▎ 摘　　要

Herein a facile strategy to self-assemble PDDA on graphene for surfactant-free synthesizing uniform and ultra-small Pd nano-crystals (Pd@PDDA-G, average size of 3.4 nm) by direct CO reduction has been accomplished. The as-prepared Pd@PDDA-G catalyst exhibits much more negative half-wave potential than the commercial Pd/C and Pd@G without using PDDA by 40 mV and 15 mV as well as much higher peak current density than latters by 2.5 and 2 times, respectively toward formic acid oxidation, demonstrating superior electrocatalytic activity. In addition, the catalyst presents better stability than both Pd@G and commercial Pd/C. The electrocatalytic enhancement mechanism could be attributed to produced uniformly ultra-small and clean Pd nanocrystals on porous graphene for high reaction surface area and fast interfacial electron transfer process. This work also offers a universal route to prepare other high performance catalysts for broad applications in energy systems and sensing devices.