The fabrication of Pt-coated, vertically aligned, nanoporous gold-nanorod arrays (see figure, left panel) that display electrocatalytically active large surface areas is described. Epitaxial platinum coatings only 1-2 monolayers thick are prepared by the spontaneous replacement of an electrochemically deposited copper layer with platinum metal. Electrochemical characterization of the resulting nanoporous nanorod arrays (see figure, right panel) is carried out as a method for probing catalytic behavior.