Exploring the reactivity and nanoscale morphology of de-alloyed layers

De-alloying of a 70Cu-30Pt alloy has been studied with a view to testing the thermodynamic prediction that a novel kind of underpotential or sub-potential electrodeposition may be possible in such highly curved nanoporous solids. After de-alloying in H₂SO₄ solution containing CuSO₄, successive cathodic processes of PtO monolayer reduction, UPD of Cu, and a Cu plating process were identified, all occurring at potentials above the Cu equilibrium potential. The maximum amount of charge in the third plating process was determined to be about three monolayers, averaged over the whole porous surface. This seems to rule out the possibility that this process is some kind of second UPD layer or other non-bulk form of Cu plating. A probable explanation is that small amounts of bulk Cu are plating into regions of high negative curvature within the de-alloyed material. However X-ray diffraction did not show any evidence of bulk Cu.