH4 selectivities with respect to 6FDA-durene, preserving 55% of the H2 permeability of 6FDA-durene. The permselective properties of the cross-linked skin of the MMM fall above the most recent permeability–selectivity trade-off lines (2008 Robeson upper bounds) for H2/CO2, H2/N2, and H2/CH4 separations. To the best of our knowledge, this is the first example of a cross-linked ZIF/polymer MMM for gas separation.

Vanadium oxide has attracted interest for energy storage applications due to its high theoretical capacitance and stable layered structure. The low electronic conductivity, of V2O5 necessitates combining with conducting materials, typically carbon. However combining with conductive carbon materials may require binders, which compromise the active surface. In this study, V2O5 nanowire (VNWs)–graphene composite flexible paper electrodes were prepared without using binders. Graphene introduces conductivity and electric double layer capacitance (EDLC) to the composite. Graphene sheets were prepared using an alkaline deoxygenation process (hGO), which is a green alternative to traditional hydrazine reduction. Coin cell type supercapacitors were assembled using the hGO–VNW paper electrodes as the anode and spectracarb fiber cloth as the cathode in a two-electrode cell configuration. Electrochemical studies for different compositions of VNWs on hGO are reported. The composite electrode hGO–VNW120, showed balanced EDL and pseudocapacitance as well as an energy density of 38.8 Wh kg−1 at a power density of 455 W kg−1. The maximum power density of 3.0 kW kg−1 was delivered at a constant current discharge rate of 5.5 A g−1. The device prepared using hGO–VNW120 anode showed a specific capacitance of 80 F g−1.

A phase-separated morphology, as observed in block copolymers, for proton exchange materials (PEM) is expected to result in improved PEM fuel cell performance. Blending hydrophilic and hydrophobic polymers provides an easier route to this phase-separated morphology especially for an otherwise difficult block copolymer synthesis. Blends of hydrophilic and hydrophobic perfluorocyclobutyl (PFCB) polymers were prepared and characterized as PEMFC membranes. The [2 π +2 π ] cyclodimerization of 4,4'-bis(trifluorovinyloxy)biphenyl and 4,4'-sulfonyl-bis(trifluorovinyloxy)biphenyl monomers afforded the hydrophobic homopolymers biphenyl perfluorocyclobutyl (BP-PFCB) and sulfonyl-bridged biphenyl perfluorocyclobutyl (SO 2 -PFCB), respectively. The hydrophilic homopolymer was prepared by post-sulfonation of the BP-PFCB using chlorosulfonic acid and thionyl chloride, yielding sulfonated biphenyl (sBP-PFCB) polymer. Blends of sBP-PFCB with SO 2 -PFCB and BP-PFCB were prepared in 1:1 mol ratios, resulting in higher ion exchange capacity (IEC) values and reduced membrane swelling by water when compared to Nafion ® . The pure hydrophilic sBP-PFCB polymer showed a 2.40 mmol/g IEC, while its 1:1 mol ratio blends with BP-PFCB and SO 2 -PFCB, gave IECs of 1.36 and 1.37 mmol/g, respectively, which are over 1.5× that of Nafion ®' s. Blending these polymers combined the mechanically and thermally stable PFCB backbone with the highly acidic sulfonated PFCB and displayed nanophase-separated morphologies without the challenge of controlling polydispersities. Proton conductivity of 6 and 8×10 −2 S/cm for the sBP-PFCB blend with BP-PFCB and SO 2 -PFCB respectively, was achieved at 80° C and 100% relative humidity. Testing a 1:1 mol ratio of sBP- and SO 2 -PFCB blend at ∼100° C and 50% relative humidity showed a higher proton conductivity of 1.5×10 −1 S/cm. These results confirm that the blends of hydrophilic (sulfonated) and hydrophobic PFCB polymers can be promising materials for fuel cell membranes.

