Activated Carbon Derived from Cucumber Peel for Use as a Supercapacitor Electrode Material.

Biowaste conversion into activated carbon is a sustainable and inexpensive approach that relieves the pressure on its disposal. Here, we prepared micro-mesoporous activated carbons (ACs) from cucumber peels through carbonization at 600 °C followed by thermal activation at different temperatures. The ACs were tested as supercapacitors for the first time. The carbon activated at 800 °C (ACP-800) showed a high specific capacitance value of 300 F/g at a scan rate of 5 mV/s in the cyclic voltammetry and 331 F/g at the current density of 0.1 A/g in the galvanostatic charge-discharge analysis. At the current density of 1 A/g, the specific discharge capacitance was 286 F/g and retained 100% capacity after 2000 cycles. Their properties were analyzed by scanning electron microscopy, energy-dispersive X-ray analysis, porosity, thermal analysis, and Fourier-transform infrared spectroscopy. The specific surface area of this sample was calculated to be 2333 m2 g-1 using the Brunauer-Emmett-Teller method. The excellent performance of ACP-800 is mainly attributed to its hierarchical porosity, as the mesopores provide connectivity between the micropores and improve the capacitive performance. These electrochemical properties enable this carbon material prepared from cucumber peels to be a potential source for supercapacitor materials.

Electrochemical Performance of Chemically Activated Carbons from Sawdust as Supercapacitor Electrodes.

Activated carbons (ACs) have been the most widespread carbon materials used in supercapacitors (SCs) due to their easy processing methods, good electrical conductivity, and abundant porosity. For the manufacture of electrodes, the obtained activated carbon based on sawdust (karagash and pine) was mixed with conductive carbon and polyvinylidene fluoride as a binder, in ratios of 75% activated carbon, 10% conductive carbon black, and 15% polyvinylidene fluoride (PVDF) in an N-methyl pyrrolidinone solution, to form a slurry and applied to a titanium foil. The total mass of each electrode was limited to vary from 2.0 to 4.0 mg. After that, the electrodes fitted with the separator and electrolyte solution were symmetrically assembled into sandwich-type cell construction. The carbon's electrochemical properties were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge (CGD) studies in a two-electrode cell in 6M KOH. The CV and CGD measurements were realized at different scan rates (5-160 mV s-1) and current densities (0.1-2.0 A g-1) in the potential window of 1 V. ACs from KOH activation showed a high specific capacitance of 202 F g-1 for karagash sawdust and 161 F g-1 for pine sawdust at low mass loading of 1.15 mg cm-2 and scan rate of 5 mV s-1 in cyclic voltammetry test and 193 and 159 F g-1 at a gravimetric current density of 0.1 A g-1 in the galvanostatic charge-discharge test. The specific discharge capacitance is 177 and 131 F g-1 at a current density of 2 A g-1. Even at a relatively high scan rate of 160 mV s-1, a decent specific capacitance of 147 F g-1 and 114 F g-1 was obtained, leading to high energy densities of 26.0 and 22.1 W h kg-1 based on averaged electrode mass. Surface properties and the porous structure of the ACs were studied by scanning electron microscopy, energy-dispersive X-ray analysis, Raman spectroscopy, and the Brunauer-Emmett-Teller method.

Biomass-Derived Porous Carbon Materials for Li-Ion Battery.

Biomass-based carbon nanofibers (CNF) were synthesized using lignin extracted from sawdust and polyacrylonitrile (PAN) (30:70) with the help of the electrospinning method and subsequent stabilization at 220 °C and carbonization at 800, 900, and 1000 °C. The synthesized CNFs were studied by scanning electron microscopy, energy-dispersive X-ray analysis, Raman spectroscopy, and the Brunauer-Emmett-Teller method. The temperature effect shows that CNF carbonized at 800 °C has excellent stability at different current densities and high capacitance. CNF 800 in the first test cycle at a current density of 100 mA/g shows an initial capacity of 798 mAh/g and an initial coulomb efficiency of 69.5%. The CNF 900 and 1000 show an initial capacity of 668 mAh/g and 594 mAh/g, and an initial Coulomb efficiency of 52% and 51%. With a long cycle (for 500 cycles), all three samples at a current density of 500 mA/g show stable cycling in different capacities (CNF 800 in the region of 300-400 mAh/g, CNF 900 and 1000 in the region of 100-200 mAh/g).

The Use of Diatomite as a Catalyst Carrier for the Synthesis of Carbon Nanotubes.

In this article, multiwalled carbon nanotubes (MWCNTs) have been synthesized on the surface of a diatomite mineral impregnated with transition metal salts using a propane-butane mixture in a chemical vapor deposition reactor at atmospheric pressure. The catalyst concentration and synthesis temperature have been varied in order to understand their effects on the formation of MWCNTs and their morphology. Diatomite was chosen as a catalyst carrier due to its elemental composition. It is mainly composed of amorphous silica, quartz and also contains such metals as Fe, K, Ca, Mn, Cr, Ti, and Zn, which makes it a promising material for use as a catalyst carrier when synthesizing carbon nanotubes (CNTs) by catalytic chemical vapor deposition (C-CVD). For the synthesis of carbon nanotubes by C-CVD on the surface of the diatomite, the following salts were used as a catalyst: CoCl2·6H2O; Ni(NO3)2·6H2O, and the concentrations of the solutions were 0.5; 1.0 and 1.5 M. Natural diatomite was characterized by X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM) analysis.