Valérie Flaud

Plasma Membranes Modified by Plasma Treatment or Deposition as Solid Electrolytes for Potential Application in Solid Alkaline Fuel Cells

In the highly competitive market of fuel cells, solid alkaline fuel cells using liquid fuel (such as cheap, non-toxic and non-valorized glycerol) and not requiring noble metal as catalyst seem quite promising. One of the main hurdles for emergence of such a technology is the development of a hydroxide-conducting membrane characterized by both high conductivity and low fuel permeability. Plasma treatments can enable to positively tune the main fuel cell membrane requirements. In this work, commercial ADP-Morgane® fluorinated polymer membranes and a new brand of cross-linked poly(aryl-ether) polymer membranes, named AMELI-32®, both containing quaternary ammonium functionalities, have been modified by argon plasma treatment or triallylamine-based plasma deposit. Under the concomitant etching/cross-linking/oxidation effects inherent to the plasma modification, transport properties (ionic exchange capacity, water uptake, ionic conductivity and fuel retention) of membranes have been improved. Consequently, using plasma modified ADP-Morgane® membrane as electrolyte in a solid alkaline fuel cell operating with glycerol as fuel has allowed increasing the maximum power density by a factor 3 when compared to the untreated membrane.

Reaction intermediate/product-induced segregation in cobalt–copper as the catalyst for hydrogen generation from the hydrolysis of sodium borohydride

Cobalt is the most attractive catalyst for hydrogen generation from the hydrolysis of sodium borohydride, NaBH4, but its potential is further improved when it is combined with an inactive element like copper. Accordingly, several cobalt–copper catalysts (CoxCu1−x, with x as a mole ratio equal to 0, 0.1, 0.25, 0.5, 0.75, 0.9 or 1) were prepared. Under our conditions, Co0.9Cu0.1 shows the best performance, being able to complete H2 evolution in <4 min (vs. <7 min for Co). However, Co0.9Cu0.1 is not as stable as expected; after the first cycle, the catalytic activity in terms of the H2 generation rate halves, and then remains quite constant for additional cycles (up to five under our conditions). XPS measurements show that the surface composition of Co0.9Cu0.1 is subject to changes during hydrolysis; the anti-segregation of copper concomitantly takes place with the segregation of cobalt. This is explained through the occurrence of borate-induced segregation, favored due to the well-known strong affinity of cobalt for borate species. In other words, the catalytic activity of cobalt can be improved through combination with copper but, under our conditions, it cannot be stabilized. This is evidenced and discussed in detail herein.

Copper hexacyanoferrate functionalized single-walled carbon nanotubes for selective cesium extraction

Single-walled carbon nanotubes (SWCNTs) are functionalized with copper hexacyanoferrate (CuHCF) nanoparticles and therefore constitutes promising solid substrates for the sorption of Cs+ ions from liquid effluents. The high mechanical resistance and large electrical conductivity of SWCNTs are associated to the ability of CuHCF nanoparticles to selectively complex Cs+ ions in order to achieve membrane-like buckypapers presenting high loading capacity of cesium. The materials are thoroughly characterized using electron microscopy, Raman scattering, X-ray photoelectron spectroscopy and thermogravimetric analyses. Cs sorption isotherms are plotted after liquid phase ionic chromatography of the Cs solutions before and after exposure to the materials. It is found that the total sorption capacity of the material reaches 230 mg.g-1, and that one third of the sorbed Cs (80 mg.g-1) is selectively complexed in the CuHCF nanoparticles grafted on SWCNTs. These high values open interesting perspectives in the integration of such materials in electrically driven devices for the controlled sorption and desorption of these ions.