Thermoacoustic performance of thin freestanding sheets of carbonized poly(acrylonitrile) and polybenzimidazole nanofibers are studied as promising candidates for thermophones. We analyze thermodynamic properties of sheets using transport parameters of single nanofibers and their aligned and randomly electrospun thin film assemblies. The electrical and thermal conductivities, thermal diffusivity, heat capacity, and infrared blackbody radiation are investigated to extract the heat exchange coefficient and enhance the energy conversion efficiency. Spectral and power dependencies of sound pressure in air are compared with carbon nanotube sheets and theoretical prediction. Despite lower thermoacoustic performance compared to that of CNT sheets, the mechanical strength and cost-effective production technology of thermophones make them very attractive for large-size sound projectors. The advantages of carbonized electrospun polymer nanofiber sheets are in the low frequency domain (1000 Hz), where the large thermal diffusion length diminishes the thermal inertia of thick (∼200 nm) nonbundled fibers and the high intrinsic thermal conductivity of fibers enhances the heat exchange coefficient. Applications of thermoacoustic projectors for loudspeakers, high power SONAR arrays, and sound cancellation are discussed.

Porous carbon nanofibers were prepared by electrospinning blend solutions of polybenzimidazole/poly-L-lactic acid (PBI/PLLA) and carbonization. During thermal treatment, PLLA was decomposed, resulting in the creation of pores in the carbon nanofibers. From SEM images, it is shown that carbon nanofibers had diameters in the range of 100-200 nm. The conversion of PBI to carbon was confirmed by Raman spectroscopy, and the surface area and pore volume of carbon nanofibers were determined using nitrogen adsorption/desorption analyses. To investigate electrochemical performances, coin-type cells were assembled using free-standing carbon nanofiber electrodes and ionic liquid electrolyte. cyclic voltammetry studies show that the PBI/PLLA-derived porous carbon nanofiber electrodes have higher capacitance due to lower electrochemical impedance compared to carbon nanofiber electrode from PBI only. These porous carbon nanofibers were activated using ammonia for further porosity improvement and annealed to remove the surface functional groups to better match the polarity of electrode and electrolyte. Ragone plots, correlating energy density with power density calculated from galvanostatic charge-discharge curves, reveal that activation/annealing further improves energy and power densities.

Gas separation for industrial, energy, and environmental applications requires low energy consumption and small footprint technology to minimize operating and capital costs for the processing of large volumes of gases. Among the separation methods currently being used, like distillation, amine scrubbing, and pressure and temperature swing adsorption, membrane-based gas separation has the potential to meet these demands. The key component, the membrane, must then be engineered to allow for high gas flux, high selectivity, and chemical and mechanical stability at the operating conditions of feed composition, pressure, and temperature. Among the new type of membranes studied that show promising results are the inorganic-based and the metal-organic framework-based mixed-matrix membranes (MOF-MMMs). A MOF is a unique material that offers the possibility of tuning the porosity of a membrane by introducing diffusional channels and forming a compatible interface with the polymer. This review details the origins of these membranes and their evolution since the first inorganic/polymer and MOF/polymer MMMs were reported in the open literature. The most significant advancements made in terms of materials, properties, and testing conditions are described in a chronological fashion.

A novel symmetrical alkylsulfonyl-substituted poly(phenylenevinylene) derivative, poly [2,5-bis-(2'-ethylhexylsulfonyl)-1,4-phenylene)vinylene] (SO2EH-PPV), was synthesized via palladium-catalyzed Stille coupling, and its electronic and optical properties were investigated. The novel PPV derivative was characterized by NMR, UV-visible absorption, photoluminescence, gel permeation chromatography, infrared spectroscopy, and cyclic voltammetry (CV). The polymer with Mw of 27,800 and a polydispersity index of 2.6 is readily soluble in common organic solvents, such as THF, chloroform, and toluene. The fluorescence quantum yield of the polymer, determined against rhodamine 6G in dilute aqueous solutions, was 0.95. The HOMO and LUMO levels of SO2EH-PPV were calculated to be -6.0 and -3.61 eV, respectively. The results obtained by CV suggest that SO2EH-PPV is a strong electron acceptor polymer. Single layer stable polymer light-emitting diode devices with the configuration of (ITO/PEDOT:PSS/SO2EH-PPV polymer/Al) were fabricated exhibiting a green light emission.

