Département des Technologies Solaires (LITEN)
The availability of low cost proton exchange membranes (PEM) with high cation selectivity is one of the most acute problems in the development of affordable redox-flow batteries. The usual strategy in the development of PEM materials includes co-polymerisation and further chemical functionalisation of various organics, which are subsequently melted or solution cast to form a thin membrane (Nafion® can be considered as the most typical for example). The redox-flow battery specifics allow the use of the polyaniline (PANI) as a promising alternative proton conducting material. The synthesis of this polymer (especially the electrochemical polymerisation) is very cheap and guarantees low final cost of the product. The use of PANI as proton exchange system is possible because the bi-polar flow reactor can be designed avoiding the physical contact between the membrane and the electrode (for example sandwiching the membrane between two glass mat tissue layers). In this way, the electric conductivity of PANI is eliminated and the latter operates only as proton exchange polymer. The nature of the partially or the fully oxidized protonated PANI is particularly suitable for composite membranes: this form of the polymer is insoluble in water, acid solutions and most of the typical organic solvents. The thesis objectives will focus on the development and characterization of such composite membranes using electrochemical cells and redox-flow battery cells employing different electrochemical couples. The molecular structure of the PANI supposes much faster proton transport due to the very dense distribution of the proton exchange groups ? theoretically each aniline monomer element can be protonated, providing very dense distribution of sites for proton hoping. Thus the study of the ?isolated? proton conductivity of the PANI apart from its electric conductivity will be another objective of the thesis, which is interesting from fundamental point of view, because almost all of the published literature on PANI discusses either its electric or mixed conductivity.