Skladování vodíku v nízkoteplotních kovových hydridech na bázi La-Ni a jejich integrace s palivovými články

Abstract

The dissertation work describes the alternative way of hydrogen storage in compact solid form in low-temperature metal hydrides and their practical application and integration with fuel cells. The main aim of the work was an attempt to modify the well-known LaNi5 metal hydride and find the optimal working temperature-pressures parameters of the alloy for reversible hydrogen sorption via fuel cells. In this part, steps have been taken to modify the LaNi5 alloy by partial replacement of La by Ce and Ni by Fe. Attempts have been made to optimize the time-temperature parameters of the alloys synthesis, and final hydrogen storage density. Alloys synthesis was performed via two different methods: by classical thermal melting of pure metals, and by the thermochemical reaction of the metal chlorides. A comparative analysis of the obtained La-Ni, La-Ce-Ni, La-Ce-Fe-Ni alloy samples was carried out. The detailed physicochemical analysis of the prepared alloys and corresponding hydrides was conducted. XRD and SEM analysis data demonstrate that an increase in the alloy synthesis temperature and sample holding time facilitates the desired LaNi5 and (LaCe)Ni5 phases formation. Unfortunately, the problem of oxidation of the samples prepared from metal chlorides still remains unsolved. Therefore, further research is needed in order to investigate the possibilities of more effective use of LiH or using a different reducing agent for the alloy thermochemical synthesis. The preliminary study of LaNi5 alloy, modified with element Fe shown the significant changes of working hydrogen sorption pressure. Modification of the LaNi5 alloy by Ce and the structured state of the storage material can also influence the thermodynamic properties and value gravimetric capacity of the hydride. (LaCe)Ni5-X-cast was traditionally cast into Cu mold and (LaCe)Ni5-X-FC was remelted and cast on water-cooled Cu-plate. The structure of the (LaCe)Ni5-X-FC sample contained fine grains and fine particles containing X (Ce) segregated on grain boundaries. The sample (LaCe)Ni5-X-FC showed higher gravimetric capacity (up to 1.55 Wt.%) at lower sorption pressure in comparison with (LaCe)Ni5-X-cast sample. The preparation of materials with various structure states could be a completely novel way for influence of thermodynamic properties of hydrogen storage materials. These materials could reach sufficient storage properties at low temperatures. The knowledge about the influence of the structure state on hydrogen storage properties can show new ways for the low-temperature metal hydrides development. The second part of the thesis declares the results of the metal hydride testing in real operation conditions during reversible hydrogen sorption. The complex hydrogen system based on hydrogen production, storage and utilization was studied. Hydrogen desorption was carried out via low and high-temperature fuel cells, with subsequent thermography analysis of the whole hydride-fuel cell system. The additional heat transfer computer simulation of the fuel cell under the load allowed to determine the waste heat which can be effectively used to desorb hydrogen from the La-Ni based low-temperature metal hydride, what allows using more efficiently both components of the hydrogen system.