Ostenfeld, Christopher Worsøe

The work here, entitled ”A Surface Science Approach to Hydrogen Storage”,concerns fundamental investigations of the magnesium-hydrogen interaction.The work is fueled by the quest to find alternative hydrogen storage materials, which is an essential part of a future hydrogen-based society. By studying well-defined magnesium films, unique insight can be gained into the atomicscale processes occurring. By growing thin magnesium films, with thicknesses around 100 atomic layers, under ultra-high vacuum conditions, and subsequently dosing hydrogen we can model the workings of a functioning magnesium particle. The first part of the work concerns the formation of ultra-thin magnesium films and the interaction with hydrogen. Here we find that hydrogen overlayers are adsorbed, and the findings are complemented by density functional theory calculations. We find, rather remarkably, that hydrogen cannot be released from magnesium, without magnesium sublimating. The second part of the thesis concerns the interaction of magnesium with oxygen, a common impurity in magnesium-based storage systems. Here, it is found that magnesium sublimation can be heavily attenuated, as a result of surface oxidation. We suggest that the oxide impurities, always present in powders, actually constitute a necessity for cyclic stability in the powders to be obtained.The last part concerns the interaction of well-defined magnesium films, with a high pressure of ultra-pure hydrogen, i.e. an exact replica of the conditions imposed on magnesium powders. Here, we find that the sticking probability of hydrogen on magnesium is extremely low, around 1·10−13. Adding a platinum overlayer to the surface results in a drastic increase in the sticking probability. However, the platinum overlayer is found to not be thermally stable. Although, no novel magnesium-based alloys were found, we managed to suggest why cyclic stability can be achieved in powder systems. We also opened up the possibility of investigating hydrogen transport on magnesium oxide, as better comprehension of this could lead to increased understanding of the system

Online Research Database In Technology

A surface science approach to hydrogen storage

http://orbit.dtu.dk/ws/files/5454264/Ost.PDF

A surface science approach to hydrogen storage

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