Sviluppo di materiali innovativi per adsorbimento H2 e realizzazione di una unità dimostrativa di bombola

Abstract

The research activity carried out during this three-year of PhD was directed towards the synthesis of new materials for the hydrogen storage. In particular, the PEEK was used as a basic polymeric matrix; this is an aromatic polymer, heat-resistant of which many properties are known. This base material does not show such chemical-physical characteristics that it can be used to bind and release H2 molecules, moreover, not being a porous material, cannot even think of a physical bond with H2. A functionalization reaction was necessary in which a certain percentage of chlorosulfonic groups on the aromatic ring of the polymer was introduced. This reaction resulted in both a slight increase in the surface area (from 9 to 19 m2/g) and also a morphological variation of the material was observed. To give the possibility to hydrogen to bind, presumably in a chemical way to the polymer, the chloride was exchanged with the permanganate ion, coming from a solution of KMnO4, that act like a precursor, which in an acidic environment is reduced to MnO2. The importance of the synthesis parameters such as time and temperature and the concentration of the precursor was verified. From the study of these parameters, different materials have been synthesized with a metal oxide load ranging from 7 to 80 wt%. The X-ray study showed that the Mn oxide synthesised is of the Birnessite type, having a characteristic lamellar structure, needle-like structure with characteristic peaks located at 2q = 12 °, 37 ° and 66 °. It was found that the increase in the percentage of oxide in the composite material is almost directly proportional to the absorption capacity. From absorption measurements by Sievert apparatus at 110 °C / 60bar, particularly interesting results were obtained, reaching 1 wt% of H2 absorption with materials having a load of 80 wt% of Mn oxide. It has been seen how the increase of the synthesis temperature at 80 °C and 95 °C does not involve any variation from the H2 adsorption but changes, probably, the structure of the oxide clusters which tend to be smaller in size. Moreover, from post volumetric measurement analysis, evident differences were found, in fact the initial MnO2 (IV) was reduced in Mn2O3 (III). For this reason, the synthesis temperature was decreased to 50 °C, reducing the analysis temperature from 110 °C to 50 °C by operating at 40 bars, in these conditions, over 3 wt% of H2 absorption was revealed, moreover, a reversible trend after three cycles of abs / des was obtained. These results seem to suggest a chemical interaction between hydrogen and the material. This material was then selected as an absorbent material to be introduced into a laboratory prototype tank (having a volume of 20L) that powered a 10W fuel cell. After increasing the material synthesis from 2 to 10 g, leaving all the chemical-physical and H2 absorption properties unaltered, the tank was designed considering some of the basic characteristics of the material. To characterize the tank two tests were designed: an electrochemical one in which the prototype was directly connected to the tank and the cell power and its life in real time was followed. Through this test, a power system had achieved a value of about 10W for an average time of 6min, less than the expected time of 20min, due to H2 losses in the tank / cell system. This problem was also recorded using the other method through mass flow and P sensors at the inlet and outlet of the tank. Considering that the system is a small demonstration developed on a laboratory scale and the components used were probably unsuitable for this purpose, by making the necessary changes and shrewdness, the H2 losses can be eliminated and, consequently, the life of the tank can reach the ideal value.