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.

This paper reports the yields and product composition obtained from the stepwise pyrolysis of pine wood in a fluidized bed reactor. The first step temperature was varied between 260 °C and 360 °C. After the first step, the solid residue was cooled to ambient temperature and pyrolyzed again at 530 °C. If the first step temperature was below 290 °C, the cumulated yields (the sum of steps 1 and 2) were identical to yields of the single-step experiment at 530 °C. This indicates that the chemical and transfer processes taking place below 290 °C do not lead to chemical and structural changes that affect the outcome of the processes occurring in the temperature range from 290 °C to 530 °C. When the first step temperature was higher than 310 °C the cumulated yields of char, water, light organic compounds, and furans were higher, whereas the cumulated yields of volatiles (gases plus organic liquids) were lower than those obtained if the pyrolysis was conducted in a single step at 530 °C. To explain these observations, a mechanism is proposed in which the main emphasis lies on the competition between routes that lead to char formation and routes that release compounds from the biomass particle. Single compounds and lumped groups could not be concentrated with the stepwise approach. A separation into lighter and heavier oils turned out to be possible.

The interplay of chemistry, heat and mass transfer at particle and reactor levels was studied for the fast pyrolysis of cellulose.

Abstract:Hydrogen is an efficient fuel which can be generated via water splitting, however hydrogen evolution occurs at high overpotential, and efficient hydrogen evolution catalysts are desired to replace state-of-the-art catalysts such as platinum. Here, we report an advanced electrocatalyst that has low overpotential, efficient charge transfers kinetics, low Tafel slope and durable. Carbon nanofibers (CNFs), obtained by carbonizing electrospun fibers, were decorated with MoS 2 using a facile hydrothermal method. The imaging of catalyst reveals a flower like morphology that allows for exposure of edge sulfur sites to maximize the HER process. HER activity of MoS 2 decorated over CNFs was compared with MoS 2 without CNFs and with commercial MoS 2 . MoS 2 grown over CNFs and MoS 2 -synthesized produced about 374 and 98 times higher current density at −0.30 V (vs. Reversible Hydrogen Electrode, RHE) compared with the MoS 2 -commercial sample, respectively. MoS 2 -commercial, MoS 2 -synthesized and MoS 2 grown over CNFs showed a Tafel slope of 165, 79 and 60 mV/decade, capacitance of 0.99, 5.87 and 15.66 mF/cm 2 , and turnover frequency of 0.013, 0.025 and 0.54 s −1 , respectively. The enhanced performance of MoS 2 -CNFs is due to large electroactive surface area, more exposure of edge sulfur to the electrolyte, and easy charge transfer from MoS 2 to the electrode through conducting CNFs.

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Hollow structures of NiAs-type cobalt sulfide have been synthesized by a facile hydrothermal method. These hollow structured cobalt sulfides exhibit excellent electrochemical properties for supercapacitor applications (867 F g À1) and respectable hydrogen evolution activity.The symmetrical supercapacitor device fabricated using cobalt sulfide nanostructures showed an areal capacitance of 260 mF cm À2 with good flexibility and high temperature stability. The specific capacitance of the supercapacitor is enhanced over 150%, when the temperature is increased from 10 to 70 C.Over the last few decades, the increasing demand for energy has motivated the scientic community to develop high performance, sustainable, cost-effective and environmentally friendly materials for energy conversion and storage applications. 1-4Undoubtedly, materials for supercapacitors and hydrogen evolution are among the widely studied ones for these purposes. Supercapacitors are electrochemical energy storage devices primarily appealing for their excellent power density and long cycle life. 4-7 Carbon based electrodes are suitable for delivering high power density but have low energy density.8 Nevertheless, in recent years, the energy density of supercapacitors has been boosted by the use of metal oxides, which in turn sacrices the cycle life.4 Second, energy generation using a cleaner and cheaper method is of high importance due to increasing concerns of carbon emission. Hydrogen generation by splitting water is highly desired. The hydrogen evolution reaction (HER) is one of the key steps in the water splitting process.9 Ideally, the thermodynamic potential for the hydrogen evolution reaction should be at 0 V (vs. SHE). However, without an efficient catalyst, this reaction occurs at high overpotential.10 Presently, platinum is the most effective and durable catalyst for the hydrogen evolution reaction, but its widespread use is precluded due to its high cost and limited availability.At this juncture, it is essential to develop cost effective, sustainable and stable materials for both supercapacitor and HER applications. Recently, transition metal chalcogenides have attracted considerable attention for energy applications such as fuel cells, supercapacitors and batteries due to their high abundance, low cost and decent performance. 17Hierarchically porous nickel sulde has been synthesized for both the HER and oxygen evolution reaction (OER).18 The synthesized nickel sulde showed overpotentials of 60 mV for the HER and 180 mV for the OER in 1.0 M KOH at a current density of 10 mA cm À2 , respectively. Sharma et al. have synthesised ower-like ZnS for charge storage applications. 19They observed a high specic capacitance (226 F g À1 ) and specic capacitance was observed to decrease by 60% on increasing the scan rate from 20 to 200 mV s À1 . Other metal suldes such as WS 2 are also synthesized for HER, supercapacitor and battery applications. [20][21][22] As an important member of the transition metal sulde family, cobalt sulde is consi...

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