Electrochemical growth and dissolution of Ni on bimetallic Pd/Au(1 1 1) substrates

In this work we study the electrochemical growth and dissolution of a Ni on Pd-Au(1 1 1) bimetallic surfaces using in situ scanning tunnelling microscopy. We also compare Ni deposition on monometallic electrodes, i.e. Au(1 1 1) and Pd(1ML)/Au(1 1 1), using electrochemical characterizations. Results evidence that the first Ni monolayer grows preferentially on Au(1 1 1) in a wide potential range, and that a full Ni monolayer covering the entire Pd-Au surface can be selectively dissolved from Pd islands. No such selectivity is observed upon growth of subsequent Ni atomic planes. We demonstrate that the Ni-substrate interactions play a key role in the above mentioned selectivity. The binding energy of Ni to Pd is found to be 80 meV smaller than of Ni to Au. The sign and the amplitude of this difference are discussed in light of the d band filling of the Pd-Au(1 1 1) bimetallic surface and the presence of adsorbed H on Pd before deposition.