The interaction of water with clean palladium films: A thermal desorption and work function study

The adsorption–thermodesorption behavior of H2O molecules on clean, thin polycrystalline Pd-films has been studied by means of work function (WF) and mass resolved temperature programmed desorption (TPD). Film morphology was varied and stabilized by annealing in the range 77–473 K. As deduced from WF changes during adsorption and TPD, unannealed films formed on glass at 77 K are highly porous. On the films at 77 K, H2O adsorbs molecularly and binds to the surface through the O-atom as suggested by the decrease in work function. Data can be rationalized assuming that during TPD, the adsorbed H2O molecules undergo decomposition. H2 never evolved from the films, not even at 473 K, suggesting that the observed H2O desorption peak at T>220 K should involve molecule rebuilding, as found in Pd single crystals.