DYNAMICS OF HYDROGEN ADSORPTION ON PROMOTER-MODIFIED AND INHIBITOR-MODIFIED NICKEL SURFACES

This paper deals with changes in the adsorption dynamics for hydrogen on Ni(111) introduced by an inhibitor (potassium) and a promoter (oxyg en). At low surface coverage each potassium atom generates an area of increased barrier height for hydrogen dissociation. DePending on the H -2-particle energy this inactive area can range from 7 to 100 adsorpti on sites. At high potassium coverage the adsorption behavior of H-2 on nickel becomes more similar to adsorption on a noble metal like coppe r, exhibiting a barrier height of about 0.3 eV. Oxygen as coadsorbate generates an inhibited area in its close surroundings, further away an area with reduced barrier height is established. A much smaller area compared to potassium is modified by each oxygen atom. For the case of oxygen and hydrogen a repulsive interaction of the coadsorbates is ob served; in contrast, potassium and hydrogen exhibit an attractive inte raction. The changes in adsorption dynamics for H-2 introduced by the coadsorbates are discussed in relation to the work functions observed.