Platinum is the best single element oxygen reduction reaction electrocatalyst. In recent years, several advanced catalysts have been suggested. One of them is the so-called "platinum monolayer electrocatalyst". In this work we demonstrate the potential-and time-resolved dissolution characteristics of such sub-monolayer platinum supported on gold in potentiodynamic and potentiostatic regimes. It is shown that the as-prepared Pt@Au is not stable, but rather shows significant dissolution of both Pt and Au similar to the pure elements. Potential-resolved dissolution profiles reveal that anodic dissolution scales with Pt coverage, while cathodic dissolution and quasi-steady-state dissolution are Pt coverage independent. This implies a significantly higher Pt coverage normalized dissolution of Pt@Au, viz. a factor of four higher dissolution amounts for Pt coverage of 0.25. The onsets of Pt and Au dissolution are also comparable to the pure elements. Only after intermixing during potential cycling does the system become somewhat stabilized. The onset of Pt transient anodic dissolution shifts to more positive values. The data obtained in the current work provide new insights into the mechanism of platinum dissolution. It also aids the understanding of the previously observed effect of stabilization of Pt catalysts by addition of Au, and will therefore guide future developments for improving catalyst performance. (C) The Author(s) 2016. Published by ECS. All rights reserved.