Romain Sescousse

Viscosity of cellulose-imidazolium-based ionic liquid solutions.

The viscosities of microcrystalline cellulose dissolved in 1-ethyl-3-methylimidazolium acetate (EMIMAc) and in 1-butyl-3-methylimidazolium chloride (BMIMCl) were studied in detail as a function of polymer concentration and temperature. The goal was to compare the flow of solutions, macromolecule hydrodynamic properties in each solvent, and the activation energies of viscous flow. Intrinsic viscosities were determined using the truncated form of the general Huggins equation. In both solvents cellulose intrinsic viscosity decreases with increasing temperature, indicating the decrease of solvent thermodynamic quality. The activation energies for both types of cellulose solutions were calculated. For cellulose-EMIMAc the Arrhenius plot showed a concave shape, and thus the Vogel-Tamman-Fulcher (VTF) approach was used. We suggest an improved method of data analysis for the determination of VTF constants and demonstrate that cellulose-EMIMAc solution viscosity obeys VTF formalism. Once the dependences of Arrhenius activation energy and VTF pseudo-activation energy were obtained for the whole range of concentrations studied, they were all shown to be described by a simple power-law function of polymer concentration.

Synthesis and Properties of Platinum Nanocatalyst Supported on Cellulose-Based Carbon Aerogel for Applications in PEMFCs

Platinum nanoparticles supported on nanostructured cellulose-based carbon aerogels (carbonized aerocellulose, CAC) were evaluated in proton exchange membrane fuel cell (PEMFC). The CAC substrate was synthesized through the dissolution, gelation, regeneration, supercritical CO2 drying and pyrolysis of cellulose. The Pt nanoparticles deposition was performed by impregnation of the CAC with H2PtCl6, followed by Pt z species reduction either under H2 at 300-400C or in basic NaBH4 solution. While H2 reduction leads to uniform Pt nanoparticles well-dispersed over the CAC surface, larger agglomerates form with NaBH4 reduction, as revealed by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The reduction methods influences the quantity of platinum deposited, which may be increased by using multiple impregnation/reduction steps. The specific surface area of Pt and specific/mass activities towards oxygen reduction of the Pt/CAC materials, investigated using the rotating disk electrode setup, are similar to those of commercial Pt/Carbon Black (CB). Finally, PEMFC unit cell testing demonstrates that a Pt/CAC sample synthesized using three successive impregnation/reduction steps, loaded at ca. 14 wt Pt/(Pt C), competes with state-of-the-art Pt/CB electrocatalysts of comparable Pt loading

Elaboration and Characterizations of Platinum Nanoparticles Supported on Cellulose-Based Carbon Aerogel

This work investigates the deposition of Pt nanoparticles onto carbonized aerocellulose (CAC), via impregnation of the CAC with H2PtCl6 followed by reduction either under H2 at 300-400{degree sign}C or in a basic NaBH4 solution. H2 reduction yields uniform Pt nanoparticles (average diameter < 2 nm) dispersed over the CAC surface, as revealed by transmission electron microscopy (TEM). Larger agglomerates can be seen in TEM images for NaBH4 reduced samples, which is confirmed by powder X-ray diffraction (XRD). A rotating disk electrode was employed to analyze the electrochemical properties of the Pt/CAC materials. The active area of the platinum nanoparticles was evaluated using hydrogen adsorption/desorption cyclic voltammetry and CO-stripping measurements. The oxygen reduction reaction kinetic parameters of the Pt/CAC materials compare well with those of commercial Pt/Carbon Black (CB). Finally, PEMFC unit cell testing demonstrates that a Pt/CAC electrocatalyst synthesized using 3 successive impregnation/reduction steps can compete with state-of-the-art Pt/CB electrocatalysts.