Investigation of hydrogen and water on fuel cell catalysts and aluminium oxide by means of neutron scattering

The motion of hydrogen and water adsorbed on Raney-nickel and tungsten carbide has been studied by slow neutron scattering with time-of-flight technique. The data are compared with calculations for different models. The main results are as follows: Hydrogen chemisorbed on nickel up to one monolayer oscillates synchronously with the surface atoms and besides this there are oscillation of high frequency against the surface. In additional layers hydrogen behaves like on tungsten carbid: the molecules are dissociated but they do not move with the surface of the adsorbens. Nevertheless the surface diffusion is small. Such weaker bonded hydrogen may be important for the catalytic process in the fuel cell. Besides this, the surface diffusion of water on tungsten carbide is important for its catalytic activity. The second topic of this work is the behaviour of hydrogen adsorbed on alumina, which is different for ortho-and parahydrogen. The measurement cannot be interpreted in terms of a hindered rotation of the molecules; the rotational motion of the molecule is coupled with the motion of its center of mass. Besides this, quasielastic scattering has been observed, which perhaps may not be due to diffusion but a consequence of resonance conversion. (orig.) 891 WBU 892 ARA