Bimetallic nanostructures utilizing Pt and other metals have garnered much interest particularly in the form of non-Pt core@Pt shell structures. The use of two-dimensional nanosheets as the catalyst core is a promising approach since the nanosheets offer high utilization and stability owing to their atomic scale thickness and extended surface. In this work, we demonstrate the pure two-dimensional growth of Pt overlayers on a Ru nanosheet core supported on a flat, non-porous glassy carbon surface. The atomically-controlled deposition of the Pt shell was carried out by Surface Limited Redox Replacement (SLRR) in a one-cell configuration, using adsorbed Cu as a mediator prepared by underpotential deposition. The catalyst surface coverage determined by Cu stripping voltammetry showed that the surface of the nanosheet catalysts was completely covered by Pt after 2 SLRR cycles and maintained the original atomic flatness of the Ru nanosheet core. Consecutive SLRR cycles resulted in the two-dimensional growth of Pt multi-layers without significant increase in roughness, in contrast to the case where a porous carbon black support was used. The catalysts performance was investigated by hydrogen oxidation reaction and oxygen reduction reaction measurements. (C) 2018 Elsevier Ltd. All rights reserved.