▎ 摘　　要

A surfactant and stabilizer free graphene-based composite with Pt nanoparticles is considered to be a promising electrocatalyst with greatly improved performance. Here we show that both the size and oxidation state of Pt nanoparticles can significantly influence the electrocatalytic performance of the nanocomposite. We have synthesized Pt-graphene nanocomposites with varied sizes and oxidation states of Pt nanoparticles and test their catalytic activity towards methanol electro-oxidation. We found that the size <1.5 nm with mixed oxidation offers methanol oxidation at lower onset potential and with better tolerance to CO poisoning. However, these benefits are lost due to catalyst durability and thus catalytic current decays rapidly with time. As the nanoparticle size increases in the range of 2-5 nm this onset potential increases, CO tolerance decreases but the catalytic current becomes more stable with time. Thus an optimum nanoparticle size of 2.2 nm shows the best catalytic activity and durability. The oxygenic platinum with variable oxidation states offers stable grafting with the graphene surface, prevents active Pt (0) sites and assists for better CO tolerance. This result would be useful in the design and development of electrocatalysts with better performances.