Sepideh Soltaninejad

Fabrication, characterization, and thermal property evaluation of silver nanofluids

Silver nanoparticles were successfully prepared in two different solvents using a microwave heating technique, with various irradiation times. The silver nanoparticles were dispersed in polar liquids (distilled water and ethylene glycol) without any other reducing agent, in the presence of the stabilizer polyvinylpyrrolidone (PVP). The optical properties, thermal properties, and morphology of the synthesized silver particles were characterized using ultraviolet-visible spectroscopy, photopyroelectric technique, and transmission electron microscopy. It was found that for the both solvents, the effect of microwave irradiation was mainly on the particles distribution, rather than the size, which enabled to make stable and homogeneous silver nanofluids. The individual spherical nanostructure of self-assembled nanoparticles has been formed during microwave irradiation. Ethylene glycol solution, due to its special properties, such as high dielectric loss, high molecular weight, and high boiling point, can serve as a good solvent for microwave heating and is found to be a more suitable medium than the distilled water. A photopyroelectric technique was carried out to measure thermal diffusivity of the samples. The precision and accuracy of this technique was established by comparing the measured thermal diffusivity of the distilled water and ethylene glycol with values reported in the literature. The thermal diffusivity ratio of the silver nanofluids increased up to 1.15 and 1.25 for distilled water and ethylene glycol, respectively.

Review of Energy and Power of Supercapacitor Using Carbon Electrodes from Fibers of Oil Palm Fruit Bunches

Energy and power capability of a supercapacitor is important because of its function to provide backup power or pulse current in electronic/electric products or systems. The choice of its electrode materials, typically such as carbon, metal oxide or conducting polymer determines the mechanism of its energy storage process. This short review focuses on the supercapacitors using porous carbon electrode prepared, respectively, from fibers of oil palm empty fruit bunches. The specific energy and specific power of these supercapacitors were analyzed to observe their trend of change with respect to the electrode preparation parameters affecting the porosity, structure, surface chemistry and electrical conductivity of electrodes, and thence influence the energy and power capability of a supercapacitor. This review found that the trend of change in specific energy and specific power was not in favor of the expectation that both the specific energy and specific power should be in increasing trend with a significant progress.

Electrochemical Characterization of Supercapacitor Electrodes Prepared by Activation of Green Monoliths Consist of Self-Adhesive Carbon Grains and Lignin

Self-adhesive carbon grains (SACG) and lignin were prepared from fibres of oil palm empty fruit bunches by a low carbonization temperature and chemical treatment methods, respectively. Green monoliths were prepared from the KOH-treated SACG mixed with the organosolv-treated lignin with their weight percentages of 0%, 5%, 10%, 15% and 20%, respectively. The green monoliths were carbonized and activated into highly porous activated carbon monoliths (ACMs) electrodes for supercapacitor applications. The electrochemical characterization using galvanostatic charge-discharge (GCD) technique was carried out on the supercapacitor cell fabricated using these electrodes. The results show that the addition of 5 wt.% lignin was optimum, corresponding to the higher values of the specific capacitance (137 Fg-1), specific energy (4.13 Wh kg-1), specific power (192 W Kg-1), and a satisfactory value of equivalent series resistance (0.467 Ω) of the supercapacitor.