High Performance Carbon Nanofiber Supercapacitor Electrode with Tuned Porous Structure

High performance capacitor devices based on electric double layer capacitor (EDLC) principle has wide advantage of higher range of cyclic stability, rate capability, temperature durability and chemically resistant. Carbon based materials such as graphene, carbon nanotubes, activated carbon and carbon nanofibers are well known supercapacitor materials derived till date. Creating pores within the physical structure has found to improve the EDLC capabilities of the material. Exfoliation of graphene, activation of carbon and activation of nanofibers via various different techniques seem to be too complicated, non-consistent and needs wide range of control parameters. Facile immiscible polymer blend technique followed by thermal treatment is used to create porous carbon nanofibers producing higher surface area of 86 m2/g. X-ray diffraction spectroscopy shows the peak at 26.3o which is for graphitic phase of carbon. Cyclic voltammetry and galvanostatic charge discharge results showed around ~ 350% of capacitance improvement for porous nanofiber to that of pure carbon nanofiber. Temperature dependence study suggested 160% capacitance improvement for the device. Electrochemical impedance spectroscopy suggests the possible reduction in resistance of the material with increasing temperature. Material showed capacitance retention of above 100% for 5000 charge-discharge cycles

A DETAILED STUDY OF NOVEL HIGH-PERFORMANCE BROMINE AND PHOSPHORUS BASED REACTIVE FLAME RETARDANTS IN HIGH-QUALITY BIO-POLYOL BASED RIGID POLYURETHANE FOAMS

Structural fire is one of the most catastrophic issues related to human safety observed from reports of National Fire Protection Association of United States in past years. Polyurethanes are one of the important structural material used as thermal insulation in housing. They are also used in automotive, construction, medical, packaging, furniture, thermal, electrical, and vibration insulation. Considering this, we have synthesized bio-based polyurethane foams using limonene-based polyol, isocyanates, and other compounds. Flame retardancy was imparted using reactive flame retardant polyols. Firstly, flame retardancy test was performed on the foams using two novel aliphatic and two novel aromatic bromine-based synthesized reactive flame retardant polyols in different concentration in foams. It was observed that bromine acts in gas as well as a condensed phase to provide flame retardancy. Moreover, it required 6% concentration of bromine in final foam to impart desired flame retardancy. Secondly, flame retardancy was studied using phosphorus-based synthesized reactive flame retardant polyol in different concentration. We observed that foams containing only 1.5% phosphorus are sufficient to provide better flame retardant properties. The study was further analyzed using cone calorimeter test. Results showed excellent flame retarding properties compared to many reported values. Lastly, another phosphorus-based novel flame retardant polyol was synthesized. This study was generalized by using soybean and castor oil-based polyols which are also widely used bio-based polyols, as a comparison to limonene-based polyol used during synthesis of the polyurethane foam. Castor oil-based foams showed the best result in flame retardant properties. Hence, thorough analysis on castor oil-based foams was performed as a representative study to understand peak heat release, total heat release, and smoke release rate of the foams. From the overall study, the addition of reactive flame retardant polyols showed improved mechanical properties and maintained their cell structure. Higher close cell content (95-100%) throughout the study was maintained by all the foams containing reactive flame retardant polyols. This suggests excellent thermal insulation properties of the foams for the desired application. Results obtained from this study can serve as an important function to overcome structural fires and assist in providing human safety

High-quality Polyurethane Foams and Sheets from Sustainable Natural Resources

Bio-polymers from sustainable natural resources serve mankind keeping environmental factors under consideration. Resources such as soybean, castor and orange oil are among highly cultivable agro-resources. Polyols formulated from these oils shows clean-environmental pathway for synthesizing polyurethane foams and sheets. Facile single-step synthesis, with negligible waste as well as byproducts produces 100% qualitative yield for polyurethane foams. Present work displays use of synthesized polyols in developing polyurethane foams and casts. Viscometry, FTIR spectroscopy, GPC and other chemical analysis were done to ensure the quality of the raw materials. Cast Sheets and foams were produced by chemical polymerization with di-phenyl methane diisocyanate using different formulations of polyols. Foams and sheets were stable until 200oC. Mercaptenized polyol sheets displayed ultimate tensile stress around 25 MPa. Hence, overall study suggests that these bio-polyols from sustainable resources serves to be very good source for polyurethane foams and sheets

