On the Underpotential-Overpotential Transition in the Deposition of Silver on Platinum.

Abstract The deposition of silver on polycrystalline platinum was investigated over a wide range of potentials, covering both underpotential and overpotential regions. The two-dimensional (2D) underpotential deposit at full coverage consists of a layer of silver 1.5 atoms thick. A Ag+Pt alloy forms at underpotentials close to the silver reversible potential. The Ag+Pt alloy is not stable at overpotentials, when a three dimensional (3D) deposit of silver is present on the platinum surface. It has been shown that a reversible 2D–3D phase transition occurs at the reversible potential, that links the underpotential deposit to the overpotential deposit.