2 research outputs found
LiFePO<sub>4</sub>/Mesoporous Carbon Hybrid Supercapacitor Based on LiTFSI/Imidazolium Ionic Liquid Electrolyte
A hybrid
SC prepared with mesoporous carbon as the negative electrode,
LiFePO<sub>4</sub> as the positive electrode, and a LiTFSI/imidazolium
ionic liquid solution as electrolyte is presented. The cell was conceived
on the basis that it offers all of the safety features of ionic liquids
(IL) and LiFePO<sub>4</sub>, in addition to the advantages of a high
energy density device. Most of the high performance hybrids so far
reported in the literature employ aqueous or organic electrolytes,
whereas studies of hybrid cells based on IL are still rare. Here,
a fundamental study was conducted to understand how the different
interfaces and mechanisms operate in a hybrid system based on IL electrolyte
and how this affects cell performance. This device was mainly characterized
using cyclic chronopotentiometry that allows cell voltage and electrode
potentials to be simultaneously recorded. By means of this technique,
it was possible to evaluate the overall behavior of the hybrid cell
and the faradaic and capacitive electrodes simultaneously and to compare
it with the performance of selected standard cells. The results show
that the cell is able to attain an energy density of 43.3 W h kg<sup>–1</sup> at 0.010 A g<sup>–1</sup> (C/5 in relation
to LiFePO<sub>4</sub>), while maintaining a good cycling performance
Thermodynamic Study of Methylene Blue Adsorption on Carbon Nanotubes Using Isothermal Titration Calorimetry: A Simple and Rigorous Approach
In
this article, a thermodynamic study of the methylene blue (MB)
adsorption on carbon nanotubes (CNT), a known model system, was carried
out by using a simple and rigorous experimental approach based on
adsorption and isothermal titration calorimetry (ITC) experiments.
Considering the thermodynamics of the process, the classical approach
using the van’t Hoff approximation provided endothermic values
for Δ<sub>ads</sub><i>H</i><sup>0</sup> while the
ITC measurements revealed that the adsorption of MB on both unmodified
and acid-modified CNTs is an exothermic process. The thermodynamic
parameters for the systems were obtained using the infinite dilution
regime and ITC data: Δ<sub>ads</sub><i>H</i><sup>0</sup> = −9.13 ± 0.02 kJ mol<sup>–1</sup>, Δ<sub>ads</sub><i>G</i><sup>0</sup> = −21.18 ± 0.61
kJ mol<sup>–1</sup>, and Δ<sub>ads</sub><i>S</i><sup>0</sup> = 40.42 ± 0.61 J K<sup>–1</sup> mol<sup>–1</sup> for u-CNT and Δ<sub>ads</sub><i>H</i><sup>0</sup> = −11.49 ± 0.34 kJ mol<sup>–1</sup>, Δ<sub>ads</sub><i>G</i><sup>0</sup> = −27.88
± 0.18 kJ mol<sup>–1</sup>, and Δ<sub>ads</sub><i>S</i><sup>0</sup> = 54.97 ± 0.38 J K<sup>–1</sup> mol<sup>–1</sup> for f-CNT. The process is both enthalpically
and entropically driven, having a more negative Δ<sub>ads</sub><i>G</i><sup>0</sup> for the system based on a modified
nanotube. With this work, we expect to increase the interest of researchers
in the study of other solid–liquid adsorption systems using
calorimetric techniques and also contribute to a more accurate characterization
of the thermodynamic properties without the use of an excessive number
of approximations