MOP-18-Derived CuO Fiber for Hybrid Supercapacitor Electrodes.

This study explores a simple method of fabricating hybrid supercapacitor electrodes, which could potentially broaden the application of this technology. The method involves electrospinning a uniform solution of Matrimid/Metal-Organic Polyhedra 18 (MOP-18) followed by carbonization at a relatively low temperature of 700 °C in air, rather than in an inert atmosphere, to create free-standing, redox-active hybrid supercapacitor electrodes. Additionally, the synthesis procedure requires no stabilization or activation steps, which enhances the cost effectiveness of the synthesized electrode materials. The resulting C/CuO composite was used as the working electrode, with a polyacrylonitrile (PAN)/Poly(methyl methacrylate) (PMMA) carbon nanofiber (CNF) electrode as the counter and 6 M KOH as the electrolyte in a T-cell configuration. The cell performance and redox activity were evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycling stability tests. Additionally, the physical and chemical structures of the electrode materials were assessed using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron spectroscopy (TEM), X-ray diffractometry (PXRD), surface area analysis and other characterization techniques. The electrode material demonstrated a specific capacitance of up to 206 F/g. Supercapacitors utilizing this material display an energy density of 10.3 Wh/kg (active material) at a current density of 1 A/g in electrochemical testing.

Pillared Carbon Membranes Derived from Cardo Polymers.

Carbon molecular sieve membranes (CMSMs) were prepared by carbonizing the high free volume polyimide BTDA-BAF that is obtained from the reaction of benzophenone-3,3',4,4'-tetracarboxylic dianhydride (BTDA) and 9,9-bis(4-aminophenyl) fluorene (BAF). The bulky cardo groups prevented a tight packing and rotation of the chains that leads to high permeabilities of their CMSMs. The incorporation of metal-organic polyhedra 18 (MOP-18, a copper-based MOP) in the BTDA-BAF polymer before pyrolysis at 550 °C prevented the collapse of the pores and the aging of the CMSMs. It was found that upon decomposition of MOP-18, a distribution of copper nanoparticles minimized the collapse of the graphitic sheets that formed the micropores and mesopores in the CMSM. The pillared CMSMs displayed CO2 and CH4 permeabilities of 12,729 and 659 Barrer, respectively, with a CO2/CH4 selectivity of 19.3 after 3 weeks of aging. The permselectivity properties of these membranes was determined to be at the 2019 Robeson upper bound. In contrast, the CMSMs from pure BTDA-BAF aged three times faster than the CMSMs from MOP-18/BTDA-BAF and exhibited lower CO2 and CH4 permeabilities of 5337 and 573 Barrer, respectively, with a CO2/CH4 selectivity of 9.3. The non-pillared CMSMs performed below the upper bound.

Two-Dimensional Hexagonal-Shaped Mesoporous Carbon Sheets for Supercapacitors.

Two-dimensional mesoporous hexagonal carbon sheets (MHCSs) have been prepared via a chemical vapor deposition method employing mesoporous Mg(OH)2 hexagonal sheets as the template and acetylene gas as the carbon precursor. MHCSs with porosity in the micropore-mesopore range have a high specific surface area of 1785 m2·g-1. The hierarchical microporous-mesoporous pore structure enables rapid ion transport across the hexagonal carbon sheets, resulting in superior electrochemical performance. The MHCS electrodes showed a maximum specific capacitance of 162 F·g-1 at 5 mV s-1 using the electrolyte 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI). MHCS symmetric coin cells exhibited a maximum energy density of 67 Wh·kg-1 at 0.5 A·g-1 and a maximum power density of 14.97 kW·kg-1 at 10 A·g-1.

Hybrid supercapacitors using electrodes from fibers comprising polymer blend-metal oxide composites with polymethacrylic acid as chelating agent.

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-1in PAN-Co3O4to 125 F g-1in 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, Co3O4nanoparticles 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.

Electrospun poly(acrylonitrile-co-itaconic acid) as a porous carbon precursor for high performance supercapacitor: study of the porosity induced by in situ porogen activity of itaconic acid.

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.

Binder free carbon nanofiber electrodes derived from polyacrylonitrile-lignin blends for high performance supercapacitors.

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.

High performance supercapacitors using lignin based electrospun carbon nanofiber electrodes in ionic liquid electrolytes.

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 Supported Lanthanum Oxide as a Template for Porous Carbon.

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.

Electrochemical energy storage performance of carbon nanofiber electrodes derived from 6FDA-durene.

Carbon nanofibers (CNFs) are promising electrode materials for electrochemical double layer capacitors due to their high porosity and electrical conductivity. CNFs were prepared by electrospinning and subsequent thermal treatment of a new precursor polymer, 6FDA-durene, without the addition of pore generating agents. The conversion of precursor nanofibers into CNFs was confirmed using Raman spectroscopy. CNFs were activated and annealed, and nitrogen adsorption/desorption measurements were conducted to determine surface area and porosity. These activated/annealed CNFs were used as binderless electrodes in coin cells with an ionic liquid electrolyte. The devices displayed a specific capacitance of 128 F g-1, an energy density of 63.4 Wh kg-1 (at 1 A g-1), and a power density of 11.0 KW kg-1 (at 7 A g-1).

