The influence of surface effects on the hydrogen absorption investigated on the V-H model system

The system V-O-H has been chosen as a model system to investigate surface e ffects on hydrogen absorption in metals. By means of XPS, SIMS, and thermal desorption mass spectrometry (TDMS) methods, the influence of oxygen segre gated from the bulk as well as adsorbed from the gas phase has been pointed out. Segregated oxygen obstructs the hydrogen absorption, whereas non-stoi chiometric and stoichiometric oxides have a preventing effect already with coverages in the range of monolayers. Ion bombardment in connection with sp utter-cleaning or SNMS and SIMS analyses produces additional absorption sit es in the surface near region for hydrogen. These can be populated by hydro gen from the gas phase during H-2 exposure or diffusing from the bulk, if t he sample was H-2 loaded before. Beside elements like vanadium, there exist alloys (e.g. TiFe, LaNi5, TiMn2) , which are particularly suitable for practical storage purposes. It is imp ortant for the further development of such alloys but also for a better und erstanding of absorption kinetics to investigate the influence of surface e ffects also on these alloys. (C) 2001 Elsevier Science B.V. All rights rese rved.