Chung-Jen Tseng

Supercapacitive performance of porous graphene nanosheets in bis(trifluoromethylsulfony)imide and bis(fluorosulfonyl)imide ionic liquid electrolytes

A method of high-heating-rate thermal reduction is used to produce porous graphene nanosheets (PGNSs). This material is characterized by a unique holey structure, which is suitable for ionic liquid (IL) electrolyte. To study the effects of electrolyte anion, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMI-TFSI) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI) ILs are used. Due to the smaller size of FSI−, EMI-FSI shows a higher conductivity and lower viscosity than those of EMI-TFSI. The specific capacitances of PGNS electrodes are 90 and 260xa0Fxa0g−1, respectively, measured in EMI-TFSI and EMI-FSI ILs at a potential scan rate of 50xa0mVxa0s−1. The PGNS symmetric cell with EMI-FSI electrolyte is able to deliver a maximum energy and power densities of 110 Wh kg−1 and 101xa0kWxa0kg−1, respectively, with a cell voltage of 3.5xa0V. In addition, 85% of the initial capacity can be retained after 2000 charge–discharge cycles.

COMBINED NATURAL CONVECTION AND RADIATION WITH TEMPERATURE-DEPENDENT PROPERTIES

This paper investigates the effects of temperature dependence of radiative properties of a medium on radiation and natural convection interaction in a rectangular enclosure. The radiative transfer equation is solved using the discrete ordinates method, and the momentum, continuity, and energy equations are solved by the finite volume method. Effects of the conduction-to-radiation parameter (Nr), Rayleigh number (Ra), and optical thickness are discussed. Results show that temperature dependence of radiative properties affects the temperature gradient, and hence the energy transport even in relatively weak radiation condition. On the other hand, temperature dependence of radiative properties has relatively insignificant effects on convection characteristics; even though it does affect the way that energy transfers into the system. As Nr is decreased or Ra is increased, the effects of temperature dependence of radiative properties become more significant.