Pt-based nanocomposites with low Pt utilization and high-activity by incorporating with other transition metals have received significant interest in catalysis. Meanwhile, loading Pt-based catalysts on graphene has great research value for improved stability and dispersity of the catalysts. Herein, a facile L-proline-mediated solvothermal strategy was reported to construct reduced graphene oxide (rGO) supported sheet-like PtCo nanocrystals (Pt78Co22 NCs/rGO) in ethylene glycol (EG). The as-synthesized nanocomposite manifested remarkably improved catalytic properties and chemical stability for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), surpassing home-made Pt29Co71 nanoparticles (NPs)/rGO, Pt83Co17 NPs/rGO, Pt52Co48 NPs, commercial Pt/C and Pt black catalysts. These scenarios demonstrated an improved catalytic performances by tailoring the feeding ratio of Pt:Co and introducing rGO as a support. This work provides some new insights to design rGO-supported Pt-based catalysts by engineering the shapes and compositions in practical fuel cells. (C) 2019 Elsevier Inc. All rights reserved.