Construction of High-Performance 3D Nanostructured Flower-Like Iron-Nickel Sulfide for Supercapacitor

The global energy crisis and environmental pollution have stimulated increasing attention to developing clean and renewable alternative energy sources. One of the most efficient and greenest energy storage devices is supercapacitor which could store energy via electrical double layer and redox reactions. Supercapacitors are widely employed for many portable electronics and hybrid electric vehicles due to their high-power density, fast charge-discharge rate, and good cycle stability. In this work, 3D nanostructured flower-like iron-nickel sulfide was synthesized on the nickel foam using a facile hydrothermal method. The iron-nickel sulfide electrode showed out­standing performance for supercapacitor with a high areal capacitance of 13.2 F/cm2 at the scan rate of 1 mV/s and 4.9 F/cm2 at the current density of 5 mA/cm2, respectively. The specific capacitance of iron-nickel sulfide was 11 and 54 times higher than that of iron-nickel oxide and nickel foam at 5 mA/cm2, respectively. Further­more, the iron-nickel sulfide electrode displayed good rate capability in the charge-discharge study. Our research suggests that designing a highly porous and 3D nano-flower like iron-nickel sulfide material could be a way to improve the charge storage capacity of energy storage devices

Expendable Graphite as an Efficient Flame-Retardant for Novel Partial Bio-Based Rigid Polyurethane Foams

Study presents a novel bio-polyol synthesized using carvone, an extract from caraway, spearmint, or dill seeds via facile thiol-ene reaction

Highly flame-retardant polyurethane foam based on reactive phosphorus polyol and limonene-based polyol

Polyurethane foams are in general flammable and their flammability can be controlled by adding flame-retardant (FR) materials. Reactive FR have the advantage of making strong bond within the polyurethane chains to provide excellent FR over time without compromising physico-mechanical properties. Here, phenyl phosphonic acid and propylene oxide-based reactive FR polyol was synthesized and used along with limonene based polyol for preparation of FR polyurethanes. All the obtained foams showed higher closed cell content (above 96%). By the addition of FR–polyol, the compressive strength of the foams showed 160% increment which could be due to reactive nature of FR–polyol. Moreover, 1.5 wt % of phosphorus (P) content reduced the self-extinguishing time of the foam from 81 (28% weight loss) to 11.2 s (weight loss of 9.8%). Cone test showed 68.6% reduction in peak heat release rate along with 23.4% reduction in thermal heat release. The change in char structure of carbon after burning was analyzed using Raman spectra which, suggests increment in the graphitic phase of the carbon over increased concentration of phosphorus. It can be concluded from this study that phosphorous based polyol could be blended with bio-based polyols to prepare highly FR and superior physico-mechanical rigid polyurethane foams. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46224

Expendable Graphite as an Efficient Flame-Retardant for Novel Partial Bio-Based Rigid Polyurethane Foams

The rigid polyurethane foam (PU) is a versatile material, used especially for construction and household applications. The current situation demands a facile, cost-efficient, and greener approach for developing the polyurethanes from bio-derived materials. In this study, we present a novel bio-polyol synthesized using carvone, an extract from caraway, spearmint, or dill seeds via facile thiol-ene reaction. Our one-step reaction uses a UV irradiation to allow the room temperature conversion of the carvone to a high purity bio-polyol, as confirmed from the standard analytical characterizations. The hydroxyl number of 365 mg KOH/g close to its theoretical limit confirms the high conversion yield of the polyol for rigid PU synthesis. To overcome the flammability issues in PU, expandable graphite (EG) powder was used as an additive flame-retardant during the synthesis step. The resulting foams with EG maintained the uniform closed cell structure (>95%) with a high compression strength of 175 kPa. The addition of EG in PU results in the formation of a protective char layer during the flammability test and reduces the weight loss from 40.70% to 3.55% and burning time from 87 to 11 s. Our results confirm that the carvone-based polyol can be a novel alternative to the petroleum polyols for an industrial-scale application