Lanthanum Hydroxide Nanorod-Templated Graphitic Hollow Carbon Nanorods for Supercapacitors.

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.

Carbonized Electrospun Nanofiber Sheets for Thermophones.

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.

Electrochemically active porous organic polymers based on corannulene.

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.

Preparation of porous carbon nanofibers derived from PBI/PLLA for supercapacitor electrodes.

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 Membranes Derived from High-Performance Immiscible Polymer Blends Compatibilized with Small Molecules.

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.

Instrument for gas permeation measurements at high pressure and high temperature.

An instrument was built for the permeation testing of flat polymer membranes under pressures up to 3.0 MPa and temperatures up to 300 °C. The high pressure, high temperature cell uses aluminum tape and a graphite gasket to minimize the leak from the high pressure side to the low pressure side, making possible the permeability measurements of slow diffusing gases such as N2. A computer program developed on a LabVIEW platform fully controls the instrument and data acquisition. It incorporates algorithms to automatically adjust the downstream volume, repressurize the upstream volume, vent the downstream volume to prevent over pressurization, and change the temperature of the permeation cell. The percent relative standard deviation of the permeability measurements was <5.5%. Flat membranes of VTEC PI-1388 polymer were tested from 0.3 to 3.0 MPa and from 35 to 300 °C. The permeabilities and fluxes of H2, CO2, and N2 increased with increasing temperature, while the H2∕CO2 ideal selectivity remained unchanged. The major contribution to increased flux arose from increments in temperature rather than pressure.

Synthesis and characterization of a novel symmetrical sulfone-substituted polyphenylene vinylene (SO2EH-PPV) for applications in light emitting devices.

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.

Vanadium oxide nanotube spherical clusters prepared on carbon fabrics for energy storage applications.

Vanadium oxide nanotubes have shown great promise as electrode materials for energy storage devices. In this study, we report the synthesis of V(2)O(5) nanotube (VNT) clusters, which form densely packed radial arrangements of VNTs on high-surface-area carbon fiber fabrics (CF). This was achieved by coating the CF with V(2)O(5) by pulsed laser deposition (PLD). Hydrothermal treatment of the PLD films in the presence of excess intercalated V(2)O(5) results in formation of well-adhered VNT clusters on the CF. The densely packed VNTs have inner and outer diameters and interlayer distances of ~24, ~70, and ~2.4 nm, respectively. Coin cell type supercapacitors (CR2032) were assembled using VNT-CF as the anode material and electrochemical properties were evaluated.

A novel dialkylthio benzo[1,2-b:4,5-b']dithiophene derivative for high open-circuit voltage in polymer solar cells.

A new dialkylthio benzo[1,2-b:4,5-b']dithiophene (S-BDT) was designed and synthesized and the polymer S-PBDT was prepared by a Stille coupling reaction. A high open-circuit voltage (V(oc)) of up to 0.99 V was achieved in polymer solar cells with PCBM.

Harvesting waste thermal energy using a carbon-nanotube-based thermo-electrochemical cell.

Low efficiencies and costly electrode materials have limited harvesting of thermal energy as electrical energy using thermo-electrochemical cells (or "thermocells"). We demonstrate thermocells, in practical configurations (from coin cells to cells that can be wrapped around exhaust pipes), that harvest low-grade thermal energy using relatively inexpensive carbon multiwalled nanotube (MWNT) electrodes. These electrodes provide high electrochemically accessible surface areas and fast redox-mediated electron transfer, which significantly enhances thermocell current generation capacity and overall efficiency. Thermocell efficiency is further improved by directly synthesizing MWNTs as vertical forests that reduce electrical and thermal resistance at electrode/substrate junctions. The efficiency of thermocells with MWNT electrodes is shown to be as high as 1.4% of Carnot efficiency, which is 3-fold higher than for previously demonstrated thermocells. With the cost of MWNTs decreasing, MWNT-based thermocells may become commercially viable for harvesting low-grade thermal energy.

Electrospinning of poly(alkoxyphenylenevinylene) and methanofullerene nanofiber blends.

Poly(p-phenylenevinylene) (PPV) derivatives have long been studied because of their attractive opto- and electroluminescent properties and have potential applications for devices such as light-emitting diodes and photovoltaics. The ability to induce alignment of these PPV derivatives may lead to the enhancement of charge mobility and their efficiency. In this study, uniform nanofibers of poly[2,5-(2'-ethylhexyloxy)]-1,4-phenylenevinylene (BEH-PPV) have been fabricated through the method of electrospinning, and an induced alignment of the polymer fibers was observed through photoluminescence data. This study also focuses on the doping of these fibers with the fullerene derivative, 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)-C(61) (PCBM), to induce more incidence of donor/acceptor junctions. Composite fibers with up to a 1:2 weight ratio of PCBM/BEH-PPV have been fabricated and exhibited an ability to quench the photoluminescence of BEH-PPV, indicative of charge transfer.