Carbon nanofibers (CNFs) were fabricated by thermal treatment of electrospun nanofibers obtained from precursor blends of polybenzimidazole (PBI) and Matrimid®. The microcarbon structures of CNFs obtained from PBI, and the 50:50 and 75:25 blends were studied using XRD and Raman spectra. Nitrogen adsorption/desorption measurements revealed that surface area and porosity of CNFs increased with an increase in Matrimid® content. Electrochemical performance of these CNF electrodes was studied for their application in energy storage devices. The CNFs from the PBI/Matrimid® (75:25)-precursor blend showed the lowest electrochemical impedance, and highest specific capacitance (111 F/g) and energy and power densities of 24 and 6 kW/kg, respectively. Steam activation and annealing further enhanced the performance resulting in a specific capacitance of 126 F/g, and energy and power densities of 49 and 7 kW/kg, respectively.

Graphene is a promising electrode material for energy storage applications. The most successful method for preparing graphene from graphite involves the oxidation of graphite to graphene oxide (GO) and reduction back to graphene. Even though different chemical and thermal methods have been developed to reduce GO to graphene, the use of less toxic materials to generate graphene still remains a challenge. In this study we developed a facile one-pot synthesis of deoxygenated graphene (hGO) via alkaline hydrothermal process, which exhibits similar properties to the graphene obtained via hydrazine reduction (i.e. the same degree of deoxygenation found in hydrazine reduced GO). Moreover, the hGO formed freestanding, binder-free paper electrodes for supercapacitors. Coin cell type (CR2032) symmetric supercapacitors were assembled using the hGO electrodes. Electrochemical characterization of hGO was carried out using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and ethylmethylimidazolium bis-(trifluoromethanesulfonyl)imide (EMITFSI) electrolytes. The results for the hGO electrodes were compared with the hydrazine reduced GO (rGO) electrode. The hGO electrode exhibits a energy density of 20 W h kg −1 and 50 W h kg −1 in LiTFSI and EMITFSI respectively, while delivering a maximum power density of 11 kW kg −1 and 14.7 kW kg −1 in LiTFSI and EMITFSI, respectively.

Carbon nanofibers were prepared using electrospinning and thermal treatment of a new precursor, poly(acrylonitrile-co-vinylimidazole). Raman spectroscopy confirmed carbonization. Steam activation resulted in high surface area of 1120 m2/g. Coin cells were assembled using ethylmethylimidazolium bis(trifluoromethylsulfonyl) imide (EMITFSI) as the electrolyte. Cyclic voltammetry showed classic box-like behavior of electrochemical double layer capacitors with specific capacitances ranging between 122 F/g (10 mV/s) and 86 F/g (300 mV/s). From Ragone plots, the maximum energy and power densities were 47.4 Wh/kg (0.5 A/g) and 7.2 kW/kg (5 A/g), respectively. Keywords: Carbon nanofibers, Supercapacitors, Copolymers, Electrospinning

Polyacrylonitrile/poly(methyl methacrylate) (PMMA) fibers containing graphene are prepared by the electrospinning method, and hierarchical porous carbon nanofibers (CNFs) are obtained after subsequent heat treatment. The hierarchical porous CNFs have an improved structure and properties because of the increased surface area, unique nanotexture and increased electrical conductivity due to the dispersion of graphene. The carbonized fiber exhibits a high surface area (over 500 m 2 g −1 ) as result of the narrow ultramicro- and mesopore size distributions (centered at approximately 0.7 and 3.7 nm, respectively), and a broad mesopore size distribution ranging from 10 to 50 nm. The hierarchical pore structures are introduced by the evolution of small gas molecules during the decomposition of the PMMA during heat treatment. The highest specific capacitance of the CNFs is 128 F g −1 , and the energy densities are 16.0–21.4 W h kg −1 in an aqueous solution and 75.0–58.2 W h kg −1 in an organic electrolyte over a power density range of 400–20,000 W kg −1 . Under constant current charging/discharging at 1 mA cm −2 for 100 cycles, the stability of the CNFs in a 6 M KOH aqueous electrolyte decreases by ∼17% compared with the initial specific capacitance value.