Jepsen, Julian

Using fuel cells in energy generation makes it possible to provide clean energy in line with the demand. Fuel cells offer a major advantage over other renewable energy sources whose generation is dependent on external influences. However, fuel cells cannot compete economically with conventional energy generation systems such as diesel generators. Such an economical constraint is partly due to the higher energy requirements of hydrogen storage. Metal hydride storage systems offer the possibility of reducing the energy intensity of storage due to low storage pressures. Heat is also required to operate such storage systems, which can be provided from the fuel cell's waste heat. To extract the heat from the fuel cell, a novel cooling circuit structure for large-scale applications is presented and simulated, considering the requirements of the metal hydride storage system regarding temperature (60 °C) and mass flow (60 kg/min). The architecture of the cooling concept consists of a primary and a secondary circuit, whereby the primary circuit is responsible for cooling the fuel cell and the secondary circuit for extracting the heat. Finally, simulation data are presented, which show the system behaviour in the event of changes in the fuel cell's electrical load and the heat consumer's thermal load. This coupling strategy shows that the cooling system is suitable for extracting the waste heat and keeping all essential parameters constant.

The hydrogen sorption behavior of the Mg2FeH6- MgH2 hydride system is investigated via in-situ synchrotron and laboratory powder X-ray diffraction (SR-PXD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), particle size distribution (PSD) and volumetric techniques. The Mg2FeH6-MgH2 hydride system is obtained by mechanical milling in argon atmosphere followed by sintering at high temperature and hydrogen pressure. In-situ SR-PXD results show that upon hydriding MgH2 is a precursor for Mg2FeH 6 formation and remained as hydrided phase in the obtained material. Diffusion constraints preclude the further formation of Mg2FeH 6. Upon dehydriding, our results suggest that MgH2 and Mg2FeH6 decompose independently in a narrow temperature range between 275 and 300 C. Moreover, the decomposition behavior of both hydrides in the Mg2FeH6-MgH2 hydride mixture is influenced by each other via dual synergetic-destabilizing effects. The final hydriding/dehydriding products and therefore the kinetic behavior of the Mg 2FeH6-MgH2 hydride system exhibits a strong dependence on the temperature and pressure conditions. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.