Spontaneous and electrodeposition of Pt on Ru(0001)

Pt was deposited onto a Ru(0001) electrode from a PtCl62--containing HClO4 solution either electrochemically or spontaneously ( i.e . without external current flow). Composition, structure and morphology of the deposit were studied by means of Auger electron spectroscopy (AES), high energy electron diffraction (RHEED), and scanning electron microscopy (SEM). At first pseudomorphic growth of a 2D-Pt adlayer takes place, while with higher coverages 3D-clusters develop for which the most densely packed [011]-rows of the Pt(111) planes are parallel with the most densely packed [1120]-rows of the Ru(0001) substrate. These Pt-clusters exhibit typical diameters between 2 and 10nm, while their average mutual separation varies with the total amount of deposit. If compared with the bare Ru(0001) surface, the samples with Pt deposits exhibit considerably enhanced activity with respect to electrooxidation of formic acid or methanol