The demand for renewable energy sources worldwide has gained tremendous research attention over the past decades. Technologies such as wind and solar have been widely researched and reported in the literature. However, economical use of these technologies has not been widespread due partly to cost and the inability for service during of-source periods. To make these technologies more competitive, research into energy storage systems has intensified over the last few decades. The idea is to devise an energy storage system that allows for storage of electricity during lean hours at a relatively cheaper value and delivery later. Energy storage and delivery technologies such as supercapacitors can store and deliver energy at a very fast rate, offering high current in a short duration. The past decade has witnessed a rapid growth in research and development in supercapacitor technology. Several electrochemical properties of the electrode material and electrolyte have been reported in the literature. Supercapacitor electrode materials such as carbon and carbon-based materials have received increasing attention because of their high specific surface area, good electrical conductivity and excellent stability in harsh environments etc. In recent years, there has been an increasing interest in biomass-derived activated carbons as an electrode material for supercapacitor applications. The development of an alternative supercapacitor electrode material from biowaste serves two main purposes: (1) It helps with waste disposal; converting waste to a useful product, and (2) it provides an economic argument for the substantiality of supercapacitor technology. This article reviews recent developments in carbon and carbon-based materials derived from biowaste for supercapacitor technology. A comparison between the various storage mechanisms and electrochemical performance of electrodes derived from biowaste is presented.Sustainability 2019, 11, 414 2 of 22 renewable energy sources such as solar energy, geothermal energy, wind energy, biofuels, etc., while electrochemical energy storage devices such as supercapacitors, rechargeable batteries, etc. have also attracted significant research [9][10][11]. It is not an overstatement to say that successful development of any renewable energy source (e.g., windmills and solar cells), hybrid and electric vehicles and smart grids depend significantly upon the availability of a suitable energy storage system. A considerable amount of literature has been published on the use of supercapacitors as a viable storage device for renewable energy. Over 20,000 articles, books etc. were published in 2017, a higher number of research work is projected for 2018 (data from google scholar). There has been a geometric increase in the research published since the year 2000. Since supercapacitors were first experimented in 1957 by engineers at General Electric, they have found commercial applications in portable electronics, transportation and aerospace industry [12,13]. These applications of supercapacitors ...

High performance carbonized bamboo fibers were synthesized for a wide range of temperature dependent energy storage applications. The structural and electrochemical properties of the carbonized bamboo fibers were studied for flexible supercapacitor applications. The galvanostatic charge-discharge studies on carbonized fibers exhibited specific capacity of ~510F/g at 0.4 A/g with energy density of 54 Wh/kg. Interestingly, the carbonized bamboo fibers displayed excellent charge storage stability without any appreciable degradation in charge storage capacity over 5,000 charge-discharge cycles. The symmetrical supercapacitor device fabricated using these carbonized bamboo fibers exhibited an areal capacitance of ~1.55 F/cm2 at room temperature. In addition to high charge storage capacity and cyclic stability, the device showed excellent flexibility without any degradation to charge storage capacity on bending the electrode. The performance of the supercapacitor device exhibited ~65% improvement at 70 °C compare to that at 10 °C. Our studies suggest that carbonized bamboo fibers are promising candidates for stable, high performance and flexible supercapacitor devices.

In search of affordable, flexible, lightweight, efficient and stable supercapacitors, metal oxides have been shown to provide high charge storage capacity but with poor cyclic stability due to structural damage occurring during the redox process. Here, we develop an efficient flexible supercapacitor obtained by carbonizing abundantly available and recyclable jute. The active material was synthesized from jute by a facile hydrothermal method and its electrochemical performance was further enhanced by chemical activation. Specific capacitance of 408 F/g at 1 mV/s using CV and 185 F/g at 500 mA/g using charge-discharge measurements with excellent flexibility (~100% retention in charge storage capacity on bending) were observed. The cyclic stability test confirmed no loss in the charge storage capacity of the electrode even after 5,000 charge-discharge measurements. In addition, a supercapacitor device fabricated using this carbonized jute showed promising specific capacitance of about 51 F/g, and improvement of over 60% in the charge storage capacity on increasing temperature from 5 to 75 °C. Based on these results, we propose that recycled jute should be considered for fabrication of high-performance flexible energy storage devices at extremely low cost.

Nickel sulfide is regarded as a material with tremendous potential for energy storage and conversion applications. However, it exists in a variety of stable compositions and obtaining a pure phase is a challenge. this study demonstrates a potentially scalable, solvent free and phase selective synthesis of uncapped α-niS, β-niS and α-β-niS composites using nickel alkyl (ethyl, octyl) xanthate precursors. Phase transformation and morphology were observed by powder-X-ray diffraction (p-XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The comparative efficiency of the synthesized samples was investigated for energy storage and generation applications, in which superior performance was observed for the niS synthesized from the short chain xanthate complex. A high specific capacitance of 1,940 F/g, 2,150 F/g and 2,250 F/g was observed at 2 mV/s for bare α-niS, β-niS and α-β-NiS composite respectively. At high current density of 1 A/g, α-niS showed the highest capacitance of 1,287 F/g, with 100% of Coulombic efficiency and 79% of capacitance retention. In the case of the oxygen evolution reaction (oeR), β-NiS showed an overpotential of 139 mV at a current density of 10 mA/cm 2 , with a Tafel slope of only 32 mV/dec, showing a fast and efficient process. It was observed that the increase in carbon chain of the synthesized self-capped nickel sulfide nanoparticles decreased the overall efficiency, both for energy storage and energy generation applications. As a step towards the implementation of sustainable energy development strategies, research on the design of high-performance energy storage and conversion systems is gathering renewed momentum 1-3. Sodium ion batteries (SIBs), lithium-ion batteries (LIBs), and supercapacitors (SCs) are examples of the most studied energy storage devices 4,5. Energy conversion systems on the other hand, constitute a series of electrochemical reactions occurring in an electrolytic cell or in a hydrogen-oxygen fuel cell 3. Hydrogen is a clean and sustainable energy carrier, currently regarded as the best alternative fuel of the future 6,7. Its generation via the electrocatalytic splitting of water is a commonly investigated energy conversion technology 8. The performance of both energy storage devices and energy conversion systems is largely influenced by the type of electroactive material employed. Generally, for energy conversion systems the goal is to develop low cost, earth-abundant and efficient electrocatalysts that will replace Pt-, Ir-and Ru-based compounds 9 , while for energy storage devices, the goal is to develop advanced electrode materials that can deliver high energy and power densities 10. Carbon-based materials 11 , conductive polymers 12 , transition metal oxides 13 , nitrides 14 , carbides 14 , phosphides 15 , and sulfides 5 are among the materials investigated for both energy storage and generation applications. Owing to their low cost, high electrochemical activity as well as mechanical and thermal stability, transition

Transitional metal oxide nanomaterials are considered to be potential electrode materials for supercapacitors.

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Currently, the sustainable fabrication of supercapacitors with enhanced properties is one of the significant research hotspots.

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.