Effect of temperature on the capacitance of carbon nanotube supercapacitors.

The effect of temperature on the kinetics and the diffusion mechanism of the ions in a supercapacitor assembled with single-walled carbon nanotube (SWNT) film electrodes and an organic electrolyte were thoroughly investigated. An improved room temperature performance of the supercapacitor was observed due to the combined effects of an increase in the conductivity of the SWNT films and surface modifications on the SWNT films by repeatedly heating and cooling the supercapacitor between the temperatures of 25 and 100 degrees C. Modified Randles equivalent circuit was employed to carry out an extensive analysis of the Nyquist spectra measured at different temperatures between 25 and 100 degrees C in order to understand the fundamentals of the capacitive and resistive variations in the supercapacitor. The experimental results and their thorough analysis will have significant impact not only on the fundamental understanding of the temperature-dependent electrode/electrolyte interfacial properties but also on supercapacitor design with appropriate electrode materials for numerous industrial and consumer applications. The supercapacitor with SWNT film electrodes was capable of withstanding current densities as high as 100 A/g, yielding eminent specific power density values of about 55 kW/kg. Ultralong galvanostatic charge-discharge cycling over 200 000 cycles with a constant current density of 20 A/g at 25 and 100 degrees C, respectively, showed excellent stability in capacitance with more than 80% efficiency. The usage of such a supercapacitor potentially enables far-reaching advances in backup energy storage and high pulse power applications.

Growth of carbon nanofibers on carbon fabric with Ni nanocatalyst prepared using pulse electrodeposition.

The pulse electrodeposition (PED) technique was utilized to deposit nanosized (≤10 nm) Ni catalysts on carbon fabric (CF). Via an in situ potential profile, the PED technique can control the Ni catalyst loading, which is an important parameter for the growth of carbon nanofibers (CNFs) on CF. The preparation of CNF-coated CF (carpet-like CF) was carried out in a thermal chemical vapor deposition system with an optimum loading of Ni catalysts deposited in the PED pulse range from 20 to 320 cycles. CNFs grown at 813 K using different pulse cycles had a narrow diameter distribution, around 15 ± 5 nm to 29 ± 7 nm; they have a hydrophobic surface, like lotus leaves. Transmission electron microscopy images confirmed the graphene structural transformation of CNFs with the growth temperature. Solid wire CNFs were initially grown at 813 K with graphene edges exposed on the external surface. At elevated growth temperatures (1073 and 1173 K), bamboo-like CNFs were obtained, with herringbone structures and intersectional hollow cores.

Anthocyanin-sensitized solar cells using carbon nanotube films as counter electrodes.

Carbon nanotube (CNT) films have been used as counter electrodes in natural dye-sensitized (anthocyanin-sensitized) solar cells to improve the cell performance. Compared with conventional cells using natural dye electrolytes and platinum as the counter electrodes, cells with a single-walled nanotube (SWNT) film counter electrode show comparable conversion efficiency, which is attributed to the increase in short circuit current density due to the high conductivity of the SWNT film.