Underpotential Co-deposition of Cu1-xPtx Alloys

Abstract

The electrodeposition of Cu1-xPtx alloys by underpotential co- deposition of Cu with Pt is demonstrated using an H2SO4-CuSO4- PtCl42- electrolyte. The composition and structure of 1 micrometer thick alloy films grown at different potentials were examined by EDS, XRD and TEM. A thermodynamic rational for the alloying process is provided by a symmetrical regular solution model whereby underpotential co-deposition of Cu is ascribed to the negative enthalpy of mixing with Pt. The observed dependence of alloy composition on potential is in good agreement with equiatomic mixing enthalpy of -18 kJ/mol, obtained from calculations by Miedema et al. An EQCM was used to provide a time resolved assessment of the alloy formation process. Simultaneous measurement of the mass and current transients during potential steps enable the effects of submonolayer underpotential deposition of Cu onto a Pt rich surface to be observed and separated from the subsequent steady-state co-deposition of Cu with Pt.