VIBRATIONAL SPECTROSCOPY STUDY OF POLYMER-BASED COMPOSITE MEMBRANES FOR FUEL CELL APPLICATIONS

Nowadays the research on new energy solutions is a key point in the development of a sustainable society. Fuel cells represent a promising system for a clean and efficient power generation, with a functioning based on the conversion of chemical energy into electricity through a chemical reaction, and pure water as waste emission if H2 is used as fuel. Among the various type of fuel cells, proton exchange membrane fuel cells (PEMFC) are characterized by low start-up time and low working temperature, and are particularly promising for automotive applications. Nevertheless, some issues are still present that limit the PEMFC diffusion on the market. One of these problems is the sharp decay of conductivity of a PEMFC crucial element, the proton conductive membrane, at high temperature (T > 100 °C) and low humidity conditions. In order to obtain membranes with better performances, an attractive strategy consists of the incorporation into the host polymer matrix of inorganic acidic materials, able to increase the system water retention and at the same time the total number of acidic sites, important for the proton conduction. Until now, a large variety of different filler and membranes materials have been studied in literature, usually with promising results in terms of membrane performances in critical conditions, but to optimize and properly tailor these systems a deeper understanding of their structures and operation mechanism is required. Experimental techniques like Raman and infrared spectroscopy represent a valuable tool to clarify the effects of the filler incorporation on the membrane structure and properties. Aim of this thesis is to carry out a systematic Raman and infrared analyses on different composite membranes containing nanosized fillers. The fillers vibrational properties, their effective inclusion into the membranes as well as the effect that the inclusion has on both fillers and polymers have been studied with micro-Raman and infrared spectroscopy. Furthermore, an analysis on the inner environment of the composite membranes carried out at different ambient relative humidities and temperatures provided additional information on the complex behaviour of these composite systems.