Water production on palladium in hydrogen-oxygen atmospheres

We have studied the water production on Pd in various oxygen-hydrogen atmospheres in combination with work function measurements, photoelectron spectroscopy and hydrogen sensitive measurements on a PdSiO 2Si structure. The existence of a critical oxygen to hydrogen pressure ratio is confirmed. Above the critical ratio, the water production rate decreases with increasing oxygen pressure and increases with increasing hydrogen pressure. Below the critical ratio, the water production rate is proportional to the oxygen pressure and independent of the hydrogen pressure. These features, together with the variations in oxygen and hydrogen coverage, are described by a simple Langmuir-Hinshelwood model, assuming that hydrogen has a large lateral mobility and that both hydrogen and oxygen adsorption-dissociation is blocked by adsorbed oxygen.