Enhanced Hydrogen-Transfer Catalytic Activity of Iridium N‑Heterocyclic Carbenes by Covalent Attachment on Carbon Nanotubes

Oxidized multiwall carbon nanotubes (<b>CNT</b>) were covalently modified with appropriate hydroxyl-ending imidazolium salts using their carboxylic acid groups. Characterization of the imidazolium-modified samples through typical solid characterization techniques, such as TGA or XPS, allows for the determination of 16 wt % in <b>CNT-1</b> and 31 wt % in <b>CNT-2</b> as the amount of the imidazolic fragments in the carbon nanotubes. The imidazolium-functionalized materials were used to prepare nanohybrid materials containing iridium N-heterocyclic carbene (NHC)-type organometallic complexes with efficiencies as high as 95%. The nanotube-supported iridium–NHC materials were active in the heterogeneous iridium-catalyzed hydrogen-transfer reduction of cyclohexanone to cyclohexanol with 2-propanol/KOH as hydrogen source. The iridium hybrid materials are more efficient than related homogeneous catalysts based on acetoxy-functionalized Ir–NHC complexes with initial TOFs up to 5550 h^–1. A good recyclability of the catalysts, without any loss of activity, and stability in air was observed

LiFePO₄/Mesoporous Carbon Hybrid Supercapacitor Based on LiTFSI/Imidazolium Ionic Liquid Electrolyte

A hybrid SC prepared with mesoporous carbon as the negative electrode, LiFePO₄ 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 LiFePO₄, 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^–1 at 0.010 A g^–1 (C/5 in relation to LiFePO₄), while maintaining a good cycling performance