Novel Biobased Polyol Using Corn Oil for Highly Flame-Retardant Polyurethane Foams

A novel bio-based polyol was synthesized using corn oil and 2-mercaptoethanol via thiol-ene reaction as an alternative to petroleum-based polyol for the synthesis of polyurethane foams. The polyol was analyzed using wet chemical techniques to obtain hydroxyl number and viscosity. Infrared spectroscopy and gel permeation chromatography were used to confirm the structural properties of the foams. Flame-retardant polyurethane foams were prepared by the addition of different concentrations of dimethyl methyl phosphonate (DMMP) in final foam composition. The effect of DMMP on the thermo-mechanical properties of the polyurethane foams was analyzed. The TGA analysis showed improved stability of the final char with addition of DMMP in the foams. All the foams maintained a well-defined cellular structure and over 95% of closed cell content. The horizontal burning test showed reduced burning time and weight loss from 115 s and 38 wt.% for the neat foams, to 3.5 s and 5.5 wt.% for DMMP-containing foams (1.94 wt.% P). The combustion test using cone calorimeter showed a considerable reduction in heat release rate and total heat release. Thus, our study shows that corn-oil based polyol can be used to produce renewable polyol for industrially producible rigid polyurethane foams. The addition of a small amount of DMMP could result in a significant reduction in the flame-retardant properties of the polyurethane foams

Polystyrene activated linear tube carbon nanofiber for durable and high-performance supercapacitors

With increasing demand for sustainable energy, it is essential to develop low cost, high performance, and environment-friendly materials for energy storage application. Metal oxides and sulfides are mostly being used as electrode materials for energy storage devices. However, their wide applications are precluded due to their higher cost, low stability, and adverse effect on the environment. Therefore, development of environment-friendly supercapacitors with low cost, high performance, and stable performance is a big challenge. Here, we report surface engineered carbon nanofibers for durable and high-performance supercapacitor. Surface engineered carbon nanofibers showed the highest specific capacitance of 277 F/g (at 1 mV/s), along with superior flexibility and cyclic stability. Moreover, they showed high energy and power density of 30.5 Wh/kg and 8.3 kW/kg, respectively. The cyclic stability showed almost 100% retention in charge storage capacity up to 5000 cycles. Electrochemical properties of a fabricated symmetrical supercapacitor device using these carbon nanofibers showed improved charge storage capacity at elevated temperatures. The charge storage capacity improved by over 150% by increasing temperature from 10 to 60 °C. Our results suggest that surface engineered carbon nanofibers could be a potential candidate for higher performance and durable supercapacitors

Synthesis and electrochemical performance of hydrothermally synthesized Co3O4 nanostructured particles in presence of urea

Morphology controlled nanostructures of Co3O4 were prepared via hydrothermal synthesis method in presence of varying content of urea as hydrolyzing agent. We demonstrate that change in weight content of hydrolyzing agent, yield profound variations in the oxide microstructure, with plate and brush like structure. This in turn resulted in significant variations in the electrocapacitive properties of these materials. Specifically, Co3O4 nanostructures that were synthesized at low urea content exhibited very favorable electrochemical properties. Amongst the Co3O4 studied, Co3O4-U0.37, prepared with 0.37 g of urea, displayed moderate surface area (50.10 m2/g), highest specific capacitance (764 F/g at 5 mV/s) and energy density (19.56 Wh/kg). The specific capacitance of all Co3O4 decreased with the increase in scan rate. The cyclic stability of Co3O4-U0.37 was studied up to 5000 cycles and about 64% retention of charge storage capacity was observed. The superior electro-capacitive behavior of the Co3O4-U0.37 was attributed to high surface area and brush like structure amongst studied Co3O4. In conclusion, it is demonstrated that the high specific capacitance is achievable in same oxide materials by the tight control of morphology of the oxides. Low hydrolyzing concentration was desired in producing high surface area architecture which provided high specific capacitance