In this study, we first report how to synthesize 3D PtNi nanosponges without using surfactants. A 3D PtNi nanosponge wrapped with graphene dots was synthesized at room temperature using formic acid as a reducing agent and N-doped carbon dot as a structure-directing reagent. 3D PtNi nanosponge was formed only in the presence of carbon dots in the reaction solution. During the reaction, the N-doped carbon dots were reduced and exfoliated to graphene dots, which encapsulated PtNi nanocrystals. The composition of the developed nanosponge can be easily controlled by adjusting the reaction temperature. The prepared material exhibited excellent catalytic activity and durability for oxygen reduction reaction as compared with commercially available Pt/C. This is due to the self-supporting structure of interconnected nanosponge and the role of the graphene shell wrapping around the PtNi nanosponge. The proposed strategy has the potential to synthesize other multi-metal nanocrystals with 3D nano sponge structures that are expected to provide high catalytic performance in other electrocatalyses such as hydrogen evolution reaction and oxygen evolution reaction.