Field of Expertise: Advanced Material Science
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Field of Expertise: Advanced Material Science | |
Plasma Deposited Proton Conductive Organic Membranes for Fuel Cells Proton conductive copolymers of hexamethyldisiloxane (HMDSO) and methacrylic acid (MAA) are synthesized by Plasma Enhanced Chemical Vapour Deposition (PECVD). The MAA provides the –COOH groups useful to conduct protons, while the HMDSO is responsible for creating the hydrophobic backbone to stabilize the structure during tests in water. With a similar CVD technique and similar copolymer composition, conductivities in the range of 70 mS/cm were reached. The aim of this new research is to achieve the same order of magnitude in proton conductivity but greater water and temperature stability. The ultimate goal is to use these copolymers as proton exchange membranes in fuel cells. The plasma polymerization represents a good solution for depositing thin films of monomers with different solubilities with great accuracy and homogeneity, at high deposition rates and with different thicknesses. This technique shows a great potential in producing a strongly bonded network of copolymers resulting in a high stability in water at 80°C. The parameters of the applied plasma (comonomer ratio, plasma power, pressure) are correlated with the properties of the deposited film. The characteristics of the film are strongly dependent on the monomer ratios. The percentage of hydrophilic acid groups retained in the copolymers is investigated by FTIR-Spectroscopy. X-ray reflectivity is used to study the swellability in water as well as the thickness and homogeneity of the coatings. We demonstrate that the coatings deposited at intermediate plasma power (20-25W) were stable in water (24h, 80°C) and were also retaining the most of the acid groups. The ionic conductivity of the membranes is measured with impedance spectroscopy. Finally the membranes are also integrated in fuel cells to test them in working conditions. |